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Revision 1.117 by root, Fri Dec 20 20:51:46 2019 UTC

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129.\" ======================================================================== 133.\" ========================================================================
130.\" 134.\"
131.IX Title "EV 1" 135.IX Title "LIBEV 3"
132.TH EV 1 "2007-12-22" "perl v5.8.8" "User Contributed Perl Documentation" 136.TH LIBEV 3 "2019-12-20" "libev-4.27" "libev - high performance full featured event loop"
137.\" For nroff, turn off justification. Always turn off hyphenation; it makes
138.\" way too many mistakes in technical documents.
139.if n .ad l
140.nh
133.SH "NAME" 141.SH "NAME"
134libev \- a high performance full\-featured event loop written in C 142libev \- a high performance full\-featured event loop written in C
135.SH "SYNOPSIS" 143.SH "SYNOPSIS"
136.IX Header "SYNOPSIS" 144.IX Header "SYNOPSIS"
137.Vb 1 145.Vb 1
138\& #include <ev.h> 146\& #include <ev.h>
139.Ve 147.Ve
140.SH "EXAMPLE PROGRAM" 148.SS "\s-1EXAMPLE PROGRAM\s0"
141.IX Header "EXAMPLE PROGRAM" 149.IX Subsection "EXAMPLE PROGRAM"
142.Vb 1
143\& #include <ev.h>
144.Ve
145.PP
146.Vb 2 150.Vb 2
151\& // a single header file is required
152\& #include <ev.h>
153\&
154\& #include <stdio.h> // for puts
155\&
156\& // every watcher type has its own typedef\*(Aqd struct
157\& // with the name ev_TYPE
147\& ev_io stdin_watcher; 158\& ev_io stdin_watcher;
148\& ev_timer timeout_watcher; 159\& ev_timer timeout_watcher;
149.Ve 160\&
150.PP 161\& // all watcher callbacks have a similar signature
151.Vb 8
152\& /* called when data readable on stdin */ 162\& // this callback is called when data is readable on stdin
153\& static void 163\& static void
154\& stdin_cb (EV_P_ struct ev_io *w, int revents) 164\& stdin_cb (EV_P_ ev_io *w, int revents)
155\& { 165\& {
156\& /* puts ("stdin ready"); */ 166\& puts ("stdin ready");
157\& ev_io_stop (EV_A_ w); /* just a syntax example */ 167\& // for one\-shot events, one must manually stop the watcher
158\& ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */ 168\& // with its corresponding stop function.
169\& ev_io_stop (EV_A_ w);
170\&
171\& // this causes all nested ev_run\*(Aqs to stop iterating
172\& ev_break (EV_A_ EVBREAK_ALL);
159\& } 173\& }
160.Ve 174\&
161.PP 175\& // another callback, this time for a time\-out
162.Vb 6
163\& static void 176\& static void
164\& timeout_cb (EV_P_ struct ev_timer *w, int revents) 177\& timeout_cb (EV_P_ ev_timer *w, int revents)
165\& { 178\& {
166\& /* puts ("timeout"); */ 179\& puts ("timeout");
167\& ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */ 180\& // this causes the innermost ev_run to stop iterating
181\& ev_break (EV_A_ EVBREAK_ONE);
168\& } 182\& }
169.Ve 183\&
170.PP
171.Vb 4
172\& int 184\& int
173\& main (void) 185\& main (void)
174\& { 186\& {
175\& struct ev_loop *loop = ev_default_loop (0); 187\& // use the default event loop unless you have special needs
176.Ve 188\& struct ev_loop *loop = EV_DEFAULT;
177.PP 189\&
178.Vb 3
179\& /* initialise an io watcher, then start it */ 190\& // initialise an io watcher, then start it
191\& // this one will watch for stdin to become readable
180\& ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ); 192\& ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
181\& ev_io_start (loop, &stdin_watcher); 193\& ev_io_start (loop, &stdin_watcher);
182.Ve 194\&
183.PP 195\& // initialise a timer watcher, then start it
184.Vb 3
185\& /* simple non-repeating 5.5 second timeout */ 196\& // simple non\-repeating 5.5 second timeout
186\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.); 197\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
187\& ev_timer_start (loop, &timeout_watcher); 198\& ev_timer_start (loop, &timeout_watcher);
188.Ve 199\&
189.PP 200\& // now wait for events to arrive
190.Vb 2
191\& /* loop till timeout or data ready */
192\& ev_loop (loop, 0); 201\& ev_run (loop, 0);
193.Ve 202\&
194.PP 203\& // break was called, so exit
195.Vb 2
196\& return 0; 204\& return 0;
197\& } 205\& }
198.Ve 206.Ve
199.SH "DESCRIPTION" 207.SH "ABOUT THIS DOCUMENT"
200.IX Header "DESCRIPTION" 208.IX Header "ABOUT THIS DOCUMENT"
209This document documents the libev software package.
210.PP
201The newest version of this document is also available as a html-formatted 211The newest version of this document is also available as an html-formatted
202web page you might find easier to navigate when reading it for the first 212web page you might find easier to navigate when reading it for the first
203time: <http://cvs.schmorp.de/libev/ev.html>. 213time: <http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
204.PP 214.PP
215While this document tries to be as complete as possible in documenting
216libev, its usage and the rationale behind its design, it is not a tutorial
217on event-based programming, nor will it introduce event-based programming
218with libev.
219.PP
220Familiarity with event based programming techniques in general is assumed
221throughout this document.
222.SH "WHAT TO READ WHEN IN A HURRY"
223.IX Header "WHAT TO READ WHEN IN A HURRY"
224This manual tries to be very detailed, but unfortunately, this also makes
225it very long. If you just want to know the basics of libev, I suggest
226reading \*(L"\s-1ANATOMY OF A WATCHER\*(R"\s0, then the \*(L"\s-1EXAMPLE PROGRAM\*(R"\s0 above and
227look up the missing functions in \*(L"\s-1GLOBAL FUNCTIONS\*(R"\s0 and the \f(CW\*(C`ev_io\*(C'\fR and
228\&\f(CW\*(C`ev_timer\*(C'\fR sections in \*(L"\s-1WATCHER TYPES\*(R"\s0.
229.SH "ABOUT LIBEV"
230.IX Header "ABOUT LIBEV"
205Libev is an event loop: you register interest in certain events (such as a 231Libev is an event loop: you register interest in certain events (such as a
206file descriptor being readable or a timeout occurring), and it will manage 232file descriptor being readable or a timeout occurring), and it will manage
207these event sources and provide your program with events. 233these event sources and provide your program with events.
208.PP 234.PP
209To do this, it must take more or less complete control over your process 235To do this, it must take more or less complete control over your process
… …
212.PP 238.PP
213You register interest in certain events by registering so-called \fIevent 239You register interest in certain events by registering so-called \fIevent
214watchers\fR, which are relatively small C structures you initialise with the 240watchers\fR, which are relatively small C structures you initialise with the
215details of the event, and then hand it over to libev by \fIstarting\fR the 241details of the event, and then hand it over to libev by \fIstarting\fR the
216watcher. 242watcher.
217.SH "FEATURES" 243.SS "\s-1FEATURES\s0"
218.IX Header "FEATURES" 244.IX Subsection "FEATURES"
219Libev supports \f(CW\*(C`select\*(C'\fR, \f(CW\*(C`poll\*(C'\fR, the Linux-specific \f(CW\*(C`epoll\*(C'\fR, the 245Libev supports \f(CW\*(C`select\*(C'\fR, \f(CW\*(C`poll\*(C'\fR, the Linux-specific aio and \f(CW\*(C`epoll\*(C'\fR
220BSD-specific \f(CW\*(C`kqueue\*(C'\fR and the Solaris-specific event port mechanisms 246interfaces, the BSD-specific \f(CW\*(C`kqueue\*(C'\fR and the Solaris-specific event port
221for file descriptor events (\f(CW\*(C`ev_io\*(C'\fR), the Linux \f(CW\*(C`inotify\*(C'\fR interface 247mechanisms for file descriptor events (\f(CW\*(C`ev_io\*(C'\fR), the Linux \f(CW\*(C`inotify\*(C'\fR
222(for \f(CW\*(C`ev_stat\*(C'\fR), relative timers (\f(CW\*(C`ev_timer\*(C'\fR), absolute timers 248interface (for \f(CW\*(C`ev_stat\*(C'\fR), Linux eventfd/signalfd (for faster and cleaner
223with customised rescheduling (\f(CW\*(C`ev_periodic\*(C'\fR), synchronous signals 249inter-thread wakeup (\f(CW\*(C`ev_async\*(C'\fR)/signal handling (\f(CW\*(C`ev_signal\*(C'\fR)) relative
224(\f(CW\*(C`ev_signal\*(C'\fR), process status change events (\f(CW\*(C`ev_child\*(C'\fR), and event 250timers (\f(CW\*(C`ev_timer\*(C'\fR), absolute timers with customised rescheduling
225watchers dealing with the event loop mechanism itself (\f(CW\*(C`ev_idle\*(C'\fR, 251(\f(CW\*(C`ev_periodic\*(C'\fR), synchronous signals (\f(CW\*(C`ev_signal\*(C'\fR), process status
226\&\f(CW\*(C`ev_embed\*(C'\fR, \f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR watchers) as well as 252change events (\f(CW\*(C`ev_child\*(C'\fR), and event watchers dealing with the event
227file watchers (\f(CW\*(C`ev_stat\*(C'\fR) and even limited support for fork events 253loop mechanism itself (\f(CW\*(C`ev_idle\*(C'\fR, \f(CW\*(C`ev_embed\*(C'\fR, \f(CW\*(C`ev_prepare\*(C'\fR and
228(\f(CW\*(C`ev_fork\*(C'\fR). 254\&\f(CW\*(C`ev_check\*(C'\fR watchers) as well as file watchers (\f(CW\*(C`ev_stat\*(C'\fR) and even
255limited support for fork events (\f(CW\*(C`ev_fork\*(C'\fR).
229.PP 256.PP
230It also is quite fast (see this 257It also is quite fast (see this
231benchmark comparing it to libevent 258benchmark <http://libev.schmorp.de/bench.html> comparing it to libevent
232for example). 259for example).
233.SH "CONVENTIONS" 260.SS "\s-1CONVENTIONS\s0"
234.IX Header "CONVENTIONS" 261.IX Subsection "CONVENTIONS"
235Libev is very configurable. In this manual the default configuration will 262Libev is very configurable. In this manual the default (and most common)
236be described, which supports multiple event loops. For more info about 263configuration will be described, which supports multiple event loops. For
237various configuration options please have a look at \fB\s-1EMBED\s0\fR section in 264more info about various configuration options please have a look at
238this manual. If libev was configured without support for multiple event 265\&\fB\s-1EMBED\s0\fR section in this manual. If libev was configured without support
239loops, then all functions taking an initial argument of name \f(CW\*(C`loop\*(C'\fR 266for multiple event loops, then all functions taking an initial argument of
240(which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) will not have this argument. 267name \f(CW\*(C`loop\*(C'\fR (which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) will not have
268this argument.
241.SH "TIME REPRESENTATION" 269.SS "\s-1TIME REPRESENTATION\s0"
242.IX Header "TIME REPRESENTATION" 270.IX Subsection "TIME REPRESENTATION"
243Libev represents time as a single floating point number, representing the 271Libev represents time as a single floating point number, representing
244(fractional) number of seconds since the (\s-1POSIX\s0) epoch (somewhere near 272the (fractional) number of seconds since the (\s-1POSIX\s0) epoch (in practice
245the beginning of 1970, details are complicated, don't ask). This type is 273somewhere near the beginning of 1970, details are complicated, don't
246called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use too. It usually aliases 274ask). This type is called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use
247to the \f(CW\*(C`double\*(C'\fR type in C, and when you need to do any calculations on 275too. It usually aliases to the \f(CW\*(C`double\*(C'\fR type in C. When you need to do
248it, you should treat it as some floatingpoint value. Unlike the name 276any calculations on it, you should treat it as some floating point value.
277.PP
249component \f(CW\*(C`stamp\*(C'\fR might indicate, it is also used for time differences 278Unlike the name component \f(CW\*(C`stamp\*(C'\fR might indicate, it is also used for
250throughout libev. 279time differences (e.g. delays) throughout libev.
280.SH "ERROR HANDLING"
281.IX Header "ERROR HANDLING"
282Libev knows three classes of errors: operating system errors, usage errors
283and internal errors (bugs).
284.PP
285When libev catches an operating system error it cannot handle (for example
286a system call indicating a condition libev cannot fix), it calls the callback
287set via \f(CW\*(C`ev_set_syserr_cb\*(C'\fR, which is supposed to fix the problem or
288abort. The default is to print a diagnostic message and to call \f(CW\*(C`abort
289()\*(C'\fR.
290.PP
291When libev detects a usage error such as a negative timer interval, then
292it will print a diagnostic message and abort (via the \f(CW\*(C`assert\*(C'\fR mechanism,
293so \f(CW\*(C`NDEBUG\*(C'\fR will disable this checking): these are programming errors in
294the libev caller and need to be fixed there.
295.PP
296Via the \f(CW\*(C`EV_FREQUENT\*(C'\fR macro you can compile in and/or enable extensive
297consistency checking code inside libev that can be used to check for
298internal inconsistencies, suually caused by application bugs.
299.PP
300Libev also has a few internal error-checking \f(CW\*(C`assert\*(C'\fRions. These do not
301trigger under normal circumstances, as they indicate either a bug in libev
302or worse.
251.SH "GLOBAL FUNCTIONS" 303.SH "GLOBAL FUNCTIONS"
252.IX Header "GLOBAL FUNCTIONS" 304.IX Header "GLOBAL FUNCTIONS"
253These functions can be called anytime, even before initialising the 305These functions can be called anytime, even before initialising the
254library in any way. 306library in any way.
255.IP "ev_tstamp ev_time ()" 4 307.IP "ev_tstamp ev_time ()" 4
256.IX Item "ev_tstamp ev_time ()" 308.IX Item "ev_tstamp ev_time ()"
257Returns the current time as libev would use it. Please note that the 309Returns the current time as libev would use it. Please note that the
258\&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp 310\&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp
259you actually want to know. 311you actually want to know. Also interesting is the combination of
312\&\f(CW\*(C`ev_now_update\*(C'\fR and \f(CW\*(C`ev_now\*(C'\fR.
260.IP "ev_sleep (ev_tstamp interval)" 4 313.IP "ev_sleep (ev_tstamp interval)" 4
261.IX Item "ev_sleep (ev_tstamp interval)" 314.IX Item "ev_sleep (ev_tstamp interval)"
262Sleep for the given interval: The current thread will be blocked until 315Sleep for the given interval: The current thread will be blocked
263either it is interrupted or the given time interval has passed. Basically 316until either it is interrupted or the given time interval has
317passed (approximately \- it might return a bit earlier even if not
318interrupted). Returns immediately if \f(CW\*(C`interval <= 0\*(C'\fR.
319.Sp
264this is a subsecond-resolution \f(CW\*(C`sleep ()\*(C'\fR. 320Basically this is a sub-second-resolution \f(CW\*(C`sleep ()\*(C'\fR.
321.Sp
322The range of the \f(CW\*(C`interval\*(C'\fR is limited \- libev only guarantees to work
323with sleep times of up to one day (\f(CW\*(C`interval <= 86400\*(C'\fR).
265.IP "int ev_version_major ()" 4 324.IP "int ev_version_major ()" 4
266.IX Item "int ev_version_major ()" 325.IX Item "int ev_version_major ()"
267.PD 0 326.PD 0
268.IP "int ev_version_minor ()" 4 327.IP "int ev_version_minor ()" 4
269.IX Item "int ev_version_minor ()" 328.IX Item "int ev_version_minor ()"
… …
281as this indicates an incompatible change. Minor versions are usually 340as this indicates an incompatible change. Minor versions are usually
282compatible to older versions, so a larger minor version alone is usually 341compatible to older versions, so a larger minor version alone is usually
283not a problem. 342not a problem.
284.Sp 343.Sp
285Example: Make sure we haven't accidentally been linked against the wrong 344Example: Make sure we haven't accidentally been linked against the wrong
286version. 345version (note, however, that this will not detect other \s-1ABI\s0 mismatches,
346such as \s-1LFS\s0 or reentrancy).
287.Sp 347.Sp
288.Vb 3 348.Vb 3
289\& assert (("libev version mismatch", 349\& assert (("libev version mismatch",
290\& ev_version_major () == EV_VERSION_MAJOR 350\& ev_version_major () == EV_VERSION_MAJOR
291\& && ev_version_minor () >= EV_VERSION_MINOR)); 351\& && ev_version_minor () >= EV_VERSION_MINOR));
292.Ve 352.Ve
293.IP "unsigned int ev_supported_backends ()" 4 353.IP "unsigned int ev_supported_backends ()" 4
294.IX Item "unsigned int ev_supported_backends ()" 354.IX Item "unsigned int ev_supported_backends ()"
295Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR 355Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR
296value) compiled into this binary of libev (independent of their 356value) compiled into this binary of libev (independent of their
… …
299.Sp 359.Sp
300Example: make sure we have the epoll method, because yeah this is cool and 360Example: make sure we have the epoll method, because yeah this is cool and
301a must have and can we have a torrent of it please!!!11 361a must have and can we have a torrent of it please!!!11
302.Sp 362.Sp
303.Vb 2 363.Vb 2
304\& assert (("sorry, no epoll, no sex", 364\& assert (("sorry, no epoll, no sex",
305\& ev_supported_backends () & EVBACKEND_EPOLL)); 365\& ev_supported_backends () & EVBACKEND_EPOLL));
306.Ve 366.Ve
307.IP "unsigned int ev_recommended_backends ()" 4 367.IP "unsigned int ev_recommended_backends ()" 4
308.IX Item "unsigned int ev_recommended_backends ()" 368.IX Item "unsigned int ev_recommended_backends ()"
309Return the set of all backends compiled into this binary of libev and also 369Return the set of all backends compiled into this binary of libev and
310recommended for this platform. This set is often smaller than the one 370also recommended for this platform, meaning it will work for most file
371descriptor types. This set is often smaller than the one returned by
311returned by \f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on 372\&\f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on most BSDs
312most BSDs and will not be autodetected unless you explicitly request it 373and will not be auto-detected unless you explicitly request it (assuming
313(assuming you know what you are doing). This is the set of backends that 374you know what you are doing). This is the set of backends that libev will
314libev will probe for if you specify no backends explicitly. 375probe for if you specify no backends explicitly.
315.IP "unsigned int ev_embeddable_backends ()" 4 376.IP "unsigned int ev_embeddable_backends ()" 4
316.IX Item "unsigned int ev_embeddable_backends ()" 377.IX Item "unsigned int ev_embeddable_backends ()"
317Returns the set of backends that are embeddable in other event loops. This 378Returns the set of backends that are embeddable in other event loops. This
318is the theoretical, all\-platform, value. To find which backends 379value is platform-specific but can include backends not available on the
319might be supported on the current system, you would need to look at 380current system. To find which embeddable backends might be supported on
320\&\f(CW\*(C`ev_embeddable_backends () & ev_supported_backends ()\*(C'\fR, likewise for 381the current system, you would need to look at \f(CW\*(C`ev_embeddable_backends ()
321recommended ones. 382& ev_supported_backends ()\*(C'\fR, likewise for recommended ones.
322.Sp 383.Sp
323See the description of \f(CW\*(C`ev_embed\*(C'\fR watchers for more info. 384See the description of \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
324.IP "ev_set_allocator (void *(*cb)(void *ptr, long size))" 4 385.IP "ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())" 4
325.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size))" 386.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())"
326Sets the allocation function to use (the prototype is similar \- the 387Sets the allocation function to use (the prototype is similar \- the
327semantics is identical \- to the realloc C function). It is used to 388semantics are identical to the \f(CW\*(C`realloc\*(C'\fR C89/SuS/POSIX function). It is
328allocate and free memory (no surprises here). If it returns zero when 389used to allocate and free memory (no surprises here). If it returns zero
329memory needs to be allocated, the library might abort or take some 390when memory needs to be allocated (\f(CW\*(C`size != 0\*(C'\fR), the library might abort
330potentially destructive action. The default is your system realloc 391or take some potentially destructive action.
331function. 392.Sp
393Since some systems (at least OpenBSD and Darwin) fail to implement
394correct \f(CW\*(C`realloc\*(C'\fR semantics, libev will use a wrapper around the system
395\&\f(CW\*(C`realloc\*(C'\fR and \f(CW\*(C`free\*(C'\fR functions by default.
332.Sp 396.Sp
333You could override this function in high-availability programs to, say, 397You could override this function in high-availability programs to, say,
334free some memory if it cannot allocate memory, to use a special allocator, 398free some memory if it cannot allocate memory, to use a special allocator,
335or even to sleep a while and retry until some memory is available. 399or even to sleep a while and retry until some memory is available.
336.Sp 400.Sp
401Example: The following is the \f(CW\*(C`realloc\*(C'\fR function that libev itself uses
402which should work with \f(CW\*(C`realloc\*(C'\fR and \f(CW\*(C`free\*(C'\fR functions of all kinds and
403is probably a good basis for your own implementation.
404.Sp
405.Vb 5
406\& static void *
407\& ev_realloc_emul (void *ptr, long size) EV_NOEXCEPT
408\& {
409\& if (size)
410\& return realloc (ptr, size);
411\&
412\& free (ptr);
413\& return 0;
414\& }
415.Ve
416.Sp
337Example: Replace the libev allocator with one that waits a bit and then 417Example: Replace the libev allocator with one that waits a bit and then
338retries). 418retries.
339.Sp 419.Sp
340.Vb 6 420.Vb 8
341\& static void * 421\& static void *
342\& persistent_realloc (void *ptr, size_t size) 422\& persistent_realloc (void *ptr, size_t size)
343\& { 423\& {
424\& if (!size)
425\& {
426\& free (ptr);
427\& return 0;
428\& }
429\&
344\& for (;;) 430\& for (;;)
345\& { 431\& {
346\& void *newptr = realloc (ptr, size); 432\& void *newptr = realloc (ptr, size);
347.Ve 433\&
348.Sp
349.Vb 2
350\& if (newptr) 434\& if (newptr)
351\& return newptr; 435\& return newptr;
352.Ve 436\&
353.Sp
354.Vb 3
355\& sleep (60); 437\& sleep (60);
356\& } 438\& }
357\& } 439\& }
358.Ve 440\&
359.Sp
360.Vb 2
361\& ... 441\& ...
362\& ev_set_allocator (persistent_realloc); 442\& ev_set_allocator (persistent_realloc);
363.Ve 443.Ve
364.IP "ev_set_syserr_cb (void (*cb)(const char *msg));" 4 444.IP "ev_set_syserr_cb (void (*cb)(const char *msg) throw ())" 4
365.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg));" 445.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg) throw ())"
366Set the callback function to call on a retryable syscall error (such 446Set the callback function to call on a retryable system call error (such
367as failed select, poll, epoll_wait). The message is a printable string 447as failed select, poll, epoll_wait). The message is a printable string
368indicating the system call or subsystem causing the problem. If this 448indicating the system call or subsystem causing the problem. If this
369callback is set, then libev will expect it to remedy the sitution, no 449callback is set, then libev will expect it to remedy the situation, no
370matter what, when it returns. That is, libev will generally retry the 450matter what, when it returns. That is, libev will generally retry the
371requested operation, or, if the condition doesn't go away, do bad stuff 451requested operation, or, if the condition doesn't go away, do bad stuff
372(such as abort). 452(such as abort).
373.Sp 453.Sp
374Example: This is basically the same thing that libev does internally, too. 454Example: This is basically the same thing that libev does internally, too.
… …
378\& fatal_error (const char *msg) 458\& fatal_error (const char *msg)
379\& { 459\& {
380\& perror (msg); 460\& perror (msg);
381\& abort (); 461\& abort ();
382\& } 462\& }
383.Ve 463\&
384.Sp
385.Vb 2
386\& ... 464\& ...
387\& ev_set_syserr_cb (fatal_error); 465\& ev_set_syserr_cb (fatal_error);
388.Ve 466.Ve
467.IP "ev_feed_signal (int signum)" 4
468.IX Item "ev_feed_signal (int signum)"
469This function can be used to \*(L"simulate\*(R" a signal receive. It is completely
470safe to call this function at any time, from any context, including signal
471handlers or random threads.
472.Sp
473Its main use is to customise signal handling in your process, especially
474in the presence of threads. For example, you could block signals
475by default in all threads (and specifying \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR when
476creating any loops), and in one thread, use \f(CW\*(C`sigwait\*(C'\fR or any other
477mechanism to wait for signals, then \*(L"deliver\*(R" them to libev by calling
478\&\f(CW\*(C`ev_feed_signal\*(C'\fR.
389.SH "FUNCTIONS CONTROLLING THE EVENT LOOP" 479.SH "FUNCTIONS CONTROLLING EVENT LOOPS"
390.IX Header "FUNCTIONS CONTROLLING THE EVENT LOOP" 480.IX Header "FUNCTIONS CONTROLLING EVENT LOOPS"
391An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR. The library knows two 481An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR (the \f(CW\*(C`struct\*(C'\fR is
392types of such loops, the \fIdefault\fR loop, which supports signals and child 482\&\fInot\fR optional in this case unless libev 3 compatibility is disabled, as
393events, and dynamically created loops which do not. 483libev 3 had an \f(CW\*(C`ev_loop\*(C'\fR function colliding with the struct name).
394.PP 484.PP
395If you use threads, a common model is to run the default event loop 485The library knows two types of such loops, the \fIdefault\fR loop, which
396in your main thread (or in a separate thread) and for each thread you 486supports child process events, and dynamically created event loops which
397create, you also create another event loop. Libev itself does no locking 487do not.
398whatsoever, so if you mix calls to the same event loop in different
399threads, make sure you lock (this is usually a bad idea, though, even if
400done correctly, because it's hideous and inefficient).
401.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4 488.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
402.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)" 489.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
403This will initialise the default event loop if it hasn't been initialised 490This returns the \*(L"default\*(R" event loop object, which is what you should
404yet and return it. If the default loop could not be initialised, returns 491normally use when you just need \*(L"the event loop\*(R". Event loop objects and
405false. If it already was initialised it simply returns it (and ignores the 492the \f(CW\*(C`flags\*(C'\fR parameter are described in more detail in the entry for
406flags. If that is troubling you, check \f(CW\*(C`ev_backend ()\*(C'\fR afterwards). 493\&\f(CW\*(C`ev_loop_new\*(C'\fR.
494.Sp
495If the default loop is already initialised then this function simply
496returns it (and ignores the flags. If that is troubling you, check
497\&\f(CW\*(C`ev_backend ()\*(C'\fR afterwards). Otherwise it will create it with the given
498flags, which should almost always be \f(CW0\fR, unless the caller is also the
499one calling \f(CW\*(C`ev_run\*(C'\fR or otherwise qualifies as \*(L"the main program\*(R".
407.Sp 500.Sp
408If you don't know what event loop to use, use the one returned from this 501If you don't know what event loop to use, use the one returned from this
409function. 502function (or via the \f(CW\*(C`EV_DEFAULT\*(C'\fR macro).
503.Sp
504Note that this function is \fInot\fR thread-safe, so if you want to use it
505from multiple threads, you have to employ some kind of mutex (note also
506that this case is unlikely, as loops cannot be shared easily between
507threads anyway).
508.Sp
509The default loop is the only loop that can handle \f(CW\*(C`ev_child\*(C'\fR watchers,
510and to do this, it always registers a handler for \f(CW\*(C`SIGCHLD\*(C'\fR. If this is
511a problem for your application you can either create a dynamic loop with
512\&\f(CW\*(C`ev_loop_new\*(C'\fR which doesn't do that, or you can simply overwrite the
513\&\f(CW\*(C`SIGCHLD\*(C'\fR signal handler \fIafter\fR calling \f(CW\*(C`ev_default_init\*(C'\fR.
514.Sp
515Example: This is the most typical usage.
516.Sp
517.Vb 2
518\& if (!ev_default_loop (0))
519\& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
520.Ve
521.Sp
522Example: Restrict libev to the select and poll backends, and do not allow
523environment settings to be taken into account:
524.Sp
525.Vb 1
526\& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
527.Ve
528.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
529.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
530This will create and initialise a new event loop object. If the loop
531could not be initialised, returns false.
532.Sp
533This function is thread-safe, and one common way to use libev with
534threads is indeed to create one loop per thread, and using the default
535loop in the \*(L"main\*(R" or \*(L"initial\*(R" thread.
410.Sp 536.Sp
411The flags argument can be used to specify special behaviour or specific 537The flags argument can be used to specify special behaviour or specific
412backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). 538backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR).
413.Sp 539.Sp
414The following flags are supported: 540The following flags are supported:
… …
419The default flags value. Use this if you have no clue (it's the right 545The default flags value. Use this if you have no clue (it's the right
420thing, believe me). 546thing, believe me).
421.ie n .IP """EVFLAG_NOENV""" 4 547.ie n .IP """EVFLAG_NOENV""" 4
422.el .IP "\f(CWEVFLAG_NOENV\fR" 4 548.el .IP "\f(CWEVFLAG_NOENV\fR" 4
423.IX Item "EVFLAG_NOENV" 549.IX Item "EVFLAG_NOENV"
424If this flag bit is ored into the flag value (or the program runs setuid 550If this flag bit is or'ed into the flag value (or the program runs setuid
425or setgid) then libev will \fInot\fR look at the environment variable 551or setgid) then libev will \fInot\fR look at the environment variable
426\&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will 552\&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will
427override the flags completely if it is found in the environment. This is 553override the flags completely if it is found in the environment. This is
428useful to try out specific backends to test their performance, or to work 554useful to try out specific backends to test their performance, to work
429around bugs. 555around bugs, or to make libev threadsafe (accessing environment variables
556cannot be done in a threadsafe way, but usually it works if no other
557thread modifies them).
430.ie n .IP """EVFLAG_FORKCHECK""" 4 558.ie n .IP """EVFLAG_FORKCHECK""" 4
431.el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4 559.el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4
432.IX Item "EVFLAG_FORKCHECK" 560.IX Item "EVFLAG_FORKCHECK"
433Instead of calling \f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR manually after 561Instead of calling \f(CW\*(C`ev_loop_fork\*(C'\fR manually after a fork, you can also
434a fork, you can also make libev check for a fork in each iteration by 562make libev check for a fork in each iteration by enabling this flag.
435enabling this flag.
436.Sp 563.Sp
437This works by calling \f(CW\*(C`getpid ()\*(C'\fR on every iteration of the loop, 564This works by calling \f(CW\*(C`getpid ()\*(C'\fR on every iteration of the loop,
438and thus this might slow down your event loop if you do a lot of loop 565and thus this might slow down your event loop if you do a lot of loop
439iterations and little real work, but is usually not noticeable (on my 566iterations and little real work, but is usually not noticeable (on my
440Linux system for example, \f(CW\*(C`getpid\*(C'\fR is actually a simple 5\-insn sequence 567GNU/Linux system for example, \f(CW\*(C`getpid\*(C'\fR is actually a simple 5\-insn
441without a syscall and thus \fIvery\fR fast, but my Linux system also has 568sequence without a system call and thus \fIvery\fR fast, but my GNU/Linux
442\&\f(CW\*(C`pthread_atfork\*(C'\fR which is even faster). 569system also has \f(CW\*(C`pthread_atfork\*(C'\fR which is even faster). (Update: glibc
570versions 2.25 apparently removed the \f(CW\*(C`getpid\*(C'\fR optimisation again).
443.Sp 571.Sp
444The big advantage of this flag is that you can forget about fork (and 572The big advantage of this flag is that you can forget about fork (and
445forget about forgetting to tell libev about forking) when you use this 573forget about forgetting to tell libev about forking, although you still
446flag. 574have to ignore \f(CW\*(C`SIGPIPE\*(C'\fR) when you use this flag.
447.Sp 575.Sp
448This flag setting cannot be overriden or specified in the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR 576This flag setting cannot be overridden or specified in the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR
449environment variable. 577environment variable.
578.ie n .IP """EVFLAG_NOINOTIFY""" 4
579.el .IP "\f(CWEVFLAG_NOINOTIFY\fR" 4
580.IX Item "EVFLAG_NOINOTIFY"
581When this flag is specified, then libev will not attempt to use the
582\&\fIinotify\fR \s-1API\s0 for its \f(CW\*(C`ev_stat\*(C'\fR watchers. Apart from debugging and
583testing, this flag can be useful to conserve inotify file descriptors, as
584otherwise each loop using \f(CW\*(C`ev_stat\*(C'\fR watchers consumes one inotify handle.
585.ie n .IP """EVFLAG_SIGNALFD""" 4
586.el .IP "\f(CWEVFLAG_SIGNALFD\fR" 4
587.IX Item "EVFLAG_SIGNALFD"
588When this flag is specified, then libev will attempt to use the
589\&\fIsignalfd\fR \s-1API\s0 for its \f(CW\*(C`ev_signal\*(C'\fR (and \f(CW\*(C`ev_child\*(C'\fR) watchers. This \s-1API\s0
590delivers signals synchronously, which makes it both faster and might make
591it possible to get the queued signal data. It can also simplify signal
592handling with threads, as long as you properly block signals in your
593threads that are not interested in handling them.
594.Sp
595Signalfd will not be used by default as this changes your signal mask, and
596there are a lot of shoddy libraries and programs (glib's threadpool for
597example) that can't properly initialise their signal masks.
598.ie n .IP """EVFLAG_NOTIMERFD""" 4
599.el .IP "\f(CWEVFLAG_NOTIMERFD\fR" 4
600.IX Item "EVFLAG_NOTIMERFD"
601When this flag is specified, the libev will avoid using a \f(CW\*(C`timerfd\*(C'\fR to
602detect time jumps. It will still be able to detect time jumps, but takes
603longer and has a lower accuracy in doing so, but saves a file descriptor
604per loop.
605.ie n .IP """EVFLAG_NOSIGMASK""" 4
606.el .IP "\f(CWEVFLAG_NOSIGMASK\fR" 4
607.IX Item "EVFLAG_NOSIGMASK"
608When this flag is specified, then libev will avoid to modify the signal
609mask. Specifically, this means you have to make sure signals are unblocked
610when you want to receive them.
611.Sp
612This behaviour is useful when you want to do your own signal handling, or
613want to handle signals only in specific threads and want to avoid libev
614unblocking the signals.
615.Sp
616It's also required by \s-1POSIX\s0 in a threaded program, as libev calls
617\&\f(CW\*(C`sigprocmask\*(C'\fR, whose behaviour is officially unspecified.
618.Sp
619This flag's behaviour will become the default in future versions of libev.
450.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4 620.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4
451.el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4 621.el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4
452.IX Item "EVBACKEND_SELECT (value 1, portable select backend)" 622.IX Item "EVBACKEND_SELECT (value 1, portable select backend)"
453This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as 623This is your standard \fBselect\fR\|(2) backend. Not \fIcompletely\fR standard, as
454libev tries to roll its own fd_set with no limits on the number of fds, 624libev tries to roll its own fd_set with no limits on the number of fds,
455but if that fails, expect a fairly low limit on the number of fds when 625but if that fails, expect a fairly low limit on the number of fds when
456using this backend. It doesn't scale too well (O(highest_fd)), but its usually 626using this backend. It doesn't scale too well (O(highest_fd)), but its
457the fastest backend for a low number of fds. 627usually the fastest backend for a low number of (low-numbered :) fds.
628.Sp
629To get good performance out of this backend you need a high amount of
630parallelism (most of the file descriptors should be busy). If you are
631writing a server, you should \f(CW\*(C`accept ()\*(C'\fR in a loop to accept as many
632connections as possible during one iteration. You might also want to have
633a look at \f(CW\*(C`ev_set_io_collect_interval ()\*(C'\fR to increase the amount of
634readiness notifications you get per iteration.
635.Sp
636This backend maps \f(CW\*(C`EV_READ\*(C'\fR to the \f(CW\*(C`readfds\*(C'\fR set and \f(CW\*(C`EV_WRITE\*(C'\fR to the
637\&\f(CW\*(C`writefds\*(C'\fR set (and to work around Microsoft Windows bugs, also onto the
638\&\f(CW\*(C`exceptfds\*(C'\fR set on that platform).
458.ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4 639.ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4
459.el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4 640.el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4
460.IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)" 641.IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)"
461And this is your standard \fIpoll\fR\|(2) backend. It's more complicated than 642And this is your standard \fBpoll\fR\|(2) backend. It's more complicated
462select, but handles sparse fds better and has no artificial limit on the 643than select, but handles sparse fds better and has no artificial
463number of fds you can use (except it will slow down considerably with a 644limit on the number of fds you can use (except it will slow down
464lot of inactive fds). It scales similarly to select, i.e. O(total_fds). 645considerably with a lot of inactive fds). It scales similarly to select,
646i.e. O(total_fds). See the entry for \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR, above, for
647performance tips.
648.Sp
649This backend maps \f(CW\*(C`EV_READ\*(C'\fR to \f(CW\*(C`POLLIN | POLLERR | POLLHUP\*(C'\fR, and
650\&\f(CW\*(C`EV_WRITE\*(C'\fR to \f(CW\*(C`POLLOUT | POLLERR | POLLHUP\*(C'\fR.
465.ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4 651.ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
466.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4 652.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
467.IX Item "EVBACKEND_EPOLL (value 4, Linux)" 653.IX Item "EVBACKEND_EPOLL (value 4, Linux)"
654Use the Linux-specific \fBepoll\fR\|(7) interface (for both pre\- and post\-2.6.9
655kernels).
656.Sp
468For few fds, this backend is a bit little slower than poll and select, 657For few fds, this backend is a bit little slower than poll and select, but
469but it scales phenomenally better. While poll and select usually scale 658it scales phenomenally better. While poll and select usually scale like
470like O(total_fds) where n is the total number of fds (or the highest fd), 659O(total_fds) where total_fds is the total number of fds (or the highest
471epoll scales either O(1) or O(active_fds). The epoll design has a number 660fd), epoll scales either O(1) or O(active_fds).
472of shortcomings, such as silently dropping events in some hard-to-detect 661.Sp
473cases and rewiring a syscall per fd change, no fork support and bad 662The epoll mechanism deserves honorable mention as the most misdesigned
474support for dup: 663of the more advanced event mechanisms: mere annoyances include silently
664dropping file descriptors, requiring a system call per change per file
665descriptor (and unnecessary guessing of parameters), problems with dup,
666returning before the timeout value, resulting in additional iterations
667(and only giving 5ms accuracy while select on the same platform gives
6680.1ms) and so on. The biggest issue is fork races, however \- if a program
669forks then \fIboth\fR parent and child process have to recreate the epoll
670set, which can take considerable time (one syscall per file descriptor)
671and is of course hard to detect.
672.Sp
673Epoll is also notoriously buggy \- embedding epoll fds \fIshould\fR work,
674but of course \fIdoesn't\fR, and epoll just loves to report events for
675totally \fIdifferent\fR file descriptors (even already closed ones, so
676one cannot even remove them from the set) than registered in the set
677(especially on \s-1SMP\s0 systems). Libev tries to counter these spurious
678notifications by employing an additional generation counter and comparing
679that against the events to filter out spurious ones, recreating the set
680when required. Epoll also erroneously rounds down timeouts, but gives you
681no way to know when and by how much, so sometimes you have to busy-wait
682because epoll returns immediately despite a nonzero timeout. And last
683not least, it also refuses to work with some file descriptors which work
684perfectly fine with \f(CW\*(C`select\*(C'\fR (files, many character devices...).
685.Sp
686Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
687cobbled together in a hurry, no thought to design or interaction with
688others. Oh, the pain, will it ever stop...
475.Sp 689.Sp
476While stopping, setting and starting an I/O watcher in the same iteration 690While stopping, setting and starting an I/O watcher in the same iteration
477will result in some caching, there is still a syscall per such incident 691will result in some caching, there is still a system call per such
478(because the fd could point to a different file description now), so its 692incident (because the same \fIfile descriptor\fR could point to a different
479best to avoid that. Also, \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors might not work 693\&\fIfile description\fR now), so its best to avoid that. Also, \f(CW\*(C`dup ()\*(C'\fR'ed
480very well if you register events for both fds. 694file descriptors might not work very well if you register events for both
695file descriptors.
481.Sp 696.Sp
482Please note that epoll sometimes generates spurious notifications, so you 697Best performance from this backend is achieved by not unregistering all
483need to use non-blocking I/O or other means to avoid blocking when no data 698watchers for a file descriptor until it has been closed, if possible,
484(or space) is available. 699i.e. keep at least one watcher active per fd at all times. Stopping and
700starting a watcher (without re-setting it) also usually doesn't cause
701extra overhead. A fork can both result in spurious notifications as well
702as in libev having to destroy and recreate the epoll object, which can
703take considerable time and thus should be avoided.
704.Sp
705All this means that, in practice, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR can be as fast or
706faster than epoll for maybe up to a hundred file descriptors, depending on
707the usage. So sad.
708.Sp
709While nominally embeddable in other event loops, this feature is broken in
710a lot of kernel revisions, but probably(!) works in current versions.
711.Sp
712This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
713\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
714.ie n .IP """EVBACKEND_LINUXAIO"" (value 64, Linux)" 4
715.el .IP "\f(CWEVBACKEND_LINUXAIO\fR (value 64, Linux)" 4
716.IX Item "EVBACKEND_LINUXAIO (value 64, Linux)"
717Use the Linux-specific Linux \s-1AIO\s0 (\fInot\fR \f(CWaio(7)\fR but \f(CWio_submit(2)\fR) event interface available in post\-4.18 kernels (but libev
718only tries to use it in 4.19+).
719.Sp
720This is another Linux train wreck of an event interface.
721.Sp
722If this backend works for you (as of this writing, it was very
723experimental), it is the best event interface available on Linux and might
724be well worth enabling it \- if it isn't available in your kernel this will
725be detected and this backend will be skipped.
726.Sp
727This backend can batch oneshot requests and supports a user-space ring
728buffer to receive events. It also doesn't suffer from most of the design
729problems of epoll (such as not being able to remove event sources from
730the epoll set), and generally sounds too good to be true. Because, this
731being the Linux kernel, of course it suffers from a whole new set of
732limitations, forcing you to fall back to epoll, inheriting all its design
733issues.
734.Sp
735For one, it is not easily embeddable (but probably could be done using
736an event fd at some extra overhead). It also is subject to a system wide
737limit that can be configured in \fI/proc/sys/fs/aio\-max\-nr\fR. If no \s-1AIO\s0
738requests are left, this backend will be skipped during initialisation, and
739will switch to epoll when the loop is active.
740.Sp
741Most problematic in practice, however, is that not all file descriptors
742work with it. For example, in Linux 5.1, \s-1TCP\s0 sockets, pipes, event fds,
743files, \fI/dev/null\fR and many others are supported, but ttys do not work
744properly (a known bug that the kernel developers don't care about, see
745<https://lore.kernel.org/patchwork/patch/1047453/>), so this is not
746(yet?) a generic event polling interface.
747.Sp
748Overall, it seems the Linux developers just don't want it to have a
749generic event handling mechanism other than \f(CW\*(C`select\*(C'\fR or \f(CW\*(C`poll\*(C'\fR.
750.Sp
751To work around all these problem, the current version of libev uses its
752epoll backend as a fallback for file descriptor types that do not work. Or
753falls back completely to epoll if the kernel acts up.
754.Sp
755This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
756\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
485.ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4 757.ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4
486.el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4 758.el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
487.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)" 759.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
488Kqueue deserves special mention, as at the time of this writing, it 760Kqueue deserves special mention, as at the time this backend was
489was broken on all BSDs except NetBSD (usually it doesn't work reliably 761implemented, it was broken on all BSDs except NetBSD (usually it doesn't
490with anything but sockets and pipes, except on Darwin, where of course 762work reliably with anything but sockets and pipes, except on Darwin,
491it's completely useless). For this reason it's not being \*(L"autodetected\*(R" 763where of course it's completely useless). Unlike epoll, however, whose
492unless you explicitly specify it explicitly in the flags (i.e. using 764brokenness is by design, these kqueue bugs can be (and mostly have been)
493\&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or libev was compiled on a known-to-be-good (\-enough) 765fixed without \s-1API\s0 changes to existing programs. For this reason it's not
494system like NetBSD. 766being \*(L"auto-detected\*(R" on all platforms unless you explicitly specify it
767in the flags (i.e. using \f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or libev was compiled on a
768known-to-be-good (\-enough) system like NetBSD.
495.Sp 769.Sp
496You still can embed kqueue into a normal poll or select backend and use it 770You still can embed kqueue into a normal poll or select backend and use it
497only for sockets (after having made sure that sockets work with kqueue on 771only for sockets (after having made sure that sockets work with kqueue on
498the target platform). See \f(CW\*(C`ev_embed\*(C'\fR watchers for more info. 772the target platform). See \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
499.Sp 773.Sp
500It scales in the same way as the epoll backend, but the interface to the 774It scales in the same way as the epoll backend, but the interface to the
501kernel is more efficient (which says nothing about its actual speed, of 775kernel is more efficient (which says nothing about its actual speed, of
502course). While stopping, setting and starting an I/O watcher does never 776course). While stopping, setting and starting an I/O watcher does never
503cause an extra syscall as with \f(CW\*(C`EVBACKEND_EPOLL\*(C'\fR, it still adds up to 777cause an extra system call as with \f(CW\*(C`EVBACKEND_EPOLL\*(C'\fR, it still adds up to
504two event changes per incident, support for \f(CW\*(C`fork ()\*(C'\fR is very bad and it 778two event changes per incident. Support for \f(CW\*(C`fork ()\*(C'\fR is very bad (you
779might have to leak fds on fork, but it's more sane than epoll) and it
505drops fds silently in similarly hard-to-detect cases. 780drops fds silently in similarly hard-to-detect cases.
781.Sp
782This backend usually performs well under most conditions.
783.Sp
784While nominally embeddable in other event loops, this doesn't work
785everywhere, so you might need to test for this. And since it is broken
786almost everywhere, you should only use it when you have a lot of sockets
787(for which it usually works), by embedding it into another event loop
788(e.g. \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR (but \f(CW\*(C`poll\*(C'\fR is of course
789also broken on \s-1OS X\s0)) and, did I mention it, using it only for sockets.
790.Sp
791This backend maps \f(CW\*(C`EV_READ\*(C'\fR into an \f(CW\*(C`EVFILT_READ\*(C'\fR kevent with
792\&\f(CW\*(C`NOTE_EOF\*(C'\fR, and \f(CW\*(C`EV_WRITE\*(C'\fR into an \f(CW\*(C`EVFILT_WRITE\*(C'\fR kevent with
793\&\f(CW\*(C`NOTE_EOF\*(C'\fR.
506.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4 794.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
507.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4 795.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
508.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)" 796.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
509This is not implemented yet (and might never be). 797This is not implemented yet (and might never be, unless you send me an
798implementation). According to reports, \f(CW\*(C`/dev/poll\*(C'\fR only supports sockets
799and is not embeddable, which would limit the usefulness of this backend
800immensely.
510.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4 801.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
511.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4 802.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
512.IX Item "EVBACKEND_PORT (value 32, Solaris 10)" 803.IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
513This uses the Solaris 10 event port mechanism. As with everything on Solaris, 804This uses the Solaris 10 event port mechanism. As with everything on Solaris,
514it's really slow, but it still scales very well (O(active_fds)). 805it's really slow, but it still scales very well (O(active_fds)).
515.Sp 806.Sp
516Please note that solaris event ports can deliver a lot of spurious 807While this backend scales well, it requires one system call per active
517notifications, so you need to use non-blocking I/O or other means to avoid 808file descriptor per loop iteration. For small and medium numbers of file
518blocking when no data (or space) is available. 809descriptors a \*(L"slow\*(R" \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR backend
810might perform better.
811.Sp
812On the positive side, this backend actually performed fully to
813specification in all tests and is fully embeddable, which is a rare feat
814among the OS-specific backends (I vastly prefer correctness over speed
815hacks).
816.Sp
817On the negative side, the interface is \fIbizarre\fR \- so bizarre that
818even sun itself gets it wrong in their code examples: The event polling
819function sometimes returns events to the caller even though an error
820occurred, but with no indication whether it has done so or not (yes, it's
821even documented that way) \- deadly for edge-triggered interfaces where you
822absolutely have to know whether an event occurred or not because you have
823to re-arm the watcher.
824.Sp
825Fortunately libev seems to be able to work around these idiocies.
826.Sp
827This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
828\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
519.ie n .IP """EVBACKEND_ALL""" 4 829.ie n .IP """EVBACKEND_ALL""" 4
520.el .IP "\f(CWEVBACKEND_ALL\fR" 4 830.el .IP "\f(CWEVBACKEND_ALL\fR" 4
521.IX Item "EVBACKEND_ALL" 831.IX Item "EVBACKEND_ALL"
522Try all backends (even potentially broken ones that wouldn't be tried 832Try all backends (even potentially broken ones that wouldn't be tried
523with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as 833with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as
524\&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR. 834\&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR.
835.Sp
836It is definitely not recommended to use this flag, use whatever
837\&\f(CW\*(C`ev_recommended_backends ()\*(C'\fR returns, or simply do not specify a backend
838at all.
839.ie n .IP """EVBACKEND_MASK""" 4
840.el .IP "\f(CWEVBACKEND_MASK\fR" 4
841.IX Item "EVBACKEND_MASK"
842Not a backend at all, but a mask to select all backend bits from a
843\&\f(CW\*(C`flags\*(C'\fR value, in case you want to mask out any backends from a flags
844value (e.g. when modifying the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR environment variable).
525.RE 845.RE
526.RS 4 846.RS 4
527.Sp 847.Sp
528If one or more of these are ored into the flags value, then only these 848If one or more of the backend flags are or'ed into the flags value,
529backends will be tried (in the reverse order as given here). If none are 849then only these backends will be tried (in the reverse order as listed
530specified, most compiled-in backend will be tried, usually in reverse 850here). If none are specified, all backends in \f(CW\*(C`ev_recommended_backends
531order of their flag values :) 851()\*(C'\fR will be tried.
532.Sp 852.Sp
533The most typical usage is like this: 853Example: Try to create a event loop that uses epoll and nothing else.
534.Sp 854.Sp
535.Vb 2 855.Vb 3
536\& if (!ev_default_loop (0)) 856\& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
537\& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?"); 857\& if (!epoller)
858\& fatal ("no epoll found here, maybe it hides under your chair");
538.Ve 859.Ve
539.Sp 860.Sp
540Restrict libev to the select and poll backends, and do not allow 861Example: Use whatever libev has to offer, but make sure that kqueue is
541environment settings to be taken into account: 862used if available.
542.Sp 863.Sp
543.Vb 1 864.Vb 1
544\& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV); 865\& struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
545.Ve 866.Ve
546.Sp 867.Sp
547Use whatever libev has to offer, but make sure that kqueue is used if 868Example: Similarly, on linux, you mgiht want to take advantage of the
548available (warning, breaks stuff, best use only with your own private 869linux aio backend if possible, but fall back to something else if that
549event loop and only if you know the \s-1OS\s0 supports your types of fds): 870isn't available.
550.Sp 871.Sp
551.Vb 1 872.Vb 1
552\& ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE); 873\& struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_LINUXAIO);
553.Ve 874.Ve
554.RE 875.RE
555.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
556.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
557Similar to \f(CW\*(C`ev_default_loop\*(C'\fR, but always creates a new event loop that is
558always distinct from the default loop. Unlike the default loop, it cannot
559handle signal and child watchers, and attempts to do so will be greeted by
560undefined behaviour (or a failed assertion if assertions are enabled).
561.Sp
562Example: Try to create a event loop that uses epoll and nothing else.
563.Sp
564.Vb 3
565\& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
566\& if (!epoller)
567\& fatal ("no epoll found here, maybe it hides under your chair");
568.Ve
569.IP "ev_default_destroy ()" 4 876.IP "ev_loop_destroy (loop)" 4
570.IX Item "ev_default_destroy ()" 877.IX Item "ev_loop_destroy (loop)"
571Destroys the default loop again (frees all memory and kernel state 878Destroys an event loop object (frees all memory and kernel state
572etc.). None of the active event watchers will be stopped in the normal 879etc.). None of the active event watchers will be stopped in the normal
573sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your 880sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your
574responsibility to either stop all watchers cleanly yoursef \fIbefore\fR 881responsibility to either stop all watchers cleanly yourself \fIbefore\fR
575calling this function, or cope with the fact afterwards (which is usually 882calling this function, or cope with the fact afterwards (which is usually
576the easiest thing, you can just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them 883the easiest thing, you can just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them
577for example). 884for example).
578.Sp 885.Sp
579Note that certain global state, such as signal state, will not be freed by 886Note that certain global state, such as signal state (and installed signal
580this function, and related watchers (such as signal and child watchers) 887handlers), will not be freed by this function, and related watchers (such
581would need to be stopped manually. 888as signal and child watchers) would need to be stopped manually.
582.Sp 889.Sp
583In general it is not advisable to call this function except in the 890This function is normally used on loop objects allocated by
584rare occasion where you really need to free e.g. the signal handling 891\&\f(CW\*(C`ev_loop_new\*(C'\fR, but it can also be used on the default loop returned by
585pipe fds. If you need dynamically allocated loops it is better to use 892\&\f(CW\*(C`ev_default_loop\*(C'\fR, in which case it is not thread-safe.
586\&\f(CW\*(C`ev_loop_new\*(C'\fR and \f(CW\*(C`ev_loop_destroy\*(C'\fR).
587.IP "ev_loop_destroy (loop)" 4
588.IX Item "ev_loop_destroy (loop)"
589Like \f(CW\*(C`ev_default_destroy\*(C'\fR, but destroys an event loop created by an
590earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR.
591.IP "ev_default_fork ()" 4
592.IX Item "ev_default_fork ()"
593This function reinitialises the kernel state for backends that have
594one. Despite the name, you can call it anytime, but it makes most sense
595after forking, in either the parent or child process (or both, but that
596again makes little sense).
597.Sp 893.Sp
598You \fImust\fR call this function in the child process after forking if and 894Note that it is not advisable to call this function on the default loop
599only if you want to use the event library in both processes. If you just 895except in the rare occasion where you really need to free its resources.
600fork+exec, you don't have to call it. 896If you need dynamically allocated loops it is better to use \f(CW\*(C`ev_loop_new\*(C'\fR
601.Sp 897and \f(CW\*(C`ev_loop_destroy\*(C'\fR.
602The function itself is quite fast and it's usually not a problem to call
603it just in case after a fork. To make this easy, the function will fit in
604quite nicely into a call to \f(CW\*(C`pthread_atfork\*(C'\fR:
605.Sp
606.Vb 1
607\& pthread_atfork (0, 0, ev_default_fork);
608.Ve
609.Sp
610At the moment, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and \f(CW\*(C`EVBACKEND_POLL\*(C'\fR are safe to use
611without calling this function, so if you force one of those backends you
612do not need to care.
613.IP "ev_loop_fork (loop)" 4 898.IP "ev_loop_fork (loop)" 4
614.IX Item "ev_loop_fork (loop)" 899.IX Item "ev_loop_fork (loop)"
615Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by 900This function sets a flag that causes subsequent \f(CW\*(C`ev_run\*(C'\fR iterations
616\&\f(CW\*(C`ev_loop_new\*(C'\fR. Yes, you have to call this on every allocated event loop 901to reinitialise the kernel state for backends that have one. Despite
617after fork, and how you do this is entirely your own problem. 902the name, you can call it anytime you are allowed to start or stop
903watchers (except inside an \f(CW\*(C`ev_prepare\*(C'\fR callback), but it makes most
904sense after forking, in the child process. You \fImust\fR call it (or use
905\&\f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR) in the child before resuming or calling \f(CW\*(C`ev_run\*(C'\fR.
906.Sp
907In addition, if you want to reuse a loop (via this function or
908\&\f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR), you \fIalso\fR have to ignore \f(CW\*(C`SIGPIPE\*(C'\fR.
909.Sp
910Again, you \fIhave\fR to call it on \fIany\fR loop that you want to re-use after
911a fork, \fIeven if you do not plan to use the loop in the parent\fR. This is
912because some kernel interfaces *cough* \fIkqueue\fR *cough* do funny things
913during fork.
914.Sp
915On the other hand, you only need to call this function in the child
916process if and only if you want to use the event loop in the child. If
917you just fork+exec or create a new loop in the child, you don't have to
918call it at all (in fact, \f(CW\*(C`epoll\*(C'\fR is so badly broken that it makes a
919difference, but libev will usually detect this case on its own and do a
920costly reset of the backend).
921.Sp
922The function itself is quite fast and it's usually not a problem to call
923it just in case after a fork.
924.Sp
925Example: Automate calling \f(CW\*(C`ev_loop_fork\*(C'\fR on the default loop when
926using pthreads.
927.Sp
928.Vb 5
929\& static void
930\& post_fork_child (void)
931\& {
932\& ev_loop_fork (EV_DEFAULT);
933\& }
934\&
935\& ...
936\& pthread_atfork (0, 0, post_fork_child);
937.Ve
938.IP "int ev_is_default_loop (loop)" 4
939.IX Item "int ev_is_default_loop (loop)"
940Returns true when the given loop is, in fact, the default loop, and false
941otherwise.
618.IP "unsigned int ev_loop_count (loop)" 4 942.IP "unsigned int ev_iteration (loop)" 4
619.IX Item "unsigned int ev_loop_count (loop)" 943.IX Item "unsigned int ev_iteration (loop)"
620Returns the count of loop iterations for the loop, which is identical to 944Returns the current iteration count for the event loop, which is identical
621the number of times libev did poll for new events. It starts at \f(CW0\fR and 945to the number of times libev did poll for new events. It starts at \f(CW0\fR
622happily wraps around with enough iterations. 946and happily wraps around with enough iterations.
623.Sp 947.Sp
624This value can sometimes be useful as a generation counter of sorts (it 948This value can sometimes be useful as a generation counter of sorts (it
625\&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with 949\&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with
626\&\f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR calls. 950\&\f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR calls \- and is incremented between the
951prepare and check phases.
952.IP "unsigned int ev_depth (loop)" 4
953.IX Item "unsigned int ev_depth (loop)"
954Returns the number of times \f(CW\*(C`ev_run\*(C'\fR was entered minus the number of
955times \f(CW\*(C`ev_run\*(C'\fR was exited normally, in other words, the recursion depth.
956.Sp
957Outside \f(CW\*(C`ev_run\*(C'\fR, this number is zero. In a callback, this number is
958\&\f(CW1\fR, unless \f(CW\*(C`ev_run\*(C'\fR was invoked recursively (or from another thread),
959in which case it is higher.
960.Sp
961Leaving \f(CW\*(C`ev_run\*(C'\fR abnormally (setjmp/longjmp, cancelling the thread,
962throwing an exception etc.), doesn't count as \*(L"exit\*(R" \- consider this
963as a hint to avoid such ungentleman-like behaviour unless it's really
964convenient, in which case it is fully supported.
627.IP "unsigned int ev_backend (loop)" 4 965.IP "unsigned int ev_backend (loop)" 4
628.IX Item "unsigned int ev_backend (loop)" 966.IX Item "unsigned int ev_backend (loop)"
629Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in 967Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
630use. 968use.
631.IP "ev_tstamp ev_now (loop)" 4 969.IP "ev_tstamp ev_now (loop)" 4
… …
633Returns the current \*(L"event loop time\*(R", which is the time the event loop 971Returns the current \*(L"event loop time\*(R", which is the time the event loop
634received events and started processing them. This timestamp does not 972received events and started processing them. This timestamp does not
635change as long as callbacks are being processed, and this is also the base 973change as long as callbacks are being processed, and this is also the base
636time used for relative timers. You can treat it as the timestamp of the 974time used for relative timers. You can treat it as the timestamp of the
637event occurring (or more correctly, libev finding out about it). 975event occurring (or more correctly, libev finding out about it).
976.IP "ev_now_update (loop)" 4
977.IX Item "ev_now_update (loop)"
978Establishes the current time by querying the kernel, updating the time
979returned by \f(CW\*(C`ev_now ()\*(C'\fR in the progress. This is a costly operation and
980is usually done automatically within \f(CW\*(C`ev_run ()\*(C'\fR.
981.Sp
982This function is rarely useful, but when some event callback runs for a
983very long time without entering the event loop, updating libev's idea of
984the current time is a good idea.
985.Sp
986See also \*(L"The special problem of time updates\*(R" in the \f(CW\*(C`ev_timer\*(C'\fR section.
987.IP "ev_suspend (loop)" 4
988.IX Item "ev_suspend (loop)"
989.PD 0
990.IP "ev_resume (loop)" 4
991.IX Item "ev_resume (loop)"
992.PD
993These two functions suspend and resume an event loop, for use when the
994loop is not used for a while and timeouts should not be processed.
995.Sp
996A typical use case would be an interactive program such as a game: When
997the user presses \f(CW\*(C`^Z\*(C'\fR to suspend the game and resumes it an hour later it
998would be best to handle timeouts as if no time had actually passed while
999the program was suspended. This can be achieved by calling \f(CW\*(C`ev_suspend\*(C'\fR
1000in your \f(CW\*(C`SIGTSTP\*(C'\fR handler, sending yourself a \f(CW\*(C`SIGSTOP\*(C'\fR and calling
1001\&\f(CW\*(C`ev_resume\*(C'\fR directly afterwards to resume timer processing.
1002.Sp
1003Effectively, all \f(CW\*(C`ev_timer\*(C'\fR watchers will be delayed by the time spend
1004between \f(CW\*(C`ev_suspend\*(C'\fR and \f(CW\*(C`ev_resume\*(C'\fR, and all \f(CW\*(C`ev_periodic\*(C'\fR watchers
1005will be rescheduled (that is, they will lose any events that would have
1006occurred while suspended).
1007.Sp
1008After calling \f(CW\*(C`ev_suspend\*(C'\fR you \fBmust not\fR call \fIany\fR function on the
1009given loop other than \f(CW\*(C`ev_resume\*(C'\fR, and you \fBmust not\fR call \f(CW\*(C`ev_resume\*(C'\fR
1010without a previous call to \f(CW\*(C`ev_suspend\*(C'\fR.
1011.Sp
1012Calling \f(CW\*(C`ev_suspend\*(C'\fR/\f(CW\*(C`ev_resume\*(C'\fR has the side effect of updating the
1013event loop time (see \f(CW\*(C`ev_now_update\*(C'\fR).
638.IP "ev_loop (loop, int flags)" 4 1014.IP "bool ev_run (loop, int flags)" 4
639.IX Item "ev_loop (loop, int flags)" 1015.IX Item "bool ev_run (loop, int flags)"
640Finally, this is it, the event handler. This function usually is called 1016Finally, this is it, the event handler. This function usually is called
641after you initialised all your watchers and you want to start handling 1017after you have initialised all your watchers and you want to start
642events. 1018handling events. It will ask the operating system for any new events, call
1019the watcher callbacks, and then repeat the whole process indefinitely: This
1020is why event loops are called \fIloops\fR.
643.Sp 1021.Sp
644If the flags argument is specified as \f(CW0\fR, it will not return until 1022If the flags argument is specified as \f(CW0\fR, it will keep handling events
645either no event watchers are active anymore or \f(CW\*(C`ev_unloop\*(C'\fR was called. 1023until either no event watchers are active anymore or \f(CW\*(C`ev_break\*(C'\fR was
1024called.
646.Sp 1025.Sp
1026The return value is false if there are no more active watchers (which
1027usually means \*(L"all jobs done\*(R" or \*(L"deadlock\*(R"), and true in all other cases
1028(which usually means " you should call \f(CW\*(C`ev_run\*(C'\fR again").
1029.Sp
647Please note that an explicit \f(CW\*(C`ev_unloop\*(C'\fR is usually better than 1030Please note that an explicit \f(CW\*(C`ev_break\*(C'\fR is usually better than
648relying on all watchers to be stopped when deciding when a program has 1031relying on all watchers to be stopped when deciding when a program has
649finished (especially in interactive programs), but having a program that 1032finished (especially in interactive programs), but having a program
650automatically loops as long as it has to and no longer by virtue of 1033that automatically loops as long as it has to and no longer by virtue
651relying on its watchers stopping correctly is a thing of beauty. 1034of relying on its watchers stopping correctly, that is truly a thing of
1035beauty.
652.Sp 1036.Sp
1037This function is \fImostly\fR exception-safe \- you can break out of a
1038\&\f(CW\*(C`ev_run\*(C'\fR call by calling \f(CW\*(C`longjmp\*(C'\fR in a callback, throwing a \*(C+
1039exception and so on. This does not decrement the \f(CW\*(C`ev_depth\*(C'\fR value, nor
1040will it clear any outstanding \f(CW\*(C`EVBREAK_ONE\*(C'\fR breaks.
1041.Sp
653A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle 1042A flags value of \f(CW\*(C`EVRUN_NOWAIT\*(C'\fR will look for new events, will handle
654those events and any outstanding ones, but will not block your process in 1043those events and any already outstanding ones, but will not wait and
655case there are no events and will return after one iteration of the loop. 1044block your process in case there are no events and will return after one
1045iteration of the loop. This is sometimes useful to poll and handle new
1046events while doing lengthy calculations, to keep the program responsive.
656.Sp 1047.Sp
657A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if 1048A flags value of \f(CW\*(C`EVRUN_ONCE\*(C'\fR will look for new events (waiting if
658neccessary) and will handle those and any outstanding ones. It will block 1049necessary) and will handle those and any already outstanding ones. It
659your process until at least one new event arrives, and will return after 1050will block your process until at least one new event arrives (which could
660one iteration of the loop. This is useful if you are waiting for some 1051be an event internal to libev itself, so there is no guarantee that a
661external event in conjunction with something not expressible using other 1052user-registered callback will be called), and will return after one
1053iteration of the loop.
1054.Sp
1055This is useful if you are waiting for some external event in conjunction
1056with something not expressible using other libev watchers (i.e. "roll your
662libev watchers. However, a pair of \f(CW\*(C`ev_prepare\*(C'\fR/\f(CW\*(C`ev_check\*(C'\fR watchers is 1057own \f(CW\*(C`ev_run\*(C'\fR"). However, a pair of \f(CW\*(C`ev_prepare\*(C'\fR/\f(CW\*(C`ev_check\*(C'\fR watchers is
663usually a better approach for this kind of thing. 1058usually a better approach for this kind of thing.
664.Sp 1059.Sp
665Here are the gory details of what \f(CW\*(C`ev_loop\*(C'\fR does: 1060Here are the gory details of what \f(CW\*(C`ev_run\*(C'\fR does (this is for your
1061understanding, not a guarantee that things will work exactly like this in
1062future versions):
666.Sp 1063.Sp
667.Vb 19 1064.Vb 10
1065\& \- Increment loop depth.
1066\& \- Reset the ev_break status.
668\& - Before the first iteration, call any pending watchers. 1067\& \- Before the first iteration, call any pending watchers.
669\& * If there are no active watchers (reference count is zero), return. 1068\& LOOP:
670\& - Queue all prepare watchers and then call all outstanding watchers. 1069\& \- If EVFLAG_FORKCHECK was used, check for a fork.
1070\& \- If a fork was detected (by any means), queue and call all fork watchers.
1071\& \- Queue and call all prepare watchers.
1072\& \- If ev_break was called, goto FINISH.
671\& - If we have been forked, recreate the kernel state. 1073\& \- If we have been forked, detach and recreate the kernel state
1074\& as to not disturb the other process.
672\& - Update the kernel state with all outstanding changes. 1075\& \- Update the kernel state with all outstanding changes.
673\& - Update the "event loop time". 1076\& \- Update the "event loop time" (ev_now ()).
674\& - Calculate for how long to block. 1077\& \- Calculate for how long to sleep or block, if at all
1078\& (active idle watchers, EVRUN_NOWAIT or not having
1079\& any active watchers at all will result in not sleeping).
1080\& \- Sleep if the I/O and timer collect interval say so.
1081\& \- Increment loop iteration counter.
675\& - Block the process, waiting for any events. 1082\& \- Block the process, waiting for any events.
676\& - Queue all outstanding I/O (fd) events. 1083\& \- Queue all outstanding I/O (fd) events.
677\& - Update the "event loop time" and do time jump handling. 1084\& \- Update the "event loop time" (ev_now ()), and do time jump adjustments.
678\& - Queue all outstanding timers. 1085\& \- Queue all expired timers.
679\& - Queue all outstanding periodics. 1086\& \- Queue all expired periodics.
680\& - If no events are pending now, queue all idle watchers. 1087\& \- Queue all idle watchers with priority higher than that of pending events.
681\& - Queue all check watchers. 1088\& \- Queue all check watchers.
682\& - Call all queued watchers in reverse order (i.e. check watchers first). 1089\& \- Call all queued watchers in reverse order (i.e. check watchers first).
683\& Signals and child watchers are implemented as I/O watchers, and will 1090\& Signals and child watchers are implemented as I/O watchers, and will
684\& be handled here by queueing them when their watcher gets executed. 1091\& be handled here by queueing them when their watcher gets executed.
685\& - If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK 1092\& \- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
686\& were used, return, otherwise continue with step *. 1093\& were used, or there are no active watchers, goto FINISH, otherwise
1094\& continue with step LOOP.
1095\& FINISH:
1096\& \- Reset the ev_break status iff it was EVBREAK_ONE.
1097\& \- Decrement the loop depth.
1098\& \- Return.
687.Ve 1099.Ve
688.Sp 1100.Sp
689Example: Queue some jobs and then loop until no events are outsanding 1101Example: Queue some jobs and then loop until no events are outstanding
690anymore. 1102anymore.
691.Sp 1103.Sp
692.Vb 4 1104.Vb 4
693\& ... queue jobs here, make sure they register event watchers as long 1105\& ... queue jobs here, make sure they register event watchers as long
694\& ... as they still have work to do (even an idle watcher will do..) 1106\& ... as they still have work to do (even an idle watcher will do..)
695\& ev_loop (my_loop, 0); 1107\& ev_run (my_loop, 0);
696\& ... jobs done. yeah! 1108\& ... jobs done or somebody called break. yeah!
697.Ve 1109.Ve
698.IP "ev_unloop (loop, how)" 4 1110.IP "ev_break (loop, how)" 4
699.IX Item "ev_unloop (loop, how)" 1111.IX Item "ev_break (loop, how)"
700Can be used to make a call to \f(CW\*(C`ev_loop\*(C'\fR return early (but only after it 1112Can be used to make a call to \f(CW\*(C`ev_run\*(C'\fR return early (but only after it
701has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either 1113has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either
702\&\f(CW\*(C`EVUNLOOP_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_loop\*(C'\fR call return, or 1114\&\f(CW\*(C`EVBREAK_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_run\*(C'\fR call return, or
703\&\f(CW\*(C`EVUNLOOP_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_loop\*(C'\fR calls return. 1115\&\f(CW\*(C`EVBREAK_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_run\*(C'\fR calls return.
1116.Sp
1117This \*(L"break state\*(R" will be cleared on the next call to \f(CW\*(C`ev_run\*(C'\fR.
1118.Sp
1119It is safe to call \f(CW\*(C`ev_break\*(C'\fR from outside any \f(CW\*(C`ev_run\*(C'\fR calls, too, in
1120which case it will have no effect.
704.IP "ev_ref (loop)" 4 1121.IP "ev_ref (loop)" 4
705.IX Item "ev_ref (loop)" 1122.IX Item "ev_ref (loop)"
706.PD 0 1123.PD 0
707.IP "ev_unref (loop)" 4 1124.IP "ev_unref (loop)" 4
708.IX Item "ev_unref (loop)" 1125.IX Item "ev_unref (loop)"
709.PD 1126.PD
710Ref/unref can be used to add or remove a reference count on the event 1127Ref/unref can be used to add or remove a reference count on the event
711loop: Every watcher keeps one reference, and as long as the reference 1128loop: Every watcher keeps one reference, and as long as the reference
712count is nonzero, \f(CW\*(C`ev_loop\*(C'\fR will not return on its own. If you have 1129count is nonzero, \f(CW\*(C`ev_run\*(C'\fR will not return on its own.
713a watcher you never unregister that should not keep \f(CW\*(C`ev_loop\*(C'\fR from 1130.Sp
714returning, \fIev_unref()\fR after starting, and \fIev_ref()\fR before stopping it. For 1131This is useful when you have a watcher that you never intend to
1132unregister, but that nevertheless should not keep \f(CW\*(C`ev_run\*(C'\fR from
1133returning. In such a case, call \f(CW\*(C`ev_unref\*(C'\fR after starting, and \f(CW\*(C`ev_ref\*(C'\fR
1134before stopping it.
1135.Sp
715example, libev itself uses this for its internal signal pipe: It is not 1136As an example, libev itself uses this for its internal signal pipe: It
716visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from exiting if 1137is not visible to the libev user and should not keep \f(CW\*(C`ev_run\*(C'\fR from
717no event watchers registered by it are active. It is also an excellent 1138exiting if no event watchers registered by it are active. It is also an
718way to do this for generic recurring timers or from within third-party 1139excellent way to do this for generic recurring timers or from within
719libraries. Just remember to \fIunref after start\fR and \fIref before stop\fR. 1140third-party libraries. Just remember to \fIunref after start\fR and \fIref
1141before stop\fR (but only if the watcher wasn't active before, or was active
1142before, respectively. Note also that libev might stop watchers itself
1143(e.g. non-repeating timers) in which case you have to \f(CW\*(C`ev_ref\*(C'\fR
1144in the callback).
720.Sp 1145.Sp
721Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_loop\*(C'\fR 1146Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_run\*(C'\fR
722running when nothing else is active. 1147running when nothing else is active.
723.Sp 1148.Sp
724.Vb 4 1149.Vb 4
725\& struct ev_signal exitsig; 1150\& ev_signal exitsig;
726\& ev_signal_init (&exitsig, sig_cb, SIGINT); 1151\& ev_signal_init (&exitsig, sig_cb, SIGINT);
727\& ev_signal_start (loop, &exitsig); 1152\& ev_signal_start (loop, &exitsig);
728\& evf_unref (loop); 1153\& ev_unref (loop);
729.Ve 1154.Ve
730.Sp 1155.Sp
731Example: For some weird reason, unregister the above signal handler again. 1156Example: For some weird reason, unregister the above signal handler again.
732.Sp 1157.Sp
733.Vb 2 1158.Vb 2
734\& ev_ref (loop); 1159\& ev_ref (loop);
735\& ev_signal_stop (loop, &exitsig); 1160\& ev_signal_stop (loop, &exitsig);
736.Ve 1161.Ve
737.IP "ev_set_io_collect_interval (loop, ev_tstamp interval)" 4 1162.IP "ev_set_io_collect_interval (loop, ev_tstamp interval)" 4
738.IX Item "ev_set_io_collect_interval (loop, ev_tstamp interval)" 1163.IX Item "ev_set_io_collect_interval (loop, ev_tstamp interval)"
739.PD 0 1164.PD 0
740.IP "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 4 1165.IP "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 4
741.IX Item "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 1166.IX Item "ev_set_timeout_collect_interval (loop, ev_tstamp interval)"
742.PD 1167.PD
743These advanced functions influence the time that libev will spend waiting 1168These advanced functions influence the time that libev will spend waiting
744for events. Both are by default \f(CW0\fR, meaning that libev will try to 1169for events. Both time intervals are by default \f(CW0\fR, meaning that libev
745invoke timer/periodic callbacks and I/O callbacks with minimum latency. 1170will try to invoke timer/periodic callbacks and I/O callbacks with minimum
1171latency.
746.Sp 1172.Sp
747Setting these to a higher value (the \f(CW\*(C`interval\*(C'\fR \fImust\fR be >= \f(CW0\fR) 1173Setting these to a higher value (the \f(CW\*(C`interval\*(C'\fR \fImust\fR be >= \f(CW0\fR)
748allows libev to delay invocation of I/O and timer/periodic callbacks to 1174allows libev to delay invocation of I/O and timer/periodic callbacks
749increase efficiency of loop iterations. 1175to increase efficiency of loop iterations (or to increase power-saving
1176opportunities).
750.Sp 1177.Sp
751The background is that sometimes your program runs just fast enough to 1178The idea is that sometimes your program runs just fast enough to handle
752handle one (or very few) event(s) per loop iteration. While this makes 1179one (or very few) event(s) per loop iteration. While this makes the
753the program responsive, it also wastes a lot of \s-1CPU\s0 time to poll for new 1180program responsive, it also wastes a lot of \s-1CPU\s0 time to poll for new
754events, especially with backends like \f(CW\*(C`select ()\*(C'\fR which have a high 1181events, especially with backends like \f(CW\*(C`select ()\*(C'\fR which have a high
755overhead for the actual polling but can deliver many events at once. 1182overhead for the actual polling but can deliver many events at once.
756.Sp 1183.Sp
757By setting a higher \fIio collect interval\fR you allow libev to spend more 1184By setting a higher \fIio collect interval\fR you allow libev to spend more
758time collecting I/O events, so you can handle more events per iteration, 1185time collecting I/O events, so you can handle more events per iteration,
759at the cost of increasing latency. Timeouts (both \f(CW\*(C`ev_periodic\*(C'\fR and 1186at the cost of increasing latency. Timeouts (both \f(CW\*(C`ev_periodic\*(C'\fR and
760\&\f(CW\*(C`ev_timer\*(C'\fR) will be not affected. Setting this to a non-null bvalue will 1187\&\f(CW\*(C`ev_timer\*(C'\fR) will not be affected. Setting this to a non-null value will
761introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations. 1188introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations. The
1189sleep time ensures that libev will not poll for I/O events more often then
1190once per this interval, on average (as long as the host time resolution is
1191good enough).
762.Sp 1192.Sp
763Likewise, by setting a higher \fItimeout collect interval\fR you allow libev 1193Likewise, by setting a higher \fItimeout collect interval\fR you allow libev
764to spend more time collecting timeouts, at the expense of increased 1194to spend more time collecting timeouts, at the expense of increased
765latency (the watcher callback will be called later). \f(CW\*(C`ev_io\*(C'\fR watchers 1195latency/jitter/inexactness (the watcher callback will be called
766will not be affected. Setting this to a non-null value will not introduce 1196later). \f(CW\*(C`ev_io\*(C'\fR watchers will not be affected. Setting this to a non-null
767any overhead in libev. 1197value will not introduce any overhead in libev.
768.Sp 1198.Sp
769Many (busy) programs can usually benefit by setting the io collect 1199Many (busy) programs can usually benefit by setting the I/O collect
770interval to a value near \f(CW0.1\fR or so, which is often enough for 1200interval to a value near \f(CW0.1\fR or so, which is often enough for
771interactive servers (of course not for games), likewise for timeouts. It 1201interactive servers (of course not for games), likewise for timeouts. It
772usually doesn't make much sense to set it to a lower value than \f(CW0.01\fR, 1202usually doesn't make much sense to set it to a lower value than \f(CW0.01\fR,
773as this approsaches the timing granularity of most systems. 1203as this approaches the timing granularity of most systems. Note that if
1204you do transactions with the outside world and you can't increase the
1205parallelity, then this setting will limit your transaction rate (if you
1206need to poll once per transaction and the I/O collect interval is 0.01,
1207then you can't do more than 100 transactions per second).
1208.Sp
1209Setting the \fItimeout collect interval\fR can improve the opportunity for
1210saving power, as the program will \*(L"bundle\*(R" timer callback invocations that
1211are \*(L"near\*(R" in time together, by delaying some, thus reducing the number of
1212times the process sleeps and wakes up again. Another useful technique to
1213reduce iterations/wake\-ups is to use \f(CW\*(C`ev_periodic\*(C'\fR watchers and make sure
1214they fire on, say, one-second boundaries only.
1215.Sp
1216Example: we only need 0.1s timeout granularity, and we wish not to poll
1217more often than 100 times per second:
1218.Sp
1219.Vb 2
1220\& ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
1221\& ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
1222.Ve
1223.IP "ev_invoke_pending (loop)" 4
1224.IX Item "ev_invoke_pending (loop)"
1225This call will simply invoke all pending watchers while resetting their
1226pending state. Normally, \f(CW\*(C`ev_run\*(C'\fR does this automatically when required,
1227but when overriding the invoke callback this call comes handy. This
1228function can be invoked from a watcher \- this can be useful for example
1229when you want to do some lengthy calculation and want to pass further
1230event handling to another thread (you still have to make sure only one
1231thread executes within \f(CW\*(C`ev_invoke_pending\*(C'\fR or \f(CW\*(C`ev_run\*(C'\fR of course).
1232.IP "int ev_pending_count (loop)" 4
1233.IX Item "int ev_pending_count (loop)"
1234Returns the number of pending watchers \- zero indicates that no watchers
1235are pending.
1236.IP "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(\s-1EV_P\s0))" 4
1237.IX Item "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))"
1238This overrides the invoke pending functionality of the loop: Instead of
1239invoking all pending watchers when there are any, \f(CW\*(C`ev_run\*(C'\fR will call
1240this callback instead. This is useful, for example, when you want to
1241invoke the actual watchers inside another context (another thread etc.).
1242.Sp
1243If you want to reset the callback, use \f(CW\*(C`ev_invoke_pending\*(C'\fR as new
1244callback.
1245.IP "ev_set_loop_release_cb (loop, void (*release)(\s-1EV_P\s0) throw (), void (*acquire)(\s-1EV_P\s0) throw ())" 4
1246.IX Item "ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())"
1247Sometimes you want to share the same loop between multiple threads. This
1248can be done relatively simply by putting mutex_lock/unlock calls around
1249each call to a libev function.
1250.Sp
1251However, \f(CW\*(C`ev_run\*(C'\fR can run an indefinite time, so it is not feasible
1252to wait for it to return. One way around this is to wake up the event
1253loop via \f(CW\*(C`ev_break\*(C'\fR and \f(CW\*(C`ev_async_send\*(C'\fR, another way is to set these
1254\&\fIrelease\fR and \fIacquire\fR callbacks on the loop.
1255.Sp
1256When set, then \f(CW\*(C`release\*(C'\fR will be called just before the thread is
1257suspended waiting for new events, and \f(CW\*(C`acquire\*(C'\fR is called just
1258afterwards.
1259.Sp
1260Ideally, \f(CW\*(C`release\*(C'\fR will just call your mutex_unlock function, and
1261\&\f(CW\*(C`acquire\*(C'\fR will just call the mutex_lock function again.
1262.Sp
1263While event loop modifications are allowed between invocations of
1264\&\f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR (that's their only purpose after all), no
1265modifications done will affect the event loop, i.e. adding watchers will
1266have no effect on the set of file descriptors being watched, or the time
1267waited. Use an \f(CW\*(C`ev_async\*(C'\fR watcher to wake up \f(CW\*(C`ev_run\*(C'\fR when you want it
1268to take note of any changes you made.
1269.Sp
1270In theory, threads executing \f(CW\*(C`ev_run\*(C'\fR will be async-cancel safe between
1271invocations of \f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR.
1272.Sp
1273See also the locking example in the \f(CW\*(C`THREADS\*(C'\fR section later in this
1274document.
1275.IP "ev_set_userdata (loop, void *data)" 4
1276.IX Item "ev_set_userdata (loop, void *data)"
1277.PD 0
1278.IP "void *ev_userdata (loop)" 4
1279.IX Item "void *ev_userdata (loop)"
1280.PD
1281Set and retrieve a single \f(CW\*(C`void *\*(C'\fR associated with a loop. When
1282\&\f(CW\*(C`ev_set_userdata\*(C'\fR has never been called, then \f(CW\*(C`ev_userdata\*(C'\fR returns
1283\&\f(CW0\fR.
1284.Sp
1285These two functions can be used to associate arbitrary data with a loop,
1286and are intended solely for the \f(CW\*(C`invoke_pending_cb\*(C'\fR, \f(CW\*(C`release\*(C'\fR and
1287\&\f(CW\*(C`acquire\*(C'\fR callbacks described above, but of course can be (ab\-)used for
1288any other purpose as well.
1289.IP "ev_verify (loop)" 4
1290.IX Item "ev_verify (loop)"
1291This function only does something when \f(CW\*(C`EV_VERIFY\*(C'\fR support has been
1292compiled in, which is the default for non-minimal builds. It tries to go
1293through all internal structures and checks them for validity. If anything
1294is found to be inconsistent, it will print an error message to standard
1295error and call \f(CW\*(C`abort ()\*(C'\fR.
1296.Sp
1297This can be used to catch bugs inside libev itself: under normal
1298circumstances, this function will never abort as of course libev keeps its
1299data structures consistent.
774.SH "ANATOMY OF A WATCHER" 1300.SH "ANATOMY OF A WATCHER"
775.IX Header "ANATOMY OF A WATCHER" 1301.IX Header "ANATOMY OF A WATCHER"
1302In the following description, uppercase \f(CW\*(C`TYPE\*(C'\fR in names stands for the
1303watcher type, e.g. \f(CW\*(C`ev_TYPE_start\*(C'\fR can mean \f(CW\*(C`ev_timer_start\*(C'\fR for timer
1304watchers and \f(CW\*(C`ev_io_start\*(C'\fR for I/O watchers.
1305.PP
776A watcher is a structure that you create and register to record your 1306A watcher is an opaque structure that you allocate and register to record
777interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to 1307your interest in some event. To make a concrete example, imagine you want
778become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher for that: 1308to wait for \s-1STDIN\s0 to become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher
1309for that:
779.PP 1310.PP
780.Vb 5 1311.Vb 5
781\& static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents) 1312\& static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
782\& { 1313\& {
783\& ev_io_stop (w); 1314\& ev_io_stop (w);
784\& ev_unloop (loop, EVUNLOOP_ALL); 1315\& ev_break (loop, EVBREAK_ALL);
785\& } 1316\& }
786.Ve 1317\&
787.PP
788.Vb 6
789\& struct ev_loop *loop = ev_default_loop (0); 1318\& struct ev_loop *loop = ev_default_loop (0);
1319\&
790\& struct ev_io stdin_watcher; 1320\& ev_io stdin_watcher;
1321\&
791\& ev_init (&stdin_watcher, my_cb); 1322\& ev_init (&stdin_watcher, my_cb);
792\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ); 1323\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
793\& ev_io_start (loop, &stdin_watcher); 1324\& ev_io_start (loop, &stdin_watcher);
1325\&
794\& ev_loop (loop, 0); 1326\& ev_run (loop, 0);
795.Ve 1327.Ve
796.PP 1328.PP
797As you can see, you are responsible for allocating the memory for your 1329As you can see, you are responsible for allocating the memory for your
798watcher structures (and it is usually a bad idea to do this on the stack, 1330watcher structures (and it is \fIusually\fR a bad idea to do this on the
799although this can sometimes be quite valid). 1331stack).
800.PP 1332.PP
1333Each watcher has an associated watcher structure (called \f(CW\*(C`struct ev_TYPE\*(C'\fR
1334or simply \f(CW\*(C`ev_TYPE\*(C'\fR, as typedefs are provided for all watcher structs).
1335.PP
801Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init 1336Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init (watcher
802(watcher *, callback)\*(C'\fR, which expects a callback to be provided. This 1337*, callback)\*(C'\fR, which expects a callback to be provided. This callback is
803callback gets invoked each time the event occurs (or, in the case of io 1338invoked each time the event occurs (or, in the case of I/O watchers, each
804watchers, each time the event loop detects that the file descriptor given 1339time the event loop detects that the file descriptor given is readable
805is readable and/or writable). 1340and/or writable).
806.PP 1341.PP
807Each watcher type has its own \f(CW\*(C`ev_<type>_set (watcher *, ...)\*(C'\fR macro 1342Each watcher type further has its own \f(CW\*(C`ev_TYPE_set (watcher *, ...)\*(C'\fR
808with arguments specific to this watcher type. There is also a macro 1343macro to configure it, with arguments specific to the watcher type. There
809to combine initialisation and setting in one call: \f(CW\*(C`ev_<type>_init 1344is also a macro to combine initialisation and setting in one call: \f(CW\*(C`ev_TYPE_init (watcher *, callback, ...)\*(C'\fR.
810(watcher *, callback, ...)\*(C'\fR.
811.PP 1345.PP
812To make the watcher actually watch out for events, you have to start it 1346To make the watcher actually watch out for events, you have to start it
813with a watcher-specific start function (\f(CW\*(C`ev_<type>_start (loop, watcher 1347with a watcher-specific start function (\f(CW\*(C`ev_TYPE_start (loop, watcher
814*)\*(C'\fR), and you can stop watching for events at any time by calling the 1348*)\*(C'\fR), and you can stop watching for events at any time by calling the
815corresponding stop function (\f(CW\*(C`ev_<type>_stop (loop, watcher *)\*(C'\fR. 1349corresponding stop function (\f(CW\*(C`ev_TYPE_stop (loop, watcher *)\*(C'\fR.
816.PP 1350.PP
817As long as your watcher is active (has been started but not stopped) you 1351As long as your watcher is active (has been started but not stopped) you
818must not touch the values stored in it. Most specifically you must never 1352must not touch the values stored in it. Most specifically you must never
819reinitialise it or call its \f(CW\*(C`set\*(C'\fR macro. 1353reinitialise it or call its \f(CW\*(C`ev_TYPE_set\*(C'\fR macro.
820.PP 1354.PP
821Each and every callback receives the event loop pointer as first, the 1355Each and every callback receives the event loop pointer as first, the
822registered watcher structure as second, and a bitset of received events as 1356registered watcher structure as second, and a bitset of received events as
823third argument. 1357third argument.
824.PP 1358.PP
… …
833.el .IP "\f(CWEV_WRITE\fR" 4 1367.el .IP "\f(CWEV_WRITE\fR" 4
834.IX Item "EV_WRITE" 1368.IX Item "EV_WRITE"
835.PD 1369.PD
836The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or 1370The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or
837writable. 1371writable.
838.ie n .IP """EV_TIMEOUT""" 4 1372.ie n .IP """EV_TIMER""" 4
839.el .IP "\f(CWEV_TIMEOUT\fR" 4 1373.el .IP "\f(CWEV_TIMER\fR" 4
840.IX Item "EV_TIMEOUT" 1374.IX Item "EV_TIMER"
841The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out. 1375The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out.
842.ie n .IP """EV_PERIODIC""" 4 1376.ie n .IP """EV_PERIODIC""" 4
843.el .IP "\f(CWEV_PERIODIC\fR" 4 1377.el .IP "\f(CWEV_PERIODIC\fR" 4
844.IX Item "EV_PERIODIC" 1378.IX Item "EV_PERIODIC"
845The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out. 1379The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out.
… …
865.PD 0 1399.PD 0
866.ie n .IP """EV_CHECK""" 4 1400.ie n .IP """EV_CHECK""" 4
867.el .IP "\f(CWEV_CHECK\fR" 4 1401.el .IP "\f(CWEV_CHECK\fR" 4
868.IX Item "EV_CHECK" 1402.IX Item "EV_CHECK"
869.PD 1403.PD
870All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_loop\*(C'\fR starts 1404All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_run\*(C'\fR starts to
871to gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are invoked just after 1405gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are queued (not invoked)
872\&\f(CW\*(C`ev_loop\*(C'\fR has gathered them, but before it invokes any callbacks for any 1406just after \f(CW\*(C`ev_run\*(C'\fR has gathered them, but before it queues any callbacks
1407for any received events. That means \f(CW\*(C`ev_prepare\*(C'\fR watchers are the last
1408watchers invoked before the event loop sleeps or polls for new events, and
1409\&\f(CW\*(C`ev_check\*(C'\fR watchers will be invoked before any other watchers of the same
1410or lower priority within an event loop iteration.
1411.Sp
873received events. Callbacks of both watcher types can start and stop as 1412Callbacks of both watcher types can start and stop as many watchers as
874many watchers as they want, and all of them will be taken into account 1413they want, and all of them will be taken into account (for example, a
875(for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep 1414\&\f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep \f(CW\*(C`ev_run\*(C'\fR from
876\&\f(CW\*(C`ev_loop\*(C'\fR from blocking). 1415blocking).
877.ie n .IP """EV_EMBED""" 4 1416.ie n .IP """EV_EMBED""" 4
878.el .IP "\f(CWEV_EMBED\fR" 4 1417.el .IP "\f(CWEV_EMBED\fR" 4
879.IX Item "EV_EMBED" 1418.IX Item "EV_EMBED"
880The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention. 1419The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention.
881.ie n .IP """EV_FORK""" 4 1420.ie n .IP """EV_FORK""" 4
882.el .IP "\f(CWEV_FORK\fR" 4 1421.el .IP "\f(CWEV_FORK\fR" 4
883.IX Item "EV_FORK" 1422.IX Item "EV_FORK"
884The event loop has been resumed in the child process after fork (see 1423The event loop has been resumed in the child process after fork (see
885\&\f(CW\*(C`ev_fork\*(C'\fR). 1424\&\f(CW\*(C`ev_fork\*(C'\fR).
1425.ie n .IP """EV_CLEANUP""" 4
1426.el .IP "\f(CWEV_CLEANUP\fR" 4
1427.IX Item "EV_CLEANUP"
1428The event loop is about to be destroyed (see \f(CW\*(C`ev_cleanup\*(C'\fR).
1429.ie n .IP """EV_ASYNC""" 4
1430.el .IP "\f(CWEV_ASYNC\fR" 4
1431.IX Item "EV_ASYNC"
1432The given async watcher has been asynchronously notified (see \f(CW\*(C`ev_async\*(C'\fR).
1433.ie n .IP """EV_CUSTOM""" 4
1434.el .IP "\f(CWEV_CUSTOM\fR" 4
1435.IX Item "EV_CUSTOM"
1436Not ever sent (or otherwise used) by libev itself, but can be freely used
1437by libev users to signal watchers (e.g. via \f(CW\*(C`ev_feed_event\*(C'\fR).
886.ie n .IP """EV_ERROR""" 4 1438.ie n .IP """EV_ERROR""" 4
887.el .IP "\f(CWEV_ERROR\fR" 4 1439.el .IP "\f(CWEV_ERROR\fR" 4
888.IX Item "EV_ERROR" 1440.IX Item "EV_ERROR"
889An unspecified error has occured, the watcher has been stopped. This might 1441An unspecified error has occurred, the watcher has been stopped. This might
890happen because the watcher could not be properly started because libev 1442happen because the watcher could not be properly started because libev
891ran out of memory, a file descriptor was found to be closed or any other 1443ran out of memory, a file descriptor was found to be closed or any other
1444problem. Libev considers these application bugs.
1445.Sp
892problem. You best act on it by reporting the problem and somehow coping 1446You best act on it by reporting the problem and somehow coping with the
893with the watcher being stopped. 1447watcher being stopped. Note that well-written programs should not receive
1448an error ever, so when your watcher receives it, this usually indicates a
1449bug in your program.
894.Sp 1450.Sp
895Libev will usually signal a few \*(L"dummy\*(R" events together with an error, 1451Libev will usually signal a few \*(L"dummy\*(R" events together with an error, for
896for example it might indicate that a fd is readable or writable, and if 1452example it might indicate that a fd is readable or writable, and if your
897your callbacks is well-written it can just attempt the operation and cope 1453callbacks is well-written it can just attempt the operation and cope with
898with the error from \fIread()\fR or \fIwrite()\fR. This will not work in multithreaded 1454the error from \fBread()\fR or \fBwrite()\fR. This will not work in multi-threaded
899programs, though, so beware. 1455programs, though, as the fd could already be closed and reused for another
1456thing, so beware.
900.Sh "\s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0" 1457.SS "\s-1GENERIC WATCHER FUNCTIONS\s0"
901.IX Subsection "GENERIC WATCHER FUNCTIONS" 1458.IX Subsection "GENERIC WATCHER FUNCTIONS"
902In the following description, \f(CW\*(C`TYPE\*(C'\fR stands for the watcher type,
903e.g. \f(CW\*(C`timer\*(C'\fR for \f(CW\*(C`ev_timer\*(C'\fR watchers and \f(CW\*(C`io\*(C'\fR for \f(CW\*(C`ev_io\*(C'\fR watchers.
904.ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4 1459.ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4
905.el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4 1460.el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4
906.IX Item "ev_init (ev_TYPE *watcher, callback)" 1461.IX Item "ev_init (ev_TYPE *watcher, callback)"
907This macro initialises the generic portion of a watcher. The contents 1462This macro initialises the generic portion of a watcher. The contents
908of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only 1463of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only
… …
912which rolls both calls into one. 1467which rolls both calls into one.
913.Sp 1468.Sp
914You can reinitialise a watcher at any time as long as it has been stopped 1469You can reinitialise a watcher at any time as long as it has been stopped
915(or never started) and there are no pending events outstanding. 1470(or never started) and there are no pending events outstanding.
916.Sp 1471.Sp
917The callback is always of type \f(CW\*(C`void (*)(ev_loop *loop, ev_TYPE *watcher, 1472The callback is always of type \f(CW\*(C`void (*)(struct ev_loop *loop, ev_TYPE *watcher,
918int revents)\*(C'\fR. 1473int revents)\*(C'\fR.
1474.Sp
1475Example: Initialise an \f(CW\*(C`ev_io\*(C'\fR watcher in two steps.
1476.Sp
1477.Vb 3
1478\& ev_io w;
1479\& ev_init (&w, my_cb);
1480\& ev_io_set (&w, STDIN_FILENO, EV_READ);
1481.Ve
919.ie n .IP """ev_TYPE_set"" (ev_TYPE *, [args])" 4 1482.ie n .IP """ev_TYPE_set"" (ev_TYPE *watcher, [args])" 4
920.el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *, [args])" 4 1483.el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *watcher, [args])" 4
921.IX Item "ev_TYPE_set (ev_TYPE *, [args])" 1484.IX Item "ev_TYPE_set (ev_TYPE *watcher, [args])"
922This macro initialises the type-specific parts of a watcher. You need to 1485This macro initialises the type-specific parts of a watcher. You need to
923call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can 1486call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can
924call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this 1487call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this
925macro on a watcher that is active (it can be pending, however, which is a 1488macro on a watcher that is active (it can be pending, however, which is a
926difference to the \f(CW\*(C`ev_init\*(C'\fR macro). 1489difference to the \f(CW\*(C`ev_init\*(C'\fR macro).
927.Sp 1490.Sp
928Although some watcher types do not have type-specific arguments 1491Although some watcher types do not have type-specific arguments
929(e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro. 1492(e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro.
1493.Sp
1494See \f(CW\*(C`ev_init\*(C'\fR, above, for an example.
930.ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4 1495.ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4
931.el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4 1496.el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4
932.IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])" 1497.IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])"
933This convinience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro 1498This convenience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro
934calls into a single call. This is the most convinient method to initialise 1499calls into a single call. This is the most convenient method to initialise
935a watcher. The same limitations apply, of course. 1500a watcher. The same limitations apply, of course.
1501.Sp
1502Example: Initialise and set an \f(CW\*(C`ev_io\*(C'\fR watcher in one step.
1503.Sp
1504.Vb 1
1505\& ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1506.Ve
936.ie n .IP """ev_TYPE_start"" (loop *, ev_TYPE *watcher)" 4 1507.ie n .IP """ev_TYPE_start"" (loop, ev_TYPE *watcher)" 4
937.el .IP "\f(CWev_TYPE_start\fR (loop *, ev_TYPE *watcher)" 4 1508.el .IP "\f(CWev_TYPE_start\fR (loop, ev_TYPE *watcher)" 4
938.IX Item "ev_TYPE_start (loop *, ev_TYPE *watcher)" 1509.IX Item "ev_TYPE_start (loop, ev_TYPE *watcher)"
939Starts (activates) the given watcher. Only active watchers will receive 1510Starts (activates) the given watcher. Only active watchers will receive
940events. If the watcher is already active nothing will happen. 1511events. If the watcher is already active nothing will happen.
1512.Sp
1513Example: Start the \f(CW\*(C`ev_io\*(C'\fR watcher that is being abused as example in this
1514whole section.
1515.Sp
1516.Vb 1
1517\& ev_io_start (EV_DEFAULT_UC, &w);
1518.Ve
941.ie n .IP """ev_TYPE_stop"" (loop *, ev_TYPE *watcher)" 4 1519.ie n .IP """ev_TYPE_stop"" (loop, ev_TYPE *watcher)" 4
942.el .IP "\f(CWev_TYPE_stop\fR (loop *, ev_TYPE *watcher)" 4 1520.el .IP "\f(CWev_TYPE_stop\fR (loop, ev_TYPE *watcher)" 4
943.IX Item "ev_TYPE_stop (loop *, ev_TYPE *watcher)" 1521.IX Item "ev_TYPE_stop (loop, ev_TYPE *watcher)"
944Stops the given watcher again (if active) and clears the pending 1522Stops the given watcher if active, and clears the pending status (whether
1523the watcher was active or not).
1524.Sp
945status. It is possible that stopped watchers are pending (for example, 1525It is possible that stopped watchers are pending \- for example,
946non-repeating timers are being stopped when they become pending), but 1526non-repeating timers are being stopped when they become pending \- but
947\&\f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor pending. If 1527calling \f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor
948you want to free or reuse the memory used by the watcher it is therefore a 1528pending. If you want to free or reuse the memory used by the watcher it is
949good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function. 1529therefore a good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function.
950.IP "bool ev_is_active (ev_TYPE *watcher)" 4 1530.IP "bool ev_is_active (ev_TYPE *watcher)" 4
951.IX Item "bool ev_is_active (ev_TYPE *watcher)" 1531.IX Item "bool ev_is_active (ev_TYPE *watcher)"
952Returns a true value iff the watcher is active (i.e. it has been started 1532Returns a true value iff the watcher is active (i.e. it has been started
953and not yet been stopped). As long as a watcher is active you must not modify 1533and not yet been stopped). As long as a watcher is active you must not modify
954it. 1534it.
… …
961make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR 1541make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR
962it). 1542it).
963.IP "callback ev_cb (ev_TYPE *watcher)" 4 1543.IP "callback ev_cb (ev_TYPE *watcher)" 4
964.IX Item "callback ev_cb (ev_TYPE *watcher)" 1544.IX Item "callback ev_cb (ev_TYPE *watcher)"
965Returns the callback currently set on the watcher. 1545Returns the callback currently set on the watcher.
966.IP "ev_cb_set (ev_TYPE *watcher, callback)" 4 1546.IP "ev_set_cb (ev_TYPE *watcher, callback)" 4
967.IX Item "ev_cb_set (ev_TYPE *watcher, callback)" 1547.IX Item "ev_set_cb (ev_TYPE *watcher, callback)"
968Change the callback. You can change the callback at virtually any time 1548Change the callback. You can change the callback at virtually any time
969(modulo threads). 1549(modulo threads).
970.IP "ev_set_priority (ev_TYPE *watcher, priority)" 4 1550.IP "ev_set_priority (ev_TYPE *watcher, int priority)" 4
971.IX Item "ev_set_priority (ev_TYPE *watcher, priority)" 1551.IX Item "ev_set_priority (ev_TYPE *watcher, int priority)"
972.PD 0 1552.PD 0
973.IP "int ev_priority (ev_TYPE *watcher)" 4 1553.IP "int ev_priority (ev_TYPE *watcher)" 4
974.IX Item "int ev_priority (ev_TYPE *watcher)" 1554.IX Item "int ev_priority (ev_TYPE *watcher)"
975.PD 1555.PD
976Set and query the priority of the watcher. The priority is a small 1556Set and query the priority of the watcher. The priority is a small
977integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR 1557integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR
978(default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked 1558(default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked
979before watchers with lower priority, but priority will not keep watchers 1559before watchers with lower priority, but priority will not keep watchers
980from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers). 1560from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers).
981.Sp 1561.Sp
982This means that priorities are \fIonly\fR used for ordering callback
983invocation after new events have been received. This is useful, for
984example, to reduce latency after idling, or more often, to bind two
985watchers on the same event and make sure one is called first.
986.Sp
987If you need to suppress invocation when higher priority events are pending 1562If you need to suppress invocation when higher priority events are pending
988you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality. 1563you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality.
989.Sp 1564.Sp
990You \fImust not\fR change the priority of a watcher as long as it is active or 1565You \fImust not\fR change the priority of a watcher as long as it is active or
991pending. 1566pending.
992.Sp 1567.Sp
1568Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is
1569fine, as long as you do not mind that the priority value you query might
1570or might not have been clamped to the valid range.
1571.Sp
993The default priority used by watchers when no priority has been set is 1572The default priority used by watchers when no priority has been set is
994always \f(CW0\fR, which is supposed to not be too high and not be too low :). 1573always \f(CW0\fR, which is supposed to not be too high and not be too low :).
995.Sp 1574.Sp
996Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is 1575See \*(L"\s-1WATCHER PRIORITY MODELS\*(R"\s0, below, for a more thorough treatment of
997fine, as long as you do not mind that the priority value you query might 1576priorities.
998or might not have been adjusted to be within valid range.
999.IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4 1577.IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4
1000.IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)" 1578.IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)"
1001Invoke the \f(CW\*(C`watcher\*(C'\fR with the given \f(CW\*(C`loop\*(C'\fR and \f(CW\*(C`revents\*(C'\fR. Neither 1579Invoke the \f(CW\*(C`watcher\*(C'\fR with the given \f(CW\*(C`loop\*(C'\fR and \f(CW\*(C`revents\*(C'\fR. Neither
1002\&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback 1580\&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback
1003can deal with that fact. 1581can deal with that fact, as both are simply passed through to the
1582callback.
1004.IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4 1583.IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4
1005.IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)" 1584.IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)"
1006If the watcher is pending, this function returns clears its pending status 1585If the watcher is pending, this function clears its pending status and
1007and returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the 1586returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the
1008watcher isn't pending it does nothing and returns \f(CW0\fR. 1587watcher isn't pending it does nothing and returns \f(CW0\fR.
1009.Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0" 1588.Sp
1010.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER" 1589Sometimes it can be useful to \*(L"poll\*(R" a watcher instead of waiting for its
1011Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change 1590callback to be invoked, which can be accomplished with this function.
1012and read at any time, libev will completely ignore it. This can be used 1591.IP "ev_feed_event (loop, ev_TYPE *watcher, int revents)" 4
1013to associate arbitrary data with your watcher. If you need more data and 1592.IX Item "ev_feed_event (loop, ev_TYPE *watcher, int revents)"
1014don't want to allocate memory and store a pointer to it in that data 1593Feeds the given event set into the event loop, as if the specified event
1015member, you can also \*(L"subclass\*(R" the watcher type and provide your own 1594had happened for the specified watcher (which must be a pointer to an
1016data: 1595initialised but not necessarily started event watcher). Obviously you must
1596not free the watcher as long as it has pending events.
1597.Sp
1598Stopping the watcher, letting libev invoke it, or calling
1599\&\f(CW\*(C`ev_clear_pending\*(C'\fR will clear the pending event, even if the watcher was
1600not started in the first place.
1601.Sp
1602See also \f(CW\*(C`ev_feed_fd_event\*(C'\fR and \f(CW\*(C`ev_feed_signal_event\*(C'\fR for related
1603functions that do not need a watcher.
1017.PP 1604.PP
1605See also the \*(L"\s-1ASSOCIATING CUSTOM DATA WITH A WATCHER\*(R"\s0 and \*(L"\s-1BUILDING YOUR
1606OWN COMPOSITE WATCHERS\*(R"\s0 idioms.
1607.SS "\s-1WATCHER STATES\s0"
1608.IX Subsection "WATCHER STATES"
1609There are various watcher states mentioned throughout this manual \-
1610active, pending and so on. In this section these states and the rules to
1611transition between them will be described in more detail \- and while these
1612rules might look complicated, they usually do \*(L"the right thing\*(R".
1613.IP "initialised" 4
1614.IX Item "initialised"
1615Before a watcher can be registered with the event loop it has to be
1616initialised. This can be done with a call to \f(CW\*(C`ev_TYPE_init\*(C'\fR, or calls to
1617\&\f(CW\*(C`ev_init\*(C'\fR followed by the watcher-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR function.
1618.Sp
1619In this state it is simply some block of memory that is suitable for
1620use in an event loop. It can be moved around, freed, reused etc. at
1621will \- as long as you either keep the memory contents intact, or call
1622\&\f(CW\*(C`ev_TYPE_init\*(C'\fR again.
1623.IP "started/running/active" 4
1624.IX Item "started/running/active"
1625Once a watcher has been started with a call to \f(CW\*(C`ev_TYPE_start\*(C'\fR it becomes
1626property of the event loop, and is actively waiting for events. While in
1627this state it cannot be accessed (except in a few documented ways), moved,
1628freed or anything else \- the only legal thing is to keep a pointer to it,
1629and call libev functions on it that are documented to work on active watchers.
1630.IP "pending" 4
1631.IX Item "pending"
1632If a watcher is active and libev determines that an event it is interested
1633in has occurred (such as a timer expiring), it will become pending. It will
1634stay in this pending state until either it is stopped or its callback is
1635about to be invoked, so it is not normally pending inside the watcher
1636callback.
1637.Sp
1638The watcher might or might not be active while it is pending (for example,
1639an expired non-repeating timer can be pending but no longer active). If it
1640is stopped, it can be freely accessed (e.g. by calling \f(CW\*(C`ev_TYPE_set\*(C'\fR),
1641but it is still property of the event loop at this time, so cannot be
1642moved, freed or reused. And if it is active the rules described in the
1643previous item still apply.
1644.Sp
1645It is also possible to feed an event on a watcher that is not active (e.g.
1646via \f(CW\*(C`ev_feed_event\*(C'\fR), in which case it becomes pending without being
1647active.
1648.IP "stopped" 4
1649.IX Item "stopped"
1650A watcher can be stopped implicitly by libev (in which case it might still
1651be pending), or explicitly by calling its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function. The
1652latter will clear any pending state the watcher might be in, regardless
1653of whether it was active or not, so stopping a watcher explicitly before
1654freeing it is often a good idea.
1655.Sp
1656While stopped (and not pending) the watcher is essentially in the
1657initialised state, that is, it can be reused, moved, modified in any way
1658you wish (but when you trash the memory block, you need to \f(CW\*(C`ev_TYPE_init\*(C'\fR
1659it again).
1660.SS "\s-1WATCHER PRIORITY MODELS\s0"
1661.IX Subsection "WATCHER PRIORITY MODELS"
1662Many event loops support \fIwatcher priorities\fR, which are usually small
1663integers that influence the ordering of event callback invocation
1664between watchers in some way, all else being equal.
1665.PP
1666In libev, watcher priorities can be set using \f(CW\*(C`ev_set_priority\*(C'\fR. See its
1667description for the more technical details such as the actual priority
1668range.
1669.PP
1670There are two common ways how these these priorities are being interpreted
1671by event loops:
1672.PP
1673In the more common lock-out model, higher priorities \*(L"lock out\*(R" invocation
1674of lower priority watchers, which means as long as higher priority
1675watchers receive events, lower priority watchers are not being invoked.
1676.PP
1677The less common only-for-ordering model uses priorities solely to order
1678callback invocation within a single event loop iteration: Higher priority
1679watchers are invoked before lower priority ones, but they all get invoked
1680before polling for new events.
1681.PP
1682Libev uses the second (only-for-ordering) model for all its watchers
1683except for idle watchers (which use the lock-out model).
1684.PP
1685The rationale behind this is that implementing the lock-out model for
1686watchers is not well supported by most kernel interfaces, and most event
1687libraries will just poll for the same events again and again as long as
1688their callbacks have not been executed, which is very inefficient in the
1689common case of one high-priority watcher locking out a mass of lower
1690priority ones.
1691.PP
1692Static (ordering) priorities are most useful when you have two or more
1693watchers handling the same resource: a typical usage example is having an
1694\&\f(CW\*(C`ev_io\*(C'\fR watcher to receive data, and an associated \f(CW\*(C`ev_timer\*(C'\fR to handle
1695timeouts. Under load, data might be received while the program handles
1696other jobs, but since timers normally get invoked first, the timeout
1697handler will be executed before checking for data. In that case, giving
1698the timer a lower priority than the I/O watcher ensures that I/O will be
1699handled first even under adverse conditions (which is usually, but not
1700always, what you want).
1701.PP
1702Since idle watchers use the \*(L"lock-out\*(R" model, meaning that idle watchers
1703will only be executed when no same or higher priority watchers have
1704received events, they can be used to implement the \*(L"lock-out\*(R" model when
1705required.
1706.PP
1707For example, to emulate how many other event libraries handle priorities,
1708you can associate an \f(CW\*(C`ev_idle\*(C'\fR watcher to each such watcher, and in
1709the normal watcher callback, you just start the idle watcher. The real
1710processing is done in the idle watcher callback. This causes libev to
1711continuously poll and process kernel event data for the watcher, but when
1712the lock-out case is known to be rare (which in turn is rare :), this is
1713workable.
1714.PP
1715Usually, however, the lock-out model implemented that way will perform
1716miserably under the type of load it was designed to handle. In that case,
1717it might be preferable to stop the real watcher before starting the
1718idle watcher, so the kernel will not have to process the event in case
1719the actual processing will be delayed for considerable time.
1720.PP
1721Here is an example of an I/O watcher that should run at a strictly lower
1722priority than the default, and which should only process data when no
1723other events are pending:
1724.PP
1018.Vb 7 1725.Vb 2
1019\& struct my_io 1726\& ev_idle idle; // actual processing watcher
1020\& { 1727\& ev_io io; // actual event watcher
1021\& struct ev_io io; 1728\&
1022\& int otherfd;
1023\& void *somedata;
1024\& struct whatever *mostinteresting;
1025\& }
1026.Ve
1027.PP
1028And since your callback will be called with a pointer to the watcher, you
1029can cast it back to your own type:
1030.PP
1031.Vb 5
1032\& static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
1033\& {
1034\& struct my_io *w = (struct my_io *)w_;
1035\& ...
1036\& }
1037.Ve
1038.PP
1039More interesting and less C\-conformant ways of casting your callback type
1040instead have been omitted.
1041.PP
1042Another common scenario is having some data structure with multiple
1043watchers:
1044.PP
1045.Vb 6
1046\& struct my_biggy
1047\& {
1048\& int some_data;
1049\& ev_timer t1;
1050\& ev_timer t2;
1051\& }
1052.Ve
1053.PP
1054In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more complicated,
1055you need to use \f(CW\*(C`offsetof\*(C'\fR:
1056.PP
1057.Vb 1
1058\& #include <stddef.h>
1059.Ve
1060.PP
1061.Vb 6
1062\& static void 1729\& static void
1063\& t1_cb (EV_P_ struct ev_timer *w, int revents) 1730\& io_cb (EV_P_ ev_io *w, int revents)
1064\& { 1731\& {
1065\& struct my_biggy big = (struct my_biggy * 1732\& // stop the I/O watcher, we received the event, but
1066\& (((char *)w) - offsetof (struct my_biggy, t1)); 1733\& // are not yet ready to handle it.
1734\& ev_io_stop (EV_A_ w);
1735\&
1736\& // start the idle watcher to handle the actual event.
1737\& // it will not be executed as long as other watchers
1738\& // with the default priority are receiving events.
1739\& ev_idle_start (EV_A_ &idle);
1067\& } 1740\& }
1068.Ve 1741\&
1069.PP
1070.Vb 6
1071\& static void 1742\& static void
1072\& t2_cb (EV_P_ struct ev_timer *w, int revents) 1743\& idle_cb (EV_P_ ev_idle *w, int revents)
1073\& { 1744\& {
1074\& struct my_biggy big = (struct my_biggy * 1745\& // actual processing
1075\& (((char *)w) - offsetof (struct my_biggy, t2)); 1746\& read (STDIN_FILENO, ...);
1747\&
1748\& // have to start the I/O watcher again, as
1749\& // we have handled the event
1750\& ev_io_start (EV_P_ &io);
1076\& } 1751\& }
1752\&
1753\& // initialisation
1754\& ev_idle_init (&idle, idle_cb);
1755\& ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
1756\& ev_io_start (EV_DEFAULT_ &io);
1077.Ve 1757.Ve
1758.PP
1759In the \*(L"real\*(R" world, it might also be beneficial to start a timer, so that
1760low-priority connections can not be locked out forever under load. This
1761enables your program to keep a lower latency for important connections
1762during short periods of high load, while not completely locking out less
1763important ones.
1078.SH "WATCHER TYPES" 1764.SH "WATCHER TYPES"
1079.IX Header "WATCHER TYPES" 1765.IX Header "WATCHER TYPES"
1080This section describes each watcher in detail, but will not repeat 1766This section describes each watcher in detail, but will not repeat
1081information given in the last section. Any initialisation/set macros, 1767information given in the last section. Any initialisation/set macros,
1082functions and members specific to the watcher type are explained. 1768functions and members specific to the watcher type are explained.
… …
1087watcher is stopped to your hearts content), or \fI[read\-write]\fR, which 1773watcher is stopped to your hearts content), or \fI[read\-write]\fR, which
1088means you can expect it to have some sensible content while the watcher 1774means you can expect it to have some sensible content while the watcher
1089is active, but you can also modify it. Modifying it may not do something 1775is active, but you can also modify it. Modifying it may not do something
1090sensible or take immediate effect (or do anything at all), but libev will 1776sensible or take immediate effect (or do anything at all), but libev will
1091not crash or malfunction in any way. 1777not crash or malfunction in any way.
1092.ie n .Sh """ev_io"" \- is this file descriptor readable or writable?" 1778.ie n .SS """ev_io"" \- is this file descriptor readable or writable?"
1093.el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable?" 1779.el .SS "\f(CWev_io\fP \- is this file descriptor readable or writable?"
1094.IX Subsection "ev_io - is this file descriptor readable or writable?" 1780.IX Subsection "ev_io - is this file descriptor readable or writable?"
1095I/O watchers check whether a file descriptor is readable or writable 1781I/O watchers check whether a file descriptor is readable or writable
1096in each iteration of the event loop, or, more precisely, when reading 1782in each iteration of the event loop, or, more precisely, when reading
1097would not block the process and writing would at least be able to write 1783would not block the process and writing would at least be able to write
1098some data. This behaviour is called level-triggering because you keep 1784some data. This behaviour is called level-triggering because you keep
… …
1103In general you can register as many read and/or write event watchers per 1789In general you can register as many read and/or write event watchers per
1104fd as you want (as long as you don't confuse yourself). Setting all file 1790fd as you want (as long as you don't confuse yourself). Setting all file
1105descriptors to non-blocking mode is also usually a good idea (but not 1791descriptors to non-blocking mode is also usually a good idea (but not
1106required if you know what you are doing). 1792required if you know what you are doing).
1107.PP 1793.PP
1108You have to be careful with dup'ed file descriptors, though. Some backends
1109(the linux epoll backend is a notable example) cannot handle dup'ed file
1110descriptors correctly if you register interest in two or more fds pointing
1111to the same underlying file/socket/etc. description (that is, they share
1112the same underlying \*(L"file open\*(R").
1113.PP
1114If you must do this, then force the use of a known-to-be-good backend
1115(at the time of this writing, this includes only \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and
1116\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR).
1117.PP
1118Another thing you have to watch out for is that it is quite easy to 1794Another thing you have to watch out for is that it is quite easy to
1119receive \*(L"spurious\*(R" readyness notifications, that is your callback might 1795receive \*(L"spurious\*(R" readiness notifications, that is, your callback might
1120be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block 1796be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block
1121because there is no data. Not only are some backends known to create a 1797because there is no data. It is very easy to get into this situation even
1122lot of those (for example solaris ports), it is very easy to get into 1798with a relatively standard program structure. Thus it is best to always
1123this situation even with a relatively standard program structure. Thus 1799use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning \f(CW\*(C`EAGAIN\*(C'\fR is far
1124it is best to always use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning
1125\&\f(CW\*(C`EAGAIN\*(C'\fR is far preferable to a program hanging until some data arrives. 1800preferable to a program hanging until some data arrives.
1126.PP 1801.PP
1127If you cannot run the fd in non-blocking mode (for example you should not 1802If you cannot run the fd in non-blocking mode (for example you should
1128play around with an Xlib connection), then you have to seperately re-test 1803not play around with an Xlib connection), then you have to separately
1129whether a file descriptor is really ready with a known-to-be good interface 1804re-test whether a file descriptor is really ready with a known-to-be good
1130such as poll (fortunately in our Xlib example, Xlib already does this on 1805interface such as poll (fortunately in the case of Xlib, it already does
1131its own, so its quite safe to use). 1806this on its own, so its quite safe to use). Some people additionally
1807use \f(CW\*(C`SIGALRM\*(C'\fR and an interval timer, just to be sure you won't block
1808indefinitely.
1809.PP
1810But really, best use non-blocking mode.
1132.PP 1811.PP
1133\fIThe special problem of disappearing file descriptors\fR 1812\fIThe special problem of disappearing file descriptors\fR
1134.IX Subsection "The special problem of disappearing file descriptors" 1813.IX Subsection "The special problem of disappearing file descriptors"
1135.PP 1814.PP
1136Some backends (e.g. kqueue, epoll) need to be told about closing a file 1815Some backends (e.g. kqueue, epoll, linuxaio) need to be told about closing
1137descriptor (either by calling \f(CW\*(C`close\*(C'\fR explicitly or by any other means, 1816a file descriptor (either due to calling \f(CW\*(C`close\*(C'\fR explicitly or any other
1138such as \f(CW\*(C`dup\*(C'\fR). The reason is that you register interest in some file 1817means, such as \f(CW\*(C`dup2\*(C'\fR). The reason is that you register interest in some
1139descriptor, but when it goes away, the operating system will silently drop 1818file descriptor, but when it goes away, the operating system will silently
1140this interest. If another file descriptor with the same number then is 1819drop this interest. If another file descriptor with the same number then
1141registered with libev, there is no efficient way to see that this is, in 1820is registered with libev, there is no efficient way to see that this is,
1142fact, a different file descriptor. 1821in fact, a different file descriptor.
1143.PP 1822.PP
1144To avoid having to explicitly tell libev about such cases, libev follows 1823To avoid having to explicitly tell libev about such cases, libev follows
1145the following policy: Each time \f(CW\*(C`ev_io_set\*(C'\fR is being called, libev 1824the following policy: Each time \f(CW\*(C`ev_io_set\*(C'\fR is being called, libev
1146will assume that this is potentially a new file descriptor, otherwise 1825will assume that this is potentially a new file descriptor, otherwise
1147it is assumed that the file descriptor stays the same. That means that 1826it is assumed that the file descriptor stays the same. That means that
… …
1154.PP 1833.PP
1155\fIThe special problem of dup'ed file descriptors\fR 1834\fIThe special problem of dup'ed file descriptors\fR
1156.IX Subsection "The special problem of dup'ed file descriptors" 1835.IX Subsection "The special problem of dup'ed file descriptors"
1157.PP 1836.PP
1158Some backends (e.g. epoll), cannot register events for file descriptors, 1837Some backends (e.g. epoll), cannot register events for file descriptors,
1159but only events for the underlying file descriptions. That menas when you 1838but only events for the underlying file descriptions. That means when you
1160have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors and register events for them, only one 1839have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or weirder constellations, and register
1161file descriptor might actually receive events. 1840events for them, only one file descriptor might actually receive events.
1162.PP 1841.PP
1163There is no workaorund possible except not registering events 1842There is no workaround possible except not registering events
1164for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or to resort to 1843for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors, or to resort to
1165\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR. 1844\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1845.PP
1846\fIThe special problem of files\fR
1847.IX Subsection "The special problem of files"
1848.PP
1849Many people try to use \f(CW\*(C`select\*(C'\fR (or libev) on file descriptors
1850representing files, and expect it to become ready when their program
1851doesn't block on disk accesses (which can take a long time on their own).
1852.PP
1853However, this cannot ever work in the \*(L"expected\*(R" way \- you get a readiness
1854notification as soon as the kernel knows whether and how much data is
1855there, and in the case of open files, that's always the case, so you
1856always get a readiness notification instantly, and your read (or possibly
1857write) will still block on the disk I/O.
1858.PP
1859Another way to view it is that in the case of sockets, pipes, character
1860devices and so on, there is another party (the sender) that delivers data
1861on its own, but in the case of files, there is no such thing: the disk
1862will not send data on its own, simply because it doesn't know what you
1863wish to read \- you would first have to request some data.
1864.PP
1865Since files are typically not-so-well supported by advanced notification
1866mechanism, libev tries hard to emulate \s-1POSIX\s0 behaviour with respect
1867to files, even though you should not use it. The reason for this is
1868convenience: sometimes you want to watch \s-1STDIN\s0 or \s-1STDOUT,\s0 which is
1869usually a tty, often a pipe, but also sometimes files or special devices
1870(for example, \f(CW\*(C`epoll\*(C'\fR on Linux works with \fI/dev/random\fR but not with
1871\&\fI/dev/urandom\fR), and even though the file might better be served with
1872asynchronous I/O instead of with non-blocking I/O, it is still useful when
1873it \*(L"just works\*(R" instead of freezing.
1874.PP
1875So avoid file descriptors pointing to files when you know it (e.g. use
1876libeio), but use them when it is convenient, e.g. for \s-1STDIN/STDOUT,\s0 or
1877when you rarely read from a file instead of from a socket, and want to
1878reuse the same code path.
1166.PP 1879.PP
1167\fIThe special problem of fork\fR 1880\fIThe special problem of fork\fR
1168.IX Subsection "The special problem of fork" 1881.IX Subsection "The special problem of fork"
1169.PP 1882.PP
1170Some backends (epoll, kqueue) do not support \f(CW\*(C`fork ()\*(C'\fR at all or exhibit 1883Some backends (epoll, kqueue, linuxaio, iouring) do not support \f(CW\*(C`fork ()\*(C'\fR
1171useless behaviour. Libev fully supports fork, but needs to be told about 1884at all or exhibit useless behaviour. Libev fully supports fork, but needs
1172it in the child. 1885to be told about it in the child if you want to continue to use it in the
1886child.
1173.PP 1887.PP
1174To support fork in your programs, you either have to call 1888To support fork in your child processes, you have to call \f(CW\*(C`ev_loop_fork
1175\&\f(CW\*(C`ev_default_fork ()\*(C'\fR or \f(CW\*(C`ev_loop_fork ()\*(C'\fR after a fork in the child, 1889()\*(C'\fR after a fork in the child, enable \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR, or resort to
1176enable \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR, or resort to \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or 1890\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1177\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR. 1891.PP
1892\fIThe special problem of \s-1SIGPIPE\s0\fR
1893.IX Subsection "The special problem of SIGPIPE"
1894.PP
1895While not really specific to libev, it is easy to forget about \f(CW\*(C`SIGPIPE\*(C'\fR:
1896when writing to a pipe whose other end has been closed, your program gets
1897sent a \s-1SIGPIPE,\s0 which, by default, aborts your program. For most programs
1898this is sensible behaviour, for daemons, this is usually undesirable.
1899.PP
1900So when you encounter spurious, unexplained daemon exits, make sure you
1901ignore \s-1SIGPIPE\s0 (and maybe make sure you log the exit status of your daemon
1902somewhere, as that would have given you a big clue).
1903.PP
1904\fIThe special problem of \f(BIaccept()\fIing when you can't\fR
1905.IX Subsection "The special problem of accept()ing when you can't"
1906.PP
1907Many implementations of the \s-1POSIX\s0 \f(CW\*(C`accept\*(C'\fR function (for example,
1908found in post\-2004 Linux) have the peculiar behaviour of not removing a
1909connection from the pending queue in all error cases.
1910.PP
1911For example, larger servers often run out of file descriptors (because
1912of resource limits), causing \f(CW\*(C`accept\*(C'\fR to fail with \f(CW\*(C`ENFILE\*(C'\fR but not
1913rejecting the connection, leading to libev signalling readiness on
1914the next iteration again (the connection still exists after all), and
1915typically causing the program to loop at 100% \s-1CPU\s0 usage.
1916.PP
1917Unfortunately, the set of errors that cause this issue differs between
1918operating systems, there is usually little the app can do to remedy the
1919situation, and no known thread-safe method of removing the connection to
1920cope with overload is known (to me).
1921.PP
1922One of the easiest ways to handle this situation is to just ignore it
1923\&\- when the program encounters an overload, it will just loop until the
1924situation is over. While this is a form of busy waiting, no \s-1OS\s0 offers an
1925event-based way to handle this situation, so it's the best one can do.
1926.PP
1927A better way to handle the situation is to log any errors other than
1928\&\f(CW\*(C`EAGAIN\*(C'\fR and \f(CW\*(C`EWOULDBLOCK\*(C'\fR, making sure not to flood the log with such
1929messages, and continue as usual, which at least gives the user an idea of
1930what could be wrong (\*(L"raise the ulimit!\*(R"). For extra points one could stop
1931the \f(CW\*(C`ev_io\*(C'\fR watcher on the listening fd \*(L"for a while\*(R", which reduces \s-1CPU\s0
1932usage.
1933.PP
1934If your program is single-threaded, then you could also keep a dummy file
1935descriptor for overload situations (e.g. by opening \fI/dev/null\fR), and
1936when you run into \f(CW\*(C`ENFILE\*(C'\fR or \f(CW\*(C`EMFILE\*(C'\fR, close it, run \f(CW\*(C`accept\*(C'\fR,
1937close that fd, and create a new dummy fd. This will gracefully refuse
1938clients under typical overload conditions.
1939.PP
1940The last way to handle it is to simply log the error and \f(CW\*(C`exit\*(C'\fR, as
1941is often done with \f(CW\*(C`malloc\*(C'\fR failures, but this results in an easy
1942opportunity for a DoS attack.
1178.PP 1943.PP
1179\fIWatcher-Specific Functions\fR 1944\fIWatcher-Specific Functions\fR
1180.IX Subsection "Watcher-Specific Functions" 1945.IX Subsection "Watcher-Specific Functions"
1181.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4 1946.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
1182.IX Item "ev_io_init (ev_io *, callback, int fd, int events)" 1947.IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
1183.PD 0 1948.PD 0
1184.IP "ev_io_set (ev_io *, int fd, int events)" 4 1949.IP "ev_io_set (ev_io *, int fd, int events)" 4
1185.IX Item "ev_io_set (ev_io *, int fd, int events)" 1950.IX Item "ev_io_set (ev_io *, int fd, int events)"
1186.PD 1951.PD
1187Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to 1952Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to
1188rceeive events for and events is either \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or 1953receive events for and \f(CW\*(C`events\*(C'\fR is either \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or
1189\&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR to receive the given events. 1954\&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR, to express the desire to receive the given events.
1190.IP "int fd [read\-only]" 4 1955.IP "int fd [read\-only]" 4
1191.IX Item "int fd [read-only]" 1956.IX Item "int fd [read-only]"
1192The file descriptor being watched. 1957The file descriptor being watched.
1193.IP "int events [read\-only]" 4 1958.IP "int events [read\-only]" 4
1194.IX Item "int events [read-only]" 1959.IX Item "int events [read-only]"
1195The events being watched. 1960The events being watched.
1196.PP 1961.PP
1962\fIExamples\fR
1963.IX Subsection "Examples"
1964.PP
1197Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well 1965Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well
1198readable, but only once. Since it is likely line\-buffered, you could 1966readable, but only once. Since it is likely line-buffered, you could
1199attempt to read a whole line in the callback. 1967attempt to read a whole line in the callback.
1200.PP 1968.PP
1201.Vb 6 1969.Vb 6
1202\& static void 1970\& static void
1203\& stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents) 1971\& stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1204\& { 1972\& {
1205\& ev_io_stop (loop, w); 1973\& ev_io_stop (loop, w);
1206\& .. read from stdin here (or from w->fd) and haqndle any I/O errors 1974\& .. read from stdin here (or from w\->fd) and handle any I/O errors
1207\& } 1975\& }
1208.Ve 1976\&
1209.PP
1210.Vb 6
1211\& ... 1977\& ...
1212\& struct ev_loop *loop = ev_default_init (0); 1978\& struct ev_loop *loop = ev_default_init (0);
1213\& struct ev_io stdin_readable; 1979\& ev_io stdin_readable;
1214\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ); 1980\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1215\& ev_io_start (loop, &stdin_readable); 1981\& ev_io_start (loop, &stdin_readable);
1216\& ev_loop (loop, 0); 1982\& ev_run (loop, 0);
1217.Ve 1983.Ve
1218.ie n .Sh """ev_timer"" \- relative and optionally repeating timeouts" 1984.ie n .SS """ev_timer"" \- relative and optionally repeating timeouts"
1219.el .Sh "\f(CWev_timer\fP \- relative and optionally repeating timeouts" 1985.el .SS "\f(CWev_timer\fP \- relative and optionally repeating timeouts"
1220.IX Subsection "ev_timer - relative and optionally repeating timeouts" 1986.IX Subsection "ev_timer - relative and optionally repeating timeouts"
1221Timer watchers are simple relative timers that generate an event after a 1987Timer watchers are simple relative timers that generate an event after a
1222given time, and optionally repeating in regular intervals after that. 1988given time, and optionally repeating in regular intervals after that.
1223.PP 1989.PP
1224The timers are based on real time, that is, if you register an event that 1990The timers are based on real time, that is, if you register an event that
1225times out after an hour and you reset your system clock to last years 1991times out after an hour and you reset your system clock to January last
1226time, it will still time out after (roughly) and hour. \*(L"Roughly\*(R" because 1992year, it will still time out after (roughly) one hour. \*(L"Roughly\*(R" because
1227detecting time jumps is hard, and some inaccuracies are unavoidable (the 1993detecting time jumps is hard, and some inaccuracies are unavoidable (the
1228monotonic clock option helps a lot here). 1994monotonic clock option helps a lot here).
1995.PP
1996The callback is guaranteed to be invoked only \fIafter\fR its timeout has
1997passed (not \fIat\fR, so on systems with very low-resolution clocks this
1998might introduce a small delay, see \*(L"the special problem of being too
1999early\*(R", below). If multiple timers become ready during the same loop
2000iteration then the ones with earlier time-out values are invoked before
2001ones of the same priority with later time-out values (but this is no
2002longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
2003.PP
2004\fIBe smart about timeouts\fR
2005.IX Subsection "Be smart about timeouts"
2006.PP
2007Many real-world problems involve some kind of timeout, usually for error
2008recovery. A typical example is an \s-1HTTP\s0 request \- if the other side hangs,
2009you want to raise some error after a while.
2010.PP
2011What follows are some ways to handle this problem, from obvious and
2012inefficient to smart and efficient.
2013.PP
2014In the following, a 60 second activity timeout is assumed \- a timeout that
2015gets reset to 60 seconds each time there is activity (e.g. each time some
2016data or other life sign was received).
2017.IP "1. Use a timer and stop, reinitialise and start it on activity." 4
2018.IX Item "1. Use a timer and stop, reinitialise and start it on activity."
2019This is the most obvious, but not the most simple way: In the beginning,
2020start the watcher:
2021.Sp
2022.Vb 2
2023\& ev_timer_init (timer, callback, 60., 0.);
2024\& ev_timer_start (loop, timer);
2025.Ve
2026.Sp
2027Then, each time there is some activity, \f(CW\*(C`ev_timer_stop\*(C'\fR it, initialise it
2028and start it again:
2029.Sp
2030.Vb 3
2031\& ev_timer_stop (loop, timer);
2032\& ev_timer_set (timer, 60., 0.);
2033\& ev_timer_start (loop, timer);
2034.Ve
2035.Sp
2036This is relatively simple to implement, but means that each time there is
2037some activity, libev will first have to remove the timer from its internal
2038data structure and then add it again. Libev tries to be fast, but it's
2039still not a constant-time operation.
2040.ie n .IP "2. Use a timer and re-start it with ""ev_timer_again"" inactivity." 4
2041.el .IP "2. Use a timer and re-start it with \f(CWev_timer_again\fR inactivity." 4
2042.IX Item "2. Use a timer and re-start it with ev_timer_again inactivity."
2043This is the easiest way, and involves using \f(CW\*(C`ev_timer_again\*(C'\fR instead of
2044\&\f(CW\*(C`ev_timer_start\*(C'\fR.
2045.Sp
2046To implement this, configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value
2047of \f(CW60\fR and then call \f(CW\*(C`ev_timer_again\*(C'\fR at start and each time you
2048successfully read or write some data. If you go into an idle state where
2049you do not expect data to travel on the socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR
2050the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will automatically restart it if need be.
2051.Sp
2052That means you can ignore both the \f(CW\*(C`ev_timer_start\*(C'\fR function and the
2053\&\f(CW\*(C`after\*(C'\fR argument to \f(CW\*(C`ev_timer_set\*(C'\fR, and only ever use the \f(CW\*(C`repeat\*(C'\fR
2054member and \f(CW\*(C`ev_timer_again\*(C'\fR.
2055.Sp
2056At start:
2057.Sp
2058.Vb 3
2059\& ev_init (timer, callback);
2060\& timer\->repeat = 60.;
2061\& ev_timer_again (loop, timer);
2062.Ve
2063.Sp
2064Each time there is some activity:
2065.Sp
2066.Vb 1
2067\& ev_timer_again (loop, timer);
2068.Ve
2069.Sp
2070It is even possible to change the time-out on the fly, regardless of
2071whether the watcher is active or not:
2072.Sp
2073.Vb 2
2074\& timer\->repeat = 30.;
2075\& ev_timer_again (loop, timer);
2076.Ve
2077.Sp
2078This is slightly more efficient then stopping/starting the timer each time
2079you want to modify its timeout value, as libev does not have to completely
2080remove and re-insert the timer from/into its internal data structure.
2081.Sp
2082It is, however, even simpler than the \*(L"obvious\*(R" way to do it.
2083.IP "3. Let the timer time out, but then re-arm it as required." 4
2084.IX Item "3. Let the timer time out, but then re-arm it as required."
2085This method is more tricky, but usually most efficient: Most timeouts are
2086relatively long compared to the intervals between other activity \- in
2087our example, within 60 seconds, there are usually many I/O events with
2088associated activity resets.
2089.Sp
2090In this case, it would be more efficient to leave the \f(CW\*(C`ev_timer\*(C'\fR alone,
2091but remember the time of last activity, and check for a real timeout only
2092within the callback:
2093.Sp
2094.Vb 3
2095\& ev_tstamp timeout = 60.;
2096\& ev_tstamp last_activity; // time of last activity
2097\& ev_timer timer;
2098\&
2099\& static void
2100\& callback (EV_P_ ev_timer *w, int revents)
2101\& {
2102\& // calculate when the timeout would happen
2103\& ev_tstamp after = last_activity \- ev_now (EV_A) + timeout;
2104\&
2105\& // if negative, it means we the timeout already occurred
2106\& if (after < 0.)
2107\& {
2108\& // timeout occurred, take action
2109\& }
2110\& else
2111\& {
2112\& // callback was invoked, but there was some recent
2113\& // activity. simply restart the timer to time out
2114\& // after "after" seconds, which is the earliest time
2115\& // the timeout can occur.
2116\& ev_timer_set (w, after, 0.);
2117\& ev_timer_start (EV_A_ w);
2118\& }
2119\& }
2120.Ve
2121.Sp
2122To summarise the callback: first calculate in how many seconds the
2123timeout will occur (by calculating the absolute time when it would occur,
2124\&\f(CW\*(C`last_activity + timeout\*(C'\fR, and subtracting the current time, \f(CW\*(C`ev_now
2125(EV_A)\*(C'\fR from that).
2126.Sp
2127If this value is negative, then we are already past the timeout, i.e. we
2128timed out, and need to do whatever is needed in this case.
2129.Sp
2130Otherwise, we now the earliest time at which the timeout would trigger,
2131and simply start the timer with this timeout value.
2132.Sp
2133In other words, each time the callback is invoked it will check whether
2134the timeout occurred. If not, it will simply reschedule itself to check
2135again at the earliest time it could time out. Rinse. Repeat.
2136.Sp
2137This scheme causes more callback invocations (about one every 60 seconds
2138minus half the average time between activity), but virtually no calls to
2139libev to change the timeout.
2140.Sp
2141To start the machinery, simply initialise the watcher and set
2142\&\f(CW\*(C`last_activity\*(C'\fR to the current time (meaning there was some activity just
2143now), then call the callback, which will \*(L"do the right thing\*(R" and start
2144the timer:
2145.Sp
2146.Vb 3
2147\& last_activity = ev_now (EV_A);
2148\& ev_init (&timer, callback);
2149\& callback (EV_A_ &timer, 0);
2150.Ve
2151.Sp
2152When there is some activity, simply store the current time in
2153\&\f(CW\*(C`last_activity\*(C'\fR, no libev calls at all:
2154.Sp
2155.Vb 2
2156\& if (activity detected)
2157\& last_activity = ev_now (EV_A);
2158.Ve
2159.Sp
2160When your timeout value changes, then the timeout can be changed by simply
2161providing a new value, stopping the timer and calling the callback, which
2162will again do the right thing (for example, time out immediately :).
2163.Sp
2164.Vb 3
2165\& timeout = new_value;
2166\& ev_timer_stop (EV_A_ &timer);
2167\& callback (EV_A_ &timer, 0);
2168.Ve
2169.Sp
2170This technique is slightly more complex, but in most cases where the
2171time-out is unlikely to be triggered, much more efficient.
2172.IP "4. Wee, just use a double-linked list for your timeouts." 4
2173.IX Item "4. Wee, just use a double-linked list for your timeouts."
2174If there is not one request, but many thousands (millions...), all
2175employing some kind of timeout with the same timeout value, then one can
2176do even better:
2177.Sp
2178When starting the timeout, calculate the timeout value and put the timeout
2179at the \fIend\fR of the list.
2180.Sp
2181Then use an \f(CW\*(C`ev_timer\*(C'\fR to fire when the timeout at the \fIbeginning\fR of
2182the list is expected to fire (for example, using the technique #3).
2183.Sp
2184When there is some activity, remove the timer from the list, recalculate
2185the timeout, append it to the end of the list again, and make sure to
2186update the \f(CW\*(C`ev_timer\*(C'\fR if it was taken from the beginning of the list.
2187.Sp
2188This way, one can manage an unlimited number of timeouts in O(1) time for
2189starting, stopping and updating the timers, at the expense of a major
2190complication, and having to use a constant timeout. The constant timeout
2191ensures that the list stays sorted.
2192.PP
2193So which method the best?
2194.PP
2195Method #2 is a simple no-brain-required solution that is adequate in most
2196situations. Method #3 requires a bit more thinking, but handles many cases
2197better, and isn't very complicated either. In most case, choosing either
2198one is fine, with #3 being better in typical situations.
2199.PP
2200Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
2201rather complicated, but extremely efficient, something that really pays
2202off after the first million or so of active timers, i.e. it's usually
2203overkill :)
2204.PP
2205\fIThe special problem of being too early\fR
2206.IX Subsection "The special problem of being too early"
2207.PP
2208If you ask a timer to call your callback after three seconds, then
2209you expect it to be invoked after three seconds \- but of course, this
2210cannot be guaranteed to infinite precision. Less obviously, it cannot be
2211guaranteed to any precision by libev \- imagine somebody suspending the
2212process with a \s-1STOP\s0 signal for a few hours for example.
2213.PP
2214So, libev tries to invoke your callback as soon as possible \fIafter\fR the
2215delay has occurred, but cannot guarantee this.
2216.PP
2217A less obvious failure mode is calling your callback too early: many event
2218loops compare timestamps with a \*(L"elapsed delay >= requested delay\*(R", but
2219this can cause your callback to be invoked much earlier than you would
2220expect.
2221.PP
2222To see why, imagine a system with a clock that only offers full second
2223resolution (think windows if you can't come up with a broken enough \s-1OS\s0
2224yourself). If you schedule a one-second timer at the time 500.9, then the
2225event loop will schedule your timeout to elapse at a system time of 500
2226(500.9 truncated to the resolution) + 1, or 501.
2227.PP
2228If an event library looks at the timeout 0.1s later, it will see \*(L"501 >=
2229501\*(R" and invoke the callback 0.1s after it was started, even though a
2230one-second delay was requested \- this is being \*(L"too early\*(R", despite best
2231intentions.
2232.PP
2233This is the reason why libev will never invoke the callback if the elapsed
2234delay equals the requested delay, but only when the elapsed delay is
2235larger than the requested delay. In the example above, libev would only invoke
2236the callback at system time 502, or 1.1s after the timer was started.
2237.PP
2238So, while libev cannot guarantee that your callback will be invoked
2239exactly when requested, it \fIcan\fR and \fIdoes\fR guarantee that the requested
2240delay has actually elapsed, or in other words, it always errs on the \*(L"too
2241late\*(R" side of things.
2242.PP
2243\fIThe special problem of time updates\fR
2244.IX Subsection "The special problem of time updates"
2245.PP
2246Establishing the current time is a costly operation (it usually takes
2247at least one system call): \s-1EV\s0 therefore updates its idea of the current
2248time only before and after \f(CW\*(C`ev_run\*(C'\fR collects new events, which causes a
2249growing difference between \f(CW\*(C`ev_now ()\*(C'\fR and \f(CW\*(C`ev_time ()\*(C'\fR when handling
2250lots of events in one iteration.
1229.PP 2251.PP
1230The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR 2252The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
1231time. This is usually the right thing as this timestamp refers to the time 2253time. This is usually the right thing as this timestamp refers to the time
1232of the event triggering whatever timeout you are modifying/starting. If 2254of the event triggering whatever timeout you are modifying/starting. If
1233you suspect event processing to be delayed and you \fIneed\fR to base the timeout 2255you suspect event processing to be delayed and you \fIneed\fR to base the
1234on the current time, use something like this to adjust for this: 2256timeout on the current time, use something like the following to adjust
2257for it:
1235.PP 2258.PP
1236.Vb 1 2259.Vb 1
1237\& ev_timer_set (&timer, after + ev_now () - ev_time (), 0.); 2260\& ev_timer_set (&timer, after + (ev_time () \- ev_now ()), 0.);
1238.Ve 2261.Ve
1239.PP 2262.PP
1240The callback is guarenteed to be invoked only when its timeout has passed, 2263If the event loop is suspended for a long time, you can also force an
1241but if multiple timers become ready during the same loop iteration then 2264update of the time returned by \f(CW\*(C`ev_now ()\*(C'\fR by calling \f(CW\*(C`ev_now_update
1242order of execution is undefined. 2265()\*(C'\fR, although that will push the event time of all outstanding events
2266further into the future.
2267.PP
2268\fIThe special problem of unsynchronised clocks\fR
2269.IX Subsection "The special problem of unsynchronised clocks"
2270.PP
2271Modern systems have a variety of clocks \- libev itself uses the normal
2272\&\*(L"wall clock\*(R" clock and, if available, the monotonic clock (to avoid time
2273jumps).
2274.PP
2275Neither of these clocks is synchronised with each other or any other clock
2276on the system, so \f(CW\*(C`ev_time ()\*(C'\fR might return a considerably different time
2277than \f(CW\*(C`gettimeofday ()\*(C'\fR or \f(CW\*(C`time ()\*(C'\fR. On a GNU/Linux system, for example,
2278a call to \f(CW\*(C`gettimeofday\*(C'\fR might return a second count that is one higher
2279than a directly following call to \f(CW\*(C`time\*(C'\fR.
2280.PP
2281The moral of this is to only compare libev-related timestamps with
2282\&\f(CW\*(C`ev_time ()\*(C'\fR and \f(CW\*(C`ev_now ()\*(C'\fR, at least if you want better precision than
2283a second or so.
2284.PP
2285One more problem arises due to this lack of synchronisation: if libev uses
2286the system monotonic clock and you compare timestamps from \f(CW\*(C`ev_time\*(C'\fR
2287or \f(CW\*(C`ev_now\*(C'\fR from when you started your timer and when your callback is
2288invoked, you will find that sometimes the callback is a bit \*(L"early\*(R".
2289.PP
2290This is because \f(CW\*(C`ev_timer\*(C'\fRs work in real time, not wall clock time, so
2291libev makes sure your callback is not invoked before the delay happened,
2292\&\fImeasured according to the real time\fR, not the system clock.
2293.PP
2294If your timeouts are based on a physical timescale (e.g. \*(L"time out this
2295connection after 100 seconds\*(R") then this shouldn't bother you as it is
2296exactly the right behaviour.
2297.PP
2298If you want to compare wall clock/system timestamps to your timers, then
2299you need to use \f(CW\*(C`ev_periodic\*(C'\fRs, as these are based on the wall clock
2300time, where your comparisons will always generate correct results.
2301.PP
2302\fIThe special problems of suspended animation\fR
2303.IX Subsection "The special problems of suspended animation"
2304.PP
2305When you leave the server world it is quite customary to hit machines that
2306can suspend/hibernate \- what happens to the clocks during such a suspend?
2307.PP
2308Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
2309all processes, while the clocks (\f(CW\*(C`times\*(C'\fR, \f(CW\*(C`CLOCK_MONOTONIC\*(C'\fR) continue
2310to run until the system is suspended, but they will not advance while the
2311system is suspended. That means, on resume, it will be as if the program
2312was frozen for a few seconds, but the suspend time will not be counted
2313towards \f(CW\*(C`ev_timer\*(C'\fR when a monotonic clock source is used. The real time
2314clock advanced as expected, but if it is used as sole clocksource, then a
2315long suspend would be detected as a time jump by libev, and timers would
2316be adjusted accordingly.
2317.PP
2318I would not be surprised to see different behaviour in different between
2319operating systems, \s-1OS\s0 versions or even different hardware.
2320.PP
2321The other form of suspend (job control, or sending a \s-1SIGSTOP\s0) will see a
2322time jump in the monotonic clocks and the realtime clock. If the program
2323is suspended for a very long time, and monotonic clock sources are in use,
2324then you can expect \f(CW\*(C`ev_timer\*(C'\fRs to expire as the full suspension time
2325will be counted towards the timers. When no monotonic clock source is in
2326use, then libev will again assume a timejump and adjust accordingly.
2327.PP
2328It might be beneficial for this latter case to call \f(CW\*(C`ev_suspend\*(C'\fR
2329and \f(CW\*(C`ev_resume\*(C'\fR in code that handles \f(CW\*(C`SIGTSTP\*(C'\fR, to at least get
2330deterministic behaviour in this case (you can do nothing against
2331\&\f(CW\*(C`SIGSTOP\*(C'\fR).
1243.PP 2332.PP
1244\fIWatcher-Specific Functions and Data Members\fR 2333\fIWatcher-Specific Functions and Data Members\fR
1245.IX Subsection "Watcher-Specific Functions and Data Members" 2334.IX Subsection "Watcher-Specific Functions and Data Members"
1246.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4 2335.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
1247.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 2336.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
1248.PD 0 2337.PD 0
1249.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4 2338.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
1250.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 2339.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
1251.PD 2340.PD
1252Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR is 2341Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds (fractional and
1253\&\f(CW0.\fR, then it will automatically be stopped. If it is positive, then the 2342negative values are supported). If \f(CW\*(C`repeat\*(C'\fR is \f(CW0.\fR, then it will
2343automatically be stopped once the timeout is reached. If it is positive,
1254timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds 2344then the timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR
1255later, again, and again, until stopped manually. 2345seconds later, again, and again, until stopped manually.
1256.Sp 2346.Sp
1257The timer itself will do a best-effort at avoiding drift, that is, if you 2347The timer itself will do a best-effort at avoiding drift, that is, if
1258configure a timer to trigger every 10 seconds, then it will trigger at 2348you configure a timer to trigger every 10 seconds, then it will normally
1259exactly 10 second intervals. If, however, your program cannot keep up with 2349trigger at exactly 10 second intervals. If, however, your program cannot
1260the timer (because it takes longer than those 10 seconds to do stuff) the 2350keep up with the timer (because it takes longer than those 10 seconds to
1261timer will not fire more than once per event loop iteration. 2351do stuff) the timer will not fire more than once per event loop iteration.
1262.IP "ev_timer_again (loop)" 4 2352.IP "ev_timer_again (loop, ev_timer *)" 4
1263.IX Item "ev_timer_again (loop)" 2353.IX Item "ev_timer_again (loop, ev_timer *)"
1264This will act as if the timer timed out and restart it again if it is 2354This will act as if the timer timed out, and restarts it again if it is
1265repeating. The exact semantics are: 2355repeating. It basically works like calling \f(CW\*(C`ev_timer_stop\*(C'\fR, updating the
2356timeout to the \f(CW\*(C`repeat\*(C'\fR value and calling \f(CW\*(C`ev_timer_start\*(C'\fR.
1266.Sp 2357.Sp
2358The exact semantics are as in the following rules, all of which will be
2359applied to the watcher:
2360.RS 4
1267If the timer is pending, its pending status is cleared. 2361.IP "If the timer is pending, the pending status is always cleared." 4
1268.Sp 2362.IX Item "If the timer is pending, the pending status is always cleared."
2363.PD 0
1269If the timer is started but nonrepeating, stop it (as if it timed out). 2364.IP "If the timer is started but non-repeating, stop it (as if it timed out, without invoking it)." 4
2365.IX Item "If the timer is started but non-repeating, stop it (as if it timed out, without invoking it)."
2366.ie n .IP "If the timer is repeating, make the ""repeat"" value the new timeout and start the timer, if necessary." 4
2367.el .IP "If the timer is repeating, make the \f(CWrepeat\fR value the new timeout and start the timer, if necessary." 4
2368.IX Item "If the timer is repeating, make the repeat value the new timeout and start the timer, if necessary."
2369.RE
2370.RS 4
2371.PD
1270.Sp 2372.Sp
1271If the timer is repeating, either start it if necessary (with the 2373This sounds a bit complicated, see \*(L"Be smart about timeouts\*(R", above, for a
1272\&\f(CW\*(C`repeat\*(C'\fR value), or reset the running timer to the \f(CW\*(C`repeat\*(C'\fR value. 2374usage example.
2375.RE
2376.IP "ev_tstamp ev_timer_remaining (loop, ev_timer *)" 4
2377.IX Item "ev_tstamp ev_timer_remaining (loop, ev_timer *)"
2378Returns the remaining time until a timer fires. If the timer is active,
2379then this time is relative to the current event loop time, otherwise it's
2380the timeout value currently configured.
1273.Sp 2381.Sp
1274This sounds a bit complicated, but here is a useful and typical 2382That is, after an \f(CW\*(C`ev_timer_set (w, 5, 7)\*(C'\fR, \f(CW\*(C`ev_timer_remaining\*(C'\fR returns
1275example: Imagine you have a tcp connection and you want a so-called idle 2383\&\f(CW5\fR. When the timer is started and one second passes, \f(CW\*(C`ev_timer_remaining\*(C'\fR
1276timeout, that is, you want to be called when there have been, say, 60 2384will return \f(CW4\fR. When the timer expires and is restarted, it will return
1277seconds of inactivity on the socket. The easiest way to do this is to 2385roughly \f(CW7\fR (likely slightly less as callback invocation takes some time,
1278configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value of \f(CW60\fR and then call 2386too), and so on.
1279\&\f(CW\*(C`ev_timer_again\*(C'\fR each time you successfully read or write some data. If
1280you go into an idle state where you do not expect data to travel on the
1281socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will
1282automatically restart it if need be.
1283.Sp
1284That means you can ignore the \f(CW\*(C`after\*(C'\fR value and \f(CW\*(C`ev_timer_start\*(C'\fR
1285altogether and only ever use the \f(CW\*(C`repeat\*(C'\fR value and \f(CW\*(C`ev_timer_again\*(C'\fR:
1286.Sp
1287.Vb 8
1288\& ev_timer_init (timer, callback, 0., 5.);
1289\& ev_timer_again (loop, timer);
1290\& ...
1291\& timer->again = 17.;
1292\& ev_timer_again (loop, timer);
1293\& ...
1294\& timer->again = 10.;
1295\& ev_timer_again (loop, timer);
1296.Ve
1297.Sp
1298This is more slightly efficient then stopping/starting the timer each time
1299you want to modify its timeout value.
1300.IP "ev_tstamp repeat [read\-write]" 4 2387.IP "ev_tstamp repeat [read\-write]" 4
1301.IX Item "ev_tstamp repeat [read-write]" 2388.IX Item "ev_tstamp repeat [read-write]"
1302The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out 2389The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out
1303or \f(CW\*(C`ev_timer_again\*(C'\fR is called and determines the next timeout (if any), 2390or \f(CW\*(C`ev_timer_again\*(C'\fR is called, and determines the next timeout (if any),
1304which is also when any modifications are taken into account. 2391which is also when any modifications are taken into account.
1305.PP 2392.PP
2393\fIExamples\fR
2394.IX Subsection "Examples"
2395.PP
1306Example: Create a timer that fires after 60 seconds. 2396Example: Create a timer that fires after 60 seconds.
1307.PP 2397.PP
1308.Vb 5 2398.Vb 5
1309\& static void 2399\& static void
1310\& one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents) 2400\& one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1311\& { 2401\& {
1312\& .. one minute over, w is actually stopped right here 2402\& .. one minute over, w is actually stopped right here
1313\& } 2403\& }
1314.Ve 2404\&
1315.PP
1316.Vb 3
1317\& struct ev_timer mytimer; 2405\& ev_timer mytimer;
1318\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.); 2406\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1319\& ev_timer_start (loop, &mytimer); 2407\& ev_timer_start (loop, &mytimer);
1320.Ve 2408.Ve
1321.PP 2409.PP
1322Example: Create a timeout timer that times out after 10 seconds of 2410Example: Create a timeout timer that times out after 10 seconds of
1323inactivity. 2411inactivity.
1324.PP 2412.PP
1325.Vb 5 2413.Vb 5
1326\& static void 2414\& static void
1327\& timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents) 2415\& timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1328\& { 2416\& {
1329\& .. ten seconds without any activity 2417\& .. ten seconds without any activity
1330\& } 2418\& }
1331.Ve 2419\&
1332.PP
1333.Vb 4
1334\& struct ev_timer mytimer; 2420\& ev_timer mytimer;
1335\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */ 2421\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1336\& ev_timer_again (&mytimer); /* start timer */ 2422\& ev_timer_again (&mytimer); /* start timer */
1337\& ev_loop (loop, 0); 2423\& ev_run (loop, 0);
1338.Ve 2424\&
1339.PP
1340.Vb 3
1341\& // and in some piece of code that gets executed on any "activity": 2425\& // and in some piece of code that gets executed on any "activity":
1342\& // reset the timeout to start ticking again at 10 seconds 2426\& // reset the timeout to start ticking again at 10 seconds
1343\& ev_timer_again (&mytimer); 2427\& ev_timer_again (&mytimer);
1344.Ve 2428.Ve
1345.ie n .Sh """ev_periodic"" \- to cron or not to cron?" 2429.ie n .SS """ev_periodic"" \- to cron or not to cron?"
1346.el .Sh "\f(CWev_periodic\fP \- to cron or not to cron?" 2430.el .SS "\f(CWev_periodic\fP \- to cron or not to cron?"
1347.IX Subsection "ev_periodic - to cron or not to cron?" 2431.IX Subsection "ev_periodic - to cron or not to cron?"
1348Periodic watchers are also timers of a kind, but they are very versatile 2432Periodic watchers are also timers of a kind, but they are very versatile
1349(and unfortunately a bit complex). 2433(and unfortunately a bit complex).
1350.PP 2434.PP
1351Unlike \f(CW\*(C`ev_timer\*(C'\fR's, they are not based on real time (or relative time) 2435Unlike \f(CW\*(C`ev_timer\*(C'\fR, periodic watchers are not based on real time (or
1352but on wallclock time (absolute time). You can tell a periodic watcher 2436relative time, the physical time that passes) but on wall clock time
1353to trigger \*(L"at\*(R" some specific point in time. For example, if you tell a 2437(absolute time, the thing you can read on your calendar or clock). The
1354periodic watcher to trigger in 10 seconds (by specifiying e.g. \f(CW\*(C`ev_now () 2438difference is that wall clock time can run faster or slower than real
1355+ 10.\*(C'\fR) and then reset your system clock to the last year, then it will 2439time, and time jumps are not uncommon (e.g. when you adjust your
1356take a year to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would trigger 2440wrist-watch).
1357roughly 10 seconds later).
1358.PP 2441.PP
1359They can also be used to implement vastly more complex timers, such as 2442You can tell a periodic watcher to trigger after some specific point
1360triggering an event on each midnight, local time or other, complicated, 2443in time: for example, if you tell a periodic watcher to trigger \*(L"in 10
1361rules. 2444seconds\*(R" (by specifying e.g. \f(CW\*(C`ev_now () + 10.\*(C'\fR, that is, an absolute time
2445not a delay) and then reset your system clock to January of the previous
2446year, then it will take a year or more to trigger the event (unlike an
2447\&\f(CW\*(C`ev_timer\*(C'\fR, which would still trigger roughly 10 seconds after starting
2448it, as it uses a relative timeout).
1362.PP 2449.PP
2450\&\f(CW\*(C`ev_periodic\*(C'\fR watchers can also be used to implement vastly more complex
2451timers, such as triggering an event on each \*(L"midnight, local time\*(R", or
2452other complicated rules. This cannot easily be done with \f(CW\*(C`ev_timer\*(C'\fR
2453watchers, as those cannot react to time jumps.
2454.PP
1363As with timers, the callback is guarenteed to be invoked only when the 2455As with timers, the callback is guaranteed to be invoked only when the
1364time (\f(CW\*(C`at\*(C'\fR) has been passed, but if multiple periodic timers become ready 2456point in time where it is supposed to trigger has passed. If multiple
1365during the same loop iteration then order of execution is undefined. 2457timers become ready during the same loop iteration then the ones with
2458earlier time-out values are invoked before ones with later time-out values
2459(but this is no longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
1366.PP 2460.PP
1367\fIWatcher-Specific Functions and Data Members\fR 2461\fIWatcher-Specific Functions and Data Members\fR
1368.IX Subsection "Watcher-Specific Functions and Data Members" 2462.IX Subsection "Watcher-Specific Functions and Data Members"
1369.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 4 2463.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
1370.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 2464.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
1371.PD 0 2465.PD 0
1372.IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4 2466.IP "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
1373.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 2467.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
1374.PD 2468.PD
1375Lots of arguments, lets sort it out... There are basically three modes of 2469Lots of arguments, let's sort it out... There are basically three modes of
1376operation, and we will explain them from simplest to complex: 2470operation, and we will explain them from simplest to most complex:
1377.RS 4 2471.RS 4
2472.IP "\(bu" 4
1378.IP "* absolute timer (at = time, interval = reschedule_cb = 0)" 4 2473absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1379.IX Item "absolute timer (at = time, interval = reschedule_cb = 0)" 2474.Sp
1380In this configuration the watcher triggers an event at the wallclock time 2475In this configuration the watcher triggers an event after the wall clock
1381\&\f(CW\*(C`at\*(C'\fR and doesn't repeat. It will not adjust when a time jump occurs, 2476time \f(CW\*(C`offset\*(C'\fR has passed. It will not repeat and will not adjust when a
1382that is, if it is to be run at January 1st 2011 then it will run when the 2477time jump occurs, that is, if it is to be run at January 1st 2011 then it
1383system time reaches or surpasses this time. 2478will be stopped and invoked when the system clock reaches or surpasses
1384.IP "* non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)" 4 2479this point in time.
1385.IX Item "non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)" 2480.IP "\(bu" 4
2481repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
2482.Sp
1386In this mode the watcher will always be scheduled to time out at the next 2483In this mode the watcher will always be scheduled to time out at the next
1387\&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N, which can also be negative) 2484\&\f(CW\*(C`offset + N * interval\*(C'\fR time (for some integer N, which can also be
1388and then repeat, regardless of any time jumps. 2485negative) and then repeat, regardless of any time jumps. The \f(CW\*(C`offset\*(C'\fR
2486argument is merely an offset into the \f(CW\*(C`interval\*(C'\fR periods.
1389.Sp 2487.Sp
1390This can be used to create timers that do not drift with respect to system 2488This can be used to create timers that do not drift with respect to the
1391time: 2489system clock, for example, here is an \f(CW\*(C`ev_periodic\*(C'\fR that triggers each
2490hour, on the hour (with respect to \s-1UTC\s0):
1392.Sp 2491.Sp
1393.Vb 1 2492.Vb 1
1394\& ev_periodic_set (&periodic, 0., 3600., 0); 2493\& ev_periodic_set (&periodic, 0., 3600., 0);
1395.Ve 2494.Ve
1396.Sp 2495.Sp
1397This doesn't mean there will always be 3600 seconds in between triggers, 2496This doesn't mean there will always be 3600 seconds in between triggers,
1398but only that the the callback will be called when the system time shows a 2497but only that the callback will be called when the system time shows a
1399full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible 2498full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
1400by 3600. 2499by 3600.
1401.Sp 2500.Sp
1402Another way to think about it (for the mathematically inclined) is that 2501Another way to think about it (for the mathematically inclined) is that
1403\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible 2502\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
1404time where \f(CW\*(C`time = at (mod interval)\*(C'\fR, regardless of any time jumps. 2503time where \f(CW\*(C`time = offset (mod interval)\*(C'\fR, regardless of any time jumps.
1405.Sp 2504.Sp
1406For numerical stability it is preferable that the \f(CW\*(C`at\*(C'\fR value is near 2505The \f(CW\*(C`interval\*(C'\fR \fI\s-1MUST\s0\fR be positive, and for numerical stability, the
1407\&\f(CW\*(C`ev_now ()\*(C'\fR (the current time), but there is no range requirement for 2506interval value should be higher than \f(CW\*(C`1/8192\*(C'\fR (which is around 100
1408this value. 2507microseconds) and \f(CW\*(C`offset\*(C'\fR should be higher than \f(CW0\fR and should have
2508at most a similar magnitude as the current time (say, within a factor of
2509ten). Typical values for offset are, in fact, \f(CW0\fR or something between
2510\&\f(CW0\fR and \f(CW\*(C`interval\*(C'\fR, which is also the recommended range.
2511.Sp
2512Note also that there is an upper limit to how often a timer can fire (\s-1CPU\s0
2513speed for example), so if \f(CW\*(C`interval\*(C'\fR is very small then timing stability
2514will of course deteriorate. Libev itself tries to be exact to be about one
2515millisecond (if the \s-1OS\s0 supports it and the machine is fast enough).
2516.IP "\(bu" 4
1409.IP "* manual reschedule mode (at and interval ignored, reschedule_cb = callback)" 4 2517manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1410.IX Item "manual reschedule mode (at and interval ignored, reschedule_cb = callback)" 2518.Sp
1411In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being 2519In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`offset\*(C'\fR are both being
1412ignored. Instead, each time the periodic watcher gets scheduled, the 2520ignored. Instead, each time the periodic watcher gets scheduled, the
1413reschedule callback will be called with the watcher as first, and the 2521reschedule callback will be called with the watcher as first, and the
1414current time as second argument. 2522current time as second argument.
1415.Sp 2523.Sp
1416\&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, 2524\&\s-1NOTE:\s0 \fIThis callback \s-1MUST NOT\s0 stop or destroy any periodic watcher, ever,
1417ever, or make any event loop modifications\fR. If you need to stop it, 2525or make \s-1ANY\s0 other event loop modifications whatsoever, unless explicitly
1418return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop it afterwards (e.g. by 2526allowed by documentation here\fR.
2527.Sp
2528If you need to stop it, return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop
1419starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is legal). 2529it afterwards (e.g. by starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is the
2530only event loop modification you are allowed to do).
1420.Sp 2531.Sp
1421Its prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic *w, 2532The callback prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(ev_periodic
1422ev_tstamp now)\*(C'\fR, e.g.: 2533*w, ev_tstamp now)\*(C'\fR, e.g.:
1423.Sp 2534.Sp
1424.Vb 4 2535.Vb 5
2536\& static ev_tstamp
1425\& static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) 2537\& my_rescheduler (ev_periodic *w, ev_tstamp now)
1426\& { 2538\& {
1427\& return now + 60.; 2539\& return now + 60.;
1428\& } 2540\& }
1429.Ve 2541.Ve
1430.Sp 2542.Sp
1431It must return the next time to trigger, based on the passed time value 2543It must return the next time to trigger, based on the passed time value
1432(that is, the lowest time value larger than to the second argument). It 2544(that is, the lowest time value larger than to the second argument). It
1433will usually be called just before the callback will be triggered, but 2545will usually be called just before the callback will be triggered, but
1434might be called at other times, too. 2546might be called at other times, too.
1435.Sp 2547.Sp
1436\&\s-1NOTE:\s0 \fIThis callback must always return a time that is later than the 2548\&\s-1NOTE:\s0 \fIThis callback must always return a time that is higher than or
1437passed \f(CI\*(C`now\*(C'\fI value\fR. Not even \f(CW\*(C`now\*(C'\fR itself will do, it \fImust\fR be larger. 2549equal to the passed \f(CI\*(C`now\*(C'\fI value\fR.
1438.Sp 2550.Sp
1439This can be used to create very complex timers, such as a timer that 2551This can be used to create very complex timers, such as a timer that
1440triggers on each midnight, local time. To do this, you would calculate the 2552triggers on \*(L"next midnight, local time\*(R". To do this, you would calculate
1441next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How 2553the next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for
1442you do this is, again, up to you (but it is not trivial, which is the main 2554this. Here is a (completely untested, no error checking) example on how to
1443reason I omitted it as an example). 2555do this:
2556.Sp
2557.Vb 1
2558\& #include <time.h>
2559\&
2560\& static ev_tstamp
2561\& my_rescheduler (ev_periodic *w, ev_tstamp now)
2562\& {
2563\& time_t tnow = (time_t)now;
2564\& struct tm tm;
2565\& localtime_r (&tnow, &tm);
2566\&
2567\& tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
2568\& ++tm.tm_mday; // midnight next day
2569\&
2570\& return mktime (&tm);
2571\& }
2572.Ve
2573.Sp
2574Note: this code might run into trouble on days that have more then two
2575midnights (beginning and end).
1444.RE 2576.RE
1445.RS 4 2577.RS 4
1446.RE 2578.RE
1447.IP "ev_periodic_again (loop, ev_periodic *)" 4 2579.IP "ev_periodic_again (loop, ev_periodic *)" 4
1448.IX Item "ev_periodic_again (loop, ev_periodic *)" 2580.IX Item "ev_periodic_again (loop, ev_periodic *)"
1449Simply stops and restarts the periodic watcher again. This is only useful 2581Simply stops and restarts the periodic watcher again. This is only useful
1450when you changed some parameters or the reschedule callback would return 2582when you changed some parameters or the reschedule callback would return
1451a different time than the last time it was called (e.g. in a crond like 2583a different time than the last time it was called (e.g. in a crond like
1452program when the crontabs have changed). 2584program when the crontabs have changed).
2585.IP "ev_tstamp ev_periodic_at (ev_periodic *)" 4
2586.IX Item "ev_tstamp ev_periodic_at (ev_periodic *)"
2587When active, returns the absolute time that the watcher is supposed
2588to trigger next. This is not the same as the \f(CW\*(C`offset\*(C'\fR argument to
2589\&\f(CW\*(C`ev_periodic_set\*(C'\fR, but indeed works even in interval and manual
2590rescheduling modes.
1453.IP "ev_tstamp offset [read\-write]" 4 2591.IP "ev_tstamp offset [read\-write]" 4
1454.IX Item "ev_tstamp offset [read-write]" 2592.IX Item "ev_tstamp offset [read-write]"
1455When repeating, this contains the offset value, otherwise this is the 2593When repeating, this contains the offset value, otherwise this is the
1456absolute point in time (the \f(CW\*(C`at\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR). 2594absolute point in time (the \f(CW\*(C`offset\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR,
2595although libev might modify this value for better numerical stability).
1457.Sp 2596.Sp
1458Can be modified any time, but changes only take effect when the periodic 2597Can be modified any time, but changes only take effect when the periodic
1459timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called. 2598timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
1460.IP "ev_tstamp interval [read\-write]" 4 2599.IP "ev_tstamp interval [read\-write]" 4
1461.IX Item "ev_tstamp interval [read-write]" 2600.IX Item "ev_tstamp interval [read-write]"
1462The current interval value. Can be modified any time, but changes only 2601The current interval value. Can be modified any time, but changes only
1463take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being 2602take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being
1464called. 2603called.
1465.IP "ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read\-write]" 4 2604.IP "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read\-write]" 4
1466.IX Item "ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]" 2605.IX Item "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]"
1467The current reschedule callback, or \f(CW0\fR, if this functionality is 2606The current reschedule callback, or \f(CW0\fR, if this functionality is
1468switched off. Can be changed any time, but changes only take effect when 2607switched off. Can be changed any time, but changes only take effect when
1469the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called. 2608the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
1470.IP "ev_tstamp at [read\-only]" 4 2609.PP
1471.IX Item "ev_tstamp at [read-only]" 2610\fIExamples\fR
1472When active, contains the absolute time that the watcher is supposed to 2611.IX Subsection "Examples"
1473trigger next.
1474.PP 2612.PP
1475Example: Call a callback every hour, or, more precisely, whenever the 2613Example: Call a callback every hour, or, more precisely, whenever the
1476system clock is divisible by 3600. The callback invocation times have 2614system time is divisible by 3600. The callback invocation times have
1477potentially a lot of jittering, but good long-term stability. 2615potentially a lot of jitter, but good long-term stability.
1478.PP 2616.PP
1479.Vb 5 2617.Vb 5
1480\& static void 2618\& static void
1481\& clock_cb (struct ev_loop *loop, struct ev_io *w, int revents) 2619\& clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1482\& { 2620\& {
1483\& ... its now a full hour (UTC, or TAI or whatever your clock follows) 2621\& ... its now a full hour (UTC, or TAI or whatever your clock follows)
1484\& } 2622\& }
1485.Ve 2623\&
1486.PP
1487.Vb 3
1488\& struct ev_periodic hourly_tick; 2624\& ev_periodic hourly_tick;
1489\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0); 2625\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1490\& ev_periodic_start (loop, &hourly_tick); 2626\& ev_periodic_start (loop, &hourly_tick);
1491.Ve 2627.Ve
1492.PP 2628.PP
1493Example: The same as above, but use a reschedule callback to do it: 2629Example: The same as above, but use a reschedule callback to do it:
1494.PP 2630.PP
1495.Vb 1 2631.Vb 1
1496\& #include <math.h> 2632\& #include <math.h>
1497.Ve 2633\&
1498.PP
1499.Vb 5
1500\& static ev_tstamp 2634\& static ev_tstamp
1501\& my_scheduler_cb (struct ev_periodic *w, ev_tstamp now) 2635\& my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1502\& { 2636\& {
1503\& return fmod (now, 3600.) + 3600.; 2637\& return now + (3600. \- fmod (now, 3600.));
1504\& } 2638\& }
1505.Ve 2639\&
1506.PP
1507.Vb 1
1508\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb); 2640\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1509.Ve 2641.Ve
1510.PP 2642.PP
1511Example: Call a callback every hour, starting now: 2643Example: Call a callback every hour, starting now:
1512.PP 2644.PP
1513.Vb 4 2645.Vb 4
1514\& struct ev_periodic hourly_tick; 2646\& ev_periodic hourly_tick;
1515\& ev_periodic_init (&hourly_tick, clock_cb, 2647\& ev_periodic_init (&hourly_tick, clock_cb,
1516\& fmod (ev_now (loop), 3600.), 3600., 0); 2648\& fmod (ev_now (loop), 3600.), 3600., 0);
1517\& ev_periodic_start (loop, &hourly_tick); 2649\& ev_periodic_start (loop, &hourly_tick);
1518.Ve 2650.Ve
1519.ie n .Sh """ev_signal"" \- signal me when a signal gets signalled!" 2651.ie n .SS """ev_signal"" \- signal me when a signal gets signalled!"
1520.el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled!" 2652.el .SS "\f(CWev_signal\fP \- signal me when a signal gets signalled!"
1521.IX Subsection "ev_signal - signal me when a signal gets signalled!" 2653.IX Subsection "ev_signal - signal me when a signal gets signalled!"
1522Signal watchers will trigger an event when the process receives a specific 2654Signal watchers will trigger an event when the process receives a specific
1523signal one or more times. Even though signals are very asynchronous, libev 2655signal one or more times. Even though signals are very asynchronous, libev
1524will try it's best to deliver signals synchronously, i.e. as part of the 2656will try its best to deliver signals synchronously, i.e. as part of the
1525normal event processing, like any other event. 2657normal event processing, like any other event.
1526.PP 2658.PP
2659If you want signals to be delivered truly asynchronously, just use
2660\&\f(CW\*(C`sigaction\*(C'\fR as you would do without libev and forget about sharing
2661the signal. You can even use \f(CW\*(C`ev_async\*(C'\fR from a signal handler to
2662synchronously wake up an event loop.
2663.PP
1527You can configure as many watchers as you like per signal. Only when the 2664You can configure as many watchers as you like for the same signal, but
1528first watcher gets started will libev actually register a signal watcher 2665only within the same loop, i.e. you can watch for \f(CW\*(C`SIGINT\*(C'\fR in your
1529with the kernel (thus it coexists with your own signal handlers as long 2666default loop and for \f(CW\*(C`SIGIO\*(C'\fR in another loop, but you cannot watch for
1530as you don't register any with libev). Similarly, when the last signal 2667\&\f(CW\*(C`SIGINT\*(C'\fR in both the default loop and another loop at the same time. At
1531watcher for a signal is stopped libev will reset the signal handler to 2668the moment, \f(CW\*(C`SIGCHLD\*(C'\fR is permanently tied to the default loop.
1532\&\s-1SIG_DFL\s0 (regardless of what it was set to before). 2669.PP
2670Only after the first watcher for a signal is started will libev actually
2671register something with the kernel. It thus coexists with your own signal
2672handlers as long as you don't register any with libev for the same signal.
2673.PP
2674If possible and supported, libev will install its handlers with
2675\&\f(CW\*(C`SA_RESTART\*(C'\fR (or equivalent) behaviour enabled, so system calls should
2676not be unduly interrupted. If you have a problem with system calls getting
2677interrupted by signals you can block all signals in an \f(CW\*(C`ev_check\*(C'\fR watcher
2678and unblock them in an \f(CW\*(C`ev_prepare\*(C'\fR watcher.
2679.PP
2680\fIThe special problem of inheritance over fork/execve/pthread_create\fR
2681.IX Subsection "The special problem of inheritance over fork/execve/pthread_create"
2682.PP
2683Both the signal mask (\f(CW\*(C`sigprocmask\*(C'\fR) and the signal disposition
2684(\f(CW\*(C`sigaction\*(C'\fR) are unspecified after starting a signal watcher (and after
2685stopping it again), that is, libev might or might not block the signal,
2686and might or might not set or restore the installed signal handler (but
2687see \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR).
2688.PP
2689While this does not matter for the signal disposition (libev never
2690sets signals to \f(CW\*(C`SIG_IGN\*(C'\fR, so handlers will be reset to \f(CW\*(C`SIG_DFL\*(C'\fR on
2691\&\f(CW\*(C`execve\*(C'\fR), this matters for the signal mask: many programs do not expect
2692certain signals to be blocked.
2693.PP
2694This means that before calling \f(CW\*(C`exec\*(C'\fR (from the child) you should reset
2695the signal mask to whatever \*(L"default\*(R" you expect (all clear is a good
2696choice usually).
2697.PP
2698The simplest way to ensure that the signal mask is reset in the child is
2699to install a fork handler with \f(CW\*(C`pthread_atfork\*(C'\fR that resets it. That will
2700catch fork calls done by libraries (such as the libc) as well.
2701.PP
2702In current versions of libev, the signal will not be blocked indefinitely
2703unless you use the \f(CW\*(C`signalfd\*(C'\fR \s-1API\s0 (\f(CW\*(C`EV_SIGNALFD\*(C'\fR). While this reduces
2704the window of opportunity for problems, it will not go away, as libev
2705\&\fIhas\fR to modify the signal mask, at least temporarily.
2706.PP
2707So I can't stress this enough: \fIIf you do not reset your signal mask when
2708you expect it to be empty, you have a race condition in your code\fR. This
2709is not a libev-specific thing, this is true for most event libraries.
2710.PP
2711\fIThe special problem of threads signal handling\fR
2712.IX Subsection "The special problem of threads signal handling"
2713.PP
2714\&\s-1POSIX\s0 threads has problematic signal handling semantics, specifically,
2715a lot of functionality (sigfd, sigwait etc.) only really works if all
2716threads in a process block signals, which is hard to achieve.
2717.PP
2718When you want to use sigwait (or mix libev signal handling with your own
2719for the same signals), you can tackle this problem by globally blocking
2720all signals before creating any threads (or creating them with a fully set
2721sigprocmask) and also specifying the \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR when creating
2722loops. Then designate one thread as \*(L"signal receiver thread\*(R" which handles
2723these signals. You can pass on any signals that libev might be interested
2724in by calling \f(CW\*(C`ev_feed_signal\*(C'\fR.
1533.PP 2725.PP
1534\fIWatcher-Specific Functions and Data Members\fR 2726\fIWatcher-Specific Functions and Data Members\fR
1535.IX Subsection "Watcher-Specific Functions and Data Members" 2727.IX Subsection "Watcher-Specific Functions and Data Members"
1536.IP "ev_signal_init (ev_signal *, callback, int signum)" 4 2728.IP "ev_signal_init (ev_signal *, callback, int signum)" 4
1537.IX Item "ev_signal_init (ev_signal *, callback, int signum)" 2729.IX Item "ev_signal_init (ev_signal *, callback, int signum)"
… …
1542Configures the watcher to trigger on the given signal number (usually one 2734Configures the watcher to trigger on the given signal number (usually one
1543of the \f(CW\*(C`SIGxxx\*(C'\fR constants). 2735of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
1544.IP "int signum [read\-only]" 4 2736.IP "int signum [read\-only]" 4
1545.IX Item "int signum [read-only]" 2737.IX Item "int signum [read-only]"
1546The signal the watcher watches out for. 2738The signal the watcher watches out for.
2739.PP
2740\fIExamples\fR
2741.IX Subsection "Examples"
2742.PP
2743Example: Try to exit cleanly on \s-1SIGINT.\s0
2744.PP
2745.Vb 5
2746\& static void
2747\& sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
2748\& {
2749\& ev_break (loop, EVBREAK_ALL);
2750\& }
2751\&
2752\& ev_signal signal_watcher;
2753\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
2754\& ev_signal_start (loop, &signal_watcher);
2755.Ve
1547.ie n .Sh """ev_child"" \- watch out for process status changes" 2756.ie n .SS """ev_child"" \- watch out for process status changes"
1548.el .Sh "\f(CWev_child\fP \- watch out for process status changes" 2757.el .SS "\f(CWev_child\fP \- watch out for process status changes"
1549.IX Subsection "ev_child - watch out for process status changes" 2758.IX Subsection "ev_child - watch out for process status changes"
1550Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to 2759Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
1551some child status changes (most typically when a child of yours dies). 2760some child status changes (most typically when a child of yours dies or
2761exits). It is permissible to install a child watcher \fIafter\fR the child
2762has been forked (which implies it might have already exited), as long
2763as the event loop isn't entered (or is continued from a watcher), i.e.,
2764forking and then immediately registering a watcher for the child is fine,
2765but forking and registering a watcher a few event loop iterations later or
2766in the next callback invocation is not.
2767.PP
2768Only the default event loop is capable of handling signals, and therefore
2769you can only register child watchers in the default event loop.
2770.PP
2771Due to some design glitches inside libev, child watchers will always be
2772handled at maximum priority (their priority is set to \f(CW\*(C`EV_MAXPRI\*(C'\fR by
2773libev)
2774.PP
2775\fIProcess Interaction\fR
2776.IX Subsection "Process Interaction"
2777.PP
2778Libev grabs \f(CW\*(C`SIGCHLD\*(C'\fR as soon as the default event loop is
2779initialised. This is necessary to guarantee proper behaviour even if the
2780first child watcher is started after the child exits. The occurrence
2781of \f(CW\*(C`SIGCHLD\*(C'\fR is recorded asynchronously, but child reaping is done
2782synchronously as part of the event loop processing. Libev always reaps all
2783children, even ones not watched.
2784.PP
2785\fIOverriding the Built-In Processing\fR
2786.IX Subsection "Overriding the Built-In Processing"
2787.PP
2788Libev offers no special support for overriding the built-in child
2789processing, but if your application collides with libev's default child
2790handler, you can override it easily by installing your own handler for
2791\&\f(CW\*(C`SIGCHLD\*(C'\fR after initialising the default loop, and making sure the
2792default loop never gets destroyed. You are encouraged, however, to use an
2793event-based approach to child reaping and thus use libev's support for
2794that, so other libev users can use \f(CW\*(C`ev_child\*(C'\fR watchers freely.
2795.PP
2796\fIStopping the Child Watcher\fR
2797.IX Subsection "Stopping the Child Watcher"
2798.PP
2799Currently, the child watcher never gets stopped, even when the
2800child terminates, so normally one needs to stop the watcher in the
2801callback. Future versions of libev might stop the watcher automatically
2802when a child exit is detected (calling \f(CW\*(C`ev_child_stop\*(C'\fR twice is not a
2803problem).
1552.PP 2804.PP
1553\fIWatcher-Specific Functions and Data Members\fR 2805\fIWatcher-Specific Functions and Data Members\fR
1554.IX Subsection "Watcher-Specific Functions and Data Members" 2806.IX Subsection "Watcher-Specific Functions and Data Members"
1555.IP "ev_child_init (ev_child *, callback, int pid)" 4 2807.IP "ev_child_init (ev_child *, callback, int pid, int trace)" 4
1556.IX Item "ev_child_init (ev_child *, callback, int pid)" 2808.IX Item "ev_child_init (ev_child *, callback, int pid, int trace)"
1557.PD 0 2809.PD 0
1558.IP "ev_child_set (ev_child *, int pid)" 4 2810.IP "ev_child_set (ev_child *, int pid, int trace)" 4
1559.IX Item "ev_child_set (ev_child *, int pid)" 2811.IX Item "ev_child_set (ev_child *, int pid, int trace)"
1560.PD 2812.PD
1561Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or 2813Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
1562\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look 2814\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
1563at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see 2815at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
1564the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems 2816the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
1565\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the 2817\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
1566process causing the status change. 2818process causing the status change. \f(CW\*(C`trace\*(C'\fR must be either \f(CW0\fR (only
2819activate the watcher when the process terminates) or \f(CW1\fR (additionally
2820activate the watcher when the process is stopped or continued).
1567.IP "int pid [read\-only]" 4 2821.IP "int pid [read\-only]" 4
1568.IX Item "int pid [read-only]" 2822.IX Item "int pid [read-only]"
1569The process id this watcher watches out for, or \f(CW0\fR, meaning any process id. 2823The process id this watcher watches out for, or \f(CW0\fR, meaning any process id.
1570.IP "int rpid [read\-write]" 4 2824.IP "int rpid [read\-write]" 4
1571.IX Item "int rpid [read-write]" 2825.IX Item "int rpid [read-write]"
… …
1573.IP "int rstatus [read\-write]" 4 2827.IP "int rstatus [read\-write]" 4
1574.IX Item "int rstatus [read-write]" 2828.IX Item "int rstatus [read-write]"
1575The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems 2829The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems
1576\&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details). 2830\&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details).
1577.PP 2831.PP
1578Example: Try to exit cleanly on \s-1SIGINT\s0 and \s-1SIGTERM\s0. 2832\fIExamples\fR
2833.IX Subsection "Examples"
1579.PP 2834.PP
2835Example: \f(CW\*(C`fork()\*(C'\fR a new process and install a child handler to wait for
2836its completion.
2837.PP
1580.Vb 5 2838.Vb 1
2839\& ev_child cw;
2840\&
1581\& static void 2841\& static void
1582\& sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents) 2842\& child_cb (EV_P_ ev_child *w, int revents)
1583\& { 2843\& {
1584\& ev_unloop (loop, EVUNLOOP_ALL); 2844\& ev_child_stop (EV_A_ w);
2845\& printf ("process %d exited with status %x\en", w\->rpid, w\->rstatus);
1585\& } 2846\& }
2847\&
2848\& pid_t pid = fork ();
2849\&
2850\& if (pid < 0)
2851\& // error
2852\& else if (pid == 0)
2853\& {
2854\& // the forked child executes here
2855\& exit (1);
2856\& }
2857\& else
2858\& {
2859\& ev_child_init (&cw, child_cb, pid, 0);
2860\& ev_child_start (EV_DEFAULT_ &cw);
2861\& }
1586.Ve 2862.Ve
1587.PP
1588.Vb 3
1589\& struct ev_signal signal_watcher;
1590\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1591\& ev_signal_start (loop, &sigint_cb);
1592.Ve
1593.ie n .Sh """ev_stat"" \- did the file attributes just change?" 2863.ie n .SS """ev_stat"" \- did the file attributes just change?"
1594.el .Sh "\f(CWev_stat\fP \- did the file attributes just change?" 2864.el .SS "\f(CWev_stat\fP \- did the file attributes just change?"
1595.IX Subsection "ev_stat - did the file attributes just change?" 2865.IX Subsection "ev_stat - did the file attributes just change?"
1596This watches a filesystem path for attribute changes. That is, it calls 2866This watches a file system path for attribute changes. That is, it calls
1597\&\f(CW\*(C`stat\*(C'\fR regularly (or when the \s-1OS\s0 says it changed) and sees if it changed 2867\&\f(CW\*(C`stat\*(C'\fR on that path in regular intervals (or when the \s-1OS\s0 says it changed)
1598compared to the last time, invoking the callback if it did. 2868and sees if it changed compared to the last time, invoking the callback
2869if it did. Starting the watcher \f(CW\*(C`stat\*(C'\fR's the file, so only changes that
2870happen after the watcher has been started will be reported.
1599.PP 2871.PP
1600The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does 2872The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does
1601not exist\*(R" is a status change like any other. The condition \*(L"path does 2873not exist\*(R" is a status change like any other. The condition \*(L"path does not
1602not exist\*(R" is signified by the \f(CW\*(C`st_nlink\*(C'\fR field being zero (which is 2874exist\*(R" (or more correctly \*(L"path cannot be stat'ed\*(R") is signified by the
1603otherwise always forced to be at least one) and all the other fields of 2875\&\f(CW\*(C`st_nlink\*(C'\fR field being zero (which is otherwise always forced to be at
1604the stat buffer having unspecified contents. 2876least one) and all the other fields of the stat buffer having unspecified
2877contents.
1605.PP 2878.PP
1606The path \fIshould\fR be absolute and \fImust not\fR end in a slash. If it is 2879The path \fImust not\fR end in a slash or contain special components such as
2880\&\f(CW\*(C`.\*(C'\fR or \f(CW\*(C`..\*(C'\fR. The path \fIshould\fR be absolute: If it is relative and
1607relative and your working directory changes, the behaviour is undefined. 2881your working directory changes, then the behaviour is undefined.
1608.PP 2882.PP
1609Since there is no standard to do this, the portable implementation simply 2883Since there is no portable change notification interface available, the
1610calls \f(CW\*(C`stat (2)\*(C'\fR regularly on the path to see if it changed somehow. You 2884portable implementation simply calls \f(CWstat(2)\fR regularly on the path
1611can specify a recommended polling interval for this case. If you specify 2885to see if it changed somehow. You can specify a recommended polling
1612a polling interval of \f(CW0\fR (highly recommended!) then a \fIsuitable, 2886interval for this case. If you specify a polling interval of \f(CW0\fR (highly
1613unspecified default\fR value will be used (which you can expect to be around 2887recommended!) then a \fIsuitable, unspecified default\fR value will be used
1614five seconds, although this might change dynamically). Libev will also 2888(which you can expect to be around five seconds, although this might
1615impose a minimum interval which is currently around \f(CW0.1\fR, but thats 2889change dynamically). Libev will also impose a minimum interval which is
1616usually overkill. 2890currently around \f(CW0.1\fR, but that's usually overkill.
1617.PP 2891.PP
1618This watcher type is not meant for massive numbers of stat watchers, 2892This watcher type is not meant for massive numbers of stat watchers,
1619as even with OS-supported change notifications, this can be 2893as even with OS-supported change notifications, this can be
1620resource\-intensive. 2894resource-intensive.
1621.PP 2895.PP
1622At the time of this writing, only the Linux inotify interface is 2896At the time of this writing, the only OS-specific interface implemented
1623implemented (implementing kqueue support is left as an exercise for the 2897is the Linux inotify interface (implementing kqueue support is left as an
1624reader). Inotify will be used to give hints only and should not change the 2898exercise for the reader. Note, however, that the author sees no way of
1625semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers, which means that libev sometimes needs 2899implementing \f(CW\*(C`ev_stat\*(C'\fR semantics with kqueue, except as a hint).
1626to fall back to regular polling again even with inotify, but changes are 2900.PP
1627usually detected immediately, and if the file exists there will be no 2901\fI\s-1ABI\s0 Issues (Largefile Support)\fR
1628polling. 2902.IX Subsection "ABI Issues (Largefile Support)"
2903.PP
2904Libev by default (unless the user overrides this) uses the default
2905compilation environment, which means that on systems with large file
2906support disabled by default, you get the 32 bit version of the stat
2907structure. When using the library from programs that change the \s-1ABI\s0 to
2908use 64 bit file offsets the programs will fail. In that case you have to
2909compile libev with the same flags to get binary compatibility. This is
2910obviously the case with any flags that change the \s-1ABI,\s0 but the problem is
2911most noticeably displayed with ev_stat and large file support.
2912.PP
2913The solution for this is to lobby your distribution maker to make large
2914file interfaces available by default (as e.g. FreeBSD does) and not
2915optional. Libev cannot simply switch on large file support because it has
2916to exchange stat structures with application programs compiled using the
2917default compilation environment.
2918.PP
2919\fIInotify and Kqueue\fR
2920.IX Subsection "Inotify and Kqueue"
2921.PP
2922When \f(CW\*(C`inotify (7)\*(C'\fR support has been compiled into libev and present at
2923runtime, it will be used to speed up change detection where possible. The
2924inotify descriptor will be created lazily when the first \f(CW\*(C`ev_stat\*(C'\fR
2925watcher is being started.
2926.PP
2927Inotify presence does not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers
2928except that changes might be detected earlier, and in some cases, to avoid
2929making regular \f(CW\*(C`stat\*(C'\fR calls. Even in the presence of inotify support
2930there are many cases where libev has to resort to regular \f(CW\*(C`stat\*(C'\fR polling,
2931but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
2932many bugs), the path exists (i.e. stat succeeds), and the path resides on
2933a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
2934xfs are fully working) libev usually gets away without polling.
2935.PP
2936There is no support for kqueue, as apparently it cannot be used to
2937implement this functionality, due to the requirement of having a file
2938descriptor open on the object at all times, and detecting renames, unlinks
2939etc. is difficult.
2940.PP
2941\fI\f(CI\*(C`stat ()\*(C'\fI is a synchronous operation\fR
2942.IX Subsection "stat () is a synchronous operation"
2943.PP
2944Libev doesn't normally do any kind of I/O itself, and so is not blocking
2945the process. The exception are \f(CW\*(C`ev_stat\*(C'\fR watchers \- those call \f(CW\*(C`stat
2946()\*(C'\fR, which is a synchronous operation.
2947.PP
2948For local paths, this usually doesn't matter: unless the system is very
2949busy or the intervals between stat's are large, a stat call will be fast,
2950as the path data is usually in memory already (except when starting the
2951watcher).
2952.PP
2953For networked file systems, calling \f(CW\*(C`stat ()\*(C'\fR can block an indefinite
2954time due to network issues, and even under good conditions, a stat call
2955often takes multiple milliseconds.
2956.PP
2957Therefore, it is best to avoid using \f(CW\*(C`ev_stat\*(C'\fR watchers on networked
2958paths, although this is fully supported by libev.
2959.PP
2960\fIThe special problem of stat time resolution\fR
2961.IX Subsection "The special problem of stat time resolution"
2962.PP
2963The \f(CW\*(C`stat ()\*(C'\fR system call only supports full-second resolution portably,
2964and even on systems where the resolution is higher, most file systems
2965still only support whole seconds.
2966.PP
2967That means that, if the time is the only thing that changes, you can
2968easily miss updates: on the first update, \f(CW\*(C`ev_stat\*(C'\fR detects a change and
2969calls your callback, which does something. When there is another update
2970within the same second, \f(CW\*(C`ev_stat\*(C'\fR will be unable to detect unless the
2971stat data does change in other ways (e.g. file size).
2972.PP
2973The solution to this is to delay acting on a change for slightly more
2974than a second (or till slightly after the next full second boundary), using
2975a roughly one-second-delay \f(CW\*(C`ev_timer\*(C'\fR (e.g. \f(CW\*(C`ev_timer_set (w, 0., 1.02);
2976ev_timer_again (loop, w)\*(C'\fR).
2977.PP
2978The \f(CW.02\fR offset is added to work around small timing inconsistencies
2979of some operating systems (where the second counter of the current time
2980might be be delayed. One such system is the Linux kernel, where a call to
2981\&\f(CW\*(C`gettimeofday\*(C'\fR might return a timestamp with a full second later than
2982a subsequent \f(CW\*(C`time\*(C'\fR call \- if the equivalent of \f(CW\*(C`time ()\*(C'\fR is used to
2983update file times then there will be a small window where the kernel uses
2984the previous second to update file times but libev might already execute
2985the timer callback).
1629.PP 2986.PP
1630\fIWatcher-Specific Functions and Data Members\fR 2987\fIWatcher-Specific Functions and Data Members\fR
1631.IX Subsection "Watcher-Specific Functions and Data Members" 2988.IX Subsection "Watcher-Specific Functions and Data Members"
1632.IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4 2989.IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4
1633.IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 2990.IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)"
… …
1639\&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to 2996\&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to
1640be detected and should normally be specified as \f(CW0\fR to let libev choose 2997be detected and should normally be specified as \f(CW0\fR to let libev choose
1641a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same 2998a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same
1642path for as long as the watcher is active. 2999path for as long as the watcher is active.
1643.Sp 3000.Sp
1644The callback will be receive \f(CW\*(C`EV_STAT\*(C'\fR when a change was detected, 3001The callback will receive an \f(CW\*(C`EV_STAT\*(C'\fR event when a change was detected,
1645relative to the attributes at the time the watcher was started (or the 3002relative to the attributes at the time the watcher was started (or the
1646last change was detected). 3003last change was detected).
1647.IP "ev_stat_stat (ev_stat *)" 4 3004.IP "ev_stat_stat (loop, ev_stat *)" 4
1648.IX Item "ev_stat_stat (ev_stat *)" 3005.IX Item "ev_stat_stat (loop, ev_stat *)"
1649Updates the stat buffer immediately with new values. If you change the 3006Updates the stat buffer immediately with new values. If you change the
1650watched path in your callback, you could call this fucntion to avoid 3007watched path in your callback, you could call this function to avoid
1651detecting this change (while introducing a race condition). Can also be 3008detecting this change (while introducing a race condition if you are not
1652useful simply to find out the new values. 3009the only one changing the path). Can also be useful simply to find out the
3010new values.
1653.IP "ev_statdata attr [read\-only]" 4 3011.IP "ev_statdata attr [read\-only]" 4
1654.IX Item "ev_statdata attr [read-only]" 3012.IX Item "ev_statdata attr [read-only]"
1655The most-recently detected attributes of the file. Although the type is of 3013The most-recently detected attributes of the file. Although the type is
1656\&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types 3014\&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types
3015suitable for your system, but you can only rely on the POSIX-standardised
1657suitable for your system. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there 3016members to be present. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there was
1658was some error while \f(CW\*(C`stat\*(C'\fRing the file. 3017some error while \f(CW\*(C`stat\*(C'\fRing the file.
1659.IP "ev_statdata prev [read\-only]" 4 3018.IP "ev_statdata prev [read\-only]" 4
1660.IX Item "ev_statdata prev [read-only]" 3019.IX Item "ev_statdata prev [read-only]"
1661The previous attributes of the file. The callback gets invoked whenever 3020The previous attributes of the file. The callback gets invoked whenever
1662\&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR. 3021\&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR, or, more precisely, one or more of these members
3022differ: \f(CW\*(C`st_dev\*(C'\fR, \f(CW\*(C`st_ino\*(C'\fR, \f(CW\*(C`st_mode\*(C'\fR, \f(CW\*(C`st_nlink\*(C'\fR, \f(CW\*(C`st_uid\*(C'\fR,
3023\&\f(CW\*(C`st_gid\*(C'\fR, \f(CW\*(C`st_rdev\*(C'\fR, \f(CW\*(C`st_size\*(C'\fR, \f(CW\*(C`st_atime\*(C'\fR, \f(CW\*(C`st_mtime\*(C'\fR, \f(CW\*(C`st_ctime\*(C'\fR.
1663.IP "ev_tstamp interval [read\-only]" 4 3024.IP "ev_tstamp interval [read\-only]" 4
1664.IX Item "ev_tstamp interval [read-only]" 3025.IX Item "ev_tstamp interval [read-only]"
1665The specified interval. 3026The specified interval.
1666.IP "const char *path [read\-only]" 4 3027.IP "const char *path [read\-only]" 4
1667.IX Item "const char *path [read-only]" 3028.IX Item "const char *path [read-only]"
1668The filesystem path that is being watched. 3029The file system path that is being watched.
3030.PP
3031\fIExamples\fR
3032.IX Subsection "Examples"
1669.PP 3033.PP
1670Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes. 3034Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes.
1671.PP 3035.PP
1672.Vb 15 3036.Vb 10
1673\& static void 3037\& static void
1674\& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents) 3038\& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1675\& { 3039\& {
1676\& /* /etc/passwd changed in some way */ 3040\& /* /etc/passwd changed in some way */
1677\& if (w->attr.st_nlink) 3041\& if (w\->attr.st_nlink)
1678\& { 3042\& {
1679\& printf ("passwd current size %ld\en", (long)w->attr.st_size); 3043\& printf ("passwd current size %ld\en", (long)w\->attr.st_size);
1680\& printf ("passwd current atime %ld\en", (long)w->attr.st_mtime); 3044\& printf ("passwd current atime %ld\en", (long)w\->attr.st_mtime);
1681\& printf ("passwd current mtime %ld\en", (long)w->attr.st_mtime); 3045\& printf ("passwd current mtime %ld\en", (long)w\->attr.st_mtime);
1682\& } 3046\& }
1683\& else 3047\& else
1684\& /* you shalt not abuse printf for puts */ 3048\& /* you shalt not abuse printf for puts */
1685\& puts ("wow, /etc/passwd is not there, expect problems. " 3049\& puts ("wow, /etc/passwd is not there, expect problems. "
1686\& "if this is windows, they already arrived\en"); 3050\& "if this is windows, they already arrived\en");
1687\& } 3051\& }
3052\&
3053\& ...
3054\& ev_stat passwd;
3055\&
3056\& ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
3057\& ev_stat_start (loop, &passwd);
1688.Ve 3058.Ve
3059.PP
3060Example: Like above, but additionally use a one-second delay so we do not
3061miss updates (however, frequent updates will delay processing, too, so
3062one might do the work both on \f(CW\*(C`ev_stat\*(C'\fR callback invocation \fIand\fR on
3063\&\f(CW\*(C`ev_timer\*(C'\fR callback invocation).
1689.PP 3064.PP
1690.Vb 2 3065.Vb 2
3066\& static ev_stat passwd;
3067\& static ev_timer timer;
3068\&
3069\& static void
3070\& timer_cb (EV_P_ ev_timer *w, int revents)
3071\& {
3072\& ev_timer_stop (EV_A_ w);
3073\&
3074\& /* now it\*(Aqs one second after the most recent passwd change */
3075\& }
3076\&
3077\& static void
3078\& stat_cb (EV_P_ ev_stat *w, int revents)
3079\& {
3080\& /* reset the one\-second timer */
3081\& ev_timer_again (EV_A_ &timer);
3082\& }
3083\&
1691\& ... 3084\& ...
1692\& ev_stat passwd;
1693.Ve
1694.PP
1695.Vb 2
1696\& ev_stat_init (&passwd, passwd_cb, "/etc/passwd"); 3085\& ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1697\& ev_stat_start (loop, &passwd); 3086\& ev_stat_start (loop, &passwd);
3087\& ev_timer_init (&timer, timer_cb, 0., 1.02);
1698.Ve 3088.Ve
1699.ie n .Sh """ev_idle"" \- when you've got nothing better to do..." 3089.ie n .SS """ev_idle"" \- when you've got nothing better to do..."
1700.el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do..." 3090.el .SS "\f(CWev_idle\fP \- when you've got nothing better to do..."
1701.IX Subsection "ev_idle - when you've got nothing better to do..." 3091.IX Subsection "ev_idle - when you've got nothing better to do..."
1702Idle watchers trigger events when no other events of the same or higher 3092Idle watchers trigger events when no other events of the same or higher
1703priority are pending (prepare, check and other idle watchers do not 3093priority are pending (prepare, check and other idle watchers do not count
1704count). 3094as receiving \*(L"events\*(R").
1705.PP 3095.PP
1706That is, as long as your process is busy handling sockets or timeouts 3096That is, as long as your process is busy handling sockets or timeouts
1707(or even signals, imagine) of the same or higher priority it will not be 3097(or even signals, imagine) of the same or higher priority it will not be
1708triggered. But when your process is idle (or only lower-priority watchers 3098triggered. But when your process is idle (or only lower-priority watchers
1709are pending), the idle watchers are being called once per event loop 3099are pending), the idle watchers are being called once per event loop
… …
1713The most noteworthy effect is that as long as any idle watchers are 3103The most noteworthy effect is that as long as any idle watchers are
1714active, the process will not block when waiting for new events. 3104active, the process will not block when waiting for new events.
1715.PP 3105.PP
1716Apart from keeping your process non-blocking (which is a useful 3106Apart from keeping your process non-blocking (which is a useful
1717effect on its own sometimes), idle watchers are a good place to do 3107effect on its own sometimes), idle watchers are a good place to do
1718\&\*(L"pseudo\-background processing\*(R", or delay processing stuff to after the 3108\&\*(L"pseudo-background processing\*(R", or delay processing stuff to after the
1719event loop has handled all outstanding events. 3109event loop has handled all outstanding events.
3110.PP
3111\fIAbusing an \f(CI\*(C`ev_idle\*(C'\fI watcher for its side-effect\fR
3112.IX Subsection "Abusing an ev_idle watcher for its side-effect"
3113.PP
3114As long as there is at least one active idle watcher, libev will never
3115sleep unnecessarily. Or in other words, it will loop as fast as possible.
3116For this to work, the idle watcher doesn't need to be invoked at all \- the
3117lowest priority will do.
3118.PP
3119This mode of operation can be useful together with an \f(CW\*(C`ev_check\*(C'\fR watcher,
3120to do something on each event loop iteration \- for example to balance load
3121between different connections.
3122.PP
3123See \*(L"Abusing an ev_check watcher for its side-effect\*(R" for a longer
3124example.
1720.PP 3125.PP
1721\fIWatcher-Specific Functions and Data Members\fR 3126\fIWatcher-Specific Functions and Data Members\fR
1722.IX Subsection "Watcher-Specific Functions and Data Members" 3127.IX Subsection "Watcher-Specific Functions and Data Members"
1723.IP "ev_idle_init (ev_signal *, callback)" 4 3128.IP "ev_idle_init (ev_idle *, callback)" 4
1724.IX Item "ev_idle_init (ev_signal *, callback)" 3129.IX Item "ev_idle_init (ev_idle *, callback)"
1725Initialises and configures the idle watcher \- it has no parameters of any 3130Initialises and configures the idle watcher \- it has no parameters of any
1726kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless, 3131kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
1727believe me. 3132believe me.
1728.PP 3133.PP
3134\fIExamples\fR
3135.IX Subsection "Examples"
3136.PP
1729Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the 3137Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the
1730callback, free it. Also, use no error checking, as usual. 3138callback, free it. Also, use no error checking, as usual.
1731.PP 3139.PP
1732.Vb 7 3140.Vb 5
1733\& static void 3141\& static void
1734\& idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents) 3142\& idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1735\& { 3143\& {
3144\& // stop the watcher
3145\& ev_idle_stop (loop, w);
3146\&
3147\& // now we can free it
1736\& free (w); 3148\& free (w);
3149\&
1737\& // now do something you wanted to do when the program has 3150\& // now do something you wanted to do when the program has
1738\& // no longer asnything immediate to do. 3151\& // no longer anything immediate to do.
1739\& } 3152\& }
1740.Ve 3153\&
1741.PP
1742.Vb 3
1743\& struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle)); 3154\& ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1744\& ev_idle_init (idle_watcher, idle_cb); 3155\& ev_idle_init (idle_watcher, idle_cb);
1745\& ev_idle_start (loop, idle_cb); 3156\& ev_idle_start (loop, idle_watcher);
1746.Ve 3157.Ve
1747.ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop!" 3158.ie n .SS """ev_prepare"" and ""ev_check"" \- customise your event loop!"
1748.el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!" 3159.el .SS "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!"
1749.IX Subsection "ev_prepare and ev_check - customise your event loop!" 3160.IX Subsection "ev_prepare and ev_check - customise your event loop!"
1750Prepare and check watchers are usually (but not always) used in tandem: 3161Prepare and check watchers are often (but not always) used in pairs:
1751prepare watchers get invoked before the process blocks and check watchers 3162prepare watchers get invoked before the process blocks and check watchers
1752afterwards. 3163afterwards.
1753.PP 3164.PP
1754You \fImust not\fR call \f(CW\*(C`ev_loop\*(C'\fR or similar functions that enter 3165You \fImust not\fR call \f(CW\*(C`ev_run\*(C'\fR (or similar functions that enter the
1755the current event loop from either \f(CW\*(C`ev_prepare\*(C'\fR or \f(CW\*(C`ev_check\*(C'\fR 3166current event loop) or \f(CW\*(C`ev_loop_fork\*(C'\fR from either \f(CW\*(C`ev_prepare\*(C'\fR or
1756watchers. Other loops than the current one are fine, however. The 3167\&\f(CW\*(C`ev_check\*(C'\fR watchers. Other loops than the current one are fine,
1757rationale behind this is that you do not need to check for recursion in 3168however. The rationale behind this is that you do not need to check
1758those watchers, i.e. the sequence will always be \f(CW\*(C`ev_prepare\*(C'\fR, blocking, 3169for recursion in those watchers, i.e. the sequence will always be
1759\&\f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each kind they will always be 3170\&\f(CW\*(C`ev_prepare\*(C'\fR, blocking, \f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each
1760called in pairs bracketing the blocking call. 3171kind they will always be called in pairs bracketing the blocking call.
1761.PP 3172.PP
1762Their main purpose is to integrate other event mechanisms into libev and 3173Their main purpose is to integrate other event mechanisms into libev and
1763their use is somewhat advanced. This could be used, for example, to track 3174their use is somewhat advanced. They could be used, for example, to track
1764variable changes, implement your own watchers, integrate net-snmp or a 3175variable changes, implement your own watchers, integrate net-snmp or a
1765coroutine library and lots more. They are also occasionally useful if 3176coroutine library and lots more. They are also occasionally useful if
1766you cache some data and want to flush it before blocking (for example, 3177you cache some data and want to flush it before blocking (for example,
1767in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR 3178in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR
1768watcher). 3179watcher).
1769.PP 3180.PP
1770This is done by examining in each prepare call which file descriptors need 3181This is done by examining in each prepare call which file descriptors
1771to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers for 3182need to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers
1772them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many libraries 3183for them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many
1773provide just this functionality). Then, in the check watcher you check for 3184libraries provide exactly this functionality). Then, in the check watcher,
1774any events that occured (by checking the pending status of all watchers 3185you check for any events that occurred (by checking the pending status
1775and stopping them) and call back into the library. The I/O and timer 3186of all watchers and stopping them) and call back into the library. The
1776callbacks will never actually be called (but must be valid nevertheless, 3187I/O and timer callbacks will never actually be called (but must be valid
1777because you never know, you know?). 3188nevertheless, because you never know, you know?).
1778.PP 3189.PP
1779As another example, the Perl Coro module uses these hooks to integrate 3190As another example, the Perl Coro module uses these hooks to integrate
1780coroutines into libev programs, by yielding to other active coroutines 3191coroutines into libev programs, by yielding to other active coroutines
1781during each prepare and only letting the process block if no coroutines 3192during each prepare and only letting the process block if no coroutines
1782are ready to run (it's actually more complicated: it only runs coroutines 3193are ready to run (it's actually more complicated: it only runs coroutines
1783with priority higher than or equal to the event loop and one coroutine 3194with priority higher than or equal to the event loop and one coroutine
1784of lower priority, but only once, using idle watchers to keep the event 3195of lower priority, but only once, using idle watchers to keep the event
1785loop from blocking if lower-priority coroutines are active, thus mapping 3196loop from blocking if lower-priority coroutines are active, thus mapping
1786low-priority coroutines to idle/background tasks). 3197low-priority coroutines to idle/background tasks).
1787.PP 3198.PP
1788It is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR) 3199When used for this purpose, it is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers
1789priority, to ensure that they are being run before any other watchers 3200highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR) priority, to ensure that they are being run before
3201any other watchers after the poll (this doesn't matter for \f(CW\*(C`ev_prepare\*(C'\fR
3202watchers).
3203.PP
1790after the poll. Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers, 3204Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers, too) should not
1791too) should not activate (\*(L"feed\*(R") events into libev. While libev fully 3205activate (\*(L"feed\*(R") events into libev. While libev fully supports this, they
1792supports this, they will be called before other \f(CW\*(C`ev_check\*(C'\fR watchers 3206might get executed before other \f(CW\*(C`ev_check\*(C'\fR watchers did their job. As
1793did their job. As \f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other 3207\&\f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other (non-libev) event
1794(non\-libev) event loops those other event loops might be in an unusable 3208loops those other event loops might be in an unusable state until their
1795state until their \f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to 3209\&\f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to coexist peacefully with
1796coexist peacefully with others). 3210others).
3211.PP
3212\fIAbusing an \f(CI\*(C`ev_check\*(C'\fI watcher for its side-effect\fR
3213.IX Subsection "Abusing an ev_check watcher for its side-effect"
3214.PP
3215\&\f(CW\*(C`ev_check\*(C'\fR (and less often also \f(CW\*(C`ev_prepare\*(C'\fR) watchers can also be
3216useful because they are called once per event loop iteration. For
3217example, if you want to handle a large number of connections fairly, you
3218normally only do a bit of work for each active connection, and if there
3219is more work to do, you wait for the next event loop iteration, so other
3220connections have a chance of making progress.
3221.PP
3222Using an \f(CW\*(C`ev_check\*(C'\fR watcher is almost enough: it will be called on the
3223next event loop iteration. However, that isn't as soon as possible \-
3224without external events, your \f(CW\*(C`ev_check\*(C'\fR watcher will not be invoked.
3225.PP
3226This is where \f(CW\*(C`ev_idle\*(C'\fR watchers come in handy \- all you need is a
3227single global idle watcher that is active as long as you have one active
3228\&\f(CW\*(C`ev_check\*(C'\fR watcher. The \f(CW\*(C`ev_idle\*(C'\fR watcher makes sure the event loop
3229will not sleep, and the \f(CW\*(C`ev_check\*(C'\fR watcher makes sure a callback gets
3230invoked. Neither watcher alone can do that.
1797.PP 3231.PP
1798\fIWatcher-Specific Functions and Data Members\fR 3232\fIWatcher-Specific Functions and Data Members\fR
1799.IX Subsection "Watcher-Specific Functions and Data Members" 3233.IX Subsection "Watcher-Specific Functions and Data Members"
1800.IP "ev_prepare_init (ev_prepare *, callback)" 4 3234.IP "ev_prepare_init (ev_prepare *, callback)" 4
1801.IX Item "ev_prepare_init (ev_prepare *, callback)" 3235.IX Item "ev_prepare_init (ev_prepare *, callback)"
… …
1803.IP "ev_check_init (ev_check *, callback)" 4 3237.IP "ev_check_init (ev_check *, callback)" 4
1804.IX Item "ev_check_init (ev_check *, callback)" 3238.IX Item "ev_check_init (ev_check *, callback)"
1805.PD 3239.PD
1806Initialises and configures the prepare or check watcher \- they have no 3240Initialises and configures the prepare or check watcher \- they have no
1807parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR 3241parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
1808macros, but using them is utterly, utterly and completely pointless. 3242macros, but using them is utterly, utterly, utterly and completely
3243pointless.
3244.PP
3245\fIExamples\fR
3246.IX Subsection "Examples"
1809.PP 3247.PP
1810There are a number of principal ways to embed other event loops or modules 3248There are a number of principal ways to embed other event loops or modules
1811into libev. Here are some ideas on how to include libadns into libev 3249into libev. Here are some ideas on how to include libadns into libev
1812(there is a Perl module named \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could 3250(there is a Perl module named \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could
1813use for an actually working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR 3251use as a working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR embeds a
1814embeds a Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0 3252Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0 into the
1815into the Glib event loop). 3253Glib event loop).
1816.PP 3254.PP
1817Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler, 3255Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler,
1818and in a check watcher, destroy them and call into libadns. What follows 3256and in a check watcher, destroy them and call into libadns. What follows
1819is pseudo-code only of course. This requires you to either use a low 3257is pseudo-code only of course. This requires you to either use a low
1820priority for the check watcher or use \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as 3258priority for the check watcher or use \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as
1821the callbacks for the IO/timeout watchers might not have been called yet. 3259the callbacks for the IO/timeout watchers might not have been called yet.
1822.PP 3260.PP
1823.Vb 2 3261.Vb 2
1824\& static ev_io iow [nfd]; 3262\& static ev_io iow [nfd];
1825\& static ev_timer tw; 3263\& static ev_timer tw;
1826.Ve 3264\&
1827.PP
1828.Vb 4
1829\& static void 3265\& static void
1830\& io_cb (ev_loop *loop, ev_io *w, int revents) 3266\& io_cb (struct ev_loop *loop, ev_io *w, int revents)
1831\& { 3267\& {
1832\& } 3268\& }
1833.Ve 3269\&
1834.PP
1835.Vb 8
1836\& // create io watchers for each fd and a timer before blocking 3270\& // create io watchers for each fd and a timer before blocking
1837\& static void 3271\& static void
1838\& adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents) 3272\& adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1839\& { 3273\& {
1840\& int timeout = 3600000; 3274\& int timeout = 3600000;
1841\& struct pollfd fds [nfd]; 3275\& struct pollfd fds [nfd];
1842\& // actual code will need to loop here and realloc etc. 3276\& // actual code will need to loop here and realloc etc.
1843\& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ())); 3277\& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1844.Ve 3278\&
1845.PP
1846.Vb 3
1847\& /* the callback is illegal, but won't be called as we stop during check */ 3279\& /* the callback is illegal, but won\*(Aqt be called as we stop during check */
1848\& ev_timer_init (&tw, 0, timeout * 1e-3); 3280\& ev_timer_init (&tw, 0, timeout * 1e\-3, 0.);
1849\& ev_timer_start (loop, &tw); 3281\& ev_timer_start (loop, &tw);
1850.Ve 3282\&
1851.PP
1852.Vb 6
1853\& // create one ev_io per pollfd 3283\& // create one ev_io per pollfd
1854\& for (int i = 0; i < nfd; ++i) 3284\& for (int i = 0; i < nfd; ++i)
1855\& { 3285\& {
1856\& ev_io_init (iow + i, io_cb, fds [i].fd, 3286\& ev_io_init (iow + i, io_cb, fds [i].fd,
1857\& ((fds [i].events & POLLIN ? EV_READ : 0) 3287\& ((fds [i].events & POLLIN ? EV_READ : 0)
1858\& | (fds [i].events & POLLOUT ? EV_WRITE : 0))); 3288\& | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1859.Ve 3289\&
1860.PP
1861.Vb 4
1862\& fds [i].revents = 0; 3290\& fds [i].revents = 0;
1863\& ev_io_start (loop, iow + i); 3291\& ev_io_start (loop, iow + i);
1864\& } 3292\& }
1865\& } 3293\& }
1866.Ve 3294\&
1867.PP
1868.Vb 5
1869\& // stop all watchers after blocking 3295\& // stop all watchers after blocking
1870\& static void 3296\& static void
1871\& adns_check_cb (ev_loop *loop, ev_check *w, int revents) 3297\& adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1872\& { 3298\& {
1873\& ev_timer_stop (loop, &tw); 3299\& ev_timer_stop (loop, &tw);
1874.Ve 3300\&
1875.PP
1876.Vb 8
1877\& for (int i = 0; i < nfd; ++i) 3301\& for (int i = 0; i < nfd; ++i)
1878\& { 3302\& {
1879\& // set the relevant poll flags 3303\& // set the relevant poll flags
1880\& // could also call adns_processreadable etc. here 3304\& // could also call adns_processreadable etc. here
1881\& struct pollfd *fd = fds + i; 3305\& struct pollfd *fd = fds + i;
1882\& int revents = ev_clear_pending (iow + i); 3306\& int revents = ev_clear_pending (iow + i);
1883\& if (revents & EV_READ ) fd->revents |= fd->events & POLLIN; 3307\& if (revents & EV_READ ) fd\->revents |= fd\->events & POLLIN;
1884\& if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT; 3308\& if (revents & EV_WRITE) fd\->revents |= fd\->events & POLLOUT;
1885.Ve 3309\&
1886.PP
1887.Vb 3
1888\& // now stop the watcher 3310\& // now stop the watcher
1889\& ev_io_stop (loop, iow + i); 3311\& ev_io_stop (loop, iow + i);
1890\& } 3312\& }
1891.Ve 3313\&
1892.PP
1893.Vb 2
1894\& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop)); 3314\& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1895\& } 3315\& }
1896.Ve 3316.Ve
1897.PP 3317.PP
1898Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR 3318Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR
1899in the prepare watcher and would dispose of the check watcher. 3319in the prepare watcher and would dispose of the check watcher.
1900.PP 3320.PP
1901Method 3: If the module to be embedded supports explicit event 3321Method 3: If the module to be embedded supports explicit event
1902notification (adns does), you can also make use of the actual watcher 3322notification (libadns does), you can also make use of the actual watcher
1903callbacks, and only destroy/create the watchers in the prepare watcher. 3323callbacks, and only destroy/create the watchers in the prepare watcher.
1904.PP 3324.PP
1905.Vb 5 3325.Vb 5
1906\& static void 3326\& static void
1907\& timer_cb (EV_P_ ev_timer *w, int revents) 3327\& timer_cb (EV_P_ ev_timer *w, int revents)
1908\& { 3328\& {
1909\& adns_state ads = (adns_state)w->data; 3329\& adns_state ads = (adns_state)w\->data;
1910\& update_now (EV_A); 3330\& update_now (EV_A);
1911.Ve 3331\&
1912.PP
1913.Vb 2
1914\& adns_processtimeouts (ads, &tv_now); 3332\& adns_processtimeouts (ads, &tv_now);
1915\& } 3333\& }
1916.Ve 3334\&
1917.PP
1918.Vb 5
1919\& static void 3335\& static void
1920\& io_cb (EV_P_ ev_io *w, int revents) 3336\& io_cb (EV_P_ ev_io *w, int revents)
1921\& { 3337\& {
1922\& adns_state ads = (adns_state)w->data; 3338\& adns_state ads = (adns_state)w\->data;
1923\& update_now (EV_A); 3339\& update_now (EV_A);
1924.Ve 3340\&
1925.PP
1926.Vb 3
1927\& if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now); 3341\& if (revents & EV_READ ) adns_processreadable (ads, w\->fd, &tv_now);
1928\& if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now); 3342\& if (revents & EV_WRITE) adns_processwriteable (ads, w\->fd, &tv_now);
1929\& } 3343\& }
1930.Ve 3344\&
1931.PP
1932.Vb 1
1933\& // do not ever call adns_afterpoll 3345\& // do not ever call adns_afterpoll
1934.Ve 3346.Ve
1935.PP 3347.PP
1936Method 4: Do not use a prepare or check watcher because the module you 3348Method 4: Do not use a prepare or check watcher because the module you
1937want to embed is too inflexible to support it. Instead, youc na override 3349want to embed is not flexible enough to support it. Instead, you can
1938their poll function. The drawback with this solution is that the main 3350override their poll function. The drawback with this solution is that the
1939loop is now no longer controllable by \s-1EV\s0. The \f(CW\*(C`Glib::EV\*(C'\fR module does 3351main loop is now no longer controllable by \s-1EV.\s0 The \f(CW\*(C`Glib::EV\*(C'\fR module uses
1940this. 3352this approach, effectively embedding \s-1EV\s0 as a client into the horrible
3353libglib event loop.
1941.PP 3354.PP
1942.Vb 4 3355.Vb 4
1943\& static gint 3356\& static gint
1944\& event_poll_func (GPollFD *fds, guint nfds, gint timeout) 3357\& event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1945\& { 3358\& {
1946\& int got_events = 0; 3359\& int got_events = 0;
1947.Ve 3360\&
1948.PP
1949.Vb 2
1950\& for (n = 0; n < nfds; ++n) 3361\& for (n = 0; n < nfds; ++n)
1951\& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events 3362\& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1952.Ve 3363\&
1953.PP
1954.Vb 2
1955\& if (timeout >= 0) 3364\& if (timeout >= 0)
1956\& // create/start timer 3365\& // create/start timer
1957.Ve 3366\&
1958.PP
1959.Vb 2
1960\& // poll 3367\& // poll
1961\& ev_loop (EV_A_ 0); 3368\& ev_run (EV_A_ 0);
1962.Ve 3369\&
1963.PP
1964.Vb 3
1965\& // stop timer again 3370\& // stop timer again
1966\& if (timeout >= 0) 3371\& if (timeout >= 0)
1967\& ev_timer_stop (EV_A_ &to); 3372\& ev_timer_stop (EV_A_ &to);
1968.Ve 3373\&
1969.PP
1970.Vb 3
1971\& // stop io watchers again - their callbacks should have set 3374\& // stop io watchers again \- their callbacks should have set
1972\& for (n = 0; n < nfds; ++n) 3375\& for (n = 0; n < nfds; ++n)
1973\& ev_io_stop (EV_A_ iow [n]); 3376\& ev_io_stop (EV_A_ iow [n]);
1974.Ve 3377\&
1975.PP
1976.Vb 2
1977\& return got_events; 3378\& return got_events;
1978\& } 3379\& }
1979.Ve 3380.Ve
1980.ie n .Sh """ev_embed"" \- when one backend isn't enough..." 3381.ie n .SS """ev_embed"" \- when one backend isn't enough..."
1981.el .Sh "\f(CWev_embed\fP \- when one backend isn't enough..." 3382.el .SS "\f(CWev_embed\fP \- when one backend isn't enough..."
1982.IX Subsection "ev_embed - when one backend isn't enough..." 3383.IX Subsection "ev_embed - when one backend isn't enough..."
1983This is a rather advanced watcher type that lets you embed one event loop 3384This is a rather advanced watcher type that lets you embed one event loop
1984into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded 3385into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded
1985loop, other types of watchers might be handled in a delayed or incorrect 3386loop, other types of watchers might be handled in a delayed or incorrect
1986fashion and must not be used). 3387fashion and must not be used).
… …
1989prioritise I/O. 3390prioritise I/O.
1990.PP 3391.PP
1991As an example for a bug workaround, the kqueue backend might only support 3392As an example for a bug workaround, the kqueue backend might only support
1992sockets on some platform, so it is unusable as generic backend, but you 3393sockets on some platform, so it is unusable as generic backend, but you
1993still want to make use of it because you have many sockets and it scales 3394still want to make use of it because you have many sockets and it scales
1994so nicely. In this case, you would create a kqueue-based loop and embed it 3395so nicely. In this case, you would create a kqueue-based loop and embed
1995into your default loop (which might use e.g. poll). Overall operation will 3396it into your default loop (which might use e.g. poll). Overall operation
1996be a bit slower because first libev has to poll and then call kevent, but 3397will be a bit slower because first libev has to call \f(CW\*(C`poll\*(C'\fR and then
1997at least you can use both at what they are best. 3398\&\f(CW\*(C`kevent\*(C'\fR, but at least you can use both mechanisms for what they are
3399best: \f(CW\*(C`kqueue\*(C'\fR for scalable sockets and \f(CW\*(C`poll\*(C'\fR if you want it to work :)
1998.PP 3400.PP
1999As for prioritising I/O: rarely you have the case where some fds have 3401As for prioritising I/O: under rare circumstances you have the case where
2000to be watched and handled very quickly (with low latency), and even 3402some fds have to be watched and handled very quickly (with low latency),
2001priorities and idle watchers might have too much overhead. In this case 3403and even priorities and idle watchers might have too much overhead. In
2002you would put all the high priority stuff in one loop and all the rest in 3404this case you would put all the high priority stuff in one loop and all
2003a second one, and embed the second one in the first. 3405the rest in a second one, and embed the second one in the first.
2004.PP 3406.PP
2005As long as the watcher is active, the callback will be invoked every time 3407As long as the watcher is active, the callback will be invoked every
2006there might be events pending in the embedded loop. The callback must then 3408time there might be events pending in the embedded loop. The callback
2007call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single sweep and invoke 3409must then call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single
2008their callbacks (you could also start an idle watcher to give the embedded 3410sweep and invoke their callbacks (the callback doesn't need to invoke the
2009loop strictly lower priority for example). You can also set the callback 3411\&\f(CW\*(C`ev_embed_sweep\*(C'\fR function directly, it could also start an idle watcher
2010to \f(CW0\fR, in which case the embed watcher will automatically execute the 3412to give the embedded loop strictly lower priority for example).
2011embedded loop sweep.
2012.PP 3413.PP
2013As long as the watcher is started it will automatically handle events. The 3414You can also set the callback to \f(CW0\fR, in which case the embed watcher
2014callback will be invoked whenever some events have been handled. You can 3415will automatically execute the embedded loop sweep whenever necessary.
2015set the callback to \f(CW0\fR to avoid having to specify one if you are not
2016interested in that.
2017.PP 3416.PP
2018Also, there have not currently been made special provisions for forking: 3417Fork detection will be handled transparently while the \f(CW\*(C`ev_embed\*(C'\fR watcher
2019when you fork, you not only have to call \f(CW\*(C`ev_loop_fork\*(C'\fR on both loops, 3418is active, i.e., the embedded loop will automatically be forked when the
2020but you will also have to stop and restart any \f(CW\*(C`ev_embed\*(C'\fR watchers 3419embedding loop forks. In other cases, the user is responsible for calling
2021yourself. 3420\&\f(CW\*(C`ev_loop_fork\*(C'\fR on the embedded loop.
2022.PP 3421.PP
2023Unfortunately, not all backends are embeddable, only the ones returned by 3422Unfortunately, not all backends are embeddable: only the ones returned by
2024\&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any 3423\&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any
2025portable one. 3424portable one.
2026.PP 3425.PP
2027So when you want to use this feature you will always have to be prepared 3426So when you want to use this feature you will always have to be prepared
2028that you cannot get an embeddable loop. The recommended way to get around 3427that you cannot get an embeddable loop. The recommended way to get around
2029this is to have a separate variables for your embeddable loop, try to 3428this is to have a separate variables for your embeddable loop, try to
2030create it, and if that fails, use the normal loop for everything: 3429create it, and if that fails, use the normal loop for everything.
2031.PP 3430.PP
2032.Vb 3 3431\fI\f(CI\*(C`ev_embed\*(C'\fI and fork\fR
2033\& struct ev_loop *loop_hi = ev_default_init (0); 3432.IX Subsection "ev_embed and fork"
2034\& struct ev_loop *loop_lo = 0;
2035\& struct ev_embed embed;
2036.Ve
2037.PP 3433.PP
2038.Vb 5 3434While the \f(CW\*(C`ev_embed\*(C'\fR watcher is running, forks in the embedding loop will
2039\& // see if there is a chance of getting one that works 3435automatically be applied to the embedded loop as well, so no special
2040\& // (remember that a flags value of 0 means autodetection) 3436fork handling is required in that case. When the watcher is not running,
2041\& loop_lo = ev_embeddable_backends () & ev_recommended_backends () 3437however, it is still the task of the libev user to call \f(CW\*(C`ev_loop_fork ()\*(C'\fR
2042\& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ()) 3438as applicable.
2043\& : 0;
2044.Ve
2045.PP
2046.Vb 8
2047\& // if we got one, then embed it, otherwise default to loop_hi
2048\& if (loop_lo)
2049\& {
2050\& ev_embed_init (&embed, 0, loop_lo);
2051\& ev_embed_start (loop_hi, &embed);
2052\& }
2053\& else
2054\& loop_lo = loop_hi;
2055.Ve
2056.PP 3439.PP
2057\fIWatcher-Specific Functions and Data Members\fR 3440\fIWatcher-Specific Functions and Data Members\fR
2058.IX Subsection "Watcher-Specific Functions and Data Members" 3441.IX Subsection "Watcher-Specific Functions and Data Members"
2059.IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4 3442.IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
2060.IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 3443.IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)"
2061.PD 0 3444.PD 0
2062.IP "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 4 3445.IP "ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)" 4
2063.IX Item "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 3446.IX Item "ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)"
2064.PD 3447.PD
2065Configures the watcher to embed the given loop, which must be 3448Configures the watcher to embed the given loop, which must be
2066embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be 3449embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be
2067invoked automatically, otherwise it is the responsibility of the callback 3450invoked automatically, otherwise it is the responsibility of the callback
2068to invoke it (it will continue to be called until the sweep has been done, 3451to invoke it (it will continue to be called until the sweep has been done,
2069if you do not want thta, you need to temporarily stop the embed watcher). 3452if you do not want that, you need to temporarily stop the embed watcher).
2070.IP "ev_embed_sweep (loop, ev_embed *)" 4 3453.IP "ev_embed_sweep (loop, ev_embed *)" 4
2071.IX Item "ev_embed_sweep (loop, ev_embed *)" 3454.IX Item "ev_embed_sweep (loop, ev_embed *)"
2072Make a single, non-blocking sweep over the embedded loop. This works 3455Make a single, non-blocking sweep over the embedded loop. This works
2073similarly to \f(CW\*(C`ev_loop (embedded_loop, EVLOOP_NONBLOCK)\*(C'\fR, but in the most 3456similarly to \f(CW\*(C`ev_run (embedded_loop, EVRUN_NOWAIT)\*(C'\fR, but in the most
2074apropriate way for embedded loops. 3457appropriate way for embedded loops.
2075.IP "struct ev_loop *other [read\-only]" 4 3458.IP "struct ev_loop *other [read\-only]" 4
2076.IX Item "struct ev_loop *other [read-only]" 3459.IX Item "struct ev_loop *other [read-only]"
2077The embedded event loop. 3460The embedded event loop.
3461.PP
3462\fIExamples\fR
3463.IX Subsection "Examples"
3464.PP
3465Example: Try to get an embeddable event loop and embed it into the default
3466event loop. If that is not possible, use the default loop. The default
3467loop is stored in \f(CW\*(C`loop_hi\*(C'\fR, while the embeddable loop is stored in
3468\&\f(CW\*(C`loop_lo\*(C'\fR (which is \f(CW\*(C`loop_hi\*(C'\fR in the case no embeddable loop can be
3469used).
3470.PP
3471.Vb 3
3472\& struct ev_loop *loop_hi = ev_default_init (0);
3473\& struct ev_loop *loop_lo = 0;
3474\& ev_embed embed;
3475\&
3476\& // see if there is a chance of getting one that works
3477\& // (remember that a flags value of 0 means autodetection)
3478\& loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3479\& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3480\& : 0;
3481\&
3482\& // if we got one, then embed it, otherwise default to loop_hi
3483\& if (loop_lo)
3484\& {
3485\& ev_embed_init (&embed, 0, loop_lo);
3486\& ev_embed_start (loop_hi, &embed);
3487\& }
3488\& else
3489\& loop_lo = loop_hi;
3490.Ve
3491.PP
3492Example: Check if kqueue is available but not recommended and create
3493a kqueue backend for use with sockets (which usually work with any
3494kqueue implementation). Store the kqueue/socket\-only event loop in
3495\&\f(CW\*(C`loop_socket\*(C'\fR. (One might optionally use \f(CW\*(C`EVFLAG_NOENV\*(C'\fR, too).
3496.PP
3497.Vb 3
3498\& struct ev_loop *loop = ev_default_init (0);
3499\& struct ev_loop *loop_socket = 0;
3500\& ev_embed embed;
3501\&
3502\& if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3503\& if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3504\& {
3505\& ev_embed_init (&embed, 0, loop_socket);
3506\& ev_embed_start (loop, &embed);
3507\& }
3508\&
3509\& if (!loop_socket)
3510\& loop_socket = loop;
3511\&
3512\& // now use loop_socket for all sockets, and loop for everything else
3513.Ve
2078.ie n .Sh """ev_fork"" \- the audacity to resume the event loop after a fork" 3514.ie n .SS """ev_fork"" \- the audacity to resume the event loop after a fork"
2079.el .Sh "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork" 3515.el .SS "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork"
2080.IX Subsection "ev_fork - the audacity to resume the event loop after a fork" 3516.IX Subsection "ev_fork - the audacity to resume the event loop after a fork"
2081Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because 3517Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because
2082whoever is a good citizen cared to tell libev about it by calling 3518whoever is a good citizen cared to tell libev about it by calling
2083\&\f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the 3519\&\f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the event loop blocks next
2084event loop blocks next and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called, 3520and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called, and only in the child
2085and only in the child after the fork. If whoever good citizen calling 3521after the fork. If whoever good citizen calling \f(CW\*(C`ev_default_fork\*(C'\fR cheats
2086\&\f(CW\*(C`ev_default_fork\*(C'\fR cheats and calls it in the wrong process, the fork 3522and calls it in the wrong process, the fork handlers will be invoked, too,
2087handlers will be invoked, too, of course. 3523of course.
3524.PP
3525\fIThe special problem of life after fork \- how is it possible?\fR
3526.IX Subsection "The special problem of life after fork - how is it possible?"
3527.PP
3528Most uses of \f(CW\*(C`fork ()\*(C'\fR consist of forking, then some simple calls to set
3529up/change the process environment, followed by a call to \f(CW\*(C`exec()\*(C'\fR. This
3530sequence should be handled by libev without any problems.
3531.PP
3532This changes when the application actually wants to do event handling
3533in the child, or both parent in child, in effect \*(L"continuing\*(R" after the
3534fork.
3535.PP
3536The default mode of operation (for libev, with application help to detect
3537forks) is to duplicate all the state in the child, as would be expected
3538when \fIeither\fR the parent \fIor\fR the child process continues.
3539.PP
3540When both processes want to continue using libev, then this is usually the
3541wrong result. In that case, usually one process (typically the parent) is
3542supposed to continue with all watchers in place as before, while the other
3543process typically wants to start fresh, i.e. without any active watchers.
3544.PP
3545The cleanest and most efficient way to achieve that with libev is to
3546simply create a new event loop, which of course will be \*(L"empty\*(R", and
3547use that for new watchers. This has the advantage of not touching more
3548memory than necessary, and thus avoiding the copy-on-write, and the
3549disadvantage of having to use multiple event loops (which do not support
3550signal watchers).
3551.PP
3552When this is not possible, or you want to use the default loop for
3553other reasons, then in the process that wants to start \*(L"fresh\*(R", call
3554\&\f(CW\*(C`ev_loop_destroy (EV_DEFAULT)\*(C'\fR followed by \f(CW\*(C`ev_default_loop (...)\*(C'\fR.
3555Destroying the default loop will \*(L"orphan\*(R" (not stop) all registered
3556watchers, so you have to be careful not to execute code that modifies
3557those watchers. Note also that in that case, you have to re-register any
3558signal watchers.
2088.PP 3559.PP
2089\fIWatcher-Specific Functions and Data Members\fR 3560\fIWatcher-Specific Functions and Data Members\fR
2090.IX Subsection "Watcher-Specific Functions and Data Members" 3561.IX Subsection "Watcher-Specific Functions and Data Members"
2091.IP "ev_fork_init (ev_signal *, callback)" 4 3562.IP "ev_fork_init (ev_fork *, callback)" 4
2092.IX Item "ev_fork_init (ev_signal *, callback)" 3563.IX Item "ev_fork_init (ev_fork *, callback)"
2093Initialises and configures the fork watcher \- it has no parameters of any 3564Initialises and configures the fork watcher \- it has no parameters of any
2094kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless, 3565kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless,
2095believe me. 3566really.
3567.ie n .SS """ev_cleanup"" \- even the best things end"
3568.el .SS "\f(CWev_cleanup\fP \- even the best things end"
3569.IX Subsection "ev_cleanup - even the best things end"
3570Cleanup watchers are called just before the event loop is being destroyed
3571by a call to \f(CW\*(C`ev_loop_destroy\*(C'\fR.
3572.PP
3573While there is no guarantee that the event loop gets destroyed, cleanup
3574watchers provide a convenient method to install cleanup hooks for your
3575program, worker threads and so on \- you just to make sure to destroy the
3576loop when you want them to be invoked.
3577.PP
3578Cleanup watchers are invoked in the same way as any other watcher. Unlike
3579all other watchers, they do not keep a reference to the event loop (which
3580makes a lot of sense if you think about it). Like all other watchers, you
3581can call libev functions in the callback, except \f(CW\*(C`ev_cleanup_start\*(C'\fR.
3582.PP
3583\fIWatcher-Specific Functions and Data Members\fR
3584.IX Subsection "Watcher-Specific Functions and Data Members"
3585.IP "ev_cleanup_init (ev_cleanup *, callback)" 4
3586.IX Item "ev_cleanup_init (ev_cleanup *, callback)"
3587Initialises and configures the cleanup watcher \- it has no parameters of
3588any kind. There is a \f(CW\*(C`ev_cleanup_set\*(C'\fR macro, but using it is utterly
3589pointless, I assure you.
3590.PP
3591Example: Register an atexit handler to destroy the default loop, so any
3592cleanup functions are called.
3593.PP
3594.Vb 5
3595\& static void
3596\& program_exits (void)
3597\& {
3598\& ev_loop_destroy (EV_DEFAULT_UC);
3599\& }
3600\&
3601\& ...
3602\& atexit (program_exits);
3603.Ve
3604.ie n .SS """ev_async"" \- how to wake up an event loop"
3605.el .SS "\f(CWev_async\fP \- how to wake up an event loop"
3606.IX Subsection "ev_async - how to wake up an event loop"
3607In general, you cannot use an \f(CW\*(C`ev_loop\*(C'\fR from multiple threads or other
3608asynchronous sources such as signal handlers (as opposed to multiple event
3609loops \- those are of course safe to use in different threads).
3610.PP
3611Sometimes, however, you need to wake up an event loop you do not control,
3612for example because it belongs to another thread. This is what \f(CW\*(C`ev_async\*(C'\fR
3613watchers do: as long as the \f(CW\*(C`ev_async\*(C'\fR watcher is active, you can signal
3614it by calling \f(CW\*(C`ev_async_send\*(C'\fR, which is thread\- and signal safe.
3615.PP
3616This functionality is very similar to \f(CW\*(C`ev_signal\*(C'\fR watchers, as signals,
3617too, are asynchronous in nature, and signals, too, will be compressed
3618(i.e. the number of callback invocations may be less than the number of
3619\&\f(CW\*(C`ev_async_send\*(C'\fR calls). In fact, you could use signal watchers as a kind
3620of \*(L"global async watchers\*(R" by using a watcher on an otherwise unused
3621signal, and \f(CW\*(C`ev_feed_signal\*(C'\fR to signal this watcher from another thread,
3622even without knowing which loop owns the signal.
3623.PP
3624\fIQueueing\fR
3625.IX Subsection "Queueing"
3626.PP
3627\&\f(CW\*(C`ev_async\*(C'\fR does not support queueing of data in any way. The reason
3628is that the author does not know of a simple (or any) algorithm for a
3629multiple-writer-single-reader queue that works in all cases and doesn't
3630need elaborate support such as pthreads or unportable memory access
3631semantics.
3632.PP
3633That means that if you want to queue data, you have to provide your own
3634queue. But at least I can tell you how to implement locking around your
3635queue:
3636.IP "queueing from a signal handler context" 4
3637.IX Item "queueing from a signal handler context"
3638To implement race-free queueing, you simply add to the queue in the signal
3639handler but you block the signal handler in the watcher callback. Here is
3640an example that does that for some fictitious \s-1SIGUSR1\s0 handler:
3641.Sp
3642.Vb 1
3643\& static ev_async mysig;
3644\&
3645\& static void
3646\& sigusr1_handler (void)
3647\& {
3648\& sometype data;
3649\&
3650\& // no locking etc.
3651\& queue_put (data);
3652\& ev_async_send (EV_DEFAULT_ &mysig);
3653\& }
3654\&
3655\& static void
3656\& mysig_cb (EV_P_ ev_async *w, int revents)
3657\& {
3658\& sometype data;
3659\& sigset_t block, prev;
3660\&
3661\& sigemptyset (&block);
3662\& sigaddset (&block, SIGUSR1);
3663\& sigprocmask (SIG_BLOCK, &block, &prev);
3664\&
3665\& while (queue_get (&data))
3666\& process (data);
3667\&
3668\& if (sigismember (&prev, SIGUSR1)
3669\& sigprocmask (SIG_UNBLOCK, &block, 0);
3670\& }
3671.Ve
3672.Sp
3673(Note: pthreads in theory requires you to use \f(CW\*(C`pthread_setmask\*(C'\fR
3674instead of \f(CW\*(C`sigprocmask\*(C'\fR when you use threads, but libev doesn't do it
3675either...).
3676.IP "queueing from a thread context" 4
3677.IX Item "queueing from a thread context"
3678The strategy for threads is different, as you cannot (easily) block
3679threads but you can easily preempt them, so to queue safely you need to
3680employ a traditional mutex lock, such as in this pthread example:
3681.Sp
3682.Vb 2
3683\& static ev_async mysig;
3684\& static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
3685\&
3686\& static void
3687\& otherthread (void)
3688\& {
3689\& // only need to lock the actual queueing operation
3690\& pthread_mutex_lock (&mymutex);
3691\& queue_put (data);
3692\& pthread_mutex_unlock (&mymutex);
3693\&
3694\& ev_async_send (EV_DEFAULT_ &mysig);
3695\& }
3696\&
3697\& static void
3698\& mysig_cb (EV_P_ ev_async *w, int revents)
3699\& {
3700\& pthread_mutex_lock (&mymutex);
3701\&
3702\& while (queue_get (&data))
3703\& process (data);
3704\&
3705\& pthread_mutex_unlock (&mymutex);
3706\& }
3707.Ve
3708.PP
3709\fIWatcher-Specific Functions and Data Members\fR
3710.IX Subsection "Watcher-Specific Functions and Data Members"
3711.IP "ev_async_init (ev_async *, callback)" 4
3712.IX Item "ev_async_init (ev_async *, callback)"
3713Initialises and configures the async watcher \- it has no parameters of any
3714kind. There is a \f(CW\*(C`ev_async_set\*(C'\fR macro, but using it is utterly pointless,
3715trust me.
3716.IP "ev_async_send (loop, ev_async *)" 4
3717.IX Item "ev_async_send (loop, ev_async *)"
3718Sends/signals/activates the given \f(CW\*(C`ev_async\*(C'\fR watcher, that is, feeds
3719an \f(CW\*(C`EV_ASYNC\*(C'\fR event on the watcher into the event loop, and instantly
3720returns.
3721.Sp
3722Unlike \f(CW\*(C`ev_feed_event\*(C'\fR, this call is safe to do from other threads,
3723signal or similar contexts (see the discussion of \f(CW\*(C`EV_ATOMIC_T\*(C'\fR in the
3724embedding section below on what exactly this means).
3725.Sp
3726Note that, as with other watchers in libev, multiple events might get
3727compressed into a single callback invocation (another way to look at
3728this is that \f(CW\*(C`ev_async\*(C'\fR watchers are level-triggered: they are set on
3729\&\f(CW\*(C`ev_async_send\*(C'\fR, reset when the event loop detects that).
3730.Sp
3731This call incurs the overhead of at most one extra system call per event
3732loop iteration, if the event loop is blocked, and no syscall at all if
3733the event loop (or your program) is processing events. That means that
3734repeated calls are basically free (there is no need to avoid calls for
3735performance reasons) and that the overhead becomes smaller (typically
3736zero) under load.
3737.IP "bool = ev_async_pending (ev_async *)" 4
3738.IX Item "bool = ev_async_pending (ev_async *)"
3739Returns a non-zero value when \f(CW\*(C`ev_async_send\*(C'\fR has been called on the
3740watcher but the event has not yet been processed (or even noted) by the
3741event loop.
3742.Sp
3743\&\f(CW\*(C`ev_async_send\*(C'\fR sets a flag in the watcher and wakes up the loop. When
3744the loop iterates next and checks for the watcher to have become active,
3745it will reset the flag again. \f(CW\*(C`ev_async_pending\*(C'\fR can be used to very
3746quickly check whether invoking the loop might be a good idea.
3747.Sp
3748Not that this does \fInot\fR check whether the watcher itself is pending,
3749only whether it has been requested to make this watcher pending: there
3750is a time window between the event loop checking and resetting the async
3751notification, and the callback being invoked.
2096.SH "OTHER FUNCTIONS" 3752.SH "OTHER FUNCTIONS"
2097.IX Header "OTHER FUNCTIONS" 3753.IX Header "OTHER FUNCTIONS"
2098There are some other functions of possible interest. Described. Here. Now. 3754There are some other functions of possible interest. Described. Here. Now.
2099.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4 3755.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)" 4
2100.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 3756.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)"
2101This function combines a simple timer and an I/O watcher, calls your 3757This function combines a simple timer and an I/O watcher, calls your
2102callback on whichever event happens first and automatically stop both 3758callback on whichever event happens first and automatically stops both
2103watchers. This is useful if you want to wait for a single event on an fd 3759watchers. This is useful if you want to wait for a single event on an fd
2104or timeout without having to allocate/configure/start/stop/free one or 3760or timeout without having to allocate/configure/start/stop/free one or
2105more watchers yourself. 3761more watchers yourself.
2106.Sp 3762.Sp
2107If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and events 3763If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and the
2108is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for the given \f(CW\*(C`fd\*(C'\fR and 3764\&\f(CW\*(C`events\*(C'\fR argument is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for
2109\&\f(CW\*(C`events\*(C'\fR set will be craeted and started. 3765the given \f(CW\*(C`fd\*(C'\fR and \f(CW\*(C`events\*(C'\fR set will be created and started.
2110.Sp 3766.Sp
2111If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be 3767If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be
2112started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and 3768started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and
2113repeat = 0) will be started. While \f(CW0\fR is a valid timeout, it is of 3769repeat = 0) will be started. \f(CW0\fR is a valid timeout.
2114dubious value.
2115.Sp 3770.Sp
2116The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and gets 3771The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and is
2117passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of 3772passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of
2118\&\f(CW\*(C`EV_ERROR\*(C'\fR, \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or \f(CW\*(C`EV_TIMEOUT\*(C'\fR) and the \f(CW\*(C`arg\*(C'\fR 3773\&\f(CW\*(C`EV_ERROR\*(C'\fR, \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or \f(CW\*(C`EV_TIMER\*(C'\fR) and the \f(CW\*(C`arg\*(C'\fR
2119value passed to \f(CW\*(C`ev_once\*(C'\fR: 3774value passed to \f(CW\*(C`ev_once\*(C'\fR. Note that it is possible to receive \fIboth\fR
3775a timeout and an io event at the same time \- you probably should give io
3776events precedence.
3777.Sp
3778Example: wait up to ten seconds for data to appear on \s-1STDIN_FILENO.\s0
2120.Sp 3779.Sp
2121.Vb 7 3780.Vb 7
2122\& static void stdin_ready (int revents, void *arg) 3781\& static void stdin_ready (int revents, void *arg)
3782\& {
3783\& if (revents & EV_READ)
3784\& /* stdin might have data for us, joy! */;
3785\& else if (revents & EV_TIMER)
3786\& /* doh, nothing entered */;
3787\& }
3788\&
3789\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3790.Ve
3791.IP "ev_feed_fd_event (loop, int fd, int revents)" 4
3792.IX Item "ev_feed_fd_event (loop, int fd, int revents)"
3793Feed an event on the given fd, as if a file descriptor backend detected
3794the given events.
3795.IP "ev_feed_signal_event (loop, int signum)" 4
3796.IX Item "ev_feed_signal_event (loop, int signum)"
3797Feed an event as if the given signal occurred. See also \f(CW\*(C`ev_feed_signal\*(C'\fR,
3798which is async-safe.
3799.SH "COMMON OR USEFUL IDIOMS (OR BOTH)"
3800.IX Header "COMMON OR USEFUL IDIOMS (OR BOTH)"
3801This section explains some common idioms that are not immediately
3802obvious. Note that examples are sprinkled over the whole manual, and this
3803section only contains stuff that wouldn't fit anywhere else.
3804.SS "\s-1ASSOCIATING CUSTOM DATA WITH A WATCHER\s0"
3805.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"
3806Each watcher has, by default, a \f(CW\*(C`void *data\*(C'\fR member that you can read
3807or modify at any time: libev will completely ignore it. This can be used
3808to associate arbitrary data with your watcher. If you need more data and
3809don't want to allocate memory separately and store a pointer to it in that
3810data member, you can also \*(L"subclass\*(R" the watcher type and provide your own
3811data:
3812.PP
3813.Vb 7
3814\& struct my_io
3815\& {
3816\& ev_io io;
3817\& int otherfd;
3818\& void *somedata;
3819\& struct whatever *mostinteresting;
3820\& };
3821\&
3822\& ...
3823\& struct my_io w;
3824\& ev_io_init (&w.io, my_cb, fd, EV_READ);
3825.Ve
3826.PP
3827And since your callback will be called with a pointer to the watcher, you
3828can cast it back to your own type:
3829.PP
3830.Vb 5
3831\& static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
3832\& {
3833\& struct my_io *w = (struct my_io *)w_;
3834\& ...
3835\& }
3836.Ve
3837.PP
3838More interesting and less C\-conformant ways of casting your callback
3839function type instead have been omitted.
3840.SS "\s-1BUILDING YOUR OWN COMPOSITE WATCHERS\s0"
3841.IX Subsection "BUILDING YOUR OWN COMPOSITE WATCHERS"
3842Another common scenario is to use some data structure with multiple
3843embedded watchers, in effect creating your own watcher that combines
3844multiple libev event sources into one \*(L"super-watcher\*(R":
3845.PP
3846.Vb 6
3847\& struct my_biggy
3848\& {
3849\& int some_data;
3850\& ev_timer t1;
3851\& ev_timer t2;
3852\& }
3853.Ve
3854.PP
3855In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more
3856complicated: Either you store the address of your \f(CW\*(C`my_biggy\*(C'\fR struct in
3857the \f(CW\*(C`data\*(C'\fR member of the watcher (for woozies or \*(C+ coders), or you need
3858to use some pointer arithmetic using \f(CW\*(C`offsetof\*(C'\fR inside your watchers (for
3859real programmers):
3860.PP
3861.Vb 1
3862\& #include <stddef.h>
3863\&
3864\& static void
3865\& t1_cb (EV_P_ ev_timer *w, int revents)
3866\& {
3867\& struct my_biggy big = (struct my_biggy *)
3868\& (((char *)w) \- offsetof (struct my_biggy, t1));
3869\& }
3870\&
3871\& static void
3872\& t2_cb (EV_P_ ev_timer *w, int revents)
3873\& {
3874\& struct my_biggy big = (struct my_biggy *)
3875\& (((char *)w) \- offsetof (struct my_biggy, t2));
3876\& }
3877.Ve
3878.SS "\s-1AVOIDING FINISHING BEFORE RETURNING\s0"
3879.IX Subsection "AVOIDING FINISHING BEFORE RETURNING"
3880Often you have structures like this in event-based programs:
3881.PP
3882.Vb 4
3883\& callback ()
2123\& { 3884\& {
2124\& if (revents & EV_TIMEOUT) 3885\& free (request);
2125\& /* doh, nothing entered */;
2126\& else if (revents & EV_READ)
2127\& /* stdin might have data for us, joy! */;
2128\& } 3886\& }
3887\&
3888\& request = start_new_request (..., callback);
2129.Ve 3889.Ve
2130.Sp 3890.PP
3891The intent is to start some \*(L"lengthy\*(R" operation. The \f(CW\*(C`request\*(C'\fR could be
3892used to cancel the operation, or do other things with it.
3893.PP
3894It's not uncommon to have code paths in \f(CW\*(C`start_new_request\*(C'\fR that
3895immediately invoke the callback, for example, to report errors. Or you add
3896some caching layer that finds that it can skip the lengthy aspects of the
3897operation and simply invoke the callback with the result.
3898.PP
3899The problem here is that this will happen \fIbefore\fR \f(CW\*(C`start_new_request\*(C'\fR
3900has returned, so \f(CW\*(C`request\*(C'\fR is not set.
3901.PP
3902Even if you pass the request by some safer means to the callback, you
3903might want to do something to the request after starting it, such as
3904canceling it, which probably isn't working so well when the callback has
3905already been invoked.
3906.PP
3907A common way around all these issues is to make sure that
3908\&\f(CW\*(C`start_new_request\*(C'\fR \fIalways\fR returns before the callback is invoked. If
3909\&\f(CW\*(C`start_new_request\*(C'\fR immediately knows the result, it can artificially
3910delay invoking the callback by using a \f(CW\*(C`prepare\*(C'\fR or \f(CW\*(C`idle\*(C'\fR watcher for
3911example, or more sneakily, by reusing an existing (stopped) watcher and
3912pushing it into the pending queue:
3913.PP
2131.Vb 1 3914.Vb 2
2132\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0); 3915\& ev_set_cb (watcher, callback);
3916\& ev_feed_event (EV_A_ watcher, 0);
2133.Ve 3917.Ve
2134.IP "ev_feed_event (ev_loop *, watcher *, int revents)" 4 3918.PP
2135.IX Item "ev_feed_event (ev_loop *, watcher *, int revents)" 3919This way, \f(CW\*(C`start_new_request\*(C'\fR can safely return before the callback is
2136Feeds the given event set into the event loop, as if the specified event 3920invoked, while not delaying callback invocation too much.
2137had happened for the specified watcher (which must be a pointer to an 3921.SS "\s-1MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS\s0"
2138initialised but not necessarily started event watcher). 3922.IX Subsection "MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS"
2139.IP "ev_feed_fd_event (ev_loop *, int fd, int revents)" 4 3923Often (especially in \s-1GUI\s0 toolkits) there are places where you have
2140.IX Item "ev_feed_fd_event (ev_loop *, int fd, int revents)" 3924\&\fImodal\fR interaction, which is most easily implemented by recursively
2141Feed an event on the given fd, as if a file descriptor backend detected 3925invoking \f(CW\*(C`ev_run\*(C'\fR.
2142the given events it. 3926.PP
2143.IP "ev_feed_signal_event (ev_loop *loop, int signum)" 4 3927This brings the problem of exiting \- a callback might want to finish the
2144.IX Item "ev_feed_signal_event (ev_loop *loop, int signum)" 3928main \f(CW\*(C`ev_run\*(C'\fR call, but not the nested one (e.g. user clicked \*(L"Quit\*(R", but
2145Feed an event as if the given signal occured (\f(CW\*(C`loop\*(C'\fR must be the default 3929a modal \*(L"Are you sure?\*(R" dialog is still waiting), or just the nested one
2146loop!). 3930and not the main one (e.g. user clocked \*(L"Ok\*(R" in a modal dialog), or some
3931other combination: In these cases, a simple \f(CW\*(C`ev_break\*(C'\fR will not work.
3932.PP
3933The solution is to maintain \*(L"break this loop\*(R" variable for each \f(CW\*(C`ev_run\*(C'\fR
3934invocation, and use a loop around \f(CW\*(C`ev_run\*(C'\fR until the condition is
3935triggered, using \f(CW\*(C`EVRUN_ONCE\*(C'\fR:
3936.PP
3937.Vb 2
3938\& // main loop
3939\& int exit_main_loop = 0;
3940\&
3941\& while (!exit_main_loop)
3942\& ev_run (EV_DEFAULT_ EVRUN_ONCE);
3943\&
3944\& // in a modal watcher
3945\& int exit_nested_loop = 0;
3946\&
3947\& while (!exit_nested_loop)
3948\& ev_run (EV_A_ EVRUN_ONCE);
3949.Ve
3950.PP
3951To exit from any of these loops, just set the corresponding exit variable:
3952.PP
3953.Vb 2
3954\& // exit modal loop
3955\& exit_nested_loop = 1;
3956\&
3957\& // exit main program, after modal loop is finished
3958\& exit_main_loop = 1;
3959\&
3960\& // exit both
3961\& exit_main_loop = exit_nested_loop = 1;
3962.Ve
3963.SS "\s-1THREAD LOCKING EXAMPLE\s0"
3964.IX Subsection "THREAD LOCKING EXAMPLE"
3965Here is a fictitious example of how to run an event loop in a different
3966thread from where callbacks are being invoked and watchers are
3967created/added/removed.
3968.PP
3969For a real-world example, see the \f(CW\*(C`EV::Loop::Async\*(C'\fR perl module,
3970which uses exactly this technique (which is suited for many high-level
3971languages).
3972.PP
3973The example uses a pthread mutex to protect the loop data, a condition
3974variable to wait for callback invocations, an async watcher to notify the
3975event loop thread and an unspecified mechanism to wake up the main thread.
3976.PP
3977First, you need to associate some data with the event loop:
3978.PP
3979.Vb 6
3980\& typedef struct {
3981\& mutex_t lock; /* global loop lock */
3982\& ev_async async_w;
3983\& thread_t tid;
3984\& cond_t invoke_cv;
3985\& } userdata;
3986\&
3987\& void prepare_loop (EV_P)
3988\& {
3989\& // for simplicity, we use a static userdata struct.
3990\& static userdata u;
3991\&
3992\& ev_async_init (&u\->async_w, async_cb);
3993\& ev_async_start (EV_A_ &u\->async_w);
3994\&
3995\& pthread_mutex_init (&u\->lock, 0);
3996\& pthread_cond_init (&u\->invoke_cv, 0);
3997\&
3998\& // now associate this with the loop
3999\& ev_set_userdata (EV_A_ u);
4000\& ev_set_invoke_pending_cb (EV_A_ l_invoke);
4001\& ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4002\&
4003\& // then create the thread running ev_run
4004\& pthread_create (&u\->tid, 0, l_run, EV_A);
4005\& }
4006.Ve
4007.PP
4008The callback for the \f(CW\*(C`ev_async\*(C'\fR watcher does nothing: the watcher is used
4009solely to wake up the event loop so it takes notice of any new watchers
4010that might have been added:
4011.PP
4012.Vb 5
4013\& static void
4014\& async_cb (EV_P_ ev_async *w, int revents)
4015\& {
4016\& // just used for the side effects
4017\& }
4018.Ve
4019.PP
4020The \f(CW\*(C`l_release\*(C'\fR and \f(CW\*(C`l_acquire\*(C'\fR callbacks simply unlock/lock the mutex
4021protecting the loop data, respectively.
4022.PP
4023.Vb 6
4024\& static void
4025\& l_release (EV_P)
4026\& {
4027\& userdata *u = ev_userdata (EV_A);
4028\& pthread_mutex_unlock (&u\->lock);
4029\& }
4030\&
4031\& static void
4032\& l_acquire (EV_P)
4033\& {
4034\& userdata *u = ev_userdata (EV_A);
4035\& pthread_mutex_lock (&u\->lock);
4036\& }
4037.Ve
4038.PP
4039The event loop thread first acquires the mutex, and then jumps straight
4040into \f(CW\*(C`ev_run\*(C'\fR:
4041.PP
4042.Vb 4
4043\& void *
4044\& l_run (void *thr_arg)
4045\& {
4046\& struct ev_loop *loop = (struct ev_loop *)thr_arg;
4047\&
4048\& l_acquire (EV_A);
4049\& pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4050\& ev_run (EV_A_ 0);
4051\& l_release (EV_A);
4052\&
4053\& return 0;
4054\& }
4055.Ve
4056.PP
4057Instead of invoking all pending watchers, the \f(CW\*(C`l_invoke\*(C'\fR callback will
4058signal the main thread via some unspecified mechanism (signals? pipe
4059writes? \f(CW\*(C`Async::Interrupt\*(C'\fR?) and then waits until all pending watchers
4060have been called (in a while loop because a) spurious wakeups are possible
4061and b) skipping inter-thread-communication when there are no pending
4062watchers is very beneficial):
4063.PP
4064.Vb 4
4065\& static void
4066\& l_invoke (EV_P)
4067\& {
4068\& userdata *u = ev_userdata (EV_A);
4069\&
4070\& while (ev_pending_count (EV_A))
4071\& {
4072\& wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4073\& pthread_cond_wait (&u\->invoke_cv, &u\->lock);
4074\& }
4075\& }
4076.Ve
4077.PP
4078Now, whenever the main thread gets told to invoke pending watchers, it
4079will grab the lock, call \f(CW\*(C`ev_invoke_pending\*(C'\fR and then signal the loop
4080thread to continue:
4081.PP
4082.Vb 4
4083\& static void
4084\& real_invoke_pending (EV_P)
4085\& {
4086\& userdata *u = ev_userdata (EV_A);
4087\&
4088\& pthread_mutex_lock (&u\->lock);
4089\& ev_invoke_pending (EV_A);
4090\& pthread_cond_signal (&u\->invoke_cv);
4091\& pthread_mutex_unlock (&u\->lock);
4092\& }
4093.Ve
4094.PP
4095Whenever you want to start/stop a watcher or do other modifications to an
4096event loop, you will now have to lock:
4097.PP
4098.Vb 2
4099\& ev_timer timeout_watcher;
4100\& userdata *u = ev_userdata (EV_A);
4101\&
4102\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4103\&
4104\& pthread_mutex_lock (&u\->lock);
4105\& ev_timer_start (EV_A_ &timeout_watcher);
4106\& ev_async_send (EV_A_ &u\->async_w);
4107\& pthread_mutex_unlock (&u\->lock);
4108.Ve
4109.PP
4110Note that sending the \f(CW\*(C`ev_async\*(C'\fR watcher is required because otherwise
4111an event loop currently blocking in the kernel will have no knowledge
4112about the newly added timer. By waking up the loop it will pick up any new
4113watchers in the next event loop iteration.
4114.SS "\s-1THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS\s0"
4115.IX Subsection "THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS"
4116While the overhead of a callback that e.g. schedules a thread is small, it
4117is still an overhead. If you embed libev, and your main usage is with some
4118kind of threads or coroutines, you might want to customise libev so that
4119doesn't need callbacks anymore.
4120.PP
4121Imagine you have coroutines that you can switch to using a function
4122\&\f(CW\*(C`switch_to (coro)\*(C'\fR, that libev runs in a coroutine called \f(CW\*(C`libev_coro\*(C'\fR
4123and that due to some magic, the currently active coroutine is stored in a
4124global called \f(CW\*(C`current_coro\*(C'\fR. Then you can build your own \*(L"wait for libev
4125event\*(R" primitive by changing \f(CW\*(C`EV_CB_DECLARE\*(C'\fR and \f(CW\*(C`EV_CB_INVOKE\*(C'\fR (note
4126the differing \f(CW\*(C`;\*(C'\fR conventions):
4127.PP
4128.Vb 2
4129\& #define EV_CB_DECLARE(type) struct my_coro *cb;
4130\& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb)
4131.Ve
4132.PP
4133That means instead of having a C callback function, you store the
4134coroutine to switch to in each watcher, and instead of having libev call
4135your callback, you instead have it switch to that coroutine.
4136.PP
4137A coroutine might now wait for an event with a function called
4138\&\f(CW\*(C`wait_for_event\*(C'\fR. (the watcher needs to be started, as always, but it doesn't
4139matter when, or whether the watcher is active or not when this function is
4140called):
4141.PP
4142.Vb 6
4143\& void
4144\& wait_for_event (ev_watcher *w)
4145\& {
4146\& ev_set_cb (w, current_coro);
4147\& switch_to (libev_coro);
4148\& }
4149.Ve
4150.PP
4151That basically suspends the coroutine inside \f(CW\*(C`wait_for_event\*(C'\fR and
4152continues the libev coroutine, which, when appropriate, switches back to
4153this or any other coroutine.
4154.PP
4155You can do similar tricks if you have, say, threads with an event queue \-
4156instead of storing a coroutine, you store the queue object and instead of
4157switching to a coroutine, you push the watcher onto the queue and notify
4158any waiters.
4159.PP
4160To embed libev, see \*(L"\s-1EMBEDDING\*(R"\s0, but in short, it's easiest to create two
4161files, \fImy_ev.h\fR and \fImy_ev.c\fR that include the respective libev files:
4162.PP
4163.Vb 4
4164\& // my_ev.h
4165\& #define EV_CB_DECLARE(type) struct my_coro *cb;
4166\& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb)
4167\& #include "../libev/ev.h"
4168\&
4169\& // my_ev.c
4170\& #define EV_H "my_ev.h"
4171\& #include "../libev/ev.c"
4172.Ve
4173.PP
4174And then use \fImy_ev.h\fR when you would normally use \fIev.h\fR, and compile
4175\&\fImy_ev.c\fR into your project. When properly specifying include paths, you
4176can even use \fIev.h\fR as header file name directly.
2147.SH "LIBEVENT EMULATION" 4177.SH "LIBEVENT EMULATION"
2148.IX Header "LIBEVENT EMULATION" 4178.IX Header "LIBEVENT EMULATION"
2149Libev offers a compatibility emulation layer for libevent. It cannot 4179Libev offers a compatibility emulation layer for libevent. It cannot
2150emulate the internals of libevent, so here are some usage hints: 4180emulate the internals of libevent, so here are some usage hints:
4181.IP "\(bu" 4
4182Only the libevent\-1.4.1\-beta \s-1API\s0 is being emulated.
4183.Sp
4184This was the newest libevent version available when libev was implemented,
4185and is still mostly unchanged in 2010.
4186.IP "\(bu" 4
2151.IP "* Use it by including <event.h>, as usual." 4 4187Use it by including <event.h>, as usual.
2152.IX Item "Use it by including <event.h>, as usual." 4188.IP "\(bu" 4
2153.PD 0 4189The following members are fully supported: ev_base, ev_callback,
2154.IP "* The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4 4190ev_arg, ev_fd, ev_res, ev_events.
2155.IX Item "The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4191.IP "\(bu" 4
2156.IP "* Avoid using ev_flags and the EVLIST_*\-macros, while it is maintained by libev, it does not work exactly the same way as in libevent (consider it a private \s-1API\s0)." 4 4192Avoid using ev_flags and the EVLIST_*\-macros, while it is
2157.IX Item "Avoid using ev_flags and the EVLIST_*-macros, while it is maintained by libev, it does not work exactly the same way as in libevent (consider it a private API)." 4193maintained by libev, it does not work exactly the same way as in libevent (consider
2158.IP "* Priorities are not currently supported. Initialising priorities will fail and all watchers will have the same priority, even though there is an ev_pri field." 4 4194it a private \s-1API\s0).
2159.IX Item "Priorities are not currently supported. Initialising priorities will fail and all watchers will have the same priority, even though there is an ev_pri field." 4195.IP "\(bu" 4
4196Priorities are not currently supported. Initialising priorities
4197will fail and all watchers will have the same priority, even though there
4198is an ev_pri field.
4199.IP "\(bu" 4
4200In libevent, the last base created gets the signals, in libev, the
4201base that registered the signal gets the signals.
4202.IP "\(bu" 4
2160.IP "* Other members are not supported." 4 4203Other members are not supported.
2161.IX Item "Other members are not supported." 4204.IP "\(bu" 4
2162.IP "* The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need to use the libev header file and library." 4 4205The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need
2163.IX Item "The libev emulation is not ABI compatible to libevent, you need to use the libev header file and library." 4206to use the libev header file and library.
2164.PD
2165.SH "\*(C+ SUPPORT" 4207.SH "\*(C+ SUPPORT"
2166.IX Header " SUPPORT" 4208.IX Header " SUPPORT"
4209.SS "C \s-1API\s0"
4210.IX Subsection "C API"
4211The normal C \s-1API\s0 should work fine when used from \*(C+: both ev.h and the
4212libev sources can be compiled as \*(C+. Therefore, code that uses the C \s-1API\s0
4213will work fine.
4214.PP
4215Proper exception specifications might have to be added to callbacks passed
4216to libev: exceptions may be thrown only from watcher callbacks, all other
4217callbacks (allocator, syserr, loop acquire/release and periodic reschedule
4218callbacks) must not throw exceptions, and might need a \f(CW\*(C`noexcept\*(C'\fR
4219specification. If you have code that needs to be compiled as both C and
4220\&\*(C+ you can use the \f(CW\*(C`EV_NOEXCEPT\*(C'\fR macro for this:
4221.PP
4222.Vb 6
4223\& static void
4224\& fatal_error (const char *msg) EV_NOEXCEPT
4225\& {
4226\& perror (msg);
4227\& abort ();
4228\& }
4229\&
4230\& ...
4231\& ev_set_syserr_cb (fatal_error);
4232.Ve
4233.PP
4234The only \s-1API\s0 functions that can currently throw exceptions are \f(CW\*(C`ev_run\*(C'\fR,
4235\&\f(CW\*(C`ev_invoke\*(C'\fR, \f(CW\*(C`ev_invoke_pending\*(C'\fR and \f(CW\*(C`ev_loop_destroy\*(C'\fR (the latter
4236because it runs cleanup watchers).
4237.PP
4238Throwing exceptions in watcher callbacks is only supported if libev itself
4239is compiled with a \*(C+ compiler or your C and \*(C+ environments allow
4240throwing exceptions through C libraries (most do).
4241.SS "\*(C+ \s-1API\s0"
4242.IX Subsection " API"
2167Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow 4243Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow
2168you to use some convinience methods to start/stop watchers and also change 4244you to use some convenience methods to start/stop watchers and also change
2169the callback model to a model using method callbacks on objects. 4245the callback model to a model using method callbacks on objects.
2170.PP 4246.PP
2171To use it, 4247To use it,
2172.PP 4248.PP
2173.Vb 1 4249.Vb 1
2174\& #include <ev++.h> 4250\& #include <ev++.h>
2175.Ve 4251.Ve
2176.PP 4252.PP
2177This automatically includes \fIev.h\fR and puts all of its definitions (many 4253This automatically includes \fIev.h\fR and puts all of its definitions (many
2178of them macros) into the global namespace. All \*(C+ specific things are 4254of them macros) into the global namespace. All \*(C+ specific things are
2179put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding 4255put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding
… …
2182Care has been taken to keep the overhead low. The only data member the \*(C+ 4258Care has been taken to keep the overhead low. The only data member the \*(C+
2183classes add (compared to plain C\-style watchers) is the event loop pointer 4259classes add (compared to plain C\-style watchers) is the event loop pointer
2184that the watcher is associated with (or no additional members at all if 4260that the watcher is associated with (or no additional members at all if
2185you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev). 4261you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev).
2186.PP 4262.PP
2187Currently, functions, and static and non-static member functions can be 4263Currently, functions, static and non-static member functions and classes
2188used as callbacks. Other types should be easy to add as long as they only 4264with \f(CW\*(C`operator ()\*(C'\fR can be used as callbacks. Other types should be easy
2189need one additional pointer for context. If you need support for other 4265to add as long as they only need one additional pointer for context. If
2190types of functors please contact the author (preferably after implementing 4266you need support for other types of functors please contact the author
2191it). 4267(preferably after implementing it).
4268.PP
4269For all this to work, your \*(C+ compiler either has to use the same calling
4270conventions as your C compiler (for static member functions), or you have
4271to embed libev and compile libev itself as \*(C+.
2192.PP 4272.PP
2193Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace: 4273Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace:
2194.ie n .IP """ev::READ""\fR, \f(CW""ev::WRITE"" etc." 4 4274.ie n .IP """ev::READ"", ""ev::WRITE"" etc." 4
2195.el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4 4275.el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4
2196.IX Item "ev::READ, ev::WRITE etc." 4276.IX Item "ev::READ, ev::WRITE etc."
2197These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc. 4277These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc.
2198macros from \fIev.h\fR. 4278macros from \fIev.h\fR.
2199.ie n .IP """ev::tstamp""\fR, \f(CW""ev::now""" 4 4279.ie n .IP """ev::tstamp"", ""ev::now""" 4
2200.el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4 4280.el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4
2201.IX Item "ev::tstamp, ev::now" 4281.IX Item "ev::tstamp, ev::now"
2202Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix. 4282Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix.
2203.ie n .IP """ev::io""\fR, \f(CW""ev::timer""\fR, \f(CW""ev::periodic""\fR, \f(CW""ev::idle""\fR, \f(CW""ev::sig"" etc." 4 4283.ie n .IP """ev::io"", ""ev::timer"", ""ev::periodic"", ""ev::idle"", ""ev::sig"" etc." 4
2204.el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4 4284.el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4
2205.IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc." 4285.IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc."
2206For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of 4286For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of
2207the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR 4287the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR
2208which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro 4288which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro
2209defines by many implementations. 4289defined by many implementations.
2210.Sp 4290.Sp
2211All of those classes have these methods: 4291All of those classes have these methods:
2212.RS 4 4292.RS 4
2213.IP "ev::TYPE::TYPE ()" 4 4293.IP "ev::TYPE::TYPE ()" 4
2214.IX Item "ev::TYPE::TYPE ()" 4294.IX Item "ev::TYPE::TYPE ()"
2215.PD 0 4295.PD 0
2216.IP "ev::TYPE::TYPE (struct ev_loop *)" 4 4296.IP "ev::TYPE::TYPE (loop)" 4
2217.IX Item "ev::TYPE::TYPE (struct ev_loop *)" 4297.IX Item "ev::TYPE::TYPE (loop)"
2218.IP "ev::TYPE::~TYPE" 4 4298.IP "ev::TYPE::~TYPE" 4
2219.IX Item "ev::TYPE::~TYPE" 4299.IX Item "ev::TYPE::~TYPE"
2220.PD 4300.PD
2221The constructor (optionally) takes an event loop to associate the watcher 4301The constructor (optionally) takes an event loop to associate the watcher
2222with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR. 4302with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR.
… …
2245thunking function, making it as fast as a direct C callback. 4325thunking function, making it as fast as a direct C callback.
2246.Sp 4326.Sp
2247Example: simple class declaration and watcher initialisation 4327Example: simple class declaration and watcher initialisation
2248.Sp 4328.Sp
2249.Vb 4 4329.Vb 4
2250\& struct myclass 4330\& struct myclass
2251\& { 4331\& {
2252\& void io_cb (ev::io &w, int revents) { } 4332\& void io_cb (ev::io &w, int revents) { }
2253\& } 4333\& }
2254.Ve 4334\&
2255.Sp
2256.Vb 3
2257\& myclass obj; 4335\& myclass obj;
2258\& ev::io iow; 4336\& ev::io iow;
2259\& iow.set <myclass, &myclass::io_cb> (&obj); 4337\& iow.set <myclass, &myclass::io_cb> (&obj);
4338.Ve
4339.IP "w\->set (object *)" 4
4340.IX Item "w->set (object *)"
4341This is a variation of a method callback \- leaving out the method to call
4342will default the method to \f(CW\*(C`operator ()\*(C'\fR, which makes it possible to use
4343functor objects without having to manually specify the \f(CW\*(C`operator ()\*(C'\fR all
4344the time. Incidentally, you can then also leave out the template argument
4345list.
4346.Sp
4347The \f(CW\*(C`operator ()\*(C'\fR method prototype must be \f(CW\*(C`void operator ()(watcher &w,
4348int revents)\*(C'\fR.
4349.Sp
4350See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
4351.Sp
4352Example: use a functor object as callback.
4353.Sp
4354.Vb 7
4355\& struct myfunctor
4356\& {
4357\& void operator() (ev::io &w, int revents)
4358\& {
4359\& ...
4360\& }
4361\& }
4362\&
4363\& myfunctor f;
4364\&
4365\& ev::io w;
4366\& w.set (&f);
2260.Ve 4367.Ve
2261.IP "w\->set<function> (void *data = 0)" 4 4368.IP "w\->set<function> (void *data = 0)" 4
2262.IX Item "w->set<function> (void *data = 0)" 4369.IX Item "w->set<function> (void *data = 0)"
2263Also sets a callback, but uses a static method or plain function as 4370Also sets a callback, but uses a static method or plain function as
2264callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's 4371callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's
… …
2266.Sp 4373.Sp
2267The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR. 4374The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR.
2268.Sp 4375.Sp
2269See the method\-\f(CW\*(C`set\*(C'\fR above for more details. 4376See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
2270.Sp 4377.Sp
2271Example: 4378Example: Use a plain function as callback.
2272.Sp 4379.Sp
2273.Vb 2 4380.Vb 2
2274\& static void io_cb (ev::io &w, int revents) { } 4381\& static void io_cb (ev::io &w, int revents) { }
2275\& iow.set <io_cb> (); 4382\& iow.set <io_cb> ();
2276.Ve 4383.Ve
2277.IP "w\->set (struct ev_loop *)" 4 4384.IP "w\->set (loop)" 4
2278.IX Item "w->set (struct ev_loop *)" 4385.IX Item "w->set (loop)"
2279Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only 4386Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only
2280do this when the watcher is inactive (and not pending either). 4387do this when the watcher is inactive (and not pending either).
2281.IP "w\->set ([args])" 4 4388.IP "w\->set ([arguments])" 4
2282.IX Item "w->set ([args])" 4389.IX Item "w->set ([arguments])"
2283Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR, with the same args. Must be 4390Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR (except for \f(CW\*(C`ev::embed\*(C'\fR watchers>),
4391with the same arguments. Either this method or a suitable start method
2284called at least once. Unlike the C counterpart, an active watcher gets 4392must be called at least once. Unlike the C counterpart, an active watcher
2285automatically stopped and restarted when reconfiguring it with this 4393gets automatically stopped and restarted when reconfiguring it with this
2286method. 4394method.
4395.Sp
4396For \f(CW\*(C`ev::embed\*(C'\fR watchers this method is called \f(CW\*(C`set_embed\*(C'\fR, to avoid
4397clashing with the \f(CW\*(C`set (loop)\*(C'\fR method.
2287.IP "w\->start ()" 4 4398.IP "w\->start ()" 4
2288.IX Item "w->start ()" 4399.IX Item "w->start ()"
2289Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the 4400Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the
2290constructor already stores the event loop. 4401constructor already stores the event loop.
4402.IP "w\->start ([arguments])" 4
4403.IX Item "w->start ([arguments])"
4404Instead of calling \f(CW\*(C`set\*(C'\fR and \f(CW\*(C`start\*(C'\fR methods separately, it is often
4405convenient to wrap them in one call. Uses the same type of arguments as
4406the configure \f(CW\*(C`set\*(C'\fR method of the watcher.
2291.IP "w\->stop ()" 4 4407.IP "w\->stop ()" 4
2292.IX Item "w->stop ()" 4408.IX Item "w->stop ()"
2293Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument. 4409Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument.
2294.ie n .IP "w\->again () (""ev::timer""\fR, \f(CW""ev::periodic"" only)" 4 4410.ie n .IP "w\->again () (""ev::timer"", ""ev::periodic"" only)" 4
2295.el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4 4411.el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4
2296.IX Item "w->again () (ev::timer, ev::periodic only)" 4412.IX Item "w->again () (ev::timer, ev::periodic only)"
2297For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding 4413For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding
2298\&\f(CW\*(C`ev_TYPE_again\*(C'\fR function. 4414\&\f(CW\*(C`ev_TYPE_again\*(C'\fR function.
2299.ie n .IP "w\->sweep () (""ev::embed"" only)" 4 4415.ie n .IP "w\->sweep () (""ev::embed"" only)" 4
… …
2306Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR. 4422Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR.
2307.RE 4423.RE
2308.RS 4 4424.RS 4
2309.RE 4425.RE
2310.PP 4426.PP
2311Example: Define a class with an \s-1IO\s0 and idle watcher, start one of them in 4427Example: Define a class with two I/O and idle watchers, start the I/O
2312the constructor. 4428watchers in the constructor.
2313.PP 4429.PP
2314.Vb 4 4430.Vb 5
2315\& class myclass 4431\& class myclass
2316\& { 4432\& {
2317\& ev_io io; void io_cb (ev::io &w, int revents); 4433\& ev::io io ; void io_cb (ev::io &w, int revents);
4434\& ev::io io2 ; void io2_cb (ev::io &w, int revents);
2318\& ev_idle idle void idle_cb (ev::idle &w, int revents); 4435\& ev::idle idle; void idle_cb (ev::idle &w, int revents);
2319.Ve 4436\&
2320.PP
2321.Vb 2
2322\& myclass (); 4437\& myclass (int fd)
2323\& }
2324.Ve
2325.PP
2326.Vb 4
2327\& myclass::myclass (int fd)
2328\& { 4438\& {
2329\& io .set <myclass, &myclass::io_cb > (this); 4439\& io .set <myclass, &myclass::io_cb > (this);
4440\& io2 .set <myclass, &myclass::io2_cb > (this);
2330\& idle.set <myclass, &myclass::idle_cb> (this); 4441\& idle.set <myclass, &myclass::idle_cb> (this);
2331.Ve 4442\&
2332.PP 4443\& io.set (fd, ev::WRITE); // configure the watcher
2333.Vb 2 4444\& io.start (); // start it whenever convenient
2334\& io.start (fd, ev::READ); 4445\&
4446\& io2.start (fd, ev::READ); // set + start in one call
4447\& }
2335\& } 4448\& };
2336.Ve 4449.Ve
4450.SH "OTHER LANGUAGE BINDINGS"
4451.IX Header "OTHER LANGUAGE BINDINGS"
4452Libev does not offer other language bindings itself, but bindings for a
4453number of languages exist in the form of third-party packages. If you know
4454any interesting language binding in addition to the ones listed here, drop
4455me a note.
4456.IP "Perl" 4
4457.IX Item "Perl"
4458The \s-1EV\s0 module implements the full libev \s-1API\s0 and is actually used to test
4459libev. \s-1EV\s0 is developed together with libev. Apart from the \s-1EV\s0 core module,
4460there are additional modules that implement libev-compatible interfaces
4461to \f(CW\*(C`libadns\*(C'\fR (\f(CW\*(C`EV::ADNS\*(C'\fR, but \f(CW\*(C`AnyEvent::DNS\*(C'\fR is preferred nowadays),
4462\&\f(CW\*(C`Net::SNMP\*(C'\fR (\f(CW\*(C`Net::SNMP::EV\*(C'\fR) and the \f(CW\*(C`libglib\*(C'\fR event core (\f(CW\*(C`Glib::EV\*(C'\fR
4463and \f(CW\*(C`EV::Glib\*(C'\fR).
4464.Sp
4465It can be found and installed via \s-1CPAN,\s0 its homepage is at
4466<http://software.schmorp.de/pkg/EV>.
4467.IP "Python" 4
4468.IX Item "Python"
4469Python bindings can be found at <http://code.google.com/p/pyev/>. It
4470seems to be quite complete and well-documented.
4471.IP "Ruby" 4
4472.IX Item "Ruby"
4473Tony Arcieri has written a ruby extension that offers access to a subset
4474of the libev \s-1API\s0 and adds file handle abstractions, asynchronous \s-1DNS\s0 and
4475more on top of it. It can be found via gem servers. Its homepage is at
4476<http://rev.rubyforge.org/>.
4477.Sp
4478Roger Pack reports that using the link order \f(CW\*(C`\-lws2_32 \-lmsvcrt\-ruby\-190\*(C'\fR
4479makes rev work even on mingw.
4480.IP "Haskell" 4
4481.IX Item "Haskell"
4482A haskell binding to libev is available at
4483<http://hackage.haskell.org/cgi\-bin/hackage\-scripts/package/hlibev>.
4484.IP "D" 4
4485.IX Item "D"
4486Leandro Lucarella has written a D language binding (\fIev.d\fR) for libev, to
4487be found at <http://www.llucax.com.ar/proj/ev.d/index.html>.
4488.IP "Ocaml" 4
4489.IX Item "Ocaml"
4490Erkki Seppala has written Ocaml bindings for libev, to be found at
4491<http://modeemi.cs.tut.fi/~flux/software/ocaml\-ev/>.
4492.IP "Lua" 4
4493.IX Item "Lua"
4494Brian Maher has written a partial interface to libev for lua (at the
4495time of this writing, only \f(CW\*(C`ev_io\*(C'\fR and \f(CW\*(C`ev_timer\*(C'\fR), to be found at
4496<http://github.com/brimworks/lua\-ev>.
4497.IP "Javascript" 4
4498.IX Item "Javascript"
4499Node.js (<http://nodejs.org>) uses libev as the underlying event library.
4500.IP "Others" 4
4501.IX Item "Others"
4502There are others, and I stopped counting.
2337.SH "MACRO MAGIC" 4503.SH "MACRO MAGIC"
2338.IX Header "MACRO MAGIC" 4504.IX Header "MACRO MAGIC"
2339Libev can be compiled with a variety of options, the most fundamantal 4505Libev can be compiled with a variety of options, the most fundamental
2340of which is \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most) 4506of which is \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most)
2341functions and callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument. 4507functions and callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument.
2342.PP 4508.PP
2343To make it easier to write programs that cope with either variant, the 4509To make it easier to write programs that cope with either variant, the
2344following macros are defined: 4510following macros are defined:
2345.ie n .IP """EV_A""\fR, \f(CW""EV_A_""" 4 4511.ie n .IP """EV_A"", ""EV_A_""" 4
2346.el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4 4512.el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4
2347.IX Item "EV_A, EV_A_" 4513.IX Item "EV_A, EV_A_"
2348This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev 4514This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev
2349loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument, 4515loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument,
2350\&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example: 4516\&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example:
2351.Sp 4517.Sp
2352.Vb 3 4518.Vb 3
2353\& ev_unref (EV_A); 4519\& ev_unref (EV_A);
2354\& ev_timer_add (EV_A_ watcher); 4520\& ev_timer_add (EV_A_ watcher);
2355\& ev_loop (EV_A_ 0); 4521\& ev_run (EV_A_ 0);
2356.Ve 4522.Ve
2357.Sp 4523.Sp
2358It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope, 4524It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope,
2359which is often provided by the following macro. 4525which is often provided by the following macro.
2360.ie n .IP """EV_P""\fR, \f(CW""EV_P_""" 4 4526.ie n .IP """EV_P"", ""EV_P_""" 4
2361.el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4 4527.el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4
2362.IX Item "EV_P, EV_P_" 4528.IX Item "EV_P, EV_P_"
2363This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev 4529This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev
2364loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter, 4530loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter,
2365\&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example: 4531\&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example:
2366.Sp 4532.Sp
2367.Vb 2 4533.Vb 2
2368\& // this is how ev_unref is being declared 4534\& // this is how ev_unref is being declared
2369\& static void ev_unref (EV_P); 4535\& static void ev_unref (EV_P);
2370.Ve 4536\&
2371.Sp
2372.Vb 2
2373\& // this is how you can declare your typical callback 4537\& // this is how you can declare your typical callback
2374\& static void cb (EV_P_ ev_timer *w, int revents) 4538\& static void cb (EV_P_ ev_timer *w, int revents)
2375.Ve 4539.Ve
2376.Sp 4540.Sp
2377It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite 4541It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite
2378suitable for use with \f(CW\*(C`EV_A\*(C'\fR. 4542suitable for use with \f(CW\*(C`EV_A\*(C'\fR.
2379.ie n .IP """EV_DEFAULT""\fR, \f(CW""EV_DEFAULT_""" 4 4543.ie n .IP """EV_DEFAULT"", ""EV_DEFAULT_""" 4
2380.el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4 4544.el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4
2381.IX Item "EV_DEFAULT, EV_DEFAULT_" 4545.IX Item "EV_DEFAULT, EV_DEFAULT_"
2382Similar to the other two macros, this gives you the value of the default 4546Similar to the other two macros, this gives you the value of the default
2383loop, if multiple loops are supported (\*(L"ev loop default\*(R"). 4547loop, if multiple loops are supported (\*(L"ev loop default\*(R"). The default loop
4548will be initialised if it isn't already initialised.
4549.Sp
4550For non-multiplicity builds, these macros do nothing, so you always have
4551to initialise the loop somewhere.
4552.ie n .IP """EV_DEFAULT_UC"", ""EV_DEFAULT_UC_""" 4
4553.el .IP "\f(CWEV_DEFAULT_UC\fR, \f(CWEV_DEFAULT_UC_\fR" 4
4554.IX Item "EV_DEFAULT_UC, EV_DEFAULT_UC_"
4555Usage identical to \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR, but requires that the
4556default loop has been initialised (\f(CW\*(C`UC\*(C'\fR == unchecked). Their behaviour
4557is undefined when the default loop has not been initialised by a previous
4558execution of \f(CW\*(C`EV_DEFAULT\*(C'\fR, \f(CW\*(C`EV_DEFAULT_\*(C'\fR or \f(CW\*(C`ev_default_init (...)\*(C'\fR.
4559.Sp
4560It is often prudent to use \f(CW\*(C`EV_DEFAULT\*(C'\fR when initialising the first
4561watcher in a function but use \f(CW\*(C`EV_DEFAULT_UC\*(C'\fR afterwards.
2384.PP 4562.PP
2385Example: Declare and initialise a check watcher, utilising the above 4563Example: Declare and initialise a check watcher, utilising the above
2386macros so it will work regardless of whether multiple loops are supported 4564macros so it will work regardless of whether multiple loops are supported
2387or not. 4565or not.
2388.PP 4566.PP
2389.Vb 5 4567.Vb 5
2390\& static void 4568\& static void
2391\& check_cb (EV_P_ ev_timer *w, int revents) 4569\& check_cb (EV_P_ ev_timer *w, int revents)
2392\& { 4570\& {
2393\& ev_check_stop (EV_A_ w); 4571\& ev_check_stop (EV_A_ w);
2394\& } 4572\& }
2395.Ve 4573\&
2396.PP
2397.Vb 4
2398\& ev_check check; 4574\& ev_check check;
2399\& ev_check_init (&check, check_cb); 4575\& ev_check_init (&check, check_cb);
2400\& ev_check_start (EV_DEFAULT_ &check); 4576\& ev_check_start (EV_DEFAULT_ &check);
2401\& ev_loop (EV_DEFAULT_ 0); 4577\& ev_run (EV_DEFAULT_ 0);
2402.Ve 4578.Ve
2403.SH "EMBEDDING" 4579.SH "EMBEDDING"
2404.IX Header "EMBEDDING" 4580.IX Header "EMBEDDING"
2405Libev can (and often is) directly embedded into host 4581Libev can (and often is) directly embedded into host
2406applications. Examples of applications that embed it include the Deliantra 4582applications. Examples of applications that embed it include the Deliantra
2407Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe) 4583Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe)
2408and rxvt\-unicode. 4584and rxvt-unicode.
2409.PP 4585.PP
2410The goal is to enable you to just copy the necessary files into your 4586The goal is to enable you to just copy the necessary files into your
2411source directory without having to change even a single line in them, so 4587source directory without having to change even a single line in them, so
2412you can easily upgrade by simply copying (or having a checked-out copy of 4588you can easily upgrade by simply copying (or having a checked-out copy of
2413libev somewhere in your source tree). 4589libev somewhere in your source tree).
2414.Sh "\s-1FILESETS\s0" 4590.SS "\s-1FILESETS\s0"
2415.IX Subsection "FILESETS" 4591.IX Subsection "FILESETS"
2416Depending on what features you need you need to include one or more sets of files 4592Depending on what features you need you need to include one or more sets of files
2417in your app. 4593in your application.
2418.PP 4594.PP
2419\fI\s-1CORE\s0 \s-1EVENT\s0 \s-1LOOP\s0\fR 4595\fI\s-1CORE EVENT LOOP\s0\fR
2420.IX Subsection "CORE EVENT LOOP" 4596.IX Subsection "CORE EVENT LOOP"
2421.PP 4597.PP
2422To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual 4598To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual
2423configuration (no autoconf): 4599configuration (no autoconf):
2424.PP 4600.PP
2425.Vb 2 4601.Vb 2
2426\& #define EV_STANDALONE 1 4602\& #define EV_STANDALONE 1
2427\& #include "ev.c" 4603\& #include "ev.c"
2428.Ve 4604.Ve
2429.PP 4605.PP
2430This will automatically include \fIev.h\fR, too, and should be done in a 4606This will automatically include \fIev.h\fR, too, and should be done in a
2431single C source file only to provide the function implementations. To use 4607single C source file only to provide the function implementations. To use
2432it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best 4608it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best
2433done by writing a wrapper around \fIev.h\fR that you can include instead and 4609done by writing a wrapper around \fIev.h\fR that you can include instead and
2434where you can put other configuration options): 4610where you can put other configuration options):
2435.PP 4611.PP
2436.Vb 2 4612.Vb 2
2437\& #define EV_STANDALONE 1 4613\& #define EV_STANDALONE 1
2438\& #include "ev.h" 4614\& #include "ev.h"
2439.Ve 4615.Ve
2440.PP 4616.PP
2441Both header files and implementation files can be compiled with a \*(C+ 4617Both header files and implementation files can be compiled with a \*(C+
2442compiler (at least, thats a stated goal, and breakage will be treated 4618compiler (at least, that's a stated goal, and breakage will be treated
2443as a bug). 4619as a bug).
2444.PP 4620.PP
2445You need the following files in your source tree, or in a directory 4621You need the following files in your source tree, or in a directory
2446in your include path (e.g. in libev/ when using \-Ilibev): 4622in your include path (e.g. in libev/ when using \-Ilibev):
2447.PP 4623.PP
2448.Vb 4 4624.Vb 4
2449\& ev.h 4625\& ev.h
2450\& ev.c 4626\& ev.c
2451\& ev_vars.h 4627\& ev_vars.h
2452\& ev_wrap.h 4628\& ev_wrap.h
2453.Ve 4629\&
2454.PP
2455.Vb 1
2456\& ev_win32.c required on win32 platforms only 4630\& ev_win32.c required on win32 platforms only
2457.Ve 4631\&
2458.PP
2459.Vb 5
2460\& ev_select.c only when select backend is enabled (which is enabled by default) 4632\& ev_select.c only when select backend is enabled
2461\& ev_poll.c only when poll backend is enabled (disabled by default) 4633\& ev_poll.c only when poll backend is enabled
2462\& ev_epoll.c only when the epoll backend is enabled (disabled by default) 4634\& ev_epoll.c only when the epoll backend is enabled
4635\& ev_linuxaio.c only when the linux aio backend is enabled
4636\& ev_iouring.c only when the linux io_uring backend is enabled
2463\& ev_kqueue.c only when the kqueue backend is enabled (disabled by default) 4637\& ev_kqueue.c only when the kqueue backend is enabled
2464\& ev_port.c only when the solaris port backend is enabled (disabled by default) 4638\& ev_port.c only when the solaris port backend is enabled
2465.Ve 4639.Ve
2466.PP 4640.PP
2467\&\fIev.c\fR includes the backend files directly when enabled, so you only need 4641\&\fIev.c\fR includes the backend files directly when enabled, so you only need
2468to compile this single file. 4642to compile this single file.
2469.PP 4643.PP
2470\fI\s-1LIBEVENT\s0 \s-1COMPATIBILITY\s0 \s-1API\s0\fR 4644\fI\s-1LIBEVENT COMPATIBILITY API\s0\fR
2471.IX Subsection "LIBEVENT COMPATIBILITY API" 4645.IX Subsection "LIBEVENT COMPATIBILITY API"
2472.PP 4646.PP
2473To include the libevent compatibility \s-1API\s0, also include: 4647To include the libevent compatibility \s-1API,\s0 also include:
2474.PP 4648.PP
2475.Vb 1 4649.Vb 1
2476\& #include "event.c" 4650\& #include "event.c"
2477.Ve 4651.Ve
2478.PP 4652.PP
2479in the file including \fIev.c\fR, and: 4653in the file including \fIev.c\fR, and:
2480.PP 4654.PP
2481.Vb 1 4655.Vb 1
2482\& #include "event.h" 4656\& #include "event.h"
2483.Ve 4657.Ve
2484.PP 4658.PP
2485in the files that want to use the libevent \s-1API\s0. This also includes \fIev.h\fR. 4659in the files that want to use the libevent \s-1API.\s0 This also includes \fIev.h\fR.
2486.PP 4660.PP
2487You need the following additional files for this: 4661You need the following additional files for this:
2488.PP 4662.PP
2489.Vb 2 4663.Vb 2
2490\& event.h 4664\& event.h
2491\& event.c 4665\& event.c
2492.Ve 4666.Ve
2493.PP 4667.PP
2494\fI\s-1AUTOCONF\s0 \s-1SUPPORT\s0\fR 4668\fI\s-1AUTOCONF SUPPORT\s0\fR
2495.IX Subsection "AUTOCONF SUPPORT" 4669.IX Subsection "AUTOCONF SUPPORT"
2496.PP 4670.PP
2497Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your config in 4671Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your configuration in
2498whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your 4672whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your
2499\&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then 4673\&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then
2500include \fIconfig.h\fR and configure itself accordingly. 4674include \fIconfig.h\fR and configure itself accordingly.
2501.PP 4675.PP
2502For this of course you need the m4 file: 4676For this of course you need the m4 file:
2503.PP 4677.PP
2504.Vb 1 4678.Vb 1
2505\& libev.m4 4679\& libev.m4
2506.Ve 4680.Ve
2507.Sh "\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0" 4681.SS "\s-1PREPROCESSOR SYMBOLS/MACROS\s0"
2508.IX Subsection "PREPROCESSOR SYMBOLS/MACROS" 4682.IX Subsection "PREPROCESSOR SYMBOLS/MACROS"
2509Libev can be configured via a variety of preprocessor symbols you have to define 4683Libev can be configured via a variety of preprocessor symbols you have to
2510before including any of its files. The default is not to build for multiplicity 4684define before including (or compiling) any of its files. The default in
2511and only include the select backend. 4685the absence of autoconf is documented for every option.
4686.PP
4687Symbols marked with \*(L"(h)\*(R" do not change the \s-1ABI,\s0 and can have different
4688values when compiling libev vs. including \fIev.h\fR, so it is permissible
4689to redefine them before including \fIev.h\fR without breaking compatibility
4690to a compiled library. All other symbols change the \s-1ABI,\s0 which means all
4691users of libev and the libev code itself must be compiled with compatible
4692settings.
4693.IP "\s-1EV_COMPAT3\s0 (h)" 4
4694.IX Item "EV_COMPAT3 (h)"
4695Backwards compatibility is a major concern for libev. This is why this
4696release of libev comes with wrappers for the functions and symbols that
4697have been renamed between libev version 3 and 4.
4698.Sp
4699You can disable these wrappers (to test compatibility with future
4700versions) by defining \f(CW\*(C`EV_COMPAT3\*(C'\fR to \f(CW0\fR when compiling your
4701sources. This has the additional advantage that you can drop the \f(CW\*(C`struct\*(C'\fR
4702from \f(CW\*(C`struct ev_loop\*(C'\fR declarations, as libev will provide an \f(CW\*(C`ev_loop\*(C'\fR
4703typedef in that case.
4704.Sp
4705In some future version, the default for \f(CW\*(C`EV_COMPAT3\*(C'\fR will become \f(CW0\fR,
4706and in some even more future version the compatibility code will be
4707removed completely.
2512.IP "\s-1EV_STANDALONE\s0" 4 4708.IP "\s-1EV_STANDALONE\s0 (h)" 4
2513.IX Item "EV_STANDALONE" 4709.IX Item "EV_STANDALONE (h)"
2514Must always be \f(CW1\fR if you do not use autoconf configuration, which 4710Must always be \f(CW1\fR if you do not use autoconf configuration, which
2515keeps libev from including \fIconfig.h\fR, and it also defines dummy 4711keeps libev from including \fIconfig.h\fR, and it also defines dummy
2516implementations for some libevent functions (such as logging, which is not 4712implementations for some libevent functions (such as logging, which is not
2517supported). It will also not define any of the structs usually found in 4713supported). It will also not define any of the structs usually found in
2518\&\fIevent.h\fR that are not directly supported by the libev core alone. 4714\&\fIevent.h\fR that are not directly supported by the libev core alone.
4715.Sp
4716In standalone mode, libev will still try to automatically deduce the
4717configuration, but has to be more conservative.
4718.IP "\s-1EV_USE_FLOOR\s0" 4
4719.IX Item "EV_USE_FLOOR"
4720If defined to be \f(CW1\fR, libev will use the \f(CW\*(C`floor ()\*(C'\fR function for its
4721periodic reschedule calculations, otherwise libev will fall back on a
4722portable (slower) implementation. If you enable this, you usually have to
4723link against libm or something equivalent. Enabling this when the \f(CW\*(C`floor\*(C'\fR
4724function is not available will fail, so the safe default is to not enable
4725this.
2519.IP "\s-1EV_USE_MONOTONIC\s0" 4 4726.IP "\s-1EV_USE_MONOTONIC\s0" 4
2520.IX Item "EV_USE_MONOTONIC" 4727.IX Item "EV_USE_MONOTONIC"
2521If defined to be \f(CW1\fR, libev will try to detect the availability of the 4728If defined to be \f(CW1\fR, libev will try to detect the availability of the
2522monotonic clock option at both compiletime and runtime. Otherwise no use 4729monotonic clock option at both compile time and runtime. Otherwise no
2523of the monotonic clock option will be attempted. If you enable this, you 4730use of the monotonic clock option will be attempted. If you enable this,
2524usually have to link against librt or something similar. Enabling it when 4731you usually have to link against librt or something similar. Enabling it
2525the functionality isn't available is safe, though, although you have 4732when the functionality isn't available is safe, though, although you have
2526to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR 4733to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR
2527function is hiding in (often \fI\-lrt\fR). 4734function is hiding in (often \fI\-lrt\fR). See also \f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
2528.IP "\s-1EV_USE_REALTIME\s0" 4 4735.IP "\s-1EV_USE_REALTIME\s0" 4
2529.IX Item "EV_USE_REALTIME" 4736.IX Item "EV_USE_REALTIME"
2530If defined to be \f(CW1\fR, libev will try to detect the availability of the 4737If defined to be \f(CW1\fR, libev will try to detect the availability of the
2531realtime clock option at compiletime (and assume its availability at 4738real-time clock option at compile time (and assume its availability
2532runtime if successful). Otherwise no use of the realtime clock option will 4739at runtime if successful). Otherwise no use of the real-time clock
2533be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR by \f(CW\*(C`clock_get 4740option will be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR
2534(CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect correctness. See the 4741by \f(CW\*(C`clock_get (CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect
2535note about libraries in the description of \f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. 4742correctness. See the note about libraries in the description of
4743\&\f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. Defaults to the opposite value of
4744\&\f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
4745.IP "\s-1EV_USE_CLOCK_SYSCALL\s0" 4
4746.IX Item "EV_USE_CLOCK_SYSCALL"
4747If defined to be \f(CW1\fR, libev will try to use a direct syscall instead
4748of calling the system-provided \f(CW\*(C`clock_gettime\*(C'\fR function. This option
4749exists because on GNU/Linux, \f(CW\*(C`clock_gettime\*(C'\fR is in \f(CW\*(C`librt\*(C'\fR, but \f(CW\*(C`librt\*(C'\fR
4750unconditionally pulls in \f(CW\*(C`libpthread\*(C'\fR, slowing down single-threaded
4751programs needlessly. Using a direct syscall is slightly slower (in
4752theory), because no optimised vdso implementation can be used, but avoids
4753the pthread dependency. Defaults to \f(CW1\fR on GNU/Linux with glibc 2.x or
4754higher, as it simplifies linking (no need for \f(CW\*(C`\-lrt\*(C'\fR).
2536.IP "\s-1EV_USE_NANOSLEEP\s0" 4 4755.IP "\s-1EV_USE_NANOSLEEP\s0" 4
2537.IX Item "EV_USE_NANOSLEEP" 4756.IX Item "EV_USE_NANOSLEEP"
2538If defined to be \f(CW1\fR, libev will assume that \f(CW\*(C`nanosleep ()\*(C'\fR is available 4757If defined to be \f(CW1\fR, libev will assume that \f(CW\*(C`nanosleep ()\*(C'\fR is available
2539and will use it for delays. Otherwise it will use \f(CW\*(C`select ()\*(C'\fR. 4758and will use it for delays. Otherwise it will use \f(CW\*(C`select ()\*(C'\fR.
4759.IP "\s-1EV_USE_EVENTFD\s0" 4
4760.IX Item "EV_USE_EVENTFD"
4761If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is
4762available and will probe for kernel support at runtime. This will improve
4763\&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption.
4764If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
47652.7 or newer, otherwise disabled.
4766.IP "\s-1EV_USE_SIGNALFD\s0" 4
4767.IX Item "EV_USE_SIGNALFD"
4768If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`signalfd ()\*(C'\fR is
4769available and will probe for kernel support at runtime. This enables
4770the use of \s-1EVFLAG_SIGNALFD\s0 for faster and simpler signal handling. If
4771undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
47722.7 or newer, otherwise disabled.
4773.IP "\s-1EV_USE_TIMERFD\s0" 4
4774.IX Item "EV_USE_TIMERFD"
4775If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`timerfd ()\*(C'\fR is
4776available and will probe for kernel support at runtime. This allows
4777libev to detect time jumps accurately. If undefined, it will be enabled
4778if the headers indicate GNU/Linux + Glibc 2.8 or newer and define
4779\&\f(CW\*(C`TFD_TIMER_CANCEL_ON_SET\*(C'\fR, otherwise disabled.
4780.IP "\s-1EV_USE_EVENTFD\s0" 4
4781.IX Item "EV_USE_EVENTFD"
4782If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is
4783available and will probe for kernel support at runtime. This will improve
4784\&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption.
4785If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
47862.7 or newer, otherwise disabled.
2540.IP "\s-1EV_USE_SELECT\s0" 4 4787.IP "\s-1EV_USE_SELECT\s0" 4
2541.IX Item "EV_USE_SELECT" 4788.IX Item "EV_USE_SELECT"
2542If undefined or defined to be \f(CW1\fR, libev will compile in support for the 4789If undefined or defined to be \f(CW1\fR, libev will compile in support for the
2543\&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at autodetection will be done: if no 4790\&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at auto-detection will be done: if no
2544other method takes over, select will be it. Otherwise the select backend 4791other method takes over, select will be it. Otherwise the select backend
2545will not be compiled in. 4792will not be compiled in.
2546.IP "\s-1EV_SELECT_USE_FD_SET\s0" 4 4793.IP "\s-1EV_SELECT_USE_FD_SET\s0" 4
2547.IX Item "EV_SELECT_USE_FD_SET" 4794.IX Item "EV_SELECT_USE_FD_SET"
2548If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR 4795If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR
2549structure. This is useful if libev doesn't compile due to a missing 4796structure. This is useful if libev doesn't compile due to a missing
2550\&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it misguesses the bitset layout on 4797\&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it mis-guesses the bitset layout
2551exotic systems. This usually limits the range of file descriptors to some 4798on exotic systems. This usually limits the range of file descriptors to
2552low limit such as 1024 or might have other limitations (winsocket only 4799some low limit such as 1024 or might have other limitations (winsocket
2553allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation, might 4800only allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation,
2554influence the size of the \f(CW\*(C`fd_set\*(C'\fR used. 4801configures the maximum size of the \f(CW\*(C`fd_set\*(C'\fR.
2555.IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4 4802.IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4
2556.IX Item "EV_SELECT_IS_WINSOCKET" 4803.IX Item "EV_SELECT_IS_WINSOCKET"
2557When defined to \f(CW1\fR, the select backend will assume that 4804When defined to \f(CW1\fR, the select backend will assume that
2558select/socket/connect etc. don't understand file descriptors but 4805select/socket/connect etc. don't understand file descriptors but
2559wants osf handles on win32 (this is the case when the select to 4806wants osf handles on win32 (this is the case when the select to
2560be used is the winsock select). This means that it will call 4807be used is the winsock select). This means that it will call
2561\&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise, 4808\&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise,
2562it is assumed that all these functions actually work on fds, even 4809it is assumed that all these functions actually work on fds, even
2563on win32. Should not be defined on non\-win32 platforms. 4810on win32. Should not be defined on non\-win32 platforms.
4811.IP "\s-1EV_FD_TO_WIN32_HANDLE\s0(fd)" 4
4812.IX Item "EV_FD_TO_WIN32_HANDLE(fd)"
4813If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR is enabled, then libev needs a way to map
4814file descriptors to socket handles. When not defining this symbol (the
4815default), then libev will call \f(CW\*(C`_get_osfhandle\*(C'\fR, which is usually
4816correct. In some cases, programs use their own file descriptor management,
4817in which case they can provide this function to map fds to socket handles.
4818.IP "\s-1EV_WIN32_HANDLE_TO_FD\s0(handle)" 4
4819.IX Item "EV_WIN32_HANDLE_TO_FD(handle)"
4820If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR then libev maps handles to file descriptors
4821using the standard \f(CW\*(C`_open_osfhandle\*(C'\fR function. For programs implementing
4822their own fd to handle mapping, overwriting this function makes it easier
4823to do so. This can be done by defining this macro to an appropriate value.
4824.IP "\s-1EV_WIN32_CLOSE_FD\s0(fd)" 4
4825.IX Item "EV_WIN32_CLOSE_FD(fd)"
4826If programs implement their own fd to handle mapping on win32, then this
4827macro can be used to override the \f(CW\*(C`close\*(C'\fR function, useful to unregister
4828file descriptors again. Note that the replacement function has to close
4829the underlying \s-1OS\s0 handle.
4830.IP "\s-1EV_USE_WSASOCKET\s0" 4
4831.IX Item "EV_USE_WSASOCKET"
4832If defined to be \f(CW1\fR, libev will use \f(CW\*(C`WSASocket\*(C'\fR to create its internal
4833communication socket, which works better in some environments. Otherwise,
4834the normal \f(CW\*(C`socket\*(C'\fR function will be used, which works better in other
4835environments.
2564.IP "\s-1EV_USE_POLL\s0" 4 4836.IP "\s-1EV_USE_POLL\s0" 4
2565.IX Item "EV_USE_POLL" 4837.IX Item "EV_USE_POLL"
2566If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2) 4838If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2)
2567backend. Otherwise it will be enabled on non\-win32 platforms. It 4839backend. Otherwise it will be enabled on non\-win32 platforms. It
2568takes precedence over select. 4840takes precedence over select.
2569.IP "\s-1EV_USE_EPOLL\s0" 4 4841.IP "\s-1EV_USE_EPOLL\s0" 4
2570.IX Item "EV_USE_EPOLL" 4842.IX Item "EV_USE_EPOLL"
2571If defined to be \f(CW1\fR, libev will compile in support for the Linux 4843If defined to be \f(CW1\fR, libev will compile in support for the Linux
2572\&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime, 4844\&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime,
2573otherwise another method will be used as fallback. This is the 4845otherwise another method will be used as fallback. This is the preferred
2574preferred backend for GNU/Linux systems. 4846backend for GNU/Linux systems. If undefined, it will be enabled if the
4847headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4848.IP "\s-1EV_USE_LINUXAIO\s0" 4
4849.IX Item "EV_USE_LINUXAIO"
4850If defined to be \f(CW1\fR, libev will compile in support for the Linux aio
4851backend (\f(CW\*(C`EV_USE_EPOLL\*(C'\fR must also be enabled). If undefined, it will be
4852enabled on linux, otherwise disabled.
4853.IP "\s-1EV_USE_IOURING\s0" 4
4854.IX Item "EV_USE_IOURING"
4855If defined to be \f(CW1\fR, libev will compile in support for the Linux
4856io_uring backend (\f(CW\*(C`EV_USE_EPOLL\*(C'\fR must also be enabled). Due to it's
4857current limitations it has to be requested explicitly. If undefined, it
4858will be enabled on linux, otherwise disabled.
2575.IP "\s-1EV_USE_KQUEUE\s0" 4 4859.IP "\s-1EV_USE_KQUEUE\s0" 4
2576.IX Item "EV_USE_KQUEUE" 4860.IX Item "EV_USE_KQUEUE"
2577If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style 4861If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style
2578\&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime, 4862\&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime,
2579otherwise another method will be used as fallback. This is the preferred 4863otherwise another method will be used as fallback. This is the preferred
… …
258910 port style backend. Its availability will be detected at runtime, 487310 port style backend. Its availability will be detected at runtime,
2590otherwise another method will be used as fallback. This is the preferred 4874otherwise another method will be used as fallback. This is the preferred
2591backend for Solaris 10 systems. 4875backend for Solaris 10 systems.
2592.IP "\s-1EV_USE_DEVPOLL\s0" 4 4876.IP "\s-1EV_USE_DEVPOLL\s0" 4
2593.IX Item "EV_USE_DEVPOLL" 4877.IX Item "EV_USE_DEVPOLL"
2594reserved for future expansion, works like the \s-1USE\s0 symbols above. 4878Reserved for future expansion, works like the \s-1USE\s0 symbols above.
2595.IP "\s-1EV_USE_INOTIFY\s0" 4 4879.IP "\s-1EV_USE_INOTIFY\s0" 4
2596.IX Item "EV_USE_INOTIFY" 4880.IX Item "EV_USE_INOTIFY"
2597If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify 4881If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify
2598interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will 4882interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will
2599be detected at runtime. 4883be detected at runtime. If undefined, it will be enabled if the headers
4884indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4885.IP "\s-1EV_NO_SMP\s0" 4
4886.IX Item "EV_NO_SMP"
4887If defined to be \f(CW1\fR, libev will assume that memory is always coherent
4888between threads, that is, threads can be used, but threads never run on
4889different cpus (or different cpu cores). This reduces dependencies
4890and makes libev faster.
4891.IP "\s-1EV_NO_THREADS\s0" 4
4892.IX Item "EV_NO_THREADS"
4893If defined to be \f(CW1\fR, libev will assume that it will never be called from
4894different threads (that includes signal handlers), which is a stronger
4895assumption than \f(CW\*(C`EV_NO_SMP\*(C'\fR, above. This reduces dependencies and makes
4896libev faster.
4897.IP "\s-1EV_ATOMIC_T\s0" 4
4898.IX Item "EV_ATOMIC_T"
4899Libev requires an integer type (suitable for storing \f(CW0\fR or \f(CW1\fR) whose
4900access is atomic with respect to other threads or signal contexts. No
4901such type is easily found in the C language, so you can provide your own
4902type that you know is safe for your purposes. It is used both for signal
4903handler \*(L"locking\*(R" as well as for signal and thread safety in \f(CW\*(C`ev_async\*(C'\fR
4904watchers.
4905.Sp
4906In the absence of this define, libev will use \f(CW\*(C`sig_atomic_t volatile\*(C'\fR
4907(from \fIsignal.h\fR), which is usually good enough on most platforms.
2600.IP "\s-1EV_H\s0" 4 4908.IP "\s-1EV_H\s0 (h)" 4
2601.IX Item "EV_H" 4909.IX Item "EV_H (h)"
2602The name of the \fIev.h\fR header file used to include it. The default if 4910The name of the \fIev.h\fR header file used to include it. The default if
2603undefined is \f(CW\*(C`<ev.h>\*(C'\fR in \fIevent.h\fR and \f(CW"ev.h"\fR in \fIev.c\fR. This 4911undefined is \f(CW"ev.h"\fR in \fIevent.h\fR, \fIev.c\fR and \fIev++.h\fR. This can be
2604can be used to virtually rename the \fIev.h\fR header file in case of conflicts. 4912used to virtually rename the \fIev.h\fR header file in case of conflicts.
2605.IP "\s-1EV_CONFIG_H\s0" 4 4913.IP "\s-1EV_CONFIG_H\s0 (h)" 4
2606.IX Item "EV_CONFIG_H" 4914.IX Item "EV_CONFIG_H (h)"
2607If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override 4915If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override
2608\&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to 4916\&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to
2609\&\f(CW\*(C`EV_H\*(C'\fR, above. 4917\&\f(CW\*(C`EV_H\*(C'\fR, above.
2610.IP "\s-1EV_EVENT_H\s0" 4 4918.IP "\s-1EV_EVENT_H\s0 (h)" 4
2611.IX Item "EV_EVENT_H" 4919.IX Item "EV_EVENT_H (h)"
2612Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea 4920Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea
2613of how the \fIevent.h\fR header can be found. 4921of how the \fIevent.h\fR header can be found, the default is \f(CW"event.h"\fR.
2614.IP "\s-1EV_PROTOTYPES\s0" 4 4922.IP "\s-1EV_PROTOTYPES\s0 (h)" 4
2615.IX Item "EV_PROTOTYPES" 4923.IX Item "EV_PROTOTYPES (h)"
2616If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function 4924If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function
2617prototypes, but still define all the structs and other symbols. This is 4925prototypes, but still define all the structs and other symbols. This is
2618occasionally useful if you want to provide your own wrapper functions 4926occasionally useful if you want to provide your own wrapper functions
2619around libev functions. 4927around libev functions.
2620.IP "\s-1EV_MULTIPLICITY\s0" 4 4928.IP "\s-1EV_MULTIPLICITY\s0" 4
… …
2622If undefined or defined to \f(CW1\fR, then all event-loop-specific functions 4930If undefined or defined to \f(CW1\fR, then all event-loop-specific functions
2623will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create 4931will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create
2624additional independent event loops. Otherwise there will be no support 4932additional independent event loops. Otherwise there will be no support
2625for multiple event loops and there is no first event loop pointer 4933for multiple event loops and there is no first event loop pointer
2626argument. Instead, all functions act on the single default loop. 4934argument. Instead, all functions act on the single default loop.
4935.Sp
4936Note that \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR will no longer provide a
4937default loop when multiplicity is switched off \- you always have to
4938initialise the loop manually in this case.
2627.IP "\s-1EV_MINPRI\s0" 4 4939.IP "\s-1EV_MINPRI\s0" 4
2628.IX Item "EV_MINPRI" 4940.IX Item "EV_MINPRI"
2629.PD 0 4941.PD 0
2630.IP "\s-1EV_MAXPRI\s0" 4 4942.IP "\s-1EV_MAXPRI\s0" 4
2631.IX Item "EV_MAXPRI" 4943.IX Item "EV_MAXPRI"
… …
2638When doing priority-based operations, libev usually has to linearly search 4950When doing priority-based operations, libev usually has to linearly search
2639all the priorities, so having many of them (hundreds) uses a lot of space 4951all the priorities, so having many of them (hundreds) uses a lot of space
2640and time, so using the defaults of five priorities (\-2 .. +2) is usually 4952and time, so using the defaults of five priorities (\-2 .. +2) is usually
2641fine. 4953fine.
2642.Sp 4954.Sp
2643If your embedding app does not need any priorities, defining these both to 4955If your embedding application does not need any priorities, defining these
2644\&\f(CW0\fR will save some memory and cpu. 4956both to \f(CW0\fR will save some memory and \s-1CPU.\s0
2645.IP "\s-1EV_PERIODIC_ENABLE\s0" 4 4957.IP "\s-1EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE, EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE, EV_ASYNC_ENABLE, EV_CHILD_ENABLE.\s0" 4
2646.IX Item "EV_PERIODIC_ENABLE" 4958.IX Item "EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE, EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE, EV_ASYNC_ENABLE, EV_CHILD_ENABLE."
2647If undefined or defined to be \f(CW1\fR, then periodic timers are supported. If 4959If undefined or defined to be \f(CW1\fR (and the platform supports it), then
2648defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of 4960the respective watcher type is supported. If defined to be \f(CW0\fR, then it
2649code. 4961is not. Disabling watcher types mainly saves code size.
2650.IP "\s-1EV_IDLE_ENABLE\s0" 4
2651.IX Item "EV_IDLE_ENABLE"
2652If undefined or defined to be \f(CW1\fR, then idle watchers are supported. If
2653defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of
2654code.
2655.IP "\s-1EV_EMBED_ENABLE\s0" 4
2656.IX Item "EV_EMBED_ENABLE"
2657If undefined or defined to be \f(CW1\fR, then embed watchers are supported. If
2658defined to be \f(CW0\fR, then they are not.
2659.IP "\s-1EV_STAT_ENABLE\s0" 4 4962.IP "\s-1EV_FEATURES\s0" 4
2660.IX Item "EV_STAT_ENABLE" 4963.IX Item "EV_FEATURES"
2661If undefined or defined to be \f(CW1\fR, then stat watchers are supported. If
2662defined to be \f(CW0\fR, then they are not.
2663.IP "\s-1EV_FORK_ENABLE\s0" 4
2664.IX Item "EV_FORK_ENABLE"
2665If undefined or defined to be \f(CW1\fR, then fork watchers are supported. If
2666defined to be \f(CW0\fR, then they are not.
2667.IP "\s-1EV_MINIMAL\s0" 4
2668.IX Item "EV_MINIMAL"
2669If you need to shave off some kilobytes of code at the expense of some 4964If you need to shave off some kilobytes of code at the expense of some
2670speed, define this symbol to \f(CW1\fR. Currently only used for gcc to override 4965speed (but with the full \s-1API\s0), you can define this symbol to request
2671some inlining decisions, saves roughly 30% codesize of amd64. 4966certain subsets of functionality. The default is to enable all features
4967that can be enabled on the platform.
4968.Sp
4969A typical way to use this symbol is to define it to \f(CW0\fR (or to a bitset
4970with some broad features you want) and then selectively re-enable
4971additional parts you want, for example if you want everything minimal,
4972but multiple event loop support, async and child watchers and the poll
4973backend, use this:
4974.Sp
4975.Vb 5
4976\& #define EV_FEATURES 0
4977\& #define EV_MULTIPLICITY 1
4978\& #define EV_USE_POLL 1
4979\& #define EV_CHILD_ENABLE 1
4980\& #define EV_ASYNC_ENABLE 1
4981.Ve
4982.Sp
4983The actual value is a bitset, it can be a combination of the following
4984values (by default, all of these are enabled):
4985.RS 4
4986.ie n .IP "1 \- faster/larger code" 4
4987.el .IP "\f(CW1\fR \- faster/larger code" 4
4988.IX Item "1 - faster/larger code"
4989Use larger code to speed up some operations.
4990.Sp
4991Currently this is used to override some inlining decisions (enlarging the
4992code size by roughly 30% on amd64).
4993.Sp
4994When optimising for size, use of compiler flags such as \f(CW\*(C`\-Os\*(C'\fR with
4995gcc is recommended, as well as \f(CW\*(C`\-DNDEBUG\*(C'\fR, as libev contains a number of
4996assertions.
4997.Sp
4998The default is off when \f(CW\*(C`_\|_OPTIMIZE_SIZE_\|_\*(C'\fR is defined by your compiler
4999(e.g. gcc with \f(CW\*(C`\-Os\*(C'\fR).
5000.ie n .IP "2 \- faster/larger data structures" 4
5001.el .IP "\f(CW2\fR \- faster/larger data structures" 4
5002.IX Item "2 - faster/larger data structures"
5003Replaces the small 2\-heap for timer management by a faster 4\-heap, larger
5004hash table sizes and so on. This will usually further increase code size
5005and can additionally have an effect on the size of data structures at
5006runtime.
5007.Sp
5008The default is off when \f(CW\*(C`_\|_OPTIMIZE_SIZE_\|_\*(C'\fR is defined by your compiler
5009(e.g. gcc with \f(CW\*(C`\-Os\*(C'\fR).
5010.ie n .IP "4 \- full \s-1API\s0 configuration" 4
5011.el .IP "\f(CW4\fR \- full \s-1API\s0 configuration" 4
5012.IX Item "4 - full API configuration"
5013This enables priorities (sets \f(CW\*(C`EV_MAXPRI\*(C'\fR=2 and \f(CW\*(C`EV_MINPRI\*(C'\fR=\-2), and
5014enables multiplicity (\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR=1).
5015.ie n .IP "8 \- full \s-1API\s0" 4
5016.el .IP "\f(CW8\fR \- full \s-1API\s0" 4
5017.IX Item "8 - full API"
5018This enables a lot of the \*(L"lesser used\*(R" \s-1API\s0 functions. See \f(CW\*(C`ev.h\*(C'\fR for
5019details on which parts of the \s-1API\s0 are still available without this
5020feature, and do not complain if this subset changes over time.
5021.ie n .IP "16 \- enable all optional watcher types" 4
5022.el .IP "\f(CW16\fR \- enable all optional watcher types" 4
5023.IX Item "16 - enable all optional watcher types"
5024Enables all optional watcher types. If you want to selectively enable
5025only some watcher types other than I/O and timers (e.g. prepare,
5026embed, async, child...) you can enable them manually by defining
5027\&\f(CW\*(C`EV_watchertype_ENABLE\*(C'\fR to \f(CW1\fR instead.
5028.ie n .IP "32 \- enable all backends" 4
5029.el .IP "\f(CW32\fR \- enable all backends" 4
5030.IX Item "32 - enable all backends"
5031This enables all backends \- without this feature, you need to enable at
5032least one backend manually (\f(CW\*(C`EV_USE_SELECT\*(C'\fR is a good choice).
5033.ie n .IP "64 \- enable OS-specific ""helper"" APIs" 4
5034.el .IP "\f(CW64\fR \- enable OS-specific ``helper'' APIs" 4
5035.IX Item "64 - enable OS-specific helper APIs"
5036Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
5037default.
5038.RE
5039.RS 4
5040.Sp
5041Compiling with \f(CW\*(C`gcc \-Os \-DEV_STANDALONE \-DEV_USE_EPOLL=1 \-DEV_FEATURES=0\*(C'\fR
5042reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
5043code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
5044watchers, timers and monotonic clock support.
5045.Sp
5046With an intelligent-enough linker (gcc+binutils are intelligent enough
5047when you use \f(CW\*(C`\-Wl,\-\-gc\-sections \-ffunction\-sections\*(C'\fR) functions unused by
5048your program might be left out as well \- a binary starting a timer and an
5049I/O watcher then might come out at only 5Kb.
5050.RE
5051.IP "\s-1EV_API_STATIC\s0" 4
5052.IX Item "EV_API_STATIC"
5053If this symbol is defined (by default it is not), then all identifiers
5054will have static linkage. This means that libev will not export any
5055identifiers, and you cannot link against libev anymore. This can be useful
5056when you embed libev, only want to use libev functions in a single file,
5057and do not want its identifiers to be visible.
5058.Sp
5059To use this, define \f(CW\*(C`EV_API_STATIC\*(C'\fR and include \fIev.c\fR in the file that
5060wants to use libev.
5061.Sp
5062This option only works when libev is compiled with a C compiler, as \*(C+
5063doesn't support the required declaration syntax.
5064.IP "\s-1EV_AVOID_STDIO\s0" 4
5065.IX Item "EV_AVOID_STDIO"
5066If this is set to \f(CW1\fR at compiletime, then libev will avoid using stdio
5067functions (printf, scanf, perror etc.). This will increase the code size
5068somewhat, but if your program doesn't otherwise depend on stdio and your
5069libc allows it, this avoids linking in the stdio library which is quite
5070big.
5071.Sp
5072Note that error messages might become less precise when this option is
5073enabled.
5074.IP "\s-1EV_NSIG\s0" 4
5075.IX Item "EV_NSIG"
5076The highest supported signal number, +1 (or, the number of
5077signals): Normally, libev tries to deduce the maximum number of signals
5078automatically, but sometimes this fails, in which case it can be
5079specified. Also, using a lower number than detected (\f(CW32\fR should be
5080good for about any system in existence) can save some memory, as libev
5081statically allocates some 12\-24 bytes per signal number.
2672.IP "\s-1EV_PID_HASHSIZE\s0" 4 5082.IP "\s-1EV_PID_HASHSIZE\s0" 4
2673.IX Item "EV_PID_HASHSIZE" 5083.IX Item "EV_PID_HASHSIZE"
2674\&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by 5084\&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by
2675pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR), usually more 5085pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR disabled),
2676than enough. If you need to manage thousands of children you might want to 5086usually more than enough. If you need to manage thousands of children you
2677increase this value (\fImust\fR be a power of two). 5087might want to increase this value (\fImust\fR be a power of two).
2678.IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4 5088.IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4
2679.IX Item "EV_INOTIFY_HASHSIZE" 5089.IX Item "EV_INOTIFY_HASHSIZE"
2680\&\f(CW\*(C`ev_staz\*(C'\fR watchers use a small hash table to distribute workload by 5090\&\f(CW\*(C`ev_stat\*(C'\fR watchers use a small hash table to distribute workload by
2681inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR), 5091inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR
2682usually more than enough. If you need to manage thousands of \f(CW\*(C`ev_stat\*(C'\fR 5092disabled), usually more than enough. If you need to manage thousands of
2683watchers you might want to increase this value (\fImust\fR be a power of 5093\&\f(CW\*(C`ev_stat\*(C'\fR watchers you might want to increase this value (\fImust\fR be a
2684two). 5094power of two).
5095.IP "\s-1EV_USE_4HEAP\s0" 4
5096.IX Item "EV_USE_4HEAP"
5097Heaps are not very cache-efficient. To improve the cache-efficiency of the
5098timer and periodics heaps, libev uses a 4\-heap when this symbol is defined
5099to \f(CW1\fR. The 4\-heap uses more complicated (longer) code but has noticeably
5100faster performance with many (thousands) of watchers.
5101.Sp
5102The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
5103will be \f(CW0\fR.
5104.IP "\s-1EV_HEAP_CACHE_AT\s0" 4
5105.IX Item "EV_HEAP_CACHE_AT"
5106Heaps are not very cache-efficient. To improve the cache-efficiency of the
5107timer and periodics heaps, libev can cache the timestamp (\fIat\fR) within
5108the heap structure (selected by defining \f(CW\*(C`EV_HEAP_CACHE_AT\*(C'\fR to \f(CW1\fR),
5109which uses 8\-12 bytes more per watcher and a few hundred bytes more code,
5110but avoids random read accesses on heap changes. This improves performance
5111noticeably with many (hundreds) of watchers.
5112.Sp
5113The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
5114will be \f(CW0\fR.
5115.IP "\s-1EV_VERIFY\s0" 4
5116.IX Item "EV_VERIFY"
5117Controls how much internal verification (see \f(CW\*(C`ev_verify ()\*(C'\fR) will
5118be done: If set to \f(CW0\fR, no internal verification code will be compiled
5119in. If set to \f(CW1\fR, then verification code will be compiled in, but not
5120called. If set to \f(CW2\fR, then the internal verification code will be
5121called once per loop, which can slow down libev. If set to \f(CW3\fR, then the
5122verification code will be called very frequently, which will slow down
5123libev considerably.
5124.Sp
5125Verification errors are reported via C's \f(CW\*(C`assert\*(C'\fR mechanism, so if you
5126disable that (e.g. by defining \f(CW\*(C`NDEBUG\*(C'\fR) then no errors will be reported.
5127.Sp
5128The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
5129will be \f(CW0\fR.
2685.IP "\s-1EV_COMMON\s0" 4 5130.IP "\s-1EV_COMMON\s0" 4
2686.IX Item "EV_COMMON" 5131.IX Item "EV_COMMON"
2687By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining 5132By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining
2688this macro to a something else you can include more and other types of 5133this macro to something else you can include more and other types of
2689members. You have to define it each time you include one of the files, 5134members. You have to define it each time you include one of the files,
2690though, and it must be identical each time. 5135though, and it must be identical each time.
2691.Sp 5136.Sp
2692For example, the perl \s-1EV\s0 module uses something like this: 5137For example, the perl \s-1EV\s0 module uses something like this:
2693.Sp 5138.Sp
2694.Vb 3 5139.Vb 3
2695\& #define EV_COMMON \e 5140\& #define EV_COMMON \e
2696\& SV *self; /* contains this struct */ \e 5141\& SV *self; /* contains this struct */ \e
2697\& SV *cb_sv, *fh /* note no trailing ";" */ 5142\& SV *cb_sv, *fh /* note no trailing ";" */
2698.Ve 5143.Ve
2699.IP "\s-1EV_CB_DECLARE\s0 (type)" 4 5144.IP "\s-1EV_CB_DECLARE\s0 (type)" 4
2700.IX Item "EV_CB_DECLARE (type)" 5145.IX Item "EV_CB_DECLARE (type)"
2701.PD 0 5146.PD 0
2702.IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4 5147.IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4
… …
2708and the way callbacks are invoked and set. Must expand to a struct member 5153and the way callbacks are invoked and set. Must expand to a struct member
2709definition and a statement, respectively. See the \fIev.h\fR header file for 5154definition and a statement, respectively. See the \fIev.h\fR header file for
2710their default definitions. One possible use for overriding these is to 5155their default definitions. One possible use for overriding these is to
2711avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use 5156avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use
2712method calls instead of plain function calls in \*(C+. 5157method calls instead of plain function calls in \*(C+.
2713.Sh "\s-1EXPORTED\s0 \s-1API\s0 \s-1SYMBOLS\s0" 5158.SS "\s-1EXPORTED API SYMBOLS\s0"
2714.IX Subsection "EXPORTED API SYMBOLS" 5159.IX Subsection "EXPORTED API SYMBOLS"
2715If you need to re-export the \s-1API\s0 (e.g. via a dll) and you need a list of 5160If you need to re-export the \s-1API\s0 (e.g. via a \s-1DLL\s0) and you need a list of
2716exported symbols, you can use the provided \fISymbol.*\fR files which list 5161exported symbols, you can use the provided \fISymbol.*\fR files which list
2717all public symbols, one per line: 5162all public symbols, one per line:
2718.Sp 5163.PP
2719.Vb 2 5164.Vb 2
2720\& Symbols.ev for libev proper 5165\& Symbols.ev for libev proper
2721\& Symbols.event for the libevent emulation 5166\& Symbols.event for the libevent emulation
2722.Ve 5167.Ve
2723.Sp 5168.PP
2724This can also be used to rename all public symbols to avoid clashes with 5169This can also be used to rename all public symbols to avoid clashes with
2725multiple versions of libev linked together (which is obviously bad in 5170multiple versions of libev linked together (which is obviously bad in
2726itself, but sometimes it is inconvinient to avoid this). 5171itself, but sometimes it is inconvenient to avoid this).
2727.Sp 5172.PP
2728A sed command like this will create wrapper \f(CW\*(C`#define\*(C'\fR's that you need to 5173A sed command like this will create wrapper \f(CW\*(C`#define\*(C'\fR's that you need to
2729include before including \fIev.h\fR: 5174include before including \fIev.h\fR:
2730.Sp 5175.PP
2731.Vb 1 5176.Vb 1
2732\& <Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h 5177\& <Symbols.ev sed \-e "s/.*/#define & myprefix_&/" >wrap.h
2733.Ve 5178.Ve
2734.Sp 5179.PP
2735This would create a file \fIwrap.h\fR which essentially looks like this: 5180This would create a file \fIwrap.h\fR which essentially looks like this:
2736.Sp 5181.PP
2737.Vb 4 5182.Vb 4
2738\& #define ev_backend myprefix_ev_backend 5183\& #define ev_backend myprefix_ev_backend
2739\& #define ev_check_start myprefix_ev_check_start 5184\& #define ev_check_start myprefix_ev_check_start
2740\& #define ev_check_stop myprefix_ev_check_stop 5185\& #define ev_check_stop myprefix_ev_check_stop
2741\& ... 5186\& ...
2742.Ve 5187.Ve
2743.Sh "\s-1EXAMPLES\s0" 5188.SS "\s-1EXAMPLES\s0"
2744.IX Subsection "EXAMPLES" 5189.IX Subsection "EXAMPLES"
2745For a real-world example of a program the includes libev 5190For a real-world example of a program the includes libev
2746verbatim, you can have a look at the \s-1EV\s0 perl module 5191verbatim, you can have a look at the \s-1EV\s0 perl module
2747(<http://software.schmorp.de/pkg/EV.html>). It has the libev files in 5192(<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
2748the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public 5193the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public
2749interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file 5194interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file
2750will be compiled. It is pretty complex because it provides its own header 5195will be compiled. It is pretty complex because it provides its own header
2751file. 5196file.
2752.Sp 5197.PP
2753The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file 5198The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file
2754that everybody includes and which overrides some configure choices: 5199that everybody includes and which overrides some configure choices:
2755.Sp 5200.PP
2756.Vb 9 5201.Vb 8
2757\& #define EV_MINIMAL 1 5202\& #define EV_FEATURES 8
2758\& #define EV_USE_POLL 0 5203\& #define EV_USE_SELECT 1
2759\& #define EV_MULTIPLICITY 0
2760\& #define EV_PERIODIC_ENABLE 0 5204\& #define EV_PREPARE_ENABLE 1
5205\& #define EV_IDLE_ENABLE 1
2761\& #define EV_STAT_ENABLE 0 5206\& #define EV_SIGNAL_ENABLE 1
2762\& #define EV_FORK_ENABLE 0 5207\& #define EV_CHILD_ENABLE 1
5208\& #define EV_USE_STDEXCEPT 0
2763\& #define EV_CONFIG_H <config.h> 5209\& #define EV_CONFIG_H <config.h>
2764\& #define EV_MINPRI 0 5210\&
2765\& #define EV_MAXPRI 0
2766.Ve
2767.Sp
2768.Vb 1
2769\& #include "ev++.h" 5211\& #include "ev++.h"
2770.Ve 5212.Ve
2771.Sp 5213.PP
2772And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled: 5214And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled:
2773.Sp 5215.PP
2774.Vb 2 5216.Vb 2
2775\& #include "ev_cpp.h" 5217\& #include "ev_cpp.h"
2776\& #include "ev.c" 5218\& #include "ev.c"
2777.Ve 5219.Ve
5220.SH "INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT"
5221.IX Header "INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT"
5222.SS "\s-1THREADS AND COROUTINES\s0"
5223.IX Subsection "THREADS AND COROUTINES"
5224\fI\s-1THREADS\s0\fR
5225.IX Subsection "THREADS"
5226.PP
5227All libev functions are reentrant and thread-safe unless explicitly
5228documented otherwise, but libev implements no locking itself. This means
5229that you can use as many loops as you want in parallel, as long as there
5230are no concurrent calls into any libev function with the same loop
5231parameter (\f(CW\*(C`ev_default_*\*(C'\fR calls have an implicit default loop parameter,
5232of course): libev guarantees that different event loops share no data
5233structures that need any locking.
5234.PP
5235Or to put it differently: calls with different loop parameters can be done
5236concurrently from multiple threads, calls with the same loop parameter
5237must be done serially (but can be done from different threads, as long as
5238only one thread ever is inside a call at any point in time, e.g. by using
5239a mutex per loop).
5240.PP
5241Specifically to support threads (and signal handlers), libev implements
5242so-called \f(CW\*(C`ev_async\*(C'\fR watchers, which allow some limited form of
5243concurrency on the same event loop, namely waking it up \*(L"from the
5244outside\*(R".
5245.PP
5246If you want to know which design (one loop, locking, or multiple loops
5247without or something else still) is best for your problem, then I cannot
5248help you, but here is some generic advice:
5249.IP "\(bu" 4
5250most applications have a main thread: use the default libev loop
5251in that thread, or create a separate thread running only the default loop.
5252.Sp
5253This helps integrating other libraries or software modules that use libev
5254themselves and don't care/know about threading.
5255.IP "\(bu" 4
5256one loop per thread is usually a good model.
5257.Sp
5258Doing this is almost never wrong, sometimes a better-performance model
5259exists, but it is always a good start.
5260.IP "\(bu" 4
5261other models exist, such as the leader/follower pattern, where one
5262loop is handed through multiple threads in a kind of round-robin fashion.
5263.Sp
5264Choosing a model is hard \- look around, learn, know that usually you can do
5265better than you currently do :\-)
5266.IP "\(bu" 4
5267often you need to talk to some other thread which blocks in the
5268event loop.
5269.Sp
5270\&\f(CW\*(C`ev_async\*(C'\fR watchers can be used to wake them up from other threads safely
5271(or from signal contexts...).
5272.Sp
5273An example use would be to communicate signals or other events that only
5274work in the default loop by registering the signal watcher with the
5275default loop and triggering an \f(CW\*(C`ev_async\*(C'\fR watcher from the default loop
5276watcher callback into the event loop interested in the signal.
5277.PP
5278See also \*(L"\s-1THREAD LOCKING EXAMPLE\*(R"\s0.
5279.PP
5280\fI\s-1COROUTINES\s0\fR
5281.IX Subsection "COROUTINES"
5282.PP
5283Libev is very accommodating to coroutines (\*(L"cooperative threads\*(R"):
5284libev fully supports nesting calls to its functions from different
5285coroutines (e.g. you can call \f(CW\*(C`ev_run\*(C'\fR on the same loop from two
5286different coroutines, and switch freely between both coroutines running
5287the loop, as long as you don't confuse yourself). The only exception is
5288that you must not do this from \f(CW\*(C`ev_periodic\*(C'\fR reschedule callbacks.
5289.PP
5290Care has been taken to ensure that libev does not keep local state inside
5291\&\f(CW\*(C`ev_run\*(C'\fR, and other calls do not usually allow for coroutine switches as
5292they do not call any callbacks.
5293.SS "\s-1COMPILER WARNINGS\s0"
5294.IX Subsection "COMPILER WARNINGS"
5295Depending on your compiler and compiler settings, you might get no or a
5296lot of warnings when compiling libev code. Some people are apparently
5297scared by this.
5298.PP
5299However, these are unavoidable for many reasons. For one, each compiler
5300has different warnings, and each user has different tastes regarding
5301warning options. \*(L"Warn-free\*(R" code therefore cannot be a goal except when
5302targeting a specific compiler and compiler-version.
5303.PP
5304Another reason is that some compiler warnings require elaborate
5305workarounds, or other changes to the code that make it less clear and less
5306maintainable.
5307.PP
5308And of course, some compiler warnings are just plain stupid, or simply
5309wrong (because they don't actually warn about the condition their message
5310seems to warn about). For example, certain older gcc versions had some
5311warnings that resulted in an extreme number of false positives. These have
5312been fixed, but some people still insist on making code warn-free with
5313such buggy versions.
5314.PP
5315While libev is written to generate as few warnings as possible,
5316\&\*(L"warn-free\*(R" code is not a goal, and it is recommended not to build libev
5317with any compiler warnings enabled unless you are prepared to cope with
5318them (e.g. by ignoring them). Remember that warnings are just that:
5319warnings, not errors, or proof of bugs.
5320.SS "\s-1VALGRIND\s0"
5321.IX Subsection "VALGRIND"
5322Valgrind has a special section here because it is a popular tool that is
5323highly useful. Unfortunately, valgrind reports are very hard to interpret.
5324.PP
5325If you think you found a bug (memory leak, uninitialised data access etc.)
5326in libev, then check twice: If valgrind reports something like:
5327.PP
5328.Vb 3
5329\& ==2274== definitely lost: 0 bytes in 0 blocks.
5330\& ==2274== possibly lost: 0 bytes in 0 blocks.
5331\& ==2274== still reachable: 256 bytes in 1 blocks.
5332.Ve
5333.PP
5334Then there is no memory leak, just as memory accounted to global variables
5335is not a memleak \- the memory is still being referenced, and didn't leak.
5336.PP
5337Similarly, under some circumstances, valgrind might report kernel bugs
5338as if it were a bug in libev (e.g. in realloc or in the poll backend,
5339although an acceptable workaround has been found here), or it might be
5340confused.
5341.PP
5342Keep in mind that valgrind is a very good tool, but only a tool. Don't
5343make it into some kind of religion.
5344.PP
5345If you are unsure about something, feel free to contact the mailing list
5346with the full valgrind report and an explanation on why you think this
5347is a bug in libev (best check the archives, too :). However, don't be
5348annoyed when you get a brisk \*(L"this is no bug\*(R" answer and take the chance
5349of learning how to interpret valgrind properly.
5350.PP
5351If you need, for some reason, empty reports from valgrind for your project
5352I suggest using suppression lists.
5353.SH "PORTABILITY NOTES"
5354.IX Header "PORTABILITY NOTES"
5355.SS "\s-1GNU/LINUX 32 BIT LIMITATIONS\s0"
5356.IX Subsection "GNU/LINUX 32 BIT LIMITATIONS"
5357GNU/Linux is the only common platform that supports 64 bit file/large file
5358interfaces but \fIdisables\fR them by default.
5359.PP
5360That means that libev compiled in the default environment doesn't support
5361files larger than 2GiB or so, which mainly affects \f(CW\*(C`ev_stat\*(C'\fR watchers.
5362.PP
5363Unfortunately, many programs try to work around this GNU/Linux issue
5364by enabling the large file \s-1API,\s0 which makes them incompatible with the
5365standard libev compiled for their system.
5366.PP
5367Likewise, libev cannot enable the large file \s-1API\s0 itself as this would
5368suddenly make it incompatible to the default compile time environment,
5369i.e. all programs not using special compile switches.
5370.SS "\s-1OS/X AND DARWIN BUGS\s0"
5371.IX Subsection "OS/X AND DARWIN BUGS"
5372The whole thing is a bug if you ask me \- basically any system interface
5373you touch is broken, whether it is locales, poll, kqueue or even the
5374OpenGL drivers.
5375.PP
5376\fI\f(CI\*(C`kqueue\*(C'\fI is buggy\fR
5377.IX Subsection "kqueue is buggy"
5378.PP
5379The kqueue syscall is broken in all known versions \- most versions support
5380only sockets, many support pipes.
5381.PP
5382Libev tries to work around this by not using \f(CW\*(C`kqueue\*(C'\fR by default on this
5383rotten platform, but of course you can still ask for it when creating a
5384loop \- embedding a socket-only kqueue loop into a select-based one is
5385probably going to work well.
5386.PP
5387\fI\f(CI\*(C`poll\*(C'\fI is buggy\fR
5388.IX Subsection "poll is buggy"
5389.PP
5390Instead of fixing \f(CW\*(C`kqueue\*(C'\fR, Apple replaced their (working) \f(CW\*(C`poll\*(C'\fR
5391implementation by something calling \f(CW\*(C`kqueue\*(C'\fR internally around the 10.5.6
5392release, so now \f(CW\*(C`kqueue\*(C'\fR \fIand\fR \f(CW\*(C`poll\*(C'\fR are broken.
5393.PP
5394Libev tries to work around this by not using \f(CW\*(C`poll\*(C'\fR by default on
5395this rotten platform, but of course you can still ask for it when creating
5396a loop.
5397.PP
5398\fI\f(CI\*(C`select\*(C'\fI is buggy\fR
5399.IX Subsection "select is buggy"
5400.PP
5401All that's left is \f(CW\*(C`select\*(C'\fR, and of course Apple found a way to fuck this
5402one up as well: On \s-1OS/X,\s0 \f(CW\*(C`select\*(C'\fR actively limits the number of file
5403descriptors you can pass in to 1024 \- your program suddenly crashes when
5404you use more.
5405.PP
5406There is an undocumented \*(L"workaround\*(R" for this \- defining
5407\&\f(CW\*(C`_DARWIN_UNLIMITED_SELECT\*(C'\fR, which libev tries to use, so select \fIshould\fR
5408work on \s-1OS/X.\s0
5409.SS "\s-1SOLARIS PROBLEMS AND WORKAROUNDS\s0"
5410.IX Subsection "SOLARIS PROBLEMS AND WORKAROUNDS"
5411\fI\f(CI\*(C`errno\*(C'\fI reentrancy\fR
5412.IX Subsection "errno reentrancy"
5413.PP
5414The default compile environment on Solaris is unfortunately so
5415thread-unsafe that you can't even use components/libraries compiled
5416without \f(CW\*(C`\-D_REENTRANT\*(C'\fR in a threaded program, which, of course, isn't
5417defined by default. A valid, if stupid, implementation choice.
5418.PP
5419If you want to use libev in threaded environments you have to make sure
5420it's compiled with \f(CW\*(C`_REENTRANT\*(C'\fR defined.
5421.PP
5422\fIEvent port backend\fR
5423.IX Subsection "Event port backend"
5424.PP
5425The scalable event interface for Solaris is called \*(L"event
5426ports\*(R". Unfortunately, this mechanism is very buggy in all major
5427releases. If you run into high \s-1CPU\s0 usage, your program freezes or you get
5428a large number of spurious wakeups, make sure you have all the relevant
5429and latest kernel patches applied. No, I don't know which ones, but there
5430are multiple ones to apply, and afterwards, event ports actually work
5431great.
5432.PP
5433If you can't get it to work, you can try running the program by setting
5434the environment variable \f(CW\*(C`LIBEV_FLAGS=3\*(C'\fR to only allow \f(CW\*(C`poll\*(C'\fR and
5435\&\f(CW\*(C`select\*(C'\fR backends.
5436.SS "\s-1AIX POLL BUG\s0"
5437.IX Subsection "AIX POLL BUG"
5438\&\s-1AIX\s0 unfortunately has a broken \f(CW\*(C`poll.h\*(C'\fR header. Libev works around
5439this by trying to avoid the poll backend altogether (i.e. it's not even
5440compiled in), which normally isn't a big problem as \f(CW\*(C`select\*(C'\fR works fine
5441with large bitsets on \s-1AIX,\s0 and \s-1AIX\s0 is dead anyway.
5442.SS "\s-1WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS\s0"
5443.IX Subsection "WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS"
5444\fIGeneral issues\fR
5445.IX Subsection "General issues"
5446.PP
5447Win32 doesn't support any of the standards (e.g. \s-1POSIX\s0) that libev
5448requires, and its I/O model is fundamentally incompatible with the \s-1POSIX\s0
5449model. Libev still offers limited functionality on this platform in
5450the form of the \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR backend, and only supports socket
5451descriptors. This only applies when using Win32 natively, not when using
5452e.g. cygwin. Actually, it only applies to the microsofts own compilers,
5453as every compiler comes with a slightly differently broken/incompatible
5454environment.
5455.PP
5456Lifting these limitations would basically require the full
5457re-implementation of the I/O system. If you are into this kind of thing,
5458then note that glib does exactly that for you in a very portable way (note
5459also that glib is the slowest event library known to man).
5460.PP
5461There is no supported compilation method available on windows except
5462embedding it into other applications.
5463.PP
5464Sensible signal handling is officially unsupported by Microsoft \- libev
5465tries its best, but under most conditions, signals will simply not work.
5466.PP
5467Not a libev limitation but worth mentioning: windows apparently doesn't
5468accept large writes: instead of resulting in a partial write, windows will
5469either accept everything or return \f(CW\*(C`ENOBUFS\*(C'\fR if the buffer is too large,
5470so make sure you only write small amounts into your sockets (less than a
5471megabyte seems safe, but this apparently depends on the amount of memory
5472available).
5473.PP
5474Due to the many, low, and arbitrary limits on the win32 platform and
5475the abysmal performance of winsockets, using a large number of sockets
5476is not recommended (and not reasonable). If your program needs to use
5477more than a hundred or so sockets, then likely it needs to use a totally
5478different implementation for windows, as libev offers the \s-1POSIX\s0 readiness
5479notification model, which cannot be implemented efficiently on windows
5480(due to Microsoft monopoly games).
5481.PP
5482A typical way to use libev under windows is to embed it (see the embedding
5483section for details) and use the following \fIevwrap.h\fR header file instead
5484of \fIev.h\fR:
5485.PP
5486.Vb 2
5487\& #define EV_STANDALONE /* keeps ev from requiring config.h */
5488\& #define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
5489\&
5490\& #include "ev.h"
5491.Ve
5492.PP
5493And compile the following \fIevwrap.c\fR file into your project (make sure
5494you do \fInot\fR compile the \fIev.c\fR or any other embedded source files!):
5495.PP
5496.Vb 2
5497\& #include "evwrap.h"
5498\& #include "ev.c"
5499.Ve
5500.PP
5501\fIThe winsocket \f(CI\*(C`select\*(C'\fI function\fR
5502.IX Subsection "The winsocket select function"
5503.PP
5504The winsocket \f(CW\*(C`select\*(C'\fR function doesn't follow \s-1POSIX\s0 in that it
5505requires socket \fIhandles\fR and not socket \fIfile descriptors\fR (it is
5506also extremely buggy). This makes select very inefficient, and also
5507requires a mapping from file descriptors to socket handles (the Microsoft
5508C runtime provides the function \f(CW\*(C`_open_osfhandle\*(C'\fR for this). See the
5509discussion of the \f(CW\*(C`EV_SELECT_USE_FD_SET\*(C'\fR, \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR and
5510\&\f(CW\*(C`EV_FD_TO_WIN32_HANDLE\*(C'\fR preprocessor symbols for more info.
5511.PP
5512The configuration for a \*(L"naked\*(R" win32 using the Microsoft runtime
5513libraries and raw winsocket select is:
5514.PP
5515.Vb 2
5516\& #define EV_USE_SELECT 1
5517\& #define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
5518.Ve
5519.PP
5520Note that winsockets handling of fd sets is O(n), so you can easily get a
5521complexity in the O(nX) range when using win32.
5522.PP
5523\fILimited number of file descriptors\fR
5524.IX Subsection "Limited number of file descriptors"
5525.PP
5526Windows has numerous arbitrary (and low) limits on things.
5527.PP
5528Early versions of winsocket's select only supported waiting for a maximum
5529of \f(CW64\fR handles (probably owning to the fact that all windows kernels
5530can only wait for \f(CW64\fR things at the same time internally; Microsoft
5531recommends spawning a chain of threads and wait for 63 handles and the
5532previous thread in each. Sounds great!).
5533.PP
5534Newer versions support more handles, but you need to define \f(CW\*(C`FD_SETSIZE\*(C'\fR
5535to some high number (e.g. \f(CW2048\fR) before compiling the winsocket select
5536call (which might be in libev or elsewhere, for example, perl and many
5537other interpreters do their own select emulation on windows).
5538.PP
5539Another limit is the number of file descriptors in the Microsoft runtime
5540libraries, which by default is \f(CW64\fR (there must be a hidden \fI64\fR
5541fetish or something like this inside Microsoft). You can increase this
5542by calling \f(CW\*(C`_setmaxstdio\*(C'\fR, which can increase this limit to \f(CW2048\fR
5543(another arbitrary limit), but is broken in many versions of the Microsoft
5544runtime libraries. This might get you to about \f(CW512\fR or \f(CW2048\fR sockets
5545(depending on windows version and/or the phase of the moon). To get more,
5546you need to wrap all I/O functions and provide your own fd management, but
5547the cost of calling select (O(nX)) will likely make this unworkable.
5548.SS "\s-1PORTABILITY REQUIREMENTS\s0"
5549.IX Subsection "PORTABILITY REQUIREMENTS"
5550In addition to a working ISO-C implementation and of course the
5551backend-specific APIs, libev relies on a few additional extensions:
5552.ie n .IP """void (*)(ev_watcher_type *, int revents)"" must have compatible calling conventions regardless of ""ev_watcher_type *""." 4
5553.el .IP "\f(CWvoid (*)(ev_watcher_type *, int revents)\fR must have compatible calling conventions regardless of \f(CWev_watcher_type *\fR." 4
5554.IX Item "void (*)(ev_watcher_type *, int revents) must have compatible calling conventions regardless of ev_watcher_type *."
5555Libev assumes not only that all watcher pointers have the same internal
5556structure (guaranteed by \s-1POSIX\s0 but not by \s-1ISO C\s0 for example), but it also
5557assumes that the same (machine) code can be used to call any watcher
5558callback: The watcher callbacks have different type signatures, but libev
5559calls them using an \f(CW\*(C`ev_watcher *\*(C'\fR internally.
5560.IP "null pointers and integer zero are represented by 0 bytes" 4
5561.IX Item "null pointers and integer zero are represented by 0 bytes"
5562Libev uses \f(CW\*(C`memset\*(C'\fR to initialise structs and arrays to \f(CW0\fR bytes, and
5563relies on this setting pointers and integers to null.
5564.IP "pointer accesses must be thread-atomic" 4
5565.IX Item "pointer accesses must be thread-atomic"
5566Accessing a pointer value must be atomic, it must both be readable and
5567writable in one piece \- this is the case on all current architectures.
5568.ie n .IP """sig_atomic_t volatile"" must be thread-atomic as well" 4
5569.el .IP "\f(CWsig_atomic_t volatile\fR must be thread-atomic as well" 4
5570.IX Item "sig_atomic_t volatile must be thread-atomic as well"
5571The type \f(CW\*(C`sig_atomic_t volatile\*(C'\fR (or whatever is defined as
5572\&\f(CW\*(C`EV_ATOMIC_T\*(C'\fR) must be atomic with respect to accesses from different
5573threads. This is not part of the specification for \f(CW\*(C`sig_atomic_t\*(C'\fR, but is
5574believed to be sufficiently portable.
5575.ie n .IP """sigprocmask"" must work in a threaded environment" 4
5576.el .IP "\f(CWsigprocmask\fR must work in a threaded environment" 4
5577.IX Item "sigprocmask must work in a threaded environment"
5578Libev uses \f(CW\*(C`sigprocmask\*(C'\fR to temporarily block signals. This is not
5579allowed in a threaded program (\f(CW\*(C`pthread_sigmask\*(C'\fR has to be used). Typical
5580pthread implementations will either allow \f(CW\*(C`sigprocmask\*(C'\fR in the \*(L"main
5581thread\*(R" or will block signals process-wide, both behaviours would
5582be compatible with libev. Interaction between \f(CW\*(C`sigprocmask\*(C'\fR and
5583\&\f(CW\*(C`pthread_sigmask\*(C'\fR could complicate things, however.
5584.Sp
5585The most portable way to handle signals is to block signals in all threads
5586except the initial one, and run the signal handling loop in the initial
5587thread as well.
5588.ie n .IP """long"" must be large enough for common memory allocation sizes" 4
5589.el .IP "\f(CWlong\fR must be large enough for common memory allocation sizes" 4
5590.IX Item "long must be large enough for common memory allocation sizes"
5591To improve portability and simplify its \s-1API,\s0 libev uses \f(CW\*(C`long\*(C'\fR internally
5592instead of \f(CW\*(C`size_t\*(C'\fR when allocating its data structures. On non-POSIX
5593systems (Microsoft...) this might be unexpectedly low, but is still at
5594least 31 bits everywhere, which is enough for hundreds of millions of
5595watchers.
5596.ie n .IP """double"" must hold a time value in seconds with enough accuracy" 4
5597.el .IP "\f(CWdouble\fR must hold a time value in seconds with enough accuracy" 4
5598.IX Item "double must hold a time value in seconds with enough accuracy"
5599The type \f(CW\*(C`double\*(C'\fR is used to represent timestamps. It is required to
5600have at least 51 bits of mantissa (and 9 bits of exponent), which is
5601good enough for at least into the year 4000 with millisecond accuracy
5602(the design goal for libev). This requirement is overfulfilled by
5603implementations using \s-1IEEE 754,\s0 which is basically all existing ones.
5604.Sp
5605With \s-1IEEE 754\s0 doubles, you get microsecond accuracy until at least the
5606year 2255 (and millisecond accuracy till the year 287396 \- by then, libev
5607is either obsolete or somebody patched it to use \f(CW\*(C`long double\*(C'\fR or
5608something like that, just kidding).
5609.PP
5610If you know of other additional requirements drop me a note.
2778.SH "COMPLEXITIES" 5611.SH "ALGORITHMIC COMPLEXITIES"
2779.IX Header "COMPLEXITIES" 5612.IX Header "ALGORITHMIC COMPLEXITIES"
2780In this section the complexities of (many of) the algorithms used inside 5613In this section the complexities of (many of) the algorithms used inside
2781libev will be explained. For complexity discussions about backends see the 5614libev will be documented. For complexity discussions about backends see
2782documentation for \f(CW\*(C`ev_default_init\*(C'\fR. 5615the documentation for \f(CW\*(C`ev_default_init\*(C'\fR.
2783.Sp 5616.PP
2784All of the following are about amortised time: If an array needs to be 5617All of the following are about amortised time: If an array needs to be
2785extended, libev needs to realloc and move the whole array, but this 5618extended, libev needs to realloc and move the whole array, but this
2786happens asymptotically never with higher number of elements, so O(1) might 5619happens asymptotically rarer with higher number of elements, so O(1) might
2787mean it might do a lengthy realloc operation in rare cases, but on average 5620mean that libev does a lengthy realloc operation in rare cases, but on
2788it is much faster and asymptotically approaches constant time. 5621average it is much faster and asymptotically approaches constant time.
2789.RS 4
2790.IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4 5622.IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4
2791.IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 5623.IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)"
2792This means that, when you have a watcher that triggers in one hour and 5624This means that, when you have a watcher that triggers in one hour and
2793there are 100 watchers that would trigger before that then inserting will 5625there are 100 watchers that would trigger before that, then inserting will
2794have to skip those 100 watchers. 5626have to skip roughly seven (\f(CW\*(C`ld 100\*(C'\fR) of these watchers.
2795.IP "Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)" 4 5627.IP "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)" 4
2796.IX Item "Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)" 5628.IX Item "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)"
2797That means that for changing a timer costs less than removing/adding them 5629That means that changing a timer costs less than removing/adding them,
2798as only the relative motion in the event queue has to be paid for. 5630as only the relative motion in the event queue has to be paid for.
2799.IP "Starting io/check/prepare/idle/signal/child watchers: O(1)" 4 5631.IP "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)" 4
2800.IX Item "Starting io/check/prepare/idle/signal/child watchers: O(1)" 5632.IX Item "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)"
2801These just add the watcher into an array or at the head of a list. 5633These just add the watcher into an array or at the head of a list.
5634.IP "Stopping check/prepare/idle/fork/async watchers: O(1)" 4
2802=item Stopping check/prepare/idle watchers: O(1) 5635.IX Item "Stopping check/prepare/idle/fork/async watchers: O(1)"
5636.PD 0
2803.IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4 5637.IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4
2804.IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))" 5638.IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))"
5639.PD
2805These watchers are stored in lists then need to be walked to find the 5640These watchers are stored in lists, so they need to be walked to find the
2806correct watcher to remove. The lists are usually short (you don't usually 5641correct watcher to remove. The lists are usually short (you don't usually
2807have many watchers waiting for the same fd or signal). 5642have many watchers waiting for the same fd or signal: one is typical, two
5643is rare).
2808.IP "Finding the next timer per loop iteration: O(1)" 4 5644.IP "Finding the next timer in each loop iteration: O(1)" 4
2809.IX Item "Finding the next timer per loop iteration: O(1)" 5645.IX Item "Finding the next timer in each loop iteration: O(1)"
2810.PD 0 5646By virtue of using a binary or 4\-heap, the next timer is always found at a
5647fixed position in the storage array.
2811.IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4 5648.IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4
2812.IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 5649.IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)"
2813.PD
2814A change means an I/O watcher gets started or stopped, which requires 5650A change means an I/O watcher gets started or stopped, which requires
2815libev to recalculate its status (and possibly tell the kernel). 5651libev to recalculate its status (and possibly tell the kernel, depending
2816.IP "Activating one watcher: O(1)" 4 5652on backend and whether \f(CW\*(C`ev_io_set\*(C'\fR was used).
2817.IX Item "Activating one watcher: O(1)" 5653.IP "Activating one watcher (putting it into the pending state): O(1)" 4
5654.IX Item "Activating one watcher (putting it into the pending state): O(1)"
2818.PD 0 5655.PD 0
2819.IP "Priority handling: O(number_of_priorities)" 4 5656.IP "Priority handling: O(number_of_priorities)" 4
2820.IX Item "Priority handling: O(number_of_priorities)" 5657.IX Item "Priority handling: O(number_of_priorities)"
2821.PD 5658.PD
2822Priorities are implemented by allocating some space for each 5659Priorities are implemented by allocating some space for each
2823priority. When doing priority-based operations, libev usually has to 5660priority. When doing priority-based operations, libev usually has to
2824linearly search all the priorities. 5661linearly search all the priorities, but starting/stopping and activating
2825.RE 5662watchers becomes O(1) with respect to priority handling.
2826.RS 4 5663.IP "Sending an ev_async: O(1)" 4
5664.IX Item "Sending an ev_async: O(1)"
5665.PD 0
5666.IP "Processing ev_async_send: O(number_of_async_watchers)" 4
5667.IX Item "Processing ev_async_send: O(number_of_async_watchers)"
5668.IP "Processing signals: O(max_signal_number)" 4
5669.IX Item "Processing signals: O(max_signal_number)"
5670.PD
5671Sending involves a system call \fIiff\fR there were no other \f(CW\*(C`ev_async_send\*(C'\fR
5672calls in the current loop iteration and the loop is currently
5673blocked. Checking for async and signal events involves iterating over all
5674running async watchers or all signal numbers.
5675.SH "PORTING FROM LIBEV 3.X TO 4.X"
5676.IX Header "PORTING FROM LIBEV 3.X TO 4.X"
5677The major version 4 introduced some incompatible changes to the \s-1API.\s0
5678.PP
5679At the moment, the \f(CW\*(C`ev.h\*(C'\fR header file provides compatibility definitions
5680for all changes, so most programs should still compile. The compatibility
5681layer might be removed in later versions of libev, so better update to the
5682new \s-1API\s0 early than late.
5683.ie n .IP """EV_COMPAT3"" backwards compatibility mechanism" 4
5684.el .IP "\f(CWEV_COMPAT3\fR backwards compatibility mechanism" 4
5685.IX Item "EV_COMPAT3 backwards compatibility mechanism"
5686The backward compatibility mechanism can be controlled by
5687\&\f(CW\*(C`EV_COMPAT3\*(C'\fR. See \*(L"\s-1PREPROCESSOR SYMBOLS/MACROS\*(R"\s0 in the \*(L"\s-1EMBEDDING\*(R"\s0
5688section.
5689.ie n .IP """ev_default_destroy"" and ""ev_default_fork"" have been removed" 4
5690.el .IP "\f(CWev_default_destroy\fR and \f(CWev_default_fork\fR have been removed" 4
5691.IX Item "ev_default_destroy and ev_default_fork have been removed"
5692These calls can be replaced easily by their \f(CW\*(C`ev_loop_xxx\*(C'\fR counterparts:
5693.Sp
5694.Vb 2
5695\& ev_loop_destroy (EV_DEFAULT_UC);
5696\& ev_loop_fork (EV_DEFAULT);
5697.Ve
5698.IP "function/symbol renames" 4
5699.IX Item "function/symbol renames"
5700A number of functions and symbols have been renamed:
5701.Sp
5702.Vb 3
5703\& ev_loop => ev_run
5704\& EVLOOP_NONBLOCK => EVRUN_NOWAIT
5705\& EVLOOP_ONESHOT => EVRUN_ONCE
5706\&
5707\& ev_unloop => ev_break
5708\& EVUNLOOP_CANCEL => EVBREAK_CANCEL
5709\& EVUNLOOP_ONE => EVBREAK_ONE
5710\& EVUNLOOP_ALL => EVBREAK_ALL
5711\&
5712\& EV_TIMEOUT => EV_TIMER
5713\&
5714\& ev_loop_count => ev_iteration
5715\& ev_loop_depth => ev_depth
5716\& ev_loop_verify => ev_verify
5717.Ve
5718.Sp
5719Most functions working on \f(CW\*(C`struct ev_loop\*(C'\fR objects don't have an
5720\&\f(CW\*(C`ev_loop_\*(C'\fR prefix, so it was removed; \f(CW\*(C`ev_loop\*(C'\fR, \f(CW\*(C`ev_unloop\*(C'\fR and
5721associated constants have been renamed to not collide with the \f(CW\*(C`struct
5722ev_loop\*(C'\fR anymore and \f(CW\*(C`EV_TIMER\*(C'\fR now follows the same naming scheme
5723as all other watcher types. Note that \f(CW\*(C`ev_loop_fork\*(C'\fR is still called
5724\&\f(CW\*(C`ev_loop_fork\*(C'\fR because it would otherwise clash with the \f(CW\*(C`ev_fork\*(C'\fR
5725typedef.
5726.ie n .IP """EV_MINIMAL"" mechanism replaced by ""EV_FEATURES""" 4
5727.el .IP "\f(CWEV_MINIMAL\fR mechanism replaced by \f(CWEV_FEATURES\fR" 4
5728.IX Item "EV_MINIMAL mechanism replaced by EV_FEATURES"
5729The preprocessor symbol \f(CW\*(C`EV_MINIMAL\*(C'\fR has been replaced by a different
5730mechanism, \f(CW\*(C`EV_FEATURES\*(C'\fR. Programs using \f(CW\*(C`EV_MINIMAL\*(C'\fR usually compile
5731and work, but the library code will of course be larger.
5732.SH "GLOSSARY"
5733.IX Header "GLOSSARY"
5734.IP "active" 4
5735.IX Item "active"
5736A watcher is active as long as it has been started and not yet stopped.
5737See \*(L"\s-1WATCHER STATES\*(R"\s0 for details.
5738.IP "application" 4
5739.IX Item "application"
5740In this document, an application is whatever is using libev.
5741.IP "backend" 4
5742.IX Item "backend"
5743The part of the code dealing with the operating system interfaces.
5744.IP "callback" 4
5745.IX Item "callback"
5746The address of a function that is called when some event has been
5747detected. Callbacks are being passed the event loop, the watcher that
5748received the event, and the actual event bitset.
5749.IP "callback/watcher invocation" 4
5750.IX Item "callback/watcher invocation"
5751The act of calling the callback associated with a watcher.
5752.IP "event" 4
5753.IX Item "event"
5754A change of state of some external event, such as data now being available
5755for reading on a file descriptor, time having passed or simply not having
5756any other events happening anymore.
5757.Sp
5758In libev, events are represented as single bits (such as \f(CW\*(C`EV_READ\*(C'\fR or
5759\&\f(CW\*(C`EV_TIMER\*(C'\fR).
5760.IP "event library" 4
5761.IX Item "event library"
5762A software package implementing an event model and loop.
5763.IP "event loop" 4
5764.IX Item "event loop"
5765An entity that handles and processes external events and converts them
5766into callback invocations.
5767.IP "event model" 4
5768.IX Item "event model"
5769The model used to describe how an event loop handles and processes
5770watchers and events.
5771.IP "pending" 4
5772.IX Item "pending"
5773A watcher is pending as soon as the corresponding event has been
5774detected. See \*(L"\s-1WATCHER STATES\*(R"\s0 for details.
5775.IP "real time" 4
5776.IX Item "real time"
5777The physical time that is observed. It is apparently strictly monotonic :)
5778.IP "wall-clock time" 4
5779.IX Item "wall-clock time"
5780The time and date as shown on clocks. Unlike real time, it can actually
5781be wrong and jump forwards and backwards, e.g. when you adjust your
5782clock.
5783.IP "watcher" 4
5784.IX Item "watcher"
5785A data structure that describes interest in certain events. Watchers need
5786to be started (attached to an event loop) before they can receive events.
2827.SH "AUTHOR" 5787.SH "AUTHOR"
2828.IX Header "AUTHOR" 5788.IX Header "AUTHOR"
2829Marc Lehmann <libev@schmorp.de>. 5789Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5790Magnusson and Emanuele Giaquinta, and minor corrections by many others.

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