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129.\" ======================================================================== 133.\" ========================================================================
130.\" 134.\"
131.IX Title ""<STANDARD INPUT>" 1" 135.IX Title "LIBEV 3"
132.TH "<STANDARD INPUT>" 1 "2007-12-09" "perl v5.8.8" "User Contributed Perl Documentation" 136.TH LIBEV 3 "2020-04-19" "libev-4.33" "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 occuring), 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
210(or thread) by executing the \fIevent loop\fR handler, and will then 236(or thread) by executing the \fIevent loop\fR handler, and will then
211communicate events via a callback mechanism. 237communicate events via a callback mechanism.
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 such. 276any calculations on it, you should treat it as some floating point value.
277.PP
278Unlike the name component \f(CW\*(C`stamp\*(C'\fR might indicate, it is also used for
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.
249.SH "GLOBAL FUNCTIONS" 303.SH "GLOBAL FUNCTIONS"
250.IX Header "GLOBAL FUNCTIONS" 304.IX Header "GLOBAL FUNCTIONS"
251These functions can be called anytime, even before initialising the 305These functions can be called anytime, even before initialising the
252library in any way. 306library in any way.
253.IP "ev_tstamp ev_time ()" 4 307.IP "ev_tstamp ev_time ()" 4
254.IX Item "ev_tstamp ev_time ()" 308.IX Item "ev_tstamp ev_time ()"
255Returns 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
256\&\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
257you 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.
313.IP "ev_sleep (ev_tstamp interval)" 4
314.IX Item "ev_sleep (ev_tstamp interval)"
315Sleep for the given interval: The current thread will be blocked
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
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).
258.IP "int ev_version_major ()" 4 324.IP "int ev_version_major ()" 4
259.IX Item "int ev_version_major ()" 325.IX Item "int ev_version_major ()"
260.PD 0 326.PD 0
261.IP "int ev_version_minor ()" 4 327.IP "int ev_version_minor ()" 4
262.IX Item "int ev_version_minor ()" 328.IX Item "int ev_version_minor ()"
263.PD 329.PD
264You can find out the major and minor version numbers of the library 330You can find out the major and minor \s-1ABI\s0 version numbers of the library
265you linked against by calling the functions \f(CW\*(C`ev_version_major\*(C'\fR and 331you linked against by calling the functions \f(CW\*(C`ev_version_major\*(C'\fR and
266\&\f(CW\*(C`ev_version_minor\*(C'\fR. If you want, you can compare against the global 332\&\f(CW\*(C`ev_version_minor\*(C'\fR. If you want, you can compare against the global
267symbols \f(CW\*(C`EV_VERSION_MAJOR\*(C'\fR and \f(CW\*(C`EV_VERSION_MINOR\*(C'\fR, which specify the 333symbols \f(CW\*(C`EV_VERSION_MAJOR\*(C'\fR and \f(CW\*(C`EV_VERSION_MINOR\*(C'\fR, which specify the
268version of the library your program was compiled against. 334version of the library your program was compiled against.
269.Sp 335.Sp
336These version numbers refer to the \s-1ABI\s0 version of the library, not the
337release version.
338.Sp
270Usually, it's a good idea to terminate if the major versions mismatch, 339Usually, it's a good idea to terminate if the major versions mismatch,
271as this indicates an incompatible change. Minor versions are usually 340as this indicates an incompatible change. Minor versions are usually
272compatible to older versions, so a larger minor version alone is usually 341compatible to older versions, so a larger minor version alone is usually
273not a problem. 342not a problem.
274.Sp 343.Sp
275Example: Make sure we haven't accidentally been linked against the wrong 344Example: Make sure we haven't accidentally been linked against the wrong
276version. 345version (note, however, that this will not detect other \s-1ABI\s0 mismatches,
346such as \s-1LFS\s0 or reentrancy).
277.Sp 347.Sp
278.Vb 3 348.Vb 3
279\& assert (("libev version mismatch", 349\& assert (("libev version mismatch",
280\& ev_version_major () == EV_VERSION_MAJOR 350\& ev_version_major () == EV_VERSION_MAJOR
281\& && ev_version_minor () >= EV_VERSION_MINOR)); 351\& && ev_version_minor () >= EV_VERSION_MINOR));
282.Ve 352.Ve
283.IP "unsigned int ev_supported_backends ()" 4 353.IP "unsigned int ev_supported_backends ()" 4
284.IX Item "unsigned int ev_supported_backends ()" 354.IX Item "unsigned int ev_supported_backends ()"
285Return 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
286value) compiled into this binary of libev (independent of their 356value) compiled into this binary of libev (independent of their
… …
289.Sp 359.Sp
290Example: 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
291a 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
292.Sp 362.Sp
293.Vb 2 363.Vb 2
294\& assert (("sorry, no epoll, no sex", 364\& assert (("sorry, no epoll, no sex",
295\& ev_supported_backends () & EVBACKEND_EPOLL)); 365\& ev_supported_backends () & EVBACKEND_EPOLL));
296.Ve 366.Ve
297.IP "unsigned int ev_recommended_backends ()" 4 367.IP "unsigned int ev_recommended_backends ()" 4
298.IX Item "unsigned int ev_recommended_backends ()" 368.IX Item "unsigned int ev_recommended_backends ()"
299Return 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
300recommended 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
301returned 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
302most BSDs and will not be autodetected unless you explicitly request it 373and will not be auto-detected unless you explicitly request it (assuming
303(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
304libev will probe for if you specify no backends explicitly. 375probe for if you specify no backends explicitly.
305.IP "unsigned int ev_embeddable_backends ()" 4 376.IP "unsigned int ev_embeddable_backends ()" 4
306.IX Item "unsigned int ev_embeddable_backends ()" 377.IX Item "unsigned int ev_embeddable_backends ()"
307Returns 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
308is the theoretical, all\-platform, value. To find which backends 379value is platform-specific but can include backends not available on the
309might be supported on the current system, you would need to look at 380current system. To find which embeddable backends might be supported on
310\&\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 ()
311recommended ones. 382& ev_supported_backends ()\*(C'\fR, likewise for recommended ones.
312.Sp 383.Sp
313See 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.
314.IP "ev_set_allocator (void *(*cb)(void *ptr, long size))" 4 385.IP "ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())" 4
315.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size))" 386.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())"
316Sets the allocation function to use (the prototype is similar \- the 387Sets the allocation function to use (the prototype is similar \- the
317semantics 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
318allocate and free memory (no surprises here). If it returns zero when 389used to allocate and free memory (no surprises here). If it returns zero
319memory 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
320potentially destructive action. The default is your system realloc 391or take some potentially destructive action.
321function. 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.
322.Sp 396.Sp
323You could override this function in high-availability programs to, say, 397You could override this function in high-availability programs to, say,
324free 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,
325or 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.
326.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
327Example: 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
328retries). 418retries.
329.Sp 419.Sp
330.Vb 6 420.Vb 8
331\& static void * 421\& static void *
332\& persistent_realloc (void *ptr, size_t size) 422\& persistent_realloc (void *ptr, size_t size)
333\& { 423\& {
424\& if (!size)
425\& {
426\& free (ptr);
427\& return 0;
428\& }
429\&
334\& for (;;) 430\& for (;;)
335\& { 431\& {
336\& void *newptr = realloc (ptr, size); 432\& void *newptr = realloc (ptr, size);
337.Ve 433\&
338.Sp
339.Vb 2
340\& if (newptr) 434\& if (newptr)
341\& return newptr; 435\& return newptr;
342.Ve 436\&
343.Sp
344.Vb 3
345\& sleep (60); 437\& sleep (60);
346\& } 438\& }
347\& } 439\& }
348.Ve 440\&
349.Sp
350.Vb 2
351\& ... 441\& ...
352\& ev_set_allocator (persistent_realloc); 442\& ev_set_allocator (persistent_realloc);
353.Ve 443.Ve
354.IP "ev_set_syserr_cb (void (*cb)(const char *msg));" 4 444.IP "ev_set_syserr_cb (void (*cb)(const char *msg) throw ())" 4
355.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg));" 445.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg) throw ())"
356Set the callback function to call on a retryable syscall error (such 446Set the callback function to call on a retryable system call error (such
357as failed select, poll, epoll_wait). The message is a printable string 447as failed select, poll, epoll_wait). The message is a printable string
358indicating the system call or subsystem causing the problem. If this 448indicating the system call or subsystem causing the problem. If this
359callback 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
360matter what, when it returns. That is, libev will generally retry the 450matter what, when it returns. That is, libev will generally retry the
361requested 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
362(such as abort). 452(such as abort).
363.Sp 453.Sp
364Example: This is basically the same thing that libev does internally, too. 454Example: This is basically the same thing that libev does internally, too.
… …
368\& fatal_error (const char *msg) 458\& fatal_error (const char *msg)
369\& { 459\& {
370\& perror (msg); 460\& perror (msg);
371\& abort (); 461\& abort ();
372\& } 462\& }
373.Ve 463\&
374.Sp
375.Vb 2
376\& ... 464\& ...
377\& ev_set_syserr_cb (fatal_error); 465\& ev_set_syserr_cb (fatal_error);
378.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.
379.SH "FUNCTIONS CONTROLLING THE EVENT LOOP" 479.SH "FUNCTIONS CONTROLLING EVENT LOOPS"
380.IX Header "FUNCTIONS CONTROLLING THE EVENT LOOP" 480.IX Header "FUNCTIONS CONTROLLING EVENT LOOPS"
381An 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
382types 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
383events, and dynamically created loops which do not. 483libev 3 had an \f(CW\*(C`ev_loop\*(C'\fR function colliding with the struct name).
384.PP 484.PP
385If 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
386in your main thread (or in a separate thread) and for each thread you 486supports child process events, and dynamically created event loops which
387create, you also create another event loop. Libev itself does no locking 487do not.
388whatsoever, so if you mix calls to the same event loop in different
389threads, make sure you lock (this is usually a bad idea, though, even if
390done correctly, because it's hideous and inefficient).
391.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4 488.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
392.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)" 489.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
393This 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
394yet 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
395false. 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
396flags. 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".
397.Sp 500.Sp
398If 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
399function. 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.
400.Sp 536.Sp
401The flags argument can be used to specify special behaviour or specific 537The flags argument can be used to specify special behaviour or specific
402backends 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).
403.Sp 539.Sp
404The following flags are supported: 540The following flags are supported:
… …
409The 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
410thing, believe me). 546thing, believe me).
411.ie n .IP """EVFLAG_NOENV""" 4 547.ie n .IP """EVFLAG_NOENV""" 4
412.el .IP "\f(CWEVFLAG_NOENV\fR" 4 548.el .IP "\f(CWEVFLAG_NOENV\fR" 4
413.IX Item "EVFLAG_NOENV" 549.IX Item "EVFLAG_NOENV"
414If 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
415or setgid) then libev will \fInot\fR look at the environment variable 551or setgid) then libev will \fInot\fR look at the environment variable
416\&\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
417override 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
418useful to try out specific backends to test their performance, or to work 554useful to try out specific backends to test their performance, to work
419around 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).
420.ie n .IP """EVFLAG_FORKCHECK""" 4 558.ie n .IP """EVFLAG_FORKCHECK""" 4
421.el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4 559.el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4
422.IX Item "EVFLAG_FORKCHECK" 560.IX Item "EVFLAG_FORKCHECK"
423Instead 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
424a 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.
425enabling this flag.
426.Sp 563.Sp
427This 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,
428and 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
429iterations and little real work, but is usually not noticeable (on my 566iterations and little real work, but is usually not noticeable (on my
430Linux 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
431without 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
432\&\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).
433.Sp 571.Sp
434The 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
435forget about forgetting to tell libev about forking) when you use this 573forget about forgetting to tell libev about forking, although you still
436flag. 574have to ignore \f(CW\*(C`SIGPIPE\*(C'\fR) when you use this flag.
437.Sp 575.Sp
438This 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
439environment 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_NOSIGMASK""" 4
599.el .IP "\f(CWEVFLAG_NOSIGMASK\fR" 4
600.IX Item "EVFLAG_NOSIGMASK"
601When this flag is specified, then libev will avoid to modify the signal
602mask. Specifically, this means you have to make sure signals are unblocked
603when you want to receive them.
604.Sp
605This behaviour is useful when you want to do your own signal handling, or
606want to handle signals only in specific threads and want to avoid libev
607unblocking the signals.
608.Sp
609It's also required by \s-1POSIX\s0 in a threaded program, as libev calls
610\&\f(CW\*(C`sigprocmask\*(C'\fR, whose behaviour is officially unspecified.
611.ie n .IP """EVFLAG_NOTIMERFD""" 4
612.el .IP "\f(CWEVFLAG_NOTIMERFD\fR" 4
613.IX Item "EVFLAG_NOTIMERFD"
614When this flag is specified, the libev will avoid using a \f(CW\*(C`timerfd\*(C'\fR to
615detect time jumps. It will still be able to detect time jumps, but takes
616longer and has a lower accuracy in doing so, but saves a file descriptor
617per loop.
618.Sp
619The current implementation only tries to use a \f(CW\*(C`timerfd\*(C'\fR when the first
620\&\f(CW\*(C`ev_periodic\*(C'\fR watcher is started and falls back on other methods if it
621cannot be created, but this behaviour might change in the future.
440.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4 622.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4
441.el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4 623.el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4
442.IX Item "EVBACKEND_SELECT (value 1, portable select backend)" 624.IX Item "EVBACKEND_SELECT (value 1, portable select backend)"
443This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as 625This is your standard \fBselect\fR\|(2) backend. Not \fIcompletely\fR standard, as
444libev tries to roll its own fd_set with no limits on the number of fds, 626libev tries to roll its own fd_set with no limits on the number of fds,
445but if that fails, expect a fairly low limit on the number of fds when 627but if that fails, expect a fairly low limit on the number of fds when
446using this backend. It doesn't scale too well (O(highest_fd)), but its usually 628using this backend. It doesn't scale too well (O(highest_fd)), but its
447the fastest backend for a low number of fds. 629usually the fastest backend for a low number of (low-numbered :) fds.
630.Sp
631To get good performance out of this backend you need a high amount of
632parallelism (most of the file descriptors should be busy). If you are
633writing a server, you should \f(CW\*(C`accept ()\*(C'\fR in a loop to accept as many
634connections as possible during one iteration. You might also want to have
635a look at \f(CW\*(C`ev_set_io_collect_interval ()\*(C'\fR to increase the amount of
636readiness notifications you get per iteration.
637.Sp
638This 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
639\&\f(CW\*(C`writefds\*(C'\fR set (and to work around Microsoft Windows bugs, also onto the
640\&\f(CW\*(C`exceptfds\*(C'\fR set on that platform).
448.ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4 641.ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4
449.el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4 642.el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4
450.IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)" 643.IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)"
451And this is your standard \fIpoll\fR\|(2) backend. It's more complicated than 644And this is your standard \fBpoll\fR\|(2) backend. It's more complicated
452select, but handles sparse fds better and has no artificial limit on the 645than select, but handles sparse fds better and has no artificial
453number of fds you can use (except it will slow down considerably with a 646limit on the number of fds you can use (except it will slow down
454lot of inactive fds). It scales similarly to select, i.e. O(total_fds). 647considerably with a lot of inactive fds). It scales similarly to select,
648i.e. O(total_fds). See the entry for \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR, above, for
649performance tips.
650.Sp
651This backend maps \f(CW\*(C`EV_READ\*(C'\fR to \f(CW\*(C`POLLIN | POLLERR | POLLHUP\*(C'\fR, and
652\&\f(CW\*(C`EV_WRITE\*(C'\fR to \f(CW\*(C`POLLOUT | POLLERR | POLLHUP\*(C'\fR.
455.ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4 653.ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
456.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4 654.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
457.IX Item "EVBACKEND_EPOLL (value 4, Linux)" 655.IX Item "EVBACKEND_EPOLL (value 4, Linux)"
656Use the Linux-specific \fBepoll\fR\|(7) interface (for both pre\- and post\-2.6.9
657kernels).
658.Sp
458For few fds, this backend is a bit little slower than poll and select, 659For few fds, this backend is a bit little slower than poll and select, but
459but it scales phenomenally better. While poll and select usually scale like 660it scales phenomenally better. While poll and select usually scale like
460O(total_fds) where n is the total number of fds (or the highest fd), epoll scales 661O(total_fds) where total_fds is the total number of fds (or the highest
461either O(1) or O(active_fds). 662fd), epoll scales either O(1) or O(active_fds).
462.Sp 663.Sp
664The epoll mechanism deserves honorable mention as the most misdesigned
665of the more advanced event mechanisms: mere annoyances include silently
666dropping file descriptors, requiring a system call per change per file
667descriptor (and unnecessary guessing of parameters), problems with dup,
668returning before the timeout value, resulting in additional iterations
669(and only giving 5ms accuracy while select on the same platform gives
6700.1ms) and so on. The biggest issue is fork races, however \- if a program
671forks then \fIboth\fR parent and child process have to recreate the epoll
672set, which can take considerable time (one syscall per file descriptor)
673and is of course hard to detect.
674.Sp
675Epoll is also notoriously buggy \- embedding epoll fds \fIshould\fR work,
676but of course \fIdoesn't\fR, and epoll just loves to report events for
677totally \fIdifferent\fR file descriptors (even already closed ones, so
678one cannot even remove them from the set) than registered in the set
679(especially on \s-1SMP\s0 systems). Libev tries to counter these spurious
680notifications by employing an additional generation counter and comparing
681that against the events to filter out spurious ones, recreating the set
682when required. Epoll also erroneously rounds down timeouts, but gives you
683no way to know when and by how much, so sometimes you have to busy-wait
684because epoll returns immediately despite a nonzero timeout. And last
685not least, it also refuses to work with some file descriptors which work
686perfectly fine with \f(CW\*(C`select\*(C'\fR (files, many character devices...).
687.Sp
688Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
689cobbled together in a hurry, no thought to design or interaction with
690others. Oh, the pain, will it ever stop...
691.Sp
463While stopping and starting an I/O watcher in the same iteration will 692While stopping, setting and starting an I/O watcher in the same iteration
464result in some caching, there is still a syscall per such incident 693will result in some caching, there is still a system call per such
465(because the fd could point to a different file description now), so its 694incident (because the same \fIfile descriptor\fR could point to a different
466best to avoid that. Also, \fIdup()\fRed file descriptors might not work very 695\&\fIfile description\fR now), so its best to avoid that. Also, \f(CW\*(C`dup ()\*(C'\fR'ed
467well if you register events for both fds. 696file descriptors might not work very well if you register events for both
697file descriptors.
468.Sp 698.Sp
469Please note that epoll sometimes generates spurious notifications, so you 699Best performance from this backend is achieved by not unregistering all
470need to use non-blocking I/O or other means to avoid blocking when no data 700watchers for a file descriptor until it has been closed, if possible,
471(or space) is available. 701i.e. keep at least one watcher active per fd at all times. Stopping and
702starting a watcher (without re-setting it) also usually doesn't cause
703extra overhead. A fork can both result in spurious notifications as well
704as in libev having to destroy and recreate the epoll object, which can
705take considerable time and thus should be avoided.
706.Sp
707All this means that, in practice, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR can be as fast or
708faster than epoll for maybe up to a hundred file descriptors, depending on
709the usage. So sad.
710.Sp
711While nominally embeddable in other event loops, this feature is broken in
712a lot of kernel revisions, but probably(!) works in current versions.
713.Sp
714This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
715\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
716.ie n .IP """EVBACKEND_LINUXAIO"" (value 64, Linux)" 4
717.el .IP "\f(CWEVBACKEND_LINUXAIO\fR (value 64, Linux)" 4
718.IX Item "EVBACKEND_LINUXAIO (value 64, Linux)"
719Use 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
720only tries to use it in 4.19+).
721.Sp
722This is another Linux train wreck of an event interface.
723.Sp
724If this backend works for you (as of this writing, it was very
725experimental), it is the best event interface available on Linux and might
726be well worth enabling it \- if it isn't available in your kernel this will
727be detected and this backend will be skipped.
728.Sp
729This backend can batch oneshot requests and supports a user-space ring
730buffer to receive events. It also doesn't suffer from most of the design
731problems of epoll (such as not being able to remove event sources from
732the epoll set), and generally sounds too good to be true. Because, this
733being the Linux kernel, of course it suffers from a whole new set of
734limitations, forcing you to fall back to epoll, inheriting all its design
735issues.
736.Sp
737For one, it is not easily embeddable (but probably could be done using
738an event fd at some extra overhead). It also is subject to a system wide
739limit that can be configured in \fI/proc/sys/fs/aio\-max\-nr\fR. If no \s-1AIO\s0
740requests are left, this backend will be skipped during initialisation, and
741will switch to epoll when the loop is active.
742.Sp
743Most problematic in practice, however, is that not all file descriptors
744work with it. For example, in Linux 5.1, \s-1TCP\s0 sockets, pipes, event fds,
745files, \fI/dev/null\fR and many others are supported, but ttys do not work
746properly (a known bug that the kernel developers don't care about, see
747<https://lore.kernel.org/patchwork/patch/1047453/>), so this is not
748(yet?) a generic event polling interface.
749.Sp
750Overall, it seems the Linux developers just don't want it to have a
751generic event handling mechanism other than \f(CW\*(C`select\*(C'\fR or \f(CW\*(C`poll\*(C'\fR.
752.Sp
753To work around all these problem, the current version of libev uses its
754epoll backend as a fallback for file descriptor types that do not work. Or
755falls back completely to epoll if the kernel acts up.
756.Sp
757This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
758\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
472.ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4 759.ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4
473.el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4 760.el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
474.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)" 761.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
475Kqueue deserves special mention, as at the time of this writing, it 762Kqueue deserves special mention, as at the time this backend was
476was broken on all BSDs except NetBSD (usually it doesn't work with 763implemented, it was broken on all BSDs except NetBSD (usually it doesn't
477anything but sockets and pipes, except on Darwin, where of course its 764work reliably with anything but sockets and pipes, except on Darwin,
478completely useless). For this reason its not being \*(L"autodetected\*(R" 765where of course it's completely useless). Unlike epoll, however, whose
479unless you explicitly specify it explicitly in the flags (i.e. using 766brokenness is by design, these kqueue bugs can be (and mostly have been)
480\&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR). 767fixed without \s-1API\s0 changes to existing programs. For this reason it's not
768being \*(L"auto-detected\*(R" on all platforms unless you explicitly specify it
769in the flags (i.e. using \f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or libev was compiled on a
770known-to-be-good (\-enough) system like NetBSD.
771.Sp
772You still can embed kqueue into a normal poll or select backend and use it
773only for sockets (after having made sure that sockets work with kqueue on
774the target platform). See \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
481.Sp 775.Sp
482It scales in the same way as the epoll backend, but the interface to the 776It scales in the same way as the epoll backend, but the interface to the
483kernel is more efficient (which says nothing about its actual speed, of 777kernel is more efficient (which says nothing about its actual speed, of
484course). While starting and stopping an I/O watcher does not cause an 778course). While stopping, setting and starting an I/O watcher does never
485extra syscall as with epoll, it still adds up to four event changes per 779cause an extra system call as with \f(CW\*(C`EVBACKEND_EPOLL\*(C'\fR, it still adds up to
486incident, so its best to avoid that. 780two event changes per incident. Support for \f(CW\*(C`fork ()\*(C'\fR is very bad (you
781might have to leak fds on fork, but it's more sane than epoll) and it
782drops fds silently in similarly hard-to-detect cases.
783.Sp
784This backend usually performs well under most conditions.
785.Sp
786While nominally embeddable in other event loops, this doesn't work
787everywhere, so you might need to test for this. And since it is broken
788almost everywhere, you should only use it when you have a lot of sockets
789(for which it usually works), by embedding it into another event loop
790(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
791also broken on \s-1OS X\s0)) and, did I mention it, using it only for sockets.
792.Sp
793This backend maps \f(CW\*(C`EV_READ\*(C'\fR into an \f(CW\*(C`EVFILT_READ\*(C'\fR kevent with
794\&\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
795\&\f(CW\*(C`NOTE_EOF\*(C'\fR.
487.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4 796.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
488.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4 797.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
489.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)" 798.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
490This is not implemented yet (and might never be). 799This is not implemented yet (and might never be, unless you send me an
800implementation). According to reports, \f(CW\*(C`/dev/poll\*(C'\fR only supports sockets
801and is not embeddable, which would limit the usefulness of this backend
802immensely.
491.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4 803.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
492.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4 804.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
493.IX Item "EVBACKEND_PORT (value 32, Solaris 10)" 805.IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
494This uses the Solaris 10 port mechanism. As with everything on Solaris, 806This uses the Solaris 10 event port mechanism. As with everything on Solaris,
495it's really slow, but it still scales very well (O(active_fds)). 807it's really slow, but it still scales very well (O(active_fds)).
496.Sp 808.Sp
497Please note that solaris ports can result in a lot of spurious 809While this backend scales well, it requires one system call per active
498notifications, so you need to use non-blocking I/O or other means to avoid 810file descriptor per loop iteration. For small and medium numbers of file
499blocking when no data (or space) is available. 811descriptors a \*(L"slow\*(R" \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR backend
812might perform better.
813.Sp
814On the positive side, this backend actually performed fully to
815specification in all tests and is fully embeddable, which is a rare feat
816among the OS-specific backends (I vastly prefer correctness over speed
817hacks).
818.Sp
819On the negative side, the interface is \fIbizarre\fR \- so bizarre that
820even sun itself gets it wrong in their code examples: The event polling
821function sometimes returns events to the caller even though an error
822occurred, but with no indication whether it has done so or not (yes, it's
823even documented that way) \- deadly for edge-triggered interfaces where you
824absolutely have to know whether an event occurred or not because you have
825to re-arm the watcher.
826.Sp
827Fortunately libev seems to be able to work around these idiocies.
828.Sp
829This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
830\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
500.ie n .IP """EVBACKEND_ALL""" 4 831.ie n .IP """EVBACKEND_ALL""" 4
501.el .IP "\f(CWEVBACKEND_ALL\fR" 4 832.el .IP "\f(CWEVBACKEND_ALL\fR" 4
502.IX Item "EVBACKEND_ALL" 833.IX Item "EVBACKEND_ALL"
503Try all backends (even potentially broken ones that wouldn't be tried 834Try all backends (even potentially broken ones that wouldn't be tried
504with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as 835with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as
505\&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR. 836\&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR.
837.Sp
838It is definitely not recommended to use this flag, use whatever
839\&\f(CW\*(C`ev_recommended_backends ()\*(C'\fR returns, or simply do not specify a backend
840at all.
841.ie n .IP """EVBACKEND_MASK""" 4
842.el .IP "\f(CWEVBACKEND_MASK\fR" 4
843.IX Item "EVBACKEND_MASK"
844Not a backend at all, but a mask to select all backend bits from a
845\&\f(CW\*(C`flags\*(C'\fR value, in case you want to mask out any backends from a flags
846value (e.g. when modifying the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR environment variable).
506.RE 847.RE
507.RS 4 848.RS 4
508.Sp 849.Sp
509If one or more of these are ored into the flags value, then only these 850If one or more of the backend flags are or'ed into the flags value,
510backends will be tried (in the reverse order as given here). If none are 851then only these backends will be tried (in the reverse order as listed
511specified, most compiled-in backend will be tried, usually in reverse 852here). If none are specified, all backends in \f(CW\*(C`ev_recommended_backends
512order of their flag values :) 853()\*(C'\fR will be tried.
513.Sp 854.Sp
514The most typical usage is like this: 855Example: Try to create a event loop that uses epoll and nothing else.
515.Sp 856.Sp
516.Vb 2 857.Vb 3
517\& if (!ev_default_loop (0)) 858\& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
518\& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?"); 859\& if (!epoller)
860\& fatal ("no epoll found here, maybe it hides under your chair");
519.Ve 861.Ve
520.Sp 862.Sp
521Restrict libev to the select and poll backends, and do not allow 863Example: Use whatever libev has to offer, but make sure that kqueue is
522environment settings to be taken into account: 864used if available.
523.Sp 865.Sp
524.Vb 1 866.Vb 1
525\& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV); 867\& struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
526.Ve 868.Ve
527.Sp 869.Sp
528Use whatever libev has to offer, but make sure that kqueue is used if 870Example: Similarly, on linux, you mgiht want to take advantage of the
529available (warning, breaks stuff, best use only with your own private 871linux aio backend if possible, but fall back to something else if that
530event loop and only if you know the \s-1OS\s0 supports your types of fds): 872isn't available.
531.Sp 873.Sp
532.Vb 1 874.Vb 1
533\& ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE); 875\& struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_LINUXAIO);
534.Ve 876.Ve
535.RE 877.RE
536.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
537.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
538Similar to \f(CW\*(C`ev_default_loop\*(C'\fR, but always creates a new event loop that is
539always distinct from the default loop. Unlike the default loop, it cannot
540handle signal and child watchers, and attempts to do so will be greeted by
541undefined behaviour (or a failed assertion if assertions are enabled).
542.Sp
543Example: Try to create a event loop that uses epoll and nothing else.
544.Sp
545.Vb 3
546\& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
547\& if (!epoller)
548\& fatal ("no epoll found here, maybe it hides under your chair");
549.Ve
550.IP "ev_default_destroy ()" 4 878.IP "ev_loop_destroy (loop)" 4
551.IX Item "ev_default_destroy ()" 879.IX Item "ev_loop_destroy (loop)"
552Destroys the default loop again (frees all memory and kernel state 880Destroys an event loop object (frees all memory and kernel state
553etc.). None of the active event watchers will be stopped in the normal 881etc.). None of the active event watchers will be stopped in the normal
554sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your 882sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your
555responsibility to either stop all watchers cleanly yoursef \fIbefore\fR 883responsibility to either stop all watchers cleanly yourself \fIbefore\fR
556calling this function, or cope with the fact afterwards (which is usually 884calling this function, or cope with the fact afterwards (which is usually
557the easiest thing, youc na just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them 885the easiest thing, you can just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them
558for example). 886for example).
559.IP "ev_loop_destroy (loop)" 4
560.IX Item "ev_loop_destroy (loop)"
561Like \f(CW\*(C`ev_default_destroy\*(C'\fR, but destroys an event loop created by an
562earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR.
563.IP "ev_default_fork ()" 4
564.IX Item "ev_default_fork ()"
565This function reinitialises the kernel state for backends that have
566one. Despite the name, you can call it anytime, but it makes most sense
567after forking, in either the parent or child process (or both, but that
568again makes little sense).
569.Sp 887.Sp
570You \fImust\fR call this function in the child process after forking if and 888Note that certain global state, such as signal state (and installed signal
571only if you want to use the event library in both processes. If you just 889handlers), will not be freed by this function, and related watchers (such
572fork+exec, you don't have to call it. 890as signal and child watchers) would need to be stopped manually.
573.Sp 891.Sp
574The function itself is quite fast and it's usually not a problem to call 892This function is normally used on loop objects allocated by
575it just in case after a fork. To make this easy, the function will fit in 893\&\f(CW\*(C`ev_loop_new\*(C'\fR, but it can also be used on the default loop returned by
576quite nicely into a call to \f(CW\*(C`pthread_atfork\*(C'\fR: 894\&\f(CW\*(C`ev_default_loop\*(C'\fR, in which case it is not thread-safe.
577.Sp 895.Sp
578.Vb 1 896Note that it is not advisable to call this function on the default loop
579\& pthread_atfork (0, 0, ev_default_fork); 897except in the rare occasion where you really need to free its resources.
580.Ve 898If you need dynamically allocated loops it is better to use \f(CW\*(C`ev_loop_new\*(C'\fR
581.Sp 899and \f(CW\*(C`ev_loop_destroy\*(C'\fR.
582At the moment, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and \f(CW\*(C`EVBACKEND_POLL\*(C'\fR are safe to use
583without calling this function, so if you force one of those backends you
584do not need to care.
585.IP "ev_loop_fork (loop)" 4 900.IP "ev_loop_fork (loop)" 4
586.IX Item "ev_loop_fork (loop)" 901.IX Item "ev_loop_fork (loop)"
587Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by 902This function sets a flag that causes subsequent \f(CW\*(C`ev_run\*(C'\fR iterations
588\&\f(CW\*(C`ev_loop_new\*(C'\fR. Yes, you have to call this on every allocated event loop 903to reinitialise the kernel state for backends that have one. Despite
589after fork, and how you do this is entirely your own problem. 904the name, you can call it anytime you are allowed to start or stop
905watchers (except inside an \f(CW\*(C`ev_prepare\*(C'\fR callback), but it makes most
906sense after forking, in the child process. You \fImust\fR call it (or use
907\&\f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR) in the child before resuming or calling \f(CW\*(C`ev_run\*(C'\fR.
908.Sp
909In addition, if you want to reuse a loop (via this function or
910\&\f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR), you \fIalso\fR have to ignore \f(CW\*(C`SIGPIPE\*(C'\fR.
911.Sp
912Again, you \fIhave\fR to call it on \fIany\fR loop that you want to re-use after
913a fork, \fIeven if you do not plan to use the loop in the parent\fR. This is
914because some kernel interfaces *cough* \fIkqueue\fR *cough* do funny things
915during fork.
916.Sp
917On the other hand, you only need to call this function in the child
918process if and only if you want to use the event loop in the child. If
919you just fork+exec or create a new loop in the child, you don't have to
920call it at all (in fact, \f(CW\*(C`epoll\*(C'\fR is so badly broken that it makes a
921difference, but libev will usually detect this case on its own and do a
922costly reset of the backend).
923.Sp
924The function itself is quite fast and it's usually not a problem to call
925it just in case after a fork.
926.Sp
927Example: Automate calling \f(CW\*(C`ev_loop_fork\*(C'\fR on the default loop when
928using pthreads.
929.Sp
930.Vb 5
931\& static void
932\& post_fork_child (void)
933\& {
934\& ev_loop_fork (EV_DEFAULT);
935\& }
936\&
937\& ...
938\& pthread_atfork (0, 0, post_fork_child);
939.Ve
940.IP "int ev_is_default_loop (loop)" 4
941.IX Item "int ev_is_default_loop (loop)"
942Returns true when the given loop is, in fact, the default loop, and false
943otherwise.
590.IP "unsigned int ev_loop_count (loop)" 4 944.IP "unsigned int ev_iteration (loop)" 4
591.IX Item "unsigned int ev_loop_count (loop)" 945.IX Item "unsigned int ev_iteration (loop)"
592Returns the count of loop iterations for the loop, which is identical to 946Returns the current iteration count for the event loop, which is identical
593the number of times libev did poll for new events. It starts at \f(CW0\fR and 947to the number of times libev did poll for new events. It starts at \f(CW0\fR
594happily wraps around with enough iterations. 948and happily wraps around with enough iterations.
595.Sp 949.Sp
596This value can sometimes be useful as a generation counter of sorts (it 950This value can sometimes be useful as a generation counter of sorts (it
597\&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with 951\&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with
598\&\f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR calls. 952\&\f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR calls \- and is incremented between the
953prepare and check phases.
954.IP "unsigned int ev_depth (loop)" 4
955.IX Item "unsigned int ev_depth (loop)"
956Returns the number of times \f(CW\*(C`ev_run\*(C'\fR was entered minus the number of
957times \f(CW\*(C`ev_run\*(C'\fR was exited normally, in other words, the recursion depth.
958.Sp
959Outside \f(CW\*(C`ev_run\*(C'\fR, this number is zero. In a callback, this number is
960\&\f(CW1\fR, unless \f(CW\*(C`ev_run\*(C'\fR was invoked recursively (or from another thread),
961in which case it is higher.
962.Sp
963Leaving \f(CW\*(C`ev_run\*(C'\fR abnormally (setjmp/longjmp, cancelling the thread,
964throwing an exception etc.), doesn't count as \*(L"exit\*(R" \- consider this
965as a hint to avoid such ungentleman-like behaviour unless it's really
966convenient, in which case it is fully supported.
599.IP "unsigned int ev_backend (loop)" 4 967.IP "unsigned int ev_backend (loop)" 4
600.IX Item "unsigned int ev_backend (loop)" 968.IX Item "unsigned int ev_backend (loop)"
601Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in 969Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
602use. 970use.
603.IP "ev_tstamp ev_now (loop)" 4 971.IP "ev_tstamp ev_now (loop)" 4
604.IX Item "ev_tstamp ev_now (loop)" 972.IX Item "ev_tstamp ev_now (loop)"
605Returns the current \*(L"event loop time\*(R", which is the time the event loop 973Returns the current \*(L"event loop time\*(R", which is the time the event loop
606received events and started processing them. This timestamp does not 974received events and started processing them. This timestamp does not
607change as long as callbacks are being processed, and this is also the base 975change as long as callbacks are being processed, and this is also the base
608time used for relative timers. You can treat it as the timestamp of the 976time used for relative timers. You can treat it as the timestamp of the
609event occuring (or more correctly, libev finding out about it). 977event occurring (or more correctly, libev finding out about it).
978.IP "ev_now_update (loop)" 4
979.IX Item "ev_now_update (loop)"
980Establishes the current time by querying the kernel, updating the time
981returned by \f(CW\*(C`ev_now ()\*(C'\fR in the progress. This is a costly operation and
982is usually done automatically within \f(CW\*(C`ev_run ()\*(C'\fR.
983.Sp
984This function is rarely useful, but when some event callback runs for a
985very long time without entering the event loop, updating libev's idea of
986the current time is a good idea.
987.Sp
988See also \*(L"The special problem of time updates\*(R" in the \f(CW\*(C`ev_timer\*(C'\fR section.
989.IP "ev_suspend (loop)" 4
990.IX Item "ev_suspend (loop)"
991.PD 0
992.IP "ev_resume (loop)" 4
993.IX Item "ev_resume (loop)"
994.PD
995These two functions suspend and resume an event loop, for use when the
996loop is not used for a while and timeouts should not be processed.
997.Sp
998A typical use case would be an interactive program such as a game: When
999the user presses \f(CW\*(C`^Z\*(C'\fR to suspend the game and resumes it an hour later it
1000would be best to handle timeouts as if no time had actually passed while
1001the program was suspended. This can be achieved by calling \f(CW\*(C`ev_suspend\*(C'\fR
1002in your \f(CW\*(C`SIGTSTP\*(C'\fR handler, sending yourself a \f(CW\*(C`SIGSTOP\*(C'\fR and calling
1003\&\f(CW\*(C`ev_resume\*(C'\fR directly afterwards to resume timer processing.
1004.Sp
1005Effectively, all \f(CW\*(C`ev_timer\*(C'\fR watchers will be delayed by the time spend
1006between \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
1007will be rescheduled (that is, they will lose any events that would have
1008occurred while suspended).
1009.Sp
1010After calling \f(CW\*(C`ev_suspend\*(C'\fR you \fBmust not\fR call \fIany\fR function on the
1011given loop other than \f(CW\*(C`ev_resume\*(C'\fR, and you \fBmust not\fR call \f(CW\*(C`ev_resume\*(C'\fR
1012without a previous call to \f(CW\*(C`ev_suspend\*(C'\fR.
1013.Sp
1014Calling \f(CW\*(C`ev_suspend\*(C'\fR/\f(CW\*(C`ev_resume\*(C'\fR has the side effect of updating the
1015event loop time (see \f(CW\*(C`ev_now_update\*(C'\fR).
610.IP "ev_loop (loop, int flags)" 4 1016.IP "bool ev_run (loop, int flags)" 4
611.IX Item "ev_loop (loop, int flags)" 1017.IX Item "bool ev_run (loop, int flags)"
612Finally, this is it, the event handler. This function usually is called 1018Finally, this is it, the event handler. This function usually is called
613after you initialised all your watchers and you want to start handling 1019after you have initialised all your watchers and you want to start
614events. 1020handling events. It will ask the operating system for any new events, call
1021the watcher callbacks, and then repeat the whole process indefinitely: This
1022is why event loops are called \fIloops\fR.
615.Sp 1023.Sp
616If the flags argument is specified as \f(CW0\fR, it will not return until 1024If the flags argument is specified as \f(CW0\fR, it will keep handling events
617either no event watchers are active anymore or \f(CW\*(C`ev_unloop\*(C'\fR was called. 1025until either no event watchers are active anymore or \f(CW\*(C`ev_break\*(C'\fR was
1026called.
618.Sp 1027.Sp
1028The return value is false if there are no more active watchers (which
1029usually means \*(L"all jobs done\*(R" or \*(L"deadlock\*(R"), and true in all other cases
1030(which usually means " you should call \f(CW\*(C`ev_run\*(C'\fR again").
1031.Sp
619Please note that an explicit \f(CW\*(C`ev_unloop\*(C'\fR is usually better than 1032Please note that an explicit \f(CW\*(C`ev_break\*(C'\fR is usually better than
620relying on all watchers to be stopped when deciding when a program has 1033relying on all watchers to be stopped when deciding when a program has
621finished (especially in interactive programs), but having a program that 1034finished (especially in interactive programs), but having a program
622automatically loops as long as it has to and no longer by virtue of 1035that automatically loops as long as it has to and no longer by virtue
623relying on its watchers stopping correctly is a thing of beauty. 1036of relying on its watchers stopping correctly, that is truly a thing of
1037beauty.
624.Sp 1038.Sp
1039This function is \fImostly\fR exception-safe \- you can break out of a
1040\&\f(CW\*(C`ev_run\*(C'\fR call by calling \f(CW\*(C`longjmp\*(C'\fR in a callback, throwing a \*(C+
1041exception and so on. This does not decrement the \f(CW\*(C`ev_depth\*(C'\fR value, nor
1042will it clear any outstanding \f(CW\*(C`EVBREAK_ONE\*(C'\fR breaks.
1043.Sp
625A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle 1044A flags value of \f(CW\*(C`EVRUN_NOWAIT\*(C'\fR will look for new events, will handle
626those events and any outstanding ones, but will not block your process in 1045those events and any already outstanding ones, but will not wait and
627case there are no events and will return after one iteration of the loop. 1046block your process in case there are no events and will return after one
1047iteration of the loop. This is sometimes useful to poll and handle new
1048events while doing lengthy calculations, to keep the program responsive.
628.Sp 1049.Sp
629A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if 1050A flags value of \f(CW\*(C`EVRUN_ONCE\*(C'\fR will look for new events (waiting if
630neccessary) and will handle those and any outstanding ones. It will block 1051necessary) and will handle those and any already outstanding ones. It
631your process until at least one new event arrives, and will return after 1052will block your process until at least one new event arrives (which could
632one iteration of the loop. This is useful if you are waiting for some 1053be an event internal to libev itself, so there is no guarantee that a
633external event in conjunction with something not expressible using other 1054user-registered callback will be called), and will return after one
1055iteration of the loop.
1056.Sp
1057This is useful if you are waiting for some external event in conjunction
1058with something not expressible using other libev watchers (i.e. "roll your
634libev watchers. However, a pair of \f(CW\*(C`ev_prepare\*(C'\fR/\f(CW\*(C`ev_check\*(C'\fR watchers is 1059own \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
635usually a better approach for this kind of thing. 1060usually a better approach for this kind of thing.
636.Sp 1061.Sp
637Here are the gory details of what \f(CW\*(C`ev_loop\*(C'\fR does: 1062Here are the gory details of what \f(CW\*(C`ev_run\*(C'\fR does (this is for your
1063understanding, not a guarantee that things will work exactly like this in
1064future versions):
638.Sp 1065.Sp
639.Vb 19 1066.Vb 10
1067\& \- Increment loop depth.
1068\& \- Reset the ev_break status.
640\& - Before the first iteration, call any pending watchers. 1069\& \- Before the first iteration, call any pending watchers.
641\& * If there are no active watchers (reference count is zero), return. 1070\& LOOP:
642\& - Queue all prepare watchers and then call all outstanding watchers. 1071\& \- If EVFLAG_FORKCHECK was used, check for a fork.
1072\& \- If a fork was detected (by any means), queue and call all fork watchers.
1073\& \- Queue and call all prepare watchers.
1074\& \- If ev_break was called, goto FINISH.
643\& - If we have been forked, recreate the kernel state. 1075\& \- If we have been forked, detach and recreate the kernel state
1076\& as to not disturb the other process.
644\& - Update the kernel state with all outstanding changes. 1077\& \- Update the kernel state with all outstanding changes.
645\& - Update the "event loop time". 1078\& \- Update the "event loop time" (ev_now ()).
646\& - Calculate for how long to block. 1079\& \- Calculate for how long to sleep or block, if at all
1080\& (active idle watchers, EVRUN_NOWAIT or not having
1081\& any active watchers at all will result in not sleeping).
1082\& \- Sleep if the I/O and timer collect interval say so.
1083\& \- Increment loop iteration counter.
647\& - Block the process, waiting for any events. 1084\& \- Block the process, waiting for any events.
648\& - Queue all outstanding I/O (fd) events. 1085\& \- Queue all outstanding I/O (fd) events.
649\& - Update the "event loop time" and do time jump handling. 1086\& \- Update the "event loop time" (ev_now ()), and do time jump adjustments.
650\& - Queue all outstanding timers. 1087\& \- Queue all expired timers.
651\& - Queue all outstanding periodics. 1088\& \- Queue all expired periodics.
652\& - If no events are pending now, queue all idle watchers. 1089\& \- Queue all idle watchers with priority higher than that of pending events.
653\& - Queue all check watchers. 1090\& \- Queue all check watchers.
654\& - Call all queued watchers in reverse order (i.e. check watchers first). 1091\& \- Call all queued watchers in reverse order (i.e. check watchers first).
655\& Signals and child watchers are implemented as I/O watchers, and will 1092\& Signals and child watchers are implemented as I/O watchers, and will
656\& be handled here by queueing them when their watcher gets executed. 1093\& be handled here by queueing them when their watcher gets executed.
657\& - If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK 1094\& \- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
658\& were used, return, otherwise continue with step *. 1095\& were used, or there are no active watchers, goto FINISH, otherwise
1096\& continue with step LOOP.
1097\& FINISH:
1098\& \- Reset the ev_break status iff it was EVBREAK_ONE.
1099\& \- Decrement the loop depth.
1100\& \- Return.
659.Ve 1101.Ve
660.Sp 1102.Sp
661Example: Queue some jobs and then loop until no events are outsanding 1103Example: Queue some jobs and then loop until no events are outstanding
662anymore. 1104anymore.
663.Sp 1105.Sp
664.Vb 4 1106.Vb 4
665\& ... queue jobs here, make sure they register event watchers as long 1107\& ... queue jobs here, make sure they register event watchers as long
666\& ... as they still have work to do (even an idle watcher will do..) 1108\& ... as they still have work to do (even an idle watcher will do..)
667\& ev_loop (my_loop, 0); 1109\& ev_run (my_loop, 0);
668\& ... jobs done. yeah! 1110\& ... jobs done or somebody called break. yeah!
669.Ve 1111.Ve
670.IP "ev_unloop (loop, how)" 4 1112.IP "ev_break (loop, how)" 4
671.IX Item "ev_unloop (loop, how)" 1113.IX Item "ev_break (loop, how)"
672Can be used to make a call to \f(CW\*(C`ev_loop\*(C'\fR return early (but only after it 1114Can be used to make a call to \f(CW\*(C`ev_run\*(C'\fR return early (but only after it
673has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either 1115has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either
674\&\f(CW\*(C`EVUNLOOP_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_loop\*(C'\fR call return, or 1116\&\f(CW\*(C`EVBREAK_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_run\*(C'\fR call return, or
675\&\f(CW\*(C`EVUNLOOP_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_loop\*(C'\fR calls return. 1117\&\f(CW\*(C`EVBREAK_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_run\*(C'\fR calls return.
1118.Sp
1119This \*(L"break state\*(R" will be cleared on the next call to \f(CW\*(C`ev_run\*(C'\fR.
1120.Sp
1121It is safe to call \f(CW\*(C`ev_break\*(C'\fR from outside any \f(CW\*(C`ev_run\*(C'\fR calls, too, in
1122which case it will have no effect.
676.IP "ev_ref (loop)" 4 1123.IP "ev_ref (loop)" 4
677.IX Item "ev_ref (loop)" 1124.IX Item "ev_ref (loop)"
678.PD 0 1125.PD 0
679.IP "ev_unref (loop)" 4 1126.IP "ev_unref (loop)" 4
680.IX Item "ev_unref (loop)" 1127.IX Item "ev_unref (loop)"
681.PD 1128.PD
682Ref/unref can be used to add or remove a reference count on the event 1129Ref/unref can be used to add or remove a reference count on the event
683loop: Every watcher keeps one reference, and as long as the reference 1130loop: Every watcher keeps one reference, and as long as the reference
684count is nonzero, \f(CW\*(C`ev_loop\*(C'\fR will not return on its own. If you have 1131count is nonzero, \f(CW\*(C`ev_run\*(C'\fR will not return on its own.
685a watcher you never unregister that should not keep \f(CW\*(C`ev_loop\*(C'\fR from 1132.Sp
686returning, \fIev_unref()\fR after starting, and \fIev_ref()\fR before stopping it. For 1133This is useful when you have a watcher that you never intend to
1134unregister, but that nevertheless should not keep \f(CW\*(C`ev_run\*(C'\fR from
1135returning. In such a case, call \f(CW\*(C`ev_unref\*(C'\fR after starting, and \f(CW\*(C`ev_ref\*(C'\fR
1136before stopping it.
1137.Sp
687example, libev itself uses this for its internal signal pipe: It is not 1138As an example, libev itself uses this for its internal signal pipe: It
688visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from exiting if 1139is not visible to the libev user and should not keep \f(CW\*(C`ev_run\*(C'\fR from
689no event watchers registered by it are active. It is also an excellent 1140exiting if no event watchers registered by it are active. It is also an
690way to do this for generic recurring timers or from within third-party 1141excellent way to do this for generic recurring timers or from within
691libraries. Just remember to \fIunref after start\fR and \fIref before stop\fR. 1142third-party libraries. Just remember to \fIunref after start\fR and \fIref
1143before stop\fR (but only if the watcher wasn't active before, or was active
1144before, respectively. Note also that libev might stop watchers itself
1145(e.g. non-repeating timers) in which case you have to \f(CW\*(C`ev_ref\*(C'\fR
1146in the callback).
692.Sp 1147.Sp
693Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_loop\*(C'\fR 1148Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_run\*(C'\fR
694running when nothing else is active. 1149running when nothing else is active.
695.Sp 1150.Sp
696.Vb 4 1151.Vb 4
697\& struct ev_signal exitsig; 1152\& ev_signal exitsig;
698\& ev_signal_init (&exitsig, sig_cb, SIGINT); 1153\& ev_signal_init (&exitsig, sig_cb, SIGINT);
699\& ev_signal_start (loop, &exitsig); 1154\& ev_signal_start (loop, &exitsig);
700\& evf_unref (loop); 1155\& ev_unref (loop);
701.Ve 1156.Ve
702.Sp 1157.Sp
703Example: For some weird reason, unregister the above signal handler again. 1158Example: For some weird reason, unregister the above signal handler again.
704.Sp 1159.Sp
705.Vb 2 1160.Vb 2
706\& ev_ref (loop); 1161\& ev_ref (loop);
707\& ev_signal_stop (loop, &exitsig); 1162\& ev_signal_stop (loop, &exitsig);
708.Ve 1163.Ve
1164.IP "ev_set_io_collect_interval (loop, ev_tstamp interval)" 4
1165.IX Item "ev_set_io_collect_interval (loop, ev_tstamp interval)"
1166.PD 0
1167.IP "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 4
1168.IX Item "ev_set_timeout_collect_interval (loop, ev_tstamp interval)"
1169.PD
1170These advanced functions influence the time that libev will spend waiting
1171for events. Both time intervals are by default \f(CW0\fR, meaning that libev
1172will try to invoke timer/periodic callbacks and I/O callbacks with minimum
1173latency.
1174.Sp
1175Setting these to a higher value (the \f(CW\*(C`interval\*(C'\fR \fImust\fR be >= \f(CW0\fR)
1176allows libev to delay invocation of I/O and timer/periodic callbacks
1177to increase efficiency of loop iterations (or to increase power-saving
1178opportunities).
1179.Sp
1180The idea is that sometimes your program runs just fast enough to handle
1181one (or very few) event(s) per loop iteration. While this makes the
1182program responsive, it also wastes a lot of \s-1CPU\s0 time to poll for new
1183events, especially with backends like \f(CW\*(C`select ()\*(C'\fR which have a high
1184overhead for the actual polling but can deliver many events at once.
1185.Sp
1186By setting a higher \fIio collect interval\fR you allow libev to spend more
1187time collecting I/O events, so you can handle more events per iteration,
1188at the cost of increasing latency. Timeouts (both \f(CW\*(C`ev_periodic\*(C'\fR and
1189\&\f(CW\*(C`ev_timer\*(C'\fR) will not be affected. Setting this to a non-null value will
1190introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations. The
1191sleep time ensures that libev will not poll for I/O events more often then
1192once per this interval, on average (as long as the host time resolution is
1193good enough).
1194.Sp
1195Likewise, by setting a higher \fItimeout collect interval\fR you allow libev
1196to spend more time collecting timeouts, at the expense of increased
1197latency/jitter/inexactness (the watcher callback will be called
1198later). \f(CW\*(C`ev_io\*(C'\fR watchers will not be affected. Setting this to a non-null
1199value will not introduce any overhead in libev.
1200.Sp
1201Many (busy) programs can usually benefit by setting the I/O collect
1202interval to a value near \f(CW0.1\fR or so, which is often enough for
1203interactive servers (of course not for games), likewise for timeouts. It
1204usually doesn't make much sense to set it to a lower value than \f(CW0.01\fR,
1205as this approaches the timing granularity of most systems. Note that if
1206you do transactions with the outside world and you can't increase the
1207parallelity, then this setting will limit your transaction rate (if you
1208need to poll once per transaction and the I/O collect interval is 0.01,
1209then you can't do more than 100 transactions per second).
1210.Sp
1211Setting the \fItimeout collect interval\fR can improve the opportunity for
1212saving power, as the program will \*(L"bundle\*(R" timer callback invocations that
1213are \*(L"near\*(R" in time together, by delaying some, thus reducing the number of
1214times the process sleeps and wakes up again. Another useful technique to
1215reduce iterations/wake\-ups is to use \f(CW\*(C`ev_periodic\*(C'\fR watchers and make sure
1216they fire on, say, one-second boundaries only.
1217.Sp
1218Example: we only need 0.1s timeout granularity, and we wish not to poll
1219more often than 100 times per second:
1220.Sp
1221.Vb 2
1222\& ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
1223\& ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
1224.Ve
1225.IP "ev_invoke_pending (loop)" 4
1226.IX Item "ev_invoke_pending (loop)"
1227This call will simply invoke all pending watchers while resetting their
1228pending state. Normally, \f(CW\*(C`ev_run\*(C'\fR does this automatically when required,
1229but when overriding the invoke callback this call comes handy. This
1230function can be invoked from a watcher \- this can be useful for example
1231when you want to do some lengthy calculation and want to pass further
1232event handling to another thread (you still have to make sure only one
1233thread executes within \f(CW\*(C`ev_invoke_pending\*(C'\fR or \f(CW\*(C`ev_run\*(C'\fR of course).
1234.IP "int ev_pending_count (loop)" 4
1235.IX Item "int ev_pending_count (loop)"
1236Returns the number of pending watchers \- zero indicates that no watchers
1237are pending.
1238.IP "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(\s-1EV_P\s0))" 4
1239.IX Item "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))"
1240This overrides the invoke pending functionality of the loop: Instead of
1241invoking all pending watchers when there are any, \f(CW\*(C`ev_run\*(C'\fR will call
1242this callback instead. This is useful, for example, when you want to
1243invoke the actual watchers inside another context (another thread etc.).
1244.Sp
1245If you want to reset the callback, use \f(CW\*(C`ev_invoke_pending\*(C'\fR as new
1246callback.
1247.IP "ev_set_loop_release_cb (loop, void (*release)(\s-1EV_P\s0) throw (), void (*acquire)(\s-1EV_P\s0) throw ())" 4
1248.IX Item "ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())"
1249Sometimes you want to share the same loop between multiple threads. This
1250can be done relatively simply by putting mutex_lock/unlock calls around
1251each call to a libev function.
1252.Sp
1253However, \f(CW\*(C`ev_run\*(C'\fR can run an indefinite time, so it is not feasible
1254to wait for it to return. One way around this is to wake up the event
1255loop via \f(CW\*(C`ev_break\*(C'\fR and \f(CW\*(C`ev_async_send\*(C'\fR, another way is to set these
1256\&\fIrelease\fR and \fIacquire\fR callbacks on the loop.
1257.Sp
1258When set, then \f(CW\*(C`release\*(C'\fR will be called just before the thread is
1259suspended waiting for new events, and \f(CW\*(C`acquire\*(C'\fR is called just
1260afterwards.
1261.Sp
1262Ideally, \f(CW\*(C`release\*(C'\fR will just call your mutex_unlock function, and
1263\&\f(CW\*(C`acquire\*(C'\fR will just call the mutex_lock function again.
1264.Sp
1265While event loop modifications are allowed between invocations of
1266\&\f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR (that's their only purpose after all), no
1267modifications done will affect the event loop, i.e. adding watchers will
1268have no effect on the set of file descriptors being watched, or the time
1269waited. Use an \f(CW\*(C`ev_async\*(C'\fR watcher to wake up \f(CW\*(C`ev_run\*(C'\fR when you want it
1270to take note of any changes you made.
1271.Sp
1272In theory, threads executing \f(CW\*(C`ev_run\*(C'\fR will be async-cancel safe between
1273invocations of \f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR.
1274.Sp
1275See also the locking example in the \f(CW\*(C`THREADS\*(C'\fR section later in this
1276document.
1277.IP "ev_set_userdata (loop, void *data)" 4
1278.IX Item "ev_set_userdata (loop, void *data)"
1279.PD 0
1280.IP "void *ev_userdata (loop)" 4
1281.IX Item "void *ev_userdata (loop)"
1282.PD
1283Set and retrieve a single \f(CW\*(C`void *\*(C'\fR associated with a loop. When
1284\&\f(CW\*(C`ev_set_userdata\*(C'\fR has never been called, then \f(CW\*(C`ev_userdata\*(C'\fR returns
1285\&\f(CW0\fR.
1286.Sp
1287These two functions can be used to associate arbitrary data with a loop,
1288and are intended solely for the \f(CW\*(C`invoke_pending_cb\*(C'\fR, \f(CW\*(C`release\*(C'\fR and
1289\&\f(CW\*(C`acquire\*(C'\fR callbacks described above, but of course can be (ab\-)used for
1290any other purpose as well.
1291.IP "ev_verify (loop)" 4
1292.IX Item "ev_verify (loop)"
1293This function only does something when \f(CW\*(C`EV_VERIFY\*(C'\fR support has been
1294compiled in, which is the default for non-minimal builds. It tries to go
1295through all internal structures and checks them for validity. If anything
1296is found to be inconsistent, it will print an error message to standard
1297error and call \f(CW\*(C`abort ()\*(C'\fR.
1298.Sp
1299This can be used to catch bugs inside libev itself: under normal
1300circumstances, this function will never abort as of course libev keeps its
1301data structures consistent.
709.SH "ANATOMY OF A WATCHER" 1302.SH "ANATOMY OF A WATCHER"
710.IX Header "ANATOMY OF A WATCHER" 1303.IX Header "ANATOMY OF A WATCHER"
1304In the following description, uppercase \f(CW\*(C`TYPE\*(C'\fR in names stands for the
1305watcher type, e.g. \f(CW\*(C`ev_TYPE_start\*(C'\fR can mean \f(CW\*(C`ev_timer_start\*(C'\fR for timer
1306watchers and \f(CW\*(C`ev_io_start\*(C'\fR for I/O watchers.
1307.PP
711A watcher is a structure that you create and register to record your 1308A watcher is an opaque structure that you allocate and register to record
712interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to 1309your interest in some event. To make a concrete example, imagine you want
713become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher for that: 1310to wait for \s-1STDIN\s0 to become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher
1311for that:
714.PP 1312.PP
715.Vb 5 1313.Vb 5
716\& static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents) 1314\& static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
717\& { 1315\& {
718\& ev_io_stop (w); 1316\& ev_io_stop (w);
719\& ev_unloop (loop, EVUNLOOP_ALL); 1317\& ev_break (loop, EVBREAK_ALL);
720\& } 1318\& }
721.Ve 1319\&
722.PP
723.Vb 6
724\& struct ev_loop *loop = ev_default_loop (0); 1320\& struct ev_loop *loop = ev_default_loop (0);
1321\&
725\& struct ev_io stdin_watcher; 1322\& ev_io stdin_watcher;
1323\&
726\& ev_init (&stdin_watcher, my_cb); 1324\& ev_init (&stdin_watcher, my_cb);
727\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ); 1325\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
728\& ev_io_start (loop, &stdin_watcher); 1326\& ev_io_start (loop, &stdin_watcher);
1327\&
729\& ev_loop (loop, 0); 1328\& ev_run (loop, 0);
730.Ve 1329.Ve
731.PP 1330.PP
732As you can see, you are responsible for allocating the memory for your 1331As you can see, you are responsible for allocating the memory for your
733watcher structures (and it is usually a bad idea to do this on the stack, 1332watcher structures (and it is \fIusually\fR a bad idea to do this on the
734although this can sometimes be quite valid). 1333stack).
735.PP 1334.PP
1335Each watcher has an associated watcher structure (called \f(CW\*(C`struct ev_TYPE\*(C'\fR
1336or simply \f(CW\*(C`ev_TYPE\*(C'\fR, as typedefs are provided for all watcher structs).
1337.PP
736Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init 1338Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init (watcher
737(watcher *, callback)\*(C'\fR, which expects a callback to be provided. This 1339*, callback)\*(C'\fR, which expects a callback to be provided. This callback is
738callback gets invoked each time the event occurs (or, in the case of io 1340invoked each time the event occurs (or, in the case of I/O watchers, each
739watchers, each time the event loop detects that the file descriptor given 1341time the event loop detects that the file descriptor given is readable
740is readable and/or writable). 1342and/or writable).
741.PP 1343.PP
742Each watcher type has its own \f(CW\*(C`ev_<type>_set (watcher *, ...)\*(C'\fR macro 1344Each watcher type further has its own \f(CW\*(C`ev_TYPE_set (watcher *, ...)\*(C'\fR
743with arguments specific to this watcher type. There is also a macro 1345macro to configure it, with arguments specific to the watcher type. There
744to combine initialisation and setting in one call: \f(CW\*(C`ev_<type>_init 1346is also a macro to combine initialisation and setting in one call: \f(CW\*(C`ev_TYPE_init (watcher *, callback, ...)\*(C'\fR.
745(watcher *, callback, ...)\*(C'\fR.
746.PP 1347.PP
747To make the watcher actually watch out for events, you have to start it 1348To make the watcher actually watch out for events, you have to start it
748with a watcher-specific start function (\f(CW\*(C`ev_<type>_start (loop, watcher 1349with a watcher-specific start function (\f(CW\*(C`ev_TYPE_start (loop, watcher
749*)\*(C'\fR), and you can stop watching for events at any time by calling the 1350*)\*(C'\fR), and you can stop watching for events at any time by calling the
750corresponding stop function (\f(CW\*(C`ev_<type>_stop (loop, watcher *)\*(C'\fR. 1351corresponding stop function (\f(CW\*(C`ev_TYPE_stop (loop, watcher *)\*(C'\fR.
751.PP 1352.PP
752As long as your watcher is active (has been started but not stopped) you 1353As long as your watcher is active (has been started but not stopped) you
753must not touch the values stored in it. Most specifically you must never 1354must not touch the values stored in it except when explicitly documented
754reinitialise it or call its \f(CW\*(C`set\*(C'\fR macro. 1355otherwise. Most specifically you must never reinitialise it or call its
1356\&\f(CW\*(C`ev_TYPE_set\*(C'\fR macro.
755.PP 1357.PP
756Each and every callback receives the event loop pointer as first, the 1358Each and every callback receives the event loop pointer as first, the
757registered watcher structure as second, and a bitset of received events as 1359registered watcher structure as second, and a bitset of received events as
758third argument. 1360third argument.
759.PP 1361.PP
… …
768.el .IP "\f(CWEV_WRITE\fR" 4 1370.el .IP "\f(CWEV_WRITE\fR" 4
769.IX Item "EV_WRITE" 1371.IX Item "EV_WRITE"
770.PD 1372.PD
771The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or 1373The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or
772writable. 1374writable.
773.ie n .IP """EV_TIMEOUT""" 4 1375.ie n .IP """EV_TIMER""" 4
774.el .IP "\f(CWEV_TIMEOUT\fR" 4 1376.el .IP "\f(CWEV_TIMER\fR" 4
775.IX Item "EV_TIMEOUT" 1377.IX Item "EV_TIMER"
776The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out. 1378The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out.
777.ie n .IP """EV_PERIODIC""" 4 1379.ie n .IP """EV_PERIODIC""" 4
778.el .IP "\f(CWEV_PERIODIC\fR" 4 1380.el .IP "\f(CWEV_PERIODIC\fR" 4
779.IX Item "EV_PERIODIC" 1381.IX Item "EV_PERIODIC"
780The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out. 1382The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out.
… …
800.PD 0 1402.PD 0
801.ie n .IP """EV_CHECK""" 4 1403.ie n .IP """EV_CHECK""" 4
802.el .IP "\f(CWEV_CHECK\fR" 4 1404.el .IP "\f(CWEV_CHECK\fR" 4
803.IX Item "EV_CHECK" 1405.IX Item "EV_CHECK"
804.PD 1406.PD
805All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_loop\*(C'\fR starts 1407All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_run\*(C'\fR starts to
806to gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are invoked just after 1408gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are queued (not invoked)
807\&\f(CW\*(C`ev_loop\*(C'\fR has gathered them, but before it invokes any callbacks for any 1409just after \f(CW\*(C`ev_run\*(C'\fR has gathered them, but before it queues any callbacks
1410for any received events. That means \f(CW\*(C`ev_prepare\*(C'\fR watchers are the last
1411watchers invoked before the event loop sleeps or polls for new events, and
1412\&\f(CW\*(C`ev_check\*(C'\fR watchers will be invoked before any other watchers of the same
1413or lower priority within an event loop iteration.
1414.Sp
808received events. Callbacks of both watcher types can start and stop as 1415Callbacks of both watcher types can start and stop as many watchers as
809many watchers as they want, and all of them will be taken into account 1416they want, and all of them will be taken into account (for example, a
810(for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep 1417\&\f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep \f(CW\*(C`ev_run\*(C'\fR from
811\&\f(CW\*(C`ev_loop\*(C'\fR from blocking). 1418blocking).
812.ie n .IP """EV_EMBED""" 4 1419.ie n .IP """EV_EMBED""" 4
813.el .IP "\f(CWEV_EMBED\fR" 4 1420.el .IP "\f(CWEV_EMBED\fR" 4
814.IX Item "EV_EMBED" 1421.IX Item "EV_EMBED"
815The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention. 1422The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention.
816.ie n .IP """EV_FORK""" 4 1423.ie n .IP """EV_FORK""" 4
817.el .IP "\f(CWEV_FORK\fR" 4 1424.el .IP "\f(CWEV_FORK\fR" 4
818.IX Item "EV_FORK" 1425.IX Item "EV_FORK"
819The event loop has been resumed in the child process after fork (see 1426The event loop has been resumed in the child process after fork (see
820\&\f(CW\*(C`ev_fork\*(C'\fR). 1427\&\f(CW\*(C`ev_fork\*(C'\fR).
1428.ie n .IP """EV_CLEANUP""" 4
1429.el .IP "\f(CWEV_CLEANUP\fR" 4
1430.IX Item "EV_CLEANUP"
1431The event loop is about to be destroyed (see \f(CW\*(C`ev_cleanup\*(C'\fR).
1432.ie n .IP """EV_ASYNC""" 4
1433.el .IP "\f(CWEV_ASYNC\fR" 4
1434.IX Item "EV_ASYNC"
1435The given async watcher has been asynchronously notified (see \f(CW\*(C`ev_async\*(C'\fR).
1436.ie n .IP """EV_CUSTOM""" 4
1437.el .IP "\f(CWEV_CUSTOM\fR" 4
1438.IX Item "EV_CUSTOM"
1439Not ever sent (or otherwise used) by libev itself, but can be freely used
1440by libev users to signal watchers (e.g. via \f(CW\*(C`ev_feed_event\*(C'\fR).
821.ie n .IP """EV_ERROR""" 4 1441.ie n .IP """EV_ERROR""" 4
822.el .IP "\f(CWEV_ERROR\fR" 4 1442.el .IP "\f(CWEV_ERROR\fR" 4
823.IX Item "EV_ERROR" 1443.IX Item "EV_ERROR"
824An unspecified error has occured, the watcher has been stopped. This might 1444An unspecified error has occurred, the watcher has been stopped. This might
825happen because the watcher could not be properly started because libev 1445happen because the watcher could not be properly started because libev
826ran out of memory, a file descriptor was found to be closed or any other 1446ran out of memory, a file descriptor was found to be closed or any other
1447problem. Libev considers these application bugs.
1448.Sp
827problem. You best act on it by reporting the problem and somehow coping 1449You best act on it by reporting the problem and somehow coping with the
828with the watcher being stopped. 1450watcher being stopped. Note that well-written programs should not receive
1451an error ever, so when your watcher receives it, this usually indicates a
1452bug in your program.
829.Sp 1453.Sp
830Libev will usually signal a few \*(L"dummy\*(R" events together with an error, 1454Libev will usually signal a few \*(L"dummy\*(R" events together with an error, for
831for example it might indicate that a fd is readable or writable, and if 1455example it might indicate that a fd is readable or writable, and if your
832your callbacks is well-written it can just attempt the operation and cope 1456callbacks is well-written it can just attempt the operation and cope with
833with the error from \fIread()\fR or \fIwrite()\fR. This will not work in multithreaded 1457the error from \fBread()\fR or \fBwrite()\fR. This will not work in multi-threaded
834programs, though, so beware. 1458programs, though, as the fd could already be closed and reused for another
1459thing, so beware.
835.Sh "\s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0" 1460.SS "\s-1GENERIC WATCHER FUNCTIONS\s0"
836.IX Subsection "GENERIC WATCHER FUNCTIONS" 1461.IX Subsection "GENERIC WATCHER FUNCTIONS"
837In the following description, \f(CW\*(C`TYPE\*(C'\fR stands for the watcher type,
838e.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.
839.ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4 1462.ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4
840.el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4 1463.el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4
841.IX Item "ev_init (ev_TYPE *watcher, callback)" 1464.IX Item "ev_init (ev_TYPE *watcher, callback)"
842This macro initialises the generic portion of a watcher. The contents 1465This macro initialises the generic portion of a watcher. The contents
843of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only 1466of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only
… …
847which rolls both calls into one. 1470which rolls both calls into one.
848.Sp 1471.Sp
849You can reinitialise a watcher at any time as long as it has been stopped 1472You can reinitialise a watcher at any time as long as it has been stopped
850(or never started) and there are no pending events outstanding. 1473(or never started) and there are no pending events outstanding.
851.Sp 1474.Sp
852The callback is always of type \f(CW\*(C`void (*)(ev_loop *loop, ev_TYPE *watcher, 1475The callback is always of type \f(CW\*(C`void (*)(struct ev_loop *loop, ev_TYPE *watcher,
853int revents)\*(C'\fR. 1476int revents)\*(C'\fR.
1477.Sp
1478Example: Initialise an \f(CW\*(C`ev_io\*(C'\fR watcher in two steps.
1479.Sp
1480.Vb 3
1481\& ev_io w;
1482\& ev_init (&w, my_cb);
1483\& ev_io_set (&w, STDIN_FILENO, EV_READ);
1484.Ve
854.ie n .IP """ev_TYPE_set"" (ev_TYPE *, [args])" 4 1485.ie n .IP """ev_TYPE_set"" (ev_TYPE *watcher, [args])" 4
855.el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *, [args])" 4 1486.el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *watcher, [args])" 4
856.IX Item "ev_TYPE_set (ev_TYPE *, [args])" 1487.IX Item "ev_TYPE_set (ev_TYPE *watcher, [args])"
857This macro initialises the type-specific parts of a watcher. You need to 1488This macro initialises the type-specific parts of a watcher. You need to
858call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can 1489call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can
859call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this 1490call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this
860macro on a watcher that is active (it can be pending, however, which is a 1491macro on a watcher that is active (it can be pending, however, which is a
861difference to the \f(CW\*(C`ev_init\*(C'\fR macro). 1492difference to the \f(CW\*(C`ev_init\*(C'\fR macro).
862.Sp 1493.Sp
863Although some watcher types do not have type-specific arguments 1494Although some watcher types do not have type-specific arguments
864(e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro. 1495(e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro.
1496.Sp
1497See \f(CW\*(C`ev_init\*(C'\fR, above, for an example.
865.ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4 1498.ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4
866.el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4 1499.el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4
867.IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])" 1500.IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])"
868This convinience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro 1501This convenience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro
869calls into a single call. This is the most convinient method to initialise 1502calls into a single call. This is the most convenient method to initialise
870a watcher. The same limitations apply, of course. 1503a watcher. The same limitations apply, of course.
1504.Sp
1505Example: Initialise and set an \f(CW\*(C`ev_io\*(C'\fR watcher in one step.
1506.Sp
1507.Vb 1
1508\& ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1509.Ve
871.ie n .IP """ev_TYPE_start"" (loop *, ev_TYPE *watcher)" 4 1510.ie n .IP """ev_TYPE_start"" (loop, ev_TYPE *watcher)" 4
872.el .IP "\f(CWev_TYPE_start\fR (loop *, ev_TYPE *watcher)" 4 1511.el .IP "\f(CWev_TYPE_start\fR (loop, ev_TYPE *watcher)" 4
873.IX Item "ev_TYPE_start (loop *, ev_TYPE *watcher)" 1512.IX Item "ev_TYPE_start (loop, ev_TYPE *watcher)"
874Starts (activates) the given watcher. Only active watchers will receive 1513Starts (activates) the given watcher. Only active watchers will receive
875events. If the watcher is already active nothing will happen. 1514events. If the watcher is already active nothing will happen.
1515.Sp
1516Example: Start the \f(CW\*(C`ev_io\*(C'\fR watcher that is being abused as example in this
1517whole section.
1518.Sp
1519.Vb 1
1520\& ev_io_start (EV_DEFAULT_UC, &w);
1521.Ve
876.ie n .IP """ev_TYPE_stop"" (loop *, ev_TYPE *watcher)" 4 1522.ie n .IP """ev_TYPE_stop"" (loop, ev_TYPE *watcher)" 4
877.el .IP "\f(CWev_TYPE_stop\fR (loop *, ev_TYPE *watcher)" 4 1523.el .IP "\f(CWev_TYPE_stop\fR (loop, ev_TYPE *watcher)" 4
878.IX Item "ev_TYPE_stop (loop *, ev_TYPE *watcher)" 1524.IX Item "ev_TYPE_stop (loop, ev_TYPE *watcher)"
879Stops the given watcher again (if active) and clears the pending 1525Stops the given watcher if active, and clears the pending status (whether
1526the watcher was active or not).
1527.Sp
880status. It is possible that stopped watchers are pending (for example, 1528It is possible that stopped watchers are pending \- for example,
881non-repeating timers are being stopped when they become pending), but 1529non-repeating timers are being stopped when they become pending \- but
882\&\f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor pending. If 1530calling \f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor
883you want to free or reuse the memory used by the watcher it is therefore a 1531pending. If you want to free or reuse the memory used by the watcher it is
884good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function. 1532therefore a good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function.
885.IP "bool ev_is_active (ev_TYPE *watcher)" 4 1533.IP "bool ev_is_active (ev_TYPE *watcher)" 4
886.IX Item "bool ev_is_active (ev_TYPE *watcher)" 1534.IX Item "bool ev_is_active (ev_TYPE *watcher)"
887Returns a true value iff the watcher is active (i.e. it has been started 1535Returns a true value iff the watcher is active (i.e. it has been started
888and not yet been stopped). As long as a watcher is active you must not modify 1536and not yet been stopped). As long as a watcher is active you must not modify
889it. 1537it unless documented otherwise.
890.IP "bool ev_is_pending (ev_TYPE *watcher)" 4 1538.IP "bool ev_is_pending (ev_TYPE *watcher)" 4
891.IX Item "bool ev_is_pending (ev_TYPE *watcher)" 1539.IX Item "bool ev_is_pending (ev_TYPE *watcher)"
892Returns a true value iff the watcher is pending, (i.e. it has outstanding 1540Returns a true value iff the watcher is pending, (i.e. it has outstanding
893events but its callback has not yet been invoked). As long as a watcher 1541events but its callback has not yet been invoked). As long as a watcher
894is pending (but not active) you must not call an init function on it (but 1542is pending (but not active) you must not call an init function on it (but
… …
896make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR 1544make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR
897it). 1545it).
898.IP "callback ev_cb (ev_TYPE *watcher)" 4 1546.IP "callback ev_cb (ev_TYPE *watcher)" 4
899.IX Item "callback ev_cb (ev_TYPE *watcher)" 1547.IX Item "callback ev_cb (ev_TYPE *watcher)"
900Returns the callback currently set on the watcher. 1548Returns the callback currently set on the watcher.
901.IP "ev_cb_set (ev_TYPE *watcher, callback)" 4 1549.IP "ev_set_cb (ev_TYPE *watcher, callback)" 4
902.IX Item "ev_cb_set (ev_TYPE *watcher, callback)" 1550.IX Item "ev_set_cb (ev_TYPE *watcher, callback)"
903Change the callback. You can change the callback at virtually any time 1551Change the callback. You can change the callback at virtually any time
904(modulo threads). 1552(modulo threads).
905.IP "ev_set_priority (ev_TYPE *watcher, priority)" 4 1553.IP "ev_set_priority (ev_TYPE *watcher, int priority)" 4
906.IX Item "ev_set_priority (ev_TYPE *watcher, priority)" 1554.IX Item "ev_set_priority (ev_TYPE *watcher, int priority)"
907.PD 0 1555.PD 0
908.IP "int ev_priority (ev_TYPE *watcher)" 4 1556.IP "int ev_priority (ev_TYPE *watcher)" 4
909.IX Item "int ev_priority (ev_TYPE *watcher)" 1557.IX Item "int ev_priority (ev_TYPE *watcher)"
910.PD 1558.PD
911Set and query the priority of the watcher. The priority is a small 1559Set and query the priority of the watcher. The priority is a small
912integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR 1560integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR
913(default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked 1561(default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked
914before watchers with lower priority, but priority will not keep watchers 1562before watchers with lower priority, but priority will not keep watchers
915from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers). 1563from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers).
916.Sp 1564.Sp
917This means that priorities are \fIonly\fR used for ordering callback
918invocation after new events have been received. This is useful, for
919example, to reduce latency after idling, or more often, to bind two
920watchers on the same event and make sure one is called first.
921.Sp
922If you need to suppress invocation when higher priority events are pending 1565If you need to suppress invocation when higher priority events are pending
923you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality. 1566you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality.
924.Sp 1567.Sp
925You \fImust not\fR change the priority of a watcher as long as it is active or 1568You \fImust not\fR change the priority of a watcher as long as it is active or
926pending. 1569pending.
927.Sp 1570.Sp
1571Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is
1572fine, as long as you do not mind that the priority value you query might
1573or might not have been clamped to the valid range.
1574.Sp
928The default priority used by watchers when no priority has been set is 1575The default priority used by watchers when no priority has been set is
929always \f(CW0\fR, which is supposed to not be too high and not be too low :). 1576always \f(CW0\fR, which is supposed to not be too high and not be too low :).
930.Sp 1577.Sp
931Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is 1578See \*(L"\s-1WATCHER PRIORITY MODELS\*(R"\s0, below, for a more thorough treatment of
932fine, as long as you do not mind that the priority value you query might 1579priorities.
933or might not have been adjusted to be within valid range.
934.IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4 1580.IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4
935.IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)" 1581.IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)"
936Invoke the \f(CW\*(C`watcher\*(C'\fR with the given \f(CW\*(C`loop\*(C'\fR and \f(CW\*(C`revents\*(C'\fR. Neither 1582Invoke the \f(CW\*(C`watcher\*(C'\fR with the given \f(CW\*(C`loop\*(C'\fR and \f(CW\*(C`revents\*(C'\fR. Neither
937\&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback 1583\&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback
938can deal with that fact. 1584can deal with that fact, as both are simply passed through to the
1585callback.
939.IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4 1586.IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4
940.IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)" 1587.IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)"
941If the watcher is pending, this function returns clears its pending status 1588If the watcher is pending, this function clears its pending status and
942and returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the 1589returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the
943watcher isn't pending it does nothing and returns \f(CW0\fR. 1590watcher isn't pending it does nothing and returns \f(CW0\fR.
944.Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0" 1591.Sp
945.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER" 1592Sometimes it can be useful to \*(L"poll\*(R" a watcher instead of waiting for its
946Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change 1593callback to be invoked, which can be accomplished with this function.
947and read at any time, libev will completely ignore it. This can be used 1594.IP "ev_feed_event (loop, ev_TYPE *watcher, int revents)" 4
948to associate arbitrary data with your watcher. If you need more data and 1595.IX Item "ev_feed_event (loop, ev_TYPE *watcher, int revents)"
949don't want to allocate memory and store a pointer to it in that data 1596Feeds the given event set into the event loop, as if the specified event
950member, you can also \*(L"subclass\*(R" the watcher type and provide your own 1597had happened for the specified watcher (which must be a pointer to an
951data: 1598initialised but not necessarily started event watcher). Obviously you must
1599not free the watcher as long as it has pending events.
1600.Sp
1601Stopping the watcher, letting libev invoke it, or calling
1602\&\f(CW\*(C`ev_clear_pending\*(C'\fR will clear the pending event, even if the watcher was
1603not started in the first place.
1604.Sp
1605See also \f(CW\*(C`ev_feed_fd_event\*(C'\fR and \f(CW\*(C`ev_feed_signal_event\*(C'\fR for related
1606functions that do not need a watcher.
952.PP 1607.PP
1608See also the \*(L"\s-1ASSOCIATING CUSTOM DATA WITH A WATCHER\*(R"\s0 and \*(L"\s-1BUILDING YOUR
1609OWN COMPOSITE WATCHERS\*(R"\s0 idioms.
1610.SS "\s-1WATCHER STATES\s0"
1611.IX Subsection "WATCHER STATES"
1612There are various watcher states mentioned throughout this manual \-
1613active, pending and so on. In this section these states and the rules to
1614transition between them will be described in more detail \- and while these
1615rules might look complicated, they usually do \*(L"the right thing\*(R".
1616.IP "initialised" 4
1617.IX Item "initialised"
1618Before a watcher can be registered with the event loop it has to be
1619initialised. This can be done with a call to \f(CW\*(C`ev_TYPE_init\*(C'\fR, or calls to
1620\&\f(CW\*(C`ev_init\*(C'\fR followed by the watcher-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR function.
1621.Sp
1622In this state it is simply some block of memory that is suitable for
1623use in an event loop. It can be moved around, freed, reused etc. at
1624will \- as long as you either keep the memory contents intact, or call
1625\&\f(CW\*(C`ev_TYPE_init\*(C'\fR again.
1626.IP "started/running/active" 4
1627.IX Item "started/running/active"
1628Once a watcher has been started with a call to \f(CW\*(C`ev_TYPE_start\*(C'\fR it becomes
1629property of the event loop, and is actively waiting for events. While in
1630this state it cannot be accessed (except in a few documented ways), moved,
1631freed or anything else \- the only legal thing is to keep a pointer to it,
1632and call libev functions on it that are documented to work on active watchers.
1633.IP "pending" 4
1634.IX Item "pending"
1635If a watcher is active and libev determines that an event it is interested
1636in has occurred (such as a timer expiring), it will become pending. It will
1637stay in this pending state until either it is stopped or its callback is
1638about to be invoked, so it is not normally pending inside the watcher
1639callback.
1640.Sp
1641The watcher might or might not be active while it is pending (for example,
1642an expired non-repeating timer can be pending but no longer active). If it
1643is stopped, it can be freely accessed (e.g. by calling \f(CW\*(C`ev_TYPE_set\*(C'\fR),
1644but it is still property of the event loop at this time, so cannot be
1645moved, freed or reused. And if it is active the rules described in the
1646previous item still apply.
1647.Sp
1648It is also possible to feed an event on a watcher that is not active (e.g.
1649via \f(CW\*(C`ev_feed_event\*(C'\fR), in which case it becomes pending without being
1650active.
1651.IP "stopped" 4
1652.IX Item "stopped"
1653A watcher can be stopped implicitly by libev (in which case it might still
1654be pending), or explicitly by calling its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function. The
1655latter will clear any pending state the watcher might be in, regardless
1656of whether it was active or not, so stopping a watcher explicitly before
1657freeing it is often a good idea.
1658.Sp
1659While stopped (and not pending) the watcher is essentially in the
1660initialised state, that is, it can be reused, moved, modified in any way
1661you wish (but when you trash the memory block, you need to \f(CW\*(C`ev_TYPE_init\*(C'\fR
1662it again).
1663.SS "\s-1WATCHER PRIORITY MODELS\s0"
1664.IX Subsection "WATCHER PRIORITY MODELS"
1665Many event loops support \fIwatcher priorities\fR, which are usually small
1666integers that influence the ordering of event callback invocation
1667between watchers in some way, all else being equal.
1668.PP
1669In libev, watcher priorities can be set using \f(CW\*(C`ev_set_priority\*(C'\fR. See its
1670description for the more technical details such as the actual priority
1671range.
1672.PP
1673There are two common ways how these these priorities are being interpreted
1674by event loops:
1675.PP
1676In the more common lock-out model, higher priorities \*(L"lock out\*(R" invocation
1677of lower priority watchers, which means as long as higher priority
1678watchers receive events, lower priority watchers are not being invoked.
1679.PP
1680The less common only-for-ordering model uses priorities solely to order
1681callback invocation within a single event loop iteration: Higher priority
1682watchers are invoked before lower priority ones, but they all get invoked
1683before polling for new events.
1684.PP
1685Libev uses the second (only-for-ordering) model for all its watchers
1686except for idle watchers (which use the lock-out model).
1687.PP
1688The rationale behind this is that implementing the lock-out model for
1689watchers is not well supported by most kernel interfaces, and most event
1690libraries will just poll for the same events again and again as long as
1691their callbacks have not been executed, which is very inefficient in the
1692common case of one high-priority watcher locking out a mass of lower
1693priority ones.
1694.PP
1695Static (ordering) priorities are most useful when you have two or more
1696watchers handling the same resource: a typical usage example is having an
1697\&\f(CW\*(C`ev_io\*(C'\fR watcher to receive data, and an associated \f(CW\*(C`ev_timer\*(C'\fR to handle
1698timeouts. Under load, data might be received while the program handles
1699other jobs, but since timers normally get invoked first, the timeout
1700handler will be executed before checking for data. In that case, giving
1701the timer a lower priority than the I/O watcher ensures that I/O will be
1702handled first even under adverse conditions (which is usually, but not
1703always, what you want).
1704.PP
1705Since idle watchers use the \*(L"lock-out\*(R" model, meaning that idle watchers
1706will only be executed when no same or higher priority watchers have
1707received events, they can be used to implement the \*(L"lock-out\*(R" model when
1708required.
1709.PP
1710For example, to emulate how many other event libraries handle priorities,
1711you can associate an \f(CW\*(C`ev_idle\*(C'\fR watcher to each such watcher, and in
1712the normal watcher callback, you just start the idle watcher. The real
1713processing is done in the idle watcher callback. This causes libev to
1714continuously poll and process kernel event data for the watcher, but when
1715the lock-out case is known to be rare (which in turn is rare :), this is
1716workable.
1717.PP
1718Usually, however, the lock-out model implemented that way will perform
1719miserably under the type of load it was designed to handle. In that case,
1720it might be preferable to stop the real watcher before starting the
1721idle watcher, so the kernel will not have to process the event in case
1722the actual processing will be delayed for considerable time.
1723.PP
1724Here is an example of an I/O watcher that should run at a strictly lower
1725priority than the default, and which should only process data when no
1726other events are pending:
1727.PP
953.Vb 7 1728.Vb 2
954\& struct my_io 1729\& ev_idle idle; // actual processing watcher
955\& { 1730\& ev_io io; // actual event watcher
956\& struct ev_io io; 1731\&
957\& int otherfd;
958\& void *somedata;
959\& struct whatever *mostinteresting;
960\& }
961.Ve
962.PP
963And since your callback will be called with a pointer to the watcher, you
964can cast it back to your own type:
965.PP
966.Vb 5
967\& static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
968\& {
969\& struct my_io *w = (struct my_io *)w_;
970\& ...
971\& }
972.Ve
973.PP
974More interesting and less C\-conformant ways of casting your callback type
975instead have been omitted.
976.PP
977Another common scenario is having some data structure with multiple
978watchers:
979.PP
980.Vb 6
981\& struct my_biggy
982\& {
983\& int some_data;
984\& ev_timer t1;
985\& ev_timer t2;
986\& }
987.Ve
988.PP
989In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more complicated,
990you need to use \f(CW\*(C`offsetof\*(C'\fR:
991.PP
992.Vb 1
993\& #include <stddef.h>
994.Ve
995.PP
996.Vb 6
997\& static void 1732\& static void
998\& t1_cb (EV_P_ struct ev_timer *w, int revents) 1733\& io_cb (EV_P_ ev_io *w, int revents)
999\& { 1734\& {
1000\& struct my_biggy big = (struct my_biggy * 1735\& // stop the I/O watcher, we received the event, but
1001\& (((char *)w) - offsetof (struct my_biggy, t1)); 1736\& // are not yet ready to handle it.
1737\& ev_io_stop (EV_A_ w);
1738\&
1739\& // start the idle watcher to handle the actual event.
1740\& // it will not be executed as long as other watchers
1741\& // with the default priority are receiving events.
1742\& ev_idle_start (EV_A_ &idle);
1002\& } 1743\& }
1003.Ve 1744\&
1004.PP
1005.Vb 6
1006\& static void 1745\& static void
1007\& t2_cb (EV_P_ struct ev_timer *w, int revents) 1746\& idle_cb (EV_P_ ev_idle *w, int revents)
1008\& { 1747\& {
1009\& struct my_biggy big = (struct my_biggy * 1748\& // actual processing
1010\& (((char *)w) - offsetof (struct my_biggy, t2)); 1749\& read (STDIN_FILENO, ...);
1750\&
1751\& // have to start the I/O watcher again, as
1752\& // we have handled the event
1753\& ev_io_start (EV_P_ &io);
1011\& } 1754\& }
1755\&
1756\& // initialisation
1757\& ev_idle_init (&idle, idle_cb);
1758\& ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
1759\& ev_io_start (EV_DEFAULT_ &io);
1012.Ve 1760.Ve
1761.PP
1762In the \*(L"real\*(R" world, it might also be beneficial to start a timer, so that
1763low-priority connections can not be locked out forever under load. This
1764enables your program to keep a lower latency for important connections
1765during short periods of high load, while not completely locking out less
1766important ones.
1013.SH "WATCHER TYPES" 1767.SH "WATCHER TYPES"
1014.IX Header "WATCHER TYPES" 1768.IX Header "WATCHER TYPES"
1015This section describes each watcher in detail, but will not repeat 1769This section describes each watcher in detail, but will not repeat
1016information given in the last section. Any initialisation/set macros, 1770information given in the last section. Any initialisation/set macros,
1017functions and members specific to the watcher type are explained. 1771functions and members specific to the watcher type are explained.
1018.PP 1772.PP
1019Members are additionally marked with either \fI[read\-only]\fR, meaning that, 1773Most members are additionally marked with either \fI[read\-only]\fR, meaning
1020while the watcher is active, you can look at the member and expect some 1774that, while the watcher is active, you can look at the member and expect
1021sensible content, but you must not modify it (you can modify it while the 1775some sensible content, but you must not modify it (you can modify it while
1022watcher is stopped to your hearts content), or \fI[read\-write]\fR, which 1776the watcher is stopped to your hearts content), or \fI[read\-write]\fR, which
1023means you can expect it to have some sensible content while the watcher 1777means you can expect it to have some sensible content while the watcher is
1024is active, but you can also modify it. Modifying it may not do something 1778active, but you can also modify it (within the same thread as the event
1779loop, i.e. without creating data races). Modifying it may not do something
1025sensible or take immediate effect (or do anything at all), but libev will 1780sensible or take immediate effect (or do anything at all), but libev will
1026not crash or malfunction in any way. 1781not crash or malfunction in any way.
1782.PP
1783In any case, the documentation for each member will explain what the
1784effects are, and if there are any additional access restrictions.
1027.ie n .Sh """ev_io"" \- is this file descriptor readable or writable?" 1785.ie n .SS """ev_io"" \- is this file descriptor readable or writable?"
1028.el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable?" 1786.el .SS "\f(CWev_io\fP \- is this file descriptor readable or writable?"
1029.IX Subsection "ev_io - is this file descriptor readable or writable?" 1787.IX Subsection "ev_io - is this file descriptor readable or writable?"
1030I/O watchers check whether a file descriptor is readable or writable 1788I/O watchers check whether a file descriptor is readable or writable
1031in each iteration of the event loop, or, more precisely, when reading 1789in each iteration of the event loop, or, more precisely, when reading
1032would not block the process and writing would at least be able to write 1790would not block the process and writing would at least be able to write
1033some data. This behaviour is called level-triggering because you keep 1791some data. This behaviour is called level-triggering because you keep
… …
1038In general you can register as many read and/or write event watchers per 1796In general you can register as many read and/or write event watchers per
1039fd as you want (as long as you don't confuse yourself). Setting all file 1797fd as you want (as long as you don't confuse yourself). Setting all file
1040descriptors to non-blocking mode is also usually a good idea (but not 1798descriptors to non-blocking mode is also usually a good idea (but not
1041required if you know what you are doing). 1799required if you know what you are doing).
1042.PP 1800.PP
1043You have to be careful with dup'ed file descriptors, though. Some backends
1044(the linux epoll backend is a notable example) cannot handle dup'ed file
1045descriptors correctly if you register interest in two or more fds pointing
1046to the same underlying file/socket/etc. description (that is, they share
1047the same underlying \*(L"file open\*(R").
1048.PP
1049If you must do this, then force the use of a known-to-be-good backend
1050(at the time of this writing, this includes only \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and
1051\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR).
1052.PP
1053Another thing you have to watch out for is that it is quite easy to 1801Another thing you have to watch out for is that it is quite easy to
1054receive \*(L"spurious\*(R" readyness notifications, that is your callback might 1802receive \*(L"spurious\*(R" readiness notifications, that is, your callback might
1055be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block 1803be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block
1056because there is no data. Not only are some backends known to create a 1804because there is no data. It is very easy to get into this situation even
1057lot of those (for example solaris ports), it is very easy to get into 1805with a relatively standard program structure. Thus it is best to always
1058this situation even with a relatively standard program structure. Thus 1806use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning \f(CW\*(C`EAGAIN\*(C'\fR is far
1059it is best to always use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning
1060\&\f(CW\*(C`EAGAIN\*(C'\fR is far preferable to a program hanging until some data arrives. 1807preferable to a program hanging until some data arrives.
1061.PP 1808.PP
1062If you cannot run the fd in non-blocking mode (for example you should not 1809If you cannot run the fd in non-blocking mode (for example you should
1063play around with an Xlib connection), then you have to seperately re-test 1810not play around with an Xlib connection), then you have to separately
1064whether a file descriptor is really ready with a known-to-be good interface 1811re-test whether a file descriptor is really ready with a known-to-be good
1065such as poll (fortunately in our Xlib example, Xlib already does this on 1812interface such as poll (fortunately in the case of Xlib, it already does
1066its own, so its quite safe to use). 1813this on its own, so its quite safe to use). Some people additionally
1814use \f(CW\*(C`SIGALRM\*(C'\fR and an interval timer, just to be sure you won't block
1815indefinitely.
1816.PP
1817But really, best use non-blocking mode.
1818.PP
1819\fIThe special problem of disappearing file descriptors\fR
1820.IX Subsection "The special problem of disappearing file descriptors"
1821.PP
1822Some backends (e.g. kqueue, epoll, linuxaio) need to be told about closing
1823a file descriptor (either due to calling \f(CW\*(C`close\*(C'\fR explicitly or any other
1824means, such as \f(CW\*(C`dup2\*(C'\fR). The reason is that you register interest in some
1825file descriptor, but when it goes away, the operating system will silently
1826drop this interest. If another file descriptor with the same number then
1827is registered with libev, there is no efficient way to see that this is,
1828in fact, a different file descriptor.
1829.PP
1830To avoid having to explicitly tell libev about such cases, libev follows
1831the following policy: Each time \f(CW\*(C`ev_io_set\*(C'\fR is being called, libev
1832will assume that this is potentially a new file descriptor, otherwise
1833it is assumed that the file descriptor stays the same. That means that
1834you \fIhave\fR to call \f(CW\*(C`ev_io_set\*(C'\fR (or \f(CW\*(C`ev_io_init\*(C'\fR) when you change the
1835descriptor even if the file descriptor number itself did not change.
1836.PP
1837This is how one would do it normally anyway, the important point is that
1838the libev application should not optimise around libev but should leave
1839optimisations to libev.
1840.PP
1841\fIThe special problem of dup'ed file descriptors\fR
1842.IX Subsection "The special problem of dup'ed file descriptors"
1843.PP
1844Some backends (e.g. epoll), cannot register events for file descriptors,
1845but only events for the underlying file descriptions. That means when you
1846have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or weirder constellations, and register
1847events for them, only one file descriptor might actually receive events.
1848.PP
1849There is no workaround possible except not registering events
1850for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors, or to resort to
1851\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1852.PP
1853\fIThe special problem of files\fR
1854.IX Subsection "The special problem of files"
1855.PP
1856Many people try to use \f(CW\*(C`select\*(C'\fR (or libev) on file descriptors
1857representing files, and expect it to become ready when their program
1858doesn't block on disk accesses (which can take a long time on their own).
1859.PP
1860However, this cannot ever work in the \*(L"expected\*(R" way \- you get a readiness
1861notification as soon as the kernel knows whether and how much data is
1862there, and in the case of open files, that's always the case, so you
1863always get a readiness notification instantly, and your read (or possibly
1864write) will still block on the disk I/O.
1865.PP
1866Another way to view it is that in the case of sockets, pipes, character
1867devices and so on, there is another party (the sender) that delivers data
1868on its own, but in the case of files, there is no such thing: the disk
1869will not send data on its own, simply because it doesn't know what you
1870wish to read \- you would first have to request some data.
1871.PP
1872Since files are typically not-so-well supported by advanced notification
1873mechanism, libev tries hard to emulate \s-1POSIX\s0 behaviour with respect
1874to files, even though you should not use it. The reason for this is
1875convenience: sometimes you want to watch \s-1STDIN\s0 or \s-1STDOUT,\s0 which is
1876usually a tty, often a pipe, but also sometimes files or special devices
1877(for example, \f(CW\*(C`epoll\*(C'\fR on Linux works with \fI/dev/random\fR but not with
1878\&\fI/dev/urandom\fR), and even though the file might better be served with
1879asynchronous I/O instead of with non-blocking I/O, it is still useful when
1880it \*(L"just works\*(R" instead of freezing.
1881.PP
1882So avoid file descriptors pointing to files when you know it (e.g. use
1883libeio), but use them when it is convenient, e.g. for \s-1STDIN/STDOUT,\s0 or
1884when you rarely read from a file instead of from a socket, and want to
1885reuse the same code path.
1886.PP
1887\fIThe special problem of fork\fR
1888.IX Subsection "The special problem of fork"
1889.PP
1890Some backends (epoll, kqueue, linuxaio, iouring) do not support \f(CW\*(C`fork ()\*(C'\fR
1891at all or exhibit useless behaviour. Libev fully supports fork, but needs
1892to be told about it in the child if you want to continue to use it in the
1893child.
1894.PP
1895To support fork in your child processes, you have to call \f(CW\*(C`ev_loop_fork
1896()\*(C'\fR after a fork in the child, enable \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR, or resort to
1897\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1898.PP
1899\fIThe special problem of \s-1SIGPIPE\s0\fR
1900.IX Subsection "The special problem of SIGPIPE"
1901.PP
1902While not really specific to libev, it is easy to forget about \f(CW\*(C`SIGPIPE\*(C'\fR:
1903when writing to a pipe whose other end has been closed, your program gets
1904sent a \s-1SIGPIPE,\s0 which, by default, aborts your program. For most programs
1905this is sensible behaviour, for daemons, this is usually undesirable.
1906.PP
1907So when you encounter spurious, unexplained daemon exits, make sure you
1908ignore \s-1SIGPIPE\s0 (and maybe make sure you log the exit status of your daemon
1909somewhere, as that would have given you a big clue).
1910.PP
1911\fIThe special problem of \f(BIaccept()\fIing when you can't\fR
1912.IX Subsection "The special problem of accept()ing when you can't"
1913.PP
1914Many implementations of the \s-1POSIX\s0 \f(CW\*(C`accept\*(C'\fR function (for example,
1915found in post\-2004 Linux) have the peculiar behaviour of not removing a
1916connection from the pending queue in all error cases.
1917.PP
1918For example, larger servers often run out of file descriptors (because
1919of resource limits), causing \f(CW\*(C`accept\*(C'\fR to fail with \f(CW\*(C`ENFILE\*(C'\fR but not
1920rejecting the connection, leading to libev signalling readiness on
1921the next iteration again (the connection still exists after all), and
1922typically causing the program to loop at 100% \s-1CPU\s0 usage.
1923.PP
1924Unfortunately, the set of errors that cause this issue differs between
1925operating systems, there is usually little the app can do to remedy the
1926situation, and no known thread-safe method of removing the connection to
1927cope with overload is known (to me).
1928.PP
1929One of the easiest ways to handle this situation is to just ignore it
1930\&\- when the program encounters an overload, it will just loop until the
1931situation is over. While this is a form of busy waiting, no \s-1OS\s0 offers an
1932event-based way to handle this situation, so it's the best one can do.
1933.PP
1934A better way to handle the situation is to log any errors other than
1935\&\f(CW\*(C`EAGAIN\*(C'\fR and \f(CW\*(C`EWOULDBLOCK\*(C'\fR, making sure not to flood the log with such
1936messages, and continue as usual, which at least gives the user an idea of
1937what could be wrong (\*(L"raise the ulimit!\*(R"). For extra points one could stop
1938the \f(CW\*(C`ev_io\*(C'\fR watcher on the listening fd \*(L"for a while\*(R", which reduces \s-1CPU\s0
1939usage.
1940.PP
1941If your program is single-threaded, then you could also keep a dummy file
1942descriptor for overload situations (e.g. by opening \fI/dev/null\fR), and
1943when 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,
1944close that fd, and create a new dummy fd. This will gracefully refuse
1945clients under typical overload conditions.
1946.PP
1947The last way to handle it is to simply log the error and \f(CW\*(C`exit\*(C'\fR, as
1948is often done with \f(CW\*(C`malloc\*(C'\fR failures, but this results in an easy
1949opportunity for a DoS attack.
1950.PP
1951\fIWatcher-Specific Functions\fR
1952.IX Subsection "Watcher-Specific Functions"
1067.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4 1953.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
1068.IX Item "ev_io_init (ev_io *, callback, int fd, int events)" 1954.IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
1069.PD 0 1955.PD 0
1070.IP "ev_io_set (ev_io *, int fd, int events)" 4 1956.IP "ev_io_set (ev_io *, int fd, int events)" 4
1071.IX Item "ev_io_set (ev_io *, int fd, int events)" 1957.IX Item "ev_io_set (ev_io *, int fd, int events)"
1072.PD 1958.PD
1073Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to 1959Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to
1074rceeive events for and events is either \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or 1960receive 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, both
1075\&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR to receive the given events. 1961\&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR or \f(CW0\fR, to express the desire to receive the given
1962events.
1963.Sp
1964Note that setting the \f(CW\*(C`events\*(C'\fR to \f(CW0\fR and starting the watcher is
1965supported, but not specially optimized \- if your program sometimes happens
1966to generate this combination this is fine, but if it is easy to avoid
1967starting an io watcher watching for no events you should do so.
1968.IP "ev_io_modify (ev_io *, int events)" 4
1969.IX Item "ev_io_modify (ev_io *, int events)"
1970Similar to \f(CW\*(C`ev_io_set\*(C'\fR, but only changes the requested events. Using this
1971might be faster with some backends, as libev can assume that the \f(CW\*(C`fd\*(C'\fR
1972still refers to the same underlying file description, something it cannot
1973do when using \f(CW\*(C`ev_io_set\*(C'\fR.
1076.IP "int fd [read\-only]" 4 1974.IP "int fd [no\-modify]" 4
1077.IX Item "int fd [read-only]" 1975.IX Item "int fd [no-modify]"
1078The file descriptor being watched. 1976The file descriptor being watched. While it can be read at any time, you
1977must not modify this member even when the watcher is stopped \- always use
1978\&\f(CW\*(C`ev_io_set\*(C'\fR for that.
1079.IP "int events [read\-only]" 4 1979.IP "int events [no\-modify]" 4
1080.IX Item "int events [read-only]" 1980.IX Item "int events [no-modify]"
1081The events being watched. 1981The set of events the fd is being watched for, among other flags. Remember
1982that this is a bit set \- to test for \f(CW\*(C`EV_READ\*(C'\fR, use \f(CW\*(C`w\->events &
1983EV_READ\*(C'\fR, and similarly for \f(CW\*(C`EV_WRITE\*(C'\fR.
1984.Sp
1985As with \f(CW\*(C`fd\*(C'\fR, you must not modify this member even when the watcher is
1986stopped, always use \f(CW\*(C`ev_io_set\*(C'\fR or \f(CW\*(C`ev_io_modify\*(C'\fR for that.
1987.PP
1988\fIExamples\fR
1989.IX Subsection "Examples"
1082.PP 1990.PP
1083Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well 1991Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well
1084readable, but only once. Since it is likely line\-buffered, you could 1992readable, but only once. Since it is likely line-buffered, you could
1085attempt to read a whole line in the callback. 1993attempt to read a whole line in the callback.
1086.PP 1994.PP
1087.Vb 6 1995.Vb 6
1088\& static void 1996\& static void
1089\& stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents) 1997\& stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1090\& { 1998\& {
1091\& ev_io_stop (loop, w); 1999\& ev_io_stop (loop, w);
1092\& .. read from stdin here (or from w->fd) and haqndle any I/O errors 2000\& .. read from stdin here (or from w\->fd) and handle any I/O errors
1093\& } 2001\& }
1094.Ve 2002\&
1095.PP
1096.Vb 6
1097\& ... 2003\& ...
1098\& struct ev_loop *loop = ev_default_init (0); 2004\& struct ev_loop *loop = ev_default_init (0);
1099\& struct ev_io stdin_readable; 2005\& ev_io stdin_readable;
1100\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ); 2006\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1101\& ev_io_start (loop, &stdin_readable); 2007\& ev_io_start (loop, &stdin_readable);
1102\& ev_loop (loop, 0); 2008\& ev_run (loop, 0);
1103.Ve 2009.Ve
1104.ie n .Sh """ev_timer"" \- relative and optionally repeating timeouts" 2010.ie n .SS """ev_timer"" \- relative and optionally repeating timeouts"
1105.el .Sh "\f(CWev_timer\fP \- relative and optionally repeating timeouts" 2011.el .SS "\f(CWev_timer\fP \- relative and optionally repeating timeouts"
1106.IX Subsection "ev_timer - relative and optionally repeating timeouts" 2012.IX Subsection "ev_timer - relative and optionally repeating timeouts"
1107Timer watchers are simple relative timers that generate an event after a 2013Timer watchers are simple relative timers that generate an event after a
1108given time, and optionally repeating in regular intervals after that. 2014given time, and optionally repeating in regular intervals after that.
1109.PP 2015.PP
1110The timers are based on real time, that is, if you register an event that 2016The timers are based on real time, that is, if you register an event that
1111times out after an hour and you reset your system clock to last years 2017times out after an hour and you reset your system clock to January last
1112time, it will still time out after (roughly) and hour. \*(L"Roughly\*(R" because 2018year, it will still time out after (roughly) one hour. \*(L"Roughly\*(R" because
1113detecting time jumps is hard, and some inaccuracies are unavoidable (the 2019detecting time jumps is hard, and some inaccuracies are unavoidable (the
1114monotonic clock option helps a lot here). 2020monotonic clock option helps a lot here).
2021.PP
2022The callback is guaranteed to be invoked only \fIafter\fR its timeout has
2023passed (not \fIat\fR, so on systems with very low-resolution clocks this
2024might introduce a small delay, see \*(L"the special problem of being too
2025early\*(R", below). If multiple timers become ready during the same loop
2026iteration then the ones with earlier time-out values are invoked before
2027ones of the same priority with later time-out values (but this is no
2028longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
2029.PP
2030\fIBe smart about timeouts\fR
2031.IX Subsection "Be smart about timeouts"
2032.PP
2033Many real-world problems involve some kind of timeout, usually for error
2034recovery. A typical example is an \s-1HTTP\s0 request \- if the other side hangs,
2035you want to raise some error after a while.
2036.PP
2037What follows are some ways to handle this problem, from obvious and
2038inefficient to smart and efficient.
2039.PP
2040In the following, a 60 second activity timeout is assumed \- a timeout that
2041gets reset to 60 seconds each time there is activity (e.g. each time some
2042data or other life sign was received).
2043.IP "1. Use a timer and stop, reinitialise and start it on activity." 4
2044.IX Item "1. Use a timer and stop, reinitialise and start it on activity."
2045This is the most obvious, but not the most simple way: In the beginning,
2046start the watcher:
2047.Sp
2048.Vb 2
2049\& ev_timer_init (timer, callback, 60., 0.);
2050\& ev_timer_start (loop, timer);
2051.Ve
2052.Sp
2053Then, each time there is some activity, \f(CW\*(C`ev_timer_stop\*(C'\fR it, initialise it
2054and start it again:
2055.Sp
2056.Vb 3
2057\& ev_timer_stop (loop, timer);
2058\& ev_timer_set (timer, 60., 0.);
2059\& ev_timer_start (loop, timer);
2060.Ve
2061.Sp
2062This is relatively simple to implement, but means that each time there is
2063some activity, libev will first have to remove the timer from its internal
2064data structure and then add it again. Libev tries to be fast, but it's
2065still not a constant-time operation.
2066.ie n .IP "2. Use a timer and re-start it with ""ev_timer_again"" inactivity." 4
2067.el .IP "2. Use a timer and re-start it with \f(CWev_timer_again\fR inactivity." 4
2068.IX Item "2. Use a timer and re-start it with ev_timer_again inactivity."
2069This is the easiest way, and involves using \f(CW\*(C`ev_timer_again\*(C'\fR instead of
2070\&\f(CW\*(C`ev_timer_start\*(C'\fR.
2071.Sp
2072To implement this, configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value
2073of \f(CW60\fR and then call \f(CW\*(C`ev_timer_again\*(C'\fR at start and each time you
2074successfully read or write some data. If you go into an idle state where
2075you do not expect data to travel on the socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR
2076the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will automatically restart it if need be.
2077.Sp
2078That means you can ignore both the \f(CW\*(C`ev_timer_start\*(C'\fR function and the
2079\&\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
2080member and \f(CW\*(C`ev_timer_again\*(C'\fR.
2081.Sp
2082At start:
2083.Sp
2084.Vb 3
2085\& ev_init (timer, callback);
2086\& timer\->repeat = 60.;
2087\& ev_timer_again (loop, timer);
2088.Ve
2089.Sp
2090Each time there is some activity:
2091.Sp
2092.Vb 1
2093\& ev_timer_again (loop, timer);
2094.Ve
2095.Sp
2096It is even possible to change the time-out on the fly, regardless of
2097whether the watcher is active or not:
2098.Sp
2099.Vb 2
2100\& timer\->repeat = 30.;
2101\& ev_timer_again (loop, timer);
2102.Ve
2103.Sp
2104This is slightly more efficient then stopping/starting the timer each time
2105you want to modify its timeout value, as libev does not have to completely
2106remove and re-insert the timer from/into its internal data structure.
2107.Sp
2108It is, however, even simpler than the \*(L"obvious\*(R" way to do it.
2109.IP "3. Let the timer time out, but then re-arm it as required." 4
2110.IX Item "3. Let the timer time out, but then re-arm it as required."
2111This method is more tricky, but usually most efficient: Most timeouts are
2112relatively long compared to the intervals between other activity \- in
2113our example, within 60 seconds, there are usually many I/O events with
2114associated activity resets.
2115.Sp
2116In this case, it would be more efficient to leave the \f(CW\*(C`ev_timer\*(C'\fR alone,
2117but remember the time of last activity, and check for a real timeout only
2118within the callback:
2119.Sp
2120.Vb 3
2121\& ev_tstamp timeout = 60.;
2122\& ev_tstamp last_activity; // time of last activity
2123\& ev_timer timer;
2124\&
2125\& static void
2126\& callback (EV_P_ ev_timer *w, int revents)
2127\& {
2128\& // calculate when the timeout would happen
2129\& ev_tstamp after = last_activity \- ev_now (EV_A) + timeout;
2130\&
2131\& // if negative, it means we the timeout already occurred
2132\& if (after < 0.)
2133\& {
2134\& // timeout occurred, take action
2135\& }
2136\& else
2137\& {
2138\& // callback was invoked, but there was some recent
2139\& // activity. simply restart the timer to time out
2140\& // after "after" seconds, which is the earliest time
2141\& // the timeout can occur.
2142\& ev_timer_set (w, after, 0.);
2143\& ev_timer_start (EV_A_ w);
2144\& }
2145\& }
2146.Ve
2147.Sp
2148To summarise the callback: first calculate in how many seconds the
2149timeout will occur (by calculating the absolute time when it would occur,
2150\&\f(CW\*(C`last_activity + timeout\*(C'\fR, and subtracting the current time, \f(CW\*(C`ev_now
2151(EV_A)\*(C'\fR from that).
2152.Sp
2153If this value is negative, then we are already past the timeout, i.e. we
2154timed out, and need to do whatever is needed in this case.
2155.Sp
2156Otherwise, we now the earliest time at which the timeout would trigger,
2157and simply start the timer with this timeout value.
2158.Sp
2159In other words, each time the callback is invoked it will check whether
2160the timeout occurred. If not, it will simply reschedule itself to check
2161again at the earliest time it could time out. Rinse. Repeat.
2162.Sp
2163This scheme causes more callback invocations (about one every 60 seconds
2164minus half the average time between activity), but virtually no calls to
2165libev to change the timeout.
2166.Sp
2167To start the machinery, simply initialise the watcher and set
2168\&\f(CW\*(C`last_activity\*(C'\fR to the current time (meaning there was some activity just
2169now), then call the callback, which will \*(L"do the right thing\*(R" and start
2170the timer:
2171.Sp
2172.Vb 3
2173\& last_activity = ev_now (EV_A);
2174\& ev_init (&timer, callback);
2175\& callback (EV_A_ &timer, 0);
2176.Ve
2177.Sp
2178When there is some activity, simply store the current time in
2179\&\f(CW\*(C`last_activity\*(C'\fR, no libev calls at all:
2180.Sp
2181.Vb 2
2182\& if (activity detected)
2183\& last_activity = ev_now (EV_A);
2184.Ve
2185.Sp
2186When your timeout value changes, then the timeout can be changed by simply
2187providing a new value, stopping the timer and calling the callback, which
2188will again do the right thing (for example, time out immediately :).
2189.Sp
2190.Vb 3
2191\& timeout = new_value;
2192\& ev_timer_stop (EV_A_ &timer);
2193\& callback (EV_A_ &timer, 0);
2194.Ve
2195.Sp
2196This technique is slightly more complex, but in most cases where the
2197time-out is unlikely to be triggered, much more efficient.
2198.IP "4. Wee, just use a double-linked list for your timeouts." 4
2199.IX Item "4. Wee, just use a double-linked list for your timeouts."
2200If there is not one request, but many thousands (millions...), all
2201employing some kind of timeout with the same timeout value, then one can
2202do even better:
2203.Sp
2204When starting the timeout, calculate the timeout value and put the timeout
2205at the \fIend\fR of the list.
2206.Sp
2207Then use an \f(CW\*(C`ev_timer\*(C'\fR to fire when the timeout at the \fIbeginning\fR of
2208the list is expected to fire (for example, using the technique #3).
2209.Sp
2210When there is some activity, remove the timer from the list, recalculate
2211the timeout, append it to the end of the list again, and make sure to
2212update the \f(CW\*(C`ev_timer\*(C'\fR if it was taken from the beginning of the list.
2213.Sp
2214This way, one can manage an unlimited number of timeouts in O(1) time for
2215starting, stopping and updating the timers, at the expense of a major
2216complication, and having to use a constant timeout. The constant timeout
2217ensures that the list stays sorted.
2218.PP
2219So which method the best?
2220.PP
2221Method #2 is a simple no-brain-required solution that is adequate in most
2222situations. Method #3 requires a bit more thinking, but handles many cases
2223better, and isn't very complicated either. In most case, choosing either
2224one is fine, with #3 being better in typical situations.
2225.PP
2226Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
2227rather complicated, but extremely efficient, something that really pays
2228off after the first million or so of active timers, i.e. it's usually
2229overkill :)
2230.PP
2231\fIThe special problem of being too early\fR
2232.IX Subsection "The special problem of being too early"
2233.PP
2234If you ask a timer to call your callback after three seconds, then
2235you expect it to be invoked after three seconds \- but of course, this
2236cannot be guaranteed to infinite precision. Less obviously, it cannot be
2237guaranteed to any precision by libev \- imagine somebody suspending the
2238process with a \s-1STOP\s0 signal for a few hours for example.
2239.PP
2240So, libev tries to invoke your callback as soon as possible \fIafter\fR the
2241delay has occurred, but cannot guarantee this.
2242.PP
2243A less obvious failure mode is calling your callback too early: many event
2244loops compare timestamps with a \*(L"elapsed delay >= requested delay\*(R", but
2245this can cause your callback to be invoked much earlier than you would
2246expect.
2247.PP
2248To see why, imagine a system with a clock that only offers full second
2249resolution (think windows if you can't come up with a broken enough \s-1OS\s0
2250yourself). If you schedule a one-second timer at the time 500.9, then the
2251event loop will schedule your timeout to elapse at a system time of 500
2252(500.9 truncated to the resolution) + 1, or 501.
2253.PP
2254If an event library looks at the timeout 0.1s later, it will see \*(L"501 >=
2255501\*(R" and invoke the callback 0.1s after it was started, even though a
2256one-second delay was requested \- this is being \*(L"too early\*(R", despite best
2257intentions.
2258.PP
2259This is the reason why libev will never invoke the callback if the elapsed
2260delay equals the requested delay, but only when the elapsed delay is
2261larger than the requested delay. In the example above, libev would only invoke
2262the callback at system time 502, or 1.1s after the timer was started.
2263.PP
2264So, while libev cannot guarantee that your callback will be invoked
2265exactly when requested, it \fIcan\fR and \fIdoes\fR guarantee that the requested
2266delay has actually elapsed, or in other words, it always errs on the \*(L"too
2267late\*(R" side of things.
2268.PP
2269\fIThe special problem of time updates\fR
2270.IX Subsection "The special problem of time updates"
2271.PP
2272Establishing the current time is a costly operation (it usually takes
2273at least one system call): \s-1EV\s0 therefore updates its idea of the current
2274time only before and after \f(CW\*(C`ev_run\*(C'\fR collects new events, which causes a
2275growing difference between \f(CW\*(C`ev_now ()\*(C'\fR and \f(CW\*(C`ev_time ()\*(C'\fR when handling
2276lots of events in one iteration.
1115.PP 2277.PP
1116The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR 2278The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
1117time. This is usually the right thing as this timestamp refers to the time 2279time. This is usually the right thing as this timestamp refers to the time
1118of the event triggering whatever timeout you are modifying/starting. If 2280of the event triggering whatever timeout you are modifying/starting. If
1119you suspect event processing to be delayed and you \fIneed\fR to base the timeout 2281you suspect event processing to be delayed and you \fIneed\fR to base the
1120on the current time, use something like this to adjust for this: 2282timeout on the current time, use something like the following to adjust
2283for it:
1121.PP 2284.PP
1122.Vb 1 2285.Vb 1
1123\& ev_timer_set (&timer, after + ev_now () - ev_time (), 0.); 2286\& ev_timer_set (&timer, after + (ev_time () \- ev_now ()), 0.);
1124.Ve 2287.Ve
1125.PP 2288.PP
1126The callback is guarenteed to be invoked only when its timeout has passed, 2289If the event loop is suspended for a long time, you can also force an
1127but if multiple timers become ready during the same loop iteration then 2290update of the time returned by \f(CW\*(C`ev_now ()\*(C'\fR by calling \f(CW\*(C`ev_now_update
1128order of execution is undefined. 2291()\*(C'\fR, although that will push the event time of all outstanding events
2292further into the future.
2293.PP
2294\fIThe special problem of unsynchronised clocks\fR
2295.IX Subsection "The special problem of unsynchronised clocks"
2296.PP
2297Modern systems have a variety of clocks \- libev itself uses the normal
2298\&\*(L"wall clock\*(R" clock and, if available, the monotonic clock (to avoid time
2299jumps).
2300.PP
2301Neither of these clocks is synchronised with each other or any other clock
2302on the system, so \f(CW\*(C`ev_time ()\*(C'\fR might return a considerably different time
2303than \f(CW\*(C`gettimeofday ()\*(C'\fR or \f(CW\*(C`time ()\*(C'\fR. On a GNU/Linux system, for example,
2304a call to \f(CW\*(C`gettimeofday\*(C'\fR might return a second count that is one higher
2305than a directly following call to \f(CW\*(C`time\*(C'\fR.
2306.PP
2307The moral of this is to only compare libev-related timestamps with
2308\&\f(CW\*(C`ev_time ()\*(C'\fR and \f(CW\*(C`ev_now ()\*(C'\fR, at least if you want better precision than
2309a second or so.
2310.PP
2311One more problem arises due to this lack of synchronisation: if libev uses
2312the system monotonic clock and you compare timestamps from \f(CW\*(C`ev_time\*(C'\fR
2313or \f(CW\*(C`ev_now\*(C'\fR from when you started your timer and when your callback is
2314invoked, you will find that sometimes the callback is a bit \*(L"early\*(R".
2315.PP
2316This is because \f(CW\*(C`ev_timer\*(C'\fRs work in real time, not wall clock time, so
2317libev makes sure your callback is not invoked before the delay happened,
2318\&\fImeasured according to the real time\fR, not the system clock.
2319.PP
2320If your timeouts are based on a physical timescale (e.g. \*(L"time out this
2321connection after 100 seconds\*(R") then this shouldn't bother you as it is
2322exactly the right behaviour.
2323.PP
2324If you want to compare wall clock/system timestamps to your timers, then
2325you need to use \f(CW\*(C`ev_periodic\*(C'\fRs, as these are based on the wall clock
2326time, where your comparisons will always generate correct results.
2327.PP
2328\fIThe special problems of suspended animation\fR
2329.IX Subsection "The special problems of suspended animation"
2330.PP
2331When you leave the server world it is quite customary to hit machines that
2332can suspend/hibernate \- what happens to the clocks during such a suspend?
2333.PP
2334Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
2335all processes, while the clocks (\f(CW\*(C`times\*(C'\fR, \f(CW\*(C`CLOCK_MONOTONIC\*(C'\fR) continue
2336to run until the system is suspended, but they will not advance while the
2337system is suspended. That means, on resume, it will be as if the program
2338was frozen for a few seconds, but the suspend time will not be counted
2339towards \f(CW\*(C`ev_timer\*(C'\fR when a monotonic clock source is used. The real time
2340clock advanced as expected, but if it is used as sole clocksource, then a
2341long suspend would be detected as a time jump by libev, and timers would
2342be adjusted accordingly.
2343.PP
2344I would not be surprised to see different behaviour in different between
2345operating systems, \s-1OS\s0 versions or even different hardware.
2346.PP
2347The other form of suspend (job control, or sending a \s-1SIGSTOP\s0) will see a
2348time jump in the monotonic clocks and the realtime clock. If the program
2349is suspended for a very long time, and monotonic clock sources are in use,
2350then you can expect \f(CW\*(C`ev_timer\*(C'\fRs to expire as the full suspension time
2351will be counted towards the timers. When no monotonic clock source is in
2352use, then libev will again assume a timejump and adjust accordingly.
2353.PP
2354It might be beneficial for this latter case to call \f(CW\*(C`ev_suspend\*(C'\fR
2355and \f(CW\*(C`ev_resume\*(C'\fR in code that handles \f(CW\*(C`SIGTSTP\*(C'\fR, to at least get
2356deterministic behaviour in this case (you can do nothing against
2357\&\f(CW\*(C`SIGSTOP\*(C'\fR).
2358.PP
2359\fIWatcher-Specific Functions and Data Members\fR
2360.IX Subsection "Watcher-Specific Functions and Data Members"
1129.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4 2361.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
1130.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 2362.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
1131.PD 0 2363.PD 0
1132.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4 2364.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
1133.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 2365.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
1134.PD 2366.PD
1135Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR is 2367Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds (fractional and
1136\&\f(CW0.\fR, then it will automatically be stopped. If it is positive, then the 2368negative values are supported). If \f(CW\*(C`repeat\*(C'\fR is \f(CW0.\fR, then it will
2369automatically be stopped once the timeout is reached. If it is positive,
1137timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds 2370then the timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR
1138later, again, and again, until stopped manually. 2371seconds later, again, and again, until stopped manually.
1139.Sp 2372.Sp
1140The timer itself will do a best-effort at avoiding drift, that is, if you 2373The timer itself will do a best-effort at avoiding drift, that is, if
1141configure a timer to trigger every 10 seconds, then it will trigger at 2374you configure a timer to trigger every 10 seconds, then it will normally
1142exactly 10 second intervals. If, however, your program cannot keep up with 2375trigger at exactly 10 second intervals. If, however, your program cannot
1143the timer (because it takes longer than those 10 seconds to do stuff) the 2376keep up with the timer (because it takes longer than those 10 seconds to
1144timer will not fire more than once per event loop iteration. 2377do stuff) the timer will not fire more than once per event loop iteration.
1145.IP "ev_timer_again (loop)" 4 2378.IP "ev_timer_again (loop, ev_timer *)" 4
1146.IX Item "ev_timer_again (loop)" 2379.IX Item "ev_timer_again (loop, ev_timer *)"
1147This will act as if the timer timed out and restart it again if it is 2380This will act as if the timer timed out, and restarts it again if it is
1148repeating. The exact semantics are: 2381repeating. It basically works like calling \f(CW\*(C`ev_timer_stop\*(C'\fR, updating the
2382timeout to the \f(CW\*(C`repeat\*(C'\fR value and calling \f(CW\*(C`ev_timer_start\*(C'\fR.
1149.Sp 2383.Sp
2384The exact semantics are as in the following rules, all of which will be
2385applied to the watcher:
2386.RS 4
1150If the timer is pending, its pending status is cleared. 2387.IP "If the timer is pending, the pending status is always cleared." 4
1151.Sp 2388.IX Item "If the timer is pending, the pending status is always cleared."
2389.PD 0
1152If the timer is started but nonrepeating, stop it (as if it timed out). 2390.IP "If the timer is started but non-repeating, stop it (as if it timed out, without invoking it)." 4
2391.IX Item "If the timer is started but non-repeating, stop it (as if it timed out, without invoking it)."
2392.ie n .IP "If the timer is repeating, make the ""repeat"" value the new timeout and start the timer, if necessary." 4
2393.el .IP "If the timer is repeating, make the \f(CWrepeat\fR value the new timeout and start the timer, if necessary." 4
2394.IX Item "If the timer is repeating, make the repeat value the new timeout and start the timer, if necessary."
2395.RE
2396.RS 4
2397.PD
1153.Sp 2398.Sp
1154If the timer is repeating, either start it if necessary (with the 2399This sounds a bit complicated, see \*(L"Be smart about timeouts\*(R", above, for a
1155\&\f(CW\*(C`repeat\*(C'\fR value), or reset the running timer to the \f(CW\*(C`repeat\*(C'\fR value. 2400usage example.
2401.RE
2402.IP "ev_tstamp ev_timer_remaining (loop, ev_timer *)" 4
2403.IX Item "ev_tstamp ev_timer_remaining (loop, ev_timer *)"
2404Returns the remaining time until a timer fires. If the timer is active,
2405then this time is relative to the current event loop time, otherwise it's
2406the timeout value currently configured.
1156.Sp 2407.Sp
1157This sounds a bit complicated, but here is a useful and typical 2408That is, after an \f(CW\*(C`ev_timer_set (w, 5, 7)\*(C'\fR, \f(CW\*(C`ev_timer_remaining\*(C'\fR returns
1158example: Imagine you have a tcp connection and you want a so-called idle 2409\&\f(CW5\fR. When the timer is started and one second passes, \f(CW\*(C`ev_timer_remaining\*(C'\fR
1159timeout, that is, you want to be called when there have been, say, 60 2410will return \f(CW4\fR. When the timer expires and is restarted, it will return
1160seconds of inactivity on the socket. The easiest way to do this is to 2411roughly \f(CW7\fR (likely slightly less as callback invocation takes some time,
1161configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value of \f(CW60\fR and then call 2412too), and so on.
1162\&\f(CW\*(C`ev_timer_again\*(C'\fR each time you successfully read or write some data. If
1163you go into an idle state where you do not expect data to travel on the
1164socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will
1165automatically restart it if need be.
1166.Sp
1167That means you can ignore the \f(CW\*(C`after\*(C'\fR value and \f(CW\*(C`ev_timer_start\*(C'\fR
1168altogether and only ever use the \f(CW\*(C`repeat\*(C'\fR value and \f(CW\*(C`ev_timer_again\*(C'\fR:
1169.Sp
1170.Vb 8
1171\& ev_timer_init (timer, callback, 0., 5.);
1172\& ev_timer_again (loop, timer);
1173\& ...
1174\& timer->again = 17.;
1175\& ev_timer_again (loop, timer);
1176\& ...
1177\& timer->again = 10.;
1178\& ev_timer_again (loop, timer);
1179.Ve
1180.Sp
1181This is more slightly efficient then stopping/starting the timer each time
1182you want to modify its timeout value.
1183.IP "ev_tstamp repeat [read\-write]" 4 2413.IP "ev_tstamp repeat [read\-write]" 4
1184.IX Item "ev_tstamp repeat [read-write]" 2414.IX Item "ev_tstamp repeat [read-write]"
1185The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out 2415The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out
1186or \f(CW\*(C`ev_timer_again\*(C'\fR is called and determines the next timeout (if any), 2416or \f(CW\*(C`ev_timer_again\*(C'\fR is called, and determines the next timeout (if any),
1187which is also when any modifications are taken into account. 2417which is also when any modifications are taken into account.
1188.PP 2418.PP
2419\fIExamples\fR
2420.IX Subsection "Examples"
2421.PP
1189Example: Create a timer that fires after 60 seconds. 2422Example: Create a timer that fires after 60 seconds.
1190.PP 2423.PP
1191.Vb 5 2424.Vb 5
1192\& static void 2425\& static void
1193\& one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents) 2426\& one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1194\& { 2427\& {
1195\& .. one minute over, w is actually stopped right here 2428\& .. one minute over, w is actually stopped right here
1196\& } 2429\& }
1197.Ve 2430\&
1198.PP
1199.Vb 3
1200\& struct ev_timer mytimer; 2431\& ev_timer mytimer;
1201\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.); 2432\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1202\& ev_timer_start (loop, &mytimer); 2433\& ev_timer_start (loop, &mytimer);
1203.Ve 2434.Ve
1204.PP 2435.PP
1205Example: Create a timeout timer that times out after 10 seconds of 2436Example: Create a timeout timer that times out after 10 seconds of
1206inactivity. 2437inactivity.
1207.PP 2438.PP
1208.Vb 5 2439.Vb 5
1209\& static void 2440\& static void
1210\& timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents) 2441\& timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1211\& { 2442\& {
1212\& .. ten seconds without any activity 2443\& .. ten seconds without any activity
1213\& } 2444\& }
1214.Ve 2445\&
1215.PP
1216.Vb 4
1217\& struct ev_timer mytimer; 2446\& ev_timer mytimer;
1218\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */ 2447\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1219\& ev_timer_again (&mytimer); /* start timer */ 2448\& ev_timer_again (&mytimer); /* start timer */
1220\& ev_loop (loop, 0); 2449\& ev_run (loop, 0);
1221.Ve 2450\&
1222.PP
1223.Vb 3
1224\& // and in some piece of code that gets executed on any "activity": 2451\& // and in some piece of code that gets executed on any "activity":
1225\& // reset the timeout to start ticking again at 10 seconds 2452\& // reset the timeout to start ticking again at 10 seconds
1226\& ev_timer_again (&mytimer); 2453\& ev_timer_again (&mytimer);
1227.Ve 2454.Ve
1228.ie n .Sh """ev_periodic"" \- to cron or not to cron?" 2455.ie n .SS """ev_periodic"" \- to cron or not to cron?"
1229.el .Sh "\f(CWev_periodic\fP \- to cron or not to cron?" 2456.el .SS "\f(CWev_periodic\fP \- to cron or not to cron?"
1230.IX Subsection "ev_periodic - to cron or not to cron?" 2457.IX Subsection "ev_periodic - to cron or not to cron?"
1231Periodic watchers are also timers of a kind, but they are very versatile 2458Periodic watchers are also timers of a kind, but they are very versatile
1232(and unfortunately a bit complex). 2459(and unfortunately a bit complex).
1233.PP 2460.PP
1234Unlike \f(CW\*(C`ev_timer\*(C'\fR's, they are not based on real time (or relative time) 2461Unlike \f(CW\*(C`ev_timer\*(C'\fR, periodic watchers are not based on real time (or
1235but on wallclock time (absolute time). You can tell a periodic watcher 2462relative time, the physical time that passes) but on wall clock time
1236to trigger \*(L"at\*(R" some specific point in time. For example, if you tell a 2463(absolute time, the thing you can read on your calendar or clock). The
1237periodic watcher to trigger in 10 seconds (by specifiying e.g. \f(CW\*(C`ev_now () 2464difference is that wall clock time can run faster or slower than real
1238+ 10.\*(C'\fR) and then reset your system clock to the last year, then it will 2465time, and time jumps are not uncommon (e.g. when you adjust your
1239take a year to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would trigger 2466wrist-watch).
1240roughly 10 seconds later).
1241.PP 2467.PP
1242They can also be used to implement vastly more complex timers, such as 2468You can tell a periodic watcher to trigger after some specific point
1243triggering an event on each midnight, local time or other, complicated, 2469in time: for example, if you tell a periodic watcher to trigger \*(L"in 10
1244rules. 2470seconds\*(R" (by specifying e.g. \f(CW\*(C`ev_now () + 10.\*(C'\fR, that is, an absolute time
2471not a delay) and then reset your system clock to January of the previous
2472year, then it will take a year or more to trigger the event (unlike an
2473\&\f(CW\*(C`ev_timer\*(C'\fR, which would still trigger roughly 10 seconds after starting
2474it, as it uses a relative timeout).
1245.PP 2475.PP
2476\&\f(CW\*(C`ev_periodic\*(C'\fR watchers can also be used to implement vastly more complex
2477timers, such as triggering an event on each \*(L"midnight, local time\*(R", or
2478other complicated rules. This cannot easily be done with \f(CW\*(C`ev_timer\*(C'\fR
2479watchers, as those cannot react to time jumps.
2480.PP
1246As with timers, the callback is guarenteed to be invoked only when the 2481As with timers, the callback is guaranteed to be invoked only when the
1247time (\f(CW\*(C`at\*(C'\fR) has been passed, but if multiple periodic timers become ready 2482point in time where it is supposed to trigger has passed. If multiple
1248during the same loop iteration then order of execution is undefined. 2483timers become ready during the same loop iteration then the ones with
2484earlier time-out values are invoked before ones with later time-out values
2485(but this is no longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
2486.PP
2487\fIWatcher-Specific Functions and Data Members\fR
2488.IX Subsection "Watcher-Specific Functions and Data Members"
1249.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 4 2489.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
1250.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 2490.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
1251.PD 0 2491.PD 0
1252.IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4 2492.IP "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
1253.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 2493.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
1254.PD 2494.PD
1255Lots of arguments, lets sort it out... There are basically three modes of 2495Lots of arguments, let's sort it out... There are basically three modes of
1256operation, and we will explain them from simplest to complex: 2496operation, and we will explain them from simplest to most complex:
1257.RS 4 2497.RS 4
2498.IP "\(bu" 4
1258.IP "* absolute timer (at = time, interval = reschedule_cb = 0)" 4 2499absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1259.IX Item "absolute timer (at = time, interval = reschedule_cb = 0)" 2500.Sp
1260In this configuration the watcher triggers an event at the wallclock time 2501In this configuration the watcher triggers an event after the wall clock
1261\&\f(CW\*(C`at\*(C'\fR and doesn't repeat. It will not adjust when a time jump occurs, 2502time \f(CW\*(C`offset\*(C'\fR has passed. It will not repeat and will not adjust when a
1262that is, if it is to be run at January 1st 2011 then it will run when the 2503time jump occurs, that is, if it is to be run at January 1st 2011 then it
1263system time reaches or surpasses this time. 2504will be stopped and invoked when the system clock reaches or surpasses
1264.IP "* non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)" 4 2505this point in time.
1265.IX Item "non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)" 2506.IP "\(bu" 4
2507repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
2508.Sp
1266In this mode the watcher will always be scheduled to time out at the next 2509In this mode the watcher will always be scheduled to time out at the next
1267\&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N, which can also be negative) 2510\&\f(CW\*(C`offset + N * interval\*(C'\fR time (for some integer N, which can also be
1268and then repeat, regardless of any time jumps. 2511negative) and then repeat, regardless of any time jumps. The \f(CW\*(C`offset\*(C'\fR
2512argument is merely an offset into the \f(CW\*(C`interval\*(C'\fR periods.
1269.Sp 2513.Sp
1270This can be used to create timers that do not drift with respect to system 2514This can be used to create timers that do not drift with respect to the
1271time: 2515system clock, for example, here is an \f(CW\*(C`ev_periodic\*(C'\fR that triggers each
2516hour, on the hour (with respect to \s-1UTC\s0):
1272.Sp 2517.Sp
1273.Vb 1 2518.Vb 1
1274\& ev_periodic_set (&periodic, 0., 3600., 0); 2519\& ev_periodic_set (&periodic, 0., 3600., 0);
1275.Ve 2520.Ve
1276.Sp 2521.Sp
1277This doesn't mean there will always be 3600 seconds in between triggers, 2522This doesn't mean there will always be 3600 seconds in between triggers,
1278but only that the the callback will be called when the system time shows a 2523but only that the callback will be called when the system time shows a
1279full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible 2524full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
1280by 3600. 2525by 3600.
1281.Sp 2526.Sp
1282Another way to think about it (for the mathematically inclined) is that 2527Another way to think about it (for the mathematically inclined) is that
1283\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible 2528\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
1284time where \f(CW\*(C`time = at (mod interval)\*(C'\fR, regardless of any time jumps. 2529time where \f(CW\*(C`time = offset (mod interval)\*(C'\fR, regardless of any time jumps.
1285.Sp 2530.Sp
1286For numerical stability it is preferable that the \f(CW\*(C`at\*(C'\fR value is near 2531The \f(CW\*(C`interval\*(C'\fR \fI\s-1MUST\s0\fR be positive, and for numerical stability, the
1287\&\f(CW\*(C`ev_now ()\*(C'\fR (the current time), but there is no range requirement for 2532interval value should be higher than \f(CW\*(C`1/8192\*(C'\fR (which is around 100
1288this value. 2533microseconds) and \f(CW\*(C`offset\*(C'\fR should be higher than \f(CW0\fR and should have
2534at most a similar magnitude as the current time (say, within a factor of
2535ten). Typical values for offset are, in fact, \f(CW0\fR or something between
2536\&\f(CW0\fR and \f(CW\*(C`interval\*(C'\fR, which is also the recommended range.
2537.Sp
2538Note also that there is an upper limit to how often a timer can fire (\s-1CPU\s0
2539speed for example), so if \f(CW\*(C`interval\*(C'\fR is very small then timing stability
2540will of course deteriorate. Libev itself tries to be exact to be about one
2541millisecond (if the \s-1OS\s0 supports it and the machine is fast enough).
2542.IP "\(bu" 4
1289.IP "* manual reschedule mode (at and interval ignored, reschedule_cb = callback)" 4 2543manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1290.IX Item "manual reschedule mode (at and interval ignored, reschedule_cb = callback)" 2544.Sp
1291In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being 2545In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`offset\*(C'\fR are both being
1292ignored. Instead, each time the periodic watcher gets scheduled, the 2546ignored. Instead, each time the periodic watcher gets scheduled, the
1293reschedule callback will be called with the watcher as first, and the 2547reschedule callback will be called with the watcher as first, and the
1294current time as second argument. 2548current time as second argument.
1295.Sp 2549.Sp
1296\&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, 2550\&\s-1NOTE:\s0 \fIThis callback \s-1MUST NOT\s0 stop or destroy any periodic watcher, ever,
1297ever, or make any event loop modifications\fR. If you need to stop it, 2551or make \s-1ANY\s0 other event loop modifications whatsoever, unless explicitly
1298return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop it afterwards (e.g. by 2552allowed by documentation here\fR.
2553.Sp
2554If you need to stop it, return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop
1299starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is legal). 2555it afterwards (e.g. by starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is the
2556only event loop modification you are allowed to do).
1300.Sp 2557.Sp
1301Its prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic *w, 2558The callback prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(ev_periodic
1302ev_tstamp now)\*(C'\fR, e.g.: 2559*w, ev_tstamp now)\*(C'\fR, e.g.:
1303.Sp 2560.Sp
1304.Vb 4 2561.Vb 5
2562\& static ev_tstamp
1305\& static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) 2563\& my_rescheduler (ev_periodic *w, ev_tstamp now)
1306\& { 2564\& {
1307\& return now + 60.; 2565\& return now + 60.;
1308\& } 2566\& }
1309.Ve 2567.Ve
1310.Sp 2568.Sp
1311It must return the next time to trigger, based on the passed time value 2569It must return the next time to trigger, based on the passed time value
1312(that is, the lowest time value larger than to the second argument). It 2570(that is, the lowest time value larger than to the second argument). It
1313will usually be called just before the callback will be triggered, but 2571will usually be called just before the callback will be triggered, but
1314might be called at other times, too. 2572might be called at other times, too.
1315.Sp 2573.Sp
1316\&\s-1NOTE:\s0 \fIThis callback must always return a time that is later than the 2574\&\s-1NOTE:\s0 \fIThis callback must always return a time that is higher than or
1317passed \f(CI\*(C`now\*(C'\fI value\fR. Not even \f(CW\*(C`now\*(C'\fR itself will do, it \fImust\fR be larger. 2575equal to the passed \f(CI\*(C`now\*(C'\fI value\fR.
1318.Sp 2576.Sp
1319This can be used to create very complex timers, such as a timer that 2577This can be used to create very complex timers, such as a timer that
1320triggers on each midnight, local time. To do this, you would calculate the 2578triggers on \*(L"next midnight, local time\*(R". To do this, you would calculate
1321next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How 2579the next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for
1322you do this is, again, up to you (but it is not trivial, which is the main 2580this. Here is a (completely untested, no error checking) example on how to
1323reason I omitted it as an example). 2581do this:
2582.Sp
2583.Vb 1
2584\& #include <time.h>
2585\&
2586\& static ev_tstamp
2587\& my_rescheduler (ev_periodic *w, ev_tstamp now)
2588\& {
2589\& time_t tnow = (time_t)now;
2590\& struct tm tm;
2591\& localtime_r (&tnow, &tm);
2592\&
2593\& tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
2594\& ++tm.tm_mday; // midnight next day
2595\&
2596\& return mktime (&tm);
2597\& }
2598.Ve
2599.Sp
2600Note: this code might run into trouble on days that have more then two
2601midnights (beginning and end).
1324.RE 2602.RE
1325.RS 4 2603.RS 4
1326.RE 2604.RE
1327.IP "ev_periodic_again (loop, ev_periodic *)" 4 2605.IP "ev_periodic_again (loop, ev_periodic *)" 4
1328.IX Item "ev_periodic_again (loop, ev_periodic *)" 2606.IX Item "ev_periodic_again (loop, ev_periodic *)"
1329Simply stops and restarts the periodic watcher again. This is only useful 2607Simply stops and restarts the periodic watcher again. This is only useful
1330when you changed some parameters or the reschedule callback would return 2608when you changed some parameters or the reschedule callback would return
1331a different time than the last time it was called (e.g. in a crond like 2609a different time than the last time it was called (e.g. in a crond like
1332program when the crontabs have changed). 2610program when the crontabs have changed).
2611.IP "ev_tstamp ev_periodic_at (ev_periodic *)" 4
2612.IX Item "ev_tstamp ev_periodic_at (ev_periodic *)"
2613When active, returns the absolute time that the watcher is supposed
2614to trigger next. This is not the same as the \f(CW\*(C`offset\*(C'\fR argument to
2615\&\f(CW\*(C`ev_periodic_set\*(C'\fR, but indeed works even in interval and manual
2616rescheduling modes.
1333.IP "ev_tstamp offset [read\-write]" 4 2617.IP "ev_tstamp offset [read\-write]" 4
1334.IX Item "ev_tstamp offset [read-write]" 2618.IX Item "ev_tstamp offset [read-write]"
1335When repeating, this contains the offset value, otherwise this is the 2619When repeating, this contains the offset value, otherwise this is the
1336absolute point in time (the \f(CW\*(C`at\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR). 2620absolute point in time (the \f(CW\*(C`offset\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR,
2621although libev might modify this value for better numerical stability).
1337.Sp 2622.Sp
1338Can be modified any time, but changes only take effect when the periodic 2623Can be modified any time, but changes only take effect when the periodic
1339timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called. 2624timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
1340.IP "ev_tstamp interval [read\-write]" 4 2625.IP "ev_tstamp interval [read\-write]" 4
1341.IX Item "ev_tstamp interval [read-write]" 2626.IX Item "ev_tstamp interval [read-write]"
1342The current interval value. Can be modified any time, but changes only 2627The current interval value. Can be modified any time, but changes only
1343take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being 2628take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being
1344called. 2629called.
1345.IP "ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read\-write]" 4 2630.IP "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read\-write]" 4
1346.IX Item "ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]" 2631.IX Item "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]"
1347The current reschedule callback, or \f(CW0\fR, if this functionality is 2632The current reschedule callback, or \f(CW0\fR, if this functionality is
1348switched off. Can be changed any time, but changes only take effect when 2633switched off. Can be changed any time, but changes only take effect when
1349the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called. 2634the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
1350.PP 2635.PP
2636\fIExamples\fR
2637.IX Subsection "Examples"
2638.PP
1351Example: Call a callback every hour, or, more precisely, whenever the 2639Example: Call a callback every hour, or, more precisely, whenever the
1352system clock is divisible by 3600. The callback invocation times have 2640system time is divisible by 3600. The callback invocation times have
1353potentially a lot of jittering, but good long-term stability. 2641potentially a lot of jitter, but good long-term stability.
1354.PP 2642.PP
1355.Vb 5 2643.Vb 5
1356\& static void 2644\& static void
1357\& clock_cb (struct ev_loop *loop, struct ev_io *w, int revents) 2645\& clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1358\& { 2646\& {
1359\& ... its now a full hour (UTC, or TAI or whatever your clock follows) 2647\& ... its now a full hour (UTC, or TAI or whatever your clock follows)
1360\& } 2648\& }
1361.Ve 2649\&
1362.PP
1363.Vb 3
1364\& struct ev_periodic hourly_tick; 2650\& ev_periodic hourly_tick;
1365\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0); 2651\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1366\& ev_periodic_start (loop, &hourly_tick); 2652\& ev_periodic_start (loop, &hourly_tick);
1367.Ve 2653.Ve
1368.PP 2654.PP
1369Example: The same as above, but use a reschedule callback to do it: 2655Example: The same as above, but use a reschedule callback to do it:
1370.PP 2656.PP
1371.Vb 1 2657.Vb 1
1372\& #include <math.h> 2658\& #include <math.h>
1373.Ve 2659\&
1374.PP
1375.Vb 5
1376\& static ev_tstamp 2660\& static ev_tstamp
1377\& my_scheduler_cb (struct ev_periodic *w, ev_tstamp now) 2661\& my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1378\& { 2662\& {
1379\& return fmod (now, 3600.) + 3600.; 2663\& return now + (3600. \- fmod (now, 3600.));
1380\& } 2664\& }
1381.Ve 2665\&
1382.PP
1383.Vb 1
1384\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb); 2666\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1385.Ve 2667.Ve
1386.PP 2668.PP
1387Example: Call a callback every hour, starting now: 2669Example: Call a callback every hour, starting now:
1388.PP 2670.PP
1389.Vb 4 2671.Vb 4
1390\& struct ev_periodic hourly_tick; 2672\& ev_periodic hourly_tick;
1391\& ev_periodic_init (&hourly_tick, clock_cb, 2673\& ev_periodic_init (&hourly_tick, clock_cb,
1392\& fmod (ev_now (loop), 3600.), 3600., 0); 2674\& fmod (ev_now (loop), 3600.), 3600., 0);
1393\& ev_periodic_start (loop, &hourly_tick); 2675\& ev_periodic_start (loop, &hourly_tick);
1394.Ve 2676.Ve
1395.ie n .Sh """ev_signal"" \- signal me when a signal gets signalled!" 2677.ie n .SS """ev_signal"" \- signal me when a signal gets signalled!"
1396.el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled!" 2678.el .SS "\f(CWev_signal\fP \- signal me when a signal gets signalled!"
1397.IX Subsection "ev_signal - signal me when a signal gets signalled!" 2679.IX Subsection "ev_signal - signal me when a signal gets signalled!"
1398Signal watchers will trigger an event when the process receives a specific 2680Signal watchers will trigger an event when the process receives a specific
1399signal one or more times. Even though signals are very asynchronous, libev 2681signal one or more times. Even though signals are very asynchronous, libev
1400will try it's best to deliver signals synchronously, i.e. as part of the 2682will try its best to deliver signals synchronously, i.e. as part of the
1401normal event processing, like any other event. 2683normal event processing, like any other event.
1402.PP 2684.PP
2685If you want signals to be delivered truly asynchronously, just use
2686\&\f(CW\*(C`sigaction\*(C'\fR as you would do without libev and forget about sharing
2687the signal. You can even use \f(CW\*(C`ev_async\*(C'\fR from a signal handler to
2688synchronously wake up an event loop.
2689.PP
1403You can configure as many watchers as you like per signal. Only when the 2690You can configure as many watchers as you like for the same signal, but
1404first watcher gets started will libev actually register a signal watcher 2691only within the same loop, i.e. you can watch for \f(CW\*(C`SIGINT\*(C'\fR in your
1405with the kernel (thus it coexists with your own signal handlers as long 2692default loop and for \f(CW\*(C`SIGIO\*(C'\fR in another loop, but you cannot watch for
1406as you don't register any with libev). Similarly, when the last signal 2693\&\f(CW\*(C`SIGINT\*(C'\fR in both the default loop and another loop at the same time. At
1407watcher for a signal is stopped libev will reset the signal handler to 2694the moment, \f(CW\*(C`SIGCHLD\*(C'\fR is permanently tied to the default loop.
1408\&\s-1SIG_DFL\s0 (regardless of what it was set to before). 2695.PP
2696Only after the first watcher for a signal is started will libev actually
2697register something with the kernel. It thus coexists with your own signal
2698handlers as long as you don't register any with libev for the same signal.
2699.PP
2700If possible and supported, libev will install its handlers with
2701\&\f(CW\*(C`SA_RESTART\*(C'\fR (or equivalent) behaviour enabled, so system calls should
2702not be unduly interrupted. If you have a problem with system calls getting
2703interrupted by signals you can block all signals in an \f(CW\*(C`ev_check\*(C'\fR watcher
2704and unblock them in an \f(CW\*(C`ev_prepare\*(C'\fR watcher.
2705.PP
2706\fIThe special problem of inheritance over fork/execve/pthread_create\fR
2707.IX Subsection "The special problem of inheritance over fork/execve/pthread_create"
2708.PP
2709Both the signal mask (\f(CW\*(C`sigprocmask\*(C'\fR) and the signal disposition
2710(\f(CW\*(C`sigaction\*(C'\fR) are unspecified after starting a signal watcher (and after
2711stopping it again), that is, libev might or might not block the signal,
2712and might or might not set or restore the installed signal handler (but
2713see \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR).
2714.PP
2715While this does not matter for the signal disposition (libev never
2716sets signals to \f(CW\*(C`SIG_IGN\*(C'\fR, so handlers will be reset to \f(CW\*(C`SIG_DFL\*(C'\fR on
2717\&\f(CW\*(C`execve\*(C'\fR), this matters for the signal mask: many programs do not expect
2718certain signals to be blocked.
2719.PP
2720This means that before calling \f(CW\*(C`exec\*(C'\fR (from the child) you should reset
2721the signal mask to whatever \*(L"default\*(R" you expect (all clear is a good
2722choice usually).
2723.PP
2724The simplest way to ensure that the signal mask is reset in the child is
2725to install a fork handler with \f(CW\*(C`pthread_atfork\*(C'\fR that resets it. That will
2726catch fork calls done by libraries (such as the libc) as well.
2727.PP
2728In current versions of libev, the signal will not be blocked indefinitely
2729unless you use the \f(CW\*(C`signalfd\*(C'\fR \s-1API\s0 (\f(CW\*(C`EV_SIGNALFD\*(C'\fR). While this reduces
2730the window of opportunity for problems, it will not go away, as libev
2731\&\fIhas\fR to modify the signal mask, at least temporarily.
2732.PP
2733So I can't stress this enough: \fIIf you do not reset your signal mask when
2734you expect it to be empty, you have a race condition in your code\fR. This
2735is not a libev-specific thing, this is true for most event libraries.
2736.PP
2737\fIThe special problem of threads signal handling\fR
2738.IX Subsection "The special problem of threads signal handling"
2739.PP
2740\&\s-1POSIX\s0 threads has problematic signal handling semantics, specifically,
2741a lot of functionality (sigfd, sigwait etc.) only really works if all
2742threads in a process block signals, which is hard to achieve.
2743.PP
2744When you want to use sigwait (or mix libev signal handling with your own
2745for the same signals), you can tackle this problem by globally blocking
2746all signals before creating any threads (or creating them with a fully set
2747sigprocmask) and also specifying the \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR when creating
2748loops. Then designate one thread as \*(L"signal receiver thread\*(R" which handles
2749these signals. You can pass on any signals that libev might be interested
2750in by calling \f(CW\*(C`ev_feed_signal\*(C'\fR.
2751.PP
2752\fIWatcher-Specific Functions and Data Members\fR
2753.IX Subsection "Watcher-Specific Functions and Data Members"
1409.IP "ev_signal_init (ev_signal *, callback, int signum)" 4 2754.IP "ev_signal_init (ev_signal *, callback, int signum)" 4
1410.IX Item "ev_signal_init (ev_signal *, callback, int signum)" 2755.IX Item "ev_signal_init (ev_signal *, callback, int signum)"
1411.PD 0 2756.PD 0
1412.IP "ev_signal_set (ev_signal *, int signum)" 4 2757.IP "ev_signal_set (ev_signal *, int signum)" 4
1413.IX Item "ev_signal_set (ev_signal *, int signum)" 2758.IX Item "ev_signal_set (ev_signal *, int signum)"
… …
1415Configures the watcher to trigger on the given signal number (usually one 2760Configures the watcher to trigger on the given signal number (usually one
1416of the \f(CW\*(C`SIGxxx\*(C'\fR constants). 2761of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
1417.IP "int signum [read\-only]" 4 2762.IP "int signum [read\-only]" 4
1418.IX Item "int signum [read-only]" 2763.IX Item "int signum [read-only]"
1419The signal the watcher watches out for. 2764The signal the watcher watches out for.
2765.PP
2766\fIExamples\fR
2767.IX Subsection "Examples"
2768.PP
2769Example: Try to exit cleanly on \s-1SIGINT.\s0
2770.PP
2771.Vb 5
2772\& static void
2773\& sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
2774\& {
2775\& ev_break (loop, EVBREAK_ALL);
2776\& }
2777\&
2778\& ev_signal signal_watcher;
2779\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
2780\& ev_signal_start (loop, &signal_watcher);
2781.Ve
1420.ie n .Sh """ev_child"" \- watch out for process status changes" 2782.ie n .SS """ev_child"" \- watch out for process status changes"
1421.el .Sh "\f(CWev_child\fP \- watch out for process status changes" 2783.el .SS "\f(CWev_child\fP \- watch out for process status changes"
1422.IX Subsection "ev_child - watch out for process status changes" 2784.IX Subsection "ev_child - watch out for process status changes"
1423Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to 2785Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
1424some child status changes (most typically when a child of yours dies). 2786some child status changes (most typically when a child of yours dies or
2787exits). It is permissible to install a child watcher \fIafter\fR the child
2788has been forked (which implies it might have already exited), as long
2789as the event loop isn't entered (or is continued from a watcher), i.e.,
2790forking and then immediately registering a watcher for the child is fine,
2791but forking and registering a watcher a few event loop iterations later or
2792in the next callback invocation is not.
2793.PP
2794Only the default event loop is capable of handling signals, and therefore
2795you can only register child watchers in the default event loop.
2796.PP
2797Due to some design glitches inside libev, child watchers will always be
2798handled at maximum priority (their priority is set to \f(CW\*(C`EV_MAXPRI\*(C'\fR by
2799libev)
2800.PP
2801\fIProcess Interaction\fR
2802.IX Subsection "Process Interaction"
2803.PP
2804Libev grabs \f(CW\*(C`SIGCHLD\*(C'\fR as soon as the default event loop is
2805initialised. This is necessary to guarantee proper behaviour even if the
2806first child watcher is started after the child exits. The occurrence
2807of \f(CW\*(C`SIGCHLD\*(C'\fR is recorded asynchronously, but child reaping is done
2808synchronously as part of the event loop processing. Libev always reaps all
2809children, even ones not watched.
2810.PP
2811\fIOverriding the Built-In Processing\fR
2812.IX Subsection "Overriding the Built-In Processing"
2813.PP
2814Libev offers no special support for overriding the built-in child
2815processing, but if your application collides with libev's default child
2816handler, you can override it easily by installing your own handler for
2817\&\f(CW\*(C`SIGCHLD\*(C'\fR after initialising the default loop, and making sure the
2818default loop never gets destroyed. You are encouraged, however, to use an
2819event-based approach to child reaping and thus use libev's support for
2820that, so other libev users can use \f(CW\*(C`ev_child\*(C'\fR watchers freely.
2821.PP
2822\fIStopping the Child Watcher\fR
2823.IX Subsection "Stopping the Child Watcher"
2824.PP
2825Currently, the child watcher never gets stopped, even when the
2826child terminates, so normally one needs to stop the watcher in the
2827callback. Future versions of libev might stop the watcher automatically
2828when a child exit is detected (calling \f(CW\*(C`ev_child_stop\*(C'\fR twice is not a
2829problem).
2830.PP
2831\fIWatcher-Specific Functions and Data Members\fR
2832.IX Subsection "Watcher-Specific Functions and Data Members"
1425.IP "ev_child_init (ev_child *, callback, int pid)" 4 2833.IP "ev_child_init (ev_child *, callback, int pid, int trace)" 4
1426.IX Item "ev_child_init (ev_child *, callback, int pid)" 2834.IX Item "ev_child_init (ev_child *, callback, int pid, int trace)"
1427.PD 0 2835.PD 0
1428.IP "ev_child_set (ev_child *, int pid)" 4 2836.IP "ev_child_set (ev_child *, int pid, int trace)" 4
1429.IX Item "ev_child_set (ev_child *, int pid)" 2837.IX Item "ev_child_set (ev_child *, int pid, int trace)"
1430.PD 2838.PD
1431Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or 2839Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
1432\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look 2840\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
1433at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see 2841at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
1434the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems 2842the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
1435\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the 2843\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
1436process causing the status change. 2844process causing the status change. \f(CW\*(C`trace\*(C'\fR must be either \f(CW0\fR (only
2845activate the watcher when the process terminates) or \f(CW1\fR (additionally
2846activate the watcher when the process is stopped or continued).
1437.IP "int pid [read\-only]" 4 2847.IP "int pid [read\-only]" 4
1438.IX Item "int pid [read-only]" 2848.IX Item "int pid [read-only]"
1439The process id this watcher watches out for, or \f(CW0\fR, meaning any process id. 2849The process id this watcher watches out for, or \f(CW0\fR, meaning any process id.
1440.IP "int rpid [read\-write]" 4 2850.IP "int rpid [read\-write]" 4
1441.IX Item "int rpid [read-write]" 2851.IX Item "int rpid [read-write]"
… …
1443.IP "int rstatus [read\-write]" 4 2853.IP "int rstatus [read\-write]" 4
1444.IX Item "int rstatus [read-write]" 2854.IX Item "int rstatus [read-write]"
1445The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems 2855The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems
1446\&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details). 2856\&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details).
1447.PP 2857.PP
1448Example: Try to exit cleanly on \s-1SIGINT\s0 and \s-1SIGTERM\s0. 2858\fIExamples\fR
2859.IX Subsection "Examples"
1449.PP 2860.PP
2861Example: \f(CW\*(C`fork()\*(C'\fR a new process and install a child handler to wait for
2862its completion.
2863.PP
1450.Vb 5 2864.Vb 1
2865\& ev_child cw;
2866\&
1451\& static void 2867\& static void
1452\& sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents) 2868\& child_cb (EV_P_ ev_child *w, int revents)
1453\& { 2869\& {
1454\& ev_unloop (loop, EVUNLOOP_ALL); 2870\& ev_child_stop (EV_A_ w);
2871\& printf ("process %d exited with status %x\en", w\->rpid, w\->rstatus);
1455\& } 2872\& }
2873\&
2874\& pid_t pid = fork ();
2875\&
2876\& if (pid < 0)
2877\& // error
2878\& else if (pid == 0)
2879\& {
2880\& // the forked child executes here
2881\& exit (1);
2882\& }
2883\& else
2884\& {
2885\& ev_child_init (&cw, child_cb, pid, 0);
2886\& ev_child_start (EV_DEFAULT_ &cw);
2887\& }
1456.Ve 2888.Ve
1457.PP
1458.Vb 3
1459\& struct ev_signal signal_watcher;
1460\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1461\& ev_signal_start (loop, &sigint_cb);
1462.Ve
1463.ie n .Sh """ev_stat"" \- did the file attributes just change?" 2889.ie n .SS """ev_stat"" \- did the file attributes just change?"
1464.el .Sh "\f(CWev_stat\fP \- did the file attributes just change?" 2890.el .SS "\f(CWev_stat\fP \- did the file attributes just change?"
1465.IX Subsection "ev_stat - did the file attributes just change?" 2891.IX Subsection "ev_stat - did the file attributes just change?"
1466This watches a filesystem path for attribute changes. That is, it calls 2892This watches a file system path for attribute changes. That is, it calls
1467\&\f(CW\*(C`stat\*(C'\fR regularly (or when the \s-1OS\s0 says it changed) and sees if it changed 2893\&\f(CW\*(C`stat\*(C'\fR on that path in regular intervals (or when the \s-1OS\s0 says it changed)
1468compared to the last time, invoking the callback if it did. 2894and sees if it changed compared to the last time, invoking the callback
2895if it did. Starting the watcher \f(CW\*(C`stat\*(C'\fR's the file, so only changes that
2896happen after the watcher has been started will be reported.
1469.PP 2897.PP
1470The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does 2898The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does
1471not exist\*(R" is a status change like any other. The condition \*(L"path does 2899not exist\*(R" is a status change like any other. The condition \*(L"path does not
1472not exist\*(R" is signified by the \f(CW\*(C`st_nlink\*(C'\fR field being zero (which is 2900exist\*(R" (or more correctly \*(L"path cannot be stat'ed\*(R") is signified by the
1473otherwise always forced to be at least one) and all the other fields of 2901\&\f(CW\*(C`st_nlink\*(C'\fR field being zero (which is otherwise always forced to be at
1474the stat buffer having unspecified contents. 2902least one) and all the other fields of the stat buffer having unspecified
2903contents.
1475.PP 2904.PP
1476The path \fIshould\fR be absolute and \fImust not\fR end in a slash. If it is 2905The path \fImust not\fR end in a slash or contain special components such as
2906\&\f(CW\*(C`.\*(C'\fR or \f(CW\*(C`..\*(C'\fR. The path \fIshould\fR be absolute: If it is relative and
1477relative and your working directory changes, the behaviour is undefined. 2907your working directory changes, then the behaviour is undefined.
1478.PP 2908.PP
1479Since there is no standard to do this, the portable implementation simply 2909Since there is no portable change notification interface available, the
1480calls \f(CW\*(C`stat (2)\*(C'\fR regularly on the path to see if it changed somehow. You 2910portable implementation simply calls \f(CWstat(2)\fR regularly on the path
1481can specify a recommended polling interval for this case. If you specify 2911to see if it changed somehow. You can specify a recommended polling
1482a polling interval of \f(CW0\fR (highly recommended!) then a \fIsuitable, 2912interval for this case. If you specify a polling interval of \f(CW0\fR (highly
1483unspecified default\fR value will be used (which you can expect to be around 2913recommended!) then a \fIsuitable, unspecified default\fR value will be used
1484five seconds, although this might change dynamically). Libev will also 2914(which you can expect to be around five seconds, although this might
1485impose a minimum interval which is currently around \f(CW0.1\fR, but thats 2915change dynamically). Libev will also impose a minimum interval which is
1486usually overkill. 2916currently around \f(CW0.1\fR, but that's usually overkill.
1487.PP 2917.PP
1488This watcher type is not meant for massive numbers of stat watchers, 2918This watcher type is not meant for massive numbers of stat watchers,
1489as even with OS-supported change notifications, this can be 2919as even with OS-supported change notifications, this can be
1490resource\-intensive. 2920resource-intensive.
1491.PP 2921.PP
1492At the time of this writing, only the Linux inotify interface is 2922At the time of this writing, the only OS-specific interface implemented
1493implemented (implementing kqueue support is left as an exercise for the 2923is the Linux inotify interface (implementing kqueue support is left as an
1494reader). Inotify will be used to give hints only and should not change the 2924exercise for the reader. Note, however, that the author sees no way of
1495semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers, which means that libev sometimes needs 2925implementing \f(CW\*(C`ev_stat\*(C'\fR semantics with kqueue, except as a hint).
1496to fall back to regular polling again even with inotify, but changes are 2926.PP
1497usually detected immediately, and if the file exists there will be no 2927\fI\s-1ABI\s0 Issues (Largefile Support)\fR
1498polling. 2928.IX Subsection "ABI Issues (Largefile Support)"
2929.PP
2930Libev by default (unless the user overrides this) uses the default
2931compilation environment, which means that on systems with large file
2932support disabled by default, you get the 32 bit version of the stat
2933structure. When using the library from programs that change the \s-1ABI\s0 to
2934use 64 bit file offsets the programs will fail. In that case you have to
2935compile libev with the same flags to get binary compatibility. This is
2936obviously the case with any flags that change the \s-1ABI,\s0 but the problem is
2937most noticeably displayed with ev_stat and large file support.
2938.PP
2939The solution for this is to lobby your distribution maker to make large
2940file interfaces available by default (as e.g. FreeBSD does) and not
2941optional. Libev cannot simply switch on large file support because it has
2942to exchange stat structures with application programs compiled using the
2943default compilation environment.
2944.PP
2945\fIInotify and Kqueue\fR
2946.IX Subsection "Inotify and Kqueue"
2947.PP
2948When \f(CW\*(C`inotify (7)\*(C'\fR support has been compiled into libev and present at
2949runtime, it will be used to speed up change detection where possible. The
2950inotify descriptor will be created lazily when the first \f(CW\*(C`ev_stat\*(C'\fR
2951watcher is being started.
2952.PP
2953Inotify presence does not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers
2954except that changes might be detected earlier, and in some cases, to avoid
2955making regular \f(CW\*(C`stat\*(C'\fR calls. Even in the presence of inotify support
2956there are many cases where libev has to resort to regular \f(CW\*(C`stat\*(C'\fR polling,
2957but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
2958many bugs), the path exists (i.e. stat succeeds), and the path resides on
2959a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
2960xfs are fully working) libev usually gets away without polling.
2961.PP
2962There is no support for kqueue, as apparently it cannot be used to
2963implement this functionality, due to the requirement of having a file
2964descriptor open on the object at all times, and detecting renames, unlinks
2965etc. is difficult.
2966.PP
2967\fI\f(CI\*(C`stat ()\*(C'\fI is a synchronous operation\fR
2968.IX Subsection "stat () is a synchronous operation"
2969.PP
2970Libev doesn't normally do any kind of I/O itself, and so is not blocking
2971the process. The exception are \f(CW\*(C`ev_stat\*(C'\fR watchers \- those call \f(CW\*(C`stat
2972()\*(C'\fR, which is a synchronous operation.
2973.PP
2974For local paths, this usually doesn't matter: unless the system is very
2975busy or the intervals between stat's are large, a stat call will be fast,
2976as the path data is usually in memory already (except when starting the
2977watcher).
2978.PP
2979For networked file systems, calling \f(CW\*(C`stat ()\*(C'\fR can block an indefinite
2980time due to network issues, and even under good conditions, a stat call
2981often takes multiple milliseconds.
2982.PP
2983Therefore, it is best to avoid using \f(CW\*(C`ev_stat\*(C'\fR watchers on networked
2984paths, although this is fully supported by libev.
2985.PP
2986\fIThe special problem of stat time resolution\fR
2987.IX Subsection "The special problem of stat time resolution"
2988.PP
2989The \f(CW\*(C`stat ()\*(C'\fR system call only supports full-second resolution portably,
2990and even on systems where the resolution is higher, most file systems
2991still only support whole seconds.
2992.PP
2993That means that, if the time is the only thing that changes, you can
2994easily miss updates: on the first update, \f(CW\*(C`ev_stat\*(C'\fR detects a change and
2995calls your callback, which does something. When there is another update
2996within the same second, \f(CW\*(C`ev_stat\*(C'\fR will be unable to detect unless the
2997stat data does change in other ways (e.g. file size).
2998.PP
2999The solution to this is to delay acting on a change for slightly more
3000than a second (or till slightly after the next full second boundary), using
3001a roughly one-second-delay \f(CW\*(C`ev_timer\*(C'\fR (e.g. \f(CW\*(C`ev_timer_set (w, 0., 1.02);
3002ev_timer_again (loop, w)\*(C'\fR).
3003.PP
3004The \f(CW.02\fR offset is added to work around small timing inconsistencies
3005of some operating systems (where the second counter of the current time
3006might be be delayed. One such system is the Linux kernel, where a call to
3007\&\f(CW\*(C`gettimeofday\*(C'\fR might return a timestamp with a full second later than
3008a subsequent \f(CW\*(C`time\*(C'\fR call \- if the equivalent of \f(CW\*(C`time ()\*(C'\fR is used to
3009update file times then there will be a small window where the kernel uses
3010the previous second to update file times but libev might already execute
3011the timer callback).
3012.PP
3013\fIWatcher-Specific Functions and Data Members\fR
3014.IX Subsection "Watcher-Specific Functions and Data Members"
1499.IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4 3015.IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4
1500.IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 3016.IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)"
1501.PD 0 3017.PD 0
1502.IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4 3018.IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4
1503.IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 3019.IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)"
… …
1506\&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to 3022\&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to
1507be detected and should normally be specified as \f(CW0\fR to let libev choose 3023be detected and should normally be specified as \f(CW0\fR to let libev choose
1508a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same 3024a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same
1509path for as long as the watcher is active. 3025path for as long as the watcher is active.
1510.Sp 3026.Sp
1511The callback will be receive \f(CW\*(C`EV_STAT\*(C'\fR when a change was detected, 3027The callback will receive an \f(CW\*(C`EV_STAT\*(C'\fR event when a change was detected,
1512relative to the attributes at the time the watcher was started (or the 3028relative to the attributes at the time the watcher was started (or the
1513last change was detected). 3029last change was detected).
1514.IP "ev_stat_stat (ev_stat *)" 4 3030.IP "ev_stat_stat (loop, ev_stat *)" 4
1515.IX Item "ev_stat_stat (ev_stat *)" 3031.IX Item "ev_stat_stat (loop, ev_stat *)"
1516Updates the stat buffer immediately with new values. If you change the 3032Updates the stat buffer immediately with new values. If you change the
1517watched path in your callback, you could call this fucntion to avoid 3033watched path in your callback, you could call this function to avoid
1518detecting this change (while introducing a race condition). Can also be 3034detecting this change (while introducing a race condition if you are not
1519useful simply to find out the new values. 3035the only one changing the path). Can also be useful simply to find out the
3036new values.
1520.IP "ev_statdata attr [read\-only]" 4 3037.IP "ev_statdata attr [read\-only]" 4
1521.IX Item "ev_statdata attr [read-only]" 3038.IX Item "ev_statdata attr [read-only]"
1522The most-recently detected attributes of the file. Although the type is of 3039The most-recently detected attributes of the file. Although the type is
1523\&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types 3040\&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types
3041suitable for your system, but you can only rely on the POSIX-standardised
1524suitable for your system. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there 3042members to be present. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there was
1525was some error while \f(CW\*(C`stat\*(C'\fRing the file. 3043some error while \f(CW\*(C`stat\*(C'\fRing the file.
1526.IP "ev_statdata prev [read\-only]" 4 3044.IP "ev_statdata prev [read\-only]" 4
1527.IX Item "ev_statdata prev [read-only]" 3045.IX Item "ev_statdata prev [read-only]"
1528The previous attributes of the file. The callback gets invoked whenever 3046The previous attributes of the file. The callback gets invoked whenever
1529\&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR. 3047\&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR, or, more precisely, one or more of these members
3048differ: \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,
3049\&\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.
1530.IP "ev_tstamp interval [read\-only]" 4 3050.IP "ev_tstamp interval [read\-only]" 4
1531.IX Item "ev_tstamp interval [read-only]" 3051.IX Item "ev_tstamp interval [read-only]"
1532The specified interval. 3052The specified interval.
1533.IP "const char *path [read\-only]" 4 3053.IP "const char *path [read\-only]" 4
1534.IX Item "const char *path [read-only]" 3054.IX Item "const char *path [read-only]"
1535The filesystem path that is being watched. 3055The file system path that is being watched.
3056.PP
3057\fIExamples\fR
3058.IX Subsection "Examples"
1536.PP 3059.PP
1537Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes. 3060Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes.
1538.PP 3061.PP
1539.Vb 15 3062.Vb 10
1540\& static void 3063\& static void
1541\& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents) 3064\& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1542\& { 3065\& {
1543\& /* /etc/passwd changed in some way */ 3066\& /* /etc/passwd changed in some way */
1544\& if (w->attr.st_nlink) 3067\& if (w\->attr.st_nlink)
1545\& { 3068\& {
1546\& printf ("passwd current size %ld\en", (long)w->attr.st_size); 3069\& printf ("passwd current size %ld\en", (long)w\->attr.st_size);
1547\& printf ("passwd current atime %ld\en", (long)w->attr.st_mtime); 3070\& printf ("passwd current atime %ld\en", (long)w\->attr.st_mtime);
1548\& printf ("passwd current mtime %ld\en", (long)w->attr.st_mtime); 3071\& printf ("passwd current mtime %ld\en", (long)w\->attr.st_mtime);
1549\& } 3072\& }
1550\& else 3073\& else
1551\& /* you shalt not abuse printf for puts */ 3074\& /* you shalt not abuse printf for puts */
1552\& puts ("wow, /etc/passwd is not there, expect problems. " 3075\& puts ("wow, /etc/passwd is not there, expect problems. "
1553\& "if this is windows, they already arrived\en"); 3076\& "if this is windows, they already arrived\en");
1554\& } 3077\& }
3078\&
3079\& ...
3080\& ev_stat passwd;
3081\&
3082\& ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
3083\& ev_stat_start (loop, &passwd);
1555.Ve 3084.Ve
3085.PP
3086Example: Like above, but additionally use a one-second delay so we do not
3087miss updates (however, frequent updates will delay processing, too, so
3088one might do the work both on \f(CW\*(C`ev_stat\*(C'\fR callback invocation \fIand\fR on
3089\&\f(CW\*(C`ev_timer\*(C'\fR callback invocation).
1556.PP 3090.PP
1557.Vb 2 3091.Vb 2
3092\& static ev_stat passwd;
3093\& static ev_timer timer;
3094\&
3095\& static void
3096\& timer_cb (EV_P_ ev_timer *w, int revents)
3097\& {
3098\& ev_timer_stop (EV_A_ w);
3099\&
3100\& /* now it\*(Aqs one second after the most recent passwd change */
3101\& }
3102\&
3103\& static void
3104\& stat_cb (EV_P_ ev_stat *w, int revents)
3105\& {
3106\& /* reset the one\-second timer */
3107\& ev_timer_again (EV_A_ &timer);
3108\& }
3109\&
1558\& ... 3110\& ...
1559\& ev_stat passwd;
1560.Ve
1561.PP
1562.Vb 2
1563\& ev_stat_init (&passwd, passwd_cb, "/etc/passwd"); 3111\& ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1564\& ev_stat_start (loop, &passwd); 3112\& ev_stat_start (loop, &passwd);
3113\& ev_timer_init (&timer, timer_cb, 0., 1.02);
1565.Ve 3114.Ve
1566.ie n .Sh """ev_idle"" \- when you've got nothing better to do..." 3115.ie n .SS """ev_idle"" \- when you've got nothing better to do..."
1567.el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do..." 3116.el .SS "\f(CWev_idle\fP \- when you've got nothing better to do..."
1568.IX Subsection "ev_idle - when you've got nothing better to do..." 3117.IX Subsection "ev_idle - when you've got nothing better to do..."
1569Idle watchers trigger events when no other events of the same or higher 3118Idle watchers trigger events when no other events of the same or higher
1570priority are pending (prepare, check and other idle watchers do not 3119priority are pending (prepare, check and other idle watchers do not count
1571count). 3120as receiving \*(L"events\*(R").
1572.PP 3121.PP
1573That is, as long as your process is busy handling sockets or timeouts 3122That is, as long as your process is busy handling sockets or timeouts
1574(or even signals, imagine) of the same or higher priority it will not be 3123(or even signals, imagine) of the same or higher priority it will not be
1575triggered. But when your process is idle (or only lower-priority watchers 3124triggered. But when your process is idle (or only lower-priority watchers
1576are pending), the idle watchers are being called once per event loop 3125are pending), the idle watchers are being called once per event loop
… …
1580The most noteworthy effect is that as long as any idle watchers are 3129The most noteworthy effect is that as long as any idle watchers are
1581active, the process will not block when waiting for new events. 3130active, the process will not block when waiting for new events.
1582.PP 3131.PP
1583Apart from keeping your process non-blocking (which is a useful 3132Apart from keeping your process non-blocking (which is a useful
1584effect on its own sometimes), idle watchers are a good place to do 3133effect on its own sometimes), idle watchers are a good place to do
1585\&\*(L"pseudo\-background processing\*(R", or delay processing stuff to after the 3134\&\*(L"pseudo-background processing\*(R", or delay processing stuff to after the
1586event loop has handled all outstanding events. 3135event loop has handled all outstanding events.
3136.PP
3137\fIAbusing an \f(CI\*(C`ev_idle\*(C'\fI watcher for its side-effect\fR
3138.IX Subsection "Abusing an ev_idle watcher for its side-effect"
3139.PP
3140As long as there is at least one active idle watcher, libev will never
3141sleep unnecessarily. Or in other words, it will loop as fast as possible.
3142For this to work, the idle watcher doesn't need to be invoked at all \- the
3143lowest priority will do.
3144.PP
3145This mode of operation can be useful together with an \f(CW\*(C`ev_check\*(C'\fR watcher,
3146to do something on each event loop iteration \- for example to balance load
3147between different connections.
3148.PP
3149See \*(L"Abusing an ev_check watcher for its side-effect\*(R" for a longer
3150example.
3151.PP
3152\fIWatcher-Specific Functions and Data Members\fR
3153.IX Subsection "Watcher-Specific Functions and Data Members"
1587.IP "ev_idle_init (ev_signal *, callback)" 4 3154.IP "ev_idle_init (ev_idle *, callback)" 4
1588.IX Item "ev_idle_init (ev_signal *, callback)" 3155.IX Item "ev_idle_init (ev_idle *, callback)"
1589Initialises and configures the idle watcher \- it has no parameters of any 3156Initialises and configures the idle watcher \- it has no parameters of any
1590kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless, 3157kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
1591believe me. 3158believe me.
1592.PP 3159.PP
3160\fIExamples\fR
3161.IX Subsection "Examples"
3162.PP
1593Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the 3163Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the
1594callback, free it. Also, use no error checking, as usual. 3164callback, free it. Also, use no error checking, as usual.
1595.PP 3165.PP
1596.Vb 7 3166.Vb 5
1597\& static void 3167\& static void
1598\& idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents) 3168\& idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1599\& { 3169\& {
3170\& // stop the watcher
3171\& ev_idle_stop (loop, w);
3172\&
3173\& // now we can free it
1600\& free (w); 3174\& free (w);
3175\&
1601\& // now do something you wanted to do when the program has 3176\& // now do something you wanted to do when the program has
1602\& // no longer asnything immediate to do. 3177\& // no longer anything immediate to do.
1603\& } 3178\& }
1604.Ve 3179\&
1605.PP
1606.Vb 3
1607\& struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle)); 3180\& ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1608\& ev_idle_init (idle_watcher, idle_cb); 3181\& ev_idle_init (idle_watcher, idle_cb);
1609\& ev_idle_start (loop, idle_cb); 3182\& ev_idle_start (loop, idle_watcher);
1610.Ve 3183.Ve
1611.ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop!" 3184.ie n .SS """ev_prepare"" and ""ev_check"" \- customise your event loop!"
1612.el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!" 3185.el .SS "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!"
1613.IX Subsection "ev_prepare and ev_check - customise your event loop!" 3186.IX Subsection "ev_prepare and ev_check - customise your event loop!"
1614Prepare and check watchers are usually (but not always) used in tandem: 3187Prepare and check watchers are often (but not always) used in pairs:
1615prepare watchers get invoked before the process blocks and check watchers 3188prepare watchers get invoked before the process blocks and check watchers
1616afterwards. 3189afterwards.
1617.PP 3190.PP
1618You \fImust not\fR call \f(CW\*(C`ev_loop\*(C'\fR or similar functions that enter 3191You \fImust not\fR call \f(CW\*(C`ev_run\*(C'\fR (or similar functions that enter the
1619the current event loop from either \f(CW\*(C`ev_prepare\*(C'\fR or \f(CW\*(C`ev_check\*(C'\fR 3192current event loop) or \f(CW\*(C`ev_loop_fork\*(C'\fR from either \f(CW\*(C`ev_prepare\*(C'\fR or
1620watchers. Other loops than the current one are fine, however. The 3193\&\f(CW\*(C`ev_check\*(C'\fR watchers. Other loops than the current one are fine,
1621rationale behind this is that you do not need to check for recursion in 3194however. The rationale behind this is that you do not need to check
1622those watchers, i.e. the sequence will always be \f(CW\*(C`ev_prepare\*(C'\fR, blocking, 3195for recursion in those watchers, i.e. the sequence will always be
1623\&\f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each kind they will always be 3196\&\f(CW\*(C`ev_prepare\*(C'\fR, blocking, \f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each
1624called in pairs bracketing the blocking call. 3197kind they will always be called in pairs bracketing the blocking call.
1625.PP 3198.PP
1626Their main purpose is to integrate other event mechanisms into libev and 3199Their main purpose is to integrate other event mechanisms into libev and
1627their use is somewhat advanced. This could be used, for example, to track 3200their use is somewhat advanced. They could be used, for example, to track
1628variable changes, implement your own watchers, integrate net-snmp or a 3201variable changes, implement your own watchers, integrate net-snmp or a
1629coroutine library and lots more. They are also occasionally useful if 3202coroutine library and lots more. They are also occasionally useful if
1630you cache some data and want to flush it before blocking (for example, 3203you cache some data and want to flush it before blocking (for example,
1631in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR 3204in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR
1632watcher). 3205watcher).
1633.PP 3206.PP
1634This is done by examining in each prepare call which file descriptors need 3207This is done by examining in each prepare call which file descriptors
1635to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers for 3208need to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers
1636them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many libraries 3209for them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many
1637provide just this functionality). Then, in the check watcher you check for 3210libraries provide exactly this functionality). Then, in the check watcher,
1638any events that occured (by checking the pending status of all watchers 3211you check for any events that occurred (by checking the pending status
1639and stopping them) and call back into the library. The I/O and timer 3212of all watchers and stopping them) and call back into the library. The
1640callbacks will never actually be called (but must be valid nevertheless, 3213I/O and timer callbacks will never actually be called (but must be valid
1641because you never know, you know?). 3214nevertheless, because you never know, you know?).
1642.PP 3215.PP
1643As another example, the Perl Coro module uses these hooks to integrate 3216As another example, the Perl Coro module uses these hooks to integrate
1644coroutines into libev programs, by yielding to other active coroutines 3217coroutines into libev programs, by yielding to other active coroutines
1645during each prepare and only letting the process block if no coroutines 3218during each prepare and only letting the process block if no coroutines
1646are ready to run (it's actually more complicated: it only runs coroutines 3219are ready to run (it's actually more complicated: it only runs coroutines
1647with priority higher than or equal to the event loop and one coroutine 3220with priority higher than or equal to the event loop and one coroutine
1648of lower priority, but only once, using idle watchers to keep the event 3221of lower priority, but only once, using idle watchers to keep the event
1649loop from blocking if lower-priority coroutines are active, thus mapping 3222loop from blocking if lower-priority coroutines are active, thus mapping
1650low-priority coroutines to idle/background tasks). 3223low-priority coroutines to idle/background tasks).
1651.PP 3224.PP
1652It is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR) 3225When used for this purpose, it is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers
1653priority, to ensure that they are being run before any other watchers 3226highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR) priority, to ensure that they are being run before
3227any other watchers after the poll (this doesn't matter for \f(CW\*(C`ev_prepare\*(C'\fR
3228watchers).
3229.PP
1654after the poll. Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers, 3230Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers, too) should not
1655too) should not activate (\*(L"feed\*(R") events into libev. While libev fully 3231activate (\*(L"feed\*(R") events into libev. While libev fully supports this, they
1656supports this, they will be called before other \f(CW\*(C`ev_check\*(C'\fR watchers did 3232might get executed before other \f(CW\*(C`ev_check\*(C'\fR watchers did their job. As
1657their job. As \f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other event 3233\&\f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other (non-libev) event
1658loops those other event loops might be in an unusable state until their 3234loops those other event loops might be in an unusable state until their
1659\&\f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to coexist peacefully with 3235\&\f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to coexist peacefully with
1660others). 3236others).
3237.PP
3238\fIAbusing an \f(CI\*(C`ev_check\*(C'\fI watcher for its side-effect\fR
3239.IX Subsection "Abusing an ev_check watcher for its side-effect"
3240.PP
3241\&\f(CW\*(C`ev_check\*(C'\fR (and less often also \f(CW\*(C`ev_prepare\*(C'\fR) watchers can also be
3242useful because they are called once per event loop iteration. For
3243example, if you want to handle a large number of connections fairly, you
3244normally only do a bit of work for each active connection, and if there
3245is more work to do, you wait for the next event loop iteration, so other
3246connections have a chance of making progress.
3247.PP
3248Using an \f(CW\*(C`ev_check\*(C'\fR watcher is almost enough: it will be called on the
3249next event loop iteration. However, that isn't as soon as possible \-
3250without external events, your \f(CW\*(C`ev_check\*(C'\fR watcher will not be invoked.
3251.PP
3252This is where \f(CW\*(C`ev_idle\*(C'\fR watchers come in handy \- all you need is a
3253single global idle watcher that is active as long as you have one active
3254\&\f(CW\*(C`ev_check\*(C'\fR watcher. The \f(CW\*(C`ev_idle\*(C'\fR watcher makes sure the event loop
3255will not sleep, and the \f(CW\*(C`ev_check\*(C'\fR watcher makes sure a callback gets
3256invoked. Neither watcher alone can do that.
3257.PP
3258\fIWatcher-Specific Functions and Data Members\fR
3259.IX Subsection "Watcher-Specific Functions and Data Members"
1661.IP "ev_prepare_init (ev_prepare *, callback)" 4 3260.IP "ev_prepare_init (ev_prepare *, callback)" 4
1662.IX Item "ev_prepare_init (ev_prepare *, callback)" 3261.IX Item "ev_prepare_init (ev_prepare *, callback)"
1663.PD 0 3262.PD 0
1664.IP "ev_check_init (ev_check *, callback)" 4 3263.IP "ev_check_init (ev_check *, callback)" 4
1665.IX Item "ev_check_init (ev_check *, callback)" 3264.IX Item "ev_check_init (ev_check *, callback)"
1666.PD 3265.PD
1667Initialises and configures the prepare or check watcher \- they have no 3266Initialises and configures the prepare or check watcher \- they have no
1668parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR 3267parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
1669macros, but using them is utterly, utterly and completely pointless. 3268macros, but using them is utterly, utterly, utterly and completely
3269pointless.
3270.PP
3271\fIExamples\fR
3272.IX Subsection "Examples"
1670.PP 3273.PP
1671There are a number of principal ways to embed other event loops or modules 3274There are a number of principal ways to embed other event loops or modules
1672into libev. Here are some ideas on how to include libadns into libev 3275into libev. Here are some ideas on how to include libadns into libev
1673(there is a Perl module named \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could 3276(there is a Perl module named \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could
1674use for an actually working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR 3277use as a working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR embeds a
1675embeds a Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0 3278Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0 into the
1676into the Glib event loop). 3279Glib event loop).
1677.PP 3280.PP
1678Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler, 3281Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler,
1679and in a check watcher, destroy them and call into libadns. What follows 3282and in a check watcher, destroy them and call into libadns. What follows
1680is pseudo-code only of course. This requires you to either use a low 3283is pseudo-code only of course. This requires you to either use a low
1681priority for the check watcher or use \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as 3284priority for the check watcher or use \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as
1682the callbacks for the IO/timeout watchers might not have been called yet. 3285the callbacks for the IO/timeout watchers might not have been called yet.
1683.PP 3286.PP
1684.Vb 2 3287.Vb 2
1685\& static ev_io iow [nfd]; 3288\& static ev_io iow [nfd];
1686\& static ev_timer tw; 3289\& static ev_timer tw;
1687.Ve 3290\&
1688.PP
1689.Vb 4
1690\& static void 3291\& static void
1691\& io_cb (ev_loop *loop, ev_io *w, int revents) 3292\& io_cb (struct ev_loop *loop, ev_io *w, int revents)
1692\& { 3293\& {
1693\& } 3294\& }
1694.Ve 3295\&
1695.PP
1696.Vb 8
1697\& // create io watchers for each fd and a timer before blocking 3296\& // create io watchers for each fd and a timer before blocking
1698\& static void 3297\& static void
1699\& adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents) 3298\& adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1700\& { 3299\& {
1701\& int timeout = 3600000; 3300\& int timeout = 3600000;
1702\& struct pollfd fds [nfd]; 3301\& struct pollfd fds [nfd];
1703\& // actual code will need to loop here and realloc etc. 3302\& // actual code will need to loop here and realloc etc.
1704\& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ())); 3303\& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1705.Ve 3304\&
1706.PP
1707.Vb 3
1708\& /* the callback is illegal, but won't be called as we stop during check */ 3305\& /* the callback is illegal, but won\*(Aqt be called as we stop during check */
1709\& ev_timer_init (&tw, 0, timeout * 1e-3); 3306\& ev_timer_init (&tw, 0, timeout * 1e\-3, 0.);
1710\& ev_timer_start (loop, &tw); 3307\& ev_timer_start (loop, &tw);
1711.Ve 3308\&
1712.PP
1713.Vb 6
1714\& // create one ev_io per pollfd 3309\& // create one ev_io per pollfd
1715\& for (int i = 0; i < nfd; ++i) 3310\& for (int i = 0; i < nfd; ++i)
1716\& { 3311\& {
1717\& ev_io_init (iow + i, io_cb, fds [i].fd, 3312\& ev_io_init (iow + i, io_cb, fds [i].fd,
1718\& ((fds [i].events & POLLIN ? EV_READ : 0) 3313\& ((fds [i].events & POLLIN ? EV_READ : 0)
1719\& | (fds [i].events & POLLOUT ? EV_WRITE : 0))); 3314\& | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1720.Ve 3315\&
1721.PP
1722.Vb 4
1723\& fds [i].revents = 0; 3316\& fds [i].revents = 0;
1724\& ev_io_start (loop, iow + i); 3317\& ev_io_start (loop, iow + i);
1725\& } 3318\& }
1726\& } 3319\& }
1727.Ve 3320\&
1728.PP
1729.Vb 5
1730\& // stop all watchers after blocking 3321\& // stop all watchers after blocking
1731\& static void 3322\& static void
1732\& adns_check_cb (ev_loop *loop, ev_check *w, int revents) 3323\& adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1733\& { 3324\& {
1734\& ev_timer_stop (loop, &tw); 3325\& ev_timer_stop (loop, &tw);
1735.Ve 3326\&
1736.PP
1737.Vb 8
1738\& for (int i = 0; i < nfd; ++i) 3327\& for (int i = 0; i < nfd; ++i)
1739\& { 3328\& {
1740\& // set the relevant poll flags 3329\& // set the relevant poll flags
1741\& // could also call adns_processreadable etc. here 3330\& // could also call adns_processreadable etc. here
1742\& struct pollfd *fd = fds + i; 3331\& struct pollfd *fd = fds + i;
1743\& int revents = ev_clear_pending (iow + i); 3332\& int revents = ev_clear_pending (iow + i);
1744\& if (revents & EV_READ ) fd->revents |= fd->events & POLLIN; 3333\& if (revents & EV_READ ) fd\->revents |= fd\->events & POLLIN;
1745\& if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT; 3334\& if (revents & EV_WRITE) fd\->revents |= fd\->events & POLLOUT;
1746.Ve 3335\&
1747.PP
1748.Vb 3
1749\& // now stop the watcher 3336\& // now stop the watcher
1750\& ev_io_stop (loop, iow + i); 3337\& ev_io_stop (loop, iow + i);
1751\& } 3338\& }
1752.Ve 3339\&
1753.PP
1754.Vb 2
1755\& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop)); 3340\& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1756\& } 3341\& }
1757.Ve 3342.Ve
1758.PP 3343.PP
1759Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR 3344Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR
1760in the prepare watcher and would dispose of the check watcher. 3345in the prepare watcher and would dispose of the check watcher.
1761.PP 3346.PP
1762Method 3: If the module to be embedded supports explicit event 3347Method 3: If the module to be embedded supports explicit event
1763notification (adns does), you can also make use of the actual watcher 3348notification (libadns does), you can also make use of the actual watcher
1764callbacks, and only destroy/create the watchers in the prepare watcher. 3349callbacks, and only destroy/create the watchers in the prepare watcher.
1765.PP 3350.PP
1766.Vb 5 3351.Vb 5
1767\& static void 3352\& static void
1768\& timer_cb (EV_P_ ev_timer *w, int revents) 3353\& timer_cb (EV_P_ ev_timer *w, int revents)
1769\& { 3354\& {
1770\& adns_state ads = (adns_state)w->data; 3355\& adns_state ads = (adns_state)w\->data;
1771\& update_now (EV_A); 3356\& update_now (EV_A);
1772.Ve 3357\&
1773.PP
1774.Vb 2
1775\& adns_processtimeouts (ads, &tv_now); 3358\& adns_processtimeouts (ads, &tv_now);
1776\& } 3359\& }
1777.Ve 3360\&
1778.PP
1779.Vb 5
1780\& static void 3361\& static void
1781\& io_cb (EV_P_ ev_io *w, int revents) 3362\& io_cb (EV_P_ ev_io *w, int revents)
1782\& { 3363\& {
1783\& adns_state ads = (adns_state)w->data; 3364\& adns_state ads = (adns_state)w\->data;
1784\& update_now (EV_A); 3365\& update_now (EV_A);
1785.Ve 3366\&
1786.PP
1787.Vb 3
1788\& if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now); 3367\& if (revents & EV_READ ) adns_processreadable (ads, w\->fd, &tv_now);
1789\& if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now); 3368\& if (revents & EV_WRITE) adns_processwriteable (ads, w\->fd, &tv_now);
1790\& } 3369\& }
1791.Ve 3370\&
1792.PP
1793.Vb 1
1794\& // do not ever call adns_afterpoll 3371\& // do not ever call adns_afterpoll
1795.Ve 3372.Ve
1796.PP 3373.PP
1797Method 4: Do not use a prepare or check watcher because the module you 3374Method 4: Do not use a prepare or check watcher because the module you
1798want to embed is too inflexible to support it. Instead, youc na override 3375want to embed is not flexible enough to support it. Instead, you can
1799their poll function. The drawback with this solution is that the main 3376override their poll function. The drawback with this solution is that the
1800loop is now no longer controllable by \s-1EV\s0. The \f(CW\*(C`Glib::EV\*(C'\fR module does 3377main loop is now no longer controllable by \s-1EV.\s0 The \f(CW\*(C`Glib::EV\*(C'\fR module uses
1801this. 3378this approach, effectively embedding \s-1EV\s0 as a client into the horrible
3379libglib event loop.
1802.PP 3380.PP
1803.Vb 4 3381.Vb 4
1804\& static gint 3382\& static gint
1805\& event_poll_func (GPollFD *fds, guint nfds, gint timeout) 3383\& event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1806\& { 3384\& {
1807\& int got_events = 0; 3385\& int got_events = 0;
1808.Ve 3386\&
1809.PP
1810.Vb 2
1811\& for (n = 0; n < nfds; ++n) 3387\& for (n = 0; n < nfds; ++n)
1812\& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events 3388\& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1813.Ve 3389\&
1814.PP
1815.Vb 2
1816\& if (timeout >= 0) 3390\& if (timeout >= 0)
1817\& // create/start timer 3391\& // create/start timer
1818.Ve 3392\&
1819.PP
1820.Vb 2
1821\& // poll 3393\& // poll
1822\& ev_loop (EV_A_ 0); 3394\& ev_run (EV_A_ 0);
1823.Ve 3395\&
1824.PP
1825.Vb 3
1826\& // stop timer again 3396\& // stop timer again
1827\& if (timeout >= 0) 3397\& if (timeout >= 0)
1828\& ev_timer_stop (EV_A_ &to); 3398\& ev_timer_stop (EV_A_ &to);
1829.Ve 3399\&
1830.PP
1831.Vb 3
1832\& // stop io watchers again - their callbacks should have set 3400\& // stop io watchers again \- their callbacks should have set
1833\& for (n = 0; n < nfds; ++n) 3401\& for (n = 0; n < nfds; ++n)
1834\& ev_io_stop (EV_A_ iow [n]); 3402\& ev_io_stop (EV_A_ iow [n]);
1835.Ve 3403\&
1836.PP
1837.Vb 2
1838\& return got_events; 3404\& return got_events;
1839\& } 3405\& }
1840.Ve 3406.Ve
1841.ie n .Sh """ev_embed"" \- when one backend isn't enough..." 3407.ie n .SS """ev_embed"" \- when one backend isn't enough..."
1842.el .Sh "\f(CWev_embed\fP \- when one backend isn't enough..." 3408.el .SS "\f(CWev_embed\fP \- when one backend isn't enough..."
1843.IX Subsection "ev_embed - when one backend isn't enough..." 3409.IX Subsection "ev_embed - when one backend isn't enough..."
1844This is a rather advanced watcher type that lets you embed one event loop 3410This is a rather advanced watcher type that lets you embed one event loop
1845into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded 3411into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded
1846loop, other types of watchers might be handled in a delayed or incorrect 3412loop, other types of watchers might be handled in a delayed or incorrect
1847fashion and must not be used). 3413fashion and must not be used).
… …
1850prioritise I/O. 3416prioritise I/O.
1851.PP 3417.PP
1852As an example for a bug workaround, the kqueue backend might only support 3418As an example for a bug workaround, the kqueue backend might only support
1853sockets on some platform, so it is unusable as generic backend, but you 3419sockets on some platform, so it is unusable as generic backend, but you
1854still want to make use of it because you have many sockets and it scales 3420still want to make use of it because you have many sockets and it scales
1855so nicely. In this case, you would create a kqueue-based loop and embed it 3421so nicely. In this case, you would create a kqueue-based loop and embed
1856into your default loop (which might use e.g. poll). Overall operation will 3422it into your default loop (which might use e.g. poll). Overall operation
1857be a bit slower because first libev has to poll and then call kevent, but 3423will be a bit slower because first libev has to call \f(CW\*(C`poll\*(C'\fR and then
1858at least you can use both at what they are best. 3424\&\f(CW\*(C`kevent\*(C'\fR, but at least you can use both mechanisms for what they are
3425best: \f(CW\*(C`kqueue\*(C'\fR for scalable sockets and \f(CW\*(C`poll\*(C'\fR if you want it to work :)
1859.PP 3426.PP
1860As for prioritising I/O: rarely you have the case where some fds have 3427As for prioritising I/O: under rare circumstances you have the case where
1861to be watched and handled very quickly (with low latency), and even 3428some fds have to be watched and handled very quickly (with low latency),
1862priorities and idle watchers might have too much overhead. In this case 3429and even priorities and idle watchers might have too much overhead. In
1863you would put all the high priority stuff in one loop and all the rest in 3430this case you would put all the high priority stuff in one loop and all
1864a second one, and embed the second one in the first. 3431the rest in a second one, and embed the second one in the first.
1865.PP 3432.PP
1866As long as the watcher is active, the callback will be invoked every time 3433As long as the watcher is active, the callback will be invoked every
1867there might be events pending in the embedded loop. The callback must then 3434time there might be events pending in the embedded loop. The callback
1868call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single sweep and invoke 3435must then call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single
1869their callbacks (you could also start an idle watcher to give the embedded 3436sweep and invoke their callbacks (the callback doesn't need to invoke the
1870loop strictly lower priority for example). You can also set the callback 3437\&\f(CW\*(C`ev_embed_sweep\*(C'\fR function directly, it could also start an idle watcher
1871to \f(CW0\fR, in which case the embed watcher will automatically execute the 3438to give the embedded loop strictly lower priority for example).
1872embedded loop sweep.
1873.PP 3439.PP
1874As long as the watcher is started it will automatically handle events. The 3440You can also set the callback to \f(CW0\fR, in which case the embed watcher
1875callback will be invoked whenever some events have been handled. You can 3441will automatically execute the embedded loop sweep whenever necessary.
1876set the callback to \f(CW0\fR to avoid having to specify one if you are not
1877interested in that.
1878.PP 3442.PP
1879Also, there have not currently been made special provisions for forking: 3443Fork detection will be handled transparently while the \f(CW\*(C`ev_embed\*(C'\fR watcher
1880when you fork, you not only have to call \f(CW\*(C`ev_loop_fork\*(C'\fR on both loops, 3444is active, i.e., the embedded loop will automatically be forked when the
1881but you will also have to stop and restart any \f(CW\*(C`ev_embed\*(C'\fR watchers 3445embedding loop forks. In other cases, the user is responsible for calling
1882yourself. 3446\&\f(CW\*(C`ev_loop_fork\*(C'\fR on the embedded loop.
1883.PP 3447.PP
1884Unfortunately, not all backends are embeddable, only the ones returned by 3448Unfortunately, not all backends are embeddable: only the ones returned by
1885\&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any 3449\&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any
1886portable one. 3450portable one.
1887.PP 3451.PP
1888So when you want to use this feature you will always have to be prepared 3452So when you want to use this feature you will always have to be prepared
1889that you cannot get an embeddable loop. The recommended way to get around 3453that you cannot get an embeddable loop. The recommended way to get around
1890this is to have a separate variables for your embeddable loop, try to 3454this is to have a separate variables for your embeddable loop, try to
1891create it, and if that fails, use the normal loop for everything: 3455create it, and if that fails, use the normal loop for everything.
1892.PP 3456.PP
1893.Vb 3 3457\fI\f(CI\*(C`ev_embed\*(C'\fI and fork\fR
1894\& struct ev_loop *loop_hi = ev_default_init (0); 3458.IX Subsection "ev_embed and fork"
1895\& struct ev_loop *loop_lo = 0;
1896\& struct ev_embed embed;
1897.Ve
1898.PP 3459.PP
1899.Vb 5 3460While the \f(CW\*(C`ev_embed\*(C'\fR watcher is running, forks in the embedding loop will
1900\& // see if there is a chance of getting one that works 3461automatically be applied to the embedded loop as well, so no special
1901\& // (remember that a flags value of 0 means autodetection) 3462fork handling is required in that case. When the watcher is not running,
1902\& loop_lo = ev_embeddable_backends () & ev_recommended_backends () 3463however, it is still the task of the libev user to call \f(CW\*(C`ev_loop_fork ()\*(C'\fR
1903\& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ()) 3464as applicable.
1904\& : 0;
1905.Ve
1906.PP 3465.PP
1907.Vb 8 3466\fIWatcher-Specific Functions and Data Members\fR
1908\& // if we got one, then embed it, otherwise default to loop_hi 3467.IX Subsection "Watcher-Specific Functions and Data Members"
1909\& if (loop_lo)
1910\& {
1911\& ev_embed_init (&embed, 0, loop_lo);
1912\& ev_embed_start (loop_hi, &embed);
1913\& }
1914\& else
1915\& loop_lo = loop_hi;
1916.Ve
1917.IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4 3468.IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
1918.IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 3469.IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)"
1919.PD 0 3470.PD 0
1920.IP "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 4 3471.IP "ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)" 4
1921.IX Item "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 3472.IX Item "ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)"
1922.PD 3473.PD
1923Configures the watcher to embed the given loop, which must be 3474Configures the watcher to embed the given loop, which must be
1924embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be 3475embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be
1925invoked automatically, otherwise it is the responsibility of the callback 3476invoked automatically, otherwise it is the responsibility of the callback
1926to invoke it (it will continue to be called until the sweep has been done, 3477to invoke it (it will continue to be called until the sweep has been done,
1927if you do not want thta, you need to temporarily stop the embed watcher). 3478if you do not want that, you need to temporarily stop the embed watcher).
1928.IP "ev_embed_sweep (loop, ev_embed *)" 4 3479.IP "ev_embed_sweep (loop, ev_embed *)" 4
1929.IX Item "ev_embed_sweep (loop, ev_embed *)" 3480.IX Item "ev_embed_sweep (loop, ev_embed *)"
1930Make a single, non-blocking sweep over the embedded loop. This works 3481Make a single, non-blocking sweep over the embedded loop. This works
1931similarly to \f(CW\*(C`ev_loop (embedded_loop, EVLOOP_NONBLOCK)\*(C'\fR, but in the most 3482similarly to \f(CW\*(C`ev_run (embedded_loop, EVRUN_NOWAIT)\*(C'\fR, but in the most
1932apropriate way for embedded loops. 3483appropriate way for embedded loops.
1933.IP "struct ev_loop *loop [read\-only]" 4 3484.IP "struct ev_loop *other [read\-only]" 4
1934.IX Item "struct ev_loop *loop [read-only]" 3485.IX Item "struct ev_loop *other [read-only]"
1935The embedded event loop. 3486The embedded event loop.
3487.PP
3488\fIExamples\fR
3489.IX Subsection "Examples"
3490.PP
3491Example: Try to get an embeddable event loop and embed it into the default
3492event loop. If that is not possible, use the default loop. The default
3493loop is stored in \f(CW\*(C`loop_hi\*(C'\fR, while the embeddable loop is stored in
3494\&\f(CW\*(C`loop_lo\*(C'\fR (which is \f(CW\*(C`loop_hi\*(C'\fR in the case no embeddable loop can be
3495used).
3496.PP
3497.Vb 3
3498\& struct ev_loop *loop_hi = ev_default_init (0);
3499\& struct ev_loop *loop_lo = 0;
3500\& ev_embed embed;
3501\&
3502\& // see if there is a chance of getting one that works
3503\& // (remember that a flags value of 0 means autodetection)
3504\& loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3505\& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3506\& : 0;
3507\&
3508\& // if we got one, then embed it, otherwise default to loop_hi
3509\& if (loop_lo)
3510\& {
3511\& ev_embed_init (&embed, 0, loop_lo);
3512\& ev_embed_start (loop_hi, &embed);
3513\& }
3514\& else
3515\& loop_lo = loop_hi;
3516.Ve
3517.PP
3518Example: Check if kqueue is available but not recommended and create
3519a kqueue backend for use with sockets (which usually work with any
3520kqueue implementation). Store the kqueue/socket\-only event loop in
3521\&\f(CW\*(C`loop_socket\*(C'\fR. (One might optionally use \f(CW\*(C`EVFLAG_NOENV\*(C'\fR, too).
3522.PP
3523.Vb 3
3524\& struct ev_loop *loop = ev_default_init (0);
3525\& struct ev_loop *loop_socket = 0;
3526\& ev_embed embed;
3527\&
3528\& if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3529\& if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3530\& {
3531\& ev_embed_init (&embed, 0, loop_socket);
3532\& ev_embed_start (loop, &embed);
3533\& }
3534\&
3535\& if (!loop_socket)
3536\& loop_socket = loop;
3537\&
3538\& // now use loop_socket for all sockets, and loop for everything else
3539.Ve
1936.ie n .Sh """ev_fork"" \- the audacity to resume the event loop after a fork" 3540.ie n .SS """ev_fork"" \- the audacity to resume the event loop after a fork"
1937.el .Sh "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork" 3541.el .SS "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork"
1938.IX Subsection "ev_fork - the audacity to resume the event loop after a fork" 3542.IX Subsection "ev_fork - the audacity to resume the event loop after a fork"
1939Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because 3543Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because
1940whoever is a good citizen cared to tell libev about it by calling 3544whoever is a good citizen cared to tell libev about it by calling
1941\&\f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the 3545\&\f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the event loop blocks next
1942event loop blocks next and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called, 3546and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called, and only in the child
1943and only in the child after the fork. If whoever good citizen calling 3547after the fork. If whoever good citizen calling \f(CW\*(C`ev_default_fork\*(C'\fR cheats
1944\&\f(CW\*(C`ev_default_fork\*(C'\fR cheats and calls it in the wrong process, the fork 3548and calls it in the wrong process, the fork handlers will be invoked, too,
1945handlers will be invoked, too, of course. 3549of course.
3550.PP
3551\fIThe special problem of life after fork \- how is it possible?\fR
3552.IX Subsection "The special problem of life after fork - how is it possible?"
3553.PP
3554Most uses of \f(CW\*(C`fork ()\*(C'\fR consist of forking, then some simple calls to set
3555up/change the process environment, followed by a call to \f(CW\*(C`exec()\*(C'\fR. This
3556sequence should be handled by libev without any problems.
3557.PP
3558This changes when the application actually wants to do event handling
3559in the child, or both parent in child, in effect \*(L"continuing\*(R" after the
3560fork.
3561.PP
3562The default mode of operation (for libev, with application help to detect
3563forks) is to duplicate all the state in the child, as would be expected
3564when \fIeither\fR the parent \fIor\fR the child process continues.
3565.PP
3566When both processes want to continue using libev, then this is usually the
3567wrong result. In that case, usually one process (typically the parent) is
3568supposed to continue with all watchers in place as before, while the other
3569process typically wants to start fresh, i.e. without any active watchers.
3570.PP
3571The cleanest and most efficient way to achieve that with libev is to
3572simply create a new event loop, which of course will be \*(L"empty\*(R", and
3573use that for new watchers. This has the advantage of not touching more
3574memory than necessary, and thus avoiding the copy-on-write, and the
3575disadvantage of having to use multiple event loops (which do not support
3576signal watchers).
3577.PP
3578When this is not possible, or you want to use the default loop for
3579other reasons, then in the process that wants to start \*(L"fresh\*(R", call
3580\&\f(CW\*(C`ev_loop_destroy (EV_DEFAULT)\*(C'\fR followed by \f(CW\*(C`ev_default_loop (...)\*(C'\fR.
3581Destroying the default loop will \*(L"orphan\*(R" (not stop) all registered
3582watchers, so you have to be careful not to execute code that modifies
3583those watchers. Note also that in that case, you have to re-register any
3584signal watchers.
3585.PP
3586\fIWatcher-Specific Functions and Data Members\fR
3587.IX Subsection "Watcher-Specific Functions and Data Members"
1946.IP "ev_fork_init (ev_signal *, callback)" 4 3588.IP "ev_fork_init (ev_fork *, callback)" 4
1947.IX Item "ev_fork_init (ev_signal *, callback)" 3589.IX Item "ev_fork_init (ev_fork *, callback)"
1948Initialises and configures the fork watcher \- it has no parameters of any 3590Initialises and configures the fork watcher \- it has no parameters of any
1949kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless, 3591kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless,
1950believe me. 3592really.
3593.ie n .SS """ev_cleanup"" \- even the best things end"
3594.el .SS "\f(CWev_cleanup\fP \- even the best things end"
3595.IX Subsection "ev_cleanup - even the best things end"
3596Cleanup watchers are called just before the event loop is being destroyed
3597by a call to \f(CW\*(C`ev_loop_destroy\*(C'\fR.
3598.PP
3599While there is no guarantee that the event loop gets destroyed, cleanup
3600watchers provide a convenient method to install cleanup hooks for your
3601program, worker threads and so on \- you just to make sure to destroy the
3602loop when you want them to be invoked.
3603.PP
3604Cleanup watchers are invoked in the same way as any other watcher. Unlike
3605all other watchers, they do not keep a reference to the event loop (which
3606makes a lot of sense if you think about it). Like all other watchers, you
3607can call libev functions in the callback, except \f(CW\*(C`ev_cleanup_start\*(C'\fR.
3608.PP
3609\fIWatcher-Specific Functions and Data Members\fR
3610.IX Subsection "Watcher-Specific Functions and Data Members"
3611.IP "ev_cleanup_init (ev_cleanup *, callback)" 4
3612.IX Item "ev_cleanup_init (ev_cleanup *, callback)"
3613Initialises and configures the cleanup watcher \- it has no parameters of
3614any kind. There is a \f(CW\*(C`ev_cleanup_set\*(C'\fR macro, but using it is utterly
3615pointless, I assure you.
3616.PP
3617Example: Register an atexit handler to destroy the default loop, so any
3618cleanup functions are called.
3619.PP
3620.Vb 5
3621\& static void
3622\& program_exits (void)
3623\& {
3624\& ev_loop_destroy (EV_DEFAULT_UC);
3625\& }
3626\&
3627\& ...
3628\& atexit (program_exits);
3629.Ve
3630.ie n .SS """ev_async"" \- how to wake up an event loop"
3631.el .SS "\f(CWev_async\fP \- how to wake up an event loop"
3632.IX Subsection "ev_async - how to wake up an event loop"
3633In general, you cannot use an \f(CW\*(C`ev_loop\*(C'\fR from multiple threads or other
3634asynchronous sources such as signal handlers (as opposed to multiple event
3635loops \- those are of course safe to use in different threads).
3636.PP
3637Sometimes, however, you need to wake up an event loop you do not control,
3638for example because it belongs to another thread. This is what \f(CW\*(C`ev_async\*(C'\fR
3639watchers do: as long as the \f(CW\*(C`ev_async\*(C'\fR watcher is active, you can signal
3640it by calling \f(CW\*(C`ev_async_send\*(C'\fR, which is thread\- and signal safe.
3641.PP
3642This functionality is very similar to \f(CW\*(C`ev_signal\*(C'\fR watchers, as signals,
3643too, are asynchronous in nature, and signals, too, will be compressed
3644(i.e. the number of callback invocations may be less than the number of
3645\&\f(CW\*(C`ev_async_send\*(C'\fR calls). In fact, you could use signal watchers as a kind
3646of \*(L"global async watchers\*(R" by using a watcher on an otherwise unused
3647signal, and \f(CW\*(C`ev_feed_signal\*(C'\fR to signal this watcher from another thread,
3648even without knowing which loop owns the signal.
3649.PP
3650\fIQueueing\fR
3651.IX Subsection "Queueing"
3652.PP
3653\&\f(CW\*(C`ev_async\*(C'\fR does not support queueing of data in any way. The reason
3654is that the author does not know of a simple (or any) algorithm for a
3655multiple-writer-single-reader queue that works in all cases and doesn't
3656need elaborate support such as pthreads or unportable memory access
3657semantics.
3658.PP
3659That means that if you want to queue data, you have to provide your own
3660queue. But at least I can tell you how to implement locking around your
3661queue:
3662.IP "queueing from a signal handler context" 4
3663.IX Item "queueing from a signal handler context"
3664To implement race-free queueing, you simply add to the queue in the signal
3665handler but you block the signal handler in the watcher callback. Here is
3666an example that does that for some fictitious \s-1SIGUSR1\s0 handler:
3667.Sp
3668.Vb 1
3669\& static ev_async mysig;
3670\&
3671\& static void
3672\& sigusr1_handler (void)
3673\& {
3674\& sometype data;
3675\&
3676\& // no locking etc.
3677\& queue_put (data);
3678\& ev_async_send (EV_DEFAULT_ &mysig);
3679\& }
3680\&
3681\& static void
3682\& mysig_cb (EV_P_ ev_async *w, int revents)
3683\& {
3684\& sometype data;
3685\& sigset_t block, prev;
3686\&
3687\& sigemptyset (&block);
3688\& sigaddset (&block, SIGUSR1);
3689\& sigprocmask (SIG_BLOCK, &block, &prev);
3690\&
3691\& while (queue_get (&data))
3692\& process (data);
3693\&
3694\& if (sigismember (&prev, SIGUSR1)
3695\& sigprocmask (SIG_UNBLOCK, &block, 0);
3696\& }
3697.Ve
3698.Sp
3699(Note: pthreads in theory requires you to use \f(CW\*(C`pthread_setmask\*(C'\fR
3700instead of \f(CW\*(C`sigprocmask\*(C'\fR when you use threads, but libev doesn't do it
3701either...).
3702.IP "queueing from a thread context" 4
3703.IX Item "queueing from a thread context"
3704The strategy for threads is different, as you cannot (easily) block
3705threads but you can easily preempt them, so to queue safely you need to
3706employ a traditional mutex lock, such as in this pthread example:
3707.Sp
3708.Vb 2
3709\& static ev_async mysig;
3710\& static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
3711\&
3712\& static void
3713\& otherthread (void)
3714\& {
3715\& // only need to lock the actual queueing operation
3716\& pthread_mutex_lock (&mymutex);
3717\& queue_put (data);
3718\& pthread_mutex_unlock (&mymutex);
3719\&
3720\& ev_async_send (EV_DEFAULT_ &mysig);
3721\& }
3722\&
3723\& static void
3724\& mysig_cb (EV_P_ ev_async *w, int revents)
3725\& {
3726\& pthread_mutex_lock (&mymutex);
3727\&
3728\& while (queue_get (&data))
3729\& process (data);
3730\&
3731\& pthread_mutex_unlock (&mymutex);
3732\& }
3733.Ve
3734.PP
3735\fIWatcher-Specific Functions and Data Members\fR
3736.IX Subsection "Watcher-Specific Functions and Data Members"
3737.IP "ev_async_init (ev_async *, callback)" 4
3738.IX Item "ev_async_init (ev_async *, callback)"
3739Initialises and configures the async watcher \- it has no parameters of any
3740kind. There is a \f(CW\*(C`ev_async_set\*(C'\fR macro, but using it is utterly pointless,
3741trust me.
3742.IP "ev_async_send (loop, ev_async *)" 4
3743.IX Item "ev_async_send (loop, ev_async *)"
3744Sends/signals/activates the given \f(CW\*(C`ev_async\*(C'\fR watcher, that is, feeds
3745an \f(CW\*(C`EV_ASYNC\*(C'\fR event on the watcher into the event loop, and instantly
3746returns.
3747.Sp
3748Unlike \f(CW\*(C`ev_feed_event\*(C'\fR, this call is safe to do from other threads,
3749signal or similar contexts (see the discussion of \f(CW\*(C`EV_ATOMIC_T\*(C'\fR in the
3750embedding section below on what exactly this means).
3751.Sp
3752Note that, as with other watchers in libev, multiple events might get
3753compressed into a single callback invocation (another way to look at
3754this is that \f(CW\*(C`ev_async\*(C'\fR watchers are level-triggered: they are set on
3755\&\f(CW\*(C`ev_async_send\*(C'\fR, reset when the event loop detects that).
3756.Sp
3757This call incurs the overhead of at most one extra system call per event
3758loop iteration, if the event loop is blocked, and no syscall at all if
3759the event loop (or your program) is processing events. That means that
3760repeated calls are basically free (there is no need to avoid calls for
3761performance reasons) and that the overhead becomes smaller (typically
3762zero) under load.
3763.IP "bool = ev_async_pending (ev_async *)" 4
3764.IX Item "bool = ev_async_pending (ev_async *)"
3765Returns a non-zero value when \f(CW\*(C`ev_async_send\*(C'\fR has been called on the
3766watcher but the event has not yet been processed (or even noted) by the
3767event loop.
3768.Sp
3769\&\f(CW\*(C`ev_async_send\*(C'\fR sets a flag in the watcher and wakes up the loop. When
3770the loop iterates next and checks for the watcher to have become active,
3771it will reset the flag again. \f(CW\*(C`ev_async_pending\*(C'\fR can be used to very
3772quickly check whether invoking the loop might be a good idea.
3773.Sp
3774Not that this does \fInot\fR check whether the watcher itself is pending,
3775only whether it has been requested to make this watcher pending: there
3776is a time window between the event loop checking and resetting the async
3777notification, and the callback being invoked.
1951.SH "OTHER FUNCTIONS" 3778.SH "OTHER FUNCTIONS"
1952.IX Header "OTHER FUNCTIONS" 3779.IX Header "OTHER FUNCTIONS"
1953There are some other functions of possible interest. Described. Here. Now. 3780There are some other functions of possible interest. Described. Here. Now.
1954.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4 3781.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)" 4
1955.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 3782.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)"
1956This function combines a simple timer and an I/O watcher, calls your 3783This function combines a simple timer and an I/O watcher, calls your
1957callback on whichever event happens first and automatically stop both 3784callback on whichever event happens first and automatically stops both
1958watchers. This is useful if you want to wait for a single event on an fd 3785watchers. This is useful if you want to wait for a single event on an fd
1959or timeout without having to allocate/configure/start/stop/free one or 3786or timeout without having to allocate/configure/start/stop/free one or
1960more watchers yourself. 3787more watchers yourself.
1961.Sp 3788.Sp
1962If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and events 3789If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and the
1963is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for the given \f(CW\*(C`fd\*(C'\fR and 3790\&\f(CW\*(C`events\*(C'\fR argument is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for
1964\&\f(CW\*(C`events\*(C'\fR set will be craeted and started. 3791the given \f(CW\*(C`fd\*(C'\fR and \f(CW\*(C`events\*(C'\fR set will be created and started.
1965.Sp 3792.Sp
1966If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be 3793If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be
1967started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and 3794started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and
1968repeat = 0) will be started. While \f(CW0\fR is a valid timeout, it is of 3795repeat = 0) will be started. \f(CW0\fR is a valid timeout.
1969dubious value.
1970.Sp 3796.Sp
1971The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and gets 3797The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and is
1972passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of 3798passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of
1973\&\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 3799\&\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
1974value passed to \f(CW\*(C`ev_once\*(C'\fR: 3800value passed to \f(CW\*(C`ev_once\*(C'\fR. Note that it is possible to receive \fIboth\fR
3801a timeout and an io event at the same time \- you probably should give io
3802events precedence.
3803.Sp
3804Example: wait up to ten seconds for data to appear on \s-1STDIN_FILENO.\s0
1975.Sp 3805.Sp
1976.Vb 7 3806.Vb 7
1977\& static void stdin_ready (int revents, void *arg) 3807\& static void stdin_ready (int revents, void *arg)
3808\& {
3809\& if (revents & EV_READ)
3810\& /* stdin might have data for us, joy! */;
3811\& else if (revents & EV_TIMER)
3812\& /* doh, nothing entered */;
3813\& }
3814\&
3815\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3816.Ve
3817.IP "ev_feed_fd_event (loop, int fd, int revents)" 4
3818.IX Item "ev_feed_fd_event (loop, int fd, int revents)"
3819Feed an event on the given fd, as if a file descriptor backend detected
3820the given events.
3821.IP "ev_feed_signal_event (loop, int signum)" 4
3822.IX Item "ev_feed_signal_event (loop, int signum)"
3823Feed an event as if the given signal occurred. See also \f(CW\*(C`ev_feed_signal\*(C'\fR,
3824which is async-safe.
3825.SH "COMMON OR USEFUL IDIOMS (OR BOTH)"
3826.IX Header "COMMON OR USEFUL IDIOMS (OR BOTH)"
3827This section explains some common idioms that are not immediately
3828obvious. Note that examples are sprinkled over the whole manual, and this
3829section only contains stuff that wouldn't fit anywhere else.
3830.SS "\s-1ASSOCIATING CUSTOM DATA WITH A WATCHER\s0"
3831.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"
3832Each watcher has, by default, a \f(CW\*(C`void *data\*(C'\fR member that you can read
3833or modify at any time: libev will completely ignore it. This can be used
3834to associate arbitrary data with your watcher. If you need more data and
3835don't want to allocate memory separately and store a pointer to it in that
3836data member, you can also \*(L"subclass\*(R" the watcher type and provide your own
3837data:
3838.PP
3839.Vb 7
3840\& struct my_io
3841\& {
3842\& ev_io io;
3843\& int otherfd;
3844\& void *somedata;
3845\& struct whatever *mostinteresting;
3846\& };
3847\&
3848\& ...
3849\& struct my_io w;
3850\& ev_io_init (&w.io, my_cb, fd, EV_READ);
3851.Ve
3852.PP
3853And since your callback will be called with a pointer to the watcher, you
3854can cast it back to your own type:
3855.PP
3856.Vb 5
3857\& static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
3858\& {
3859\& struct my_io *w = (struct my_io *)w_;
3860\& ...
3861\& }
3862.Ve
3863.PP
3864More interesting and less C\-conformant ways of casting your callback
3865function type instead have been omitted.
3866.SS "\s-1BUILDING YOUR OWN COMPOSITE WATCHERS\s0"
3867.IX Subsection "BUILDING YOUR OWN COMPOSITE WATCHERS"
3868Another common scenario is to use some data structure with multiple
3869embedded watchers, in effect creating your own watcher that combines
3870multiple libev event sources into one \*(L"super-watcher\*(R":
3871.PP
3872.Vb 6
3873\& struct my_biggy
3874\& {
3875\& int some_data;
3876\& ev_timer t1;
3877\& ev_timer t2;
3878\& }
3879.Ve
3880.PP
3881In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more
3882complicated: Either you store the address of your \f(CW\*(C`my_biggy\*(C'\fR struct in
3883the \f(CW\*(C`data\*(C'\fR member of the watcher (for woozies or \*(C+ coders), or you need
3884to use some pointer arithmetic using \f(CW\*(C`offsetof\*(C'\fR inside your watchers (for
3885real programmers):
3886.PP
3887.Vb 1
3888\& #include <stddef.h>
3889\&
3890\& static void
3891\& t1_cb (EV_P_ ev_timer *w, int revents)
3892\& {
3893\& struct my_biggy big = (struct my_biggy *)
3894\& (((char *)w) \- offsetof (struct my_biggy, t1));
3895\& }
3896\&
3897\& static void
3898\& t2_cb (EV_P_ ev_timer *w, int revents)
3899\& {
3900\& struct my_biggy big = (struct my_biggy *)
3901\& (((char *)w) \- offsetof (struct my_biggy, t2));
3902\& }
3903.Ve
3904.SS "\s-1AVOIDING FINISHING BEFORE RETURNING\s0"
3905.IX Subsection "AVOIDING FINISHING BEFORE RETURNING"
3906Often you have structures like this in event-based programs:
3907.PP
3908.Vb 4
3909\& callback ()
1978\& { 3910\& {
1979\& if (revents & EV_TIMEOUT) 3911\& free (request);
1980\& /* doh, nothing entered */;
1981\& else if (revents & EV_READ)
1982\& /* stdin might have data for us, joy! */;
1983\& } 3912\& }
3913\&
3914\& request = start_new_request (..., callback);
1984.Ve 3915.Ve
1985.Sp 3916.PP
3917The intent is to start some \*(L"lengthy\*(R" operation. The \f(CW\*(C`request\*(C'\fR could be
3918used to cancel the operation, or do other things with it.
3919.PP
3920It's not uncommon to have code paths in \f(CW\*(C`start_new_request\*(C'\fR that
3921immediately invoke the callback, for example, to report errors. Or you add
3922some caching layer that finds that it can skip the lengthy aspects of the
3923operation and simply invoke the callback with the result.
3924.PP
3925The problem here is that this will happen \fIbefore\fR \f(CW\*(C`start_new_request\*(C'\fR
3926has returned, so \f(CW\*(C`request\*(C'\fR is not set.
3927.PP
3928Even if you pass the request by some safer means to the callback, you
3929might want to do something to the request after starting it, such as
3930canceling it, which probably isn't working so well when the callback has
3931already been invoked.
3932.PP
3933A common way around all these issues is to make sure that
3934\&\f(CW\*(C`start_new_request\*(C'\fR \fIalways\fR returns before the callback is invoked. If
3935\&\f(CW\*(C`start_new_request\*(C'\fR immediately knows the result, it can artificially
3936delay invoking the callback by using a \f(CW\*(C`prepare\*(C'\fR or \f(CW\*(C`idle\*(C'\fR watcher for
3937example, or more sneakily, by reusing an existing (stopped) watcher and
3938pushing it into the pending queue:
3939.PP
1986.Vb 1 3940.Vb 2
1987\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0); 3941\& ev_set_cb (watcher, callback);
3942\& ev_feed_event (EV_A_ watcher, 0);
1988.Ve 3943.Ve
1989.IP "ev_feed_event (ev_loop *, watcher *, int revents)" 4 3944.PP
1990.IX Item "ev_feed_event (ev_loop *, watcher *, int revents)" 3945This way, \f(CW\*(C`start_new_request\*(C'\fR can safely return before the callback is
1991Feeds the given event set into the event loop, as if the specified event 3946invoked, while not delaying callback invocation too much.
1992had happened for the specified watcher (which must be a pointer to an 3947.SS "\s-1MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS\s0"
1993initialised but not necessarily started event watcher). 3948.IX Subsection "MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS"
1994.IP "ev_feed_fd_event (ev_loop *, int fd, int revents)" 4 3949Often (especially in \s-1GUI\s0 toolkits) there are places where you have
1995.IX Item "ev_feed_fd_event (ev_loop *, int fd, int revents)" 3950\&\fImodal\fR interaction, which is most easily implemented by recursively
1996Feed an event on the given fd, as if a file descriptor backend detected 3951invoking \f(CW\*(C`ev_run\*(C'\fR.
1997the given events it. 3952.PP
1998.IP "ev_feed_signal_event (ev_loop *loop, int signum)" 4 3953This brings the problem of exiting \- a callback might want to finish the
1999.IX Item "ev_feed_signal_event (ev_loop *loop, int signum)" 3954main \f(CW\*(C`ev_run\*(C'\fR call, but not the nested one (e.g. user clicked \*(L"Quit\*(R", but
2000Feed an event as if the given signal occured (\f(CW\*(C`loop\*(C'\fR must be the default 3955a modal \*(L"Are you sure?\*(R" dialog is still waiting), or just the nested one
2001loop!). 3956and not the main one (e.g. user clocked \*(L"Ok\*(R" in a modal dialog), or some
3957other combination: In these cases, a simple \f(CW\*(C`ev_break\*(C'\fR will not work.
3958.PP
3959The solution is to maintain \*(L"break this loop\*(R" variable for each \f(CW\*(C`ev_run\*(C'\fR
3960invocation, and use a loop around \f(CW\*(C`ev_run\*(C'\fR until the condition is
3961triggered, using \f(CW\*(C`EVRUN_ONCE\*(C'\fR:
3962.PP
3963.Vb 2
3964\& // main loop
3965\& int exit_main_loop = 0;
3966\&
3967\& while (!exit_main_loop)
3968\& ev_run (EV_DEFAULT_ EVRUN_ONCE);
3969\&
3970\& // in a modal watcher
3971\& int exit_nested_loop = 0;
3972\&
3973\& while (!exit_nested_loop)
3974\& ev_run (EV_A_ EVRUN_ONCE);
3975.Ve
3976.PP
3977To exit from any of these loops, just set the corresponding exit variable:
3978.PP
3979.Vb 2
3980\& // exit modal loop
3981\& exit_nested_loop = 1;
3982\&
3983\& // exit main program, after modal loop is finished
3984\& exit_main_loop = 1;
3985\&
3986\& // exit both
3987\& exit_main_loop = exit_nested_loop = 1;
3988.Ve
3989.SS "\s-1THREAD LOCKING EXAMPLE\s0"
3990.IX Subsection "THREAD LOCKING EXAMPLE"
3991Here is a fictitious example of how to run an event loop in a different
3992thread from where callbacks are being invoked and watchers are
3993created/added/removed.
3994.PP
3995For a real-world example, see the \f(CW\*(C`EV::Loop::Async\*(C'\fR perl module,
3996which uses exactly this technique (which is suited for many high-level
3997languages).
3998.PP
3999The example uses a pthread mutex to protect the loop data, a condition
4000variable to wait for callback invocations, an async watcher to notify the
4001event loop thread and an unspecified mechanism to wake up the main thread.
4002.PP
4003First, you need to associate some data with the event loop:
4004.PP
4005.Vb 6
4006\& typedef struct {
4007\& mutex_t lock; /* global loop lock */
4008\& ev_async async_w;
4009\& thread_t tid;
4010\& cond_t invoke_cv;
4011\& } userdata;
4012\&
4013\& void prepare_loop (EV_P)
4014\& {
4015\& // for simplicity, we use a static userdata struct.
4016\& static userdata u;
4017\&
4018\& ev_async_init (&u\->async_w, async_cb);
4019\& ev_async_start (EV_A_ &u\->async_w);
4020\&
4021\& pthread_mutex_init (&u\->lock, 0);
4022\& pthread_cond_init (&u\->invoke_cv, 0);
4023\&
4024\& // now associate this with the loop
4025\& ev_set_userdata (EV_A_ u);
4026\& ev_set_invoke_pending_cb (EV_A_ l_invoke);
4027\& ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4028\&
4029\& // then create the thread running ev_run
4030\& pthread_create (&u\->tid, 0, l_run, EV_A);
4031\& }
4032.Ve
4033.PP
4034The callback for the \f(CW\*(C`ev_async\*(C'\fR watcher does nothing: the watcher is used
4035solely to wake up the event loop so it takes notice of any new watchers
4036that might have been added:
4037.PP
4038.Vb 5
4039\& static void
4040\& async_cb (EV_P_ ev_async *w, int revents)
4041\& {
4042\& // just used for the side effects
4043\& }
4044.Ve
4045.PP
4046The \f(CW\*(C`l_release\*(C'\fR and \f(CW\*(C`l_acquire\*(C'\fR callbacks simply unlock/lock the mutex
4047protecting the loop data, respectively.
4048.PP
4049.Vb 6
4050\& static void
4051\& l_release (EV_P)
4052\& {
4053\& userdata *u = ev_userdata (EV_A);
4054\& pthread_mutex_unlock (&u\->lock);
4055\& }
4056\&
4057\& static void
4058\& l_acquire (EV_P)
4059\& {
4060\& userdata *u = ev_userdata (EV_A);
4061\& pthread_mutex_lock (&u\->lock);
4062\& }
4063.Ve
4064.PP
4065The event loop thread first acquires the mutex, and then jumps straight
4066into \f(CW\*(C`ev_run\*(C'\fR:
4067.PP
4068.Vb 4
4069\& void *
4070\& l_run (void *thr_arg)
4071\& {
4072\& struct ev_loop *loop = (struct ev_loop *)thr_arg;
4073\&
4074\& l_acquire (EV_A);
4075\& pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4076\& ev_run (EV_A_ 0);
4077\& l_release (EV_A);
4078\&
4079\& return 0;
4080\& }
4081.Ve
4082.PP
4083Instead of invoking all pending watchers, the \f(CW\*(C`l_invoke\*(C'\fR callback will
4084signal the main thread via some unspecified mechanism (signals? pipe
4085writes? \f(CW\*(C`Async::Interrupt\*(C'\fR?) and then waits until all pending watchers
4086have been called (in a while loop because a) spurious wakeups are possible
4087and b) skipping inter-thread-communication when there are no pending
4088watchers is very beneficial):
4089.PP
4090.Vb 4
4091\& static void
4092\& l_invoke (EV_P)
4093\& {
4094\& userdata *u = ev_userdata (EV_A);
4095\&
4096\& while (ev_pending_count (EV_A))
4097\& {
4098\& wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4099\& pthread_cond_wait (&u\->invoke_cv, &u\->lock);
4100\& }
4101\& }
4102.Ve
4103.PP
4104Now, whenever the main thread gets told to invoke pending watchers, it
4105will grab the lock, call \f(CW\*(C`ev_invoke_pending\*(C'\fR and then signal the loop
4106thread to continue:
4107.PP
4108.Vb 4
4109\& static void
4110\& real_invoke_pending (EV_P)
4111\& {
4112\& userdata *u = ev_userdata (EV_A);
4113\&
4114\& pthread_mutex_lock (&u\->lock);
4115\& ev_invoke_pending (EV_A);
4116\& pthread_cond_signal (&u\->invoke_cv);
4117\& pthread_mutex_unlock (&u\->lock);
4118\& }
4119.Ve
4120.PP
4121Whenever you want to start/stop a watcher or do other modifications to an
4122event loop, you will now have to lock:
4123.PP
4124.Vb 2
4125\& ev_timer timeout_watcher;
4126\& userdata *u = ev_userdata (EV_A);
4127\&
4128\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4129\&
4130\& pthread_mutex_lock (&u\->lock);
4131\& ev_timer_start (EV_A_ &timeout_watcher);
4132\& ev_async_send (EV_A_ &u\->async_w);
4133\& pthread_mutex_unlock (&u\->lock);
4134.Ve
4135.PP
4136Note that sending the \f(CW\*(C`ev_async\*(C'\fR watcher is required because otherwise
4137an event loop currently blocking in the kernel will have no knowledge
4138about the newly added timer. By waking up the loop it will pick up any new
4139watchers in the next event loop iteration.
4140.SS "\s-1THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS\s0"
4141.IX Subsection "THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS"
4142While the overhead of a callback that e.g. schedules a thread is small, it
4143is still an overhead. If you embed libev, and your main usage is with some
4144kind of threads or coroutines, you might want to customise libev so that
4145doesn't need callbacks anymore.
4146.PP
4147Imagine you have coroutines that you can switch to using a function
4148\&\f(CW\*(C`switch_to (coro)\*(C'\fR, that libev runs in a coroutine called \f(CW\*(C`libev_coro\*(C'\fR
4149and that due to some magic, the currently active coroutine is stored in a
4150global called \f(CW\*(C`current_coro\*(C'\fR. Then you can build your own \*(L"wait for libev
4151event\*(R" primitive by changing \f(CW\*(C`EV_CB_DECLARE\*(C'\fR and \f(CW\*(C`EV_CB_INVOKE\*(C'\fR (note
4152the differing \f(CW\*(C`;\*(C'\fR conventions):
4153.PP
4154.Vb 2
4155\& #define EV_CB_DECLARE(type) struct my_coro *cb;
4156\& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb)
4157.Ve
4158.PP
4159That means instead of having a C callback function, you store the
4160coroutine to switch to in each watcher, and instead of having libev call
4161your callback, you instead have it switch to that coroutine.
4162.PP
4163A coroutine might now wait for an event with a function called
4164\&\f(CW\*(C`wait_for_event\*(C'\fR. (the watcher needs to be started, as always, but it doesn't
4165matter when, or whether the watcher is active or not when this function is
4166called):
4167.PP
4168.Vb 6
4169\& void
4170\& wait_for_event (ev_watcher *w)
4171\& {
4172\& ev_set_cb (w, current_coro);
4173\& switch_to (libev_coro);
4174\& }
4175.Ve
4176.PP
4177That basically suspends the coroutine inside \f(CW\*(C`wait_for_event\*(C'\fR and
4178continues the libev coroutine, which, when appropriate, switches back to
4179this or any other coroutine.
4180.PP
4181You can do similar tricks if you have, say, threads with an event queue \-
4182instead of storing a coroutine, you store the queue object and instead of
4183switching to a coroutine, you push the watcher onto the queue and notify
4184any waiters.
4185.PP
4186To embed libev, see \*(L"\s-1EMBEDDING\*(R"\s0, but in short, it's easiest to create two
4187files, \fImy_ev.h\fR and \fImy_ev.c\fR that include the respective libev files:
4188.PP
4189.Vb 4
4190\& // my_ev.h
4191\& #define EV_CB_DECLARE(type) struct my_coro *cb;
4192\& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb)
4193\& #include "../libev/ev.h"
4194\&
4195\& // my_ev.c
4196\& #define EV_H "my_ev.h"
4197\& #include "../libev/ev.c"
4198.Ve
4199.PP
4200And then use \fImy_ev.h\fR when you would normally use \fIev.h\fR, and compile
4201\&\fImy_ev.c\fR into your project. When properly specifying include paths, you
4202can even use \fIev.h\fR as header file name directly.
2002.SH "LIBEVENT EMULATION" 4203.SH "LIBEVENT EMULATION"
2003.IX Header "LIBEVENT EMULATION" 4204.IX Header "LIBEVENT EMULATION"
2004Libev offers a compatibility emulation layer for libevent. It cannot 4205Libev offers a compatibility emulation layer for libevent. It cannot
2005emulate the internals of libevent, so here are some usage hints: 4206emulate the internals of libevent, so here are some usage hints:
4207.IP "\(bu" 4
4208Only the libevent\-1.4.1\-beta \s-1API\s0 is being emulated.
4209.Sp
4210This was the newest libevent version available when libev was implemented,
4211and is still mostly unchanged in 2010.
4212.IP "\(bu" 4
2006.IP "* Use it by including <event.h>, as usual." 4 4213Use it by including <event.h>, as usual.
2007.IX Item "Use it by including <event.h>, as usual." 4214.IP "\(bu" 4
2008.PD 0 4215The following members are fully supported: ev_base, ev_callback,
2009.IP "* The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4 4216ev_arg, ev_fd, ev_res, ev_events.
2010.IX Item "The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4217.IP "\(bu" 4
2011.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 4218Avoid using ev_flags and the EVLIST_*\-macros, while it is
2012.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)." 4219maintained by libev, it does not work exactly the same way as in libevent (consider
2013.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 4220it a private \s-1API\s0).
2014.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." 4221.IP "\(bu" 4
4222Priorities are not currently supported. Initialising priorities
4223will fail and all watchers will have the same priority, even though there
4224is an ev_pri field.
4225.IP "\(bu" 4
4226In libevent, the last base created gets the signals, in libev, the
4227base that registered the signal gets the signals.
4228.IP "\(bu" 4
2015.IP "* Other members are not supported." 4 4229Other members are not supported.
2016.IX Item "Other members are not supported." 4230.IP "\(bu" 4
2017.IP "* The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need to use the libev header file and library." 4 4231The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need
2018.IX Item "The libev emulation is not ABI compatible to libevent, you need to use the libev header file and library." 4232to use the libev header file and library.
2019.PD
2020.SH "\*(C+ SUPPORT" 4233.SH "\*(C+ SUPPORT"
2021.IX Header " SUPPORT" 4234.IX Header " SUPPORT"
4235.SS "C \s-1API\s0"
4236.IX Subsection "C API"
4237The normal C \s-1API\s0 should work fine when used from \*(C+: both ev.h and the
4238libev sources can be compiled as \*(C+. Therefore, code that uses the C \s-1API\s0
4239will work fine.
4240.PP
4241Proper exception specifications might have to be added to callbacks passed
4242to libev: exceptions may be thrown only from watcher callbacks, all other
4243callbacks (allocator, syserr, loop acquire/release and periodic reschedule
4244callbacks) must not throw exceptions, and might need a \f(CW\*(C`noexcept\*(C'\fR
4245specification. If you have code that needs to be compiled as both C and
4246\&\*(C+ you can use the \f(CW\*(C`EV_NOEXCEPT\*(C'\fR macro for this:
4247.PP
4248.Vb 6
4249\& static void
4250\& fatal_error (const char *msg) EV_NOEXCEPT
4251\& {
4252\& perror (msg);
4253\& abort ();
4254\& }
4255\&
4256\& ...
4257\& ev_set_syserr_cb (fatal_error);
4258.Ve
4259.PP
4260The only \s-1API\s0 functions that can currently throw exceptions are \f(CW\*(C`ev_run\*(C'\fR,
4261\&\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
4262because it runs cleanup watchers).
4263.PP
4264Throwing exceptions in watcher callbacks is only supported if libev itself
4265is compiled with a \*(C+ compiler or your C and \*(C+ environments allow
4266throwing exceptions through C libraries (most do).
4267.SS "\*(C+ \s-1API\s0"
4268.IX Subsection " API"
2022Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow 4269Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow
2023you to use some convinience methods to start/stop watchers and also change 4270you to use some convenience methods to start/stop watchers and also change
2024the callback model to a model using method callbacks on objects. 4271the callback model to a model using method callbacks on objects.
2025.PP 4272.PP
2026To use it, 4273To use it,
2027.PP 4274.PP
2028.Vb 1 4275.Vb 1
2029\& #include <ev++.h> 4276\& #include <ev++.h>
2030.Ve 4277.Ve
2031.PP 4278.PP
2032This automatically includes \fIev.h\fR and puts all of its definitions (many 4279This automatically includes \fIev.h\fR and puts all of its definitions (many
2033of them macros) into the global namespace. All \*(C+ specific things are 4280of them macros) into the global namespace. All \*(C+ specific things are
2034put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding 4281put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding
… …
2037Care has been taken to keep the overhead low. The only data member the \*(C+ 4284Care has been taken to keep the overhead low. The only data member the \*(C+
2038classes add (compared to plain C\-style watchers) is the event loop pointer 4285classes add (compared to plain C\-style watchers) is the event loop pointer
2039that the watcher is associated with (or no additional members at all if 4286that the watcher is associated with (or no additional members at all if
2040you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev). 4287you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev).
2041.PP 4288.PP
2042Currently, functions, and static and non-static member functions can be 4289Currently, functions, static and non-static member functions and classes
2043used as callbacks. Other types should be easy to add as long as they only 4290with \f(CW\*(C`operator ()\*(C'\fR can be used as callbacks. Other types should be easy
2044need one additional pointer for context. If you need support for other 4291to add as long as they only need one additional pointer for context. If
2045types of functors please contact the author (preferably after implementing 4292you need support for other types of functors please contact the author
2046it). 4293(preferably after implementing it).
4294.PP
4295For all this to work, your \*(C+ compiler either has to use the same calling
4296conventions as your C compiler (for static member functions), or you have
4297to embed libev and compile libev itself as \*(C+.
2047.PP 4298.PP
2048Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace: 4299Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace:
2049.ie n .IP """ev::READ""\fR, \f(CW""ev::WRITE"" etc." 4 4300.ie n .IP """ev::READ"", ""ev::WRITE"" etc." 4
2050.el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4 4301.el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4
2051.IX Item "ev::READ, ev::WRITE etc." 4302.IX Item "ev::READ, ev::WRITE etc."
2052These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc. 4303These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc.
2053macros from \fIev.h\fR. 4304macros from \fIev.h\fR.
2054.ie n .IP """ev::tstamp""\fR, \f(CW""ev::now""" 4 4305.ie n .IP """ev::tstamp"", ""ev::now""" 4
2055.el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4 4306.el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4
2056.IX Item "ev::tstamp, ev::now" 4307.IX Item "ev::tstamp, ev::now"
2057Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix. 4308Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix.
2058.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 4309.ie n .IP """ev::io"", ""ev::timer"", ""ev::periodic"", ""ev::idle"", ""ev::sig"" etc." 4
2059.el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4 4310.el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4
2060.IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc." 4311.IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc."
2061For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of 4312For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of
2062the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR 4313the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR
2063which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro 4314which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro
2064defines by many implementations. 4315defined by many implementations.
2065.Sp 4316.Sp
2066All of those classes have these methods: 4317All of those classes have these methods:
2067.RS 4 4318.RS 4
2068.IP "ev::TYPE::TYPE ()" 4 4319.IP "ev::TYPE::TYPE ()" 4
2069.IX Item "ev::TYPE::TYPE ()" 4320.IX Item "ev::TYPE::TYPE ()"
2070.PD 0 4321.PD 0
2071.IP "ev::TYPE::TYPE (struct ev_loop *)" 4 4322.IP "ev::TYPE::TYPE (loop)" 4
2072.IX Item "ev::TYPE::TYPE (struct ev_loop *)" 4323.IX Item "ev::TYPE::TYPE (loop)"
2073.IP "ev::TYPE::~TYPE" 4 4324.IP "ev::TYPE::~TYPE" 4
2074.IX Item "ev::TYPE::~TYPE" 4325.IX Item "ev::TYPE::~TYPE"
2075.PD 4326.PD
2076The constructor (optionally) takes an event loop to associate the watcher 4327The constructor (optionally) takes an event loop to associate the watcher
2077with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR. 4328with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR.
… …
2100thunking function, making it as fast as a direct C callback. 4351thunking function, making it as fast as a direct C callback.
2101.Sp 4352.Sp
2102Example: simple class declaration and watcher initialisation 4353Example: simple class declaration and watcher initialisation
2103.Sp 4354.Sp
2104.Vb 4 4355.Vb 4
2105\& struct myclass 4356\& struct myclass
2106\& { 4357\& {
2107\& void io_cb (ev::io &w, int revents) { } 4358\& void io_cb (ev::io &w, int revents) { }
2108\& } 4359\& }
2109.Ve 4360\&
2110.Sp
2111.Vb 3
2112\& myclass obj; 4361\& myclass obj;
2113\& ev::io iow; 4362\& ev::io iow;
2114\& iow.set <myclass, &myclass::io_cb> (&obj); 4363\& iow.set <myclass, &myclass::io_cb> (&obj);
4364.Ve
4365.IP "w\->set (object *)" 4
4366.IX Item "w->set (object *)"
4367This is a variation of a method callback \- leaving out the method to call
4368will default the method to \f(CW\*(C`operator ()\*(C'\fR, which makes it possible to use
4369functor objects without having to manually specify the \f(CW\*(C`operator ()\*(C'\fR all
4370the time. Incidentally, you can then also leave out the template argument
4371list.
4372.Sp
4373The \f(CW\*(C`operator ()\*(C'\fR method prototype must be \f(CW\*(C`void operator ()(watcher &w,
4374int revents)\*(C'\fR.
4375.Sp
4376See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
4377.Sp
4378Example: use a functor object as callback.
4379.Sp
4380.Vb 7
4381\& struct myfunctor
4382\& {
4383\& void operator() (ev::io &w, int revents)
4384\& {
4385\& ...
4386\& }
4387\& }
4388\&
4389\& myfunctor f;
4390\&
4391\& ev::io w;
4392\& w.set (&f);
2115.Ve 4393.Ve
2116.IP "w\->set<function> (void *data = 0)" 4 4394.IP "w\->set<function> (void *data = 0)" 4
2117.IX Item "w->set<function> (void *data = 0)" 4395.IX Item "w->set<function> (void *data = 0)"
2118Also sets a callback, but uses a static method or plain function as 4396Also sets a callback, but uses a static method or plain function as
2119callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's 4397callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's
… …
2121.Sp 4399.Sp
2122The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR. 4400The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR.
2123.Sp 4401.Sp
2124See the method\-\f(CW\*(C`set\*(C'\fR above for more details. 4402See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
2125.Sp 4403.Sp
2126Example: 4404Example: Use a plain function as callback.
2127.Sp 4405.Sp
2128.Vb 2 4406.Vb 2
2129\& static void io_cb (ev::io &w, int revents) { } 4407\& static void io_cb (ev::io &w, int revents) { }
2130\& iow.set <io_cb> (); 4408\& iow.set <io_cb> ();
2131.Ve 4409.Ve
2132.IP "w\->set (struct ev_loop *)" 4 4410.IP "w\->set (loop)" 4
2133.IX Item "w->set (struct ev_loop *)" 4411.IX Item "w->set (loop)"
2134Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only 4412Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only
2135do this when the watcher is inactive (and not pending either). 4413do this when the watcher is inactive (and not pending either).
2136.IP "w\->set ([args])" 4 4414.IP "w\->set ([arguments])" 4
2137.IX Item "w->set ([args])" 4415.IX Item "w->set ([arguments])"
2138Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR, with the same args. Must be 4416Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR (except for \f(CW\*(C`ev::embed\*(C'\fR watchers>),
4417with the same arguments. Either this method or a suitable start method
2139called at least once. Unlike the C counterpart, an active watcher gets 4418must be called at least once. Unlike the C counterpart, an active watcher
2140automatically stopped and restarted when reconfiguring it with this 4419gets automatically stopped and restarted when reconfiguring it with this
2141method. 4420method.
4421.Sp
4422For \f(CW\*(C`ev::embed\*(C'\fR watchers this method is called \f(CW\*(C`set_embed\*(C'\fR, to avoid
4423clashing with the \f(CW\*(C`set (loop)\*(C'\fR method.
4424.Sp
4425For \f(CW\*(C`ev::io\*(C'\fR watchers there is an additional \f(CW\*(C`set\*(C'\fR method that acepts a
4426new event mask only, and internally calls \f(CW\*(C`ev_io_modfify\*(C'\fR.
2142.IP "w\->start ()" 4 4427.IP "w\->start ()" 4
2143.IX Item "w->start ()" 4428.IX Item "w->start ()"
2144Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the 4429Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the
2145constructor already stores the event loop. 4430constructor already stores the event loop.
4431.IP "w\->start ([arguments])" 4
4432.IX Item "w->start ([arguments])"
4433Instead of calling \f(CW\*(C`set\*(C'\fR and \f(CW\*(C`start\*(C'\fR methods separately, it is often
4434convenient to wrap them in one call. Uses the same type of arguments as
4435the configure \f(CW\*(C`set\*(C'\fR method of the watcher.
2146.IP "w\->stop ()" 4 4436.IP "w\->stop ()" 4
2147.IX Item "w->stop ()" 4437.IX Item "w->stop ()"
2148Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument. 4438Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument.
2149.ie n .IP "w\->again () ""ev::timer""\fR, \f(CW""ev::periodic"" only" 4 4439.ie n .IP "w\->again () (""ev::timer"", ""ev::periodic"" only)" 4
2150.el .IP "w\->again () \f(CWev::timer\fR, \f(CWev::periodic\fR only" 4 4440.el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4
2151.IX Item "w->again () ev::timer, ev::periodic only" 4441.IX Item "w->again () (ev::timer, ev::periodic only)"
2152For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding 4442For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding
2153\&\f(CW\*(C`ev_TYPE_again\*(C'\fR function. 4443\&\f(CW\*(C`ev_TYPE_again\*(C'\fR function.
2154.ie n .IP "w\->sweep () ""ev::embed"" only" 4 4444.ie n .IP "w\->sweep () (""ev::embed"" only)" 4
2155.el .IP "w\->sweep () \f(CWev::embed\fR only" 4 4445.el .IP "w\->sweep () (\f(CWev::embed\fR only)" 4
2156.IX Item "w->sweep () ev::embed only" 4446.IX Item "w->sweep () (ev::embed only)"
2157Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR. 4447Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR.
2158.ie n .IP "w\->update () ""ev::stat"" only" 4 4448.ie n .IP "w\->update () (""ev::stat"" only)" 4
2159.el .IP "w\->update () \f(CWev::stat\fR only" 4 4449.el .IP "w\->update () (\f(CWev::stat\fR only)" 4
2160.IX Item "w->update () ev::stat only" 4450.IX Item "w->update () (ev::stat only)"
2161Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR. 4451Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR.
2162.RE 4452.RE
2163.RS 4 4453.RS 4
2164.RE 4454.RE
2165.PP 4455.PP
2166Example: Define a class with an \s-1IO\s0 and idle watcher, start one of them in 4456Example: Define a class with two I/O and idle watchers, start the I/O
2167the constructor. 4457watchers in the constructor.
2168.PP 4458.PP
2169.Vb 4 4459.Vb 5
2170\& class myclass 4460\& class myclass
2171\& { 4461\& {
2172\& ev_io io; void io_cb (ev::io &w, int revents); 4462\& ev::io io ; void io_cb (ev::io &w, int revents);
4463\& ev::io io2 ; void io2_cb (ev::io &w, int revents);
2173\& ev_idle idle void idle_cb (ev::idle &w, int revents); 4464\& ev::idle idle; void idle_cb (ev::idle &w, int revents);
2174.Ve 4465\&
2175.PP
2176.Vb 2
2177\& myclass (); 4466\& myclass (int fd)
2178\& }
2179.Ve
2180.PP
2181.Vb 4
2182\& myclass::myclass (int fd)
2183\& { 4467\& {
2184\& io .set <myclass, &myclass::io_cb > (this); 4468\& io .set <myclass, &myclass::io_cb > (this);
4469\& io2 .set <myclass, &myclass::io2_cb > (this);
2185\& idle.set <myclass, &myclass::idle_cb> (this); 4470\& idle.set <myclass, &myclass::idle_cb> (this);
2186.Ve 4471\&
2187.PP 4472\& io.set (fd, ev::WRITE); // configure the watcher
2188.Vb 2 4473\& io.start (); // start it whenever convenient
2189\& io.start (fd, ev::READ); 4474\&
4475\& io2.start (fd, ev::READ); // set + start in one call
4476\& }
2190\& } 4477\& };
2191.Ve 4478.Ve
4479.SH "OTHER LANGUAGE BINDINGS"
4480.IX Header "OTHER LANGUAGE BINDINGS"
4481Libev does not offer other language bindings itself, but bindings for a
4482number of languages exist in the form of third-party packages. If you know
4483any interesting language binding in addition to the ones listed here, drop
4484me a note.
4485.IP "Perl" 4
4486.IX Item "Perl"
4487The \s-1EV\s0 module implements the full libev \s-1API\s0 and is actually used to test
4488libev. \s-1EV\s0 is developed together with libev. Apart from the \s-1EV\s0 core module,
4489there are additional modules that implement libev-compatible interfaces
4490to \f(CW\*(C`libadns\*(C'\fR (\f(CW\*(C`EV::ADNS\*(C'\fR, but \f(CW\*(C`AnyEvent::DNS\*(C'\fR is preferred nowadays),
4491\&\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
4492and \f(CW\*(C`EV::Glib\*(C'\fR).
4493.Sp
4494It can be found and installed via \s-1CPAN,\s0 its homepage is at
4495<http://software.schmorp.de/pkg/EV>.
4496.IP "Python" 4
4497.IX Item "Python"
4498Python bindings can be found at <http://code.google.com/p/pyev/>. It
4499seems to be quite complete and well-documented.
4500.IP "Ruby" 4
4501.IX Item "Ruby"
4502Tony Arcieri has written a ruby extension that offers access to a subset
4503of the libev \s-1API\s0 and adds file handle abstractions, asynchronous \s-1DNS\s0 and
4504more on top of it. It can be found via gem servers. Its homepage is at
4505<http://rev.rubyforge.org/>.
4506.Sp
4507Roger Pack reports that using the link order \f(CW\*(C`\-lws2_32 \-lmsvcrt\-ruby\-190\*(C'\fR
4508makes rev work even on mingw.
4509.IP "Haskell" 4
4510.IX Item "Haskell"
4511A haskell binding to libev is available at
4512<http://hackage.haskell.org/cgi\-bin/hackage\-scripts/package/hlibev>.
4513.IP "D" 4
4514.IX Item "D"
4515Leandro Lucarella has written a D language binding (\fIev.d\fR) for libev, to
4516be found at <http://www.llucax.com.ar/proj/ev.d/index.html>.
4517.IP "Ocaml" 4
4518.IX Item "Ocaml"
4519Erkki Seppala has written Ocaml bindings for libev, to be found at
4520<http://modeemi.cs.tut.fi/~flux/software/ocaml\-ev/>.
4521.IP "Lua" 4
4522.IX Item "Lua"
4523Brian Maher has written a partial interface to libev for lua (at the
4524time of this writing, only \f(CW\*(C`ev_io\*(C'\fR and \f(CW\*(C`ev_timer\*(C'\fR), to be found at
4525<http://github.com/brimworks/lua\-ev>.
4526.IP "Javascript" 4
4527.IX Item "Javascript"
4528Node.js (<http://nodejs.org>) uses libev as the underlying event library.
4529.IP "Others" 4
4530.IX Item "Others"
4531There are others, and I stopped counting.
2192.SH "MACRO MAGIC" 4532.SH "MACRO MAGIC"
2193.IX Header "MACRO MAGIC" 4533.IX Header "MACRO MAGIC"
2194Libev can be compiled with a variety of options, the most fundemantal is 4534Libev can be compiled with a variety of options, the most fundamental
2195\&\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most) functions and 4535of which is \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most)
2196callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument. 4536functions and callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument.
2197.PP 4537.PP
2198To make it easier to write programs that cope with either variant, the 4538To make it easier to write programs that cope with either variant, the
2199following macros are defined: 4539following macros are defined:
2200.ie n .IP """EV_A""\fR, \f(CW""EV_A_""" 4 4540.ie n .IP """EV_A"", ""EV_A_""" 4
2201.el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4 4541.el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4
2202.IX Item "EV_A, EV_A_" 4542.IX Item "EV_A, EV_A_"
2203This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev 4543This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev
2204loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument, 4544loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument,
2205\&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example: 4545\&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example:
2206.Sp 4546.Sp
2207.Vb 3 4547.Vb 3
2208\& ev_unref (EV_A); 4548\& ev_unref (EV_A);
2209\& ev_timer_add (EV_A_ watcher); 4549\& ev_timer_add (EV_A_ watcher);
2210\& ev_loop (EV_A_ 0); 4550\& ev_run (EV_A_ 0);
2211.Ve 4551.Ve
2212.Sp 4552.Sp
2213It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope, 4553It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope,
2214which is often provided by the following macro. 4554which is often provided by the following macro.
2215.ie n .IP """EV_P""\fR, \f(CW""EV_P_""" 4 4555.ie n .IP """EV_P"", ""EV_P_""" 4
2216.el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4 4556.el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4
2217.IX Item "EV_P, EV_P_" 4557.IX Item "EV_P, EV_P_"
2218This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev 4558This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev
2219loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter, 4559loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter,
2220\&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example: 4560\&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example:
2221.Sp 4561.Sp
2222.Vb 2 4562.Vb 2
2223\& // this is how ev_unref is being declared 4563\& // this is how ev_unref is being declared
2224\& static void ev_unref (EV_P); 4564\& static void ev_unref (EV_P);
2225.Ve 4565\&
2226.Sp
2227.Vb 2
2228\& // this is how you can declare your typical callback 4566\& // this is how you can declare your typical callback
2229\& static void cb (EV_P_ ev_timer *w, int revents) 4567\& static void cb (EV_P_ ev_timer *w, int revents)
2230.Ve 4568.Ve
2231.Sp 4569.Sp
2232It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite 4570It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite
2233suitable for use with \f(CW\*(C`EV_A\*(C'\fR. 4571suitable for use with \f(CW\*(C`EV_A\*(C'\fR.
2234.ie n .IP """EV_DEFAULT""\fR, \f(CW""EV_DEFAULT_""" 4 4572.ie n .IP """EV_DEFAULT"", ""EV_DEFAULT_""" 4
2235.el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4 4573.el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4
2236.IX Item "EV_DEFAULT, EV_DEFAULT_" 4574.IX Item "EV_DEFAULT, EV_DEFAULT_"
2237Similar to the other two macros, this gives you the value of the default 4575Similar to the other two macros, this gives you the value of the default
2238loop, if multiple loops are supported (\*(L"ev loop default\*(R"). 4576loop, if multiple loops are supported (\*(L"ev loop default\*(R"). The default loop
4577will be initialised if it isn't already initialised.
4578.Sp
4579For non-multiplicity builds, these macros do nothing, so you always have
4580to initialise the loop somewhere.
4581.ie n .IP """EV_DEFAULT_UC"", ""EV_DEFAULT_UC_""" 4
4582.el .IP "\f(CWEV_DEFAULT_UC\fR, \f(CWEV_DEFAULT_UC_\fR" 4
4583.IX Item "EV_DEFAULT_UC, EV_DEFAULT_UC_"
4584Usage identical to \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR, but requires that the
4585default loop has been initialised (\f(CW\*(C`UC\*(C'\fR == unchecked). Their behaviour
4586is undefined when the default loop has not been initialised by a previous
4587execution of \f(CW\*(C`EV_DEFAULT\*(C'\fR, \f(CW\*(C`EV_DEFAULT_\*(C'\fR or \f(CW\*(C`ev_default_init (...)\*(C'\fR.
4588.Sp
4589It is often prudent to use \f(CW\*(C`EV_DEFAULT\*(C'\fR when initialising the first
4590watcher in a function but use \f(CW\*(C`EV_DEFAULT_UC\*(C'\fR afterwards.
2239.PP 4591.PP
2240Example: Declare and initialise a check watcher, utilising the above 4592Example: Declare and initialise a check watcher, utilising the above
2241macros so it will work regardless of whether multiple loops are supported 4593macros so it will work regardless of whether multiple loops are supported
2242or not. 4594or not.
2243.PP 4595.PP
2244.Vb 5 4596.Vb 5
2245\& static void 4597\& static void
2246\& check_cb (EV_P_ ev_timer *w, int revents) 4598\& check_cb (EV_P_ ev_timer *w, int revents)
2247\& { 4599\& {
2248\& ev_check_stop (EV_A_ w); 4600\& ev_check_stop (EV_A_ w);
2249\& } 4601\& }
2250.Ve 4602\&
2251.PP
2252.Vb 4
2253\& ev_check check; 4603\& ev_check check;
2254\& ev_check_init (&check, check_cb); 4604\& ev_check_init (&check, check_cb);
2255\& ev_check_start (EV_DEFAULT_ &check); 4605\& ev_check_start (EV_DEFAULT_ &check);
2256\& ev_loop (EV_DEFAULT_ 0); 4606\& ev_run (EV_DEFAULT_ 0);
2257.Ve 4607.Ve
2258.SH "EMBEDDING" 4608.SH "EMBEDDING"
2259.IX Header "EMBEDDING" 4609.IX Header "EMBEDDING"
2260Libev can (and often is) directly embedded into host 4610Libev can (and often is) directly embedded into host
2261applications. Examples of applications that embed it include the Deliantra 4611applications. Examples of applications that embed it include the Deliantra
2262Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe) 4612Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe)
2263and rxvt\-unicode. 4613and rxvt-unicode.
2264.PP 4614.PP
2265The goal is to enable you to just copy the neecssary files into your 4615The goal is to enable you to just copy the necessary files into your
2266source directory without having to change even a single line in them, so 4616source directory without having to change even a single line in them, so
2267you can easily upgrade by simply copying (or having a checked-out copy of 4617you can easily upgrade by simply copying (or having a checked-out copy of
2268libev somewhere in your source tree). 4618libev somewhere in your source tree).
2269.Sh "\s-1FILESETS\s0" 4619.SS "\s-1FILESETS\s0"
2270.IX Subsection "FILESETS" 4620.IX Subsection "FILESETS"
2271Depending on what features you need you need to include one or more sets of files 4621Depending on what features you need you need to include one or more sets of files
2272in your app. 4622in your application.
2273.PP 4623.PP
2274\fI\s-1CORE\s0 \s-1EVENT\s0 \s-1LOOP\s0\fR 4624\fI\s-1CORE EVENT LOOP\s0\fR
2275.IX Subsection "CORE EVENT LOOP" 4625.IX Subsection "CORE EVENT LOOP"
2276.PP 4626.PP
2277To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual 4627To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual
2278configuration (no autoconf): 4628configuration (no autoconf):
2279.PP 4629.PP
2280.Vb 2 4630.Vb 2
2281\& #define EV_STANDALONE 1 4631\& #define EV_STANDALONE 1
2282\& #include "ev.c" 4632\& #include "ev.c"
2283.Ve 4633.Ve
2284.PP 4634.PP
2285This will automatically include \fIev.h\fR, too, and should be done in a 4635This will automatically include \fIev.h\fR, too, and should be done in a
2286single C source file only to provide the function implementations. To use 4636single C source file only to provide the function implementations. To use
2287it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best 4637it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best
2288done by writing a wrapper around \fIev.h\fR that you can include instead and 4638done by writing a wrapper around \fIev.h\fR that you can include instead and
2289where you can put other configuration options): 4639where you can put other configuration options):
2290.PP 4640.PP
2291.Vb 2 4641.Vb 2
2292\& #define EV_STANDALONE 1 4642\& #define EV_STANDALONE 1
2293\& #include "ev.h" 4643\& #include "ev.h"
2294.Ve 4644.Ve
2295.PP 4645.PP
2296Both header files and implementation files can be compiled with a \*(C+ 4646Both header files and implementation files can be compiled with a \*(C+
2297compiler (at least, thats a stated goal, and breakage will be treated 4647compiler (at least, that's a stated goal, and breakage will be treated
2298as a bug). 4648as a bug).
2299.PP 4649.PP
2300You need the following files in your source tree, or in a directory 4650You need the following files in your source tree, or in a directory
2301in your include path (e.g. in libev/ when using \-Ilibev): 4651in your include path (e.g. in libev/ when using \-Ilibev):
2302.PP 4652.PP
2303.Vb 4 4653.Vb 4
2304\& ev.h 4654\& ev.h
2305\& ev.c 4655\& ev.c
2306\& ev_vars.h 4656\& ev_vars.h
2307\& ev_wrap.h 4657\& ev_wrap.h
2308.Ve 4658\&
2309.PP
2310.Vb 1
2311\& ev_win32.c required on win32 platforms only 4659\& ev_win32.c required on win32 platforms only
2312.Ve 4660\&
2313.PP
2314.Vb 5
2315\& ev_select.c only when select backend is enabled (which is enabled by default) 4661\& ev_select.c only when select backend is enabled
2316\& ev_poll.c only when poll backend is enabled (disabled by default) 4662\& ev_poll.c only when poll backend is enabled
2317\& ev_epoll.c only when the epoll backend is enabled (disabled by default) 4663\& ev_epoll.c only when the epoll backend is enabled
4664\& ev_linuxaio.c only when the linux aio backend is enabled
4665\& ev_iouring.c only when the linux io_uring backend is enabled
2318\& ev_kqueue.c only when the kqueue backend is enabled (disabled by default) 4666\& ev_kqueue.c only when the kqueue backend is enabled
2319\& ev_port.c only when the solaris port backend is enabled (disabled by default) 4667\& ev_port.c only when the solaris port backend is enabled
2320.Ve 4668.Ve
2321.PP 4669.PP
2322\&\fIev.c\fR includes the backend files directly when enabled, so you only need 4670\&\fIev.c\fR includes the backend files directly when enabled, so you only need
2323to compile this single file. 4671to compile this single file.
2324.PP 4672.PP
2325\fI\s-1LIBEVENT\s0 \s-1COMPATIBILITY\s0 \s-1API\s0\fR 4673\fI\s-1LIBEVENT COMPATIBILITY API\s0\fR
2326.IX Subsection "LIBEVENT COMPATIBILITY API" 4674.IX Subsection "LIBEVENT COMPATIBILITY API"
2327.PP 4675.PP
2328To include the libevent compatibility \s-1API\s0, also include: 4676To include the libevent compatibility \s-1API,\s0 also include:
2329.PP 4677.PP
2330.Vb 1 4678.Vb 1
2331\& #include "event.c" 4679\& #include "event.c"
2332.Ve 4680.Ve
2333.PP 4681.PP
2334in the file including \fIev.c\fR, and: 4682in the file including \fIev.c\fR, and:
2335.PP 4683.PP
2336.Vb 1 4684.Vb 1
2337\& #include "event.h" 4685\& #include "event.h"
2338.Ve 4686.Ve
2339.PP 4687.PP
2340in the files that want to use the libevent \s-1API\s0. This also includes \fIev.h\fR. 4688in the files that want to use the libevent \s-1API.\s0 This also includes \fIev.h\fR.
2341.PP 4689.PP
2342You need the following additional files for this: 4690You need the following additional files for this:
2343.PP 4691.PP
2344.Vb 2 4692.Vb 2
2345\& event.h 4693\& event.h
2346\& event.c 4694\& event.c
2347.Ve 4695.Ve
2348.PP 4696.PP
2349\fI\s-1AUTOCONF\s0 \s-1SUPPORT\s0\fR 4697\fI\s-1AUTOCONF SUPPORT\s0\fR
2350.IX Subsection "AUTOCONF SUPPORT" 4698.IX Subsection "AUTOCONF SUPPORT"
2351.PP 4699.PP
2352Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your config in 4700Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your configuration in
2353whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your 4701whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your
2354\&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then 4702\&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then
2355include \fIconfig.h\fR and configure itself accordingly. 4703include \fIconfig.h\fR and configure itself accordingly.
2356.PP 4704.PP
2357For this of course you need the m4 file: 4705For this of course you need the m4 file:
2358.PP 4706.PP
2359.Vb 1 4707.Vb 1
2360\& libev.m4 4708\& libev.m4
2361.Ve 4709.Ve
2362.Sh "\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0" 4710.SS "\s-1PREPROCESSOR SYMBOLS/MACROS\s0"
2363.IX Subsection "PREPROCESSOR SYMBOLS/MACROS" 4711.IX Subsection "PREPROCESSOR SYMBOLS/MACROS"
2364Libev can be configured via a variety of preprocessor symbols you have to define 4712Libev can be configured via a variety of preprocessor symbols you have to
2365before including any of its files. The default is not to build for multiplicity 4713define before including (or compiling) any of its files. The default in
2366and only include the select backend. 4714the absence of autoconf is documented for every option.
4715.PP
4716Symbols marked with \*(L"(h)\*(R" do not change the \s-1ABI,\s0 and can have different
4717values when compiling libev vs. including \fIev.h\fR, so it is permissible
4718to redefine them before including \fIev.h\fR without breaking compatibility
4719to a compiled library. All other symbols change the \s-1ABI,\s0 which means all
4720users of libev and the libev code itself must be compiled with compatible
4721settings.
4722.IP "\s-1EV_COMPAT3\s0 (h)" 4
4723.IX Item "EV_COMPAT3 (h)"
4724Backwards compatibility is a major concern for libev. This is why this
4725release of libev comes with wrappers for the functions and symbols that
4726have been renamed between libev version 3 and 4.
4727.Sp
4728You can disable these wrappers (to test compatibility with future
4729versions) by defining \f(CW\*(C`EV_COMPAT3\*(C'\fR to \f(CW0\fR when compiling your
4730sources. This has the additional advantage that you can drop the \f(CW\*(C`struct\*(C'\fR
4731from \f(CW\*(C`struct ev_loop\*(C'\fR declarations, as libev will provide an \f(CW\*(C`ev_loop\*(C'\fR
4732typedef in that case.
4733.Sp
4734In some future version, the default for \f(CW\*(C`EV_COMPAT3\*(C'\fR will become \f(CW0\fR,
4735and in some even more future version the compatibility code will be
4736removed completely.
2367.IP "\s-1EV_STANDALONE\s0" 4 4737.IP "\s-1EV_STANDALONE\s0 (h)" 4
2368.IX Item "EV_STANDALONE" 4738.IX Item "EV_STANDALONE (h)"
2369Must always be \f(CW1\fR if you do not use autoconf configuration, which 4739Must always be \f(CW1\fR if you do not use autoconf configuration, which
2370keeps libev from including \fIconfig.h\fR, and it also defines dummy 4740keeps libev from including \fIconfig.h\fR, and it also defines dummy
2371implementations for some libevent functions (such as logging, which is not 4741implementations for some libevent functions (such as logging, which is not
2372supported). It will also not define any of the structs usually found in 4742supported). It will also not define any of the structs usually found in
2373\&\fIevent.h\fR that are not directly supported by the libev core alone. 4743\&\fIevent.h\fR that are not directly supported by the libev core alone.
4744.Sp
4745In standalone mode, libev will still try to automatically deduce the
4746configuration, but has to be more conservative.
4747.IP "\s-1EV_USE_FLOOR\s0" 4
4748.IX Item "EV_USE_FLOOR"
4749If defined to be \f(CW1\fR, libev will use the \f(CW\*(C`floor ()\*(C'\fR function for its
4750periodic reschedule calculations, otherwise libev will fall back on a
4751portable (slower) implementation. If you enable this, you usually have to
4752link against libm or something equivalent. Enabling this when the \f(CW\*(C`floor\*(C'\fR
4753function is not available will fail, so the safe default is to not enable
4754this.
2374.IP "\s-1EV_USE_MONOTONIC\s0" 4 4755.IP "\s-1EV_USE_MONOTONIC\s0" 4
2375.IX Item "EV_USE_MONOTONIC" 4756.IX Item "EV_USE_MONOTONIC"
2376If defined to be \f(CW1\fR, libev will try to detect the availability of the 4757If defined to be \f(CW1\fR, libev will try to detect the availability of the
2377monotonic clock option at both compiletime and runtime. Otherwise no use 4758monotonic clock option at both compile time and runtime. Otherwise no
2378of the monotonic clock option will be attempted. If you enable this, you 4759use of the monotonic clock option will be attempted. If you enable this,
2379usually have to link against librt or something similar. Enabling it when 4760you usually have to link against librt or something similar. Enabling it
2380the functionality isn't available is safe, though, althoguh you have 4761when the functionality isn't available is safe, though, although you have
2381to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR 4762to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR
2382function is hiding in (often \fI\-lrt\fR). 4763function is hiding in (often \fI\-lrt\fR). See also \f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
2383.IP "\s-1EV_USE_REALTIME\s0" 4 4764.IP "\s-1EV_USE_REALTIME\s0" 4
2384.IX Item "EV_USE_REALTIME" 4765.IX Item "EV_USE_REALTIME"
2385If defined to be \f(CW1\fR, libev will try to detect the availability of the 4766If defined to be \f(CW1\fR, libev will try to detect the availability of the
2386realtime clock option at compiletime (and assume its availability at 4767real-time clock option at compile time (and assume its availability
2387runtime if successful). Otherwise no use of the realtime clock option will 4768at runtime if successful). Otherwise no use of the real-time clock
2388be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR by \f(CW\*(C`clock_get 4769option will be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR
2389(CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect correctness. See tzhe note about libraries 4770by \f(CW\*(C`clock_get (CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect
2390in the description of \f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. 4771correctness. See the note about libraries in the description of
4772\&\f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. Defaults to the opposite value of
4773\&\f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
4774.IP "\s-1EV_USE_CLOCK_SYSCALL\s0" 4
4775.IX Item "EV_USE_CLOCK_SYSCALL"
4776If defined to be \f(CW1\fR, libev will try to use a direct syscall instead
4777of calling the system-provided \f(CW\*(C`clock_gettime\*(C'\fR function. This option
4778exists 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
4779unconditionally pulls in \f(CW\*(C`libpthread\*(C'\fR, slowing down single-threaded
4780programs needlessly. Using a direct syscall is slightly slower (in
4781theory), because no optimised vdso implementation can be used, but avoids
4782the pthread dependency. Defaults to \f(CW1\fR on GNU/Linux with glibc 2.x or
4783higher, as it simplifies linking (no need for \f(CW\*(C`\-lrt\*(C'\fR).
4784.IP "\s-1EV_USE_NANOSLEEP\s0" 4
4785.IX Item "EV_USE_NANOSLEEP"
4786If defined to be \f(CW1\fR, libev will assume that \f(CW\*(C`nanosleep ()\*(C'\fR is available
4787and will use it for delays. Otherwise it will use \f(CW\*(C`select ()\*(C'\fR.
4788.IP "\s-1EV_USE_EVENTFD\s0" 4
4789.IX Item "EV_USE_EVENTFD"
4790If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is
4791available and will probe for kernel support at runtime. This will improve
4792\&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption.
4793If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
47942.7 or newer, otherwise disabled.
4795.IP "\s-1EV_USE_SIGNALFD\s0" 4
4796.IX Item "EV_USE_SIGNALFD"
4797If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`signalfd ()\*(C'\fR is
4798available and will probe for kernel support at runtime. This enables
4799the use of \s-1EVFLAG_SIGNALFD\s0 for faster and simpler signal handling. If
4800undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
48012.7 or newer, otherwise disabled.
4802.IP "\s-1EV_USE_TIMERFD\s0" 4
4803.IX Item "EV_USE_TIMERFD"
4804If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`timerfd ()\*(C'\fR is
4805available and will probe for kernel support at runtime. This allows
4806libev to detect time jumps accurately. If undefined, it will be enabled
4807if the headers indicate GNU/Linux + Glibc 2.8 or newer and define
4808\&\f(CW\*(C`TFD_TIMER_CANCEL_ON_SET\*(C'\fR, otherwise disabled.
4809.IP "\s-1EV_USE_EVENTFD\s0" 4
4810.IX Item "EV_USE_EVENTFD"
4811If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is
4812available and will probe for kernel support at runtime. This will improve
4813\&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption.
4814If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
48152.7 or newer, otherwise disabled.
2391.IP "\s-1EV_USE_SELECT\s0" 4 4816.IP "\s-1EV_USE_SELECT\s0" 4
2392.IX Item "EV_USE_SELECT" 4817.IX Item "EV_USE_SELECT"
2393If undefined or defined to be \f(CW1\fR, libev will compile in support for the 4818If undefined or defined to be \f(CW1\fR, libev will compile in support for the
2394\&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at autodetection will be done: if no 4819\&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at auto-detection will be done: if no
2395other method takes over, select will be it. Otherwise the select backend 4820other method takes over, select will be it. Otherwise the select backend
2396will not be compiled in. 4821will not be compiled in.
2397.IP "\s-1EV_SELECT_USE_FD_SET\s0" 4 4822.IP "\s-1EV_SELECT_USE_FD_SET\s0" 4
2398.IX Item "EV_SELECT_USE_FD_SET" 4823.IX Item "EV_SELECT_USE_FD_SET"
2399If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR 4824If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR
2400structure. This is useful if libev doesn't compile due to a missing 4825structure. This is useful if libev doesn't compile due to a missing
2401\&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it misguesses the bitset layout on 4826\&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it mis-guesses the bitset layout
2402exotic systems. This usually limits the range of file descriptors to some 4827on exotic systems. This usually limits the range of file descriptors to
2403low limit such as 1024 or might have other limitations (winsocket only 4828some low limit such as 1024 or might have other limitations (winsocket
2404allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation, might 4829only allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation,
2405influence the size of the \f(CW\*(C`fd_set\*(C'\fR used. 4830configures the maximum size of the \f(CW\*(C`fd_set\*(C'\fR.
2406.IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4 4831.IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4
2407.IX Item "EV_SELECT_IS_WINSOCKET" 4832.IX Item "EV_SELECT_IS_WINSOCKET"
2408When defined to \f(CW1\fR, the select backend will assume that 4833When defined to \f(CW1\fR, the select backend will assume that
2409select/socket/connect etc. don't understand file descriptors but 4834select/socket/connect etc. don't understand file descriptors but
2410wants osf handles on win32 (this is the case when the select to 4835wants osf handles on win32 (this is the case when the select to
2411be used is the winsock select). This means that it will call 4836be used is the winsock select). This means that it will call
2412\&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise, 4837\&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise,
2413it is assumed that all these functions actually work on fds, even 4838it is assumed that all these functions actually work on fds, even
2414on win32. Should not be defined on non\-win32 platforms. 4839on win32. Should not be defined on non\-win32 platforms.
4840.IP "\s-1EV_FD_TO_WIN32_HANDLE\s0(fd)" 4
4841.IX Item "EV_FD_TO_WIN32_HANDLE(fd)"
4842If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR is enabled, then libev needs a way to map
4843file descriptors to socket handles. When not defining this symbol (the
4844default), then libev will call \f(CW\*(C`_get_osfhandle\*(C'\fR, which is usually
4845correct. In some cases, programs use their own file descriptor management,
4846in which case they can provide this function to map fds to socket handles.
4847.IP "\s-1EV_WIN32_HANDLE_TO_FD\s0(handle)" 4
4848.IX Item "EV_WIN32_HANDLE_TO_FD(handle)"
4849If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR then libev maps handles to file descriptors
4850using the standard \f(CW\*(C`_open_osfhandle\*(C'\fR function. For programs implementing
4851their own fd to handle mapping, overwriting this function makes it easier
4852to do so. This can be done by defining this macro to an appropriate value.
4853.IP "\s-1EV_WIN32_CLOSE_FD\s0(fd)" 4
4854.IX Item "EV_WIN32_CLOSE_FD(fd)"
4855If programs implement their own fd to handle mapping on win32, then this
4856macro can be used to override the \f(CW\*(C`close\*(C'\fR function, useful to unregister
4857file descriptors again. Note that the replacement function has to close
4858the underlying \s-1OS\s0 handle.
4859.IP "\s-1EV_USE_WSASOCKET\s0" 4
4860.IX Item "EV_USE_WSASOCKET"
4861If defined to be \f(CW1\fR, libev will use \f(CW\*(C`WSASocket\*(C'\fR to create its internal
4862communication socket, which works better in some environments. Otherwise,
4863the normal \f(CW\*(C`socket\*(C'\fR function will be used, which works better in other
4864environments.
2415.IP "\s-1EV_USE_POLL\s0" 4 4865.IP "\s-1EV_USE_POLL\s0" 4
2416.IX Item "EV_USE_POLL" 4866.IX Item "EV_USE_POLL"
2417If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2) 4867If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2)
2418backend. Otherwise it will be enabled on non\-win32 platforms. It 4868backend. Otherwise it will be enabled on non\-win32 platforms. It
2419takes precedence over select. 4869takes precedence over select.
2420.IP "\s-1EV_USE_EPOLL\s0" 4 4870.IP "\s-1EV_USE_EPOLL\s0" 4
2421.IX Item "EV_USE_EPOLL" 4871.IX Item "EV_USE_EPOLL"
2422If defined to be \f(CW1\fR, libev will compile in support for the Linux 4872If defined to be \f(CW1\fR, libev will compile in support for the Linux
2423\&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime, 4873\&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime,
2424otherwise another method will be used as fallback. This is the 4874otherwise another method will be used as fallback. This is the preferred
2425preferred backend for GNU/Linux systems. 4875backend for GNU/Linux systems. If undefined, it will be enabled if the
4876headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4877.IP "\s-1EV_USE_LINUXAIO\s0" 4
4878.IX Item "EV_USE_LINUXAIO"
4879If defined to be \f(CW1\fR, libev will compile in support for the Linux aio
4880backend (\f(CW\*(C`EV_USE_EPOLL\*(C'\fR must also be enabled). If undefined, it will be
4881enabled on linux, otherwise disabled.
4882.IP "\s-1EV_USE_IOURING\s0" 4
4883.IX Item "EV_USE_IOURING"
4884If defined to be \f(CW1\fR, libev will compile in support for the Linux
4885io_uring backend (\f(CW\*(C`EV_USE_EPOLL\*(C'\fR must also be enabled). Due to it's
4886current limitations it has to be requested explicitly. If undefined, it
4887will be enabled on linux, otherwise disabled.
2426.IP "\s-1EV_USE_KQUEUE\s0" 4 4888.IP "\s-1EV_USE_KQUEUE\s0" 4
2427.IX Item "EV_USE_KQUEUE" 4889.IX Item "EV_USE_KQUEUE"
2428If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style 4890If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style
2429\&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime, 4891\&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime,
2430otherwise another method will be used as fallback. This is the preferred 4892otherwise another method will be used as fallback. This is the preferred
… …
244010 port style backend. Its availability will be detected at runtime, 490210 port style backend. Its availability will be detected at runtime,
2441otherwise another method will be used as fallback. This is the preferred 4903otherwise another method will be used as fallback. This is the preferred
2442backend for Solaris 10 systems. 4904backend for Solaris 10 systems.
2443.IP "\s-1EV_USE_DEVPOLL\s0" 4 4905.IP "\s-1EV_USE_DEVPOLL\s0" 4
2444.IX Item "EV_USE_DEVPOLL" 4906.IX Item "EV_USE_DEVPOLL"
2445reserved for future expansion, works like the \s-1USE\s0 symbols above. 4907Reserved for future expansion, works like the \s-1USE\s0 symbols above.
2446.IP "\s-1EV_USE_INOTIFY\s0" 4 4908.IP "\s-1EV_USE_INOTIFY\s0" 4
2447.IX Item "EV_USE_INOTIFY" 4909.IX Item "EV_USE_INOTIFY"
2448If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify 4910If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify
2449interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will 4911interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will
2450be detected at runtime. 4912be detected at runtime. If undefined, it will be enabled if the headers
4913indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4914.IP "\s-1EV_NO_SMP\s0" 4
4915.IX Item "EV_NO_SMP"
4916If defined to be \f(CW1\fR, libev will assume that memory is always coherent
4917between threads, that is, threads can be used, but threads never run on
4918different cpus (or different cpu cores). This reduces dependencies
4919and makes libev faster.
4920.IP "\s-1EV_NO_THREADS\s0" 4
4921.IX Item "EV_NO_THREADS"
4922If defined to be \f(CW1\fR, libev will assume that it will never be called from
4923different threads (that includes signal handlers), which is a stronger
4924assumption than \f(CW\*(C`EV_NO_SMP\*(C'\fR, above. This reduces dependencies and makes
4925libev faster.
4926.IP "\s-1EV_ATOMIC_T\s0" 4
4927.IX Item "EV_ATOMIC_T"
4928Libev requires an integer type (suitable for storing \f(CW0\fR or \f(CW1\fR) whose
4929access is atomic with respect to other threads or signal contexts. No
4930such type is easily found in the C language, so you can provide your own
4931type that you know is safe for your purposes. It is used both for signal
4932handler \*(L"locking\*(R" as well as for signal and thread safety in \f(CW\*(C`ev_async\*(C'\fR
4933watchers.
4934.Sp
4935In the absence of this define, libev will use \f(CW\*(C`sig_atomic_t volatile\*(C'\fR
4936(from \fIsignal.h\fR), which is usually good enough on most platforms.
2451.IP "\s-1EV_H\s0" 4 4937.IP "\s-1EV_H\s0 (h)" 4
2452.IX Item "EV_H" 4938.IX Item "EV_H (h)"
2453The name of the \fIev.h\fR header file used to include it. The default if 4939The name of the \fIev.h\fR header file used to include it. The default if
2454undefined is \f(CW\*(C`<ev.h>\*(C'\fR in \fIevent.h\fR and \f(CW"ev.h"\fR in \fIev.c\fR. This 4940undefined is \f(CW"ev.h"\fR in \fIevent.h\fR, \fIev.c\fR and \fIev++.h\fR. This can be
2455can be used to virtually rename the \fIev.h\fR header file in case of conflicts. 4941used to virtually rename the \fIev.h\fR header file in case of conflicts.
2456.IP "\s-1EV_CONFIG_H\s0" 4 4942.IP "\s-1EV_CONFIG_H\s0 (h)" 4
2457.IX Item "EV_CONFIG_H" 4943.IX Item "EV_CONFIG_H (h)"
2458If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override 4944If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override
2459\&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to 4945\&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to
2460\&\f(CW\*(C`EV_H\*(C'\fR, above. 4946\&\f(CW\*(C`EV_H\*(C'\fR, above.
2461.IP "\s-1EV_EVENT_H\s0" 4 4947.IP "\s-1EV_EVENT_H\s0 (h)" 4
2462.IX Item "EV_EVENT_H" 4948.IX Item "EV_EVENT_H (h)"
2463Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea 4949Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea
2464of how the \fIevent.h\fR header can be found. 4950of how the \fIevent.h\fR header can be found, the default is \f(CW"event.h"\fR.
2465.IP "\s-1EV_PROTOTYPES\s0" 4 4951.IP "\s-1EV_PROTOTYPES\s0 (h)" 4
2466.IX Item "EV_PROTOTYPES" 4952.IX Item "EV_PROTOTYPES (h)"
2467If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function 4953If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function
2468prototypes, but still define all the structs and other symbols. This is 4954prototypes, but still define all the structs and other symbols. This is
2469occasionally useful if you want to provide your own wrapper functions 4955occasionally useful if you want to provide your own wrapper functions
2470around libev functions. 4956around libev functions.
2471.IP "\s-1EV_MULTIPLICITY\s0" 4 4957.IP "\s-1EV_MULTIPLICITY\s0" 4
… …
2473If undefined or defined to \f(CW1\fR, then all event-loop-specific functions 4959If undefined or defined to \f(CW1\fR, then all event-loop-specific functions
2474will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create 4960will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create
2475additional independent event loops. Otherwise there will be no support 4961additional independent event loops. Otherwise there will be no support
2476for multiple event loops and there is no first event loop pointer 4962for multiple event loops and there is no first event loop pointer
2477argument. Instead, all functions act on the single default loop. 4963argument. Instead, all functions act on the single default loop.
4964.Sp
4965Note that \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR will no longer provide a
4966default loop when multiplicity is switched off \- you always have to
4967initialise the loop manually in this case.
2478.IP "\s-1EV_MINPRI\s0" 4 4968.IP "\s-1EV_MINPRI\s0" 4
2479.IX Item "EV_MINPRI" 4969.IX Item "EV_MINPRI"
2480.PD 0 4970.PD 0
2481.IP "\s-1EV_MAXPRI\s0" 4 4971.IP "\s-1EV_MAXPRI\s0" 4
2482.IX Item "EV_MAXPRI" 4972.IX Item "EV_MAXPRI"
… …
2489When doing priority-based operations, libev usually has to linearly search 4979When doing priority-based operations, libev usually has to linearly search
2490all the priorities, so having many of them (hundreds) uses a lot of space 4980all the priorities, so having many of them (hundreds) uses a lot of space
2491and time, so using the defaults of five priorities (\-2 .. +2) is usually 4981and time, so using the defaults of five priorities (\-2 .. +2) is usually
2492fine. 4982fine.
2493.Sp 4983.Sp
2494If your embedding app does not need any priorities, defining these both to 4984If your embedding application does not need any priorities, defining these
2495\&\f(CW0\fR will save some memory and cpu. 4985both to \f(CW0\fR will save some memory and \s-1CPU.\s0
2496.IP "\s-1EV_PERIODIC_ENABLE\s0" 4 4986.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
2497.IX Item "EV_PERIODIC_ENABLE" 4987.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."
2498If undefined or defined to be \f(CW1\fR, then periodic timers are supported. If 4988If undefined or defined to be \f(CW1\fR (and the platform supports it), then
2499defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of 4989the respective watcher type is supported. If defined to be \f(CW0\fR, then it
2500code. 4990is not. Disabling watcher types mainly saves code size.
2501.IP "\s-1EV_IDLE_ENABLE\s0" 4
2502.IX Item "EV_IDLE_ENABLE"
2503If undefined or defined to be \f(CW1\fR, then idle watchers are supported. If
2504defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of
2505code.
2506.IP "\s-1EV_EMBED_ENABLE\s0" 4
2507.IX Item "EV_EMBED_ENABLE"
2508If undefined or defined to be \f(CW1\fR, then embed watchers are supported. If
2509defined to be \f(CW0\fR, then they are not.
2510.IP "\s-1EV_STAT_ENABLE\s0" 4 4991.IP "\s-1EV_FEATURES\s0" 4
2511.IX Item "EV_STAT_ENABLE" 4992.IX Item "EV_FEATURES"
2512If undefined or defined to be \f(CW1\fR, then stat watchers are supported. If
2513defined to be \f(CW0\fR, then they are not.
2514.IP "\s-1EV_FORK_ENABLE\s0" 4
2515.IX Item "EV_FORK_ENABLE"
2516If undefined or defined to be \f(CW1\fR, then fork watchers are supported. If
2517defined to be \f(CW0\fR, then they are not.
2518.IP "\s-1EV_MINIMAL\s0" 4
2519.IX Item "EV_MINIMAL"
2520If you need to shave off some kilobytes of code at the expense of some 4993If you need to shave off some kilobytes of code at the expense of some
2521speed, define this symbol to \f(CW1\fR. Currently only used for gcc to override 4994speed (but with the full \s-1API\s0), you can define this symbol to request
2522some inlining decisions, saves roughly 30% codesize of amd64. 4995certain subsets of functionality. The default is to enable all features
4996that can be enabled on the platform.
4997.Sp
4998A typical way to use this symbol is to define it to \f(CW0\fR (or to a bitset
4999with some broad features you want) and then selectively re-enable
5000additional parts you want, for example if you want everything minimal,
5001but multiple event loop support, async and child watchers and the poll
5002backend, use this:
5003.Sp
5004.Vb 5
5005\& #define EV_FEATURES 0
5006\& #define EV_MULTIPLICITY 1
5007\& #define EV_USE_POLL 1
5008\& #define EV_CHILD_ENABLE 1
5009\& #define EV_ASYNC_ENABLE 1
5010.Ve
5011.Sp
5012The actual value is a bitset, it can be a combination of the following
5013values (by default, all of these are enabled):
5014.RS 4
5015.ie n .IP "1 \- faster/larger code" 4
5016.el .IP "\f(CW1\fR \- faster/larger code" 4
5017.IX Item "1 - faster/larger code"
5018Use larger code to speed up some operations.
5019.Sp
5020Currently this is used to override some inlining decisions (enlarging the
5021code size by roughly 30% on amd64).
5022.Sp
5023When optimising for size, use of compiler flags such as \f(CW\*(C`\-Os\*(C'\fR with
5024gcc is recommended, as well as \f(CW\*(C`\-DNDEBUG\*(C'\fR, as libev contains a number of
5025assertions.
5026.Sp
5027The default is off when \f(CW\*(C`_\|_OPTIMIZE_SIZE_\|_\*(C'\fR is defined by your compiler
5028(e.g. gcc with \f(CW\*(C`\-Os\*(C'\fR).
5029.ie n .IP "2 \- faster/larger data structures" 4
5030.el .IP "\f(CW2\fR \- faster/larger data structures" 4
5031.IX Item "2 - faster/larger data structures"
5032Replaces the small 2\-heap for timer management by a faster 4\-heap, larger
5033hash table sizes and so on. This will usually further increase code size
5034and can additionally have an effect on the size of data structures at
5035runtime.
5036.Sp
5037The default is off when \f(CW\*(C`_\|_OPTIMIZE_SIZE_\|_\*(C'\fR is defined by your compiler
5038(e.g. gcc with \f(CW\*(C`\-Os\*(C'\fR).
5039.ie n .IP "4 \- full \s-1API\s0 configuration" 4
5040.el .IP "\f(CW4\fR \- full \s-1API\s0 configuration" 4
5041.IX Item "4 - full API configuration"
5042This enables priorities (sets \f(CW\*(C`EV_MAXPRI\*(C'\fR=2 and \f(CW\*(C`EV_MINPRI\*(C'\fR=\-2), and
5043enables multiplicity (\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR=1).
5044.ie n .IP "8 \- full \s-1API\s0" 4
5045.el .IP "\f(CW8\fR \- full \s-1API\s0" 4
5046.IX Item "8 - full API"
5047This enables a lot of the \*(L"lesser used\*(R" \s-1API\s0 functions. See \f(CW\*(C`ev.h\*(C'\fR for
5048details on which parts of the \s-1API\s0 are still available without this
5049feature, and do not complain if this subset changes over time.
5050.ie n .IP "16 \- enable all optional watcher types" 4
5051.el .IP "\f(CW16\fR \- enable all optional watcher types" 4
5052.IX Item "16 - enable all optional watcher types"
5053Enables all optional watcher types. If you want to selectively enable
5054only some watcher types other than I/O and timers (e.g. prepare,
5055embed, async, child...) you can enable them manually by defining
5056\&\f(CW\*(C`EV_watchertype_ENABLE\*(C'\fR to \f(CW1\fR instead.
5057.ie n .IP "32 \- enable all backends" 4
5058.el .IP "\f(CW32\fR \- enable all backends" 4
5059.IX Item "32 - enable all backends"
5060This enables all backends \- without this feature, you need to enable at
5061least one backend manually (\f(CW\*(C`EV_USE_SELECT\*(C'\fR is a good choice).
5062.ie n .IP "64 \- enable OS-specific ""helper"" APIs" 4
5063.el .IP "\f(CW64\fR \- enable OS-specific ``helper'' APIs" 4
5064.IX Item "64 - enable OS-specific helper APIs"
5065Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
5066default.
5067.RE
5068.RS 4
5069.Sp
5070Compiling with \f(CW\*(C`gcc \-Os \-DEV_STANDALONE \-DEV_USE_EPOLL=1 \-DEV_FEATURES=0\*(C'\fR
5071reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
5072code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
5073watchers, timers and monotonic clock support.
5074.Sp
5075With an intelligent-enough linker (gcc+binutils are intelligent enough
5076when you use \f(CW\*(C`\-Wl,\-\-gc\-sections \-ffunction\-sections\*(C'\fR) functions unused by
5077your program might be left out as well \- a binary starting a timer and an
5078I/O watcher then might come out at only 5Kb.
5079.RE
5080.IP "\s-1EV_API_STATIC\s0" 4
5081.IX Item "EV_API_STATIC"
5082If this symbol is defined (by default it is not), then all identifiers
5083will have static linkage. This means that libev will not export any
5084identifiers, and you cannot link against libev anymore. This can be useful
5085when you embed libev, only want to use libev functions in a single file,
5086and do not want its identifiers to be visible.
5087.Sp
5088To use this, define \f(CW\*(C`EV_API_STATIC\*(C'\fR and include \fIev.c\fR in the file that
5089wants to use libev.
5090.Sp
5091This option only works when libev is compiled with a C compiler, as \*(C+
5092doesn't support the required declaration syntax.
5093.IP "\s-1EV_AVOID_STDIO\s0" 4
5094.IX Item "EV_AVOID_STDIO"
5095If this is set to \f(CW1\fR at compiletime, then libev will avoid using stdio
5096functions (printf, scanf, perror etc.). This will increase the code size
5097somewhat, but if your program doesn't otherwise depend on stdio and your
5098libc allows it, this avoids linking in the stdio library which is quite
5099big.
5100.Sp
5101Note that error messages might become less precise when this option is
5102enabled.
5103.IP "\s-1EV_NSIG\s0" 4
5104.IX Item "EV_NSIG"
5105The highest supported signal number, +1 (or, the number of
5106signals): Normally, libev tries to deduce the maximum number of signals
5107automatically, but sometimes this fails, in which case it can be
5108specified. Also, using a lower number than detected (\f(CW32\fR should be
5109good for about any system in existence) can save some memory, as libev
5110statically allocates some 12\-24 bytes per signal number.
2523.IP "\s-1EV_PID_HASHSIZE\s0" 4 5111.IP "\s-1EV_PID_HASHSIZE\s0" 4
2524.IX Item "EV_PID_HASHSIZE" 5112.IX Item "EV_PID_HASHSIZE"
2525\&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by 5113\&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by
2526pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR), usually more 5114pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR disabled),
2527than enough. If you need to manage thousands of children you might want to 5115usually more than enough. If you need to manage thousands of children you
2528increase this value (\fImust\fR be a power of two). 5116might want to increase this value (\fImust\fR be a power of two).
2529.IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4 5117.IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4
2530.IX Item "EV_INOTIFY_HASHSIZE" 5118.IX Item "EV_INOTIFY_HASHSIZE"
2531\&\f(CW\*(C`ev_staz\*(C'\fR watchers use a small hash table to distribute workload by 5119\&\f(CW\*(C`ev_stat\*(C'\fR watchers use a small hash table to distribute workload by
2532inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR), 5120inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR
2533usually more than enough. If you need to manage thousands of \f(CW\*(C`ev_stat\*(C'\fR 5121disabled), usually more than enough. If you need to manage thousands of
2534watchers you might want to increase this value (\fImust\fR be a power of 5122\&\f(CW\*(C`ev_stat\*(C'\fR watchers you might want to increase this value (\fImust\fR be a
2535two). 5123power of two).
5124.IP "\s-1EV_USE_4HEAP\s0" 4
5125.IX Item "EV_USE_4HEAP"
5126Heaps are not very cache-efficient. To improve the cache-efficiency of the
5127timer and periodics heaps, libev uses a 4\-heap when this symbol is defined
5128to \f(CW1\fR. The 4\-heap uses more complicated (longer) code but has noticeably
5129faster performance with many (thousands) of watchers.
5130.Sp
5131The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
5132will be \f(CW0\fR.
5133.IP "\s-1EV_HEAP_CACHE_AT\s0" 4
5134.IX Item "EV_HEAP_CACHE_AT"
5135Heaps are not very cache-efficient. To improve the cache-efficiency of the
5136timer and periodics heaps, libev can cache the timestamp (\fIat\fR) within
5137the heap structure (selected by defining \f(CW\*(C`EV_HEAP_CACHE_AT\*(C'\fR to \f(CW1\fR),
5138which uses 8\-12 bytes more per watcher and a few hundred bytes more code,
5139but avoids random read accesses on heap changes. This improves performance
5140noticeably with many (hundreds) of watchers.
5141.Sp
5142The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
5143will be \f(CW0\fR.
5144.IP "\s-1EV_VERIFY\s0" 4
5145.IX Item "EV_VERIFY"
5146Controls how much internal verification (see \f(CW\*(C`ev_verify ()\*(C'\fR) will
5147be done: If set to \f(CW0\fR, no internal verification code will be compiled
5148in. If set to \f(CW1\fR, then verification code will be compiled in, but not
5149called. If set to \f(CW2\fR, then the internal verification code will be
5150called once per loop, which can slow down libev. If set to \f(CW3\fR, then the
5151verification code will be called very frequently, which will slow down
5152libev considerably.
5153.Sp
5154Verification errors are reported via C's \f(CW\*(C`assert\*(C'\fR mechanism, so if you
5155disable that (e.g. by defining \f(CW\*(C`NDEBUG\*(C'\fR) then no errors will be reported.
5156.Sp
5157The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
5158will be \f(CW0\fR.
2536.IP "\s-1EV_COMMON\s0" 4 5159.IP "\s-1EV_COMMON\s0" 4
2537.IX Item "EV_COMMON" 5160.IX Item "EV_COMMON"
2538By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining 5161By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining
2539this macro to a something else you can include more and other types of 5162this macro to something else you can include more and other types of
2540members. You have to define it each time you include one of the files, 5163members. You have to define it each time you include one of the files,
2541though, and it must be identical each time. 5164though, and it must be identical each time.
2542.Sp 5165.Sp
2543For example, the perl \s-1EV\s0 module uses something like this: 5166For example, the perl \s-1EV\s0 module uses something like this:
2544.Sp 5167.Sp
2545.Vb 3 5168.Vb 3
2546\& #define EV_COMMON \e 5169\& #define EV_COMMON \e
2547\& SV *self; /* contains this struct */ \e 5170\& SV *self; /* contains this struct */ \e
2548\& SV *cb_sv, *fh /* note no trailing ";" */ 5171\& SV *cb_sv, *fh /* note no trailing ";" */
2549.Ve 5172.Ve
2550.IP "\s-1EV_CB_DECLARE\s0 (type)" 4 5173.IP "\s-1EV_CB_DECLARE\s0 (type)" 4
2551.IX Item "EV_CB_DECLARE (type)" 5174.IX Item "EV_CB_DECLARE (type)"
2552.PD 0 5175.PD 0
2553.IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4 5176.IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4
… …
2555.IP "ev_set_cb (ev, cb)" 4 5178.IP "ev_set_cb (ev, cb)" 4
2556.IX Item "ev_set_cb (ev, cb)" 5179.IX Item "ev_set_cb (ev, cb)"
2557.PD 5180.PD
2558Can be used to change the callback member declaration in each watcher, 5181Can be used to change the callback member declaration in each watcher,
2559and the way callbacks are invoked and set. Must expand to a struct member 5182and the way callbacks are invoked and set. Must expand to a struct member
2560definition and a statement, respectively. See the \fIev.v\fR header file for 5183definition and a statement, respectively. See the \fIev.h\fR header file for
2561their default definitions. One possible use for overriding these is to 5184their default definitions. One possible use for overriding these is to
2562avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use 5185avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use
2563method calls instead of plain function calls in \*(C+. 5186method calls instead of plain function calls in \*(C+.
5187.SS "\s-1EXPORTED API SYMBOLS\s0"
5188.IX Subsection "EXPORTED API SYMBOLS"
5189If you need to re-export the \s-1API\s0 (e.g. via a \s-1DLL\s0) and you need a list of
5190exported symbols, you can use the provided \fISymbol.*\fR files which list
5191all public symbols, one per line:
5192.PP
5193.Vb 2
5194\& Symbols.ev for libev proper
5195\& Symbols.event for the libevent emulation
5196.Ve
5197.PP
5198This can also be used to rename all public symbols to avoid clashes with
5199multiple versions of libev linked together (which is obviously bad in
5200itself, but sometimes it is inconvenient to avoid this).
5201.PP
5202A sed command like this will create wrapper \f(CW\*(C`#define\*(C'\fR's that you need to
5203include before including \fIev.h\fR:
5204.PP
5205.Vb 1
5206\& <Symbols.ev sed \-e "s/.*/#define & myprefix_&/" >wrap.h
5207.Ve
5208.PP
5209This would create a file \fIwrap.h\fR which essentially looks like this:
5210.PP
5211.Vb 4
5212\& #define ev_backend myprefix_ev_backend
5213\& #define ev_check_start myprefix_ev_check_start
5214\& #define ev_check_stop myprefix_ev_check_stop
5215\& ...
5216.Ve
2564.Sh "\s-1EXAMPLES\s0" 5217.SS "\s-1EXAMPLES\s0"
2565.IX Subsection "EXAMPLES" 5218.IX Subsection "EXAMPLES"
2566For a real-world example of a program the includes libev 5219For a real-world example of a program the includes libev
2567verbatim, you can have a look at the \s-1EV\s0 perl module 5220verbatim, you can have a look at the \s-1EV\s0 perl module
2568(<http://software.schmorp.de/pkg/EV.html>). It has the libev files in 5221(<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
2569the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public 5222the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public
2570interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file 5223interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file
2571will be compiled. It is pretty complex because it provides its own header 5224will be compiled. It is pretty complex because it provides its own header
2572file. 5225file.
2573.Sp 5226.PP
2574The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file 5227The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file
2575that everybody includes and which overrides some configure choices: 5228that everybody includes and which overrides some configure choices:
2576.Sp 5229.PP
2577.Vb 9 5230.Vb 8
2578\& #define EV_MINIMAL 1 5231\& #define EV_FEATURES 8
2579\& #define EV_USE_POLL 0 5232\& #define EV_USE_SELECT 1
2580\& #define EV_MULTIPLICITY 0
2581\& #define EV_PERIODIC_ENABLE 0 5233\& #define EV_PREPARE_ENABLE 1
5234\& #define EV_IDLE_ENABLE 1
2582\& #define EV_STAT_ENABLE 0 5235\& #define EV_SIGNAL_ENABLE 1
2583\& #define EV_FORK_ENABLE 0 5236\& #define EV_CHILD_ENABLE 1
5237\& #define EV_USE_STDEXCEPT 0
2584\& #define EV_CONFIG_H <config.h> 5238\& #define EV_CONFIG_H <config.h>
2585\& #define EV_MINPRI 0 5239\&
2586\& #define EV_MAXPRI 0
2587.Ve
2588.Sp
2589.Vb 1
2590\& #include "ev++.h" 5240\& #include "ev++.h"
2591.Ve 5241.Ve
2592.Sp 5242.PP
2593And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled: 5243And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled:
2594.Sp 5244.PP
2595.Vb 2 5245.Vb 2
2596\& #include "ev_cpp.h" 5246\& #include "ev_cpp.h"
2597\& #include "ev.c" 5247\& #include "ev.c"
2598.Ve 5248.Ve
5249.SH "INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT"
5250.IX Header "INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT"
5251.SS "\s-1THREADS AND COROUTINES\s0"
5252.IX Subsection "THREADS AND COROUTINES"
5253\fI\s-1THREADS\s0\fR
5254.IX Subsection "THREADS"
5255.PP
5256All libev functions are reentrant and thread-safe unless explicitly
5257documented otherwise, but libev implements no locking itself. This means
5258that you can use as many loops as you want in parallel, as long as there
5259are no concurrent calls into any libev function with the same loop
5260parameter (\f(CW\*(C`ev_default_*\*(C'\fR calls have an implicit default loop parameter,
5261of course): libev guarantees that different event loops share no data
5262structures that need any locking.
5263.PP
5264Or to put it differently: calls with different loop parameters can be done
5265concurrently from multiple threads, calls with the same loop parameter
5266must be done serially (but can be done from different threads, as long as
5267only one thread ever is inside a call at any point in time, e.g. by using
5268a mutex per loop).
5269.PP
5270Specifically to support threads (and signal handlers), libev implements
5271so-called \f(CW\*(C`ev_async\*(C'\fR watchers, which allow some limited form of
5272concurrency on the same event loop, namely waking it up \*(L"from the
5273outside\*(R".
5274.PP
5275If you want to know which design (one loop, locking, or multiple loops
5276without or something else still) is best for your problem, then I cannot
5277help you, but here is some generic advice:
5278.IP "\(bu" 4
5279most applications have a main thread: use the default libev loop
5280in that thread, or create a separate thread running only the default loop.
5281.Sp
5282This helps integrating other libraries or software modules that use libev
5283themselves and don't care/know about threading.
5284.IP "\(bu" 4
5285one loop per thread is usually a good model.
5286.Sp
5287Doing this is almost never wrong, sometimes a better-performance model
5288exists, but it is always a good start.
5289.IP "\(bu" 4
5290other models exist, such as the leader/follower pattern, where one
5291loop is handed through multiple threads in a kind of round-robin fashion.
5292.Sp
5293Choosing a model is hard \- look around, learn, know that usually you can do
5294better than you currently do :\-)
5295.IP "\(bu" 4
5296often you need to talk to some other thread which blocks in the
5297event loop.
5298.Sp
5299\&\f(CW\*(C`ev_async\*(C'\fR watchers can be used to wake them up from other threads safely
5300(or from signal contexts...).
5301.Sp
5302An example use would be to communicate signals or other events that only
5303work in the default loop by registering the signal watcher with the
5304default loop and triggering an \f(CW\*(C`ev_async\*(C'\fR watcher from the default loop
5305watcher callback into the event loop interested in the signal.
5306.PP
5307See also \*(L"\s-1THREAD LOCKING EXAMPLE\*(R"\s0.
5308.PP
5309\fI\s-1COROUTINES\s0\fR
5310.IX Subsection "COROUTINES"
5311.PP
5312Libev is very accommodating to coroutines (\*(L"cooperative threads\*(R"):
5313libev fully supports nesting calls to its functions from different
5314coroutines (e.g. you can call \f(CW\*(C`ev_run\*(C'\fR on the same loop from two
5315different coroutines, and switch freely between both coroutines running
5316the loop, as long as you don't confuse yourself). The only exception is
5317that you must not do this from \f(CW\*(C`ev_periodic\*(C'\fR reschedule callbacks.
5318.PP
5319Care has been taken to ensure that libev does not keep local state inside
5320\&\f(CW\*(C`ev_run\*(C'\fR, and other calls do not usually allow for coroutine switches as
5321they do not call any callbacks.
5322.SS "\s-1COMPILER WARNINGS\s0"
5323.IX Subsection "COMPILER WARNINGS"
5324Depending on your compiler and compiler settings, you might get no or a
5325lot of warnings when compiling libev code. Some people are apparently
5326scared by this.
5327.PP
5328However, these are unavoidable for many reasons. For one, each compiler
5329has different warnings, and each user has different tastes regarding
5330warning options. \*(L"Warn-free\*(R" code therefore cannot be a goal except when
5331targeting a specific compiler and compiler-version.
5332.PP
5333Another reason is that some compiler warnings require elaborate
5334workarounds, or other changes to the code that make it less clear and less
5335maintainable.
5336.PP
5337And of course, some compiler warnings are just plain stupid, or simply
5338wrong (because they don't actually warn about the condition their message
5339seems to warn about). For example, certain older gcc versions had some
5340warnings that resulted in an extreme number of false positives. These have
5341been fixed, but some people still insist on making code warn-free with
5342such buggy versions.
5343.PP
5344While libev is written to generate as few warnings as possible,
5345\&\*(L"warn-free\*(R" code is not a goal, and it is recommended not to build libev
5346with any compiler warnings enabled unless you are prepared to cope with
5347them (e.g. by ignoring them). Remember that warnings are just that:
5348warnings, not errors, or proof of bugs.
5349.SS "\s-1VALGRIND\s0"
5350.IX Subsection "VALGRIND"
5351Valgrind has a special section here because it is a popular tool that is
5352highly useful. Unfortunately, valgrind reports are very hard to interpret.
5353.PP
5354If you think you found a bug (memory leak, uninitialised data access etc.)
5355in libev, then check twice: If valgrind reports something like:
5356.PP
5357.Vb 3
5358\& ==2274== definitely lost: 0 bytes in 0 blocks.
5359\& ==2274== possibly lost: 0 bytes in 0 blocks.
5360\& ==2274== still reachable: 256 bytes in 1 blocks.
5361.Ve
5362.PP
5363Then there is no memory leak, just as memory accounted to global variables
5364is not a memleak \- the memory is still being referenced, and didn't leak.
5365.PP
5366Similarly, under some circumstances, valgrind might report kernel bugs
5367as if it were a bug in libev (e.g. in realloc or in the poll backend,
5368although an acceptable workaround has been found here), or it might be
5369confused.
5370.PP
5371Keep in mind that valgrind is a very good tool, but only a tool. Don't
5372make it into some kind of religion.
5373.PP
5374If you are unsure about something, feel free to contact the mailing list
5375with the full valgrind report and an explanation on why you think this
5376is a bug in libev (best check the archives, too :). However, don't be
5377annoyed when you get a brisk \*(L"this is no bug\*(R" answer and take the chance
5378of learning how to interpret valgrind properly.
5379.PP
5380If you need, for some reason, empty reports from valgrind for your project
5381I suggest using suppression lists.
5382.SH "PORTABILITY NOTES"
5383.IX Header "PORTABILITY NOTES"
5384.SS "\s-1GNU/LINUX 32 BIT LIMITATIONS\s0"
5385.IX Subsection "GNU/LINUX 32 BIT LIMITATIONS"
5386GNU/Linux is the only common platform that supports 64 bit file/large file
5387interfaces but \fIdisables\fR them by default.
5388.PP
5389That means that libev compiled in the default environment doesn't support
5390files larger than 2GiB or so, which mainly affects \f(CW\*(C`ev_stat\*(C'\fR watchers.
5391.PP
5392Unfortunately, many programs try to work around this GNU/Linux issue
5393by enabling the large file \s-1API,\s0 which makes them incompatible with the
5394standard libev compiled for their system.
5395.PP
5396Likewise, libev cannot enable the large file \s-1API\s0 itself as this would
5397suddenly make it incompatible to the default compile time environment,
5398i.e. all programs not using special compile switches.
5399.SS "\s-1OS/X AND DARWIN BUGS\s0"
5400.IX Subsection "OS/X AND DARWIN BUGS"
5401The whole thing is a bug if you ask me \- basically any system interface
5402you touch is broken, whether it is locales, poll, kqueue or even the
5403OpenGL drivers.
5404.PP
5405\fI\f(CI\*(C`kqueue\*(C'\fI is buggy\fR
5406.IX Subsection "kqueue is buggy"
5407.PP
5408The kqueue syscall is broken in all known versions \- most versions support
5409only sockets, many support pipes.
5410.PP
5411Libev tries to work around this by not using \f(CW\*(C`kqueue\*(C'\fR by default on this
5412rotten platform, but of course you can still ask for it when creating a
5413loop \- embedding a socket-only kqueue loop into a select-based one is
5414probably going to work well.
5415.PP
5416\fI\f(CI\*(C`poll\*(C'\fI is buggy\fR
5417.IX Subsection "poll is buggy"
5418.PP
5419Instead of fixing \f(CW\*(C`kqueue\*(C'\fR, Apple replaced their (working) \f(CW\*(C`poll\*(C'\fR
5420implementation by something calling \f(CW\*(C`kqueue\*(C'\fR internally around the 10.5.6
5421release, so now \f(CW\*(C`kqueue\*(C'\fR \fIand\fR \f(CW\*(C`poll\*(C'\fR are broken.
5422.PP
5423Libev tries to work around this by not using \f(CW\*(C`poll\*(C'\fR by default on
5424this rotten platform, but of course you can still ask for it when creating
5425a loop.
5426.PP
5427\fI\f(CI\*(C`select\*(C'\fI is buggy\fR
5428.IX Subsection "select is buggy"
5429.PP
5430All that's left is \f(CW\*(C`select\*(C'\fR, and of course Apple found a way to fuck this
5431one up as well: On \s-1OS/X,\s0 \f(CW\*(C`select\*(C'\fR actively limits the number of file
5432descriptors you can pass in to 1024 \- your program suddenly crashes when
5433you use more.
5434.PP
5435There is an undocumented \*(L"workaround\*(R" for this \- defining
5436\&\f(CW\*(C`_DARWIN_UNLIMITED_SELECT\*(C'\fR, which libev tries to use, so select \fIshould\fR
5437work on \s-1OS/X.\s0
5438.SS "\s-1SOLARIS PROBLEMS AND WORKAROUNDS\s0"
5439.IX Subsection "SOLARIS PROBLEMS AND WORKAROUNDS"
5440\fI\f(CI\*(C`errno\*(C'\fI reentrancy\fR
5441.IX Subsection "errno reentrancy"
5442.PP
5443The default compile environment on Solaris is unfortunately so
5444thread-unsafe that you can't even use components/libraries compiled
5445without \f(CW\*(C`\-D_REENTRANT\*(C'\fR in a threaded program, which, of course, isn't
5446defined by default. A valid, if stupid, implementation choice.
5447.PP
5448If you want to use libev in threaded environments you have to make sure
5449it's compiled with \f(CW\*(C`_REENTRANT\*(C'\fR defined.
5450.PP
5451\fIEvent port backend\fR
5452.IX Subsection "Event port backend"
5453.PP
5454The scalable event interface for Solaris is called \*(L"event
5455ports\*(R". Unfortunately, this mechanism is very buggy in all major
5456releases. If you run into high \s-1CPU\s0 usage, your program freezes or you get
5457a large number of spurious wakeups, make sure you have all the relevant
5458and latest kernel patches applied. No, I don't know which ones, but there
5459are multiple ones to apply, and afterwards, event ports actually work
5460great.
5461.PP
5462If you can't get it to work, you can try running the program by setting
5463the environment variable \f(CW\*(C`LIBEV_FLAGS=3\*(C'\fR to only allow \f(CW\*(C`poll\*(C'\fR and
5464\&\f(CW\*(C`select\*(C'\fR backends.
5465.SS "\s-1AIX POLL BUG\s0"
5466.IX Subsection "AIX POLL BUG"
5467\&\s-1AIX\s0 unfortunately has a broken \f(CW\*(C`poll.h\*(C'\fR header. Libev works around
5468this by trying to avoid the poll backend altogether (i.e. it's not even
5469compiled in), which normally isn't a big problem as \f(CW\*(C`select\*(C'\fR works fine
5470with large bitsets on \s-1AIX,\s0 and \s-1AIX\s0 is dead anyway.
5471.SS "\s-1WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS\s0"
5472.IX Subsection "WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS"
5473\fIGeneral issues\fR
5474.IX Subsection "General issues"
5475.PP
5476Win32 doesn't support any of the standards (e.g. \s-1POSIX\s0) that libev
5477requires, and its I/O model is fundamentally incompatible with the \s-1POSIX\s0
5478model. Libev still offers limited functionality on this platform in
5479the form of the \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR backend, and only supports socket
5480descriptors. This only applies when using Win32 natively, not when using
5481e.g. cygwin. Actually, it only applies to the microsofts own compilers,
5482as every compiler comes with a slightly differently broken/incompatible
5483environment.
5484.PP
5485Lifting these limitations would basically require the full
5486re-implementation of the I/O system. If you are into this kind of thing,
5487then note that glib does exactly that for you in a very portable way (note
5488also that glib is the slowest event library known to man).
5489.PP
5490There is no supported compilation method available on windows except
5491embedding it into other applications.
5492.PP
5493Sensible signal handling is officially unsupported by Microsoft \- libev
5494tries its best, but under most conditions, signals will simply not work.
5495.PP
5496Not a libev limitation but worth mentioning: windows apparently doesn't
5497accept large writes: instead of resulting in a partial write, windows will
5498either accept everything or return \f(CW\*(C`ENOBUFS\*(C'\fR if the buffer is too large,
5499so make sure you only write small amounts into your sockets (less than a
5500megabyte seems safe, but this apparently depends on the amount of memory
5501available).
5502.PP
5503Due to the many, low, and arbitrary limits on the win32 platform and
5504the abysmal performance of winsockets, using a large number of sockets
5505is not recommended (and not reasonable). If your program needs to use
5506more than a hundred or so sockets, then likely it needs to use a totally
5507different implementation for windows, as libev offers the \s-1POSIX\s0 readiness
5508notification model, which cannot be implemented efficiently on windows
5509(due to Microsoft monopoly games).
5510.PP
5511A typical way to use libev under windows is to embed it (see the embedding
5512section for details) and use the following \fIevwrap.h\fR header file instead
5513of \fIev.h\fR:
5514.PP
5515.Vb 2
5516\& #define EV_STANDALONE /* keeps ev from requiring config.h */
5517\& #define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
5518\&
5519\& #include "ev.h"
5520.Ve
5521.PP
5522And compile the following \fIevwrap.c\fR file into your project (make sure
5523you do \fInot\fR compile the \fIev.c\fR or any other embedded source files!):
5524.PP
5525.Vb 2
5526\& #include "evwrap.h"
5527\& #include "ev.c"
5528.Ve
5529.PP
5530\fIThe winsocket \f(CI\*(C`select\*(C'\fI function\fR
5531.IX Subsection "The winsocket select function"
5532.PP
5533The winsocket \f(CW\*(C`select\*(C'\fR function doesn't follow \s-1POSIX\s0 in that it
5534requires socket \fIhandles\fR and not socket \fIfile descriptors\fR (it is
5535also extremely buggy). This makes select very inefficient, and also
5536requires a mapping from file descriptors to socket handles (the Microsoft
5537C runtime provides the function \f(CW\*(C`_open_osfhandle\*(C'\fR for this). See the
5538discussion of the \f(CW\*(C`EV_SELECT_USE_FD_SET\*(C'\fR, \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR and
5539\&\f(CW\*(C`EV_FD_TO_WIN32_HANDLE\*(C'\fR preprocessor symbols for more info.
5540.PP
5541The configuration for a \*(L"naked\*(R" win32 using the Microsoft runtime
5542libraries and raw winsocket select is:
5543.PP
5544.Vb 2
5545\& #define EV_USE_SELECT 1
5546\& #define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
5547.Ve
5548.PP
5549Note that winsockets handling of fd sets is O(n), so you can easily get a
5550complexity in the O(nX) range when using win32.
5551.PP
5552\fILimited number of file descriptors\fR
5553.IX Subsection "Limited number of file descriptors"
5554.PP
5555Windows has numerous arbitrary (and low) limits on things.
5556.PP
5557Early versions of winsocket's select only supported waiting for a maximum
5558of \f(CW64\fR handles (probably owning to the fact that all windows kernels
5559can only wait for \f(CW64\fR things at the same time internally; Microsoft
5560recommends spawning a chain of threads and wait for 63 handles and the
5561previous thread in each. Sounds great!).
5562.PP
5563Newer versions support more handles, but you need to define \f(CW\*(C`FD_SETSIZE\*(C'\fR
5564to some high number (e.g. \f(CW2048\fR) before compiling the winsocket select
5565call (which might be in libev or elsewhere, for example, perl and many
5566other interpreters do their own select emulation on windows).
5567.PP
5568Another limit is the number of file descriptors in the Microsoft runtime
5569libraries, which by default is \f(CW64\fR (there must be a hidden \fI64\fR
5570fetish or something like this inside Microsoft). You can increase this
5571by calling \f(CW\*(C`_setmaxstdio\*(C'\fR, which can increase this limit to \f(CW2048\fR
5572(another arbitrary limit), but is broken in many versions of the Microsoft
5573runtime libraries. This might get you to about \f(CW512\fR or \f(CW2048\fR sockets
5574(depending on windows version and/or the phase of the moon). To get more,
5575you need to wrap all I/O functions and provide your own fd management, but
5576the cost of calling select (O(nX)) will likely make this unworkable.
5577.SS "\s-1PORTABILITY REQUIREMENTS\s0"
5578.IX Subsection "PORTABILITY REQUIREMENTS"
5579In addition to a working ISO-C implementation and of course the
5580backend-specific APIs, libev relies on a few additional extensions:
5581.ie n .IP """void (*)(ev_watcher_type *, int revents)"" must have compatible calling conventions regardless of ""ev_watcher_type *""." 4
5582.el .IP "\f(CWvoid (*)(ev_watcher_type *, int revents)\fR must have compatible calling conventions regardless of \f(CWev_watcher_type *\fR." 4
5583.IX Item "void (*)(ev_watcher_type *, int revents) must have compatible calling conventions regardless of ev_watcher_type *."
5584Libev assumes not only that all watcher pointers have the same internal
5585structure (guaranteed by \s-1POSIX\s0 but not by \s-1ISO C\s0 for example), but it also
5586assumes that the same (machine) code can be used to call any watcher
5587callback: The watcher callbacks have different type signatures, but libev
5588calls them using an \f(CW\*(C`ev_watcher *\*(C'\fR internally.
5589.IP "null pointers and integer zero are represented by 0 bytes" 4
5590.IX Item "null pointers and integer zero are represented by 0 bytes"
5591Libev uses \f(CW\*(C`memset\*(C'\fR to initialise structs and arrays to \f(CW0\fR bytes, and
5592relies on this setting pointers and integers to null.
5593.IP "pointer accesses must be thread-atomic" 4
5594.IX Item "pointer accesses must be thread-atomic"
5595Accessing a pointer value must be atomic, it must both be readable and
5596writable in one piece \- this is the case on all current architectures.
5597.ie n .IP """sig_atomic_t volatile"" must be thread-atomic as well" 4
5598.el .IP "\f(CWsig_atomic_t volatile\fR must be thread-atomic as well" 4
5599.IX Item "sig_atomic_t volatile must be thread-atomic as well"
5600The type \f(CW\*(C`sig_atomic_t volatile\*(C'\fR (or whatever is defined as
5601\&\f(CW\*(C`EV_ATOMIC_T\*(C'\fR) must be atomic with respect to accesses from different
5602threads. This is not part of the specification for \f(CW\*(C`sig_atomic_t\*(C'\fR, but is
5603believed to be sufficiently portable.
5604.ie n .IP """sigprocmask"" must work in a threaded environment" 4
5605.el .IP "\f(CWsigprocmask\fR must work in a threaded environment" 4
5606.IX Item "sigprocmask must work in a threaded environment"
5607Libev uses \f(CW\*(C`sigprocmask\*(C'\fR to temporarily block signals. This is not
5608allowed in a threaded program (\f(CW\*(C`pthread_sigmask\*(C'\fR has to be used). Typical
5609pthread implementations will either allow \f(CW\*(C`sigprocmask\*(C'\fR in the \*(L"main
5610thread\*(R" or will block signals process-wide, both behaviours would
5611be compatible with libev. Interaction between \f(CW\*(C`sigprocmask\*(C'\fR and
5612\&\f(CW\*(C`pthread_sigmask\*(C'\fR could complicate things, however.
5613.Sp
5614The most portable way to handle signals is to block signals in all threads
5615except the initial one, and run the signal handling loop in the initial
5616thread as well.
5617.ie n .IP """long"" must be large enough for common memory allocation sizes" 4
5618.el .IP "\f(CWlong\fR must be large enough for common memory allocation sizes" 4
5619.IX Item "long must be large enough for common memory allocation sizes"
5620To improve portability and simplify its \s-1API,\s0 libev uses \f(CW\*(C`long\*(C'\fR internally
5621instead of \f(CW\*(C`size_t\*(C'\fR when allocating its data structures. On non-POSIX
5622systems (Microsoft...) this might be unexpectedly low, but is still at
5623least 31 bits everywhere, which is enough for hundreds of millions of
5624watchers.
5625.ie n .IP """double"" must hold a time value in seconds with enough accuracy" 4
5626.el .IP "\f(CWdouble\fR must hold a time value in seconds with enough accuracy" 4
5627.IX Item "double must hold a time value in seconds with enough accuracy"
5628The type \f(CW\*(C`double\*(C'\fR is used to represent timestamps. It is required to
5629have at least 51 bits of mantissa (and 9 bits of exponent), which is
5630good enough for at least into the year 4000 with millisecond accuracy
5631(the design goal for libev). This requirement is overfulfilled by
5632implementations using \s-1IEEE 754,\s0 which is basically all existing ones.
5633.Sp
5634With \s-1IEEE 754\s0 doubles, you get microsecond accuracy until at least the
5635year 2255 (and millisecond accuracy till the year 287396 \- by then, libev
5636is either obsolete or somebody patched it to use \f(CW\*(C`long double\*(C'\fR or
5637something like that, just kidding).
5638.PP
5639If you know of other additional requirements drop me a note.
2599.SH "COMPLEXITIES" 5640.SH "ALGORITHMIC COMPLEXITIES"
2600.IX Header "COMPLEXITIES" 5641.IX Header "ALGORITHMIC COMPLEXITIES"
2601In this section the complexities of (many of) the algorithms used inside 5642In this section the complexities of (many of) the algorithms used inside
2602libev will be explained. For complexity discussions about backends see the 5643libev will be documented. For complexity discussions about backends see
2603documentation for \f(CW\*(C`ev_default_init\*(C'\fR. 5644the documentation for \f(CW\*(C`ev_default_init\*(C'\fR.
2604.Sp 5645.PP
2605All of the following are about amortised time: If an array needs to be 5646All of the following are about amortised time: If an array needs to be
2606extended, libev needs to realloc and move the whole array, but this 5647extended, libev needs to realloc and move the whole array, but this
2607happens asymptotically never with higher number of elements, so O(1) might 5648happens asymptotically rarer with higher number of elements, so O(1) might
2608mean it might do a lengthy realloc operation in rare cases, but on average 5649mean that libev does a lengthy realloc operation in rare cases, but on
2609it is much faster and asymptotically approaches constant time. 5650average it is much faster and asymptotically approaches constant time.
2610.RS 4
2611.IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4 5651.IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4
2612.IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 5652.IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)"
2613This means that, when you have a watcher that triggers in one hour and 5653This means that, when you have a watcher that triggers in one hour and
2614there are 100 watchers that would trigger before that then inserting will 5654there are 100 watchers that would trigger before that, then inserting will
2615have to skip those 100 watchers. 5655have to skip roughly seven (\f(CW\*(C`ld 100\*(C'\fR) of these watchers.
2616.IP "Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)" 4 5656.IP "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)" 4
2617.IX Item "Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)" 5657.IX Item "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)"
2618That means that for changing a timer costs less than removing/adding them 5658That means that changing a timer costs less than removing/adding them,
2619as only the relative motion in the event queue has to be paid for. 5659as only the relative motion in the event queue has to be paid for.
2620.IP "Starting io/check/prepare/idle/signal/child watchers: O(1)" 4 5660.IP "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)" 4
2621.IX Item "Starting io/check/prepare/idle/signal/child watchers: O(1)" 5661.IX Item "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)"
2622These just add the watcher into an array or at the head of a list. 5662These just add the watcher into an array or at the head of a list.
5663.IP "Stopping check/prepare/idle/fork/async watchers: O(1)" 4
2623=item Stopping check/prepare/idle watchers: O(1) 5664.IX Item "Stopping check/prepare/idle/fork/async watchers: O(1)"
5665.PD 0
2624.IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4 5666.IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4
2625.IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))" 5667.IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))"
5668.PD
2626These watchers are stored in lists then need to be walked to find the 5669These watchers are stored in lists, so they need to be walked to find the
2627correct watcher to remove. The lists are usually short (you don't usually 5670correct watcher to remove. The lists are usually short (you don't usually
2628have many watchers waiting for the same fd or signal). 5671have many watchers waiting for the same fd or signal: one is typical, two
5672is rare).
2629.IP "Finding the next timer per loop iteration: O(1)" 4 5673.IP "Finding the next timer in each loop iteration: O(1)" 4
2630.IX Item "Finding the next timer per loop iteration: O(1)" 5674.IX Item "Finding the next timer in each loop iteration: O(1)"
2631.PD 0 5675By virtue of using a binary or 4\-heap, the next timer is always found at a
5676fixed position in the storage array.
2632.IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4 5677.IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4
2633.IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 5678.IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)"
2634.PD
2635A change means an I/O watcher gets started or stopped, which requires 5679A change means an I/O watcher gets started or stopped, which requires
2636libev to recalculate its status (and possibly tell the kernel). 5680libev to recalculate its status (and possibly tell the kernel, depending
2637.IP "Activating one watcher: O(1)" 4 5681on backend and whether \f(CW\*(C`ev_io_set\*(C'\fR was used).
2638.IX Item "Activating one watcher: O(1)" 5682.IP "Activating one watcher (putting it into the pending state): O(1)" 4
5683.IX Item "Activating one watcher (putting it into the pending state): O(1)"
2639.PD 0 5684.PD 0
2640.IP "Priority handling: O(number_of_priorities)" 4 5685.IP "Priority handling: O(number_of_priorities)" 4
2641.IX Item "Priority handling: O(number_of_priorities)" 5686.IX Item "Priority handling: O(number_of_priorities)"
2642.PD 5687.PD
2643Priorities are implemented by allocating some space for each 5688Priorities are implemented by allocating some space for each
2644priority. When doing priority-based operations, libev usually has to 5689priority. When doing priority-based operations, libev usually has to
2645linearly search all the priorities. 5690linearly search all the priorities, but starting/stopping and activating
2646.RE 5691watchers becomes O(1) with respect to priority handling.
2647.RS 4 5692.IP "Sending an ev_async: O(1)" 4
5693.IX Item "Sending an ev_async: O(1)"
5694.PD 0
5695.IP "Processing ev_async_send: O(number_of_async_watchers)" 4
5696.IX Item "Processing ev_async_send: O(number_of_async_watchers)"
5697.IP "Processing signals: O(max_signal_number)" 4
5698.IX Item "Processing signals: O(max_signal_number)"
5699.PD
5700Sending involves a system call \fIiff\fR there were no other \f(CW\*(C`ev_async_send\*(C'\fR
5701calls in the current loop iteration and the loop is currently
5702blocked. Checking for async and signal events involves iterating over all
5703running async watchers or all signal numbers.
5704.SH "PORTING FROM LIBEV 3.X TO 4.X"
5705.IX Header "PORTING FROM LIBEV 3.X TO 4.X"
5706The major version 4 introduced some incompatible changes to the \s-1API.\s0
5707.PP
5708At the moment, the \f(CW\*(C`ev.h\*(C'\fR header file provides compatibility definitions
5709for all changes, so most programs should still compile. The compatibility
5710layer might be removed in later versions of libev, so better update to the
5711new \s-1API\s0 early than late.
5712.ie n .IP """EV_COMPAT3"" backwards compatibility mechanism" 4
5713.el .IP "\f(CWEV_COMPAT3\fR backwards compatibility mechanism" 4
5714.IX Item "EV_COMPAT3 backwards compatibility mechanism"
5715The backward compatibility mechanism can be controlled by
5716\&\f(CW\*(C`EV_COMPAT3\*(C'\fR. See \*(L"\s-1PREPROCESSOR SYMBOLS/MACROS\*(R"\s0 in the \*(L"\s-1EMBEDDING\*(R"\s0
5717section.
5718.ie n .IP """ev_default_destroy"" and ""ev_default_fork"" have been removed" 4
5719.el .IP "\f(CWev_default_destroy\fR and \f(CWev_default_fork\fR have been removed" 4
5720.IX Item "ev_default_destroy and ev_default_fork have been removed"
5721These calls can be replaced easily by their \f(CW\*(C`ev_loop_xxx\*(C'\fR counterparts:
5722.Sp
5723.Vb 2
5724\& ev_loop_destroy (EV_DEFAULT_UC);
5725\& ev_loop_fork (EV_DEFAULT);
5726.Ve
5727.IP "function/symbol renames" 4
5728.IX Item "function/symbol renames"
5729A number of functions and symbols have been renamed:
5730.Sp
5731.Vb 3
5732\& ev_loop => ev_run
5733\& EVLOOP_NONBLOCK => EVRUN_NOWAIT
5734\& EVLOOP_ONESHOT => EVRUN_ONCE
5735\&
5736\& ev_unloop => ev_break
5737\& EVUNLOOP_CANCEL => EVBREAK_CANCEL
5738\& EVUNLOOP_ONE => EVBREAK_ONE
5739\& EVUNLOOP_ALL => EVBREAK_ALL
5740\&
5741\& EV_TIMEOUT => EV_TIMER
5742\&
5743\& ev_loop_count => ev_iteration
5744\& ev_loop_depth => ev_depth
5745\& ev_loop_verify => ev_verify
5746.Ve
5747.Sp
5748Most functions working on \f(CW\*(C`struct ev_loop\*(C'\fR objects don't have an
5749\&\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
5750associated constants have been renamed to not collide with the \f(CW\*(C`struct
5751ev_loop\*(C'\fR anymore and \f(CW\*(C`EV_TIMER\*(C'\fR now follows the same naming scheme
5752as all other watcher types. Note that \f(CW\*(C`ev_loop_fork\*(C'\fR is still called
5753\&\f(CW\*(C`ev_loop_fork\*(C'\fR because it would otherwise clash with the \f(CW\*(C`ev_fork\*(C'\fR
5754typedef.
5755.ie n .IP """EV_MINIMAL"" mechanism replaced by ""EV_FEATURES""" 4
5756.el .IP "\f(CWEV_MINIMAL\fR mechanism replaced by \f(CWEV_FEATURES\fR" 4
5757.IX Item "EV_MINIMAL mechanism replaced by EV_FEATURES"
5758The preprocessor symbol \f(CW\*(C`EV_MINIMAL\*(C'\fR has been replaced by a different
5759mechanism, \f(CW\*(C`EV_FEATURES\*(C'\fR. Programs using \f(CW\*(C`EV_MINIMAL\*(C'\fR usually compile
5760and work, but the library code will of course be larger.
5761.SH "GLOSSARY"
5762.IX Header "GLOSSARY"
5763.IP "active" 4
5764.IX Item "active"
5765A watcher is active as long as it has been started and not yet stopped.
5766See \*(L"\s-1WATCHER STATES\*(R"\s0 for details.
5767.IP "application" 4
5768.IX Item "application"
5769In this document, an application is whatever is using libev.
5770.IP "backend" 4
5771.IX Item "backend"
5772The part of the code dealing with the operating system interfaces.
5773.IP "callback" 4
5774.IX Item "callback"
5775The address of a function that is called when some event has been
5776detected. Callbacks are being passed the event loop, the watcher that
5777received the event, and the actual event bitset.
5778.IP "callback/watcher invocation" 4
5779.IX Item "callback/watcher invocation"
5780The act of calling the callback associated with a watcher.
5781.IP "event" 4
5782.IX Item "event"
5783A change of state of some external event, such as data now being available
5784for reading on a file descriptor, time having passed or simply not having
5785any other events happening anymore.
5786.Sp
5787In libev, events are represented as single bits (such as \f(CW\*(C`EV_READ\*(C'\fR or
5788\&\f(CW\*(C`EV_TIMER\*(C'\fR).
5789.IP "event library" 4
5790.IX Item "event library"
5791A software package implementing an event model and loop.
5792.IP "event loop" 4
5793.IX Item "event loop"
5794An entity that handles and processes external events and converts them
5795into callback invocations.
5796.IP "event model" 4
5797.IX Item "event model"
5798The model used to describe how an event loop handles and processes
5799watchers and events.
5800.IP "pending" 4
5801.IX Item "pending"
5802A watcher is pending as soon as the corresponding event has been
5803detected. See \*(L"\s-1WATCHER STATES\*(R"\s0 for details.
5804.IP "real time" 4
5805.IX Item "real time"
5806The physical time that is observed. It is apparently strictly monotonic :)
5807.IP "wall-clock time" 4
5808.IX Item "wall-clock time"
5809The time and date as shown on clocks. Unlike real time, it can actually
5810be wrong and jump forwards and backwards, e.g. when you adjust your
5811clock.
5812.IP "watcher" 4
5813.IX Item "watcher"
5814A data structure that describes interest in certain events. Watchers need
5815to be started (attached to an event loop) before they can receive events.
2648.SH "AUTHOR" 5816.SH "AUTHOR"
2649.IX Header "AUTHOR" 5817.IX Header "AUTHOR"
2650Marc Lehmann <libev@schmorp.de>. 5818Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5819Magnusson and Emanuele Giaquinta, and minor corrections by many others.

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