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129.\" ======================================================================== 133.\" ========================================================================
130.\" 134.\"
131.IX Title ""<STANDARD INPUT>" 1" 135.IX Title "LIBEV 3"
132.TH "<STANDARD INPUT>" 1 "2007-11-27" "perl v5.8.8" "User Contributed Perl Documentation" 136.TH LIBEV 3 "2019-12-21" "libev-4.31" "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"
145.Vb 1
146\& #include <ev.h>
147.Ve
148.SS "\s-1EXAMPLE PROGRAM\s0"
149.IX Subsection "EXAMPLE PROGRAM"
137.Vb 2 150.Vb 2
138\& /* this is the only header you need */ 151\& // a single header file is required
139\& #include <ev.h> 152\& #include <ev.h>
140.Ve 153\&
141.PP 154\& #include <stdio.h> // for puts
142.Vb 3 155\&
143\& /* what follows is a fully working example program */ 156\& // every watcher type has its own typedef\*(Aqd struct
157\& // with the name ev_TYPE
144\& ev_io stdin_watcher; 158\& ev_io stdin_watcher;
145\& ev_timer timeout_watcher; 159\& ev_timer timeout_watcher;
146.Ve 160\&
147.PP 161\& // all watcher callbacks have a similar signature
148.Vb 8
149\& /* called when data readable on stdin */ 162\& // this callback is called when data is readable on stdin
150\& static void 163\& static void
151\& stdin_cb (EV_P_ struct ev_io *w, int revents) 164\& stdin_cb (EV_P_ ev_io *w, int revents)
152\& { 165\& {
153\& /* puts ("stdin ready"); */ 166\& puts ("stdin ready");
154\& ev_io_stop (EV_A_ w); /* just a syntax example */ 167\& // for one\-shot events, one must manually stop the watcher
155\& 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);
156\& } 173\& }
157.Ve 174\&
158.PP 175\& // another callback, this time for a time\-out
159.Vb 6
160\& static void 176\& static void
161\& timeout_cb (EV_P_ struct ev_timer *w, int revents) 177\& timeout_cb (EV_P_ ev_timer *w, int revents)
162\& { 178\& {
163\& /* puts ("timeout"); */ 179\& puts ("timeout");
164\& 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);
165\& } 182\& }
166.Ve 183\&
167.PP
168.Vb 4
169\& int 184\& int
170\& main (void) 185\& main (void)
171\& { 186\& {
172\& struct ev_loop *loop = ev_default_loop (0); 187\& // use the default event loop unless you have special needs
173.Ve 188\& struct ev_loop *loop = EV_DEFAULT;
174.PP 189\&
175.Vb 3
176\& /* 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
177\& 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);
178\& ev_io_start (loop, &stdin_watcher); 193\& ev_io_start (loop, &stdin_watcher);
179.Ve 194\&
180.PP 195\& // initialise a timer watcher, then start it
181.Vb 3
182\& /* simple non-repeating 5.5 second timeout */ 196\& // simple non\-repeating 5.5 second timeout
183\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.); 197\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
184\& ev_timer_start (loop, &timeout_watcher); 198\& ev_timer_start (loop, &timeout_watcher);
185.Ve 199\&
186.PP 200\& // now wait for events to arrive
187.Vb 2
188\& /* loop till timeout or data ready */
189\& ev_loop (loop, 0); 201\& ev_run (loop, 0);
190.Ve 202\&
191.PP 203\& // break was called, so exit
192.Vb 2
193\& return 0; 204\& return 0;
194\& } 205\& }
195.Ve 206.Ve
196.SH "DESCRIPTION" 207.SH "ABOUT THIS DOCUMENT"
197.IX Header "DESCRIPTION" 208.IX Header "ABOUT THIS DOCUMENT"
209This document documents the libev software package.
210.PP
211The newest version of this document is also available as an html-formatted
212web page you might find easier to navigate when reading it for the first
213time: <http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
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"
198Libev 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
199file descriptor being readable or a timeout occuring), and it will manage 232file descriptor being readable or a timeout occurring), and it will manage
200these event sources and provide your program with events. 233these event sources and provide your program with events.
201.PP 234.PP
202To 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
203(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
204communicate events via a callback mechanism. 237communicate events via a callback mechanism.
205.PP 238.PP
206You register interest in certain events by registering so-called \fIevent 239You register interest in certain events by registering so-called \fIevent
207watchers\fR, which are relatively small C structures you initialise with the 240watchers\fR, which are relatively small C structures you initialise with the
208details 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
209watcher. 242watcher.
210.SH "FEATURES" 243.SS "\s-1FEATURES\s0"
211.IX Header "FEATURES" 244.IX Subsection "FEATURES"
212Libev supports select, poll, the linux-specific epoll and the bsd-specific 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
213kqueue mechanisms for file descriptor events, relative timers, absolute 246interfaces, the BSD-specific \f(CW\*(C`kqueue\*(C'\fR and the Solaris-specific event port
214timers with customised rescheduling, signal events, process status change 247mechanisms for file descriptor events (\f(CW\*(C`ev_io\*(C'\fR), the Linux \f(CW\*(C`inotify\*(C'\fR
215events (related to \s-1SIGCHLD\s0), and event watchers dealing with the event 248interface (for \f(CW\*(C`ev_stat\*(C'\fR), Linux eventfd/signalfd (for faster and cleaner
216loop mechanism itself (idle, prepare and check watchers). It also is quite 249inter-thread wakeup (\f(CW\*(C`ev_async\*(C'\fR)/signal handling (\f(CW\*(C`ev_signal\*(C'\fR)) relative
217fast (see this benchmark comparing 250timers (\f(CW\*(C`ev_timer\*(C'\fR), absolute timers with customised rescheduling
218it to libevent for example). 251(\f(CW\*(C`ev_periodic\*(C'\fR), synchronous signals (\f(CW\*(C`ev_signal\*(C'\fR), process status
252change events (\f(CW\*(C`ev_child\*(C'\fR), and event watchers dealing with the event
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
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).
256.PP
257It also is quite fast (see this
258benchmark <http://libev.schmorp.de/bench.html> comparing it to libevent
259for example).
219.SH "CONVENTIONS" 260.SS "\s-1CONVENTIONS\s0"
220.IX Header "CONVENTIONS" 261.IX Subsection "CONVENTIONS"
221Libev is very configurable. In this manual the default configuration 262Libev is very configurable. In this manual the default (and most common)
222will be described, which supports multiple event loops. For more info 263configuration will be described, which supports multiple event loops. For
223about various configuration options please have a look at the file 264more info about various configuration options please have a look at
224\&\fI\s-1README\s0.embed\fR in the libev distribution. If libev was configured without 265\&\fB\s-1EMBED\s0\fR section in this manual. If libev was configured without support
225support for multiple event loops, then all functions taking an initial 266for multiple event loops, then all functions taking an initial argument of
226argument of name \f(CW\*(C`loop\*(C'\fR (which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) 267name \f(CW\*(C`loop\*(C'\fR (which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) will not have
227will not have this argument. 268this argument.
228.SH "TIME REPRESENTATION" 269.SS "\s-1TIME REPRESENTATION\s0"
229.IX Header "TIME REPRESENTATION" 270.IX Subsection "TIME REPRESENTATION"
230Libev represents time as a single floating point number, representing the 271Libev represents time as a single floating point number, representing
231(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
232the beginning of 1970, details are complicated, don't ask). This type is 273somewhere near the beginning of 1970, details are complicated, don't
233called \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
234to 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
235it, 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.
236.SH "GLOBAL FUNCTIONS" 303.SH "GLOBAL FUNCTIONS"
237.IX Header "GLOBAL FUNCTIONS" 304.IX Header "GLOBAL FUNCTIONS"
238These functions can be called anytime, even before initialising the 305These functions can be called anytime, even before initialising the
239library in any way. 306library in any way.
240.IP "ev_tstamp ev_time ()" 4 307.IP "ev_tstamp ev_time ()" 4
241.IX Item "ev_tstamp ev_time ()" 308.IX Item "ev_tstamp ev_time ()"
242Returns 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
243\&\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
244you 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).
245.IP "int ev_version_major ()" 4 324.IP "int ev_version_major ()" 4
246.IX Item "int ev_version_major ()" 325.IX Item "int ev_version_major ()"
247.PD 0 326.PD 0
248.IP "int ev_version_minor ()" 4 327.IP "int ev_version_minor ()" 4
249.IX Item "int ev_version_minor ()" 328.IX Item "int ev_version_minor ()"
250.PD 329.PD
251You 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
252you 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
253\&\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
254symbols \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
255version of the library your program was compiled against. 334version of the library your program was compiled against.
256.Sp 335.Sp
336These version numbers refer to the \s-1ABI\s0 version of the library, not the
337release version.
338.Sp
257Usually, 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,
258as this indicates an incompatible change. Minor versions are usually 340as this indicates an incompatible change. Minor versions are usually
259compatible to older versions, so a larger minor version alone is usually 341compatible to older versions, so a larger minor version alone is usually
260not a problem. 342not a problem.
261.Sp 343.Sp
262Example: make sure we haven't accidentally been linked against the wrong 344Example: Make sure we haven't accidentally been linked against the wrong
263version: 345version (note, however, that this will not detect other \s-1ABI\s0 mismatches,
346such as \s-1LFS\s0 or reentrancy).
264.Sp 347.Sp
265.Vb 3 348.Vb 3
266\& assert (("libev version mismatch", 349\& assert (("libev version mismatch",
267\& ev_version_major () == EV_VERSION_MAJOR 350\& ev_version_major () == EV_VERSION_MAJOR
268\& && ev_version_minor () >= EV_VERSION_MINOR)); 351\& && ev_version_minor () >= EV_VERSION_MINOR));
269.Ve 352.Ve
270.IP "unsigned int ev_supported_backends ()" 4 353.IP "unsigned int ev_supported_backends ()" 4
271.IX Item "unsigned int ev_supported_backends ()" 354.IX Item "unsigned int ev_supported_backends ()"
272Return 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
273value) compiled into this binary of libev (independent of their 356value) compiled into this binary of libev (independent of their
… …
276.Sp 359.Sp
277Example: 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
278a 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
279.Sp 362.Sp
280.Vb 2 363.Vb 2
281\& assert (("sorry, no epoll, no sex", 364\& assert (("sorry, no epoll, no sex",
282\& ev_supported_backends () & EVBACKEND_EPOLL)); 365\& ev_supported_backends () & EVBACKEND_EPOLL));
283.Ve 366.Ve
284.IP "unsigned int ev_recommended_backends ()" 4 367.IP "unsigned int ev_recommended_backends ()" 4
285.IX Item "unsigned int ev_recommended_backends ()" 368.IX Item "unsigned int ev_recommended_backends ()"
286Return 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
287recommended 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
288returned 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
289most BSDs and will not be autodetected unless you explicitly request it 373and will not be auto-detected unless you explicitly request it (assuming
290(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
291libev will probe for if you specify no backends explicitly. 375probe for if you specify no backends explicitly.
292.IP "unsigned int ev_embeddable_backends ()" 4 376.IP "unsigned int ev_embeddable_backends ()" 4
293.IX Item "unsigned int ev_embeddable_backends ()" 377.IX Item "unsigned int ev_embeddable_backends ()"
294Returns 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
295is the theoretical, all\-platform, value. To find which backends 379value is platform-specific but can include backends not available on the
296might be supported on the current system, you would need to look at 380current system. To find which embeddable backends might be supported on
297\&\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 ()
298recommended ones. 382& ev_supported_backends ()\*(C'\fR, likewise for recommended ones.
299.Sp 383.Sp
300See 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.
301.IP "ev_set_allocator (void *(*cb)(void *ptr, size_t size))" 4 385.IP "ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())" 4
302.IX Item "ev_set_allocator (void *(*cb)(void *ptr, size_t size))" 386.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())"
303Sets the allocation function to use (the prototype and semantics are 387Sets the allocation function to use (the prototype is similar \- the
304identical to the realloc C function). It is used to allocate and free 388semantics are identical to the \f(CW\*(C`realloc\*(C'\fR C89/SuS/POSIX function). It is
305memory (no surprises here). If it returns zero when memory needs to be 389used to allocate and free memory (no surprises here). If it returns zero
306allocated, the library might abort or take some potentially destructive 390when memory needs to be allocated (\f(CW\*(C`size != 0\*(C'\fR), the library might abort
307action. The default is your system realloc function. 391or take some potentially destructive action.
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.
308.Sp 396.Sp
309You could override this function in high-availability programs to, say, 397You could override this function in high-availability programs to, say,
310free 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,
311or 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.
312.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
313Example: 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
314retries: better than mine). 418retries.
315.Sp 419.Sp
316.Vb 6 420.Vb 8
317\& static void * 421\& static void *
318\& persistent_realloc (void *ptr, size_t size) 422\& persistent_realloc (void *ptr, size_t size)
319\& { 423\& {
424\& if (!size)
425\& {
426\& free (ptr);
427\& return 0;
428\& }
429\&
320\& for (;;) 430\& for (;;)
321\& { 431\& {
322\& void *newptr = realloc (ptr, size); 432\& void *newptr = realloc (ptr, size);
323.Ve 433\&
324.Sp
325.Vb 2
326\& if (newptr) 434\& if (newptr)
327\& return newptr; 435\& return newptr;
328.Ve 436\&
329.Sp
330.Vb 3
331\& sleep (60); 437\& sleep (60);
332\& } 438\& }
333\& } 439\& }
334.Ve 440\&
335.Sp
336.Vb 2
337\& ... 441\& ...
338\& ev_set_allocator (persistent_realloc); 442\& ev_set_allocator (persistent_realloc);
339.Ve 443.Ve
340.IP "ev_set_syserr_cb (void (*cb)(const char *msg));" 4 444.IP "ev_set_syserr_cb (void (*cb)(const char *msg) throw ())" 4
341.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg));" 445.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg) throw ())"
342Set the callback function to call on a retryable syscall error (such 446Set the callback function to call on a retryable system call error (such
343as failed select, poll, epoll_wait). The message is a printable string 447as failed select, poll, epoll_wait). The message is a printable string
344indicating the system call or subsystem causing the problem. If this 448indicating the system call or subsystem causing the problem. If this
345callback 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
346matter what, when it returns. That is, libev will generally retry the 450matter what, when it returns. That is, libev will generally retry the
347requested 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
348(such as abort). 452(such as abort).
349.Sp 453.Sp
350Example: do the same thing as libev does internally: 454Example: This is basically the same thing that libev does internally, too.
351.Sp 455.Sp
352.Vb 6 456.Vb 6
353\& static void 457\& static void
354\& fatal_error (const char *msg) 458\& fatal_error (const char *msg)
355\& { 459\& {
356\& perror (msg); 460\& perror (msg);
357\& abort (); 461\& abort ();
358\& } 462\& }
359.Ve 463\&
360.Sp
361.Vb 2
362\& ... 464\& ...
363\& ev_set_syserr_cb (fatal_error); 465\& ev_set_syserr_cb (fatal_error);
364.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.
365.SH "FUNCTIONS CONTROLLING THE EVENT LOOP" 479.SH "FUNCTIONS CONTROLLING EVENT LOOPS"
366.IX Header "FUNCTIONS CONTROLLING THE EVENT LOOP" 480.IX Header "FUNCTIONS CONTROLLING EVENT LOOPS"
367An 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
368types 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
369events, and dynamically created loops which do not. 483libev 3 had an \f(CW\*(C`ev_loop\*(C'\fR function colliding with the struct name).
370.PP 484.PP
371If 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
372in your main thread (or in a separate thread) and for each thread you 486supports child process events, and dynamically created event loops which
373create, you also create another event loop. Libev itself does no locking 487do not.
374whatsoever, so if you mix calls to the same event loop in different
375threads, make sure you lock (this is usually a bad idea, though, even if
376done correctly, because it's hideous and inefficient).
377.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4 488.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
378.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)" 489.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
379This 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
380yet 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
381false. 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
382flags. 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".
383.Sp 500.Sp
384If 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
385function. 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.
386.Sp 536.Sp
387The flags argument can be used to specify special behaviour or specific 537The flags argument can be used to specify special behaviour or specific
388backends 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).
389.Sp 539.Sp
390The following flags are supported: 540The following flags are supported:
… …
395The 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
396thing, believe me). 546thing, believe me).
397.ie n .IP """EVFLAG_NOENV""" 4 547.ie n .IP """EVFLAG_NOENV""" 4
398.el .IP "\f(CWEVFLAG_NOENV\fR" 4 548.el .IP "\f(CWEVFLAG_NOENV\fR" 4
399.IX Item "EVFLAG_NOENV" 549.IX Item "EVFLAG_NOENV"
400If 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
401or setgid) then libev will \fInot\fR look at the environment variable 551or setgid) then libev will \fInot\fR look at the environment variable
402\&\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
403override 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
404useful to try out specific backends to test their performance, or to work 554useful to try out specific backends to test their performance, to work
405around 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).
558.ie n .IP """EVFLAG_FORKCHECK""" 4
559.el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4
560.IX Item "EVFLAG_FORKCHECK"
561Instead of calling \f(CW\*(C`ev_loop_fork\*(C'\fR manually after a fork, you can also
562make libev check for a fork in each iteration by enabling this flag.
563.Sp
564This works by calling \f(CW\*(C`getpid ()\*(C'\fR on every iteration of the loop,
565and thus this might slow down your event loop if you do a lot of loop
566iterations and little real work, but is usually not noticeable (on my
567GNU/Linux system for example, \f(CW\*(C`getpid\*(C'\fR is actually a simple 5\-insn
568sequence without a system call and thus \fIvery\fR fast, but my GNU/Linux
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).
571.Sp
572The big advantage of this flag is that you can forget about fork (and
573forget about forgetting to tell libev about forking, although you still
574have to ignore \f(CW\*(C`SIGPIPE\*(C'\fR) when you use this flag.
575.Sp
576This flag setting cannot be overridden or specified in the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR
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.
406.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4 622.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4
407.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
408.IX Item "EVBACKEND_SELECT (value 1, portable select backend)" 624.IX Item "EVBACKEND_SELECT (value 1, portable select backend)"
409This 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
410libev 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,
411but 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
412using 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
413the 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).
414.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
415.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
416.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)"
417And 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
418select, but handles sparse fds better and has no artificial limit on the 645than select, but handles sparse fds better and has no artificial
419number 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
420lot 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.
421.ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4 653.ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
422.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4 654.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
423.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
424For 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
425but it scales phenomenally better. While poll and select usually scale like 660it scales phenomenally better. While poll and select usually scale like
426O(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
427either O(1) or O(active_fds). 662fd), epoll scales either O(1) or O(active_fds).
428.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
429While 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
430result in some caching, there is still a syscall per such incident 693will result in some caching, there is still a system call per such
431(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
432best 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
433well if you register events for both fds. 696file descriptors might not work very well if you register events for both
697file descriptors.
434.Sp 698.Sp
435Please note that epoll sometimes generates spurious notifications, so you 699Best performance from this backend is achieved by not unregistering all
436need 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,
437(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.
438.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
439.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
440.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)" 761.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
441Kqueue deserves special mention, as at the time of this writing, it 762Kqueue deserves special mention, as at the time this backend was
442was 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
443anything but sockets and pipes, except on Darwin, where of course its 764work reliably with anything but sockets and pipes, except on Darwin,
444completely useless). For this reason its not being \*(L"autodetected\*(R" 765where of course it's completely useless). Unlike epoll, however, whose
445unless you explicitly specify it explicitly in the flags (i.e. using 766brokenness is by design, these kqueue bugs can be (and mostly have been)
446\&\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.
447.Sp 775.Sp
448It 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
449kernel is more efficient (which says nothing about its actual speed, of 777kernel is more efficient (which says nothing about its actual speed, of
450course). While starting and stopping an I/O watcher does not cause an 778course). While stopping, setting and starting an I/O watcher does never
451extra 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
452incident, 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.
453.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4 796.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
454.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4 797.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
455.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)" 798.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
456This 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.
457.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4 803.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
458.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4 804.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
459.IX Item "EVBACKEND_PORT (value 32, Solaris 10)" 805.IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
460This uses the Solaris 10 port mechanism. As with everything on Solaris, 806This uses the Solaris 10 event port mechanism. As with everything on Solaris,
461it'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)).
462.Sp 808.Sp
463Please note that solaris ports can result in a lot of spurious 809While this backend scales well, it requires one system call per active
464notifications, 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
465blocking 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.
466.ie n .IP """EVBACKEND_ALL""" 4 831.ie n .IP """EVBACKEND_ALL""" 4
467.el .IP "\f(CWEVBACKEND_ALL\fR" 4 832.el .IP "\f(CWEVBACKEND_ALL\fR" 4
468.IX Item "EVBACKEND_ALL" 833.IX Item "EVBACKEND_ALL"
469Try all backends (even potentially broken ones that wouldn't be tried 834Try all backends (even potentially broken ones that wouldn't be tried
470with \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
471\&\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).
472.RE 847.RE
473.RS 4 848.RS 4
474.Sp 849.Sp
475If 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,
476backends 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
477specified, most compiled-in backend will be tried, usually in reverse 852here). If none are specified, all backends in \f(CW\*(C`ev_recommended_backends
478order of their flag values :) 853()\*(C'\fR will be tried.
479.Sp 854.Sp
480The most typical usage is like this: 855Example: Try to create a event loop that uses epoll and nothing else.
481.Sp 856.Sp
482.Vb 2 857.Vb 3
483\& if (!ev_default_loop (0)) 858\& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
484\& 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");
485.Ve 861.Ve
486.Sp 862.Sp
487Restrict libev to the select and poll backends, and do not allow 863Example: Use whatever libev has to offer, but make sure that kqueue is
488environment settings to be taken into account: 864used if available.
489.Sp 865.Sp
490.Vb 1 866.Vb 1
491\& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV); 867\& struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
492.Ve 868.Ve
493.Sp 869.Sp
494Use 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
495available (warning, breaks stuff, best use only with your own private 871linux aio backend if possible, but fall back to something else if that
496event loop and only if you know the \s-1OS\s0 supports your types of fds): 872isn't available.
497.Sp 873.Sp
498.Vb 1 874.Vb 1
499\& ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE); 875\& struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_LINUXAIO);
500.Ve 876.Ve
501.RE 877.RE
502.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
503.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
504Similar to \f(CW\*(C`ev_default_loop\*(C'\fR, but always creates a new event loop that is
505always distinct from the default loop. Unlike the default loop, it cannot
506handle signal and child watchers, and attempts to do so will be greeted by
507undefined behaviour (or a failed assertion if assertions are enabled).
508.Sp
509Example: try to create a event loop that uses epoll and nothing else.
510.Sp
511.Vb 3
512\& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
513\& if (!epoller)
514\& fatal ("no epoll found here, maybe it hides under your chair");
515.Ve
516.IP "ev_default_destroy ()" 4 878.IP "ev_loop_destroy (loop)" 4
517.IX Item "ev_default_destroy ()" 879.IX Item "ev_loop_destroy (loop)"
518Destroys the default loop again (frees all memory and kernel state 880Destroys an event loop object (frees all memory and kernel state
519etc.). 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
520sense, 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
521responsibility to either stop all watchers cleanly yoursef \fIbefore\fR 883responsibility to either stop all watchers cleanly yourself \fIbefore\fR
522calling this function, or cope with the fact afterwards (which is usually 884calling this function, or cope with the fact afterwards (which is usually
523the 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
524for example). 886for example).
525.IP "ev_loop_destroy (loop)" 4
526.IX Item "ev_loop_destroy (loop)"
527Like \f(CW\*(C`ev_default_destroy\*(C'\fR, but destroys an event loop created by an
528earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR.
529.IP "ev_default_fork ()" 4
530.IX Item "ev_default_fork ()"
531This function reinitialises the kernel state for backends that have
532one. Despite the name, you can call it anytime, but it makes most sense
533after forking, in either the parent or child process (or both, but that
534again makes little sense).
535.Sp 887.Sp
536You \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
537only 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
538fork+exec, you don't have to call it. 890as signal and child watchers) would need to be stopped manually.
539.Sp 891.Sp
540The function itself is quite fast and it's usually not a problem to call 892This function is normally used on loop objects allocated by
541it 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
542quite 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.
543.Sp 895.Sp
544.Vb 1 896Note that it is not advisable to call this function on the default loop
545\& pthread_atfork (0, 0, ev_default_fork); 897except in the rare occasion where you really need to free its resources.
546.Ve 898If you need dynamically allocated loops it is better to use \f(CW\*(C`ev_loop_new\*(C'\fR
547.Sp 899and \f(CW\*(C`ev_loop_destroy\*(C'\fR.
548At the moment, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and \f(CW\*(C`EVBACKEND_POLL\*(C'\fR are safe to use
549without calling this function, so if you force one of those backends you
550do not need to care.
551.IP "ev_loop_fork (loop)" 4 900.IP "ev_loop_fork (loop)" 4
552.IX Item "ev_loop_fork (loop)" 901.IX Item "ev_loop_fork (loop)"
553Like \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
554\&\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
555after 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.
944.IP "unsigned int ev_iteration (loop)" 4
945.IX Item "unsigned int ev_iteration (loop)"
946Returns the current iteration count for the event loop, which is identical
947to the number of times libev did poll for new events. It starts at \f(CW0\fR
948and happily wraps around with enough iterations.
949.Sp
950This value can sometimes be useful as a generation counter of sorts (it
951\&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with
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.
556.IP "unsigned int ev_backend (loop)" 4 967.IP "unsigned int ev_backend (loop)" 4
557.IX Item "unsigned int ev_backend (loop)" 968.IX Item "unsigned int ev_backend (loop)"
558Returns 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
559use. 970use.
560.IP "ev_tstamp ev_now (loop)" 4 971.IP "ev_tstamp ev_now (loop)" 4
561.IX Item "ev_tstamp ev_now (loop)" 972.IX Item "ev_tstamp ev_now (loop)"
562Returns 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
563received events and started processing them. This timestamp does not 974received events and started processing them. This timestamp does not
564change 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
565time 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
566event 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).
567.IP "ev_loop (loop, int flags)" 4 1016.IP "bool ev_run (loop, int flags)" 4
568.IX Item "ev_loop (loop, int flags)" 1017.IX Item "bool ev_run (loop, int flags)"
569Finally, this is it, the event handler. This function usually is called 1018Finally, this is it, the event handler. This function usually is called
570after you initialised all your watchers and you want to start handling 1019after you have initialised all your watchers and you want to start
571events. 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.
572.Sp 1023.Sp
573If 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
574either 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.
575.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
576Please 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
577relying 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
578finished (especially in interactive programs), but having a program that 1034finished (especially in interactive programs), but having a program
579automatically 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
580relying on its watchers stopping correctly is a thing of beauty. 1036of relying on its watchers stopping correctly, that is truly a thing of
1037beauty.
581.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
582A 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
583those events and any outstanding ones, but will not block your process in 1045those events and any already outstanding ones, but will not wait and
584case 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.
585.Sp 1049.Sp
586A 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
587neccessary) and will handle those and any outstanding ones. It will block 1051necessary) and will handle those and any already outstanding ones. It
588your 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
589one 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
590external 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
591libev 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
592usually a better approach for this kind of thing. 1060usually a better approach for this kind of thing.
593.Sp 1061.Sp
594Here 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):
595.Sp 1065.Sp
596.Vb 18 1066.Vb 10
597\& * If there are no active watchers (reference count is zero), return. 1067\& \- Increment loop depth.
598\& - Queue prepare watchers and then call all outstanding watchers. 1068\& \- Reset the ev_break status.
1069\& \- Before the first iteration, call any pending watchers.
1070\& LOOP:
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.
599\& - 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.
600\& - Update the kernel state with all outstanding changes. 1077\& \- Update the kernel state with all outstanding changes.
601\& - Update the "event loop time". 1078\& \- Update the "event loop time" (ev_now ()).
602\& - 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.
603\& - Block the process, waiting for any events. 1084\& \- Block the process, waiting for any events.
604\& - Queue all outstanding I/O (fd) events. 1085\& \- Queue all outstanding I/O (fd) events.
605\& - Update the "event loop time" and do time jump handling. 1086\& \- Update the "event loop time" (ev_now ()), and do time jump adjustments.
606\& - Queue all outstanding timers. 1087\& \- Queue all expired timers.
607\& - Queue all outstanding periodics. 1088\& \- Queue all expired periodics.
608\& - If no events are pending now, queue all idle watchers. 1089\& \- Queue all idle watchers with priority higher than that of pending events.
609\& - Queue all check watchers. 1090\& \- Queue all check watchers.
610\& - 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).
611\& 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
612\& be handled here by queueing them when their watcher gets executed. 1093\& be handled here by queueing them when their watcher gets executed.
613\& - 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
614\& 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.
615.Ve 1101.Ve
616.Sp 1102.Sp
617Example: queue some jobs and then loop until no events are outsanding 1103Example: Queue some jobs and then loop until no events are outstanding
618anymore. 1104anymore.
619.Sp 1105.Sp
620.Vb 4 1106.Vb 4
621\& ... queue jobs here, make sure they register event watchers as long 1107\& ... queue jobs here, make sure they register event watchers as long
622\& ... 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..)
623\& ev_loop (my_loop, 0); 1109\& ev_run (my_loop, 0);
624\& ... jobs done. yeah! 1110\& ... jobs done or somebody called break. yeah!
625.Ve 1111.Ve
626.IP "ev_unloop (loop, how)" 4 1112.IP "ev_break (loop, how)" 4
627.IX Item "ev_unloop (loop, how)" 1113.IX Item "ev_break (loop, how)"
628Can 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
629has 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
630\&\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
631\&\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.
632.IP "ev_ref (loop)" 4 1123.IP "ev_ref (loop)" 4
633.IX Item "ev_ref (loop)" 1124.IX Item "ev_ref (loop)"
634.PD 0 1125.PD 0
635.IP "ev_unref (loop)" 4 1126.IP "ev_unref (loop)" 4
636.IX Item "ev_unref (loop)" 1127.IX Item "ev_unref (loop)"
637.PD 1128.PD
638Ref/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
639loop: Every watcher keeps one reference, and as long as the reference 1130loop: Every watcher keeps one reference, and as long as the reference
640count 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.
641a watcher you never unregister that should not keep \f(CW\*(C`ev_loop\*(C'\fR from 1132.Sp
642returning, \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
643example, 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
644visible 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
645no 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
646way to do this for generic recurring timers or from within third-party 1141excellent way to do this for generic recurring timers or from within
647libraries. 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).
648.Sp 1147.Sp
649Example: 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
650running when nothing else is active. 1149running when nothing else is active.
651.Sp 1150.Sp
652.Vb 4 1151.Vb 4
653\& struct dv_signal exitsig; 1152\& ev_signal exitsig;
654\& ev_signal_init (&exitsig, sig_cb, SIGINT); 1153\& ev_signal_init (&exitsig, sig_cb, SIGINT);
655\& ev_signal_start (myloop, &exitsig); 1154\& ev_signal_start (loop, &exitsig);
656\& evf_unref (myloop); 1155\& ev_unref (loop);
657.Ve 1156.Ve
658.Sp 1157.Sp
659Example: for some weird reason, unregister the above signal handler again. 1158Example: For some weird reason, unregister the above signal handler again.
660.Sp 1159.Sp
661.Vb 2 1160.Vb 2
662\& ev_ref (myloop); 1161\& ev_ref (loop);
663\& ev_signal_stop (myloop, &exitsig); 1162\& ev_signal_stop (loop, &exitsig);
664.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.
665.SH "ANATOMY OF A WATCHER" 1302.SH "ANATOMY OF A WATCHER"
666.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
667A 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
668interest 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
669become 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:
670.PP 1312.PP
671.Vb 5 1313.Vb 5
672\& 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)
673\& { 1315\& {
674\& ev_io_stop (w); 1316\& ev_io_stop (w);
675\& ev_unloop (loop, EVUNLOOP_ALL); 1317\& ev_break (loop, EVBREAK_ALL);
676\& } 1318\& }
677.Ve 1319\&
678.PP
679.Vb 6
680\& struct ev_loop *loop = ev_default_loop (0); 1320\& struct ev_loop *loop = ev_default_loop (0);
1321\&
681\& struct ev_io stdin_watcher; 1322\& ev_io stdin_watcher;
1323\&
682\& ev_init (&stdin_watcher, my_cb); 1324\& ev_init (&stdin_watcher, my_cb);
683\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ); 1325\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
684\& ev_io_start (loop, &stdin_watcher); 1326\& ev_io_start (loop, &stdin_watcher);
1327\&
685\& ev_loop (loop, 0); 1328\& ev_run (loop, 0);
686.Ve 1329.Ve
687.PP 1330.PP
688As 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
689watcher 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
690although this can sometimes be quite valid). 1333stack).
691.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
692Each 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
693(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
694callback 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
695watchers, each time the event loop detects that the file descriptor given 1341time the event loop detects that the file descriptor given is readable
696is readable and/or writable). 1342and/or writable).
697.PP 1343.PP
698Each 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
699with arguments specific to this watcher type. There is also a macro 1345macro to configure it, with arguments specific to the watcher type. There
700to 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.
701(watcher *, callback, ...)\*(C'\fR.
702.PP 1347.PP
703To 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
704with 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
705*)\*(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
706corresponding 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.
707.PP 1352.PP
708As 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
709must not touch the values stored in it. Most specifically you must never 1354must not touch the values stored in it. Most specifically you must never
710reinitialise it or call its \f(CW\*(C`set\*(C'\fR macro. 1355reinitialise it or call its \f(CW\*(C`ev_TYPE_set\*(C'\fR macro.
711.PP 1356.PP
712Each and every callback receives the event loop pointer as first, the 1357Each and every callback receives the event loop pointer as first, the
713registered watcher structure as second, and a bitset of received events as 1358registered watcher structure as second, and a bitset of received events as
714third argument. 1359third argument.
715.PP 1360.PP
… …
724.el .IP "\f(CWEV_WRITE\fR" 4 1369.el .IP "\f(CWEV_WRITE\fR" 4
725.IX Item "EV_WRITE" 1370.IX Item "EV_WRITE"
726.PD 1371.PD
727The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or 1372The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or
728writable. 1373writable.
729.ie n .IP """EV_TIMEOUT""" 4 1374.ie n .IP """EV_TIMER""" 4
730.el .IP "\f(CWEV_TIMEOUT\fR" 4 1375.el .IP "\f(CWEV_TIMER\fR" 4
731.IX Item "EV_TIMEOUT" 1376.IX Item "EV_TIMER"
732The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out. 1377The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out.
733.ie n .IP """EV_PERIODIC""" 4 1378.ie n .IP """EV_PERIODIC""" 4
734.el .IP "\f(CWEV_PERIODIC\fR" 4 1379.el .IP "\f(CWEV_PERIODIC\fR" 4
735.IX Item "EV_PERIODIC" 1380.IX Item "EV_PERIODIC"
736The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out. 1381The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out.
… …
756.PD 0 1401.PD 0
757.ie n .IP """EV_CHECK""" 4 1402.ie n .IP """EV_CHECK""" 4
758.el .IP "\f(CWEV_CHECK\fR" 4 1403.el .IP "\f(CWEV_CHECK\fR" 4
759.IX Item "EV_CHECK" 1404.IX Item "EV_CHECK"
760.PD 1405.PD
761All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_loop\*(C'\fR starts 1406All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_run\*(C'\fR starts to
762to gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are invoked just after 1407gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are queued (not invoked)
763\&\f(CW\*(C`ev_loop\*(C'\fR has gathered them, but before it invokes any callbacks for any 1408just after \f(CW\*(C`ev_run\*(C'\fR has gathered them, but before it queues any callbacks
1409for any received events. That means \f(CW\*(C`ev_prepare\*(C'\fR watchers are the last
1410watchers invoked before the event loop sleeps or polls for new events, and
1411\&\f(CW\*(C`ev_check\*(C'\fR watchers will be invoked before any other watchers of the same
1412or lower priority within an event loop iteration.
1413.Sp
764received events. Callbacks of both watcher types can start and stop as 1414Callbacks of both watcher types can start and stop as many watchers as
765many watchers as they want, and all of them will be taken into account 1415they want, and all of them will be taken into account (for example, a
766(for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep 1416\&\f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep \f(CW\*(C`ev_run\*(C'\fR from
767\&\f(CW\*(C`ev_loop\*(C'\fR from blocking). 1417blocking).
768.ie n .IP """EV_EMBED""" 4 1418.ie n .IP """EV_EMBED""" 4
769.el .IP "\f(CWEV_EMBED\fR" 4 1419.el .IP "\f(CWEV_EMBED\fR" 4
770.IX Item "EV_EMBED" 1420.IX Item "EV_EMBED"
771The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention. 1421The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention.
772.ie n .IP """EV_FORK""" 4 1422.ie n .IP """EV_FORK""" 4
773.el .IP "\f(CWEV_FORK\fR" 4 1423.el .IP "\f(CWEV_FORK\fR" 4
774.IX Item "EV_FORK" 1424.IX Item "EV_FORK"
775The event loop has been resumed in the child process after fork (see 1425The event loop has been resumed in the child process after fork (see
776\&\f(CW\*(C`ev_fork\*(C'\fR). 1426\&\f(CW\*(C`ev_fork\*(C'\fR).
1427.ie n .IP """EV_CLEANUP""" 4
1428.el .IP "\f(CWEV_CLEANUP\fR" 4
1429.IX Item "EV_CLEANUP"
1430The event loop is about to be destroyed (see \f(CW\*(C`ev_cleanup\*(C'\fR).
1431.ie n .IP """EV_ASYNC""" 4
1432.el .IP "\f(CWEV_ASYNC\fR" 4
1433.IX Item "EV_ASYNC"
1434The given async watcher has been asynchronously notified (see \f(CW\*(C`ev_async\*(C'\fR).
1435.ie n .IP """EV_CUSTOM""" 4
1436.el .IP "\f(CWEV_CUSTOM\fR" 4
1437.IX Item "EV_CUSTOM"
1438Not ever sent (or otherwise used) by libev itself, but can be freely used
1439by libev users to signal watchers (e.g. via \f(CW\*(C`ev_feed_event\*(C'\fR).
777.ie n .IP """EV_ERROR""" 4 1440.ie n .IP """EV_ERROR""" 4
778.el .IP "\f(CWEV_ERROR\fR" 4 1441.el .IP "\f(CWEV_ERROR\fR" 4
779.IX Item "EV_ERROR" 1442.IX Item "EV_ERROR"
780An unspecified error has occured, the watcher has been stopped. This might 1443An unspecified error has occurred, the watcher has been stopped. This might
781happen because the watcher could not be properly started because libev 1444happen because the watcher could not be properly started because libev
782ran out of memory, a file descriptor was found to be closed or any other 1445ran out of memory, a file descriptor was found to be closed or any other
1446problem. Libev considers these application bugs.
1447.Sp
783problem. You best act on it by reporting the problem and somehow coping 1448You best act on it by reporting the problem and somehow coping with the
784with the watcher being stopped. 1449watcher being stopped. Note that well-written programs should not receive
1450an error ever, so when your watcher receives it, this usually indicates a
1451bug in your program.
785.Sp 1452.Sp
786Libev will usually signal a few \*(L"dummy\*(R" events together with an error, 1453Libev will usually signal a few \*(L"dummy\*(R" events together with an error, for
787for example it might indicate that a fd is readable or writable, and if 1454example it might indicate that a fd is readable or writable, and if your
788your callbacks is well-written it can just attempt the operation and cope 1455callbacks is well-written it can just attempt the operation and cope with
789with the error from \fIread()\fR or \fIwrite()\fR. This will not work in multithreaded 1456the error from \fBread()\fR or \fBwrite()\fR. This will not work in multi-threaded
790programs, though, so beware. 1457programs, though, as the fd could already be closed and reused for another
1458thing, so beware.
791.Sh "\s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0" 1459.SS "\s-1GENERIC WATCHER FUNCTIONS\s0"
792.IX Subsection "GENERIC WATCHER FUNCTIONS" 1460.IX Subsection "GENERIC WATCHER FUNCTIONS"
793In the following description, \f(CW\*(C`TYPE\*(C'\fR stands for the watcher type,
794e.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.
795.ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4 1461.ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4
796.el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4 1462.el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4
797.IX Item "ev_init (ev_TYPE *watcher, callback)" 1463.IX Item "ev_init (ev_TYPE *watcher, callback)"
798This macro initialises the generic portion of a watcher. The contents 1464This macro initialises the generic portion of a watcher. The contents
799of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only 1465of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only
… …
803which rolls both calls into one. 1469which rolls both calls into one.
804.Sp 1470.Sp
805You can reinitialise a watcher at any time as long as it has been stopped 1471You can reinitialise a watcher at any time as long as it has been stopped
806(or never started) and there are no pending events outstanding. 1472(or never started) and there are no pending events outstanding.
807.Sp 1473.Sp
808The callback is always of type \f(CW\*(C`void (*)(ev_loop *loop, ev_TYPE *watcher, 1474The callback is always of type \f(CW\*(C`void (*)(struct ev_loop *loop, ev_TYPE *watcher,
809int revents)\*(C'\fR. 1475int revents)\*(C'\fR.
1476.Sp
1477Example: Initialise an \f(CW\*(C`ev_io\*(C'\fR watcher in two steps.
1478.Sp
1479.Vb 3
1480\& ev_io w;
1481\& ev_init (&w, my_cb);
1482\& ev_io_set (&w, STDIN_FILENO, EV_READ);
1483.Ve
810.ie n .IP """ev_TYPE_set"" (ev_TYPE *, [args])" 4 1484.ie n .IP """ev_TYPE_set"" (ev_TYPE *watcher, [args])" 4
811.el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *, [args])" 4 1485.el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *watcher, [args])" 4
812.IX Item "ev_TYPE_set (ev_TYPE *, [args])" 1486.IX Item "ev_TYPE_set (ev_TYPE *watcher, [args])"
813This macro initialises the type-specific parts of a watcher. You need to 1487This macro initialises the type-specific parts of a watcher. You need to
814call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can 1488call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can
815call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this 1489call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this
816macro on a watcher that is active (it can be pending, however, which is a 1490macro on a watcher that is active (it can be pending, however, which is a
817difference to the \f(CW\*(C`ev_init\*(C'\fR macro). 1491difference to the \f(CW\*(C`ev_init\*(C'\fR macro).
818.Sp 1492.Sp
819Although some watcher types do not have type-specific arguments 1493Although some watcher types do not have type-specific arguments
820(e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro. 1494(e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro.
1495.Sp
1496See \f(CW\*(C`ev_init\*(C'\fR, above, for an example.
821.ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4 1497.ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4
822.el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4 1498.el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4
823.IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])" 1499.IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])"
824This convinience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro 1500This convenience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro
825calls into a single call. This is the most convinient method to initialise 1501calls into a single call. This is the most convenient method to initialise
826a watcher. The same limitations apply, of course. 1502a watcher. The same limitations apply, of course.
1503.Sp
1504Example: Initialise and set an \f(CW\*(C`ev_io\*(C'\fR watcher in one step.
1505.Sp
1506.Vb 1
1507\& ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1508.Ve
827.ie n .IP """ev_TYPE_start"" (loop *, ev_TYPE *watcher)" 4 1509.ie n .IP """ev_TYPE_start"" (loop, ev_TYPE *watcher)" 4
828.el .IP "\f(CWev_TYPE_start\fR (loop *, ev_TYPE *watcher)" 4 1510.el .IP "\f(CWev_TYPE_start\fR (loop, ev_TYPE *watcher)" 4
829.IX Item "ev_TYPE_start (loop *, ev_TYPE *watcher)" 1511.IX Item "ev_TYPE_start (loop, ev_TYPE *watcher)"
830Starts (activates) the given watcher. Only active watchers will receive 1512Starts (activates) the given watcher. Only active watchers will receive
831events. If the watcher is already active nothing will happen. 1513events. If the watcher is already active nothing will happen.
1514.Sp
1515Example: Start the \f(CW\*(C`ev_io\*(C'\fR watcher that is being abused as example in this
1516whole section.
1517.Sp
1518.Vb 1
1519\& ev_io_start (EV_DEFAULT_UC, &w);
1520.Ve
832.ie n .IP """ev_TYPE_stop"" (loop *, ev_TYPE *watcher)" 4 1521.ie n .IP """ev_TYPE_stop"" (loop, ev_TYPE *watcher)" 4
833.el .IP "\f(CWev_TYPE_stop\fR (loop *, ev_TYPE *watcher)" 4 1522.el .IP "\f(CWev_TYPE_stop\fR (loop, ev_TYPE *watcher)" 4
834.IX Item "ev_TYPE_stop (loop *, ev_TYPE *watcher)" 1523.IX Item "ev_TYPE_stop (loop, ev_TYPE *watcher)"
835Stops the given watcher again (if active) and clears the pending 1524Stops the given watcher if active, and clears the pending status (whether
1525the watcher was active or not).
1526.Sp
836status. It is possible that stopped watchers are pending (for example, 1527It is possible that stopped watchers are pending \- for example,
837non-repeating timers are being stopped when they become pending), but 1528non-repeating timers are being stopped when they become pending \- but
838\&\f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor pending. If 1529calling \f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor
839you want to free or reuse the memory used by the watcher it is therefore a 1530pending. If you want to free or reuse the memory used by the watcher it is
840good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function. 1531therefore a good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function.
841.IP "bool ev_is_active (ev_TYPE *watcher)" 4 1532.IP "bool ev_is_active (ev_TYPE *watcher)" 4
842.IX Item "bool ev_is_active (ev_TYPE *watcher)" 1533.IX Item "bool ev_is_active (ev_TYPE *watcher)"
843Returns a true value iff the watcher is active (i.e. it has been started 1534Returns a true value iff the watcher is active (i.e. it has been started
844and not yet been stopped). As long as a watcher is active you must not modify 1535and not yet been stopped). As long as a watcher is active you must not modify
845it. 1536it.
846.IP "bool ev_is_pending (ev_TYPE *watcher)" 4 1537.IP "bool ev_is_pending (ev_TYPE *watcher)" 4
847.IX Item "bool ev_is_pending (ev_TYPE *watcher)" 1538.IX Item "bool ev_is_pending (ev_TYPE *watcher)"
848Returns a true value iff the watcher is pending, (i.e. it has outstanding 1539Returns a true value iff the watcher is pending, (i.e. it has outstanding
849events but its callback has not yet been invoked). As long as a watcher 1540events but its callback has not yet been invoked). As long as a watcher
850is pending (but not active) you must not call an init function on it (but 1541is pending (but not active) you must not call an init function on it (but
851\&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe) and you must make sure the watcher is available to 1542\&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe), you must not change its priority, and you must
852libev (e.g. you cnanot \f(CW\*(C`free ()\*(C'\fR it). 1543make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR
1544it).
853.IP "callback = ev_cb (ev_TYPE *watcher)" 4 1545.IP "callback ev_cb (ev_TYPE *watcher)" 4
854.IX Item "callback = ev_cb (ev_TYPE *watcher)" 1546.IX Item "callback ev_cb (ev_TYPE *watcher)"
855Returns the callback currently set on the watcher. 1547Returns the callback currently set on the watcher.
856.IP "ev_cb_set (ev_TYPE *watcher, callback)" 4 1548.IP "ev_set_cb (ev_TYPE *watcher, callback)" 4
857.IX Item "ev_cb_set (ev_TYPE *watcher, callback)" 1549.IX Item "ev_set_cb (ev_TYPE *watcher, callback)"
858Change the callback. You can change the callback at virtually any time 1550Change the callback. You can change the callback at virtually any time
859(modulo threads). 1551(modulo threads).
860.Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0" 1552.IP "ev_set_priority (ev_TYPE *watcher, int priority)" 4
861.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER" 1553.IX Item "ev_set_priority (ev_TYPE *watcher, int priority)"
862Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change 1554.PD 0
863and read at any time, libev will completely ignore it. This can be used 1555.IP "int ev_priority (ev_TYPE *watcher)" 4
864to associate arbitrary data with your watcher. If you need more data and 1556.IX Item "int ev_priority (ev_TYPE *watcher)"
865don't want to allocate memory and store a pointer to it in that data 1557.PD
866member, you can also \*(L"subclass\*(R" the watcher type and provide your own 1558Set and query the priority of the watcher. The priority is a small
867data: 1559integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR
1560(default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked
1561before watchers with lower priority, but priority will not keep watchers
1562from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers).
1563.Sp
1564If you need to suppress invocation when higher priority events are pending
1565you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality.
1566.Sp
1567You \fImust not\fR change the priority of a watcher as long as it is active or
1568pending.
1569.Sp
1570Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is
1571fine, as long as you do not mind that the priority value you query might
1572or might not have been clamped to the valid range.
1573.Sp
1574The default priority used by watchers when no priority has been set is
1575always \f(CW0\fR, which is supposed to not be too high and not be too low :).
1576.Sp
1577See \*(L"\s-1WATCHER PRIORITY MODELS\*(R"\s0, below, for a more thorough treatment of
1578priorities.
1579.IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4
1580.IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)"
1581Invoke the \f(CW\*(C`watcher\*(C'\fR with the given \f(CW\*(C`loop\*(C'\fR and \f(CW\*(C`revents\*(C'\fR. Neither
1582\&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback
1583can deal with that fact, as both are simply passed through to the
1584callback.
1585.IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4
1586.IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)"
1587If the watcher is pending, this function clears its pending status and
1588returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the
1589watcher isn't pending it does nothing and returns \f(CW0\fR.
1590.Sp
1591Sometimes it can be useful to \*(L"poll\*(R" a watcher instead of waiting for its
1592callback to be invoked, which can be accomplished with this function.
1593.IP "ev_feed_event (loop, ev_TYPE *watcher, int revents)" 4
1594.IX Item "ev_feed_event (loop, ev_TYPE *watcher, int revents)"
1595Feeds the given event set into the event loop, as if the specified event
1596had happened for the specified watcher (which must be a pointer to an
1597initialised but not necessarily started event watcher). Obviously you must
1598not free the watcher as long as it has pending events.
1599.Sp
1600Stopping the watcher, letting libev invoke it, or calling
1601\&\f(CW\*(C`ev_clear_pending\*(C'\fR will clear the pending event, even if the watcher was
1602not started in the first place.
1603.Sp
1604See also \f(CW\*(C`ev_feed_fd_event\*(C'\fR and \f(CW\*(C`ev_feed_signal_event\*(C'\fR for related
1605functions that do not need a watcher.
868.PP 1606.PP
1607See also the \*(L"\s-1ASSOCIATING CUSTOM DATA WITH A WATCHER\*(R"\s0 and \*(L"\s-1BUILDING YOUR
1608OWN COMPOSITE WATCHERS\*(R"\s0 idioms.
1609.SS "\s-1WATCHER STATES\s0"
1610.IX Subsection "WATCHER STATES"
1611There are various watcher states mentioned throughout this manual \-
1612active, pending and so on. In this section these states and the rules to
1613transition between them will be described in more detail \- and while these
1614rules might look complicated, they usually do \*(L"the right thing\*(R".
1615.IP "initialised" 4
1616.IX Item "initialised"
1617Before a watcher can be registered with the event loop it has to be
1618initialised. This can be done with a call to \f(CW\*(C`ev_TYPE_init\*(C'\fR, or calls to
1619\&\f(CW\*(C`ev_init\*(C'\fR followed by the watcher-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR function.
1620.Sp
1621In this state it is simply some block of memory that is suitable for
1622use in an event loop. It can be moved around, freed, reused etc. at
1623will \- as long as you either keep the memory contents intact, or call
1624\&\f(CW\*(C`ev_TYPE_init\*(C'\fR again.
1625.IP "started/running/active" 4
1626.IX Item "started/running/active"
1627Once a watcher has been started with a call to \f(CW\*(C`ev_TYPE_start\*(C'\fR it becomes
1628property of the event loop, and is actively waiting for events. While in
1629this state it cannot be accessed (except in a few documented ways), moved,
1630freed or anything else \- the only legal thing is to keep a pointer to it,
1631and call libev functions on it that are documented to work on active watchers.
1632.IP "pending" 4
1633.IX Item "pending"
1634If a watcher is active and libev determines that an event it is interested
1635in has occurred (such as a timer expiring), it will become pending. It will
1636stay in this pending state until either it is stopped or its callback is
1637about to be invoked, so it is not normally pending inside the watcher
1638callback.
1639.Sp
1640The watcher might or might not be active while it is pending (for example,
1641an expired non-repeating timer can be pending but no longer active). If it
1642is stopped, it can be freely accessed (e.g. by calling \f(CW\*(C`ev_TYPE_set\*(C'\fR),
1643but it is still property of the event loop at this time, so cannot be
1644moved, freed or reused. And if it is active the rules described in the
1645previous item still apply.
1646.Sp
1647It is also possible to feed an event on a watcher that is not active (e.g.
1648via \f(CW\*(C`ev_feed_event\*(C'\fR), in which case it becomes pending without being
1649active.
1650.IP "stopped" 4
1651.IX Item "stopped"
1652A watcher can be stopped implicitly by libev (in which case it might still
1653be pending), or explicitly by calling its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function. The
1654latter will clear any pending state the watcher might be in, regardless
1655of whether it was active or not, so stopping a watcher explicitly before
1656freeing it is often a good idea.
1657.Sp
1658While stopped (and not pending) the watcher is essentially in the
1659initialised state, that is, it can be reused, moved, modified in any way
1660you wish (but when you trash the memory block, you need to \f(CW\*(C`ev_TYPE_init\*(C'\fR
1661it again).
1662.SS "\s-1WATCHER PRIORITY MODELS\s0"
1663.IX Subsection "WATCHER PRIORITY MODELS"
1664Many event loops support \fIwatcher priorities\fR, which are usually small
1665integers that influence the ordering of event callback invocation
1666between watchers in some way, all else being equal.
1667.PP
1668In libev, watcher priorities can be set using \f(CW\*(C`ev_set_priority\*(C'\fR. See its
1669description for the more technical details such as the actual priority
1670range.
1671.PP
1672There are two common ways how these these priorities are being interpreted
1673by event loops:
1674.PP
1675In the more common lock-out model, higher priorities \*(L"lock out\*(R" invocation
1676of lower priority watchers, which means as long as higher priority
1677watchers receive events, lower priority watchers are not being invoked.
1678.PP
1679The less common only-for-ordering model uses priorities solely to order
1680callback invocation within a single event loop iteration: Higher priority
1681watchers are invoked before lower priority ones, but they all get invoked
1682before polling for new events.
1683.PP
1684Libev uses the second (only-for-ordering) model for all its watchers
1685except for idle watchers (which use the lock-out model).
1686.PP
1687The rationale behind this is that implementing the lock-out model for
1688watchers is not well supported by most kernel interfaces, and most event
1689libraries will just poll for the same events again and again as long as
1690their callbacks have not been executed, which is very inefficient in the
1691common case of one high-priority watcher locking out a mass of lower
1692priority ones.
1693.PP
1694Static (ordering) priorities are most useful when you have two or more
1695watchers handling the same resource: a typical usage example is having an
1696\&\f(CW\*(C`ev_io\*(C'\fR watcher to receive data, and an associated \f(CW\*(C`ev_timer\*(C'\fR to handle
1697timeouts. Under load, data might be received while the program handles
1698other jobs, but since timers normally get invoked first, the timeout
1699handler will be executed before checking for data. In that case, giving
1700the timer a lower priority than the I/O watcher ensures that I/O will be
1701handled first even under adverse conditions (which is usually, but not
1702always, what you want).
1703.PP
1704Since idle watchers use the \*(L"lock-out\*(R" model, meaning that idle watchers
1705will only be executed when no same or higher priority watchers have
1706received events, they can be used to implement the \*(L"lock-out\*(R" model when
1707required.
1708.PP
1709For example, to emulate how many other event libraries handle priorities,
1710you can associate an \f(CW\*(C`ev_idle\*(C'\fR watcher to each such watcher, and in
1711the normal watcher callback, you just start the idle watcher. The real
1712processing is done in the idle watcher callback. This causes libev to
1713continuously poll and process kernel event data for the watcher, but when
1714the lock-out case is known to be rare (which in turn is rare :), this is
1715workable.
1716.PP
1717Usually, however, the lock-out model implemented that way will perform
1718miserably under the type of load it was designed to handle. In that case,
1719it might be preferable to stop the real watcher before starting the
1720idle watcher, so the kernel will not have to process the event in case
1721the actual processing will be delayed for considerable time.
1722.PP
1723Here is an example of an I/O watcher that should run at a strictly lower
1724priority than the default, and which should only process data when no
1725other events are pending:
1726.PP
869.Vb 7 1727.Vb 2
870\& struct my_io 1728\& ev_idle idle; // actual processing watcher
1729\& ev_io io; // actual event watcher
1730\&
1731\& static void
1732\& io_cb (EV_P_ ev_io *w, int revents)
871\& { 1733\& {
872\& struct ev_io io; 1734\& // stop the I/O watcher, we received the event, but
873\& int otherfd; 1735\& // are not yet ready to handle it.
874\& void *somedata; 1736\& ev_io_stop (EV_A_ w);
875\& struct whatever *mostinteresting; 1737\&
1738\& // start the idle watcher to handle the actual event.
1739\& // it will not be executed as long as other watchers
1740\& // with the default priority are receiving events.
1741\& ev_idle_start (EV_A_ &idle);
876\& } 1742\& }
877.Ve 1743\&
878.PP 1744\& static void
879And since your callback will be called with a pointer to the watcher, you 1745\& idle_cb (EV_P_ ev_idle *w, int revents)
880can cast it back to your own type:
881.PP
882.Vb 5
883\& static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
884\& { 1746\& {
885\& struct my_io *w = (struct my_io *)w_; 1747\& // actual processing
886\& ... 1748\& read (STDIN_FILENO, ...);
1749\&
1750\& // have to start the I/O watcher again, as
1751\& // we have handled the event
1752\& ev_io_start (EV_P_ &io);
887\& } 1753\& }
1754\&
1755\& // initialisation
1756\& ev_idle_init (&idle, idle_cb);
1757\& ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
1758\& ev_io_start (EV_DEFAULT_ &io);
888.Ve 1759.Ve
889.PP 1760.PP
890More interesting and less C\-conformant ways of catsing your callback type 1761In the \*(L"real\*(R" world, it might also be beneficial to start a timer, so that
891have been omitted.... 1762low-priority connections can not be locked out forever under load. This
1763enables your program to keep a lower latency for important connections
1764during short periods of high load, while not completely locking out less
1765important ones.
892.SH "WATCHER TYPES" 1766.SH "WATCHER TYPES"
893.IX Header "WATCHER TYPES" 1767.IX Header "WATCHER TYPES"
894This section describes each watcher in detail, but will not repeat 1768This section describes each watcher in detail, but will not repeat
895information given in the last section. Any initialisation/set macros, 1769information given in the last section. Any initialisation/set macros,
896functions and members specific to the watcher type are explained. 1770functions and members specific to the watcher type are explained.
… …
901watcher is stopped to your hearts content), or \fI[read\-write]\fR, which 1775watcher is stopped to your hearts content), or \fI[read\-write]\fR, which
902means you can expect it to have some sensible content while the watcher 1776means you can expect it to have some sensible content while the watcher
903is active, but you can also modify it. Modifying it may not do something 1777is active, but you can also modify it. Modifying it may not do something
904sensible or take immediate effect (or do anything at all), but libev will 1778sensible or take immediate effect (or do anything at all), but libev will
905not crash or malfunction in any way. 1779not crash or malfunction in any way.
906.ie n .Sh """ev_io"" \- is this file descriptor readable or writable?" 1780.ie n .SS """ev_io"" \- is this file descriptor readable or writable?"
907.el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable?" 1781.el .SS "\f(CWev_io\fP \- is this file descriptor readable or writable?"
908.IX Subsection "ev_io - is this file descriptor readable or writable?" 1782.IX Subsection "ev_io - is this file descriptor readable or writable?"
909I/O watchers check whether a file descriptor is readable or writable 1783I/O watchers check whether a file descriptor is readable or writable
910in each iteration of the event loop, or, more precisely, when reading 1784in each iteration of the event loop, or, more precisely, when reading
911would not block the process and writing would at least be able to write 1785would not block the process and writing would at least be able to write
912some data. This behaviour is called level-triggering because you keep 1786some data. This behaviour is called level-triggering because you keep
… …
917In general you can register as many read and/or write event watchers per 1791In general you can register as many read and/or write event watchers per
918fd as you want (as long as you don't confuse yourself). Setting all file 1792fd as you want (as long as you don't confuse yourself). Setting all file
919descriptors to non-blocking mode is also usually a good idea (but not 1793descriptors to non-blocking mode is also usually a good idea (but not
920required if you know what you are doing). 1794required if you know what you are doing).
921.PP 1795.PP
922You have to be careful with dup'ed file descriptors, though. Some backends
923(the linux epoll backend is a notable example) cannot handle dup'ed file
924descriptors correctly if you register interest in two or more fds pointing
925to the same underlying file/socket/etc. description (that is, they share
926the same underlying \*(L"file open\*(R").
927.PP
928If you must do this, then force the use of a known-to-be-good backend
929(at the time of this writing, this includes only \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and
930\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR).
931.PP
932Another thing you have to watch out for is that it is quite easy to 1796Another thing you have to watch out for is that it is quite easy to
933receive \*(L"spurious\*(R" readyness notifications, that is your callback might 1797receive \*(L"spurious\*(R" readiness notifications, that is, your callback might
934be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block 1798be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block
935because there is no data. Not only are some backends known to create a 1799because there is no data. It is very easy to get into this situation even
936lot of those (for example solaris ports), it is very easy to get into 1800with a relatively standard program structure. Thus it is best to always
937this situation even with a relatively standard program structure. Thus 1801use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning \f(CW\*(C`EAGAIN\*(C'\fR is far
938it is best to always use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning
939\&\f(CW\*(C`EAGAIN\*(C'\fR is far preferable to a program hanging until some data arrives. 1802preferable to a program hanging until some data arrives.
940.PP 1803.PP
941If you cannot run the fd in non-blocking mode (for example you should not 1804If you cannot run the fd in non-blocking mode (for example you should
942play around with an Xlib connection), then you have to seperately re-test 1805not play around with an Xlib connection), then you have to separately
943wether a file descriptor is really ready with a known-to-be good interface 1806re-test whether a file descriptor is really ready with a known-to-be good
944such as poll (fortunately in our Xlib example, Xlib already does this on 1807interface such as poll (fortunately in the case of Xlib, it already does
945its own, so its quite safe to use). 1808this on its own, so its quite safe to use). Some people additionally
1809use \f(CW\*(C`SIGALRM\*(C'\fR and an interval timer, just to be sure you won't block
1810indefinitely.
1811.PP
1812But really, best use non-blocking mode.
1813.PP
1814\fIThe special problem of disappearing file descriptors\fR
1815.IX Subsection "The special problem of disappearing file descriptors"
1816.PP
1817Some backends (e.g. kqueue, epoll, linuxaio) need to be told about closing
1818a file descriptor (either due to calling \f(CW\*(C`close\*(C'\fR explicitly or any other
1819means, such as \f(CW\*(C`dup2\*(C'\fR). The reason is that you register interest in some
1820file descriptor, but when it goes away, the operating system will silently
1821drop this interest. If another file descriptor with the same number then
1822is registered with libev, there is no efficient way to see that this is,
1823in fact, a different file descriptor.
1824.PP
1825To avoid having to explicitly tell libev about such cases, libev follows
1826the following policy: Each time \f(CW\*(C`ev_io_set\*(C'\fR is being called, libev
1827will assume that this is potentially a new file descriptor, otherwise
1828it is assumed that the file descriptor stays the same. That means that
1829you \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
1830descriptor even if the file descriptor number itself did not change.
1831.PP
1832This is how one would do it normally anyway, the important point is that
1833the libev application should not optimise around libev but should leave
1834optimisations to libev.
1835.PP
1836\fIThe special problem of dup'ed file descriptors\fR
1837.IX Subsection "The special problem of dup'ed file descriptors"
1838.PP
1839Some backends (e.g. epoll), cannot register events for file descriptors,
1840but only events for the underlying file descriptions. That means when you
1841have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or weirder constellations, and register
1842events for them, only one file descriptor might actually receive events.
1843.PP
1844There is no workaround possible except not registering events
1845for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors, or to resort to
1846\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1847.PP
1848\fIThe special problem of files\fR
1849.IX Subsection "The special problem of files"
1850.PP
1851Many people try to use \f(CW\*(C`select\*(C'\fR (or libev) on file descriptors
1852representing files, and expect it to become ready when their program
1853doesn't block on disk accesses (which can take a long time on their own).
1854.PP
1855However, this cannot ever work in the \*(L"expected\*(R" way \- you get a readiness
1856notification as soon as the kernel knows whether and how much data is
1857there, and in the case of open files, that's always the case, so you
1858always get a readiness notification instantly, and your read (or possibly
1859write) will still block on the disk I/O.
1860.PP
1861Another way to view it is that in the case of sockets, pipes, character
1862devices and so on, there is another party (the sender) that delivers data
1863on its own, but in the case of files, there is no such thing: the disk
1864will not send data on its own, simply because it doesn't know what you
1865wish to read \- you would first have to request some data.
1866.PP
1867Since files are typically not-so-well supported by advanced notification
1868mechanism, libev tries hard to emulate \s-1POSIX\s0 behaviour with respect
1869to files, even though you should not use it. The reason for this is
1870convenience: sometimes you want to watch \s-1STDIN\s0 or \s-1STDOUT,\s0 which is
1871usually a tty, often a pipe, but also sometimes files or special devices
1872(for example, \f(CW\*(C`epoll\*(C'\fR on Linux works with \fI/dev/random\fR but not with
1873\&\fI/dev/urandom\fR), and even though the file might better be served with
1874asynchronous I/O instead of with non-blocking I/O, it is still useful when
1875it \*(L"just works\*(R" instead of freezing.
1876.PP
1877So avoid file descriptors pointing to files when you know it (e.g. use
1878libeio), but use them when it is convenient, e.g. for \s-1STDIN/STDOUT,\s0 or
1879when you rarely read from a file instead of from a socket, and want to
1880reuse the same code path.
1881.PP
1882\fIThe special problem of fork\fR
1883.IX Subsection "The special problem of fork"
1884.PP
1885Some backends (epoll, kqueue, linuxaio, iouring) do not support \f(CW\*(C`fork ()\*(C'\fR
1886at all or exhibit useless behaviour. Libev fully supports fork, but needs
1887to be told about it in the child if you want to continue to use it in the
1888child.
1889.PP
1890To support fork in your child processes, you have to call \f(CW\*(C`ev_loop_fork
1891()\*(C'\fR after a fork in the child, enable \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR, or resort to
1892\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1893.PP
1894\fIThe special problem of \s-1SIGPIPE\s0\fR
1895.IX Subsection "The special problem of SIGPIPE"
1896.PP
1897While not really specific to libev, it is easy to forget about \f(CW\*(C`SIGPIPE\*(C'\fR:
1898when writing to a pipe whose other end has been closed, your program gets
1899sent a \s-1SIGPIPE,\s0 which, by default, aborts your program. For most programs
1900this is sensible behaviour, for daemons, this is usually undesirable.
1901.PP
1902So when you encounter spurious, unexplained daemon exits, make sure you
1903ignore \s-1SIGPIPE\s0 (and maybe make sure you log the exit status of your daemon
1904somewhere, as that would have given you a big clue).
1905.PP
1906\fIThe special problem of \f(BIaccept()\fIing when you can't\fR
1907.IX Subsection "The special problem of accept()ing when you can't"
1908.PP
1909Many implementations of the \s-1POSIX\s0 \f(CW\*(C`accept\*(C'\fR function (for example,
1910found in post\-2004 Linux) have the peculiar behaviour of not removing a
1911connection from the pending queue in all error cases.
1912.PP
1913For example, larger servers often run out of file descriptors (because
1914of resource limits), causing \f(CW\*(C`accept\*(C'\fR to fail with \f(CW\*(C`ENFILE\*(C'\fR but not
1915rejecting the connection, leading to libev signalling readiness on
1916the next iteration again (the connection still exists after all), and
1917typically causing the program to loop at 100% \s-1CPU\s0 usage.
1918.PP
1919Unfortunately, the set of errors that cause this issue differs between
1920operating systems, there is usually little the app can do to remedy the
1921situation, and no known thread-safe method of removing the connection to
1922cope with overload is known (to me).
1923.PP
1924One of the easiest ways to handle this situation is to just ignore it
1925\&\- when the program encounters an overload, it will just loop until the
1926situation is over. While this is a form of busy waiting, no \s-1OS\s0 offers an
1927event-based way to handle this situation, so it's the best one can do.
1928.PP
1929A better way to handle the situation is to log any errors other than
1930\&\f(CW\*(C`EAGAIN\*(C'\fR and \f(CW\*(C`EWOULDBLOCK\*(C'\fR, making sure not to flood the log with such
1931messages, and continue as usual, which at least gives the user an idea of
1932what could be wrong (\*(L"raise the ulimit!\*(R"). For extra points one could stop
1933the \f(CW\*(C`ev_io\*(C'\fR watcher on the listening fd \*(L"for a while\*(R", which reduces \s-1CPU\s0
1934usage.
1935.PP
1936If your program is single-threaded, then you could also keep a dummy file
1937descriptor for overload situations (e.g. by opening \fI/dev/null\fR), and
1938when 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,
1939close that fd, and create a new dummy fd. This will gracefully refuse
1940clients under typical overload conditions.
1941.PP
1942The last way to handle it is to simply log the error and \f(CW\*(C`exit\*(C'\fR, as
1943is often done with \f(CW\*(C`malloc\*(C'\fR failures, but this results in an easy
1944opportunity for a DoS attack.
1945.PP
1946\fIWatcher-Specific Functions\fR
1947.IX Subsection "Watcher-Specific Functions"
946.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4 1948.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
947.IX Item "ev_io_init (ev_io *, callback, int fd, int events)" 1949.IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
948.PD 0 1950.PD 0
949.IP "ev_io_set (ev_io *, int fd, int events)" 4 1951.IP "ev_io_set (ev_io *, int fd, int events)" 4
950.IX Item "ev_io_set (ev_io *, int fd, int events)" 1952.IX Item "ev_io_set (ev_io *, int fd, int events)"
951.PD 1953.PD
952Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to 1954Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to
953rceeive events for and events is either \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or 1955receive events for and \f(CW\*(C`events\*(C'\fR is either \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or
954\&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR to receive the given events. 1956\&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR, to express the desire to receive the given events.
955.IP "int fd [read\-only]" 4 1957.IP "int fd [read\-only]" 4
956.IX Item "int fd [read-only]" 1958.IX Item "int fd [read-only]"
957The file descriptor being watched. 1959The file descriptor being watched.
958.IP "int events [read\-only]" 4 1960.IP "int events [read\-only]" 4
959.IX Item "int events [read-only]" 1961.IX Item "int events [read-only]"
960The events being watched. 1962The events being watched.
961.PP 1963.PP
1964\fIExamples\fR
1965.IX Subsection "Examples"
1966.PP
962Example: call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well 1967Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well
963readable, but only once. Since it is likely line\-buffered, you could 1968readable, but only once. Since it is likely line-buffered, you could
964attempt to read a whole line in the callback: 1969attempt to read a whole line in the callback.
965.PP 1970.PP
966.Vb 6 1971.Vb 6
967\& static void 1972\& static void
968\& stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents) 1973\& stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
969\& { 1974\& {
970\& ev_io_stop (loop, w); 1975\& ev_io_stop (loop, w);
971\& .. read from stdin here (or from w->fd) and haqndle any I/O errors 1976\& .. read from stdin here (or from w\->fd) and handle any I/O errors
972\& } 1977\& }
973.Ve 1978\&
974.PP
975.Vb 6
976\& ... 1979\& ...
977\& struct ev_loop *loop = ev_default_init (0); 1980\& struct ev_loop *loop = ev_default_init (0);
978\& struct ev_io stdin_readable; 1981\& ev_io stdin_readable;
979\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ); 1982\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
980\& ev_io_start (loop, &stdin_readable); 1983\& ev_io_start (loop, &stdin_readable);
981\& ev_loop (loop, 0); 1984\& ev_run (loop, 0);
982.Ve 1985.Ve
983.ie n .Sh """ev_timer"" \- relative and optionally repeating timeouts" 1986.ie n .SS """ev_timer"" \- relative and optionally repeating timeouts"
984.el .Sh "\f(CWev_timer\fP \- relative and optionally repeating timeouts" 1987.el .SS "\f(CWev_timer\fP \- relative and optionally repeating timeouts"
985.IX Subsection "ev_timer - relative and optionally repeating timeouts" 1988.IX Subsection "ev_timer - relative and optionally repeating timeouts"
986Timer watchers are simple relative timers that generate an event after a 1989Timer watchers are simple relative timers that generate an event after a
987given time, and optionally repeating in regular intervals after that. 1990given time, and optionally repeating in regular intervals after that.
988.PP 1991.PP
989The timers are based on real time, that is, if you register an event that 1992The timers are based on real time, that is, if you register an event that
990times out after an hour and you reset your system clock to last years 1993times out after an hour and you reset your system clock to January last
991time, it will still time out after (roughly) and hour. \*(L"Roughly\*(R" because 1994year, it will still time out after (roughly) one hour. \*(L"Roughly\*(R" because
992detecting time jumps is hard, and some inaccuracies are unavoidable (the 1995detecting time jumps is hard, and some inaccuracies are unavoidable (the
993monotonic clock option helps a lot here). 1996monotonic clock option helps a lot here).
1997.PP
1998The callback is guaranteed to be invoked only \fIafter\fR its timeout has
1999passed (not \fIat\fR, so on systems with very low-resolution clocks this
2000might introduce a small delay, see \*(L"the special problem of being too
2001early\*(R", below). If multiple timers become ready during the same loop
2002iteration then the ones with earlier time-out values are invoked before
2003ones of the same priority with later time-out values (but this is no
2004longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
2005.PP
2006\fIBe smart about timeouts\fR
2007.IX Subsection "Be smart about timeouts"
2008.PP
2009Many real-world problems involve some kind of timeout, usually for error
2010recovery. A typical example is an \s-1HTTP\s0 request \- if the other side hangs,
2011you want to raise some error after a while.
2012.PP
2013What follows are some ways to handle this problem, from obvious and
2014inefficient to smart and efficient.
2015.PP
2016In the following, a 60 second activity timeout is assumed \- a timeout that
2017gets reset to 60 seconds each time there is activity (e.g. each time some
2018data or other life sign was received).
2019.IP "1. Use a timer and stop, reinitialise and start it on activity." 4
2020.IX Item "1. Use a timer and stop, reinitialise and start it on activity."
2021This is the most obvious, but not the most simple way: In the beginning,
2022start the watcher:
2023.Sp
2024.Vb 2
2025\& ev_timer_init (timer, callback, 60., 0.);
2026\& ev_timer_start (loop, timer);
2027.Ve
2028.Sp
2029Then, each time there is some activity, \f(CW\*(C`ev_timer_stop\*(C'\fR it, initialise it
2030and start it again:
2031.Sp
2032.Vb 3
2033\& ev_timer_stop (loop, timer);
2034\& ev_timer_set (timer, 60., 0.);
2035\& ev_timer_start (loop, timer);
2036.Ve
2037.Sp
2038This is relatively simple to implement, but means that each time there is
2039some activity, libev will first have to remove the timer from its internal
2040data structure and then add it again. Libev tries to be fast, but it's
2041still not a constant-time operation.
2042.ie n .IP "2. Use a timer and re-start it with ""ev_timer_again"" inactivity." 4
2043.el .IP "2. Use a timer and re-start it with \f(CWev_timer_again\fR inactivity." 4
2044.IX Item "2. Use a timer and re-start it with ev_timer_again inactivity."
2045This is the easiest way, and involves using \f(CW\*(C`ev_timer_again\*(C'\fR instead of
2046\&\f(CW\*(C`ev_timer_start\*(C'\fR.
2047.Sp
2048To implement this, configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value
2049of \f(CW60\fR and then call \f(CW\*(C`ev_timer_again\*(C'\fR at start and each time you
2050successfully read or write some data. If you go into an idle state where
2051you do not expect data to travel on the socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR
2052the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will automatically restart it if need be.
2053.Sp
2054That means you can ignore both the \f(CW\*(C`ev_timer_start\*(C'\fR function and the
2055\&\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
2056member and \f(CW\*(C`ev_timer_again\*(C'\fR.
2057.Sp
2058At start:
2059.Sp
2060.Vb 3
2061\& ev_init (timer, callback);
2062\& timer\->repeat = 60.;
2063\& ev_timer_again (loop, timer);
2064.Ve
2065.Sp
2066Each time there is some activity:
2067.Sp
2068.Vb 1
2069\& ev_timer_again (loop, timer);
2070.Ve
2071.Sp
2072It is even possible to change the time-out on the fly, regardless of
2073whether the watcher is active or not:
2074.Sp
2075.Vb 2
2076\& timer\->repeat = 30.;
2077\& ev_timer_again (loop, timer);
2078.Ve
2079.Sp
2080This is slightly more efficient then stopping/starting the timer each time
2081you want to modify its timeout value, as libev does not have to completely
2082remove and re-insert the timer from/into its internal data structure.
2083.Sp
2084It is, however, even simpler than the \*(L"obvious\*(R" way to do it.
2085.IP "3. Let the timer time out, but then re-arm it as required." 4
2086.IX Item "3. Let the timer time out, but then re-arm it as required."
2087This method is more tricky, but usually most efficient: Most timeouts are
2088relatively long compared to the intervals between other activity \- in
2089our example, within 60 seconds, there are usually many I/O events with
2090associated activity resets.
2091.Sp
2092In this case, it would be more efficient to leave the \f(CW\*(C`ev_timer\*(C'\fR alone,
2093but remember the time of last activity, and check for a real timeout only
2094within the callback:
2095.Sp
2096.Vb 3
2097\& ev_tstamp timeout = 60.;
2098\& ev_tstamp last_activity; // time of last activity
2099\& ev_timer timer;
2100\&
2101\& static void
2102\& callback (EV_P_ ev_timer *w, int revents)
2103\& {
2104\& // calculate when the timeout would happen
2105\& ev_tstamp after = last_activity \- ev_now (EV_A) + timeout;
2106\&
2107\& // if negative, it means we the timeout already occurred
2108\& if (after < 0.)
2109\& {
2110\& // timeout occurred, take action
2111\& }
2112\& else
2113\& {
2114\& // callback was invoked, but there was some recent
2115\& // activity. simply restart the timer to time out
2116\& // after "after" seconds, which is the earliest time
2117\& // the timeout can occur.
2118\& ev_timer_set (w, after, 0.);
2119\& ev_timer_start (EV_A_ w);
2120\& }
2121\& }
2122.Ve
2123.Sp
2124To summarise the callback: first calculate in how many seconds the
2125timeout will occur (by calculating the absolute time when it would occur,
2126\&\f(CW\*(C`last_activity + timeout\*(C'\fR, and subtracting the current time, \f(CW\*(C`ev_now
2127(EV_A)\*(C'\fR from that).
2128.Sp
2129If this value is negative, then we are already past the timeout, i.e. we
2130timed out, and need to do whatever is needed in this case.
2131.Sp
2132Otherwise, we now the earliest time at which the timeout would trigger,
2133and simply start the timer with this timeout value.
2134.Sp
2135In other words, each time the callback is invoked it will check whether
2136the timeout occurred. If not, it will simply reschedule itself to check
2137again at the earliest time it could time out. Rinse. Repeat.
2138.Sp
2139This scheme causes more callback invocations (about one every 60 seconds
2140minus half the average time between activity), but virtually no calls to
2141libev to change the timeout.
2142.Sp
2143To start the machinery, simply initialise the watcher and set
2144\&\f(CW\*(C`last_activity\*(C'\fR to the current time (meaning there was some activity just
2145now), then call the callback, which will \*(L"do the right thing\*(R" and start
2146the timer:
2147.Sp
2148.Vb 3
2149\& last_activity = ev_now (EV_A);
2150\& ev_init (&timer, callback);
2151\& callback (EV_A_ &timer, 0);
2152.Ve
2153.Sp
2154When there is some activity, simply store the current time in
2155\&\f(CW\*(C`last_activity\*(C'\fR, no libev calls at all:
2156.Sp
2157.Vb 2
2158\& if (activity detected)
2159\& last_activity = ev_now (EV_A);
2160.Ve
2161.Sp
2162When your timeout value changes, then the timeout can be changed by simply
2163providing a new value, stopping the timer and calling the callback, which
2164will again do the right thing (for example, time out immediately :).
2165.Sp
2166.Vb 3
2167\& timeout = new_value;
2168\& ev_timer_stop (EV_A_ &timer);
2169\& callback (EV_A_ &timer, 0);
2170.Ve
2171.Sp
2172This technique is slightly more complex, but in most cases where the
2173time-out is unlikely to be triggered, much more efficient.
2174.IP "4. Wee, just use a double-linked list for your timeouts." 4
2175.IX Item "4. Wee, just use a double-linked list for your timeouts."
2176If there is not one request, but many thousands (millions...), all
2177employing some kind of timeout with the same timeout value, then one can
2178do even better:
2179.Sp
2180When starting the timeout, calculate the timeout value and put the timeout
2181at the \fIend\fR of the list.
2182.Sp
2183Then use an \f(CW\*(C`ev_timer\*(C'\fR to fire when the timeout at the \fIbeginning\fR of
2184the list is expected to fire (for example, using the technique #3).
2185.Sp
2186When there is some activity, remove the timer from the list, recalculate
2187the timeout, append it to the end of the list again, and make sure to
2188update the \f(CW\*(C`ev_timer\*(C'\fR if it was taken from the beginning of the list.
2189.Sp
2190This way, one can manage an unlimited number of timeouts in O(1) time for
2191starting, stopping and updating the timers, at the expense of a major
2192complication, and having to use a constant timeout. The constant timeout
2193ensures that the list stays sorted.
2194.PP
2195So which method the best?
2196.PP
2197Method #2 is a simple no-brain-required solution that is adequate in most
2198situations. Method #3 requires a bit more thinking, but handles many cases
2199better, and isn't very complicated either. In most case, choosing either
2200one is fine, with #3 being better in typical situations.
2201.PP
2202Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
2203rather complicated, but extremely efficient, something that really pays
2204off after the first million or so of active timers, i.e. it's usually
2205overkill :)
2206.PP
2207\fIThe special problem of being too early\fR
2208.IX Subsection "The special problem of being too early"
2209.PP
2210If you ask a timer to call your callback after three seconds, then
2211you expect it to be invoked after three seconds \- but of course, this
2212cannot be guaranteed to infinite precision. Less obviously, it cannot be
2213guaranteed to any precision by libev \- imagine somebody suspending the
2214process with a \s-1STOP\s0 signal for a few hours for example.
2215.PP
2216So, libev tries to invoke your callback as soon as possible \fIafter\fR the
2217delay has occurred, but cannot guarantee this.
2218.PP
2219A less obvious failure mode is calling your callback too early: many event
2220loops compare timestamps with a \*(L"elapsed delay >= requested delay\*(R", but
2221this can cause your callback to be invoked much earlier than you would
2222expect.
2223.PP
2224To see why, imagine a system with a clock that only offers full second
2225resolution (think windows if you can't come up with a broken enough \s-1OS\s0
2226yourself). If you schedule a one-second timer at the time 500.9, then the
2227event loop will schedule your timeout to elapse at a system time of 500
2228(500.9 truncated to the resolution) + 1, or 501.
2229.PP
2230If an event library looks at the timeout 0.1s later, it will see \*(L"501 >=
2231501\*(R" and invoke the callback 0.1s after it was started, even though a
2232one-second delay was requested \- this is being \*(L"too early\*(R", despite best
2233intentions.
2234.PP
2235This is the reason why libev will never invoke the callback if the elapsed
2236delay equals the requested delay, but only when the elapsed delay is
2237larger than the requested delay. In the example above, libev would only invoke
2238the callback at system time 502, or 1.1s after the timer was started.
2239.PP
2240So, while libev cannot guarantee that your callback will be invoked
2241exactly when requested, it \fIcan\fR and \fIdoes\fR guarantee that the requested
2242delay has actually elapsed, or in other words, it always errs on the \*(L"too
2243late\*(R" side of things.
2244.PP
2245\fIThe special problem of time updates\fR
2246.IX Subsection "The special problem of time updates"
2247.PP
2248Establishing the current time is a costly operation (it usually takes
2249at least one system call): \s-1EV\s0 therefore updates its idea of the current
2250time only before and after \f(CW\*(C`ev_run\*(C'\fR collects new events, which causes a
2251growing difference between \f(CW\*(C`ev_now ()\*(C'\fR and \f(CW\*(C`ev_time ()\*(C'\fR when handling
2252lots of events in one iteration.
994.PP 2253.PP
995The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR 2254The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
996time. This is usually the right thing as this timestamp refers to the time 2255time. This is usually the right thing as this timestamp refers to the time
997of the event triggering whatever timeout you are modifying/starting. If 2256of the event triggering whatever timeout you are modifying/starting. If
998you suspect event processing to be delayed and you \fIneed\fR to base the timeout 2257you suspect event processing to be delayed and you \fIneed\fR to base the
999on the current time, use something like this to adjust for this: 2258timeout on the current time, use something like the following to adjust
2259for it:
1000.PP 2260.PP
1001.Vb 1 2261.Vb 1
1002\& ev_timer_set (&timer, after + ev_now () - ev_time (), 0.); 2262\& ev_timer_set (&timer, after + (ev_time () \- ev_now ()), 0.);
1003.Ve 2263.Ve
1004.PP 2264.PP
1005The callback is guarenteed to be invoked only when its timeout has passed, 2265If the event loop is suspended for a long time, you can also force an
1006but if multiple timers become ready during the same loop iteration then 2266update of the time returned by \f(CW\*(C`ev_now ()\*(C'\fR by calling \f(CW\*(C`ev_now_update
1007order of execution is undefined. 2267()\*(C'\fR, although that will push the event time of all outstanding events
2268further into the future.
2269.PP
2270\fIThe special problem of unsynchronised clocks\fR
2271.IX Subsection "The special problem of unsynchronised clocks"
2272.PP
2273Modern systems have a variety of clocks \- libev itself uses the normal
2274\&\*(L"wall clock\*(R" clock and, if available, the monotonic clock (to avoid time
2275jumps).
2276.PP
2277Neither of these clocks is synchronised with each other or any other clock
2278on the system, so \f(CW\*(C`ev_time ()\*(C'\fR might return a considerably different time
2279than \f(CW\*(C`gettimeofday ()\*(C'\fR or \f(CW\*(C`time ()\*(C'\fR. On a GNU/Linux system, for example,
2280a call to \f(CW\*(C`gettimeofday\*(C'\fR might return a second count that is one higher
2281than a directly following call to \f(CW\*(C`time\*(C'\fR.
2282.PP
2283The moral of this is to only compare libev-related timestamps with
2284\&\f(CW\*(C`ev_time ()\*(C'\fR and \f(CW\*(C`ev_now ()\*(C'\fR, at least if you want better precision than
2285a second or so.
2286.PP
2287One more problem arises due to this lack of synchronisation: if libev uses
2288the system monotonic clock and you compare timestamps from \f(CW\*(C`ev_time\*(C'\fR
2289or \f(CW\*(C`ev_now\*(C'\fR from when you started your timer and when your callback is
2290invoked, you will find that sometimes the callback is a bit \*(L"early\*(R".
2291.PP
2292This is because \f(CW\*(C`ev_timer\*(C'\fRs work in real time, not wall clock time, so
2293libev makes sure your callback is not invoked before the delay happened,
2294\&\fImeasured according to the real time\fR, not the system clock.
2295.PP
2296If your timeouts are based on a physical timescale (e.g. \*(L"time out this
2297connection after 100 seconds\*(R") then this shouldn't bother you as it is
2298exactly the right behaviour.
2299.PP
2300If you want to compare wall clock/system timestamps to your timers, then
2301you need to use \f(CW\*(C`ev_periodic\*(C'\fRs, as these are based on the wall clock
2302time, where your comparisons will always generate correct results.
2303.PP
2304\fIThe special problems of suspended animation\fR
2305.IX Subsection "The special problems of suspended animation"
2306.PP
2307When you leave the server world it is quite customary to hit machines that
2308can suspend/hibernate \- what happens to the clocks during such a suspend?
2309.PP
2310Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
2311all processes, while the clocks (\f(CW\*(C`times\*(C'\fR, \f(CW\*(C`CLOCK_MONOTONIC\*(C'\fR) continue
2312to run until the system is suspended, but they will not advance while the
2313system is suspended. That means, on resume, it will be as if the program
2314was frozen for a few seconds, but the suspend time will not be counted
2315towards \f(CW\*(C`ev_timer\*(C'\fR when a monotonic clock source is used. The real time
2316clock advanced as expected, but if it is used as sole clocksource, then a
2317long suspend would be detected as a time jump by libev, and timers would
2318be adjusted accordingly.
2319.PP
2320I would not be surprised to see different behaviour in different between
2321operating systems, \s-1OS\s0 versions or even different hardware.
2322.PP
2323The other form of suspend (job control, or sending a \s-1SIGSTOP\s0) will see a
2324time jump in the monotonic clocks and the realtime clock. If the program
2325is suspended for a very long time, and monotonic clock sources are in use,
2326then you can expect \f(CW\*(C`ev_timer\*(C'\fRs to expire as the full suspension time
2327will be counted towards the timers. When no monotonic clock source is in
2328use, then libev will again assume a timejump and adjust accordingly.
2329.PP
2330It might be beneficial for this latter case to call \f(CW\*(C`ev_suspend\*(C'\fR
2331and \f(CW\*(C`ev_resume\*(C'\fR in code that handles \f(CW\*(C`SIGTSTP\*(C'\fR, to at least get
2332deterministic behaviour in this case (you can do nothing against
2333\&\f(CW\*(C`SIGSTOP\*(C'\fR).
2334.PP
2335\fIWatcher-Specific Functions and Data Members\fR
2336.IX Subsection "Watcher-Specific Functions and Data Members"
1008.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4 2337.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
1009.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 2338.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
1010.PD 0 2339.PD 0
1011.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4 2340.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
1012.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 2341.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
1013.PD 2342.PD
1014Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR is 2343Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds (fractional and
1015\&\f(CW0.\fR, then it will automatically be stopped. If it is positive, then the 2344negative values are supported). If \f(CW\*(C`repeat\*(C'\fR is \f(CW0.\fR, then it will
2345automatically be stopped once the timeout is reached. If it is positive,
1016timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds 2346then the timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR
1017later, again, and again, until stopped manually. 2347seconds later, again, and again, until stopped manually.
1018.Sp 2348.Sp
1019The timer itself will do a best-effort at avoiding drift, that is, if you 2349The timer itself will do a best-effort at avoiding drift, that is, if
1020configure a timer to trigger every 10 seconds, then it will trigger at 2350you configure a timer to trigger every 10 seconds, then it will normally
1021exactly 10 second intervals. If, however, your program cannot keep up with 2351trigger at exactly 10 second intervals. If, however, your program cannot
1022the timer (because it takes longer than those 10 seconds to do stuff) the 2352keep up with the timer (because it takes longer than those 10 seconds to
1023timer will not fire more than once per event loop iteration. 2353do stuff) the timer will not fire more than once per event loop iteration.
1024.IP "ev_timer_again (loop)" 4 2354.IP "ev_timer_again (loop, ev_timer *)" 4
1025.IX Item "ev_timer_again (loop)" 2355.IX Item "ev_timer_again (loop, ev_timer *)"
1026This will act as if the timer timed out and restart it again if it is 2356This will act as if the timer timed out, and restarts it again if it is
1027repeating. The exact semantics are: 2357repeating. It basically works like calling \f(CW\*(C`ev_timer_stop\*(C'\fR, updating the
2358timeout to the \f(CW\*(C`repeat\*(C'\fR value and calling \f(CW\*(C`ev_timer_start\*(C'\fR.
1028.Sp 2359.Sp
1029If the timer is started but nonrepeating, stop it. 2360The exact semantics are as in the following rules, all of which will be
2361applied to the watcher:
2362.RS 4
2363.IP "If the timer is pending, the pending status is always cleared." 4
2364.IX Item "If the timer is pending, the pending status is always cleared."
2365.PD 0
2366.IP "If the timer is started but non-repeating, stop it (as if it timed out, without invoking it)." 4
2367.IX Item "If the timer is started but non-repeating, stop it (as if it timed out, without invoking it)."
2368.ie n .IP "If the timer is repeating, make the ""repeat"" value the new timeout and start the timer, if necessary." 4
2369.el .IP "If the timer is repeating, make the \f(CWrepeat\fR value the new timeout and start the timer, if necessary." 4
2370.IX Item "If the timer is repeating, make the repeat value the new timeout and start the timer, if necessary."
2371.RE
2372.RS 4
2373.PD
1030.Sp 2374.Sp
1031If the timer is repeating, either start it if necessary (with the repeat 2375This sounds a bit complicated, see \*(L"Be smart about timeouts\*(R", above, for a
1032value), or reset the running timer to the repeat value. 2376usage example.
2377.RE
2378.IP "ev_tstamp ev_timer_remaining (loop, ev_timer *)" 4
2379.IX Item "ev_tstamp ev_timer_remaining (loop, ev_timer *)"
2380Returns the remaining time until a timer fires. If the timer is active,
2381then this time is relative to the current event loop time, otherwise it's
2382the timeout value currently configured.
1033.Sp 2383.Sp
1034This sounds a bit complicated, but here is a useful and typical 2384That is, after an \f(CW\*(C`ev_timer_set (w, 5, 7)\*(C'\fR, \f(CW\*(C`ev_timer_remaining\*(C'\fR returns
1035example: Imagine you have a tcp connection and you want a so-called 2385\&\f(CW5\fR. When the timer is started and one second passes, \f(CW\*(C`ev_timer_remaining\*(C'\fR
1036idle timeout, that is, you want to be called when there have been, 2386will return \f(CW4\fR. When the timer expires and is restarted, it will return
1037say, 60 seconds of inactivity on the socket. The easiest way to do 2387roughly \f(CW7\fR (likely slightly less as callback invocation takes some time,
1038this is to configure an \f(CW\*(C`ev_timer\*(C'\fR with \f(CW\*(C`after\*(C'\fR=\f(CW\*(C`repeat\*(C'\fR=\f(CW60\fR and calling 2388too), and so on.
1039\&\f(CW\*(C`ev_timer_again\*(C'\fR each time you successfully read or write some data. If
1040you go into an idle state where you do not expect data to travel on the
1041socket, you can stop the timer, and again will automatically restart it if
1042need be.
1043.Sp
1044You can also ignore the \f(CW\*(C`after\*(C'\fR value and \f(CW\*(C`ev_timer_start\*(C'\fR altogether
1045and only ever use the \f(CW\*(C`repeat\*(C'\fR value:
1046.Sp
1047.Vb 8
1048\& ev_timer_init (timer, callback, 0., 5.);
1049\& ev_timer_again (loop, timer);
1050\& ...
1051\& timer->again = 17.;
1052\& ev_timer_again (loop, timer);
1053\& ...
1054\& timer->again = 10.;
1055\& ev_timer_again (loop, timer);
1056.Ve
1057.Sp
1058This is more efficient then stopping/starting the timer eahc time you want
1059to modify its timeout value.
1060.IP "ev_tstamp repeat [read\-write]" 4 2389.IP "ev_tstamp repeat [read\-write]" 4
1061.IX Item "ev_tstamp repeat [read-write]" 2390.IX Item "ev_tstamp repeat [read-write]"
1062The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out 2391The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out
1063or \f(CW\*(C`ev_timer_again\*(C'\fR is called and determines the next timeout (if any), 2392or \f(CW\*(C`ev_timer_again\*(C'\fR is called, and determines the next timeout (if any),
1064which is also when any modifications are taken into account. 2393which is also when any modifications are taken into account.
1065.PP 2394.PP
2395\fIExamples\fR
2396.IX Subsection "Examples"
2397.PP
1066Example: create a timer that fires after 60 seconds. 2398Example: Create a timer that fires after 60 seconds.
1067.PP 2399.PP
1068.Vb 5 2400.Vb 5
1069\& static void 2401\& static void
1070\& one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents) 2402\& one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1071\& { 2403\& {
1072\& .. one minute over, w is actually stopped right here 2404\& .. one minute over, w is actually stopped right here
1073\& } 2405\& }
1074.Ve 2406\&
1075.PP
1076.Vb 3
1077\& struct ev_timer mytimer; 2407\& ev_timer mytimer;
1078\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.); 2408\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1079\& ev_timer_start (loop, &mytimer); 2409\& ev_timer_start (loop, &mytimer);
1080.Ve 2410.Ve
1081.PP 2411.PP
1082Example: create a timeout timer that times out after 10 seconds of 2412Example: Create a timeout timer that times out after 10 seconds of
1083inactivity. 2413inactivity.
1084.PP 2414.PP
1085.Vb 5 2415.Vb 5
1086\& static void 2416\& static void
1087\& timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents) 2417\& timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1088\& { 2418\& {
1089\& .. ten seconds without any activity 2419\& .. ten seconds without any activity
1090\& } 2420\& }
1091.Ve 2421\&
1092.PP
1093.Vb 4
1094\& struct ev_timer mytimer; 2422\& ev_timer mytimer;
1095\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */ 2423\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1096\& ev_timer_again (&mytimer); /* start timer */ 2424\& ev_timer_again (&mytimer); /* start timer */
1097\& ev_loop (loop, 0); 2425\& ev_run (loop, 0);
1098.Ve 2426\&
1099.PP
1100.Vb 3
1101\& // and in some piece of code that gets executed on any "activity": 2427\& // and in some piece of code that gets executed on any "activity":
1102\& // reset the timeout to start ticking again at 10 seconds 2428\& // reset the timeout to start ticking again at 10 seconds
1103\& ev_timer_again (&mytimer); 2429\& ev_timer_again (&mytimer);
1104.Ve 2430.Ve
1105.ie n .Sh """ev_periodic"" \- to cron or not to cron?" 2431.ie n .SS """ev_periodic"" \- to cron or not to cron?"
1106.el .Sh "\f(CWev_periodic\fP \- to cron or not to cron?" 2432.el .SS "\f(CWev_periodic\fP \- to cron or not to cron?"
1107.IX Subsection "ev_periodic - to cron or not to cron?" 2433.IX Subsection "ev_periodic - to cron or not to cron?"
1108Periodic watchers are also timers of a kind, but they are very versatile 2434Periodic watchers are also timers of a kind, but they are very versatile
1109(and unfortunately a bit complex). 2435(and unfortunately a bit complex).
1110.PP 2436.PP
1111Unlike \f(CW\*(C`ev_timer\*(C'\fR's, they are not based on real time (or relative time) 2437Unlike \f(CW\*(C`ev_timer\*(C'\fR, periodic watchers are not based on real time (or
1112but on wallclock time (absolute time). You can tell a periodic watcher 2438relative time, the physical time that passes) but on wall clock time
1113to trigger \*(L"at\*(R" some specific point in time. For example, if you tell a 2439(absolute time, the thing you can read on your calendar or clock). The
1114periodic watcher to trigger in 10 seconds (by specifiying e.g. \f(CW\*(C`ev_now () 2440difference is that wall clock time can run faster or slower than real
1115+ 10.\*(C'\fR) and then reset your system clock to the last year, then it will 2441time, and time jumps are not uncommon (e.g. when you adjust your
1116take a year to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would trigger 2442wrist-watch).
1117roughly 10 seconds later and of course not if you reset your system time
1118again).
1119.PP 2443.PP
1120They can also be used to implement vastly more complex timers, such as 2444You can tell a periodic watcher to trigger after some specific point
1121triggering an event on eahc midnight, local time. 2445in time: for example, if you tell a periodic watcher to trigger \*(L"in 10
2446seconds\*(R" (by specifying e.g. \f(CW\*(C`ev_now () + 10.\*(C'\fR, that is, an absolute time
2447not a delay) and then reset your system clock to January of the previous
2448year, then it will take a year or more to trigger the event (unlike an
2449\&\f(CW\*(C`ev_timer\*(C'\fR, which would still trigger roughly 10 seconds after starting
2450it, as it uses a relative timeout).
1122.PP 2451.PP
2452\&\f(CW\*(C`ev_periodic\*(C'\fR watchers can also be used to implement vastly more complex
2453timers, such as triggering an event on each \*(L"midnight, local time\*(R", or
2454other complicated rules. This cannot easily be done with \f(CW\*(C`ev_timer\*(C'\fR
2455watchers, as those cannot react to time jumps.
2456.PP
1123As with timers, the callback is guarenteed to be invoked only when the 2457As with timers, the callback is guaranteed to be invoked only when the
1124time (\f(CW\*(C`at\*(C'\fR) has been passed, but if multiple periodic timers become ready 2458point in time where it is supposed to trigger has passed. If multiple
1125during the same loop iteration then order of execution is undefined. 2459timers become ready during the same loop iteration then the ones with
2460earlier time-out values are invoked before ones with later time-out values
2461(but this is no longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
2462.PP
2463\fIWatcher-Specific Functions and Data Members\fR
2464.IX Subsection "Watcher-Specific Functions and Data Members"
1126.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 4 2465.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
1127.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 2466.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
1128.PD 0 2467.PD 0
1129.IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4 2468.IP "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
1130.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 2469.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
1131.PD 2470.PD
1132Lots of arguments, lets sort it out... There are basically three modes of 2471Lots of arguments, let's sort it out... There are basically three modes of
1133operation, and we will explain them from simplest to complex: 2472operation, and we will explain them from simplest to most complex:
1134.RS 4 2473.RS 4
1135.IP "* absolute timer (interval = reschedule_cb = 0)" 4 2474.IP "\(bu" 4
1136.IX Item "absolute timer (interval = reschedule_cb = 0)" 2475absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
2476.Sp
1137In this configuration the watcher triggers an event at the wallclock time 2477In this configuration the watcher triggers an event after the wall clock
1138\&\f(CW\*(C`at\*(C'\fR and doesn't repeat. It will not adjust when a time jump occurs, 2478time \f(CW\*(C`offset\*(C'\fR has passed. It will not repeat and will not adjust when a
1139that is, if it is to be run at January 1st 2011 then it will run when the 2479time jump occurs, that is, if it is to be run at January 1st 2011 then it
1140system time reaches or surpasses this time. 2480will be stopped and invoked when the system clock reaches or surpasses
1141.IP "* non-repeating interval timer (interval > 0, reschedule_cb = 0)" 4 2481this point in time.
1142.IX Item "non-repeating interval timer (interval > 0, reschedule_cb = 0)" 2482.IP "\(bu" 4
2483repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
2484.Sp
1143In this mode the watcher will always be scheduled to time out at the next 2485In this mode the watcher will always be scheduled to time out at the next
1144\&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N) and then repeat, regardless 2486\&\f(CW\*(C`offset + N * interval\*(C'\fR time (for some integer N, which can also be
1145of any time jumps. 2487negative) and then repeat, regardless of any time jumps. The \f(CW\*(C`offset\*(C'\fR
2488argument is merely an offset into the \f(CW\*(C`interval\*(C'\fR periods.
1146.Sp 2489.Sp
1147This can be used to create timers that do not drift with respect to system 2490This can be used to create timers that do not drift with respect to the
1148time: 2491system clock, for example, here is an \f(CW\*(C`ev_periodic\*(C'\fR that triggers each
2492hour, on the hour (with respect to \s-1UTC\s0):
1149.Sp 2493.Sp
1150.Vb 1 2494.Vb 1
1151\& ev_periodic_set (&periodic, 0., 3600., 0); 2495\& ev_periodic_set (&periodic, 0., 3600., 0);
1152.Ve 2496.Ve
1153.Sp 2497.Sp
1154This doesn't mean there will always be 3600 seconds in between triggers, 2498This doesn't mean there will always be 3600 seconds in between triggers,
1155but only that the the callback will be called when the system time shows a 2499but only that the callback will be called when the system time shows a
1156full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible 2500full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
1157by 3600. 2501by 3600.
1158.Sp 2502.Sp
1159Another way to think about it (for the mathematically inclined) is that 2503Another way to think about it (for the mathematically inclined) is that
1160\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible 2504\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
1161time where \f(CW\*(C`time = at (mod interval)\*(C'\fR, regardless of any time jumps. 2505time where \f(CW\*(C`time = offset (mod interval)\*(C'\fR, regardless of any time jumps.
1162.IP "* manual reschedule mode (reschedule_cb = callback)" 4 2506.Sp
1163.IX Item "manual reschedule mode (reschedule_cb = callback)" 2507The \f(CW\*(C`interval\*(C'\fR \fI\s-1MUST\s0\fR be positive, and for numerical stability, the
2508interval value should be higher than \f(CW\*(C`1/8192\*(C'\fR (which is around 100
2509microseconds) and \f(CW\*(C`offset\*(C'\fR should be higher than \f(CW0\fR and should have
2510at most a similar magnitude as the current time (say, within a factor of
2511ten). Typical values for offset are, in fact, \f(CW0\fR or something between
2512\&\f(CW0\fR and \f(CW\*(C`interval\*(C'\fR, which is also the recommended range.
2513.Sp
2514Note also that there is an upper limit to how often a timer can fire (\s-1CPU\s0
2515speed for example), so if \f(CW\*(C`interval\*(C'\fR is very small then timing stability
2516will of course deteriorate. Libev itself tries to be exact to be about one
2517millisecond (if the \s-1OS\s0 supports it and the machine is fast enough).
2518.IP "\(bu" 4
2519manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
2520.Sp
1164In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being 2521In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`offset\*(C'\fR are both being
1165ignored. Instead, each time the periodic watcher gets scheduled, the 2522ignored. Instead, each time the periodic watcher gets scheduled, the
1166reschedule callback will be called with the watcher as first, and the 2523reschedule callback will be called with the watcher as first, and the
1167current time as second argument. 2524current time as second argument.
1168.Sp 2525.Sp
1169\&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, 2526\&\s-1NOTE:\s0 \fIThis callback \s-1MUST NOT\s0 stop or destroy any periodic watcher, ever,
1170ever, or make any event loop modifications\fR. If you need to stop it, 2527or make \s-1ANY\s0 other event loop modifications whatsoever, unless explicitly
1171return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop it afterwards (e.g. by 2528allowed by documentation here\fR.
1172starting a prepare watcher).
1173.Sp 2529.Sp
2530If you need to stop it, return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop
2531it afterwards (e.g. by starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is the
2532only event loop modification you are allowed to do).
2533.Sp
1174Its prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic *w, 2534The callback prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(ev_periodic
1175ev_tstamp now)\*(C'\fR, e.g.: 2535*w, ev_tstamp now)\*(C'\fR, e.g.:
1176.Sp 2536.Sp
1177.Vb 4 2537.Vb 5
2538\& static ev_tstamp
1178\& static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) 2539\& my_rescheduler (ev_periodic *w, ev_tstamp now)
1179\& { 2540\& {
1180\& return now + 60.; 2541\& return now + 60.;
1181\& } 2542\& }
1182.Ve 2543.Ve
1183.Sp 2544.Sp
1184It must return the next time to trigger, based on the passed time value 2545It must return the next time to trigger, based on the passed time value
1185(that is, the lowest time value larger than to the second argument). It 2546(that is, the lowest time value larger than to the second argument). It
1186will usually be called just before the callback will be triggered, but 2547will usually be called just before the callback will be triggered, but
1187might be called at other times, too. 2548might be called at other times, too.
1188.Sp 2549.Sp
1189\&\s-1NOTE:\s0 \fIThis callback must always return a time that is later than the 2550\&\s-1NOTE:\s0 \fIThis callback must always return a time that is higher than or
1190passed \f(CI\*(C`now\*(C'\fI value\fR. Not even \f(CW\*(C`now\*(C'\fR itself will do, it \fImust\fR be larger. 2551equal to the passed \f(CI\*(C`now\*(C'\fI value\fR.
1191.Sp 2552.Sp
1192This can be used to create very complex timers, such as a timer that 2553This can be used to create very complex timers, such as a timer that
1193triggers on each midnight, local time. To do this, you would calculate the 2554triggers on \*(L"next midnight, local time\*(R". To do this, you would calculate
1194next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How 2555the next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for
1195you do this is, again, up to you (but it is not trivial, which is the main 2556this. Here is a (completely untested, no error checking) example on how to
1196reason I omitted it as an example). 2557do this:
2558.Sp
2559.Vb 1
2560\& #include <time.h>
2561\&
2562\& static ev_tstamp
2563\& my_rescheduler (ev_periodic *w, ev_tstamp now)
2564\& {
2565\& time_t tnow = (time_t)now;
2566\& struct tm tm;
2567\& localtime_r (&tnow, &tm);
2568\&
2569\& tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
2570\& ++tm.tm_mday; // midnight next day
2571\&
2572\& return mktime (&tm);
2573\& }
2574.Ve
2575.Sp
2576Note: this code might run into trouble on days that have more then two
2577midnights (beginning and end).
1197.RE 2578.RE
1198.RS 4 2579.RS 4
1199.RE 2580.RE
1200.IP "ev_periodic_again (loop, ev_periodic *)" 4 2581.IP "ev_periodic_again (loop, ev_periodic *)" 4
1201.IX Item "ev_periodic_again (loop, ev_periodic *)" 2582.IX Item "ev_periodic_again (loop, ev_periodic *)"
1202Simply stops and restarts the periodic watcher again. This is only useful 2583Simply stops and restarts the periodic watcher again. This is only useful
1203when you changed some parameters or the reschedule callback would return 2584when you changed some parameters or the reschedule callback would return
1204a different time than the last time it was called (e.g. in a crond like 2585a different time than the last time it was called (e.g. in a crond like
1205program when the crontabs have changed). 2586program when the crontabs have changed).
2587.IP "ev_tstamp ev_periodic_at (ev_periodic *)" 4
2588.IX Item "ev_tstamp ev_periodic_at (ev_periodic *)"
2589When active, returns the absolute time that the watcher is supposed
2590to trigger next. This is not the same as the \f(CW\*(C`offset\*(C'\fR argument to
2591\&\f(CW\*(C`ev_periodic_set\*(C'\fR, but indeed works even in interval and manual
2592rescheduling modes.
2593.IP "ev_tstamp offset [read\-write]" 4
2594.IX Item "ev_tstamp offset [read-write]"
2595When repeating, this contains the offset value, otherwise this is the
2596absolute point in time (the \f(CW\*(C`offset\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR,
2597although libev might modify this value for better numerical stability).
2598.Sp
2599Can be modified any time, but changes only take effect when the periodic
2600timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
1206.IP "ev_tstamp interval [read\-write]" 4 2601.IP "ev_tstamp interval [read\-write]" 4
1207.IX Item "ev_tstamp interval [read-write]" 2602.IX Item "ev_tstamp interval [read-write]"
1208The current interval value. Can be modified any time, but changes only 2603The current interval value. Can be modified any time, but changes only
1209take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being 2604take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being
1210called. 2605called.
1211.IP "ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read\-write]" 4 2606.IP "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read\-write]" 4
1212.IX Item "ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]" 2607.IX Item "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]"
1213The current reschedule callback, or \f(CW0\fR, if this functionality is 2608The current reschedule callback, or \f(CW0\fR, if this functionality is
1214switched off. Can be changed any time, but changes only take effect when 2609switched off. Can be changed any time, but changes only take effect when
1215the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called. 2610the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
1216.PP 2611.PP
2612\fIExamples\fR
2613.IX Subsection "Examples"
2614.PP
1217Example: call a callback every hour, or, more precisely, whenever the 2615Example: Call a callback every hour, or, more precisely, whenever the
1218system clock is divisible by 3600. The callback invocation times have 2616system time is divisible by 3600. The callback invocation times have
1219potentially a lot of jittering, but good long-term stability. 2617potentially a lot of jitter, but good long-term stability.
1220.PP 2618.PP
1221.Vb 5 2619.Vb 5
1222\& static void 2620\& static void
1223\& clock_cb (struct ev_loop *loop, struct ev_io *w, int revents) 2621\& clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1224\& { 2622\& {
1225\& ... its now a full hour (UTC, or TAI or whatever your clock follows) 2623\& ... its now a full hour (UTC, or TAI or whatever your clock follows)
1226\& } 2624\& }
1227.Ve 2625\&
1228.PP
1229.Vb 3
1230\& struct ev_periodic hourly_tick; 2626\& ev_periodic hourly_tick;
1231\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0); 2627\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1232\& ev_periodic_start (loop, &hourly_tick); 2628\& ev_periodic_start (loop, &hourly_tick);
1233.Ve 2629.Ve
1234.PP 2630.PP
1235Example: the same as above, but use a reschedule callback to do it: 2631Example: The same as above, but use a reschedule callback to do it:
1236.PP 2632.PP
1237.Vb 1 2633.Vb 1
1238\& #include <math.h> 2634\& #include <math.h>
1239.Ve 2635\&
1240.PP
1241.Vb 5
1242\& static ev_tstamp 2636\& static ev_tstamp
1243\& my_scheduler_cb (struct ev_periodic *w, ev_tstamp now) 2637\& my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1244\& { 2638\& {
1245\& return fmod (now, 3600.) + 3600.; 2639\& return now + (3600. \- fmod (now, 3600.));
1246\& } 2640\& }
1247.Ve 2641\&
1248.PP
1249.Vb 1
1250\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb); 2642\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1251.Ve 2643.Ve
1252.PP 2644.PP
1253Example: call a callback every hour, starting now: 2645Example: Call a callback every hour, starting now:
1254.PP 2646.PP
1255.Vb 4 2647.Vb 4
1256\& struct ev_periodic hourly_tick; 2648\& ev_periodic hourly_tick;
1257\& ev_periodic_init (&hourly_tick, clock_cb, 2649\& ev_periodic_init (&hourly_tick, clock_cb,
1258\& fmod (ev_now (loop), 3600.), 3600., 0); 2650\& fmod (ev_now (loop), 3600.), 3600., 0);
1259\& ev_periodic_start (loop, &hourly_tick); 2651\& ev_periodic_start (loop, &hourly_tick);
1260.Ve 2652.Ve
1261.ie n .Sh """ev_signal"" \- signal me when a signal gets signalled!" 2653.ie n .SS """ev_signal"" \- signal me when a signal gets signalled!"
1262.el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled!" 2654.el .SS "\f(CWev_signal\fP \- signal me when a signal gets signalled!"
1263.IX Subsection "ev_signal - signal me when a signal gets signalled!" 2655.IX Subsection "ev_signal - signal me when a signal gets signalled!"
1264Signal watchers will trigger an event when the process receives a specific 2656Signal watchers will trigger an event when the process receives a specific
1265signal one or more times. Even though signals are very asynchronous, libev 2657signal one or more times. Even though signals are very asynchronous, libev
1266will try it's best to deliver signals synchronously, i.e. as part of the 2658will try its best to deliver signals synchronously, i.e. as part of the
1267normal event processing, like any other event. 2659normal event processing, like any other event.
1268.PP 2660.PP
2661If you want signals to be delivered truly asynchronously, just use
2662\&\f(CW\*(C`sigaction\*(C'\fR as you would do without libev and forget about sharing
2663the signal. You can even use \f(CW\*(C`ev_async\*(C'\fR from a signal handler to
2664synchronously wake up an event loop.
2665.PP
1269You can configure as many watchers as you like per signal. Only when the 2666You can configure as many watchers as you like for the same signal, but
1270first watcher gets started will libev actually register a signal watcher 2667only within the same loop, i.e. you can watch for \f(CW\*(C`SIGINT\*(C'\fR in your
1271with the kernel (thus it coexists with your own signal handlers as long 2668default loop and for \f(CW\*(C`SIGIO\*(C'\fR in another loop, but you cannot watch for
1272as you don't register any with libev). Similarly, when the last signal 2669\&\f(CW\*(C`SIGINT\*(C'\fR in both the default loop and another loop at the same time. At
1273watcher for a signal is stopped libev will reset the signal handler to 2670the moment, \f(CW\*(C`SIGCHLD\*(C'\fR is permanently tied to the default loop.
1274\&\s-1SIG_DFL\s0 (regardless of what it was set to before). 2671.PP
2672Only after the first watcher for a signal is started will libev actually
2673register something with the kernel. It thus coexists with your own signal
2674handlers as long as you don't register any with libev for the same signal.
2675.PP
2676If possible and supported, libev will install its handlers with
2677\&\f(CW\*(C`SA_RESTART\*(C'\fR (or equivalent) behaviour enabled, so system calls should
2678not be unduly interrupted. If you have a problem with system calls getting
2679interrupted by signals you can block all signals in an \f(CW\*(C`ev_check\*(C'\fR watcher
2680and unblock them in an \f(CW\*(C`ev_prepare\*(C'\fR watcher.
2681.PP
2682\fIThe special problem of inheritance over fork/execve/pthread_create\fR
2683.IX Subsection "The special problem of inheritance over fork/execve/pthread_create"
2684.PP
2685Both the signal mask (\f(CW\*(C`sigprocmask\*(C'\fR) and the signal disposition
2686(\f(CW\*(C`sigaction\*(C'\fR) are unspecified after starting a signal watcher (and after
2687stopping it again), that is, libev might or might not block the signal,
2688and might or might not set or restore the installed signal handler (but
2689see \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR).
2690.PP
2691While this does not matter for the signal disposition (libev never
2692sets signals to \f(CW\*(C`SIG_IGN\*(C'\fR, so handlers will be reset to \f(CW\*(C`SIG_DFL\*(C'\fR on
2693\&\f(CW\*(C`execve\*(C'\fR), this matters for the signal mask: many programs do not expect
2694certain signals to be blocked.
2695.PP
2696This means that before calling \f(CW\*(C`exec\*(C'\fR (from the child) you should reset
2697the signal mask to whatever \*(L"default\*(R" you expect (all clear is a good
2698choice usually).
2699.PP
2700The simplest way to ensure that the signal mask is reset in the child is
2701to install a fork handler with \f(CW\*(C`pthread_atfork\*(C'\fR that resets it. That will
2702catch fork calls done by libraries (such as the libc) as well.
2703.PP
2704In current versions of libev, the signal will not be blocked indefinitely
2705unless you use the \f(CW\*(C`signalfd\*(C'\fR \s-1API\s0 (\f(CW\*(C`EV_SIGNALFD\*(C'\fR). While this reduces
2706the window of opportunity for problems, it will not go away, as libev
2707\&\fIhas\fR to modify the signal mask, at least temporarily.
2708.PP
2709So I can't stress this enough: \fIIf you do not reset your signal mask when
2710you expect it to be empty, you have a race condition in your code\fR. This
2711is not a libev-specific thing, this is true for most event libraries.
2712.PP
2713\fIThe special problem of threads signal handling\fR
2714.IX Subsection "The special problem of threads signal handling"
2715.PP
2716\&\s-1POSIX\s0 threads has problematic signal handling semantics, specifically,
2717a lot of functionality (sigfd, sigwait etc.) only really works if all
2718threads in a process block signals, which is hard to achieve.
2719.PP
2720When you want to use sigwait (or mix libev signal handling with your own
2721for the same signals), you can tackle this problem by globally blocking
2722all signals before creating any threads (or creating them with a fully set
2723sigprocmask) and also specifying the \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR when creating
2724loops. Then designate one thread as \*(L"signal receiver thread\*(R" which handles
2725these signals. You can pass on any signals that libev might be interested
2726in by calling \f(CW\*(C`ev_feed_signal\*(C'\fR.
2727.PP
2728\fIWatcher-Specific Functions and Data Members\fR
2729.IX Subsection "Watcher-Specific Functions and Data Members"
1275.IP "ev_signal_init (ev_signal *, callback, int signum)" 4 2730.IP "ev_signal_init (ev_signal *, callback, int signum)" 4
1276.IX Item "ev_signal_init (ev_signal *, callback, int signum)" 2731.IX Item "ev_signal_init (ev_signal *, callback, int signum)"
1277.PD 0 2732.PD 0
1278.IP "ev_signal_set (ev_signal *, int signum)" 4 2733.IP "ev_signal_set (ev_signal *, int signum)" 4
1279.IX Item "ev_signal_set (ev_signal *, int signum)" 2734.IX Item "ev_signal_set (ev_signal *, int signum)"
… …
1281Configures the watcher to trigger on the given signal number (usually one 2736Configures the watcher to trigger on the given signal number (usually one
1282of the \f(CW\*(C`SIGxxx\*(C'\fR constants). 2737of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
1283.IP "int signum [read\-only]" 4 2738.IP "int signum [read\-only]" 4
1284.IX Item "int signum [read-only]" 2739.IX Item "int signum [read-only]"
1285The signal the watcher watches out for. 2740The signal the watcher watches out for.
2741.PP
2742\fIExamples\fR
2743.IX Subsection "Examples"
2744.PP
2745Example: Try to exit cleanly on \s-1SIGINT.\s0
2746.PP
2747.Vb 5
2748\& static void
2749\& sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
2750\& {
2751\& ev_break (loop, EVBREAK_ALL);
2752\& }
2753\&
2754\& ev_signal signal_watcher;
2755\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
2756\& ev_signal_start (loop, &signal_watcher);
2757.Ve
1286.ie n .Sh """ev_child"" \- watch out for process status changes" 2758.ie n .SS """ev_child"" \- watch out for process status changes"
1287.el .Sh "\f(CWev_child\fP \- watch out for process status changes" 2759.el .SS "\f(CWev_child\fP \- watch out for process status changes"
1288.IX Subsection "ev_child - watch out for process status changes" 2760.IX Subsection "ev_child - watch out for process status changes"
1289Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to 2761Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
1290some child status changes (most typically when a child of yours dies). 2762some child status changes (most typically when a child of yours dies or
2763exits). It is permissible to install a child watcher \fIafter\fR the child
2764has been forked (which implies it might have already exited), as long
2765as the event loop isn't entered (or is continued from a watcher), i.e.,
2766forking and then immediately registering a watcher for the child is fine,
2767but forking and registering a watcher a few event loop iterations later or
2768in the next callback invocation is not.
2769.PP
2770Only the default event loop is capable of handling signals, and therefore
2771you can only register child watchers in the default event loop.
2772.PP
2773Due to some design glitches inside libev, child watchers will always be
2774handled at maximum priority (their priority is set to \f(CW\*(C`EV_MAXPRI\*(C'\fR by
2775libev)
2776.PP
2777\fIProcess Interaction\fR
2778.IX Subsection "Process Interaction"
2779.PP
2780Libev grabs \f(CW\*(C`SIGCHLD\*(C'\fR as soon as the default event loop is
2781initialised. This is necessary to guarantee proper behaviour even if the
2782first child watcher is started after the child exits. The occurrence
2783of \f(CW\*(C`SIGCHLD\*(C'\fR is recorded asynchronously, but child reaping is done
2784synchronously as part of the event loop processing. Libev always reaps all
2785children, even ones not watched.
2786.PP
2787\fIOverriding the Built-In Processing\fR
2788.IX Subsection "Overriding the Built-In Processing"
2789.PP
2790Libev offers no special support for overriding the built-in child
2791processing, but if your application collides with libev's default child
2792handler, you can override it easily by installing your own handler for
2793\&\f(CW\*(C`SIGCHLD\*(C'\fR after initialising the default loop, and making sure the
2794default loop never gets destroyed. You are encouraged, however, to use an
2795event-based approach to child reaping and thus use libev's support for
2796that, so other libev users can use \f(CW\*(C`ev_child\*(C'\fR watchers freely.
2797.PP
2798\fIStopping the Child Watcher\fR
2799.IX Subsection "Stopping the Child Watcher"
2800.PP
2801Currently, the child watcher never gets stopped, even when the
2802child terminates, so normally one needs to stop the watcher in the
2803callback. Future versions of libev might stop the watcher automatically
2804when a child exit is detected (calling \f(CW\*(C`ev_child_stop\*(C'\fR twice is not a
2805problem).
2806.PP
2807\fIWatcher-Specific Functions and Data Members\fR
2808.IX Subsection "Watcher-Specific Functions and Data Members"
1291.IP "ev_child_init (ev_child *, callback, int pid)" 4 2809.IP "ev_child_init (ev_child *, callback, int pid, int trace)" 4
1292.IX Item "ev_child_init (ev_child *, callback, int pid)" 2810.IX Item "ev_child_init (ev_child *, callback, int pid, int trace)"
1293.PD 0 2811.PD 0
1294.IP "ev_child_set (ev_child *, int pid)" 4 2812.IP "ev_child_set (ev_child *, int pid, int trace)" 4
1295.IX Item "ev_child_set (ev_child *, int pid)" 2813.IX Item "ev_child_set (ev_child *, int pid, int trace)"
1296.PD 2814.PD
1297Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or 2815Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
1298\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look 2816\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
1299at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see 2817at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
1300the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems 2818the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
1301\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the 2819\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
1302process causing the status change. 2820process causing the status change. \f(CW\*(C`trace\*(C'\fR must be either \f(CW0\fR (only
2821activate the watcher when the process terminates) or \f(CW1\fR (additionally
2822activate the watcher when the process is stopped or continued).
1303.IP "int pid [read\-only]" 4 2823.IP "int pid [read\-only]" 4
1304.IX Item "int pid [read-only]" 2824.IX Item "int pid [read-only]"
1305The process id this watcher watches out for, or \f(CW0\fR, meaning any process id. 2825The process id this watcher watches out for, or \f(CW0\fR, meaning any process id.
1306.IP "int rpid [read\-write]" 4 2826.IP "int rpid [read\-write]" 4
1307.IX Item "int rpid [read-write]" 2827.IX Item "int rpid [read-write]"
… …
1309.IP "int rstatus [read\-write]" 4 2829.IP "int rstatus [read\-write]" 4
1310.IX Item "int rstatus [read-write]" 2830.IX Item "int rstatus [read-write]"
1311The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems 2831The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems
1312\&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details). 2832\&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details).
1313.PP 2833.PP
1314Example: try to exit cleanly on \s-1SIGINT\s0 and \s-1SIGTERM\s0. 2834\fIExamples\fR
2835.IX Subsection "Examples"
1315.PP 2836.PP
2837Example: \f(CW\*(C`fork()\*(C'\fR a new process and install a child handler to wait for
2838its completion.
2839.PP
1316.Vb 5 2840.Vb 1
2841\& ev_child cw;
2842\&
1317\& static void 2843\& static void
1318\& sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents) 2844\& child_cb (EV_P_ ev_child *w, int revents)
1319\& { 2845\& {
1320\& ev_unloop (loop, EVUNLOOP_ALL); 2846\& ev_child_stop (EV_A_ w);
2847\& printf ("process %d exited with status %x\en", w\->rpid, w\->rstatus);
1321\& } 2848\& }
2849\&
2850\& pid_t pid = fork ();
2851\&
2852\& if (pid < 0)
2853\& // error
2854\& else if (pid == 0)
2855\& {
2856\& // the forked child executes here
2857\& exit (1);
2858\& }
2859\& else
2860\& {
2861\& ev_child_init (&cw, child_cb, pid, 0);
2862\& ev_child_start (EV_DEFAULT_ &cw);
2863\& }
1322.Ve 2864.Ve
1323.PP
1324.Vb 3
1325\& struct ev_signal signal_watcher;
1326\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1327\& ev_signal_start (loop, &sigint_cb);
1328.Ve
1329.ie n .Sh """ev_stat"" \- did the file attributes just change?" 2865.ie n .SS """ev_stat"" \- did the file attributes just change?"
1330.el .Sh "\f(CWev_stat\fP \- did the file attributes just change?" 2866.el .SS "\f(CWev_stat\fP \- did the file attributes just change?"
1331.IX Subsection "ev_stat - did the file attributes just change?" 2867.IX Subsection "ev_stat - did the file attributes just change?"
1332This watches a filesystem path for attribute changes. That is, it calls 2868This watches a file system path for attribute changes. That is, it calls
1333\&\f(CW\*(C`stat\*(C'\fR regularly (or when the \s-1OS\s0 says it changed) and sees if it changed 2869\&\f(CW\*(C`stat\*(C'\fR on that path in regular intervals (or when the \s-1OS\s0 says it changed)
1334compared to the last time, invoking the callback if it did. 2870and sees if it changed compared to the last time, invoking the callback
2871if it did. Starting the watcher \f(CW\*(C`stat\*(C'\fR's the file, so only changes that
2872happen after the watcher has been started will be reported.
1335.PP 2873.PP
1336The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does 2874The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does
1337not exist\*(R" is a status change like any other. The condition \*(L"path does 2875not exist\*(R" is a status change like any other. The condition \*(L"path does not
1338not exist\*(R" is signified by the \f(CW\*(C`st_nlink\*(C'\fR field being zero (which is 2876exist\*(R" (or more correctly \*(L"path cannot be stat'ed\*(R") is signified by the
1339otherwise always forced to be at least one) and all the other fields of 2877\&\f(CW\*(C`st_nlink\*(C'\fR field being zero (which is otherwise always forced to be at
1340the stat buffer having unspecified contents. 2878least one) and all the other fields of the stat buffer having unspecified
2879contents.
1341.PP 2880.PP
1342Since there is no standard to do this, the portable implementation simply 2881The path \fImust not\fR end in a slash or contain special components such as
1343calls \f(CW\*(C`stat (2)\*(C'\fR regulalry on the path to see if it changed somehow. You 2882\&\f(CW\*(C`.\*(C'\fR or \f(CW\*(C`..\*(C'\fR. The path \fIshould\fR be absolute: If it is relative and
1344can specify a recommended polling interval for this case. If you specify 2883your working directory changes, then the behaviour is undefined.
1345a polling interval of \f(CW0\fR (highly recommended!) then a \fIsuitable, 2884.PP
1346unspecified default\fR value will be used (which you can expect to be around 2885Since there is no portable change notification interface available, the
1347five seconds, although this might change dynamically). Libev will also 2886portable implementation simply calls \f(CWstat(2)\fR regularly on the path
1348impose a minimum interval which is currently around \f(CW0.1\fR, but thats 2887to see if it changed somehow. You can specify a recommended polling
1349usually overkill. 2888interval for this case. If you specify a polling interval of \f(CW0\fR (highly
2889recommended!) then a \fIsuitable, unspecified default\fR value will be used
2890(which you can expect to be around five seconds, although this might
2891change dynamically). Libev will also impose a minimum interval which is
2892currently around \f(CW0.1\fR, but that's usually overkill.
1350.PP 2893.PP
1351This watcher type is not meant for massive numbers of stat watchers, 2894This watcher type is not meant for massive numbers of stat watchers,
1352as even with OS-supported change notifications, this can be 2895as even with OS-supported change notifications, this can be
1353resource\-intensive. 2896resource-intensive.
1354.PP 2897.PP
1355At the time of this writing, no specific \s-1OS\s0 backends are implemented, but 2898At the time of this writing, the only OS-specific interface implemented
1356if demand increases, at least a kqueue and inotify backend will be added. 2899is the Linux inotify interface (implementing kqueue support is left as an
2900exercise for the reader. Note, however, that the author sees no way of
2901implementing \f(CW\*(C`ev_stat\*(C'\fR semantics with kqueue, except as a hint).
2902.PP
2903\fI\s-1ABI\s0 Issues (Largefile Support)\fR
2904.IX Subsection "ABI Issues (Largefile Support)"
2905.PP
2906Libev by default (unless the user overrides this) uses the default
2907compilation environment, which means that on systems with large file
2908support disabled by default, you get the 32 bit version of the stat
2909structure. When using the library from programs that change the \s-1ABI\s0 to
2910use 64 bit file offsets the programs will fail. In that case you have to
2911compile libev with the same flags to get binary compatibility. This is
2912obviously the case with any flags that change the \s-1ABI,\s0 but the problem is
2913most noticeably displayed with ev_stat and large file support.
2914.PP
2915The solution for this is to lobby your distribution maker to make large
2916file interfaces available by default (as e.g. FreeBSD does) and not
2917optional. Libev cannot simply switch on large file support because it has
2918to exchange stat structures with application programs compiled using the
2919default compilation environment.
2920.PP
2921\fIInotify and Kqueue\fR
2922.IX Subsection "Inotify and Kqueue"
2923.PP
2924When \f(CW\*(C`inotify (7)\*(C'\fR support has been compiled into libev and present at
2925runtime, it will be used to speed up change detection where possible. The
2926inotify descriptor will be created lazily when the first \f(CW\*(C`ev_stat\*(C'\fR
2927watcher is being started.
2928.PP
2929Inotify presence does not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers
2930except that changes might be detected earlier, and in some cases, to avoid
2931making regular \f(CW\*(C`stat\*(C'\fR calls. Even in the presence of inotify support
2932there are many cases where libev has to resort to regular \f(CW\*(C`stat\*(C'\fR polling,
2933but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
2934many bugs), the path exists (i.e. stat succeeds), and the path resides on
2935a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
2936xfs are fully working) libev usually gets away without polling.
2937.PP
2938There is no support for kqueue, as apparently it cannot be used to
2939implement this functionality, due to the requirement of having a file
2940descriptor open on the object at all times, and detecting renames, unlinks
2941etc. is difficult.
2942.PP
2943\fI\f(CI\*(C`stat ()\*(C'\fI is a synchronous operation\fR
2944.IX Subsection "stat () is a synchronous operation"
2945.PP
2946Libev doesn't normally do any kind of I/O itself, and so is not blocking
2947the process. The exception are \f(CW\*(C`ev_stat\*(C'\fR watchers \- those call \f(CW\*(C`stat
2948()\*(C'\fR, which is a synchronous operation.
2949.PP
2950For local paths, this usually doesn't matter: unless the system is very
2951busy or the intervals between stat's are large, a stat call will be fast,
2952as the path data is usually in memory already (except when starting the
2953watcher).
2954.PP
2955For networked file systems, calling \f(CW\*(C`stat ()\*(C'\fR can block an indefinite
2956time due to network issues, and even under good conditions, a stat call
2957often takes multiple milliseconds.
2958.PP
2959Therefore, it is best to avoid using \f(CW\*(C`ev_stat\*(C'\fR watchers on networked
2960paths, although this is fully supported by libev.
2961.PP
2962\fIThe special problem of stat time resolution\fR
2963.IX Subsection "The special problem of stat time resolution"
2964.PP
2965The \f(CW\*(C`stat ()\*(C'\fR system call only supports full-second resolution portably,
2966and even on systems where the resolution is higher, most file systems
2967still only support whole seconds.
2968.PP
2969That means that, if the time is the only thing that changes, you can
2970easily miss updates: on the first update, \f(CW\*(C`ev_stat\*(C'\fR detects a change and
2971calls your callback, which does something. When there is another update
2972within the same second, \f(CW\*(C`ev_stat\*(C'\fR will be unable to detect unless the
2973stat data does change in other ways (e.g. file size).
2974.PP
2975The solution to this is to delay acting on a change for slightly more
2976than a second (or till slightly after the next full second boundary), using
2977a roughly one-second-delay \f(CW\*(C`ev_timer\*(C'\fR (e.g. \f(CW\*(C`ev_timer_set (w, 0., 1.02);
2978ev_timer_again (loop, w)\*(C'\fR).
2979.PP
2980The \f(CW.02\fR offset is added to work around small timing inconsistencies
2981of some operating systems (where the second counter of the current time
2982might be be delayed. One such system is the Linux kernel, where a call to
2983\&\f(CW\*(C`gettimeofday\*(C'\fR might return a timestamp with a full second later than
2984a subsequent \f(CW\*(C`time\*(C'\fR call \- if the equivalent of \f(CW\*(C`time ()\*(C'\fR is used to
2985update file times then there will be a small window where the kernel uses
2986the previous second to update file times but libev might already execute
2987the timer callback).
2988.PP
2989\fIWatcher-Specific Functions and Data Members\fR
2990.IX Subsection "Watcher-Specific Functions and Data Members"
1357.IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4 2991.IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4
1358.IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 2992.IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)"
1359.PD 0 2993.PD 0
1360.IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4 2994.IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4
1361.IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 2995.IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)"
… …
1364\&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to 2998\&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to
1365be detected and should normally be specified as \f(CW0\fR to let libev choose 2999be detected and should normally be specified as \f(CW0\fR to let libev choose
1366a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same 3000a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same
1367path for as long as the watcher is active. 3001path for as long as the watcher is active.
1368.Sp 3002.Sp
1369The callback will be receive \f(CW\*(C`EV_STAT\*(C'\fR when a change was detected, 3003The callback will receive an \f(CW\*(C`EV_STAT\*(C'\fR event when a change was detected,
1370relative to the attributes at the time the watcher was started (or the 3004relative to the attributes at the time the watcher was started (or the
1371last change was detected). 3005last change was detected).
1372.IP "ev_stat_stat (ev_stat *)" 4 3006.IP "ev_stat_stat (loop, ev_stat *)" 4
1373.IX Item "ev_stat_stat (ev_stat *)" 3007.IX Item "ev_stat_stat (loop, ev_stat *)"
1374Updates the stat buffer immediately with new values. If you change the 3008Updates the stat buffer immediately with new values. If you change the
1375watched path in your callback, you could call this fucntion to avoid 3009watched path in your callback, you could call this function to avoid
1376detecting this change (while introducing a race condition). Can also be 3010detecting this change (while introducing a race condition if you are not
1377useful simply to find out the new values. 3011the only one changing the path). Can also be useful simply to find out the
3012new values.
1378.IP "ev_statdata attr [read\-only]" 4 3013.IP "ev_statdata attr [read\-only]" 4
1379.IX Item "ev_statdata attr [read-only]" 3014.IX Item "ev_statdata attr [read-only]"
1380The most-recently detected attributes of the file. Although the type is of 3015The most-recently detected attributes of the file. Although the type is
1381\&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types 3016\&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types
3017suitable for your system, but you can only rely on the POSIX-standardised
1382suitable for your system. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there 3018members to be present. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there was
1383was some error while \f(CW\*(C`stat\*(C'\fRing the file. 3019some error while \f(CW\*(C`stat\*(C'\fRing the file.
1384.IP "ev_statdata prev [read\-only]" 4 3020.IP "ev_statdata prev [read\-only]" 4
1385.IX Item "ev_statdata prev [read-only]" 3021.IX Item "ev_statdata prev [read-only]"
1386The previous attributes of the file. The callback gets invoked whenever 3022The previous attributes of the file. The callback gets invoked whenever
1387\&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR. 3023\&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR, or, more precisely, one or more of these members
3024differ: \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,
3025\&\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.
1388.IP "ev_tstamp interval [read\-only]" 4 3026.IP "ev_tstamp interval [read\-only]" 4
1389.IX Item "ev_tstamp interval [read-only]" 3027.IX Item "ev_tstamp interval [read-only]"
1390The specified interval. 3028The specified interval.
1391.IP "const char *path [read\-only]" 4 3029.IP "const char *path [read\-only]" 4
1392.IX Item "const char *path [read-only]" 3030.IX Item "const char *path [read-only]"
1393The filesystem path that is being watched. 3031The file system path that is being watched.
3032.PP
3033\fIExamples\fR
3034.IX Subsection "Examples"
1394.PP 3035.PP
1395Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes. 3036Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes.
1396.PP 3037.PP
1397.Vb 15 3038.Vb 10
1398\& static void 3039\& static void
1399\& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents) 3040\& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1400\& { 3041\& {
1401\& /* /etc/passwd changed in some way */ 3042\& /* /etc/passwd changed in some way */
1402\& if (w->attr.st_nlink) 3043\& if (w\->attr.st_nlink)
1403\& { 3044\& {
1404\& printf ("passwd current size %ld\en", (long)w->attr.st_size); 3045\& printf ("passwd current size %ld\en", (long)w\->attr.st_size);
1405\& printf ("passwd current atime %ld\en", (long)w->attr.st_mtime); 3046\& printf ("passwd current atime %ld\en", (long)w\->attr.st_mtime);
1406\& printf ("passwd current mtime %ld\en", (long)w->attr.st_mtime); 3047\& printf ("passwd current mtime %ld\en", (long)w\->attr.st_mtime);
1407\& } 3048\& }
1408\& else 3049\& else
1409\& /* you shalt not abuse printf for puts */ 3050\& /* you shalt not abuse printf for puts */
1410\& puts ("wow, /etc/passwd is not there, expect problems. " 3051\& puts ("wow, /etc/passwd is not there, expect problems. "
1411\& "if this is windows, they already arrived\en"); 3052\& "if this is windows, they already arrived\en");
1412\& } 3053\& }
3054\&
3055\& ...
3056\& ev_stat passwd;
3057\&
3058\& ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
3059\& ev_stat_start (loop, &passwd);
1413.Ve 3060.Ve
3061.PP
3062Example: Like above, but additionally use a one-second delay so we do not
3063miss updates (however, frequent updates will delay processing, too, so
3064one might do the work both on \f(CW\*(C`ev_stat\*(C'\fR callback invocation \fIand\fR on
3065\&\f(CW\*(C`ev_timer\*(C'\fR callback invocation).
1414.PP 3066.PP
1415.Vb 2 3067.Vb 2
3068\& static ev_stat passwd;
3069\& static ev_timer timer;
3070\&
3071\& static void
3072\& timer_cb (EV_P_ ev_timer *w, int revents)
3073\& {
3074\& ev_timer_stop (EV_A_ w);
3075\&
3076\& /* now it\*(Aqs one second after the most recent passwd change */
3077\& }
3078\&
3079\& static void
3080\& stat_cb (EV_P_ ev_stat *w, int revents)
3081\& {
3082\& /* reset the one\-second timer */
3083\& ev_timer_again (EV_A_ &timer);
3084\& }
3085\&
1416\& ... 3086\& ...
1417\& ev_stat passwd;
1418.Ve
1419.PP
1420.Vb 2
1421\& ev_stat_init (&passwd, passwd_cb, "/etc/passwd"); 3087\& ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1422\& ev_stat_start (loop, &passwd); 3088\& ev_stat_start (loop, &passwd);
3089\& ev_timer_init (&timer, timer_cb, 0., 1.02);
1423.Ve 3090.Ve
1424.ie n .Sh """ev_idle"" \- when you've got nothing better to do..." 3091.ie n .SS """ev_idle"" \- when you've got nothing better to do..."
1425.el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do..." 3092.el .SS "\f(CWev_idle\fP \- when you've got nothing better to do..."
1426.IX Subsection "ev_idle - when you've got nothing better to do..." 3093.IX Subsection "ev_idle - when you've got nothing better to do..."
1427Idle watchers trigger events when there are no other events are pending 3094Idle watchers trigger events when no other events of the same or higher
1428(prepare, check and other idle watchers do not count). That is, as long 3095priority are pending (prepare, check and other idle watchers do not count
1429as your process is busy handling sockets or timeouts (or even signals, 3096as receiving \*(L"events\*(R").
1430imagine) it will not be triggered. But when your process is idle all idle 3097.PP
1431watchers are being called again and again, once per event loop iteration \- 3098That is, as long as your process is busy handling sockets or timeouts
3099(or even signals, imagine) of the same or higher priority it will not be
3100triggered. But when your process is idle (or only lower-priority watchers
3101are pending), the idle watchers are being called once per event loop
1432until stopped, that is, or your process receives more events and becomes 3102iteration \- until stopped, that is, or your process receives more events
1433busy. 3103and becomes busy again with higher priority stuff.
1434.PP 3104.PP
1435The most noteworthy effect is that as long as any idle watchers are 3105The most noteworthy effect is that as long as any idle watchers are
1436active, the process will not block when waiting for new events. 3106active, the process will not block when waiting for new events.
1437.PP 3107.PP
1438Apart from keeping your process non-blocking (which is a useful 3108Apart from keeping your process non-blocking (which is a useful
1439effect on its own sometimes), idle watchers are a good place to do 3109effect on its own sometimes), idle watchers are a good place to do
1440\&\*(L"pseudo\-background processing\*(R", or delay processing stuff to after the 3110\&\*(L"pseudo-background processing\*(R", or delay processing stuff to after the
1441event loop has handled all outstanding events. 3111event loop has handled all outstanding events.
3112.PP
3113\fIAbusing an \f(CI\*(C`ev_idle\*(C'\fI watcher for its side-effect\fR
3114.IX Subsection "Abusing an ev_idle watcher for its side-effect"
3115.PP
3116As long as there is at least one active idle watcher, libev will never
3117sleep unnecessarily. Or in other words, it will loop as fast as possible.
3118For this to work, the idle watcher doesn't need to be invoked at all \- the
3119lowest priority will do.
3120.PP
3121This mode of operation can be useful together with an \f(CW\*(C`ev_check\*(C'\fR watcher,
3122to do something on each event loop iteration \- for example to balance load
3123between different connections.
3124.PP
3125See \*(L"Abusing an ev_check watcher for its side-effect\*(R" for a longer
3126example.
3127.PP
3128\fIWatcher-Specific Functions and Data Members\fR
3129.IX Subsection "Watcher-Specific Functions and Data Members"
1442.IP "ev_idle_init (ev_signal *, callback)" 4 3130.IP "ev_idle_init (ev_idle *, callback)" 4
1443.IX Item "ev_idle_init (ev_signal *, callback)" 3131.IX Item "ev_idle_init (ev_idle *, callback)"
1444Initialises and configures the idle watcher \- it has no parameters of any 3132Initialises and configures the idle watcher \- it has no parameters of any
1445kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless, 3133kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
1446believe me. 3134believe me.
1447.PP 3135.PP
3136\fIExamples\fR
3137.IX Subsection "Examples"
3138.PP
1448Example: dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR, start it, and in the 3139Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the
1449callback, free it. Alos, use no error checking, as usual. 3140callback, free it. Also, use no error checking, as usual.
1450.PP 3141.PP
1451.Vb 7 3142.Vb 5
1452\& static void 3143\& static void
1453\& idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents) 3144\& idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1454\& { 3145\& {
3146\& // stop the watcher
3147\& ev_idle_stop (loop, w);
3148\&
3149\& // now we can free it
1455\& free (w); 3150\& free (w);
3151\&
1456\& // now do something you wanted to do when the program has 3152\& // now do something you wanted to do when the program has
1457\& // no longer asnything immediate to do. 3153\& // no longer anything immediate to do.
1458\& } 3154\& }
1459.Ve 3155\&
1460.PP
1461.Vb 3
1462\& struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle)); 3156\& ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1463\& ev_idle_init (idle_watcher, idle_cb); 3157\& ev_idle_init (idle_watcher, idle_cb);
1464\& ev_idle_start (loop, idle_cb); 3158\& ev_idle_start (loop, idle_watcher);
1465.Ve 3159.Ve
1466.ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop!" 3160.ie n .SS """ev_prepare"" and ""ev_check"" \- customise your event loop!"
1467.el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!" 3161.el .SS "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!"
1468.IX Subsection "ev_prepare and ev_check - customise your event loop!" 3162.IX Subsection "ev_prepare and ev_check - customise your event loop!"
1469Prepare and check watchers are usually (but not always) used in tandem: 3163Prepare and check watchers are often (but not always) used in pairs:
1470prepare watchers get invoked before the process blocks and check watchers 3164prepare watchers get invoked before the process blocks and check watchers
1471afterwards. 3165afterwards.
1472.PP 3166.PP
1473You \fImust not\fR call \f(CW\*(C`ev_loop\*(C'\fR or similar functions that enter 3167You \fImust not\fR call \f(CW\*(C`ev_run\*(C'\fR (or similar functions that enter the
1474the current event loop from either \f(CW\*(C`ev_prepare\*(C'\fR or \f(CW\*(C`ev_check\*(C'\fR 3168current event loop) or \f(CW\*(C`ev_loop_fork\*(C'\fR from either \f(CW\*(C`ev_prepare\*(C'\fR or
1475watchers. Other loops than the current one are fine, however. The 3169\&\f(CW\*(C`ev_check\*(C'\fR watchers. Other loops than the current one are fine,
1476rationale behind this is that you do not need to check for recursion in 3170however. The rationale behind this is that you do not need to check
1477those watchers, i.e. the sequence will always be \f(CW\*(C`ev_prepare\*(C'\fR, blocking, 3171for recursion in those watchers, i.e. the sequence will always be
1478\&\f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each kind they will always be 3172\&\f(CW\*(C`ev_prepare\*(C'\fR, blocking, \f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each
1479called in pairs bracketing the blocking call. 3173kind they will always be called in pairs bracketing the blocking call.
1480.PP 3174.PP
1481Their main purpose is to integrate other event mechanisms into libev and 3175Their main purpose is to integrate other event mechanisms into libev and
1482their use is somewhat advanced. This could be used, for example, to track 3176their use is somewhat advanced. They could be used, for example, to track
1483variable changes, implement your own watchers, integrate net-snmp or a 3177variable changes, implement your own watchers, integrate net-snmp or a
1484coroutine library and lots more. They are also occasionally useful if 3178coroutine library and lots more. They are also occasionally useful if
1485you cache some data and want to flush it before blocking (for example, 3179you cache some data and want to flush it before blocking (for example,
1486in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR 3180in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR
1487watcher). 3181watcher).
1488.PP 3182.PP
1489This is done by examining in each prepare call which file descriptors need 3183This is done by examining in each prepare call which file descriptors
1490to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers for 3184need to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers
1491them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many libraries 3185for them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many
1492provide just this functionality). Then, in the check watcher you check for 3186libraries provide exactly this functionality). Then, in the check watcher,
1493any events that occured (by checking the pending status of all watchers 3187you check for any events that occurred (by checking the pending status
1494and stopping them) and call back into the library. The I/O and timer 3188of all watchers and stopping them) and call back into the library. The
1495callbacks will never actually be called (but must be valid nevertheless, 3189I/O and timer callbacks will never actually be called (but must be valid
1496because you never know, you know?). 3190nevertheless, because you never know, you know?).
1497.PP 3191.PP
1498As another example, the Perl Coro module uses these hooks to integrate 3192As another example, the Perl Coro module uses these hooks to integrate
1499coroutines into libev programs, by yielding to other active coroutines 3193coroutines into libev programs, by yielding to other active coroutines
1500during each prepare and only letting the process block if no coroutines 3194during each prepare and only letting the process block if no coroutines
1501are ready to run (it's actually more complicated: it only runs coroutines 3195are ready to run (it's actually more complicated: it only runs coroutines
1502with priority higher than or equal to the event loop and one coroutine 3196with priority higher than or equal to the event loop and one coroutine
1503of lower priority, but only once, using idle watchers to keep the event 3197of lower priority, but only once, using idle watchers to keep the event
1504loop from blocking if lower-priority coroutines are active, thus mapping 3198loop from blocking if lower-priority coroutines are active, thus mapping
1505low-priority coroutines to idle/background tasks). 3199low-priority coroutines to idle/background tasks).
3200.PP
3201When used for this purpose, it is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers
3202highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR) priority, to ensure that they are being run before
3203any other watchers after the poll (this doesn't matter for \f(CW\*(C`ev_prepare\*(C'\fR
3204watchers).
3205.PP
3206Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers, too) should not
3207activate (\*(L"feed\*(R") events into libev. While libev fully supports this, they
3208might get executed before other \f(CW\*(C`ev_check\*(C'\fR watchers did their job. As
3209\&\f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other (non-libev) event
3210loops those other event loops might be in an unusable state until their
3211\&\f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to coexist peacefully with
3212others).
3213.PP
3214\fIAbusing an \f(CI\*(C`ev_check\*(C'\fI watcher for its side-effect\fR
3215.IX Subsection "Abusing an ev_check watcher for its side-effect"
3216.PP
3217\&\f(CW\*(C`ev_check\*(C'\fR (and less often also \f(CW\*(C`ev_prepare\*(C'\fR) watchers can also be
3218useful because they are called once per event loop iteration. For
3219example, if you want to handle a large number of connections fairly, you
3220normally only do a bit of work for each active connection, and if there
3221is more work to do, you wait for the next event loop iteration, so other
3222connections have a chance of making progress.
3223.PP
3224Using an \f(CW\*(C`ev_check\*(C'\fR watcher is almost enough: it will be called on the
3225next event loop iteration. However, that isn't as soon as possible \-
3226without external events, your \f(CW\*(C`ev_check\*(C'\fR watcher will not be invoked.
3227.PP
3228This is where \f(CW\*(C`ev_idle\*(C'\fR watchers come in handy \- all you need is a
3229single global idle watcher that is active as long as you have one active
3230\&\f(CW\*(C`ev_check\*(C'\fR watcher. The \f(CW\*(C`ev_idle\*(C'\fR watcher makes sure the event loop
3231will not sleep, and the \f(CW\*(C`ev_check\*(C'\fR watcher makes sure a callback gets
3232invoked. Neither watcher alone can do that.
3233.PP
3234\fIWatcher-Specific Functions and Data Members\fR
3235.IX Subsection "Watcher-Specific Functions and Data Members"
1506.IP "ev_prepare_init (ev_prepare *, callback)" 4 3236.IP "ev_prepare_init (ev_prepare *, callback)" 4
1507.IX Item "ev_prepare_init (ev_prepare *, callback)" 3237.IX Item "ev_prepare_init (ev_prepare *, callback)"
1508.PD 0 3238.PD 0
1509.IP "ev_check_init (ev_check *, callback)" 4 3239.IP "ev_check_init (ev_check *, callback)" 4
1510.IX Item "ev_check_init (ev_check *, callback)" 3240.IX Item "ev_check_init (ev_check *, callback)"
1511.PD 3241.PD
1512Initialises and configures the prepare or check watcher \- they have no 3242Initialises and configures the prepare or check watcher \- they have no
1513parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR 3243parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
1514macros, but using them is utterly, utterly and completely pointless. 3244macros, but using them is utterly, utterly, utterly and completely
3245pointless.
1515.PP 3246.PP
1516Example: To include a library such as adns, you would add \s-1IO\s0 watchers 3247\fIExamples\fR
1517and a timeout watcher in a prepare handler, as required by libadns, and 3248.IX Subsection "Examples"
3249.PP
3250There are a number of principal ways to embed other event loops or modules
3251into libev. Here are some ideas on how to include libadns into libev
3252(there is a Perl module named \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could
3253use as a working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR embeds a
3254Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0 into the
3255Glib event loop).
3256.PP
3257Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler,
1518in a check watcher, destroy them and call into libadns. What follows is 3258and in a check watcher, destroy them and call into libadns. What follows
1519pseudo-code only of course: 3259is pseudo-code only of course. This requires you to either use a low
3260priority for the check watcher or use \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as
3261the callbacks for the IO/timeout watchers might not have been called yet.
1520.PP 3262.PP
1521.Vb 2 3263.Vb 2
1522\& static ev_io iow [nfd]; 3264\& static ev_io iow [nfd];
1523\& static ev_timer tw; 3265\& static ev_timer tw;
1524.Ve 3266\&
1525.PP
1526.Vb 9
1527\& static void 3267\& static void
1528\& io_cb (ev_loop *loop, ev_io *w, int revents) 3268\& io_cb (struct ev_loop *loop, ev_io *w, int revents)
1529\& { 3269\& {
1530\& // set the relevant poll flags
1531\& // could also call adns_processreadable etc. here
1532\& struct pollfd *fd = (struct pollfd *)w->data;
1533\& if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1534\& if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1535\& } 3270\& }
1536.Ve 3271\&
1537.PP
1538.Vb 7
1539\& // create io watchers for each fd and a timer before blocking 3272\& // create io watchers for each fd and a timer before blocking
1540\& static void 3273\& static void
1541\& adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents) 3274\& adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1542\& { 3275\& {
1543\& int timeout = 3600000;truct pollfd fds [nfd]; 3276\& int timeout = 3600000;
3277\& struct pollfd fds [nfd];
1544\& // actual code will need to loop here and realloc etc. 3278\& // actual code will need to loop here and realloc etc.
1545\& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ())); 3279\& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1546.Ve 3280\&
1547.PP
1548.Vb 3
1549\& /* the callback is illegal, but won't be called as we stop during check */ 3281\& /* the callback is illegal, but won\*(Aqt be called as we stop during check */
1550\& ev_timer_init (&tw, 0, timeout * 1e-3); 3282\& ev_timer_init (&tw, 0, timeout * 1e\-3, 0.);
1551\& ev_timer_start (loop, &tw); 3283\& ev_timer_start (loop, &tw);
1552.Ve 3284\&
1553.PP
1554.Vb 6
1555\& // create on ev_io per pollfd 3285\& // create one ev_io per pollfd
1556\& for (int i = 0; i < nfd; ++i) 3286\& for (int i = 0; i < nfd; ++i)
1557\& { 3287\& {
1558\& ev_io_init (iow + i, io_cb, fds [i].fd, 3288\& ev_io_init (iow + i, io_cb, fds [i].fd,
1559\& ((fds [i].events & POLLIN ? EV_READ : 0) 3289\& ((fds [i].events & POLLIN ? EV_READ : 0)
1560\& | (fds [i].events & POLLOUT ? EV_WRITE : 0))); 3290\& | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
3291\&
3292\& fds [i].revents = 0;
3293\& ev_io_start (loop, iow + i);
3294\& }
3295\& }
3296\&
3297\& // stop all watchers after blocking
3298\& static void
3299\& adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
3300\& {
3301\& ev_timer_stop (loop, &tw);
3302\&
3303\& for (int i = 0; i < nfd; ++i)
3304\& {
3305\& // set the relevant poll flags
3306\& // could also call adns_processreadable etc. here
3307\& struct pollfd *fd = fds + i;
3308\& int revents = ev_clear_pending (iow + i);
3309\& if (revents & EV_READ ) fd\->revents |= fd\->events & POLLIN;
3310\& if (revents & EV_WRITE) fd\->revents |= fd\->events & POLLOUT;
3311\&
3312\& // now stop the watcher
3313\& ev_io_stop (loop, iow + i);
3314\& }
3315\&
3316\& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
3317\& }
1561.Ve 3318.Ve
3319.PP
3320Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR
3321in the prepare watcher and would dispose of the check watcher.
3322.PP
3323Method 3: If the module to be embedded supports explicit event
3324notification (libadns does), you can also make use of the actual watcher
3325callbacks, and only destroy/create the watchers in the prepare watcher.
1562.PP 3326.PP
1563.Vb 5 3327.Vb 5
1564\& fds [i].revents = 0;
1565\& iow [i].data = fds + i;
1566\& ev_io_start (loop, iow + i);
1567\& }
1568\& }
1569.Ve
1570.PP
1571.Vb 5
1572\& // stop all watchers after blocking
1573\& static void 3328\& static void
1574\& adns_check_cb (ev_loop *loop, ev_check *w, int revents) 3329\& timer_cb (EV_P_ ev_timer *w, int revents)
1575\& { 3330\& {
1576\& ev_timer_stop (loop, &tw); 3331\& adns_state ads = (adns_state)w\->data;
1577.Ve 3332\& update_now (EV_A);
1578.PP 3333\&
1579.Vb 2 3334\& adns_processtimeouts (ads, &tv_now);
1580\& for (int i = 0; i < nfd; ++i)
1581\& ev_io_stop (loop, iow + i);
1582.Ve
1583.PP
1584.Vb 2
1585\& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1586\& } 3335\& }
3336\&
3337\& static void
3338\& io_cb (EV_P_ ev_io *w, int revents)
3339\& {
3340\& adns_state ads = (adns_state)w\->data;
3341\& update_now (EV_A);
3342\&
3343\& if (revents & EV_READ ) adns_processreadable (ads, w\->fd, &tv_now);
3344\& if (revents & EV_WRITE) adns_processwriteable (ads, w\->fd, &tv_now);
3345\& }
3346\&
3347\& // do not ever call adns_afterpoll
1587.Ve 3348.Ve
3349.PP
3350Method 4: Do not use a prepare or check watcher because the module you
3351want to embed is not flexible enough to support it. Instead, you can
3352override their poll function. The drawback with this solution is that the
3353main loop is now no longer controllable by \s-1EV.\s0 The \f(CW\*(C`Glib::EV\*(C'\fR module uses
3354this approach, effectively embedding \s-1EV\s0 as a client into the horrible
3355libglib event loop.
3356.PP
3357.Vb 4
3358\& static gint
3359\& event_poll_func (GPollFD *fds, guint nfds, gint timeout)
3360\& {
3361\& int got_events = 0;
3362\&
3363\& for (n = 0; n < nfds; ++n)
3364\& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
3365\&
3366\& if (timeout >= 0)
3367\& // create/start timer
3368\&
3369\& // poll
3370\& ev_run (EV_A_ 0);
3371\&
3372\& // stop timer again
3373\& if (timeout >= 0)
3374\& ev_timer_stop (EV_A_ &to);
3375\&
3376\& // stop io watchers again \- their callbacks should have set
3377\& for (n = 0; n < nfds; ++n)
3378\& ev_io_stop (EV_A_ iow [n]);
3379\&
3380\& return got_events;
3381\& }
3382.Ve
1588.ie n .Sh """ev_embed"" \- when one backend isn't enough..." 3383.ie n .SS """ev_embed"" \- when one backend isn't enough..."
1589.el .Sh "\f(CWev_embed\fP \- when one backend isn't enough..." 3384.el .SS "\f(CWev_embed\fP \- when one backend isn't enough..."
1590.IX Subsection "ev_embed - when one backend isn't enough..." 3385.IX Subsection "ev_embed - when one backend isn't enough..."
1591This is a rather advanced watcher type that lets you embed one event loop 3386This is a rather advanced watcher type that lets you embed one event loop
1592into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded 3387into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded
1593loop, other types of watchers might be handled in a delayed or incorrect 3388loop, other types of watchers might be handled in a delayed or incorrect
1594fashion and must not be used). 3389fashion and must not be used).
… …
1597prioritise I/O. 3392prioritise I/O.
1598.PP 3393.PP
1599As an example for a bug workaround, the kqueue backend might only support 3394As an example for a bug workaround, the kqueue backend might only support
1600sockets on some platform, so it is unusable as generic backend, but you 3395sockets on some platform, so it is unusable as generic backend, but you
1601still want to make use of it because you have many sockets and it scales 3396still want to make use of it because you have many sockets and it scales
1602so nicely. In this case, you would create a kqueue-based loop and embed it 3397so nicely. In this case, you would create a kqueue-based loop and embed
1603into your default loop (which might use e.g. poll). Overall operation will 3398it into your default loop (which might use e.g. poll). Overall operation
1604be a bit slower because first libev has to poll and then call kevent, but 3399will be a bit slower because first libev has to call \f(CW\*(C`poll\*(C'\fR and then
1605at least you can use both at what they are best. 3400\&\f(CW\*(C`kevent\*(C'\fR, but at least you can use both mechanisms for what they are
3401best: \f(CW\*(C`kqueue\*(C'\fR for scalable sockets and \f(CW\*(C`poll\*(C'\fR if you want it to work :)
1606.PP 3402.PP
1607As for prioritising I/O: rarely you have the case where some fds have 3403As for prioritising I/O: under rare circumstances you have the case where
1608to be watched and handled very quickly (with low latency), and even 3404some fds have to be watched and handled very quickly (with low latency),
1609priorities and idle watchers might have too much overhead. In this case 3405and even priorities and idle watchers might have too much overhead. In
1610you would put all the high priority stuff in one loop and all the rest in 3406this case you would put all the high priority stuff in one loop and all
1611a second one, and embed the second one in the first. 3407the rest in a second one, and embed the second one in the first.
1612.PP 3408.PP
1613As long as the watcher is active, the callback will be invoked every time 3409As long as the watcher is active, the callback will be invoked every
1614there might be events pending in the embedded loop. The callback must then 3410time there might be events pending in the embedded loop. The callback
1615call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single sweep and invoke 3411must then call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single
1616their callbacks (you could also start an idle watcher to give the embedded 3412sweep and invoke their callbacks (the callback doesn't need to invoke the
1617loop strictly lower priority for example). You can also set the callback 3413\&\f(CW\*(C`ev_embed_sweep\*(C'\fR function directly, it could also start an idle watcher
1618to \f(CW0\fR, in which case the embed watcher will automatically execute the 3414to give the embedded loop strictly lower priority for example).
1619embedded loop sweep.
1620.PP 3415.PP
1621As long as the watcher is started it will automatically handle events. The 3416You can also set the callback to \f(CW0\fR, in which case the embed watcher
1622callback will be invoked whenever some events have been handled. You can 3417will automatically execute the embedded loop sweep whenever necessary.
1623set the callback to \f(CW0\fR to avoid having to specify one if you are not
1624interested in that.
1625.PP 3418.PP
1626Also, there have not currently been made special provisions for forking: 3419Fork detection will be handled transparently while the \f(CW\*(C`ev_embed\*(C'\fR watcher
1627when you fork, you not only have to call \f(CW\*(C`ev_loop_fork\*(C'\fR on both loops, 3420is active, i.e., the embedded loop will automatically be forked when the
1628but you will also have to stop and restart any \f(CW\*(C`ev_embed\*(C'\fR watchers 3421embedding loop forks. In other cases, the user is responsible for calling
1629yourself. 3422\&\f(CW\*(C`ev_loop_fork\*(C'\fR on the embedded loop.
1630.PP 3423.PP
1631Unfortunately, not all backends are embeddable, only the ones returned by 3424Unfortunately, not all backends are embeddable: only the ones returned by
1632\&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any 3425\&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any
1633portable one. 3426portable one.
1634.PP 3427.PP
1635So when you want to use this feature you will always have to be prepared 3428So when you want to use this feature you will always have to be prepared
1636that you cannot get an embeddable loop. The recommended way to get around 3429that you cannot get an embeddable loop. The recommended way to get around
1637this is to have a separate variables for your embeddable loop, try to 3430this is to have a separate variables for your embeddable loop, try to
1638create it, and if that fails, use the normal loop for everything: 3431create it, and if that fails, use the normal loop for everything.
1639.PP 3432.PP
1640.Vb 3 3433\fI\f(CI\*(C`ev_embed\*(C'\fI and fork\fR
1641\& struct ev_loop *loop_hi = ev_default_init (0); 3434.IX Subsection "ev_embed and fork"
1642\& struct ev_loop *loop_lo = 0;
1643\& struct ev_embed embed;
1644.Ve
1645.PP 3435.PP
1646.Vb 5 3436While the \f(CW\*(C`ev_embed\*(C'\fR watcher is running, forks in the embedding loop will
1647\& // see if there is a chance of getting one that works 3437automatically be applied to the embedded loop as well, so no special
1648\& // (remember that a flags value of 0 means autodetection) 3438fork handling is required in that case. When the watcher is not running,
1649\& loop_lo = ev_embeddable_backends () & ev_recommended_backends () 3439however, it is still the task of the libev user to call \f(CW\*(C`ev_loop_fork ()\*(C'\fR
1650\& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ()) 3440as applicable.
1651\& : 0;
1652.Ve
1653.PP 3441.PP
1654.Vb 8 3442\fIWatcher-Specific Functions and Data Members\fR
1655\& // if we got one, then embed it, otherwise default to loop_hi 3443.IX Subsection "Watcher-Specific Functions and Data Members"
1656\& if (loop_lo)
1657\& {
1658\& ev_embed_init (&embed, 0, loop_lo);
1659\& ev_embed_start (loop_hi, &embed);
1660\& }
1661\& else
1662\& loop_lo = loop_hi;
1663.Ve
1664.IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4 3444.IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
1665.IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 3445.IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)"
1666.PD 0 3446.PD 0
1667.IP "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 4 3447.IP "ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)" 4
1668.IX Item "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 3448.IX Item "ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)"
1669.PD 3449.PD
1670Configures the watcher to embed the given loop, which must be 3450Configures the watcher to embed the given loop, which must be
1671embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be 3451embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be
1672invoked automatically, otherwise it is the responsibility of the callback 3452invoked automatically, otherwise it is the responsibility of the callback
1673to invoke it (it will continue to be called until the sweep has been done, 3453to invoke it (it will continue to be called until the sweep has been done,
1674if you do not want thta, you need to temporarily stop the embed watcher). 3454if you do not want that, you need to temporarily stop the embed watcher).
1675.IP "ev_embed_sweep (loop, ev_embed *)" 4 3455.IP "ev_embed_sweep (loop, ev_embed *)" 4
1676.IX Item "ev_embed_sweep (loop, ev_embed *)" 3456.IX Item "ev_embed_sweep (loop, ev_embed *)"
1677Make a single, non-blocking sweep over the embedded loop. This works 3457Make a single, non-blocking sweep over the embedded loop. This works
1678similarly to \f(CW\*(C`ev_loop (embedded_loop, EVLOOP_NONBLOCK)\*(C'\fR, but in the most 3458similarly to \f(CW\*(C`ev_run (embedded_loop, EVRUN_NOWAIT)\*(C'\fR, but in the most
1679apropriate way for embedded loops. 3459appropriate way for embedded loops.
1680.IP "struct ev_loop *loop [read\-only]" 4 3460.IP "struct ev_loop *other [read\-only]" 4
1681.IX Item "struct ev_loop *loop [read-only]" 3461.IX Item "struct ev_loop *other [read-only]"
1682The embedded event loop. 3462The embedded event loop.
3463.PP
3464\fIExamples\fR
3465.IX Subsection "Examples"
3466.PP
3467Example: Try to get an embeddable event loop and embed it into the default
3468event loop. If that is not possible, use the default loop. The default
3469loop is stored in \f(CW\*(C`loop_hi\*(C'\fR, while the embeddable loop is stored in
3470\&\f(CW\*(C`loop_lo\*(C'\fR (which is \f(CW\*(C`loop_hi\*(C'\fR in the case no embeddable loop can be
3471used).
3472.PP
3473.Vb 3
3474\& struct ev_loop *loop_hi = ev_default_init (0);
3475\& struct ev_loop *loop_lo = 0;
3476\& ev_embed embed;
3477\&
3478\& // see if there is a chance of getting one that works
3479\& // (remember that a flags value of 0 means autodetection)
3480\& loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3481\& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3482\& : 0;
3483\&
3484\& // if we got one, then embed it, otherwise default to loop_hi
3485\& if (loop_lo)
3486\& {
3487\& ev_embed_init (&embed, 0, loop_lo);
3488\& ev_embed_start (loop_hi, &embed);
3489\& }
3490\& else
3491\& loop_lo = loop_hi;
3492.Ve
3493.PP
3494Example: Check if kqueue is available but not recommended and create
3495a kqueue backend for use with sockets (which usually work with any
3496kqueue implementation). Store the kqueue/socket\-only event loop in
3497\&\f(CW\*(C`loop_socket\*(C'\fR. (One might optionally use \f(CW\*(C`EVFLAG_NOENV\*(C'\fR, too).
3498.PP
3499.Vb 3
3500\& struct ev_loop *loop = ev_default_init (0);
3501\& struct ev_loop *loop_socket = 0;
3502\& ev_embed embed;
3503\&
3504\& if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3505\& if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3506\& {
3507\& ev_embed_init (&embed, 0, loop_socket);
3508\& ev_embed_start (loop, &embed);
3509\& }
3510\&
3511\& if (!loop_socket)
3512\& loop_socket = loop;
3513\&
3514\& // now use loop_socket for all sockets, and loop for everything else
3515.Ve
1683.ie n .Sh """ev_fork"" \- the audacity to resume the event loop after a fork" 3516.ie n .SS """ev_fork"" \- the audacity to resume the event loop after a fork"
1684.el .Sh "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork" 3517.el .SS "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork"
1685.IX Subsection "ev_fork - the audacity to resume the event loop after a fork" 3518.IX Subsection "ev_fork - the audacity to resume the event loop after a fork"
1686Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because 3519Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because
1687whoever is a good citizen cared to tell libev about it by calling 3520whoever is a good citizen cared to tell libev about it by calling
1688\&\f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the 3521\&\f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the event loop blocks next
1689event loop blocks next and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called, 3522and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called, and only in the child
1690and only in the child after the fork. If whoever good citizen calling 3523after the fork. If whoever good citizen calling \f(CW\*(C`ev_default_fork\*(C'\fR cheats
1691\&\f(CW\*(C`ev_default_fork\*(C'\fR cheats and calls it in the wrong process, the fork 3524and calls it in the wrong process, the fork handlers will be invoked, too,
1692handlers will be invoked, too, of course. 3525of course.
3526.PP
3527\fIThe special problem of life after fork \- how is it possible?\fR
3528.IX Subsection "The special problem of life after fork - how is it possible?"
3529.PP
3530Most uses of \f(CW\*(C`fork ()\*(C'\fR consist of forking, then some simple calls to set
3531up/change the process environment, followed by a call to \f(CW\*(C`exec()\*(C'\fR. This
3532sequence should be handled by libev without any problems.
3533.PP
3534This changes when the application actually wants to do event handling
3535in the child, or both parent in child, in effect \*(L"continuing\*(R" after the
3536fork.
3537.PP
3538The default mode of operation (for libev, with application help to detect
3539forks) is to duplicate all the state in the child, as would be expected
3540when \fIeither\fR the parent \fIor\fR the child process continues.
3541.PP
3542When both processes want to continue using libev, then this is usually the
3543wrong result. In that case, usually one process (typically the parent) is
3544supposed to continue with all watchers in place as before, while the other
3545process typically wants to start fresh, i.e. without any active watchers.
3546.PP
3547The cleanest and most efficient way to achieve that with libev is to
3548simply create a new event loop, which of course will be \*(L"empty\*(R", and
3549use that for new watchers. This has the advantage of not touching more
3550memory than necessary, and thus avoiding the copy-on-write, and the
3551disadvantage of having to use multiple event loops (which do not support
3552signal watchers).
3553.PP
3554When this is not possible, or you want to use the default loop for
3555other reasons, then in the process that wants to start \*(L"fresh\*(R", call
3556\&\f(CW\*(C`ev_loop_destroy (EV_DEFAULT)\*(C'\fR followed by \f(CW\*(C`ev_default_loop (...)\*(C'\fR.
3557Destroying the default loop will \*(L"orphan\*(R" (not stop) all registered
3558watchers, so you have to be careful not to execute code that modifies
3559those watchers. Note also that in that case, you have to re-register any
3560signal watchers.
3561.PP
3562\fIWatcher-Specific Functions and Data Members\fR
3563.IX Subsection "Watcher-Specific Functions and Data Members"
1693.IP "ev_fork_init (ev_signal *, callback)" 4 3564.IP "ev_fork_init (ev_fork *, callback)" 4
1694.IX Item "ev_fork_init (ev_signal *, callback)" 3565.IX Item "ev_fork_init (ev_fork *, callback)"
1695Initialises and configures the fork watcher \- it has no parameters of any 3566Initialises and configures the fork watcher \- it has no parameters of any
1696kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless, 3567kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless,
1697believe me. 3568really.
3569.ie n .SS """ev_cleanup"" \- even the best things end"
3570.el .SS "\f(CWev_cleanup\fP \- even the best things end"
3571.IX Subsection "ev_cleanup - even the best things end"
3572Cleanup watchers are called just before the event loop is being destroyed
3573by a call to \f(CW\*(C`ev_loop_destroy\*(C'\fR.
3574.PP
3575While there is no guarantee that the event loop gets destroyed, cleanup
3576watchers provide a convenient method to install cleanup hooks for your
3577program, worker threads and so on \- you just to make sure to destroy the
3578loop when you want them to be invoked.
3579.PP
3580Cleanup watchers are invoked in the same way as any other watcher. Unlike
3581all other watchers, they do not keep a reference to the event loop (which
3582makes a lot of sense if you think about it). Like all other watchers, you
3583can call libev functions in the callback, except \f(CW\*(C`ev_cleanup_start\*(C'\fR.
3584.PP
3585\fIWatcher-Specific Functions and Data Members\fR
3586.IX Subsection "Watcher-Specific Functions and Data Members"
3587.IP "ev_cleanup_init (ev_cleanup *, callback)" 4
3588.IX Item "ev_cleanup_init (ev_cleanup *, callback)"
3589Initialises and configures the cleanup watcher \- it has no parameters of
3590any kind. There is a \f(CW\*(C`ev_cleanup_set\*(C'\fR macro, but using it is utterly
3591pointless, I assure you.
3592.PP
3593Example: Register an atexit handler to destroy the default loop, so any
3594cleanup functions are called.
3595.PP
3596.Vb 5
3597\& static void
3598\& program_exits (void)
3599\& {
3600\& ev_loop_destroy (EV_DEFAULT_UC);
3601\& }
3602\&
3603\& ...
3604\& atexit (program_exits);
3605.Ve
3606.ie n .SS """ev_async"" \- how to wake up an event loop"
3607.el .SS "\f(CWev_async\fP \- how to wake up an event loop"
3608.IX Subsection "ev_async - how to wake up an event loop"
3609In general, you cannot use an \f(CW\*(C`ev_loop\*(C'\fR from multiple threads or other
3610asynchronous sources such as signal handlers (as opposed to multiple event
3611loops \- those are of course safe to use in different threads).
3612.PP
3613Sometimes, however, you need to wake up an event loop you do not control,
3614for example because it belongs to another thread. This is what \f(CW\*(C`ev_async\*(C'\fR
3615watchers do: as long as the \f(CW\*(C`ev_async\*(C'\fR watcher is active, you can signal
3616it by calling \f(CW\*(C`ev_async_send\*(C'\fR, which is thread\- and signal safe.
3617.PP
3618This functionality is very similar to \f(CW\*(C`ev_signal\*(C'\fR watchers, as signals,
3619too, are asynchronous in nature, and signals, too, will be compressed
3620(i.e. the number of callback invocations may be less than the number of
3621\&\f(CW\*(C`ev_async_send\*(C'\fR calls). In fact, you could use signal watchers as a kind
3622of \*(L"global async watchers\*(R" by using a watcher on an otherwise unused
3623signal, and \f(CW\*(C`ev_feed_signal\*(C'\fR to signal this watcher from another thread,
3624even without knowing which loop owns the signal.
3625.PP
3626\fIQueueing\fR
3627.IX Subsection "Queueing"
3628.PP
3629\&\f(CW\*(C`ev_async\*(C'\fR does not support queueing of data in any way. The reason
3630is that the author does not know of a simple (or any) algorithm for a
3631multiple-writer-single-reader queue that works in all cases and doesn't
3632need elaborate support such as pthreads or unportable memory access
3633semantics.
3634.PP
3635That means that if you want to queue data, you have to provide your own
3636queue. But at least I can tell you how to implement locking around your
3637queue:
3638.IP "queueing from a signal handler context" 4
3639.IX Item "queueing from a signal handler context"
3640To implement race-free queueing, you simply add to the queue in the signal
3641handler but you block the signal handler in the watcher callback. Here is
3642an example that does that for some fictitious \s-1SIGUSR1\s0 handler:
3643.Sp
3644.Vb 1
3645\& static ev_async mysig;
3646\&
3647\& static void
3648\& sigusr1_handler (void)
3649\& {
3650\& sometype data;
3651\&
3652\& // no locking etc.
3653\& queue_put (data);
3654\& ev_async_send (EV_DEFAULT_ &mysig);
3655\& }
3656\&
3657\& static void
3658\& mysig_cb (EV_P_ ev_async *w, int revents)
3659\& {
3660\& sometype data;
3661\& sigset_t block, prev;
3662\&
3663\& sigemptyset (&block);
3664\& sigaddset (&block, SIGUSR1);
3665\& sigprocmask (SIG_BLOCK, &block, &prev);
3666\&
3667\& while (queue_get (&data))
3668\& process (data);
3669\&
3670\& if (sigismember (&prev, SIGUSR1)
3671\& sigprocmask (SIG_UNBLOCK, &block, 0);
3672\& }
3673.Ve
3674.Sp
3675(Note: pthreads in theory requires you to use \f(CW\*(C`pthread_setmask\*(C'\fR
3676instead of \f(CW\*(C`sigprocmask\*(C'\fR when you use threads, but libev doesn't do it
3677either...).
3678.IP "queueing from a thread context" 4
3679.IX Item "queueing from a thread context"
3680The strategy for threads is different, as you cannot (easily) block
3681threads but you can easily preempt them, so to queue safely you need to
3682employ a traditional mutex lock, such as in this pthread example:
3683.Sp
3684.Vb 2
3685\& static ev_async mysig;
3686\& static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
3687\&
3688\& static void
3689\& otherthread (void)
3690\& {
3691\& // only need to lock the actual queueing operation
3692\& pthread_mutex_lock (&mymutex);
3693\& queue_put (data);
3694\& pthread_mutex_unlock (&mymutex);
3695\&
3696\& ev_async_send (EV_DEFAULT_ &mysig);
3697\& }
3698\&
3699\& static void
3700\& mysig_cb (EV_P_ ev_async *w, int revents)
3701\& {
3702\& pthread_mutex_lock (&mymutex);
3703\&
3704\& while (queue_get (&data))
3705\& process (data);
3706\&
3707\& pthread_mutex_unlock (&mymutex);
3708\& }
3709.Ve
3710.PP
3711\fIWatcher-Specific Functions and Data Members\fR
3712.IX Subsection "Watcher-Specific Functions and Data Members"
3713.IP "ev_async_init (ev_async *, callback)" 4
3714.IX Item "ev_async_init (ev_async *, callback)"
3715Initialises and configures the async watcher \- it has no parameters of any
3716kind. There is a \f(CW\*(C`ev_async_set\*(C'\fR macro, but using it is utterly pointless,
3717trust me.
3718.IP "ev_async_send (loop, ev_async *)" 4
3719.IX Item "ev_async_send (loop, ev_async *)"
3720Sends/signals/activates the given \f(CW\*(C`ev_async\*(C'\fR watcher, that is, feeds
3721an \f(CW\*(C`EV_ASYNC\*(C'\fR event on the watcher into the event loop, and instantly
3722returns.
3723.Sp
3724Unlike \f(CW\*(C`ev_feed_event\*(C'\fR, this call is safe to do from other threads,
3725signal or similar contexts (see the discussion of \f(CW\*(C`EV_ATOMIC_T\*(C'\fR in the
3726embedding section below on what exactly this means).
3727.Sp
3728Note that, as with other watchers in libev, multiple events might get
3729compressed into a single callback invocation (another way to look at
3730this is that \f(CW\*(C`ev_async\*(C'\fR watchers are level-triggered: they are set on
3731\&\f(CW\*(C`ev_async_send\*(C'\fR, reset when the event loop detects that).
3732.Sp
3733This call incurs the overhead of at most one extra system call per event
3734loop iteration, if the event loop is blocked, and no syscall at all if
3735the event loop (or your program) is processing events. That means that
3736repeated calls are basically free (there is no need to avoid calls for
3737performance reasons) and that the overhead becomes smaller (typically
3738zero) under load.
3739.IP "bool = ev_async_pending (ev_async *)" 4
3740.IX Item "bool = ev_async_pending (ev_async *)"
3741Returns a non-zero value when \f(CW\*(C`ev_async_send\*(C'\fR has been called on the
3742watcher but the event has not yet been processed (or even noted) by the
3743event loop.
3744.Sp
3745\&\f(CW\*(C`ev_async_send\*(C'\fR sets a flag in the watcher and wakes up the loop. When
3746the loop iterates next and checks for the watcher to have become active,
3747it will reset the flag again. \f(CW\*(C`ev_async_pending\*(C'\fR can be used to very
3748quickly check whether invoking the loop might be a good idea.
3749.Sp
3750Not that this does \fInot\fR check whether the watcher itself is pending,
3751only whether it has been requested to make this watcher pending: there
3752is a time window between the event loop checking and resetting the async
3753notification, and the callback being invoked.
1698.SH "OTHER FUNCTIONS" 3754.SH "OTHER FUNCTIONS"
1699.IX Header "OTHER FUNCTIONS" 3755.IX Header "OTHER FUNCTIONS"
1700There are some other functions of possible interest. Described. Here. Now. 3756There are some other functions of possible interest. Described. Here. Now.
1701.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4 3757.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)" 4
1702.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 3758.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)"
1703This function combines a simple timer and an I/O watcher, calls your 3759This function combines a simple timer and an I/O watcher, calls your
1704callback on whichever event happens first and automatically stop both 3760callback on whichever event happens first and automatically stops both
1705watchers. This is useful if you want to wait for a single event on an fd 3761watchers. This is useful if you want to wait for a single event on an fd
1706or timeout without having to allocate/configure/start/stop/free one or 3762or timeout without having to allocate/configure/start/stop/free one or
1707more watchers yourself. 3763more watchers yourself.
1708.Sp 3764.Sp
1709If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and events 3765If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and the
1710is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for the given \f(CW\*(C`fd\*(C'\fR and 3766\&\f(CW\*(C`events\*(C'\fR argument is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for
1711\&\f(CW\*(C`events\*(C'\fR set will be craeted and started. 3767the given \f(CW\*(C`fd\*(C'\fR and \f(CW\*(C`events\*(C'\fR set will be created and started.
1712.Sp 3768.Sp
1713If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be 3769If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be
1714started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and 3770started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and
1715repeat = 0) will be started. While \f(CW0\fR is a valid timeout, it is of 3771repeat = 0) will be started. \f(CW0\fR is a valid timeout.
1716dubious value.
1717.Sp 3772.Sp
1718The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and gets 3773The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and is
1719passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of 3774passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of
1720\&\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 3775\&\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
1721value passed to \f(CW\*(C`ev_once\*(C'\fR: 3776value passed to \f(CW\*(C`ev_once\*(C'\fR. Note that it is possible to receive \fIboth\fR
3777a timeout and an io event at the same time \- you probably should give io
3778events precedence.
3779.Sp
3780Example: wait up to ten seconds for data to appear on \s-1STDIN_FILENO.\s0
1722.Sp 3781.Sp
1723.Vb 7 3782.Vb 7
1724\& static void stdin_ready (int revents, void *arg) 3783\& static void stdin_ready (int revents, void *arg)
3784\& {
3785\& if (revents & EV_READ)
3786\& /* stdin might have data for us, joy! */;
3787\& else if (revents & EV_TIMER)
3788\& /* doh, nothing entered */;
3789\& }
3790\&
3791\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3792.Ve
3793.IP "ev_feed_fd_event (loop, int fd, int revents)" 4
3794.IX Item "ev_feed_fd_event (loop, int fd, int revents)"
3795Feed an event on the given fd, as if a file descriptor backend detected
3796the given events.
3797.IP "ev_feed_signal_event (loop, int signum)" 4
3798.IX Item "ev_feed_signal_event (loop, int signum)"
3799Feed an event as if the given signal occurred. See also \f(CW\*(C`ev_feed_signal\*(C'\fR,
3800which is async-safe.
3801.SH "COMMON OR USEFUL IDIOMS (OR BOTH)"
3802.IX Header "COMMON OR USEFUL IDIOMS (OR BOTH)"
3803This section explains some common idioms that are not immediately
3804obvious. Note that examples are sprinkled over the whole manual, and this
3805section only contains stuff that wouldn't fit anywhere else.
3806.SS "\s-1ASSOCIATING CUSTOM DATA WITH A WATCHER\s0"
3807.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"
3808Each watcher has, by default, a \f(CW\*(C`void *data\*(C'\fR member that you can read
3809or modify at any time: libev will completely ignore it. This can be used
3810to associate arbitrary data with your watcher. If you need more data and
3811don't want to allocate memory separately and store a pointer to it in that
3812data member, you can also \*(L"subclass\*(R" the watcher type and provide your own
3813data:
3814.PP
3815.Vb 7
3816\& struct my_io
3817\& {
3818\& ev_io io;
3819\& int otherfd;
3820\& void *somedata;
3821\& struct whatever *mostinteresting;
3822\& };
3823\&
3824\& ...
3825\& struct my_io w;
3826\& ev_io_init (&w.io, my_cb, fd, EV_READ);
3827.Ve
3828.PP
3829And since your callback will be called with a pointer to the watcher, you
3830can cast it back to your own type:
3831.PP
3832.Vb 5
3833\& static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
3834\& {
3835\& struct my_io *w = (struct my_io *)w_;
3836\& ...
3837\& }
3838.Ve
3839.PP
3840More interesting and less C\-conformant ways of casting your callback
3841function type instead have been omitted.
3842.SS "\s-1BUILDING YOUR OWN COMPOSITE WATCHERS\s0"
3843.IX Subsection "BUILDING YOUR OWN COMPOSITE WATCHERS"
3844Another common scenario is to use some data structure with multiple
3845embedded watchers, in effect creating your own watcher that combines
3846multiple libev event sources into one \*(L"super-watcher\*(R":
3847.PP
3848.Vb 6
3849\& struct my_biggy
3850\& {
3851\& int some_data;
3852\& ev_timer t1;
3853\& ev_timer t2;
3854\& }
3855.Ve
3856.PP
3857In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more
3858complicated: Either you store the address of your \f(CW\*(C`my_biggy\*(C'\fR struct in
3859the \f(CW\*(C`data\*(C'\fR member of the watcher (for woozies or \*(C+ coders), or you need
3860to use some pointer arithmetic using \f(CW\*(C`offsetof\*(C'\fR inside your watchers (for
3861real programmers):
3862.PP
3863.Vb 1
3864\& #include <stddef.h>
3865\&
3866\& static void
3867\& t1_cb (EV_P_ ev_timer *w, int revents)
3868\& {
3869\& struct my_biggy big = (struct my_biggy *)
3870\& (((char *)w) \- offsetof (struct my_biggy, t1));
3871\& }
3872\&
3873\& static void
3874\& t2_cb (EV_P_ ev_timer *w, int revents)
3875\& {
3876\& struct my_biggy big = (struct my_biggy *)
3877\& (((char *)w) \- offsetof (struct my_biggy, t2));
3878\& }
3879.Ve
3880.SS "\s-1AVOIDING FINISHING BEFORE RETURNING\s0"
3881.IX Subsection "AVOIDING FINISHING BEFORE RETURNING"
3882Often you have structures like this in event-based programs:
3883.PP
3884.Vb 4
3885\& callback ()
1725\& { 3886\& {
1726\& if (revents & EV_TIMEOUT) 3887\& free (request);
1727\& /* doh, nothing entered */;
1728\& else if (revents & EV_READ)
1729\& /* stdin might have data for us, joy! */;
1730\& } 3888\& }
3889\&
3890\& request = start_new_request (..., callback);
1731.Ve 3891.Ve
1732.Sp 3892.PP
3893The intent is to start some \*(L"lengthy\*(R" operation. The \f(CW\*(C`request\*(C'\fR could be
3894used to cancel the operation, or do other things with it.
3895.PP
3896It's not uncommon to have code paths in \f(CW\*(C`start_new_request\*(C'\fR that
3897immediately invoke the callback, for example, to report errors. Or you add
3898some caching layer that finds that it can skip the lengthy aspects of the
3899operation and simply invoke the callback with the result.
3900.PP
3901The problem here is that this will happen \fIbefore\fR \f(CW\*(C`start_new_request\*(C'\fR
3902has returned, so \f(CW\*(C`request\*(C'\fR is not set.
3903.PP
3904Even if you pass the request by some safer means to the callback, you
3905might want to do something to the request after starting it, such as
3906canceling it, which probably isn't working so well when the callback has
3907already been invoked.
3908.PP
3909A common way around all these issues is to make sure that
3910\&\f(CW\*(C`start_new_request\*(C'\fR \fIalways\fR returns before the callback is invoked. If
3911\&\f(CW\*(C`start_new_request\*(C'\fR immediately knows the result, it can artificially
3912delay invoking the callback by using a \f(CW\*(C`prepare\*(C'\fR or \f(CW\*(C`idle\*(C'\fR watcher for
3913example, or more sneakily, by reusing an existing (stopped) watcher and
3914pushing it into the pending queue:
3915.PP
1733.Vb 1 3916.Vb 2
1734\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0); 3917\& ev_set_cb (watcher, callback);
3918\& ev_feed_event (EV_A_ watcher, 0);
1735.Ve 3919.Ve
1736.IP "ev_feed_event (ev_loop *, watcher *, int revents)" 4 3920.PP
1737.IX Item "ev_feed_event (ev_loop *, watcher *, int revents)" 3921This way, \f(CW\*(C`start_new_request\*(C'\fR can safely return before the callback is
1738Feeds the given event set into the event loop, as if the specified event 3922invoked, while not delaying callback invocation too much.
1739had happened for the specified watcher (which must be a pointer to an 3923.SS "\s-1MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS\s0"
1740initialised but not necessarily started event watcher). 3924.IX Subsection "MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS"
1741.IP "ev_feed_fd_event (ev_loop *, int fd, int revents)" 4 3925Often (especially in \s-1GUI\s0 toolkits) there are places where you have
1742.IX Item "ev_feed_fd_event (ev_loop *, int fd, int revents)" 3926\&\fImodal\fR interaction, which is most easily implemented by recursively
1743Feed an event on the given fd, as if a file descriptor backend detected 3927invoking \f(CW\*(C`ev_run\*(C'\fR.
1744the given events it. 3928.PP
1745.IP "ev_feed_signal_event (ev_loop *loop, int signum)" 4 3929This brings the problem of exiting \- a callback might want to finish the
1746.IX Item "ev_feed_signal_event (ev_loop *loop, int signum)" 3930main \f(CW\*(C`ev_run\*(C'\fR call, but not the nested one (e.g. user clicked \*(L"Quit\*(R", but
1747Feed an event as if the given signal occured (\f(CW\*(C`loop\*(C'\fR must be the default 3931a modal \*(L"Are you sure?\*(R" dialog is still waiting), or just the nested one
1748loop!). 3932and not the main one (e.g. user clocked \*(L"Ok\*(R" in a modal dialog), or some
3933other combination: In these cases, a simple \f(CW\*(C`ev_break\*(C'\fR will not work.
3934.PP
3935The solution is to maintain \*(L"break this loop\*(R" variable for each \f(CW\*(C`ev_run\*(C'\fR
3936invocation, and use a loop around \f(CW\*(C`ev_run\*(C'\fR until the condition is
3937triggered, using \f(CW\*(C`EVRUN_ONCE\*(C'\fR:
3938.PP
3939.Vb 2
3940\& // main loop
3941\& int exit_main_loop = 0;
3942\&
3943\& while (!exit_main_loop)
3944\& ev_run (EV_DEFAULT_ EVRUN_ONCE);
3945\&
3946\& // in a modal watcher
3947\& int exit_nested_loop = 0;
3948\&
3949\& while (!exit_nested_loop)
3950\& ev_run (EV_A_ EVRUN_ONCE);
3951.Ve
3952.PP
3953To exit from any of these loops, just set the corresponding exit variable:
3954.PP
3955.Vb 2
3956\& // exit modal loop
3957\& exit_nested_loop = 1;
3958\&
3959\& // exit main program, after modal loop is finished
3960\& exit_main_loop = 1;
3961\&
3962\& // exit both
3963\& exit_main_loop = exit_nested_loop = 1;
3964.Ve
3965.SS "\s-1THREAD LOCKING EXAMPLE\s0"
3966.IX Subsection "THREAD LOCKING EXAMPLE"
3967Here is a fictitious example of how to run an event loop in a different
3968thread from where callbacks are being invoked and watchers are
3969created/added/removed.
3970.PP
3971For a real-world example, see the \f(CW\*(C`EV::Loop::Async\*(C'\fR perl module,
3972which uses exactly this technique (which is suited for many high-level
3973languages).
3974.PP
3975The example uses a pthread mutex to protect the loop data, a condition
3976variable to wait for callback invocations, an async watcher to notify the
3977event loop thread and an unspecified mechanism to wake up the main thread.
3978.PP
3979First, you need to associate some data with the event loop:
3980.PP
3981.Vb 6
3982\& typedef struct {
3983\& mutex_t lock; /* global loop lock */
3984\& ev_async async_w;
3985\& thread_t tid;
3986\& cond_t invoke_cv;
3987\& } userdata;
3988\&
3989\& void prepare_loop (EV_P)
3990\& {
3991\& // for simplicity, we use a static userdata struct.
3992\& static userdata u;
3993\&
3994\& ev_async_init (&u\->async_w, async_cb);
3995\& ev_async_start (EV_A_ &u\->async_w);
3996\&
3997\& pthread_mutex_init (&u\->lock, 0);
3998\& pthread_cond_init (&u\->invoke_cv, 0);
3999\&
4000\& // now associate this with the loop
4001\& ev_set_userdata (EV_A_ u);
4002\& ev_set_invoke_pending_cb (EV_A_ l_invoke);
4003\& ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4004\&
4005\& // then create the thread running ev_run
4006\& pthread_create (&u\->tid, 0, l_run, EV_A);
4007\& }
4008.Ve
4009.PP
4010The callback for the \f(CW\*(C`ev_async\*(C'\fR watcher does nothing: the watcher is used
4011solely to wake up the event loop so it takes notice of any new watchers
4012that might have been added:
4013.PP
4014.Vb 5
4015\& static void
4016\& async_cb (EV_P_ ev_async *w, int revents)
4017\& {
4018\& // just used for the side effects
4019\& }
4020.Ve
4021.PP
4022The \f(CW\*(C`l_release\*(C'\fR and \f(CW\*(C`l_acquire\*(C'\fR callbacks simply unlock/lock the mutex
4023protecting the loop data, respectively.
4024.PP
4025.Vb 6
4026\& static void
4027\& l_release (EV_P)
4028\& {
4029\& userdata *u = ev_userdata (EV_A);
4030\& pthread_mutex_unlock (&u\->lock);
4031\& }
4032\&
4033\& static void
4034\& l_acquire (EV_P)
4035\& {
4036\& userdata *u = ev_userdata (EV_A);
4037\& pthread_mutex_lock (&u\->lock);
4038\& }
4039.Ve
4040.PP
4041The event loop thread first acquires the mutex, and then jumps straight
4042into \f(CW\*(C`ev_run\*(C'\fR:
4043.PP
4044.Vb 4
4045\& void *
4046\& l_run (void *thr_arg)
4047\& {
4048\& struct ev_loop *loop = (struct ev_loop *)thr_arg;
4049\&
4050\& l_acquire (EV_A);
4051\& pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4052\& ev_run (EV_A_ 0);
4053\& l_release (EV_A);
4054\&
4055\& return 0;
4056\& }
4057.Ve
4058.PP
4059Instead of invoking all pending watchers, the \f(CW\*(C`l_invoke\*(C'\fR callback will
4060signal the main thread via some unspecified mechanism (signals? pipe
4061writes? \f(CW\*(C`Async::Interrupt\*(C'\fR?) and then waits until all pending watchers
4062have been called (in a while loop because a) spurious wakeups are possible
4063and b) skipping inter-thread-communication when there are no pending
4064watchers is very beneficial):
4065.PP
4066.Vb 4
4067\& static void
4068\& l_invoke (EV_P)
4069\& {
4070\& userdata *u = ev_userdata (EV_A);
4071\&
4072\& while (ev_pending_count (EV_A))
4073\& {
4074\& wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4075\& pthread_cond_wait (&u\->invoke_cv, &u\->lock);
4076\& }
4077\& }
4078.Ve
4079.PP
4080Now, whenever the main thread gets told to invoke pending watchers, it
4081will grab the lock, call \f(CW\*(C`ev_invoke_pending\*(C'\fR and then signal the loop
4082thread to continue:
4083.PP
4084.Vb 4
4085\& static void
4086\& real_invoke_pending (EV_P)
4087\& {
4088\& userdata *u = ev_userdata (EV_A);
4089\&
4090\& pthread_mutex_lock (&u\->lock);
4091\& ev_invoke_pending (EV_A);
4092\& pthread_cond_signal (&u\->invoke_cv);
4093\& pthread_mutex_unlock (&u\->lock);
4094\& }
4095.Ve
4096.PP
4097Whenever you want to start/stop a watcher or do other modifications to an
4098event loop, you will now have to lock:
4099.PP
4100.Vb 2
4101\& ev_timer timeout_watcher;
4102\& userdata *u = ev_userdata (EV_A);
4103\&
4104\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4105\&
4106\& pthread_mutex_lock (&u\->lock);
4107\& ev_timer_start (EV_A_ &timeout_watcher);
4108\& ev_async_send (EV_A_ &u\->async_w);
4109\& pthread_mutex_unlock (&u\->lock);
4110.Ve
4111.PP
4112Note that sending the \f(CW\*(C`ev_async\*(C'\fR watcher is required because otherwise
4113an event loop currently blocking in the kernel will have no knowledge
4114about the newly added timer. By waking up the loop it will pick up any new
4115watchers in the next event loop iteration.
4116.SS "\s-1THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS\s0"
4117.IX Subsection "THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS"
4118While the overhead of a callback that e.g. schedules a thread is small, it
4119is still an overhead. If you embed libev, and your main usage is with some
4120kind of threads or coroutines, you might want to customise libev so that
4121doesn't need callbacks anymore.
4122.PP
4123Imagine you have coroutines that you can switch to using a function
4124\&\f(CW\*(C`switch_to (coro)\*(C'\fR, that libev runs in a coroutine called \f(CW\*(C`libev_coro\*(C'\fR
4125and that due to some magic, the currently active coroutine is stored in a
4126global called \f(CW\*(C`current_coro\*(C'\fR. Then you can build your own \*(L"wait for libev
4127event\*(R" primitive by changing \f(CW\*(C`EV_CB_DECLARE\*(C'\fR and \f(CW\*(C`EV_CB_INVOKE\*(C'\fR (note
4128the differing \f(CW\*(C`;\*(C'\fR conventions):
4129.PP
4130.Vb 2
4131\& #define EV_CB_DECLARE(type) struct my_coro *cb;
4132\& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb)
4133.Ve
4134.PP
4135That means instead of having a C callback function, you store the
4136coroutine to switch to in each watcher, and instead of having libev call
4137your callback, you instead have it switch to that coroutine.
4138.PP
4139A coroutine might now wait for an event with a function called
4140\&\f(CW\*(C`wait_for_event\*(C'\fR. (the watcher needs to be started, as always, but it doesn't
4141matter when, or whether the watcher is active or not when this function is
4142called):
4143.PP
4144.Vb 6
4145\& void
4146\& wait_for_event (ev_watcher *w)
4147\& {
4148\& ev_set_cb (w, current_coro);
4149\& switch_to (libev_coro);
4150\& }
4151.Ve
4152.PP
4153That basically suspends the coroutine inside \f(CW\*(C`wait_for_event\*(C'\fR and
4154continues the libev coroutine, which, when appropriate, switches back to
4155this or any other coroutine.
4156.PP
4157You can do similar tricks if you have, say, threads with an event queue \-
4158instead of storing a coroutine, you store the queue object and instead of
4159switching to a coroutine, you push the watcher onto the queue and notify
4160any waiters.
4161.PP
4162To embed libev, see \*(L"\s-1EMBEDDING\*(R"\s0, but in short, it's easiest to create two
4163files, \fImy_ev.h\fR and \fImy_ev.c\fR that include the respective libev files:
4164.PP
4165.Vb 4
4166\& // my_ev.h
4167\& #define EV_CB_DECLARE(type) struct my_coro *cb;
4168\& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb)
4169\& #include "../libev/ev.h"
4170\&
4171\& // my_ev.c
4172\& #define EV_H "my_ev.h"
4173\& #include "../libev/ev.c"
4174.Ve
4175.PP
4176And then use \fImy_ev.h\fR when you would normally use \fIev.h\fR, and compile
4177\&\fImy_ev.c\fR into your project. When properly specifying include paths, you
4178can even use \fIev.h\fR as header file name directly.
1749.SH "LIBEVENT EMULATION" 4179.SH "LIBEVENT EMULATION"
1750.IX Header "LIBEVENT EMULATION" 4180.IX Header "LIBEVENT EMULATION"
1751Libev offers a compatibility emulation layer for libevent. It cannot 4181Libev offers a compatibility emulation layer for libevent. It cannot
1752emulate the internals of libevent, so here are some usage hints: 4182emulate the internals of libevent, so here are some usage hints:
4183.IP "\(bu" 4
4184Only the libevent\-1.4.1\-beta \s-1API\s0 is being emulated.
4185.Sp
4186This was the newest libevent version available when libev was implemented,
4187and is still mostly unchanged in 2010.
4188.IP "\(bu" 4
1753.IP "* Use it by including <event.h>, as usual." 4 4189Use it by including <event.h>, as usual.
1754.IX Item "Use it by including <event.h>, as usual." 4190.IP "\(bu" 4
1755.PD 0 4191The following members are fully supported: ev_base, ev_callback,
1756.IP "* The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4 4192ev_arg, ev_fd, ev_res, ev_events.
1757.IX Item "The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4193.IP "\(bu" 4
1758.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 4194Avoid using ev_flags and the EVLIST_*\-macros, while it is
1759.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)." 4195maintained by libev, it does not work exactly the same way as in libevent (consider
1760.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 4196it a private \s-1API\s0).
1761.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." 4197.IP "\(bu" 4
4198Priorities are not currently supported. Initialising priorities
4199will fail and all watchers will have the same priority, even though there
4200is an ev_pri field.
4201.IP "\(bu" 4
4202In libevent, the last base created gets the signals, in libev, the
4203base that registered the signal gets the signals.
4204.IP "\(bu" 4
1762.IP "* Other members are not supported." 4 4205Other members are not supported.
1763.IX Item "Other members are not supported." 4206.IP "\(bu" 4
1764.IP "* The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need to use the libev header file and library." 4 4207The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need
1765.IX Item "The libev emulation is not ABI compatible to libevent, you need to use the libev header file and library." 4208to use the libev header file and library.
1766.PD
1767.SH "\*(C+ SUPPORT" 4209.SH "\*(C+ SUPPORT"
1768.IX Header " SUPPORT" 4210.IX Header " SUPPORT"
4211.SS "C \s-1API\s0"
4212.IX Subsection "C API"
4213The normal C \s-1API\s0 should work fine when used from \*(C+: both ev.h and the
4214libev sources can be compiled as \*(C+. Therefore, code that uses the C \s-1API\s0
4215will work fine.
4216.PP
4217Proper exception specifications might have to be added to callbacks passed
4218to libev: exceptions may be thrown only from watcher callbacks, all other
4219callbacks (allocator, syserr, loop acquire/release and periodic reschedule
4220callbacks) must not throw exceptions, and might need a \f(CW\*(C`noexcept\*(C'\fR
4221specification. If you have code that needs to be compiled as both C and
4222\&\*(C+ you can use the \f(CW\*(C`EV_NOEXCEPT\*(C'\fR macro for this:
4223.PP
4224.Vb 6
4225\& static void
4226\& fatal_error (const char *msg) EV_NOEXCEPT
4227\& {
4228\& perror (msg);
4229\& abort ();
4230\& }
4231\&
4232\& ...
4233\& ev_set_syserr_cb (fatal_error);
4234.Ve
4235.PP
4236The only \s-1API\s0 functions that can currently throw exceptions are \f(CW\*(C`ev_run\*(C'\fR,
4237\&\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
4238because it runs cleanup watchers).
4239.PP
4240Throwing exceptions in watcher callbacks is only supported if libev itself
4241is compiled with a \*(C+ compiler or your C and \*(C+ environments allow
4242throwing exceptions through C libraries (most do).
4243.SS "\*(C+ \s-1API\s0"
4244.IX Subsection " API"
1769Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow 4245Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow
1770you to use some convinience methods to start/stop watchers and also change 4246you to use some convenience methods to start/stop watchers and also change
1771the callback model to a model using method callbacks on objects. 4247the callback model to a model using method callbacks on objects.
1772.PP 4248.PP
1773To use it, 4249To use it,
1774.PP 4250.PP
1775.Vb 1 4251.Vb 1
1776\& #include <ev++.h> 4252\& #include <ev++.h>
1777.Ve 4253.Ve
1778.PP 4254.PP
1779(it is not installed by default). This automatically includes \fIev.h\fR 4255This automatically includes \fIev.h\fR and puts all of its definitions (many
1780and puts all of its definitions (many of them macros) into the global 4256of them macros) into the global namespace. All \*(C+ specific things are
1781namespace. All \*(C+ specific things are put into the \f(CW\*(C`ev\*(C'\fR namespace. 4257put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding
4258options as \fIev.h\fR, most notably \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR.
1782.PP 4259.PP
1783It should support all the same embedding options as \fIev.h\fR, most notably 4260Care has been taken to keep the overhead low. The only data member the \*(C+
1784\&\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. 4261classes add (compared to plain C\-style watchers) is the event loop pointer
4262that the watcher is associated with (or no additional members at all if
4263you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev).
4264.PP
4265Currently, functions, static and non-static member functions and classes
4266with \f(CW\*(C`operator ()\*(C'\fR can be used as callbacks. Other types should be easy
4267to add as long as they only need one additional pointer for context. If
4268you need support for other types of functors please contact the author
4269(preferably after implementing it).
4270.PP
4271For all this to work, your \*(C+ compiler either has to use the same calling
4272conventions as your C compiler (for static member functions), or you have
4273to embed libev and compile libev itself as \*(C+.
1785.PP 4274.PP
1786Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace: 4275Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace:
1787.ie n .IP """ev::READ""\fR, \f(CW""ev::WRITE"" etc." 4 4276.ie n .IP """ev::READ"", ""ev::WRITE"" etc." 4
1788.el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4 4277.el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4
1789.IX Item "ev::READ, ev::WRITE etc." 4278.IX Item "ev::READ, ev::WRITE etc."
1790These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc. 4279These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc.
1791macros from \fIev.h\fR. 4280macros from \fIev.h\fR.
1792.ie n .IP """ev::tstamp""\fR, \f(CW""ev::now""" 4 4281.ie n .IP """ev::tstamp"", ""ev::now""" 4
1793.el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4 4282.el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4
1794.IX Item "ev::tstamp, ev::now" 4283.IX Item "ev::tstamp, ev::now"
1795Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix. 4284Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix.
1796.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 4285.ie n .IP """ev::io"", ""ev::timer"", ""ev::periodic"", ""ev::idle"", ""ev::sig"" etc." 4
1797.el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4 4286.el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4
1798.IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc." 4287.IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc."
1799For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of 4288For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of
1800the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR 4289the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR
1801which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro 4290which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro
1802defines by many implementations. 4291defined by many implementations.
1803.Sp 4292.Sp
1804All of those classes have these methods: 4293All of those classes have these methods:
1805.RS 4 4294.RS 4
1806.IP "ev::TYPE::TYPE (object *, object::method *)" 4 4295.IP "ev::TYPE::TYPE ()" 4
1807.IX Item "ev::TYPE::TYPE (object *, object::method *)" 4296.IX Item "ev::TYPE::TYPE ()"
1808.PD 0 4297.PD 0
1809.IP "ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)" 4 4298.IP "ev::TYPE::TYPE (loop)" 4
1810.IX Item "ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)" 4299.IX Item "ev::TYPE::TYPE (loop)"
1811.IP "ev::TYPE::~TYPE" 4 4300.IP "ev::TYPE::~TYPE" 4
1812.IX Item "ev::TYPE::~TYPE" 4301.IX Item "ev::TYPE::~TYPE"
1813.PD 4302.PD
1814The constructor takes a pointer to an object and a method pointer to 4303The constructor (optionally) takes an event loop to associate the watcher
1815the event handler callback to call in this class. The constructor calls 4304with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR.
1816\&\f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the \f(CW\*(C`set\*(C'\fR method 4305.Sp
1817before starting it. If you do not specify a loop then the constructor 4306The constructor calls \f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the
1818automatically associates the default loop with this watcher. 4307\&\f(CW\*(C`set\*(C'\fR method before starting it.
4308.Sp
4309It will not set a callback, however: You have to call the templated \f(CW\*(C`set\*(C'\fR
4310method to set a callback before you can start the watcher.
4311.Sp
4312(The reason why you have to use a method is a limitation in \*(C+ which does
4313not allow explicit template arguments for constructors).
1819.Sp 4314.Sp
1820The destructor automatically stops the watcher if it is active. 4315The destructor automatically stops the watcher if it is active.
4316.IP "w\->set<class, &class::method> (object *)" 4
4317.IX Item "w->set<class, &class::method> (object *)"
4318This method sets the callback method to call. The method has to have a
4319signature of \f(CW\*(C`void (*)(ev_TYPE &, int)\*(C'\fR, it receives the watcher as
4320first argument and the \f(CW\*(C`revents\*(C'\fR as second. The object must be given as
4321parameter and is stored in the \f(CW\*(C`data\*(C'\fR member of the watcher.
4322.Sp
4323This method synthesizes efficient thunking code to call your method from
4324the C callback that libev requires. If your compiler can inline your
4325callback (i.e. it is visible to it at the place of the \f(CW\*(C`set\*(C'\fR call and
4326your compiler is good :), then the method will be fully inlined into the
4327thunking function, making it as fast as a direct C callback.
4328.Sp
4329Example: simple class declaration and watcher initialisation
4330.Sp
4331.Vb 4
4332\& struct myclass
4333\& {
4334\& void io_cb (ev::io &w, int revents) { }
4335\& }
4336\&
4337\& myclass obj;
4338\& ev::io iow;
4339\& iow.set <myclass, &myclass::io_cb> (&obj);
4340.Ve
4341.IP "w\->set (object *)" 4
4342.IX Item "w->set (object *)"
4343This is a variation of a method callback \- leaving out the method to call
4344will default the method to \f(CW\*(C`operator ()\*(C'\fR, which makes it possible to use
4345functor objects without having to manually specify the \f(CW\*(C`operator ()\*(C'\fR all
4346the time. Incidentally, you can then also leave out the template argument
4347list.
4348.Sp
4349The \f(CW\*(C`operator ()\*(C'\fR method prototype must be \f(CW\*(C`void operator ()(watcher &w,
4350int revents)\*(C'\fR.
4351.Sp
4352See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
4353.Sp
4354Example: use a functor object as callback.
4355.Sp
4356.Vb 7
4357\& struct myfunctor
4358\& {
4359\& void operator() (ev::io &w, int revents)
4360\& {
4361\& ...
4362\& }
4363\& }
4364\&
4365\& myfunctor f;
4366\&
4367\& ev::io w;
4368\& w.set (&f);
4369.Ve
4370.IP "w\->set<function> (void *data = 0)" 4
4371.IX Item "w->set<function> (void *data = 0)"
4372Also sets a callback, but uses a static method or plain function as
4373callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's
4374\&\f(CW\*(C`data\*(C'\fR member and is free for you to use.
4375.Sp
4376The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR.
4377.Sp
4378See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
4379.Sp
4380Example: Use a plain function as callback.
4381.Sp
4382.Vb 2
4383\& static void io_cb (ev::io &w, int revents) { }
4384\& iow.set <io_cb> ();
4385.Ve
1821.IP "w\->set (struct ev_loop *)" 4 4386.IP "w\->set (loop)" 4
1822.IX Item "w->set (struct ev_loop *)" 4387.IX Item "w->set (loop)"
1823Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only 4388Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only
1824do this when the watcher is inactive (and not pending either). 4389do this when the watcher is inactive (and not pending either).
1825.IP "w\->set ([args])" 4 4390.IP "w\->set ([arguments])" 4
1826.IX Item "w->set ([args])" 4391.IX Item "w->set ([arguments])"
1827Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR, with the same args. Must be 4392Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR (except for \f(CW\*(C`ev::embed\*(C'\fR watchers>),
4393with the same arguments. Either this method or a suitable start method
1828called at least once. Unlike the C counterpart, an active watcher gets 4394must be called at least once. Unlike the C counterpart, an active watcher
1829automatically stopped and restarted. 4395gets automatically stopped and restarted when reconfiguring it with this
4396method.
4397.Sp
4398For \f(CW\*(C`ev::embed\*(C'\fR watchers this method is called \f(CW\*(C`set_embed\*(C'\fR, to avoid
4399clashing with the \f(CW\*(C`set (loop)\*(C'\fR method.
1830.IP "w\->start ()" 4 4400.IP "w\->start ()" 4
1831.IX Item "w->start ()" 4401.IX Item "w->start ()"
1832Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument as the 4402Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the
1833constructor already takes the loop. 4403constructor already stores the event loop.
4404.IP "w\->start ([arguments])" 4
4405.IX Item "w->start ([arguments])"
4406Instead of calling \f(CW\*(C`set\*(C'\fR and \f(CW\*(C`start\*(C'\fR methods separately, it is often
4407convenient to wrap them in one call. Uses the same type of arguments as
4408the configure \f(CW\*(C`set\*(C'\fR method of the watcher.
1834.IP "w\->stop ()" 4 4409.IP "w\->stop ()" 4
1835.IX Item "w->stop ()" 4410.IX Item "w->stop ()"
1836Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument. 4411Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument.
1837.ie n .IP "w\->again () ""ev::timer""\fR, \f(CW""ev::periodic"" only" 4 4412.ie n .IP "w\->again () (""ev::timer"", ""ev::periodic"" only)" 4
1838.el .IP "w\->again () \f(CWev::timer\fR, \f(CWev::periodic\fR only" 4 4413.el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4
1839.IX Item "w->again () ev::timer, ev::periodic only" 4414.IX Item "w->again () (ev::timer, ev::periodic only)"
1840For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding 4415For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding
1841\&\f(CW\*(C`ev_TYPE_again\*(C'\fR function. 4416\&\f(CW\*(C`ev_TYPE_again\*(C'\fR function.
1842.ie n .IP "w\->sweep () ""ev::embed"" only" 4 4417.ie n .IP "w\->sweep () (""ev::embed"" only)" 4
1843.el .IP "w\->sweep () \f(CWev::embed\fR only" 4 4418.el .IP "w\->sweep () (\f(CWev::embed\fR only)" 4
1844.IX Item "w->sweep () ev::embed only" 4419.IX Item "w->sweep () (ev::embed only)"
1845Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR. 4420Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR.
1846.ie n .IP "w\->update () ""ev::stat"" only" 4 4421.ie n .IP "w\->update () (""ev::stat"" only)" 4
1847.el .IP "w\->update () \f(CWev::stat\fR only" 4 4422.el .IP "w\->update () (\f(CWev::stat\fR only)" 4
1848.IX Item "w->update () ev::stat only" 4423.IX Item "w->update () (ev::stat only)"
1849Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR. 4424Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR.
1850.RE 4425.RE
1851.RS 4 4426.RS 4
1852.RE 4427.RE
1853.PP 4428.PP
1854Example: Define a class with an \s-1IO\s0 and idle watcher, start one of them in 4429Example: Define a class with two I/O and idle watchers, start the I/O
1855the constructor. 4430watchers in the constructor.
1856.PP 4431.PP
1857.Vb 4 4432.Vb 5
1858\& class myclass 4433\& class myclass
1859\& { 4434\& {
1860\& ev_io io; void io_cb (ev::io &w, int revents); 4435\& ev::io io ; void io_cb (ev::io &w, int revents);
4436\& ev::io io2 ; void io2_cb (ev::io &w, int revents);
1861\& ev_idle idle void idle_cb (ev::idle &w, int revents); 4437\& ev::idle idle; void idle_cb (ev::idle &w, int revents);
1862.Ve 4438\&
1863.PP
1864.Vb 2
1865\& myclass (); 4439\& myclass (int fd)
4440\& {
4441\& io .set <myclass, &myclass::io_cb > (this);
4442\& io2 .set <myclass, &myclass::io2_cb > (this);
4443\& idle.set <myclass, &myclass::idle_cb> (this);
4444\&
4445\& io.set (fd, ev::WRITE); // configure the watcher
4446\& io.start (); // start it whenever convenient
4447\&
4448\& io2.start (fd, ev::READ); // set + start in one call
4449\& }
1866\& } 4450\& };
1867.Ve 4451.Ve
1868.PP 4452.SH "OTHER LANGUAGE BINDINGS"
1869.Vb 6 4453.IX Header "OTHER LANGUAGE BINDINGS"
1870\& myclass::myclass (int fd) 4454Libev does not offer other language bindings itself, but bindings for a
1871\& : io (this, &myclass::io_cb), 4455number of languages exist in the form of third-party packages. If you know
1872\& idle (this, &myclass::idle_cb) 4456any interesting language binding in addition to the ones listed here, drop
1873\& { 4457me a note.
1874\& io.start (fd, ev::READ); 4458.IP "Perl" 4
1875\& } 4459.IX Item "Perl"
1876.Ve 4460The \s-1EV\s0 module implements the full libev \s-1API\s0 and is actually used to test
4461libev. \s-1EV\s0 is developed together with libev. Apart from the \s-1EV\s0 core module,
4462there are additional modules that implement libev-compatible interfaces
4463to \f(CW\*(C`libadns\*(C'\fR (\f(CW\*(C`EV::ADNS\*(C'\fR, but \f(CW\*(C`AnyEvent::DNS\*(C'\fR is preferred nowadays),
4464\&\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
4465and \f(CW\*(C`EV::Glib\*(C'\fR).
4466.Sp
4467It can be found and installed via \s-1CPAN,\s0 its homepage is at
4468<http://software.schmorp.de/pkg/EV>.
4469.IP "Python" 4
4470.IX Item "Python"
4471Python bindings can be found at <http://code.google.com/p/pyev/>. It
4472seems to be quite complete and well-documented.
4473.IP "Ruby" 4
4474.IX Item "Ruby"
4475Tony Arcieri has written a ruby extension that offers access to a subset
4476of the libev \s-1API\s0 and adds file handle abstractions, asynchronous \s-1DNS\s0 and
4477more on top of it. It can be found via gem servers. Its homepage is at
4478<http://rev.rubyforge.org/>.
4479.Sp
4480Roger Pack reports that using the link order \f(CW\*(C`\-lws2_32 \-lmsvcrt\-ruby\-190\*(C'\fR
4481makes rev work even on mingw.
4482.IP "Haskell" 4
4483.IX Item "Haskell"
4484A haskell binding to libev is available at
4485<http://hackage.haskell.org/cgi\-bin/hackage\-scripts/package/hlibev>.
4486.IP "D" 4
4487.IX Item "D"
4488Leandro Lucarella has written a D language binding (\fIev.d\fR) for libev, to
4489be found at <http://www.llucax.com.ar/proj/ev.d/index.html>.
4490.IP "Ocaml" 4
4491.IX Item "Ocaml"
4492Erkki Seppala has written Ocaml bindings for libev, to be found at
4493<http://modeemi.cs.tut.fi/~flux/software/ocaml\-ev/>.
4494.IP "Lua" 4
4495.IX Item "Lua"
4496Brian Maher has written a partial interface to libev for lua (at the
4497time of this writing, only \f(CW\*(C`ev_io\*(C'\fR and \f(CW\*(C`ev_timer\*(C'\fR), to be found at
4498<http://github.com/brimworks/lua\-ev>.
4499.IP "Javascript" 4
4500.IX Item "Javascript"
4501Node.js (<http://nodejs.org>) uses libev as the underlying event library.
4502.IP "Others" 4
4503.IX Item "Others"
4504There are others, and I stopped counting.
1877.SH "MACRO MAGIC" 4505.SH "MACRO MAGIC"
1878.IX Header "MACRO MAGIC" 4506.IX Header "MACRO MAGIC"
1879Libev can be compiled with a variety of options, the most fundemantal is 4507Libev can be compiled with a variety of options, the most fundamental
1880\&\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines wether (most) functions and 4508of which is \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most)
1881callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument. 4509functions and callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument.
1882.PP 4510.PP
1883To make it easier to write programs that cope with either variant, the 4511To make it easier to write programs that cope with either variant, the
1884following macros are defined: 4512following macros are defined:
1885.ie n .IP """EV_A""\fR, \f(CW""EV_A_""" 4 4513.ie n .IP """EV_A"", ""EV_A_""" 4
1886.el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4 4514.el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4
1887.IX Item "EV_A, EV_A_" 4515.IX Item "EV_A, EV_A_"
1888This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev 4516This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev
1889loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument, 4517loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument,
1890\&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example: 4518\&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example:
1891.Sp 4519.Sp
1892.Vb 3 4520.Vb 3
1893\& ev_unref (EV_A); 4521\& ev_unref (EV_A);
1894\& ev_timer_add (EV_A_ watcher); 4522\& ev_timer_add (EV_A_ watcher);
1895\& ev_loop (EV_A_ 0); 4523\& ev_run (EV_A_ 0);
1896.Ve 4524.Ve
1897.Sp 4525.Sp
1898It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope, 4526It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope,
1899which is often provided by the following macro. 4527which is often provided by the following macro.
1900.ie n .IP """EV_P""\fR, \f(CW""EV_P_""" 4 4528.ie n .IP """EV_P"", ""EV_P_""" 4
1901.el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4 4529.el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4
1902.IX Item "EV_P, EV_P_" 4530.IX Item "EV_P, EV_P_"
1903This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev 4531This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev
1904loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter, 4532loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter,
1905\&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example: 4533\&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example:
1906.Sp 4534.Sp
1907.Vb 2 4535.Vb 2
1908\& // this is how ev_unref is being declared 4536\& // this is how ev_unref is being declared
1909\& static void ev_unref (EV_P); 4537\& static void ev_unref (EV_P);
1910.Ve 4538\&
1911.Sp
1912.Vb 2
1913\& // this is how you can declare your typical callback 4539\& // this is how you can declare your typical callback
1914\& static void cb (EV_P_ ev_timer *w, int revents) 4540\& static void cb (EV_P_ ev_timer *w, int revents)
1915.Ve 4541.Ve
1916.Sp 4542.Sp
1917It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite 4543It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite
1918suitable for use with \f(CW\*(C`EV_A\*(C'\fR. 4544suitable for use with \f(CW\*(C`EV_A\*(C'\fR.
1919.ie n .IP """EV_DEFAULT""\fR, \f(CW""EV_DEFAULT_""" 4 4545.ie n .IP """EV_DEFAULT"", ""EV_DEFAULT_""" 4
1920.el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4 4546.el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4
1921.IX Item "EV_DEFAULT, EV_DEFAULT_" 4547.IX Item "EV_DEFAULT, EV_DEFAULT_"
1922Similar to the other two macros, this gives you the value of the default 4548Similar to the other two macros, this gives you the value of the default
1923loop, if multiple loops are supported (\*(L"ev loop default\*(R"). 4549loop, if multiple loops are supported (\*(L"ev loop default\*(R"). The default loop
4550will be initialised if it isn't already initialised.
4551.Sp
4552For non-multiplicity builds, these macros do nothing, so you always have
4553to initialise the loop somewhere.
4554.ie n .IP """EV_DEFAULT_UC"", ""EV_DEFAULT_UC_""" 4
4555.el .IP "\f(CWEV_DEFAULT_UC\fR, \f(CWEV_DEFAULT_UC_\fR" 4
4556.IX Item "EV_DEFAULT_UC, EV_DEFAULT_UC_"
4557Usage identical to \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR, but requires that the
4558default loop has been initialised (\f(CW\*(C`UC\*(C'\fR == unchecked). Their behaviour
4559is undefined when the default loop has not been initialised by a previous
4560execution of \f(CW\*(C`EV_DEFAULT\*(C'\fR, \f(CW\*(C`EV_DEFAULT_\*(C'\fR or \f(CW\*(C`ev_default_init (...)\*(C'\fR.
4561.Sp
4562It is often prudent to use \f(CW\*(C`EV_DEFAULT\*(C'\fR when initialising the first
4563watcher in a function but use \f(CW\*(C`EV_DEFAULT_UC\*(C'\fR afterwards.
1924.PP 4564.PP
1925Example: Declare and initialise a check watcher, working regardless of 4565Example: Declare and initialise a check watcher, utilising the above
1926wether multiple loops are supported or not. 4566macros so it will work regardless of whether multiple loops are supported
4567or not.
1927.PP 4568.PP
1928.Vb 5 4569.Vb 5
1929\& static void 4570\& static void
1930\& check_cb (EV_P_ ev_timer *w, int revents) 4571\& check_cb (EV_P_ ev_timer *w, int revents)
1931\& { 4572\& {
1932\& ev_check_stop (EV_A_ w); 4573\& ev_check_stop (EV_A_ w);
1933\& } 4574\& }
1934.Ve 4575\&
1935.PP
1936.Vb 4
1937\& ev_check check; 4576\& ev_check check;
1938\& ev_check_init (&check, check_cb); 4577\& ev_check_init (&check, check_cb);
1939\& ev_check_start (EV_DEFAULT_ &check); 4578\& ev_check_start (EV_DEFAULT_ &check);
1940\& ev_loop (EV_DEFAULT_ 0); 4579\& ev_run (EV_DEFAULT_ 0);
1941.Ve 4580.Ve
1942.SH "EMBEDDING" 4581.SH "EMBEDDING"
1943.IX Header "EMBEDDING" 4582.IX Header "EMBEDDING"
1944Libev can (and often is) directly embedded into host 4583Libev can (and often is) directly embedded into host
1945applications. Examples of applications that embed it include the Deliantra 4584applications. Examples of applications that embed it include the Deliantra
1946Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe) 4585Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe)
1947and rxvt\-unicode. 4586and rxvt-unicode.
1948.PP 4587.PP
1949The goal is to enable you to just copy the neecssary files into your 4588The goal is to enable you to just copy the necessary files into your
1950source directory without having to change even a single line in them, so 4589source directory without having to change even a single line in them, so
1951you can easily upgrade by simply copying (or having a checked-out copy of 4590you can easily upgrade by simply copying (or having a checked-out copy of
1952libev somewhere in your source tree). 4591libev somewhere in your source tree).
1953.Sh "\s-1FILESETS\s0" 4592.SS "\s-1FILESETS\s0"
1954.IX Subsection "FILESETS" 4593.IX Subsection "FILESETS"
1955Depending on what features you need you need to include one or more sets of files 4594Depending on what features you need you need to include one or more sets of files
1956in your app. 4595in your application.
1957.PP 4596.PP
1958\fI\s-1CORE\s0 \s-1EVENT\s0 \s-1LOOP\s0\fR 4597\fI\s-1CORE EVENT LOOP\s0\fR
1959.IX Subsection "CORE EVENT LOOP" 4598.IX Subsection "CORE EVENT LOOP"
1960.PP 4599.PP
1961To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual 4600To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual
1962configuration (no autoconf): 4601configuration (no autoconf):
1963.PP 4602.PP
1964.Vb 2 4603.Vb 2
1965\& #define EV_STANDALONE 1 4604\& #define EV_STANDALONE 1
1966\& #include "ev.c" 4605\& #include "ev.c"
1967.Ve 4606.Ve
1968.PP 4607.PP
1969This will automatically include \fIev.h\fR, too, and should be done in a 4608This will automatically include \fIev.h\fR, too, and should be done in a
1970single C source file only to provide the function implementations. To use 4609single C source file only to provide the function implementations. To use
1971it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best 4610it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best
1972done by writing a wrapper around \fIev.h\fR that you can include instead and 4611done by writing a wrapper around \fIev.h\fR that you can include instead and
1973where you can put other configuration options): 4612where you can put other configuration options):
1974.PP 4613.PP
1975.Vb 2 4614.Vb 2
1976\& #define EV_STANDALONE 1 4615\& #define EV_STANDALONE 1
1977\& #include "ev.h" 4616\& #include "ev.h"
1978.Ve 4617.Ve
1979.PP 4618.PP
1980Both header files and implementation files can be compiled with a \*(C+ 4619Both header files and implementation files can be compiled with a \*(C+
1981compiler (at least, thats a stated goal, and breakage will be treated 4620compiler (at least, that's a stated goal, and breakage will be treated
1982as a bug). 4621as a bug).
1983.PP 4622.PP
1984You need the following files in your source tree, or in a directory 4623You need the following files in your source tree, or in a directory
1985in your include path (e.g. in libev/ when using \-Ilibev): 4624in your include path (e.g. in libev/ when using \-Ilibev):
1986.PP 4625.PP
1987.Vb 4 4626.Vb 4
1988\& ev.h 4627\& ev.h
1989\& ev.c 4628\& ev.c
1990\& ev_vars.h 4629\& ev_vars.h
1991\& ev_wrap.h 4630\& ev_wrap.h
1992.Ve 4631\&
1993.PP
1994.Vb 1
1995\& ev_win32.c required on win32 platforms only 4632\& ev_win32.c required on win32 platforms only
1996.Ve 4633\&
1997.PP
1998.Vb 5
1999\& ev_select.c only when select backend is enabled (which is by default) 4634\& ev_select.c only when select backend is enabled
2000\& ev_poll.c only when poll backend is enabled (disabled by default) 4635\& ev_poll.c only when poll backend is enabled
2001\& ev_epoll.c only when the epoll backend is enabled (disabled by default) 4636\& ev_epoll.c only when the epoll backend is enabled
4637\& ev_linuxaio.c only when the linux aio backend is enabled
4638\& ev_iouring.c only when the linux io_uring backend is enabled
2002\& ev_kqueue.c only when the kqueue backend is enabled (disabled by default) 4639\& ev_kqueue.c only when the kqueue backend is enabled
2003\& ev_port.c only when the solaris port backend is enabled (disabled by default) 4640\& ev_port.c only when the solaris port backend is enabled
2004.Ve 4641.Ve
2005.PP 4642.PP
2006\&\fIev.c\fR includes the backend files directly when enabled, so you only need 4643\&\fIev.c\fR includes the backend files directly when enabled, so you only need
2007to compile this single file. 4644to compile this single file.
2008.PP 4645.PP
2009\fI\s-1LIBEVENT\s0 \s-1COMPATIBILITY\s0 \s-1API\s0\fR 4646\fI\s-1LIBEVENT COMPATIBILITY API\s0\fR
2010.IX Subsection "LIBEVENT COMPATIBILITY API" 4647.IX Subsection "LIBEVENT COMPATIBILITY API"
2011.PP 4648.PP
2012To include the libevent compatibility \s-1API\s0, also include: 4649To include the libevent compatibility \s-1API,\s0 also include:
2013.PP 4650.PP
2014.Vb 1 4651.Vb 1
2015\& #include "event.c" 4652\& #include "event.c"
2016.Ve 4653.Ve
2017.PP 4654.PP
2018in the file including \fIev.c\fR, and: 4655in the file including \fIev.c\fR, and:
2019.PP 4656.PP
2020.Vb 1 4657.Vb 1
2021\& #include "event.h" 4658\& #include "event.h"
2022.Ve 4659.Ve
2023.PP 4660.PP
2024in the files that want to use the libevent \s-1API\s0. This also includes \fIev.h\fR. 4661in the files that want to use the libevent \s-1API.\s0 This also includes \fIev.h\fR.
2025.PP 4662.PP
2026You need the following additional files for this: 4663You need the following additional files for this:
2027.PP 4664.PP
2028.Vb 2 4665.Vb 2
2029\& event.h 4666\& event.h
2030\& event.c 4667\& event.c
2031.Ve 4668.Ve
2032.PP 4669.PP
2033\fI\s-1AUTOCONF\s0 \s-1SUPPORT\s0\fR 4670\fI\s-1AUTOCONF SUPPORT\s0\fR
2034.IX Subsection "AUTOCONF SUPPORT" 4671.IX Subsection "AUTOCONF SUPPORT"
2035.PP 4672.PP
2036Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your config in 4673Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your configuration in
2037whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your 4674whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your
2038\&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then 4675\&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then
2039include \fIconfig.h\fR and configure itself accordingly. 4676include \fIconfig.h\fR and configure itself accordingly.
2040.PP 4677.PP
2041For this of course you need the m4 file: 4678For this of course you need the m4 file:
2042.PP 4679.PP
2043.Vb 1 4680.Vb 1
2044\& libev.m4 4681\& libev.m4
2045.Ve 4682.Ve
2046.Sh "\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0" 4683.SS "\s-1PREPROCESSOR SYMBOLS/MACROS\s0"
2047.IX Subsection "PREPROCESSOR SYMBOLS/MACROS" 4684.IX Subsection "PREPROCESSOR SYMBOLS/MACROS"
2048Libev can be configured via a variety of preprocessor symbols you have to define 4685Libev can be configured via a variety of preprocessor symbols you have to
2049before including any of its files. The default is not to build for multiplicity 4686define before including (or compiling) any of its files. The default in
2050and only include the select backend. 4687the absence of autoconf is documented for every option.
4688.PP
4689Symbols marked with \*(L"(h)\*(R" do not change the \s-1ABI,\s0 and can have different
4690values when compiling libev vs. including \fIev.h\fR, so it is permissible
4691to redefine them before including \fIev.h\fR without breaking compatibility
4692to a compiled library. All other symbols change the \s-1ABI,\s0 which means all
4693users of libev and the libev code itself must be compiled with compatible
4694settings.
4695.IP "\s-1EV_COMPAT3\s0 (h)" 4
4696.IX Item "EV_COMPAT3 (h)"
4697Backwards compatibility is a major concern for libev. This is why this
4698release of libev comes with wrappers for the functions and symbols that
4699have been renamed between libev version 3 and 4.
4700.Sp
4701You can disable these wrappers (to test compatibility with future
4702versions) by defining \f(CW\*(C`EV_COMPAT3\*(C'\fR to \f(CW0\fR when compiling your
4703sources. This has the additional advantage that you can drop the \f(CW\*(C`struct\*(C'\fR
4704from \f(CW\*(C`struct ev_loop\*(C'\fR declarations, as libev will provide an \f(CW\*(C`ev_loop\*(C'\fR
4705typedef in that case.
4706.Sp
4707In some future version, the default for \f(CW\*(C`EV_COMPAT3\*(C'\fR will become \f(CW0\fR,
4708and in some even more future version the compatibility code will be
4709removed completely.
2051.IP "\s-1EV_STANDALONE\s0" 4 4710.IP "\s-1EV_STANDALONE\s0 (h)" 4
2052.IX Item "EV_STANDALONE" 4711.IX Item "EV_STANDALONE (h)"
2053Must always be \f(CW1\fR if you do not use autoconf configuration, which 4712Must always be \f(CW1\fR if you do not use autoconf configuration, which
2054keeps libev from including \fIconfig.h\fR, and it also defines dummy 4713keeps libev from including \fIconfig.h\fR, and it also defines dummy
2055implementations for some libevent functions (such as logging, which is not 4714implementations for some libevent functions (such as logging, which is not
2056supported). It will also not define any of the structs usually found in 4715supported). It will also not define any of the structs usually found in
2057\&\fIevent.h\fR that are not directly supported by the libev core alone. 4716\&\fIevent.h\fR that are not directly supported by the libev core alone.
4717.Sp
4718In standalone mode, libev will still try to automatically deduce the
4719configuration, but has to be more conservative.
4720.IP "\s-1EV_USE_FLOOR\s0" 4
4721.IX Item "EV_USE_FLOOR"
4722If defined to be \f(CW1\fR, libev will use the \f(CW\*(C`floor ()\*(C'\fR function for its
4723periodic reschedule calculations, otherwise libev will fall back on a
4724portable (slower) implementation. If you enable this, you usually have to
4725link against libm or something equivalent. Enabling this when the \f(CW\*(C`floor\*(C'\fR
4726function is not available will fail, so the safe default is to not enable
4727this.
2058.IP "\s-1EV_USE_MONOTONIC\s0" 4 4728.IP "\s-1EV_USE_MONOTONIC\s0" 4
2059.IX Item "EV_USE_MONOTONIC" 4729.IX Item "EV_USE_MONOTONIC"
2060If defined to be \f(CW1\fR, libev will try to detect the availability of the 4730If defined to be \f(CW1\fR, libev will try to detect the availability of the
2061monotonic clock option at both compiletime and runtime. Otherwise no use 4731monotonic clock option at both compile time and runtime. Otherwise no
2062of the monotonic clock option will be attempted. If you enable this, you 4732use of the monotonic clock option will be attempted. If you enable this,
2063usually have to link against librt or something similar. Enabling it when 4733you usually have to link against librt or something similar. Enabling it
2064the functionality isn't available is safe, though, althoguh you have 4734when the functionality isn't available is safe, though, although you have
2065to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR 4735to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR
2066function is hiding in (often \fI\-lrt\fR). 4736function is hiding in (often \fI\-lrt\fR). See also \f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
2067.IP "\s-1EV_USE_REALTIME\s0" 4 4737.IP "\s-1EV_USE_REALTIME\s0" 4
2068.IX Item "EV_USE_REALTIME" 4738.IX Item "EV_USE_REALTIME"
2069If defined to be \f(CW1\fR, libev will try to detect the availability of the 4739If defined to be \f(CW1\fR, libev will try to detect the availability of the
2070realtime clock option at compiletime (and assume its availability at 4740real-time clock option at compile time (and assume its availability
2071runtime if successful). Otherwise no use of the realtime clock option will 4741at runtime if successful). Otherwise no use of the real-time clock
2072be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR by \f(CW\*(C`clock_get 4742option will be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR
2073(CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect correctness. See tzhe note about libraries 4743by \f(CW\*(C`clock_get (CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect
2074in the description of \f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. 4744correctness. See the note about libraries in the description of
4745\&\f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. Defaults to the opposite value of
4746\&\f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
4747.IP "\s-1EV_USE_CLOCK_SYSCALL\s0" 4
4748.IX Item "EV_USE_CLOCK_SYSCALL"
4749If defined to be \f(CW1\fR, libev will try to use a direct syscall instead
4750of calling the system-provided \f(CW\*(C`clock_gettime\*(C'\fR function. This option
4751exists 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
4752unconditionally pulls in \f(CW\*(C`libpthread\*(C'\fR, slowing down single-threaded
4753programs needlessly. Using a direct syscall is slightly slower (in
4754theory), because no optimised vdso implementation can be used, but avoids
4755the pthread dependency. Defaults to \f(CW1\fR on GNU/Linux with glibc 2.x or
4756higher, as it simplifies linking (no need for \f(CW\*(C`\-lrt\*(C'\fR).
4757.IP "\s-1EV_USE_NANOSLEEP\s0" 4
4758.IX Item "EV_USE_NANOSLEEP"
4759If defined to be \f(CW1\fR, libev will assume that \f(CW\*(C`nanosleep ()\*(C'\fR is available
4760and will use it for delays. Otherwise it will use \f(CW\*(C`select ()\*(C'\fR.
4761.IP "\s-1EV_USE_EVENTFD\s0" 4
4762.IX Item "EV_USE_EVENTFD"
4763If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is
4764available and will probe for kernel support at runtime. This will improve
4765\&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption.
4766If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
47672.7 or newer, otherwise disabled.
4768.IP "\s-1EV_USE_SIGNALFD\s0" 4
4769.IX Item "EV_USE_SIGNALFD"
4770If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`signalfd ()\*(C'\fR is
4771available and will probe for kernel support at runtime. This enables
4772the use of \s-1EVFLAG_SIGNALFD\s0 for faster and simpler signal handling. If
4773undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
47742.7 or newer, otherwise disabled.
4775.IP "\s-1EV_USE_TIMERFD\s0" 4
4776.IX Item "EV_USE_TIMERFD"
4777If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`timerfd ()\*(C'\fR is
4778available and will probe for kernel support at runtime. This allows
4779libev to detect time jumps accurately. If undefined, it will be enabled
4780if the headers indicate GNU/Linux + Glibc 2.8 or newer and define
4781\&\f(CW\*(C`TFD_TIMER_CANCEL_ON_SET\*(C'\fR, otherwise disabled.
4782.IP "\s-1EV_USE_EVENTFD\s0" 4
4783.IX Item "EV_USE_EVENTFD"
4784If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is
4785available and will probe for kernel support at runtime. This will improve
4786\&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption.
4787If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
47882.7 or newer, otherwise disabled.
2075.IP "\s-1EV_USE_SELECT\s0" 4 4789.IP "\s-1EV_USE_SELECT\s0" 4
2076.IX Item "EV_USE_SELECT" 4790.IX Item "EV_USE_SELECT"
2077If undefined or defined to be \f(CW1\fR, libev will compile in support for the 4791If undefined or defined to be \f(CW1\fR, libev will compile in support for the
2078\&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at autodetection will be done: if no 4792\&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at auto-detection will be done: if no
2079other method takes over, select will be it. Otherwise the select backend 4793other method takes over, select will be it. Otherwise the select backend
2080will not be compiled in. 4794will not be compiled in.
2081.IP "\s-1EV_SELECT_USE_FD_SET\s0" 4 4795.IP "\s-1EV_SELECT_USE_FD_SET\s0" 4
2082.IX Item "EV_SELECT_USE_FD_SET" 4796.IX Item "EV_SELECT_USE_FD_SET"
2083If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR 4797If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR
2084structure. This is useful if libev doesn't compile due to a missing 4798structure. This is useful if libev doesn't compile due to a missing
2085\&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it misguesses the bitset layout on 4799\&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it mis-guesses the bitset layout
2086exotic systems. This usually limits the range of file descriptors to some 4800on exotic systems. This usually limits the range of file descriptors to
2087low limit such as 1024 or might have other limitations (winsocket only 4801some low limit such as 1024 or might have other limitations (winsocket
2088allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation, might 4802only allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation,
2089influence the size of the \f(CW\*(C`fd_set\*(C'\fR used. 4803configures the maximum size of the \f(CW\*(C`fd_set\*(C'\fR.
2090.IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4 4804.IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4
2091.IX Item "EV_SELECT_IS_WINSOCKET" 4805.IX Item "EV_SELECT_IS_WINSOCKET"
2092When defined to \f(CW1\fR, the select backend will assume that 4806When defined to \f(CW1\fR, the select backend will assume that
2093select/socket/connect etc. don't understand file descriptors but 4807select/socket/connect etc. don't understand file descriptors but
2094wants osf handles on win32 (this is the case when the select to 4808wants osf handles on win32 (this is the case when the select to
2095be used is the winsock select). This means that it will call 4809be used is the winsock select). This means that it will call
2096\&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise, 4810\&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise,
2097it is assumed that all these functions actually work on fds, even 4811it is assumed that all these functions actually work on fds, even
2098on win32. Should not be defined on non\-win32 platforms. 4812on win32. Should not be defined on non\-win32 platforms.
4813.IP "\s-1EV_FD_TO_WIN32_HANDLE\s0(fd)" 4
4814.IX Item "EV_FD_TO_WIN32_HANDLE(fd)"
4815If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR is enabled, then libev needs a way to map
4816file descriptors to socket handles. When not defining this symbol (the
4817default), then libev will call \f(CW\*(C`_get_osfhandle\*(C'\fR, which is usually
4818correct. In some cases, programs use their own file descriptor management,
4819in which case they can provide this function to map fds to socket handles.
4820.IP "\s-1EV_WIN32_HANDLE_TO_FD\s0(handle)" 4
4821.IX Item "EV_WIN32_HANDLE_TO_FD(handle)"
4822If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR then libev maps handles to file descriptors
4823using the standard \f(CW\*(C`_open_osfhandle\*(C'\fR function. For programs implementing
4824their own fd to handle mapping, overwriting this function makes it easier
4825to do so. This can be done by defining this macro to an appropriate value.
4826.IP "\s-1EV_WIN32_CLOSE_FD\s0(fd)" 4
4827.IX Item "EV_WIN32_CLOSE_FD(fd)"
4828If programs implement their own fd to handle mapping on win32, then this
4829macro can be used to override the \f(CW\*(C`close\*(C'\fR function, useful to unregister
4830file descriptors again. Note that the replacement function has to close
4831the underlying \s-1OS\s0 handle.
4832.IP "\s-1EV_USE_WSASOCKET\s0" 4
4833.IX Item "EV_USE_WSASOCKET"
4834If defined to be \f(CW1\fR, libev will use \f(CW\*(C`WSASocket\*(C'\fR to create its internal
4835communication socket, which works better in some environments. Otherwise,
4836the normal \f(CW\*(C`socket\*(C'\fR function will be used, which works better in other
4837environments.
2099.IP "\s-1EV_USE_POLL\s0" 4 4838.IP "\s-1EV_USE_POLL\s0" 4
2100.IX Item "EV_USE_POLL" 4839.IX Item "EV_USE_POLL"
2101If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2) 4840If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2)
2102backend. Otherwise it will be enabled on non\-win32 platforms. It 4841backend. Otherwise it will be enabled on non\-win32 platforms. It
2103takes precedence over select. 4842takes precedence over select.
2104.IP "\s-1EV_USE_EPOLL\s0" 4 4843.IP "\s-1EV_USE_EPOLL\s0" 4
2105.IX Item "EV_USE_EPOLL" 4844.IX Item "EV_USE_EPOLL"
2106If defined to be \f(CW1\fR, libev will compile in support for the Linux 4845If defined to be \f(CW1\fR, libev will compile in support for the Linux
2107\&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime, 4846\&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime,
2108otherwise another method will be used as fallback. This is the 4847otherwise another method will be used as fallback. This is the preferred
2109preferred backend for GNU/Linux systems. 4848backend for GNU/Linux systems. If undefined, it will be enabled if the
4849headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4850.IP "\s-1EV_USE_LINUXAIO\s0" 4
4851.IX Item "EV_USE_LINUXAIO"
4852If defined to be \f(CW1\fR, libev will compile in support for the Linux aio
4853backend (\f(CW\*(C`EV_USE_EPOLL\*(C'\fR must also be enabled). If undefined, it will be
4854enabled on linux, otherwise disabled.
4855.IP "\s-1EV_USE_IOURING\s0" 4
4856.IX Item "EV_USE_IOURING"
4857If defined to be \f(CW1\fR, libev will compile in support for the Linux
4858io_uring backend (\f(CW\*(C`EV_USE_EPOLL\*(C'\fR must also be enabled). Due to it's
4859current limitations it has to be requested explicitly. If undefined, it
4860will be enabled on linux, otherwise disabled.
2110.IP "\s-1EV_USE_KQUEUE\s0" 4 4861.IP "\s-1EV_USE_KQUEUE\s0" 4
2111.IX Item "EV_USE_KQUEUE" 4862.IX Item "EV_USE_KQUEUE"
2112If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style 4863If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style
2113\&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime, 4864\&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime,
2114otherwise another method will be used as fallback. This is the preferred 4865otherwise another method will be used as fallback. This is the preferred
… …
212410 port style backend. Its availability will be detected at runtime, 487510 port style backend. Its availability will be detected at runtime,
2125otherwise another method will be used as fallback. This is the preferred 4876otherwise another method will be used as fallback. This is the preferred
2126backend for Solaris 10 systems. 4877backend for Solaris 10 systems.
2127.IP "\s-1EV_USE_DEVPOLL\s0" 4 4878.IP "\s-1EV_USE_DEVPOLL\s0" 4
2128.IX Item "EV_USE_DEVPOLL" 4879.IX Item "EV_USE_DEVPOLL"
2129reserved for future expansion, works like the \s-1USE\s0 symbols above. 4880Reserved for future expansion, works like the \s-1USE\s0 symbols above.
4881.IP "\s-1EV_USE_INOTIFY\s0" 4
4882.IX Item "EV_USE_INOTIFY"
4883If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify
4884interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will
4885be detected at runtime. If undefined, it will be enabled if the headers
4886indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4887.IP "\s-1EV_NO_SMP\s0" 4
4888.IX Item "EV_NO_SMP"
4889If defined to be \f(CW1\fR, libev will assume that memory is always coherent
4890between threads, that is, threads can be used, but threads never run on
4891different cpus (or different cpu cores). This reduces dependencies
4892and makes libev faster.
4893.IP "\s-1EV_NO_THREADS\s0" 4
4894.IX Item "EV_NO_THREADS"
4895If defined to be \f(CW1\fR, libev will assume that it will never be called from
4896different threads (that includes signal handlers), which is a stronger
4897assumption than \f(CW\*(C`EV_NO_SMP\*(C'\fR, above. This reduces dependencies and makes
4898libev faster.
4899.IP "\s-1EV_ATOMIC_T\s0" 4
4900.IX Item "EV_ATOMIC_T"
4901Libev requires an integer type (suitable for storing \f(CW0\fR or \f(CW1\fR) whose
4902access is atomic with respect to other threads or signal contexts. No
4903such type is easily found in the C language, so you can provide your own
4904type that you know is safe for your purposes. It is used both for signal
4905handler \*(L"locking\*(R" as well as for signal and thread safety in \f(CW\*(C`ev_async\*(C'\fR
4906watchers.
4907.Sp
4908In the absence of this define, libev will use \f(CW\*(C`sig_atomic_t volatile\*(C'\fR
4909(from \fIsignal.h\fR), which is usually good enough on most platforms.
2130.IP "\s-1EV_H\s0" 4 4910.IP "\s-1EV_H\s0 (h)" 4
2131.IX Item "EV_H" 4911.IX Item "EV_H (h)"
2132The name of the \fIev.h\fR header file used to include it. The default if 4912The name of the \fIev.h\fR header file used to include it. The default if
2133undefined is \f(CW\*(C`<ev.h>\*(C'\fR in \fIevent.h\fR and \f(CW"ev.h"\fR in \fIev.c\fR. This 4913undefined is \f(CW"ev.h"\fR in \fIevent.h\fR, \fIev.c\fR and \fIev++.h\fR. This can be
2134can be used to virtually rename the \fIev.h\fR header file in case of conflicts. 4914used to virtually rename the \fIev.h\fR header file in case of conflicts.
2135.IP "\s-1EV_CONFIG_H\s0" 4 4915.IP "\s-1EV_CONFIG_H\s0 (h)" 4
2136.IX Item "EV_CONFIG_H" 4916.IX Item "EV_CONFIG_H (h)"
2137If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override 4917If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override
2138\&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to 4918\&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to
2139\&\f(CW\*(C`EV_H\*(C'\fR, above. 4919\&\f(CW\*(C`EV_H\*(C'\fR, above.
2140.IP "\s-1EV_EVENT_H\s0" 4 4920.IP "\s-1EV_EVENT_H\s0 (h)" 4
2141.IX Item "EV_EVENT_H" 4921.IX Item "EV_EVENT_H (h)"
2142Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea 4922Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea
2143of how the \fIevent.h\fR header can be found. 4923of how the \fIevent.h\fR header can be found, the default is \f(CW"event.h"\fR.
2144.IP "\s-1EV_PROTOTYPES\s0" 4 4924.IP "\s-1EV_PROTOTYPES\s0 (h)" 4
2145.IX Item "EV_PROTOTYPES" 4925.IX Item "EV_PROTOTYPES (h)"
2146If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function 4926If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function
2147prototypes, but still define all the structs and other symbols. This is 4927prototypes, but still define all the structs and other symbols. This is
2148occasionally useful if you want to provide your own wrapper functions 4928occasionally useful if you want to provide your own wrapper functions
2149around libev functions. 4929around libev functions.
2150.IP "\s-1EV_MULTIPLICITY\s0" 4 4930.IP "\s-1EV_MULTIPLICITY\s0" 4
… …
2152If undefined or defined to \f(CW1\fR, then all event-loop-specific functions 4932If undefined or defined to \f(CW1\fR, then all event-loop-specific functions
2153will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create 4933will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create
2154additional independent event loops. Otherwise there will be no support 4934additional independent event loops. Otherwise there will be no support
2155for multiple event loops and there is no first event loop pointer 4935for multiple event loops and there is no first event loop pointer
2156argument. Instead, all functions act on the single default loop. 4936argument. Instead, all functions act on the single default loop.
2157.IP "\s-1EV_PERIODIC_ENABLE\s0" 4 4937.Sp
2158.IX Item "EV_PERIODIC_ENABLE" 4938Note that \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR will no longer provide a
2159If undefined or defined to be \f(CW1\fR, then periodic timers are supported. If 4939default loop when multiplicity is switched off \- you always have to
2160defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of 4940initialise the loop manually in this case.
2161code.
2162.IP "\s-1EV_EMBED_ENABLE\s0" 4
2163.IX Item "EV_EMBED_ENABLE"
2164If undefined or defined to be \f(CW1\fR, then embed watchers are supported. If
2165defined to be \f(CW0\fR, then they are not.
2166.IP "\s-1EV_STAT_ENABLE\s0" 4
2167.IX Item "EV_STAT_ENABLE"
2168If undefined or defined to be \f(CW1\fR, then stat watchers are supported. If
2169defined to be \f(CW0\fR, then they are not.
2170.IP "\s-1EV_FORK_ENABLE\s0" 4
2171.IX Item "EV_FORK_ENABLE"
2172If undefined or defined to be \f(CW1\fR, then fork watchers are supported. If
2173defined to be \f(CW0\fR, then they are not.
2174.IP "\s-1EV_MINIMAL\s0" 4 4941.IP "\s-1EV_MINPRI\s0" 4
2175.IX Item "EV_MINIMAL" 4942.IX Item "EV_MINPRI"
4943.PD 0
4944.IP "\s-1EV_MAXPRI\s0" 4
4945.IX Item "EV_MAXPRI"
4946.PD
4947The range of allowed priorities. \f(CW\*(C`EV_MINPRI\*(C'\fR must be smaller or equal to
4948\&\f(CW\*(C`EV_MAXPRI\*(C'\fR, but otherwise there are no non-obvious limitations. You can
4949provide for more priorities by overriding those symbols (usually defined
4950to be \f(CW\*(C`\-2\*(C'\fR and \f(CW2\fR, respectively).
4951.Sp
4952When doing priority-based operations, libev usually has to linearly search
4953all the priorities, so having many of them (hundreds) uses a lot of space
4954and time, so using the defaults of five priorities (\-2 .. +2) is usually
4955fine.
4956.Sp
4957If your embedding application does not need any priorities, defining these
4958both to \f(CW0\fR will save some memory and \s-1CPU.\s0
4959.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
4960.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."
4961If undefined or defined to be \f(CW1\fR (and the platform supports it), then
4962the respective watcher type is supported. If defined to be \f(CW0\fR, then it
4963is not. Disabling watcher types mainly saves code size.
4964.IP "\s-1EV_FEATURES\s0" 4
4965.IX Item "EV_FEATURES"
2176If you need to shave off some kilobytes of code at the expense of some 4966If you need to shave off some kilobytes of code at the expense of some
2177speed, define this symbol to \f(CW1\fR. Currently only used for gcc to override 4967speed (but with the full \s-1API\s0), you can define this symbol to request
2178some inlining decisions, saves roughly 30% codesize of amd64. 4968certain subsets of functionality. The default is to enable all features
4969that can be enabled on the platform.
4970.Sp
4971A typical way to use this symbol is to define it to \f(CW0\fR (or to a bitset
4972with some broad features you want) and then selectively re-enable
4973additional parts you want, for example if you want everything minimal,
4974but multiple event loop support, async and child watchers and the poll
4975backend, use this:
4976.Sp
4977.Vb 5
4978\& #define EV_FEATURES 0
4979\& #define EV_MULTIPLICITY 1
4980\& #define EV_USE_POLL 1
4981\& #define EV_CHILD_ENABLE 1
4982\& #define EV_ASYNC_ENABLE 1
4983.Ve
4984.Sp
4985The actual value is a bitset, it can be a combination of the following
4986values (by default, all of these are enabled):
4987.RS 4
4988.ie n .IP "1 \- faster/larger code" 4
4989.el .IP "\f(CW1\fR \- faster/larger code" 4
4990.IX Item "1 - faster/larger code"
4991Use larger code to speed up some operations.
4992.Sp
4993Currently this is used to override some inlining decisions (enlarging the
4994code size by roughly 30% on amd64).
4995.Sp
4996When optimising for size, use of compiler flags such as \f(CW\*(C`\-Os\*(C'\fR with
4997gcc is recommended, as well as \f(CW\*(C`\-DNDEBUG\*(C'\fR, as libev contains a number of
4998assertions.
4999.Sp
5000The default is off when \f(CW\*(C`_\|_OPTIMIZE_SIZE_\|_\*(C'\fR is defined by your compiler
5001(e.g. gcc with \f(CW\*(C`\-Os\*(C'\fR).
5002.ie n .IP "2 \- faster/larger data structures" 4
5003.el .IP "\f(CW2\fR \- faster/larger data structures" 4
5004.IX Item "2 - faster/larger data structures"
5005Replaces the small 2\-heap for timer management by a faster 4\-heap, larger
5006hash table sizes and so on. This will usually further increase code size
5007and can additionally have an effect on the size of data structures at
5008runtime.
5009.Sp
5010The default is off when \f(CW\*(C`_\|_OPTIMIZE_SIZE_\|_\*(C'\fR is defined by your compiler
5011(e.g. gcc with \f(CW\*(C`\-Os\*(C'\fR).
5012.ie n .IP "4 \- full \s-1API\s0 configuration" 4
5013.el .IP "\f(CW4\fR \- full \s-1API\s0 configuration" 4
5014.IX Item "4 - full API configuration"
5015This enables priorities (sets \f(CW\*(C`EV_MAXPRI\*(C'\fR=2 and \f(CW\*(C`EV_MINPRI\*(C'\fR=\-2), and
5016enables multiplicity (\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR=1).
5017.ie n .IP "8 \- full \s-1API\s0" 4
5018.el .IP "\f(CW8\fR \- full \s-1API\s0" 4
5019.IX Item "8 - full API"
5020This enables a lot of the \*(L"lesser used\*(R" \s-1API\s0 functions. See \f(CW\*(C`ev.h\*(C'\fR for
5021details on which parts of the \s-1API\s0 are still available without this
5022feature, and do not complain if this subset changes over time.
5023.ie n .IP "16 \- enable all optional watcher types" 4
5024.el .IP "\f(CW16\fR \- enable all optional watcher types" 4
5025.IX Item "16 - enable all optional watcher types"
5026Enables all optional watcher types. If you want to selectively enable
5027only some watcher types other than I/O and timers (e.g. prepare,
5028embed, async, child...) you can enable them manually by defining
5029\&\f(CW\*(C`EV_watchertype_ENABLE\*(C'\fR to \f(CW1\fR instead.
5030.ie n .IP "32 \- enable all backends" 4
5031.el .IP "\f(CW32\fR \- enable all backends" 4
5032.IX Item "32 - enable all backends"
5033This enables all backends \- without this feature, you need to enable at
5034least one backend manually (\f(CW\*(C`EV_USE_SELECT\*(C'\fR is a good choice).
5035.ie n .IP "64 \- enable OS-specific ""helper"" APIs" 4
5036.el .IP "\f(CW64\fR \- enable OS-specific ``helper'' APIs" 4
5037.IX Item "64 - enable OS-specific helper APIs"
5038Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
5039default.
5040.RE
5041.RS 4
5042.Sp
5043Compiling with \f(CW\*(C`gcc \-Os \-DEV_STANDALONE \-DEV_USE_EPOLL=1 \-DEV_FEATURES=0\*(C'\fR
5044reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
5045code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
5046watchers, timers and monotonic clock support.
5047.Sp
5048With an intelligent-enough linker (gcc+binutils are intelligent enough
5049when you use \f(CW\*(C`\-Wl,\-\-gc\-sections \-ffunction\-sections\*(C'\fR) functions unused by
5050your program might be left out as well \- a binary starting a timer and an
5051I/O watcher then might come out at only 5Kb.
5052.RE
5053.IP "\s-1EV_API_STATIC\s0" 4
5054.IX Item "EV_API_STATIC"
5055If this symbol is defined (by default it is not), then all identifiers
5056will have static linkage. This means that libev will not export any
5057identifiers, and you cannot link against libev anymore. This can be useful
5058when you embed libev, only want to use libev functions in a single file,
5059and do not want its identifiers to be visible.
5060.Sp
5061To use this, define \f(CW\*(C`EV_API_STATIC\*(C'\fR and include \fIev.c\fR in the file that
5062wants to use libev.
5063.Sp
5064This option only works when libev is compiled with a C compiler, as \*(C+
5065doesn't support the required declaration syntax.
5066.IP "\s-1EV_AVOID_STDIO\s0" 4
5067.IX Item "EV_AVOID_STDIO"
5068If this is set to \f(CW1\fR at compiletime, then libev will avoid using stdio
5069functions (printf, scanf, perror etc.). This will increase the code size
5070somewhat, but if your program doesn't otherwise depend on stdio and your
5071libc allows it, this avoids linking in the stdio library which is quite
5072big.
5073.Sp
5074Note that error messages might become less precise when this option is
5075enabled.
5076.IP "\s-1EV_NSIG\s0" 4
5077.IX Item "EV_NSIG"
5078The highest supported signal number, +1 (or, the number of
5079signals): Normally, libev tries to deduce the maximum number of signals
5080automatically, but sometimes this fails, in which case it can be
5081specified. Also, using a lower number than detected (\f(CW32\fR should be
5082good for about any system in existence) can save some memory, as libev
5083statically allocates some 12\-24 bytes per signal number.
2179.IP "\s-1EV_PID_HASHSIZE\s0" 4 5084.IP "\s-1EV_PID_HASHSIZE\s0" 4
2180.IX Item "EV_PID_HASHSIZE" 5085.IX Item "EV_PID_HASHSIZE"
2181\&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by 5086\&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by
2182pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR), usually more 5087pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR disabled),
2183than enough. If you need to manage thousands of children you might want to 5088usually more than enough. If you need to manage thousands of children you
2184increase this value. 5089might want to increase this value (\fImust\fR be a power of two).
5090.IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4
5091.IX Item "EV_INOTIFY_HASHSIZE"
5092\&\f(CW\*(C`ev_stat\*(C'\fR watchers use a small hash table to distribute workload by
5093inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR
5094disabled), usually more than enough. If you need to manage thousands of
5095\&\f(CW\*(C`ev_stat\*(C'\fR watchers you might want to increase this value (\fImust\fR be a
5096power of two).
5097.IP "\s-1EV_USE_4HEAP\s0" 4
5098.IX Item "EV_USE_4HEAP"
5099Heaps are not very cache-efficient. To improve the cache-efficiency of the
5100timer and periodics heaps, libev uses a 4\-heap when this symbol is defined
5101to \f(CW1\fR. The 4\-heap uses more complicated (longer) code but has noticeably
5102faster performance with many (thousands) of watchers.
5103.Sp
5104The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
5105will be \f(CW0\fR.
5106.IP "\s-1EV_HEAP_CACHE_AT\s0" 4
5107.IX Item "EV_HEAP_CACHE_AT"
5108Heaps are not very cache-efficient. To improve the cache-efficiency of the
5109timer and periodics heaps, libev can cache the timestamp (\fIat\fR) within
5110the heap structure (selected by defining \f(CW\*(C`EV_HEAP_CACHE_AT\*(C'\fR to \f(CW1\fR),
5111which uses 8\-12 bytes more per watcher and a few hundred bytes more code,
5112but avoids random read accesses on heap changes. This improves performance
5113noticeably with many (hundreds) of watchers.
5114.Sp
5115The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
5116will be \f(CW0\fR.
5117.IP "\s-1EV_VERIFY\s0" 4
5118.IX Item "EV_VERIFY"
5119Controls how much internal verification (see \f(CW\*(C`ev_verify ()\*(C'\fR) will
5120be done: If set to \f(CW0\fR, no internal verification code will be compiled
5121in. If set to \f(CW1\fR, then verification code will be compiled in, but not
5122called. If set to \f(CW2\fR, then the internal verification code will be
5123called once per loop, which can slow down libev. If set to \f(CW3\fR, then the
5124verification code will be called very frequently, which will slow down
5125libev considerably.
5126.Sp
5127Verification errors are reported via C's \f(CW\*(C`assert\*(C'\fR mechanism, so if you
5128disable that (e.g. by defining \f(CW\*(C`NDEBUG\*(C'\fR) then no errors will be reported.
5129.Sp
5130The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
5131will be \f(CW0\fR.
2185.IP "\s-1EV_COMMON\s0" 4 5132.IP "\s-1EV_COMMON\s0" 4
2186.IX Item "EV_COMMON" 5133.IX Item "EV_COMMON"
2187By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining 5134By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining
2188this macro to a something else you can include more and other types of 5135this macro to something else you can include more and other types of
2189members. You have to define it each time you include one of the files, 5136members. You have to define it each time you include one of the files,
2190though, and it must be identical each time. 5137though, and it must be identical each time.
2191.Sp 5138.Sp
2192For example, the perl \s-1EV\s0 module uses something like this: 5139For example, the perl \s-1EV\s0 module uses something like this:
2193.Sp 5140.Sp
2194.Vb 3 5141.Vb 3
2195\& #define EV_COMMON \e 5142\& #define EV_COMMON \e
2196\& SV *self; /* contains this struct */ \e 5143\& SV *self; /* contains this struct */ \e
2197\& SV *cb_sv, *fh /* note no trailing ";" */ 5144\& SV *cb_sv, *fh /* note no trailing ";" */
2198.Ve 5145.Ve
2199.IP "\s-1EV_CB_DECLARE\s0 (type)" 4 5146.IP "\s-1EV_CB_DECLARE\s0 (type)" 4
2200.IX Item "EV_CB_DECLARE (type)" 5147.IX Item "EV_CB_DECLARE (type)"
2201.PD 0 5148.PD 0
2202.IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4 5149.IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4
… …
2204.IP "ev_set_cb (ev, cb)" 4 5151.IP "ev_set_cb (ev, cb)" 4
2205.IX Item "ev_set_cb (ev, cb)" 5152.IX Item "ev_set_cb (ev, cb)"
2206.PD 5153.PD
2207Can be used to change the callback member declaration in each watcher, 5154Can be used to change the callback member declaration in each watcher,
2208and the way callbacks are invoked and set. Must expand to a struct member 5155and the way callbacks are invoked and set. Must expand to a struct member
2209definition and a statement, respectively. See the \fIev.v\fR header file for 5156definition and a statement, respectively. See the \fIev.h\fR header file for
2210their default definitions. One possible use for overriding these is to 5157their default definitions. One possible use for overriding these is to
2211avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use 5158avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use
2212method calls instead of plain function calls in \*(C+. 5159method calls instead of plain function calls in \*(C+.
5160.SS "\s-1EXPORTED API SYMBOLS\s0"
5161.IX Subsection "EXPORTED API SYMBOLS"
5162If you need to re-export the \s-1API\s0 (e.g. via a \s-1DLL\s0) and you need a list of
5163exported symbols, you can use the provided \fISymbol.*\fR files which list
5164all public symbols, one per line:
5165.PP
5166.Vb 2
5167\& Symbols.ev for libev proper
5168\& Symbols.event for the libevent emulation
5169.Ve
5170.PP
5171This can also be used to rename all public symbols to avoid clashes with
5172multiple versions of libev linked together (which is obviously bad in
5173itself, but sometimes it is inconvenient to avoid this).
5174.PP
5175A sed command like this will create wrapper \f(CW\*(C`#define\*(C'\fR's that you need to
5176include before including \fIev.h\fR:
5177.PP
5178.Vb 1
5179\& <Symbols.ev sed \-e "s/.*/#define & myprefix_&/" >wrap.h
5180.Ve
5181.PP
5182This would create a file \fIwrap.h\fR which essentially looks like this:
5183.PP
5184.Vb 4
5185\& #define ev_backend myprefix_ev_backend
5186\& #define ev_check_start myprefix_ev_check_start
5187\& #define ev_check_stop myprefix_ev_check_stop
5188\& ...
5189.Ve
2213.Sh "\s-1EXAMPLES\s0" 5190.SS "\s-1EXAMPLES\s0"
2214.IX Subsection "EXAMPLES" 5191.IX Subsection "EXAMPLES"
2215For a real-world example of a program the includes libev 5192For a real-world example of a program the includes libev
2216verbatim, you can have a look at the \s-1EV\s0 perl module 5193verbatim, you can have a look at the \s-1EV\s0 perl module
2217(<http://software.schmorp.de/pkg/EV.html>). It has the libev files in 5194(<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
2218the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public 5195the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public
2219interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file 5196interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file
2220will be compiled. It is pretty complex because it provides its own header 5197will be compiled. It is pretty complex because it provides its own header
2221file. 5198file.
2222.Sp 5199.PP
2223The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file 5200The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file
2224that everybody includes and which overrides some autoconf choices: 5201that everybody includes and which overrides some configure choices:
2225.Sp 5202.PP
2226.Vb 4 5203.Vb 8
5204\& #define EV_FEATURES 8
5205\& #define EV_USE_SELECT 1
5206\& #define EV_PREPARE_ENABLE 1
5207\& #define EV_IDLE_ENABLE 1
5208\& #define EV_SIGNAL_ENABLE 1
5209\& #define EV_CHILD_ENABLE 1
2227\& #define EV_USE_POLL 0 5210\& #define EV_USE_STDEXCEPT 0
2228\& #define EV_MULTIPLICITY 0
2229\& #define EV_PERIODICS 0
2230\& #define EV_CONFIG_H <config.h> 5211\& #define EV_CONFIG_H <config.h>
2231.Ve 5212\&
2232.Sp
2233.Vb 1
2234\& #include "ev++.h" 5213\& #include "ev++.h"
2235.Ve 5214.Ve
2236.Sp 5215.PP
2237And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled: 5216And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled:
2238.Sp 5217.PP
2239.Vb 2 5218.Vb 2
2240\& #include "ev_cpp.h" 5219\& #include "ev_cpp.h"
2241\& #include "ev.c" 5220\& #include "ev.c"
2242.Ve 5221.Ve
5222.SH "INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT"
5223.IX Header "INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT"
5224.SS "\s-1THREADS AND COROUTINES\s0"
5225.IX Subsection "THREADS AND COROUTINES"
5226\fI\s-1THREADS\s0\fR
5227.IX Subsection "THREADS"
5228.PP
5229All libev functions are reentrant and thread-safe unless explicitly
5230documented otherwise, but libev implements no locking itself. This means
5231that you can use as many loops as you want in parallel, as long as there
5232are no concurrent calls into any libev function with the same loop
5233parameter (\f(CW\*(C`ev_default_*\*(C'\fR calls have an implicit default loop parameter,
5234of course): libev guarantees that different event loops share no data
5235structures that need any locking.
5236.PP
5237Or to put it differently: calls with different loop parameters can be done
5238concurrently from multiple threads, calls with the same loop parameter
5239must be done serially (but can be done from different threads, as long as
5240only one thread ever is inside a call at any point in time, e.g. by using
5241a mutex per loop).
5242.PP
5243Specifically to support threads (and signal handlers), libev implements
5244so-called \f(CW\*(C`ev_async\*(C'\fR watchers, which allow some limited form of
5245concurrency on the same event loop, namely waking it up \*(L"from the
5246outside\*(R".
5247.PP
5248If you want to know which design (one loop, locking, or multiple loops
5249without or something else still) is best for your problem, then I cannot
5250help you, but here is some generic advice:
5251.IP "\(bu" 4
5252most applications have a main thread: use the default libev loop
5253in that thread, or create a separate thread running only the default loop.
5254.Sp
5255This helps integrating other libraries or software modules that use libev
5256themselves and don't care/know about threading.
5257.IP "\(bu" 4
5258one loop per thread is usually a good model.
5259.Sp
5260Doing this is almost never wrong, sometimes a better-performance model
5261exists, but it is always a good start.
5262.IP "\(bu" 4
5263other models exist, such as the leader/follower pattern, where one
5264loop is handed through multiple threads in a kind of round-robin fashion.
5265.Sp
5266Choosing a model is hard \- look around, learn, know that usually you can do
5267better than you currently do :\-)
5268.IP "\(bu" 4
5269often you need to talk to some other thread which blocks in the
5270event loop.
5271.Sp
5272\&\f(CW\*(C`ev_async\*(C'\fR watchers can be used to wake them up from other threads safely
5273(or from signal contexts...).
5274.Sp
5275An example use would be to communicate signals or other events that only
5276work in the default loop by registering the signal watcher with the
5277default loop and triggering an \f(CW\*(C`ev_async\*(C'\fR watcher from the default loop
5278watcher callback into the event loop interested in the signal.
5279.PP
5280See also \*(L"\s-1THREAD LOCKING EXAMPLE\*(R"\s0.
5281.PP
5282\fI\s-1COROUTINES\s0\fR
5283.IX Subsection "COROUTINES"
5284.PP
5285Libev is very accommodating to coroutines (\*(L"cooperative threads\*(R"):
5286libev fully supports nesting calls to its functions from different
5287coroutines (e.g. you can call \f(CW\*(C`ev_run\*(C'\fR on the same loop from two
5288different coroutines, and switch freely between both coroutines running
5289the loop, as long as you don't confuse yourself). The only exception is
5290that you must not do this from \f(CW\*(C`ev_periodic\*(C'\fR reschedule callbacks.
5291.PP
5292Care has been taken to ensure that libev does not keep local state inside
5293\&\f(CW\*(C`ev_run\*(C'\fR, and other calls do not usually allow for coroutine switches as
5294they do not call any callbacks.
5295.SS "\s-1COMPILER WARNINGS\s0"
5296.IX Subsection "COMPILER WARNINGS"
5297Depending on your compiler and compiler settings, you might get no or a
5298lot of warnings when compiling libev code. Some people are apparently
5299scared by this.
5300.PP
5301However, these are unavoidable for many reasons. For one, each compiler
5302has different warnings, and each user has different tastes regarding
5303warning options. \*(L"Warn-free\*(R" code therefore cannot be a goal except when
5304targeting a specific compiler and compiler-version.
5305.PP
5306Another reason is that some compiler warnings require elaborate
5307workarounds, or other changes to the code that make it less clear and less
5308maintainable.
5309.PP
5310And of course, some compiler warnings are just plain stupid, or simply
5311wrong (because they don't actually warn about the condition their message
5312seems to warn about). For example, certain older gcc versions had some
5313warnings that resulted in an extreme number of false positives. These have
5314been fixed, but some people still insist on making code warn-free with
5315such buggy versions.
5316.PP
5317While libev is written to generate as few warnings as possible,
5318\&\*(L"warn-free\*(R" code is not a goal, and it is recommended not to build libev
5319with any compiler warnings enabled unless you are prepared to cope with
5320them (e.g. by ignoring them). Remember that warnings are just that:
5321warnings, not errors, or proof of bugs.
5322.SS "\s-1VALGRIND\s0"
5323.IX Subsection "VALGRIND"
5324Valgrind has a special section here because it is a popular tool that is
5325highly useful. Unfortunately, valgrind reports are very hard to interpret.
5326.PP
5327If you think you found a bug (memory leak, uninitialised data access etc.)
5328in libev, then check twice: If valgrind reports something like:
5329.PP
5330.Vb 3
5331\& ==2274== definitely lost: 0 bytes in 0 blocks.
5332\& ==2274== possibly lost: 0 bytes in 0 blocks.
5333\& ==2274== still reachable: 256 bytes in 1 blocks.
5334.Ve
5335.PP
5336Then there is no memory leak, just as memory accounted to global variables
5337is not a memleak \- the memory is still being referenced, and didn't leak.
5338.PP
5339Similarly, under some circumstances, valgrind might report kernel bugs
5340as if it were a bug in libev (e.g. in realloc or in the poll backend,
5341although an acceptable workaround has been found here), or it might be
5342confused.
5343.PP
5344Keep in mind that valgrind is a very good tool, but only a tool. Don't
5345make it into some kind of religion.
5346.PP
5347If you are unsure about something, feel free to contact the mailing list
5348with the full valgrind report and an explanation on why you think this
5349is a bug in libev (best check the archives, too :). However, don't be
5350annoyed when you get a brisk \*(L"this is no bug\*(R" answer and take the chance
5351of learning how to interpret valgrind properly.
5352.PP
5353If you need, for some reason, empty reports from valgrind for your project
5354I suggest using suppression lists.
5355.SH "PORTABILITY NOTES"
5356.IX Header "PORTABILITY NOTES"
5357.SS "\s-1GNU/LINUX 32 BIT LIMITATIONS\s0"
5358.IX Subsection "GNU/LINUX 32 BIT LIMITATIONS"
5359GNU/Linux is the only common platform that supports 64 bit file/large file
5360interfaces but \fIdisables\fR them by default.
5361.PP
5362That means that libev compiled in the default environment doesn't support
5363files larger than 2GiB or so, which mainly affects \f(CW\*(C`ev_stat\*(C'\fR watchers.
5364.PP
5365Unfortunately, many programs try to work around this GNU/Linux issue
5366by enabling the large file \s-1API,\s0 which makes them incompatible with the
5367standard libev compiled for their system.
5368.PP
5369Likewise, libev cannot enable the large file \s-1API\s0 itself as this would
5370suddenly make it incompatible to the default compile time environment,
5371i.e. all programs not using special compile switches.
5372.SS "\s-1OS/X AND DARWIN BUGS\s0"
5373.IX Subsection "OS/X AND DARWIN BUGS"
5374The whole thing is a bug if you ask me \- basically any system interface
5375you touch is broken, whether it is locales, poll, kqueue or even the
5376OpenGL drivers.
5377.PP
5378\fI\f(CI\*(C`kqueue\*(C'\fI is buggy\fR
5379.IX Subsection "kqueue is buggy"
5380.PP
5381The kqueue syscall is broken in all known versions \- most versions support
5382only sockets, many support pipes.
5383.PP
5384Libev tries to work around this by not using \f(CW\*(C`kqueue\*(C'\fR by default on this
5385rotten platform, but of course you can still ask for it when creating a
5386loop \- embedding a socket-only kqueue loop into a select-based one is
5387probably going to work well.
5388.PP
5389\fI\f(CI\*(C`poll\*(C'\fI is buggy\fR
5390.IX Subsection "poll is buggy"
5391.PP
5392Instead of fixing \f(CW\*(C`kqueue\*(C'\fR, Apple replaced their (working) \f(CW\*(C`poll\*(C'\fR
5393implementation by something calling \f(CW\*(C`kqueue\*(C'\fR internally around the 10.5.6
5394release, so now \f(CW\*(C`kqueue\*(C'\fR \fIand\fR \f(CW\*(C`poll\*(C'\fR are broken.
5395.PP
5396Libev tries to work around this by not using \f(CW\*(C`poll\*(C'\fR by default on
5397this rotten platform, but of course you can still ask for it when creating
5398a loop.
5399.PP
5400\fI\f(CI\*(C`select\*(C'\fI is buggy\fR
5401.IX Subsection "select is buggy"
5402.PP
5403All that's left is \f(CW\*(C`select\*(C'\fR, and of course Apple found a way to fuck this
5404one up as well: On \s-1OS/X,\s0 \f(CW\*(C`select\*(C'\fR actively limits the number of file
5405descriptors you can pass in to 1024 \- your program suddenly crashes when
5406you use more.
5407.PP
5408There is an undocumented \*(L"workaround\*(R" for this \- defining
5409\&\f(CW\*(C`_DARWIN_UNLIMITED_SELECT\*(C'\fR, which libev tries to use, so select \fIshould\fR
5410work on \s-1OS/X.\s0
5411.SS "\s-1SOLARIS PROBLEMS AND WORKAROUNDS\s0"
5412.IX Subsection "SOLARIS PROBLEMS AND WORKAROUNDS"
5413\fI\f(CI\*(C`errno\*(C'\fI reentrancy\fR
5414.IX Subsection "errno reentrancy"
5415.PP
5416The default compile environment on Solaris is unfortunately so
5417thread-unsafe that you can't even use components/libraries compiled
5418without \f(CW\*(C`\-D_REENTRANT\*(C'\fR in a threaded program, which, of course, isn't
5419defined by default. A valid, if stupid, implementation choice.
5420.PP
5421If you want to use libev in threaded environments you have to make sure
5422it's compiled with \f(CW\*(C`_REENTRANT\*(C'\fR defined.
5423.PP
5424\fIEvent port backend\fR
5425.IX Subsection "Event port backend"
5426.PP
5427The scalable event interface for Solaris is called \*(L"event
5428ports\*(R". Unfortunately, this mechanism is very buggy in all major
5429releases. If you run into high \s-1CPU\s0 usage, your program freezes or you get
5430a large number of spurious wakeups, make sure you have all the relevant
5431and latest kernel patches applied. No, I don't know which ones, but there
5432are multiple ones to apply, and afterwards, event ports actually work
5433great.
5434.PP
5435If you can't get it to work, you can try running the program by setting
5436the environment variable \f(CW\*(C`LIBEV_FLAGS=3\*(C'\fR to only allow \f(CW\*(C`poll\*(C'\fR and
5437\&\f(CW\*(C`select\*(C'\fR backends.
5438.SS "\s-1AIX POLL BUG\s0"
5439.IX Subsection "AIX POLL BUG"
5440\&\s-1AIX\s0 unfortunately has a broken \f(CW\*(C`poll.h\*(C'\fR header. Libev works around
5441this by trying to avoid the poll backend altogether (i.e. it's not even
5442compiled in), which normally isn't a big problem as \f(CW\*(C`select\*(C'\fR works fine
5443with large bitsets on \s-1AIX,\s0 and \s-1AIX\s0 is dead anyway.
5444.SS "\s-1WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS\s0"
5445.IX Subsection "WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS"
5446\fIGeneral issues\fR
5447.IX Subsection "General issues"
5448.PP
5449Win32 doesn't support any of the standards (e.g. \s-1POSIX\s0) that libev
5450requires, and its I/O model is fundamentally incompatible with the \s-1POSIX\s0
5451model. Libev still offers limited functionality on this platform in
5452the form of the \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR backend, and only supports socket
5453descriptors. This only applies when using Win32 natively, not when using
5454e.g. cygwin. Actually, it only applies to the microsofts own compilers,
5455as every compiler comes with a slightly differently broken/incompatible
5456environment.
5457.PP
5458Lifting these limitations would basically require the full
5459re-implementation of the I/O system. If you are into this kind of thing,
5460then note that glib does exactly that for you in a very portable way (note
5461also that glib is the slowest event library known to man).
5462.PP
5463There is no supported compilation method available on windows except
5464embedding it into other applications.
5465.PP
5466Sensible signal handling is officially unsupported by Microsoft \- libev
5467tries its best, but under most conditions, signals will simply not work.
5468.PP
5469Not a libev limitation but worth mentioning: windows apparently doesn't
5470accept large writes: instead of resulting in a partial write, windows will
5471either accept everything or return \f(CW\*(C`ENOBUFS\*(C'\fR if the buffer is too large,
5472so make sure you only write small amounts into your sockets (less than a
5473megabyte seems safe, but this apparently depends on the amount of memory
5474available).
5475.PP
5476Due to the many, low, and arbitrary limits on the win32 platform and
5477the abysmal performance of winsockets, using a large number of sockets
5478is not recommended (and not reasonable). If your program needs to use
5479more than a hundred or so sockets, then likely it needs to use a totally
5480different implementation for windows, as libev offers the \s-1POSIX\s0 readiness
5481notification model, which cannot be implemented efficiently on windows
5482(due to Microsoft monopoly games).
5483.PP
5484A typical way to use libev under windows is to embed it (see the embedding
5485section for details) and use the following \fIevwrap.h\fR header file instead
5486of \fIev.h\fR:
5487.PP
5488.Vb 2
5489\& #define EV_STANDALONE /* keeps ev from requiring config.h */
5490\& #define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
5491\&
5492\& #include "ev.h"
5493.Ve
5494.PP
5495And compile the following \fIevwrap.c\fR file into your project (make sure
5496you do \fInot\fR compile the \fIev.c\fR or any other embedded source files!):
5497.PP
5498.Vb 2
5499\& #include "evwrap.h"
5500\& #include "ev.c"
5501.Ve
5502.PP
5503\fIThe winsocket \f(CI\*(C`select\*(C'\fI function\fR
5504.IX Subsection "The winsocket select function"
5505.PP
5506The winsocket \f(CW\*(C`select\*(C'\fR function doesn't follow \s-1POSIX\s0 in that it
5507requires socket \fIhandles\fR and not socket \fIfile descriptors\fR (it is
5508also extremely buggy). This makes select very inefficient, and also
5509requires a mapping from file descriptors to socket handles (the Microsoft
5510C runtime provides the function \f(CW\*(C`_open_osfhandle\*(C'\fR for this). See the
5511discussion of the \f(CW\*(C`EV_SELECT_USE_FD_SET\*(C'\fR, \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR and
5512\&\f(CW\*(C`EV_FD_TO_WIN32_HANDLE\*(C'\fR preprocessor symbols for more info.
5513.PP
5514The configuration for a \*(L"naked\*(R" win32 using the Microsoft runtime
5515libraries and raw winsocket select is:
5516.PP
5517.Vb 2
5518\& #define EV_USE_SELECT 1
5519\& #define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
5520.Ve
5521.PP
5522Note that winsockets handling of fd sets is O(n), so you can easily get a
5523complexity in the O(nX) range when using win32.
5524.PP
5525\fILimited number of file descriptors\fR
5526.IX Subsection "Limited number of file descriptors"
5527.PP
5528Windows has numerous arbitrary (and low) limits on things.
5529.PP
5530Early versions of winsocket's select only supported waiting for a maximum
5531of \f(CW64\fR handles (probably owning to the fact that all windows kernels
5532can only wait for \f(CW64\fR things at the same time internally; Microsoft
5533recommends spawning a chain of threads and wait for 63 handles and the
5534previous thread in each. Sounds great!).
5535.PP
5536Newer versions support more handles, but you need to define \f(CW\*(C`FD_SETSIZE\*(C'\fR
5537to some high number (e.g. \f(CW2048\fR) before compiling the winsocket select
5538call (which might be in libev or elsewhere, for example, perl and many
5539other interpreters do their own select emulation on windows).
5540.PP
5541Another limit is the number of file descriptors in the Microsoft runtime
5542libraries, which by default is \f(CW64\fR (there must be a hidden \fI64\fR
5543fetish or something like this inside Microsoft). You can increase this
5544by calling \f(CW\*(C`_setmaxstdio\*(C'\fR, which can increase this limit to \f(CW2048\fR
5545(another arbitrary limit), but is broken in many versions of the Microsoft
5546runtime libraries. This might get you to about \f(CW512\fR or \f(CW2048\fR sockets
5547(depending on windows version and/or the phase of the moon). To get more,
5548you need to wrap all I/O functions and provide your own fd management, but
5549the cost of calling select (O(nX)) will likely make this unworkable.
5550.SS "\s-1PORTABILITY REQUIREMENTS\s0"
5551.IX Subsection "PORTABILITY REQUIREMENTS"
5552In addition to a working ISO-C implementation and of course the
5553backend-specific APIs, libev relies on a few additional extensions:
5554.ie n .IP """void (*)(ev_watcher_type *, int revents)"" must have compatible calling conventions regardless of ""ev_watcher_type *""." 4
5555.el .IP "\f(CWvoid (*)(ev_watcher_type *, int revents)\fR must have compatible calling conventions regardless of \f(CWev_watcher_type *\fR." 4
5556.IX Item "void (*)(ev_watcher_type *, int revents) must have compatible calling conventions regardless of ev_watcher_type *."
5557Libev assumes not only that all watcher pointers have the same internal
5558structure (guaranteed by \s-1POSIX\s0 but not by \s-1ISO C\s0 for example), but it also
5559assumes that the same (machine) code can be used to call any watcher
5560callback: The watcher callbacks have different type signatures, but libev
5561calls them using an \f(CW\*(C`ev_watcher *\*(C'\fR internally.
5562.IP "null pointers and integer zero are represented by 0 bytes" 4
5563.IX Item "null pointers and integer zero are represented by 0 bytes"
5564Libev uses \f(CW\*(C`memset\*(C'\fR to initialise structs and arrays to \f(CW0\fR bytes, and
5565relies on this setting pointers and integers to null.
5566.IP "pointer accesses must be thread-atomic" 4
5567.IX Item "pointer accesses must be thread-atomic"
5568Accessing a pointer value must be atomic, it must both be readable and
5569writable in one piece \- this is the case on all current architectures.
5570.ie n .IP """sig_atomic_t volatile"" must be thread-atomic as well" 4
5571.el .IP "\f(CWsig_atomic_t volatile\fR must be thread-atomic as well" 4
5572.IX Item "sig_atomic_t volatile must be thread-atomic as well"
5573The type \f(CW\*(C`sig_atomic_t volatile\*(C'\fR (or whatever is defined as
5574\&\f(CW\*(C`EV_ATOMIC_T\*(C'\fR) must be atomic with respect to accesses from different
5575threads. This is not part of the specification for \f(CW\*(C`sig_atomic_t\*(C'\fR, but is
5576believed to be sufficiently portable.
5577.ie n .IP """sigprocmask"" must work in a threaded environment" 4
5578.el .IP "\f(CWsigprocmask\fR must work in a threaded environment" 4
5579.IX Item "sigprocmask must work in a threaded environment"
5580Libev uses \f(CW\*(C`sigprocmask\*(C'\fR to temporarily block signals. This is not
5581allowed in a threaded program (\f(CW\*(C`pthread_sigmask\*(C'\fR has to be used). Typical
5582pthread implementations will either allow \f(CW\*(C`sigprocmask\*(C'\fR in the \*(L"main
5583thread\*(R" or will block signals process-wide, both behaviours would
5584be compatible with libev. Interaction between \f(CW\*(C`sigprocmask\*(C'\fR and
5585\&\f(CW\*(C`pthread_sigmask\*(C'\fR could complicate things, however.
5586.Sp
5587The most portable way to handle signals is to block signals in all threads
5588except the initial one, and run the signal handling loop in the initial
5589thread as well.
5590.ie n .IP """long"" must be large enough for common memory allocation sizes" 4
5591.el .IP "\f(CWlong\fR must be large enough for common memory allocation sizes" 4
5592.IX Item "long must be large enough for common memory allocation sizes"
5593To improve portability and simplify its \s-1API,\s0 libev uses \f(CW\*(C`long\*(C'\fR internally
5594instead of \f(CW\*(C`size_t\*(C'\fR when allocating its data structures. On non-POSIX
5595systems (Microsoft...) this might be unexpectedly low, but is still at
5596least 31 bits everywhere, which is enough for hundreds of millions of
5597watchers.
5598.ie n .IP """double"" must hold a time value in seconds with enough accuracy" 4
5599.el .IP "\f(CWdouble\fR must hold a time value in seconds with enough accuracy" 4
5600.IX Item "double must hold a time value in seconds with enough accuracy"
5601The type \f(CW\*(C`double\*(C'\fR is used to represent timestamps. It is required to
5602have at least 51 bits of mantissa (and 9 bits of exponent), which is
5603good enough for at least into the year 4000 with millisecond accuracy
5604(the design goal for libev). This requirement is overfulfilled by
5605implementations using \s-1IEEE 754,\s0 which is basically all existing ones.
5606.Sp
5607With \s-1IEEE 754\s0 doubles, you get microsecond accuracy until at least the
5608year 2255 (and millisecond accuracy till the year 287396 \- by then, libev
5609is either obsolete or somebody patched it to use \f(CW\*(C`long double\*(C'\fR or
5610something like that, just kidding).
5611.PP
5612If you know of other additional requirements drop me a note.
2243.SH "COMPLEXITIES" 5613.SH "ALGORITHMIC COMPLEXITIES"
2244.IX Header "COMPLEXITIES" 5614.IX Header "ALGORITHMIC COMPLEXITIES"
2245In this section the complexities of (many of) the algorithms used inside 5615In this section the complexities of (many of) the algorithms used inside
2246libev will be explained. For complexity discussions about backends see the 5616libev will be documented. For complexity discussions about backends see
2247documentation for \f(CW\*(C`ev_default_init\*(C'\fR. 5617the documentation for \f(CW\*(C`ev_default_init\*(C'\fR.
2248.RS 4 5618.PP
5619All of the following are about amortised time: If an array needs to be
5620extended, libev needs to realloc and move the whole array, but this
5621happens asymptotically rarer with higher number of elements, so O(1) might
5622mean that libev does a lengthy realloc operation in rare cases, but on
5623average it is much faster and asymptotically approaches constant time.
2249.IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4 5624.IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4
2250.IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 5625.IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)"
5626This means that, when you have a watcher that triggers in one hour and
5627there are 100 watchers that would trigger before that, then inserting will
5628have to skip roughly seven (\f(CW\*(C`ld 100\*(C'\fR) of these watchers.
5629.IP "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)" 4
5630.IX Item "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)"
5631That means that changing a timer costs less than removing/adding them,
5632as only the relative motion in the event queue has to be paid for.
5633.IP "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)" 4
5634.IX Item "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)"
5635These just add the watcher into an array or at the head of a list.
5636.IP "Stopping check/prepare/idle/fork/async watchers: O(1)" 4
5637.IX Item "Stopping check/prepare/idle/fork/async watchers: O(1)"
2251.PD 0 5638.PD 0
2252.IP "Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)" 4
2253.IX Item "Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)"
2254.IP "Starting io/check/prepare/idle/signal/child watchers: O(1)" 4
2255.IX Item "Starting io/check/prepare/idle/signal/child watchers: O(1)"
2256.IP "Stopping check/prepare/idle watchers: O(1)" 4
2257.IX Item "Stopping check/prepare/idle watchers: O(1)"
2258.IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % 16))" 4 5639.IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4
2259.IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % 16))" 5640.IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))"
5641.PD
5642These watchers are stored in lists, so they need to be walked to find the
5643correct watcher to remove. The lists are usually short (you don't usually
5644have many watchers waiting for the same fd or signal: one is typical, two
5645is rare).
2260.IP "Finding the next timer per loop iteration: O(1)" 4 5646.IP "Finding the next timer in each loop iteration: O(1)" 4
2261.IX Item "Finding the next timer per loop iteration: O(1)" 5647.IX Item "Finding the next timer in each loop iteration: O(1)"
5648By virtue of using a binary or 4\-heap, the next timer is always found at a
5649fixed position in the storage array.
2262.IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4 5650.IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4
2263.IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 5651.IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)"
2264.IP "Activating one watcher: O(1)" 4 5652A change means an I/O watcher gets started or stopped, which requires
2265.IX Item "Activating one watcher: O(1)" 5653libev to recalculate its status (and possibly tell the kernel, depending
2266.RE 5654on backend and whether \f(CW\*(C`ev_io_set\*(C'\fR was used).
2267.RS 4 5655.IP "Activating one watcher (putting it into the pending state): O(1)" 4
5656.IX Item "Activating one watcher (putting it into the pending state): O(1)"
5657.PD 0
5658.IP "Priority handling: O(number_of_priorities)" 4
5659.IX Item "Priority handling: O(number_of_priorities)"
2268.PD 5660.PD
5661Priorities are implemented by allocating some space for each
5662priority. When doing priority-based operations, libev usually has to
5663linearly search all the priorities, but starting/stopping and activating
5664watchers becomes O(1) with respect to priority handling.
5665.IP "Sending an ev_async: O(1)" 4
5666.IX Item "Sending an ev_async: O(1)"
5667.PD 0
5668.IP "Processing ev_async_send: O(number_of_async_watchers)" 4
5669.IX Item "Processing ev_async_send: O(number_of_async_watchers)"
5670.IP "Processing signals: O(max_signal_number)" 4
5671.IX Item "Processing signals: O(max_signal_number)"
5672.PD
5673Sending involves a system call \fIiff\fR there were no other \f(CW\*(C`ev_async_send\*(C'\fR
5674calls in the current loop iteration and the loop is currently
5675blocked. Checking for async and signal events involves iterating over all
5676running async watchers or all signal numbers.
5677.SH "PORTING FROM LIBEV 3.X TO 4.X"
5678.IX Header "PORTING FROM LIBEV 3.X TO 4.X"
5679The major version 4 introduced some incompatible changes to the \s-1API.\s0
5680.PP
5681At the moment, the \f(CW\*(C`ev.h\*(C'\fR header file provides compatibility definitions
5682for all changes, so most programs should still compile. The compatibility
5683layer might be removed in later versions of libev, so better update to the
5684new \s-1API\s0 early than late.
5685.ie n .IP """EV_COMPAT3"" backwards compatibility mechanism" 4
5686.el .IP "\f(CWEV_COMPAT3\fR backwards compatibility mechanism" 4
5687.IX Item "EV_COMPAT3 backwards compatibility mechanism"
5688The backward compatibility mechanism can be controlled by
5689\&\f(CW\*(C`EV_COMPAT3\*(C'\fR. See \*(L"\s-1PREPROCESSOR SYMBOLS/MACROS\*(R"\s0 in the \*(L"\s-1EMBEDDING\*(R"\s0
5690section.
5691.ie n .IP """ev_default_destroy"" and ""ev_default_fork"" have been removed" 4
5692.el .IP "\f(CWev_default_destroy\fR and \f(CWev_default_fork\fR have been removed" 4
5693.IX Item "ev_default_destroy and ev_default_fork have been removed"
5694These calls can be replaced easily by their \f(CW\*(C`ev_loop_xxx\*(C'\fR counterparts:
5695.Sp
5696.Vb 2
5697\& ev_loop_destroy (EV_DEFAULT_UC);
5698\& ev_loop_fork (EV_DEFAULT);
5699.Ve
5700.IP "function/symbol renames" 4
5701.IX Item "function/symbol renames"
5702A number of functions and symbols have been renamed:
5703.Sp
5704.Vb 3
5705\& ev_loop => ev_run
5706\& EVLOOP_NONBLOCK => EVRUN_NOWAIT
5707\& EVLOOP_ONESHOT => EVRUN_ONCE
5708\&
5709\& ev_unloop => ev_break
5710\& EVUNLOOP_CANCEL => EVBREAK_CANCEL
5711\& EVUNLOOP_ONE => EVBREAK_ONE
5712\& EVUNLOOP_ALL => EVBREAK_ALL
5713\&
5714\& EV_TIMEOUT => EV_TIMER
5715\&
5716\& ev_loop_count => ev_iteration
5717\& ev_loop_depth => ev_depth
5718\& ev_loop_verify => ev_verify
5719.Ve
5720.Sp
5721Most functions working on \f(CW\*(C`struct ev_loop\*(C'\fR objects don't have an
5722\&\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
5723associated constants have been renamed to not collide with the \f(CW\*(C`struct
5724ev_loop\*(C'\fR anymore and \f(CW\*(C`EV_TIMER\*(C'\fR now follows the same naming scheme
5725as all other watcher types. Note that \f(CW\*(C`ev_loop_fork\*(C'\fR is still called
5726\&\f(CW\*(C`ev_loop_fork\*(C'\fR because it would otherwise clash with the \f(CW\*(C`ev_fork\*(C'\fR
5727typedef.
5728.ie n .IP """EV_MINIMAL"" mechanism replaced by ""EV_FEATURES""" 4
5729.el .IP "\f(CWEV_MINIMAL\fR mechanism replaced by \f(CWEV_FEATURES\fR" 4
5730.IX Item "EV_MINIMAL mechanism replaced by EV_FEATURES"
5731The preprocessor symbol \f(CW\*(C`EV_MINIMAL\*(C'\fR has been replaced by a different
5732mechanism, \f(CW\*(C`EV_FEATURES\*(C'\fR. Programs using \f(CW\*(C`EV_MINIMAL\*(C'\fR usually compile
5733and work, but the library code will of course be larger.
5734.SH "GLOSSARY"
5735.IX Header "GLOSSARY"
5736.IP "active" 4
5737.IX Item "active"
5738A watcher is active as long as it has been started and not yet stopped.
5739See \*(L"\s-1WATCHER STATES\*(R"\s0 for details.
5740.IP "application" 4
5741.IX Item "application"
5742In this document, an application is whatever is using libev.
5743.IP "backend" 4
5744.IX Item "backend"
5745The part of the code dealing with the operating system interfaces.
5746.IP "callback" 4
5747.IX Item "callback"
5748The address of a function that is called when some event has been
5749detected. Callbacks are being passed the event loop, the watcher that
5750received the event, and the actual event bitset.
5751.IP "callback/watcher invocation" 4
5752.IX Item "callback/watcher invocation"
5753The act of calling the callback associated with a watcher.
5754.IP "event" 4
5755.IX Item "event"
5756A change of state of some external event, such as data now being available
5757for reading on a file descriptor, time having passed or simply not having
5758any other events happening anymore.
5759.Sp
5760In libev, events are represented as single bits (such as \f(CW\*(C`EV_READ\*(C'\fR or
5761\&\f(CW\*(C`EV_TIMER\*(C'\fR).
5762.IP "event library" 4
5763.IX Item "event library"
5764A software package implementing an event model and loop.
5765.IP "event loop" 4
5766.IX Item "event loop"
5767An entity that handles and processes external events and converts them
5768into callback invocations.
5769.IP "event model" 4
5770.IX Item "event model"
5771The model used to describe how an event loop handles and processes
5772watchers and events.
5773.IP "pending" 4
5774.IX Item "pending"
5775A watcher is pending as soon as the corresponding event has been
5776detected. See \*(L"\s-1WATCHER STATES\*(R"\s0 for details.
5777.IP "real time" 4
5778.IX Item "real time"
5779The physical time that is observed. It is apparently strictly monotonic :)
5780.IP "wall-clock time" 4
5781.IX Item "wall-clock time"
5782The time and date as shown on clocks. Unlike real time, it can actually
5783be wrong and jump forwards and backwards, e.g. when you adjust your
5784clock.
5785.IP "watcher" 4
5786.IX Item "watcher"
5787A data structure that describes interest in certain events. Watchers need
5788to be started (attached to an event loop) before they can receive events.
2269.SH "AUTHOR" 5789.SH "AUTHOR"
2270.IX Header "AUTHOR" 5790.IX Header "AUTHOR"
2271Marc Lehmann <libev@schmorp.de>. 5791Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5792Magnusson and Emanuele Giaquinta, and minor corrections by many others.

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