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Revision: 1.98
Committed: Thu Feb 28 02:17:11 2013 UTC (11 years, 4 months ago) by root
Branch: MAIN
CVS Tags: rel-4_15
Changes since 1.97: +5 -4 lines
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File Contents

# Content
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123 .rm #[ #] #H #V #F C
124 .\" ========================================================================
125 .\"
126 .IX Title "LIBEV 3"
127 .TH LIBEV 3 "2013-02-28" "libev-4.11" "libev - high performance full featured event loop"
128 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
129 .\" way too many mistakes in technical documents.
130 .if n .ad l
131 .nh
132 .SH "NAME"
133 libev \- a high performance full\-featured event loop written in C
134 .SH "SYNOPSIS"
135 .IX Header "SYNOPSIS"
136 .Vb 1
137 \& #include <ev.h>
138 .Ve
139 .SS "\s-1EXAMPLE\s0 \s-1PROGRAM\s0"
140 .IX Subsection "EXAMPLE PROGRAM"
141 .Vb 2
142 \& // a single header file is required
143 \& #include <ev.h>
144 \&
145 \& #include <stdio.h> // for puts
146 \&
147 \& // every watcher type has its own typedef\*(Aqd struct
148 \& // with the name ev_TYPE
149 \& ev_io stdin_watcher;
150 \& ev_timer timeout_watcher;
151 \&
152 \& // all watcher callbacks have a similar signature
153 \& // this callback is called when data is readable on stdin
154 \& static void
155 \& stdin_cb (EV_P_ ev_io *w, int revents)
156 \& {
157 \& puts ("stdin ready");
158 \& // for one\-shot events, one must manually stop the watcher
159 \& // with its corresponding stop function.
160 \& ev_io_stop (EV_A_ w);
161 \&
162 \& // this causes all nested ev_run\*(Aqs to stop iterating
163 \& ev_break (EV_A_ EVBREAK_ALL);
164 \& }
165 \&
166 \& // another callback, this time for a time\-out
167 \& static void
168 \& timeout_cb (EV_P_ ev_timer *w, int revents)
169 \& {
170 \& puts ("timeout");
171 \& // this causes the innermost ev_run to stop iterating
172 \& ev_break (EV_A_ EVBREAK_ONE);
173 \& }
174 \&
175 \& int
176 \& main (void)
177 \& {
178 \& // use the default event loop unless you have special needs
179 \& struct ev_loop *loop = EV_DEFAULT;
180 \&
181 \& // initialise an io watcher, then start it
182 \& // this one will watch for stdin to become readable
183 \& ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
184 \& ev_io_start (loop, &stdin_watcher);
185 \&
186 \& // initialise a timer watcher, then start it
187 \& // simple non\-repeating 5.5 second timeout
188 \& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
189 \& ev_timer_start (loop, &timeout_watcher);
190 \&
191 \& // now wait for events to arrive
192 \& ev_run (loop, 0);
193 \&
194 \& // break was called, so exit
195 \& return 0;
196 \& }
197 .Ve
198 .SH "ABOUT THIS DOCUMENT"
199 .IX Header "ABOUT THIS DOCUMENT"
200 This document documents the libev software package.
201 .PP
202 The newest version of this document is also available as an html-formatted
203 web page you might find easier to navigate when reading it for the first
204 time: <http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
205 .PP
206 While this document tries to be as complete as possible in documenting
207 libev, its usage and the rationale behind its design, it is not a tutorial
208 on event-based programming, nor will it introduce event-based programming
209 with libev.
210 .PP
211 Familiarity with event based programming techniques in general is assumed
212 throughout this document.
213 .SH "WHAT TO READ WHEN IN A HURRY"
214 .IX Header "WHAT TO READ WHEN IN A HURRY"
215 This manual tries to be very detailed, but unfortunately, this also makes
216 it very long. If you just want to know the basics of libev, I suggest
217 reading \*(L"\s-1ANATOMY\s0 \s-1OF\s0 A \s-1WATCHER\s0\*(R", then the \*(L"\s-1EXAMPLE\s0 \s-1PROGRAM\s0\*(R" above and
218 look up the missing functions in \*(L"\s-1GLOBAL\s0 \s-1FUNCTIONS\s0\*(R" and the \f(CW\*(C`ev_io\*(C'\fR and
219 \&\f(CW\*(C`ev_timer\*(C'\fR sections in \*(L"\s-1WATCHER\s0 \s-1TYPES\s0\*(R".
220 .SH "ABOUT LIBEV"
221 .IX Header "ABOUT LIBEV"
222 Libev is an event loop: you register interest in certain events (such as a
223 file descriptor being readable or a timeout occurring), and it will manage
224 these event sources and provide your program with events.
225 .PP
226 To do this, it must take more or less complete control over your process
227 (or thread) by executing the \fIevent loop\fR handler, and will then
228 communicate events via a callback mechanism.
229 .PP
230 You register interest in certain events by registering so-called \fIevent
231 watchers\fR, which are relatively small C structures you initialise with the
232 details of the event, and then hand it over to libev by \fIstarting\fR the
233 watcher.
234 .SS "\s-1FEATURES\s0"
235 .IX Subsection "FEATURES"
236 Libev supports \f(CW\*(C`select\*(C'\fR, \f(CW\*(C`poll\*(C'\fR, the Linux-specific \f(CW\*(C`epoll\*(C'\fR, the
237 BSD-specific \f(CW\*(C`kqueue\*(C'\fR and the Solaris-specific event port mechanisms
238 for file descriptor events (\f(CW\*(C`ev_io\*(C'\fR), the Linux \f(CW\*(C`inotify\*(C'\fR interface
239 (for \f(CW\*(C`ev_stat\*(C'\fR), Linux eventfd/signalfd (for faster and cleaner
240 inter-thread wakeup (\f(CW\*(C`ev_async\*(C'\fR)/signal handling (\f(CW\*(C`ev_signal\*(C'\fR)) relative
241 timers (\f(CW\*(C`ev_timer\*(C'\fR), absolute timers with customised rescheduling
242 (\f(CW\*(C`ev_periodic\*(C'\fR), synchronous signals (\f(CW\*(C`ev_signal\*(C'\fR), process status
243 change events (\f(CW\*(C`ev_child\*(C'\fR), and event watchers dealing with the event
244 loop mechanism itself (\f(CW\*(C`ev_idle\*(C'\fR, \f(CW\*(C`ev_embed\*(C'\fR, \f(CW\*(C`ev_prepare\*(C'\fR and
245 \&\f(CW\*(C`ev_check\*(C'\fR watchers) as well as file watchers (\f(CW\*(C`ev_stat\*(C'\fR) and even
246 limited support for fork events (\f(CW\*(C`ev_fork\*(C'\fR).
247 .PP
248 It also is quite fast (see this
249 benchmark <http://libev.schmorp.de/bench.html> comparing it to libevent
250 for example).
251 .SS "\s-1CONVENTIONS\s0"
252 .IX Subsection "CONVENTIONS"
253 Libev is very configurable. In this manual the default (and most common)
254 configuration will be described, which supports multiple event loops. For
255 more info about various configuration options please have a look at
256 \&\fB\s-1EMBED\s0\fR section in this manual. If libev was configured without support
257 for multiple event loops, then all functions taking an initial argument of
258 name \f(CW\*(C`loop\*(C'\fR (which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) will not have
259 this argument.
260 .SS "\s-1TIME\s0 \s-1REPRESENTATION\s0"
261 .IX Subsection "TIME REPRESENTATION"
262 Libev represents time as a single floating point number, representing
263 the (fractional) number of seconds since the (\s-1POSIX\s0) epoch (in practice
264 somewhere near the beginning of 1970, details are complicated, don't
265 ask). This type is called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use
266 too. It usually aliases to the \f(CW\*(C`double\*(C'\fR type in C. When you need to do
267 any calculations on it, you should treat it as some floating point value.
268 .PP
269 Unlike the name component \f(CW\*(C`stamp\*(C'\fR might indicate, it is also used for
270 time differences (e.g. delays) throughout libev.
271 .SH "ERROR HANDLING"
272 .IX Header "ERROR HANDLING"
273 Libev knows three classes of errors: operating system errors, usage errors
274 and internal errors (bugs).
275 .PP
276 When libev catches an operating system error it cannot handle (for example
277 a system call indicating a condition libev cannot fix), it calls the callback
278 set via \f(CW\*(C`ev_set_syserr_cb\*(C'\fR, which is supposed to fix the problem or
279 abort. The default is to print a diagnostic message and to call \f(CW\*(C`abort
280 ()\*(C'\fR.
281 .PP
282 When libev detects a usage error such as a negative timer interval, then
283 it will print a diagnostic message and abort (via the \f(CW\*(C`assert\*(C'\fR mechanism,
284 so \f(CW\*(C`NDEBUG\*(C'\fR will disable this checking): these are programming errors in
285 the libev caller and need to be fixed there.
286 .PP
287 Libev also has a few internal error-checking \f(CW\*(C`assert\*(C'\fRions, and also has
288 extensive consistency checking code. These do not trigger under normal
289 circumstances, as they indicate either a bug in libev or worse.
290 .SH "GLOBAL FUNCTIONS"
291 .IX Header "GLOBAL FUNCTIONS"
292 These functions can be called anytime, even before initialising the
293 library in any way.
294 .IP "ev_tstamp ev_time ()" 4
295 .IX Item "ev_tstamp ev_time ()"
296 Returns the current time as libev would use it. Please note that the
297 \&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp
298 you actually want to know. Also interesting is the combination of
299 \&\f(CW\*(C`ev_now_update\*(C'\fR and \f(CW\*(C`ev_now\*(C'\fR.
300 .IP "ev_sleep (ev_tstamp interval)" 4
301 .IX Item "ev_sleep (ev_tstamp interval)"
302 Sleep for the given interval: The current thread will be blocked
303 until either it is interrupted or the given time interval has
304 passed (approximately \- it might return a bit earlier even if not
305 interrupted). Returns immediately if \f(CW\*(C`interval <= 0\*(C'\fR.
306 .Sp
307 Basically this is a sub-second-resolution \f(CW\*(C`sleep ()\*(C'\fR.
308 .Sp
309 The range of the \f(CW\*(C`interval\*(C'\fR is limited \- libev only guarantees to work
310 with sleep times of up to one day (\f(CW\*(C`interval <= 86400\*(C'\fR).
311 .IP "int ev_version_major ()" 4
312 .IX Item "int ev_version_major ()"
313 .PD 0
314 .IP "int ev_version_minor ()" 4
315 .IX Item "int ev_version_minor ()"
316 .PD
317 You can find out the major and minor \s-1ABI\s0 version numbers of the library
318 you linked against by calling the functions \f(CW\*(C`ev_version_major\*(C'\fR and
319 \&\f(CW\*(C`ev_version_minor\*(C'\fR. If you want, you can compare against the global
320 symbols \f(CW\*(C`EV_VERSION_MAJOR\*(C'\fR and \f(CW\*(C`EV_VERSION_MINOR\*(C'\fR, which specify the
321 version of the library your program was compiled against.
322 .Sp
323 These version numbers refer to the \s-1ABI\s0 version of the library, not the
324 release version.
325 .Sp
326 Usually, it's a good idea to terminate if the major versions mismatch,
327 as this indicates an incompatible change. Minor versions are usually
328 compatible to older versions, so a larger minor version alone is usually
329 not a problem.
330 .Sp
331 Example: Make sure we haven't accidentally been linked against the wrong
332 version (note, however, that this will not detect other \s-1ABI\s0 mismatches,
333 such as \s-1LFS\s0 or reentrancy).
334 .Sp
335 .Vb 3
336 \& assert (("libev version mismatch",
337 \& ev_version_major () == EV_VERSION_MAJOR
338 \& && ev_version_minor () >= EV_VERSION_MINOR));
339 .Ve
340 .IP "unsigned int ev_supported_backends ()" 4
341 .IX Item "unsigned int ev_supported_backends ()"
342 Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR
343 value) compiled into this binary of libev (independent of their
344 availability on the system you are running on). See \f(CW\*(C`ev_default_loop\*(C'\fR for
345 a description of the set values.
346 .Sp
347 Example: make sure we have the epoll method, because yeah this is cool and
348 a must have and can we have a torrent of it please!!!11
349 .Sp
350 .Vb 2
351 \& assert (("sorry, no epoll, no sex",
352 \& ev_supported_backends () & EVBACKEND_EPOLL));
353 .Ve
354 .IP "unsigned int ev_recommended_backends ()" 4
355 .IX Item "unsigned int ev_recommended_backends ()"
356 Return the set of all backends compiled into this binary of libev and
357 also recommended for this platform, meaning it will work for most file
358 descriptor types. This set is often smaller than the one returned by
359 \&\f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on most BSDs
360 and will not be auto-detected unless you explicitly request it (assuming
361 you know what you are doing). This is the set of backends that libev will
362 probe for if you specify no backends explicitly.
363 .IP "unsigned int ev_embeddable_backends ()" 4
364 .IX Item "unsigned int ev_embeddable_backends ()"
365 Returns the set of backends that are embeddable in other event loops. This
366 value is platform-specific but can include backends not available on the
367 current system. To find which embeddable backends might be supported on
368 the current system, you would need to look at \f(CW\*(C`ev_embeddable_backends ()
369 & ev_supported_backends ()\*(C'\fR, likewise for recommended ones.
370 .Sp
371 See the description of \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
372 .IP "ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())" 4
373 .IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())"
374 Sets the allocation function to use (the prototype is similar \- the
375 semantics are identical to the \f(CW\*(C`realloc\*(C'\fR C89/SuS/POSIX function). It is
376 used to allocate and free memory (no surprises here). If it returns zero
377 when memory needs to be allocated (\f(CW\*(C`size != 0\*(C'\fR), the library might abort
378 or take some potentially destructive action.
379 .Sp
380 Since some systems (at least OpenBSD and Darwin) fail to implement
381 correct \f(CW\*(C`realloc\*(C'\fR semantics, libev will use a wrapper around the system
382 \&\f(CW\*(C`realloc\*(C'\fR and \f(CW\*(C`free\*(C'\fR functions by default.
383 .Sp
384 You could override this function in high-availability programs to, say,
385 free some memory if it cannot allocate memory, to use a special allocator,
386 or even to sleep a while and retry until some memory is available.
387 .Sp
388 Example: Replace the libev allocator with one that waits a bit and then
389 retries (example requires a standards-compliant \f(CW\*(C`realloc\*(C'\fR).
390 .Sp
391 .Vb 6
392 \& static void *
393 \& persistent_realloc (void *ptr, size_t size)
394 \& {
395 \& for (;;)
396 \& {
397 \& void *newptr = realloc (ptr, size);
398 \&
399 \& if (newptr)
400 \& return newptr;
401 \&
402 \& sleep (60);
403 \& }
404 \& }
405 \&
406 \& ...
407 \& ev_set_allocator (persistent_realloc);
408 .Ve
409 .IP "ev_set_syserr_cb (void (*cb)(const char *msg) throw ())" 4
410 .IX Item "ev_set_syserr_cb (void (*cb)(const char *msg) throw ())"
411 Set the callback function to call on a retryable system call error (such
412 as failed select, poll, epoll_wait). The message is a printable string
413 indicating the system call or subsystem causing the problem. If this
414 callback is set, then libev will expect it to remedy the situation, no
415 matter what, when it returns. That is, libev will generally retry the
416 requested operation, or, if the condition doesn't go away, do bad stuff
417 (such as abort).
418 .Sp
419 Example: This is basically the same thing that libev does internally, too.
420 .Sp
421 .Vb 6
422 \& static void
423 \& fatal_error (const char *msg)
424 \& {
425 \& perror (msg);
426 \& abort ();
427 \& }
428 \&
429 \& ...
430 \& ev_set_syserr_cb (fatal_error);
431 .Ve
432 .IP "ev_feed_signal (int signum)" 4
433 .IX Item "ev_feed_signal (int signum)"
434 This function can be used to \*(L"simulate\*(R" a signal receive. It is completely
435 safe to call this function at any time, from any context, including signal
436 handlers or random threads.
437 .Sp
438 Its main use is to customise signal handling in your process, especially
439 in the presence of threads. For example, you could block signals
440 by default in all threads (and specifying \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR when
441 creating any loops), and in one thread, use \f(CW\*(C`sigwait\*(C'\fR or any other
442 mechanism to wait for signals, then \*(L"deliver\*(R" them to libev by calling
443 \&\f(CW\*(C`ev_feed_signal\*(C'\fR.
444 .SH "FUNCTIONS CONTROLLING EVENT LOOPS"
445 .IX Header "FUNCTIONS CONTROLLING EVENT LOOPS"
446 An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR (the \f(CW\*(C`struct\*(C'\fR is
447 \&\fInot\fR optional in this case unless libev 3 compatibility is disabled, as
448 libev 3 had an \f(CW\*(C`ev_loop\*(C'\fR function colliding with the struct name).
449 .PP
450 The library knows two types of such loops, the \fIdefault\fR loop, which
451 supports child process events, and dynamically created event loops which
452 do not.
453 .IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
454 .IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
455 This returns the \*(L"default\*(R" event loop object, which is what you should
456 normally use when you just need \*(L"the event loop\*(R". Event loop objects and
457 the \f(CW\*(C`flags\*(C'\fR parameter are described in more detail in the entry for
458 \&\f(CW\*(C`ev_loop_new\*(C'\fR.
459 .Sp
460 If the default loop is already initialised then this function simply
461 returns it (and ignores the flags. If that is troubling you, check
462 \&\f(CW\*(C`ev_backend ()\*(C'\fR afterwards). Otherwise it will create it with the given
463 flags, which should almost always be \f(CW0\fR, unless the caller is also the
464 one calling \f(CW\*(C`ev_run\*(C'\fR or otherwise qualifies as \*(L"the main program\*(R".
465 .Sp
466 If you don't know what event loop to use, use the one returned from this
467 function (or via the \f(CW\*(C`EV_DEFAULT\*(C'\fR macro).
468 .Sp
469 Note that this function is \fInot\fR thread-safe, so if you want to use it
470 from multiple threads, you have to employ some kind of mutex (note also
471 that this case is unlikely, as loops cannot be shared easily between
472 threads anyway).
473 .Sp
474 The default loop is the only loop that can handle \f(CW\*(C`ev_child\*(C'\fR watchers,
475 and to do this, it always registers a handler for \f(CW\*(C`SIGCHLD\*(C'\fR. If this is
476 a problem for your application you can either create a dynamic loop with
477 \&\f(CW\*(C`ev_loop_new\*(C'\fR which doesn't do that, or you can simply overwrite the
478 \&\f(CW\*(C`SIGCHLD\*(C'\fR signal handler \fIafter\fR calling \f(CW\*(C`ev_default_init\*(C'\fR.
479 .Sp
480 Example: This is the most typical usage.
481 .Sp
482 .Vb 2
483 \& if (!ev_default_loop (0))
484 \& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
485 .Ve
486 .Sp
487 Example: Restrict libev to the select and poll backends, and do not allow
488 environment settings to be taken into account:
489 .Sp
490 .Vb 1
491 \& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
492 .Ve
493 .IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
494 .IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
495 This will create and initialise a new event loop object. If the loop
496 could not be initialised, returns false.
497 .Sp
498 This function is thread-safe, and one common way to use libev with
499 threads is indeed to create one loop per thread, and using the default
500 loop in the \*(L"main\*(R" or \*(L"initial\*(R" thread.
501 .Sp
502 The flags argument can be used to specify special behaviour or specific
503 backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR).
504 .Sp
505 The following flags are supported:
506 .RS 4
507 .ie n .IP """EVFLAG_AUTO""" 4
508 .el .IP "\f(CWEVFLAG_AUTO\fR" 4
509 .IX Item "EVFLAG_AUTO"
510 The default flags value. Use this if you have no clue (it's the right
511 thing, believe me).
512 .ie n .IP """EVFLAG_NOENV""" 4
513 .el .IP "\f(CWEVFLAG_NOENV\fR" 4
514 .IX Item "EVFLAG_NOENV"
515 If this flag bit is or'ed into the flag value (or the program runs setuid
516 or setgid) then libev will \fInot\fR look at the environment variable
517 \&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will
518 override the flags completely if it is found in the environment. This is
519 useful to try out specific backends to test their performance, or to work
520 around bugs.
521 .ie n .IP """EVFLAG_FORKCHECK""" 4
522 .el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4
523 .IX Item "EVFLAG_FORKCHECK"
524 Instead of calling \f(CW\*(C`ev_loop_fork\*(C'\fR manually after a fork, you can also
525 make libev check for a fork in each iteration by enabling this flag.
526 .Sp
527 This works by calling \f(CW\*(C`getpid ()\*(C'\fR on every iteration of the loop,
528 and thus this might slow down your event loop if you do a lot of loop
529 iterations and little real work, but is usually not noticeable (on my
530 GNU/Linux system for example, \f(CW\*(C`getpid\*(C'\fR is actually a simple 5\-insn sequence
531 without a system call and thus \fIvery\fR fast, but my GNU/Linux system also has
532 \&\f(CW\*(C`pthread_atfork\*(C'\fR which is even faster).
533 .Sp
534 The big advantage of this flag is that you can forget about fork (and
535 forget about forgetting to tell libev about forking) when you use this
536 flag.
537 .Sp
538 This flag setting cannot be overridden or specified in the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR
539 environment variable.
540 .ie n .IP """EVFLAG_NOINOTIFY""" 4
541 .el .IP "\f(CWEVFLAG_NOINOTIFY\fR" 4
542 .IX Item "EVFLAG_NOINOTIFY"
543 When this flag is specified, then libev will not attempt to use the
544 \&\fIinotify\fR \s-1API\s0 for its \f(CW\*(C`ev_stat\*(C'\fR watchers. Apart from debugging and
545 testing, this flag can be useful to conserve inotify file descriptors, as
546 otherwise each loop using \f(CW\*(C`ev_stat\*(C'\fR watchers consumes one inotify handle.
547 .ie n .IP """EVFLAG_SIGNALFD""" 4
548 .el .IP "\f(CWEVFLAG_SIGNALFD\fR" 4
549 .IX Item "EVFLAG_SIGNALFD"
550 When this flag is specified, then libev will attempt to use the
551 \&\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
552 delivers signals synchronously, which makes it both faster and might make
553 it possible to get the queued signal data. It can also simplify signal
554 handling with threads, as long as you properly block signals in your
555 threads that are not interested in handling them.
556 .Sp
557 Signalfd will not be used by default as this changes your signal mask, and
558 there are a lot of shoddy libraries and programs (glib's threadpool for
559 example) that can't properly initialise their signal masks.
560 .ie n .IP """EVFLAG_NOSIGMASK""" 4
561 .el .IP "\f(CWEVFLAG_NOSIGMASK\fR" 4
562 .IX Item "EVFLAG_NOSIGMASK"
563 When this flag is specified, then libev will avoid to modify the signal
564 mask. Specifically, this means you have to make sure signals are unblocked
565 when you want to receive them.
566 .Sp
567 This behaviour is useful when you want to do your own signal handling, or
568 want to handle signals only in specific threads and want to avoid libev
569 unblocking the signals.
570 .Sp
571 It's also required by \s-1POSIX\s0 in a threaded program, as libev calls
572 \&\f(CW\*(C`sigprocmask\*(C'\fR, whose behaviour is officially unspecified.
573 .Sp
574 This flag's behaviour will become the default in future versions of libev.
575 .ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4
576 .el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4
577 .IX Item "EVBACKEND_SELECT (value 1, portable select backend)"
578 This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as
579 libev tries to roll its own fd_set with no limits on the number of fds,
580 but if that fails, expect a fairly low limit on the number of fds when
581 using this backend. It doesn't scale too well (O(highest_fd)), but its
582 usually the fastest backend for a low number of (low-numbered :) fds.
583 .Sp
584 To get good performance out of this backend you need a high amount of
585 parallelism (most of the file descriptors should be busy). If you are
586 writing a server, you should \f(CW\*(C`accept ()\*(C'\fR in a loop to accept as many
587 connections as possible during one iteration. You might also want to have
588 a look at \f(CW\*(C`ev_set_io_collect_interval ()\*(C'\fR to increase the amount of
589 readiness notifications you get per iteration.
590 .Sp
591 This 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
592 \&\f(CW\*(C`writefds\*(C'\fR set (and to work around Microsoft Windows bugs, also onto the
593 \&\f(CW\*(C`exceptfds\*(C'\fR set on that platform).
594 .ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4
595 .el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4
596 .IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)"
597 And this is your standard \fIpoll\fR\|(2) backend. It's more complicated
598 than select, but handles sparse fds better and has no artificial
599 limit on the number of fds you can use (except it will slow down
600 considerably with a lot of inactive fds). It scales similarly to select,
601 i.e. O(total_fds). See the entry for \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR, above, for
602 performance tips.
603 .Sp
604 This backend maps \f(CW\*(C`EV_READ\*(C'\fR to \f(CW\*(C`POLLIN | POLLERR | POLLHUP\*(C'\fR, and
605 \&\f(CW\*(C`EV_WRITE\*(C'\fR to \f(CW\*(C`POLLOUT | POLLERR | POLLHUP\*(C'\fR.
606 .ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
607 .el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
608 .IX Item "EVBACKEND_EPOLL (value 4, Linux)"
609 Use the linux-specific \fIepoll\fR\|(7) interface (for both pre\- and post\-2.6.9
610 kernels).
611 .Sp
612 For few fds, this backend is a bit little slower than poll and select, but
613 it scales phenomenally better. While poll and select usually scale like
614 O(total_fds) where total_fds is the total number of fds (or the highest
615 fd), epoll scales either O(1) or O(active_fds).
616 .Sp
617 The epoll mechanism deserves honorable mention as the most misdesigned
618 of the more advanced event mechanisms: mere annoyances include silently
619 dropping file descriptors, requiring a system call per change per file
620 descriptor (and unnecessary guessing of parameters), problems with dup,
621 returning before the timeout value, resulting in additional iterations
622 (and only giving 5ms accuracy while select on the same platform gives
623 0.1ms) and so on. The biggest issue is fork races, however \- if a program
624 forks then \fIboth\fR parent and child process have to recreate the epoll
625 set, which can take considerable time (one syscall per file descriptor)
626 and is of course hard to detect.
627 .Sp
628 Epoll is also notoriously buggy \- embedding epoll fds \fIshould\fR work,
629 but of course \fIdoesn't\fR, and epoll just loves to report events for
630 totally \fIdifferent\fR file descriptors (even already closed ones, so
631 one cannot even remove them from the set) than registered in the set
632 (especially on \s-1SMP\s0 systems). Libev tries to counter these spurious
633 notifications by employing an additional generation counter and comparing
634 that against the events to filter out spurious ones, recreating the set
635 when required. Epoll also erroneously rounds down timeouts, but gives you
636 no way to know when and by how much, so sometimes you have to busy-wait
637 because epoll returns immediately despite a nonzero timeout. And last
638 not least, it also refuses to work with some file descriptors which work
639 perfectly fine with \f(CW\*(C`select\*(C'\fR (files, many character devices...).
640 .Sp
641 Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
642 cobbled together in a hurry, no thought to design or interaction with
643 others. Oh, the pain, will it ever stop...
644 .Sp
645 While stopping, setting and starting an I/O watcher in the same iteration
646 will result in some caching, there is still a system call per such
647 incident (because the same \fIfile descriptor\fR could point to a different
648 \&\fIfile description\fR now), so its best to avoid that. Also, \f(CW\*(C`dup ()\*(C'\fR'ed
649 file descriptors might not work very well if you register events for both
650 file descriptors.
651 .Sp
652 Best performance from this backend is achieved by not unregistering all
653 watchers for a file descriptor until it has been closed, if possible,
654 i.e. keep at least one watcher active per fd at all times. Stopping and
655 starting a watcher (without re-setting it) also usually doesn't cause
656 extra overhead. A fork can both result in spurious notifications as well
657 as in libev having to destroy and recreate the epoll object, which can
658 take considerable time and thus should be avoided.
659 .Sp
660 All this means that, in practice, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR can be as fast or
661 faster than epoll for maybe up to a hundred file descriptors, depending on
662 the usage. So sad.
663 .Sp
664 While nominally embeddable in other event loops, this feature is broken in
665 all kernel versions tested so far.
666 .Sp
667 This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
668 \&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
669 .ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4
670 .el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
671 .IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
672 Kqueue deserves special mention, as at the time of this writing, it
673 was broken on all BSDs except NetBSD (usually it doesn't work reliably
674 with anything but sockets and pipes, except on Darwin, where of course
675 it's completely useless). Unlike epoll, however, whose brokenness
676 is by design, these kqueue bugs can (and eventually will) be fixed
677 without \s-1API\s0 changes to existing programs. For this reason it's not being
678 \&\*(L"auto-detected\*(R" unless you explicitly specify it in the flags (i.e. using
679 \&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or libev was compiled on a known-to-be-good (\-enough)
680 system like NetBSD.
681 .Sp
682 You still can embed kqueue into a normal poll or select backend and use it
683 only for sockets (after having made sure that sockets work with kqueue on
684 the target platform). See \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
685 .Sp
686 It scales in the same way as the epoll backend, but the interface to the
687 kernel is more efficient (which says nothing about its actual speed, of
688 course). While stopping, setting and starting an I/O watcher does never
689 cause an extra system call as with \f(CW\*(C`EVBACKEND_EPOLL\*(C'\fR, it still adds up to
690 two event changes per incident. Support for \f(CW\*(C`fork ()\*(C'\fR is very bad (you
691 might have to leak fd's on fork, but it's more sane than epoll) and it
692 drops fds silently in similarly hard-to-detect cases.
693 .Sp
694 This backend usually performs well under most conditions.
695 .Sp
696 While nominally embeddable in other event loops, this doesn't work
697 everywhere, so you might need to test for this. And since it is broken
698 almost everywhere, you should only use it when you have a lot of sockets
699 (for which it usually works), by embedding it into another event loop
700 (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
701 also broken on \s-1OS\s0 X)) and, did I mention it, using it only for sockets.
702 .Sp
703 This backend maps \f(CW\*(C`EV_READ\*(C'\fR into an \f(CW\*(C`EVFILT_READ\*(C'\fR kevent with
704 \&\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
705 \&\f(CW\*(C`NOTE_EOF\*(C'\fR.
706 .ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
707 .el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
708 .IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
709 This is not implemented yet (and might never be, unless you send me an
710 implementation). According to reports, \f(CW\*(C`/dev/poll\*(C'\fR only supports sockets
711 and is not embeddable, which would limit the usefulness of this backend
712 immensely.
713 .ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
714 .el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
715 .IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
716 This uses the Solaris 10 event port mechanism. As with everything on Solaris,
717 it's really slow, but it still scales very well (O(active_fds)).
718 .Sp
719 While this backend scales well, it requires one system call per active
720 file descriptor per loop iteration. For small and medium numbers of file
721 descriptors a \*(L"slow\*(R" \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR backend
722 might perform better.
723 .Sp
724 On the positive side, this backend actually performed fully to
725 specification in all tests and is fully embeddable, which is a rare feat
726 among the OS-specific backends (I vastly prefer correctness over speed
727 hacks).
728 .Sp
729 On the negative side, the interface is \fIbizarre\fR \- so bizarre that
730 even sun itself gets it wrong in their code examples: The event polling
731 function sometimes returns events to the caller even though an error
732 occurred, but with no indication whether it has done so or not (yes, it's
733 even documented that way) \- deadly for edge-triggered interfaces where you
734 absolutely have to know whether an event occurred or not because you have
735 to re-arm the watcher.
736 .Sp
737 Fortunately libev seems to be able to work around these idiocies.
738 .Sp
739 This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
740 \&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
741 .ie n .IP """EVBACKEND_ALL""" 4
742 .el .IP "\f(CWEVBACKEND_ALL\fR" 4
743 .IX Item "EVBACKEND_ALL"
744 Try all backends (even potentially broken ones that wouldn't be tried
745 with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as
746 \&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR.
747 .Sp
748 It is definitely not recommended to use this flag, use whatever
749 \&\f(CW\*(C`ev_recommended_backends ()\*(C'\fR returns, or simply do not specify a backend
750 at all.
751 .ie n .IP """EVBACKEND_MASK""" 4
752 .el .IP "\f(CWEVBACKEND_MASK\fR" 4
753 .IX Item "EVBACKEND_MASK"
754 Not a backend at all, but a mask to select all backend bits from a
755 \&\f(CW\*(C`flags\*(C'\fR value, in case you want to mask out any backends from a flags
756 value (e.g. when modifying the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR environment variable).
757 .RE
758 .RS 4
759 .Sp
760 If one or more of the backend flags are or'ed into the flags value,
761 then only these backends will be tried (in the reverse order as listed
762 here). If none are specified, all backends in \f(CW\*(C`ev_recommended_backends
763 ()\*(C'\fR will be tried.
764 .Sp
765 Example: Try to create a event loop that uses epoll and nothing else.
766 .Sp
767 .Vb 3
768 \& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
769 \& if (!epoller)
770 \& fatal ("no epoll found here, maybe it hides under your chair");
771 .Ve
772 .Sp
773 Example: Use whatever libev has to offer, but make sure that kqueue is
774 used if available.
775 .Sp
776 .Vb 1
777 \& struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
778 .Ve
779 .RE
780 .IP "ev_loop_destroy (loop)" 4
781 .IX Item "ev_loop_destroy (loop)"
782 Destroys an event loop object (frees all memory and kernel state
783 etc.). None of the active event watchers will be stopped in the normal
784 sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your
785 responsibility to either stop all watchers cleanly yourself \fIbefore\fR
786 calling this function, or cope with the fact afterwards (which is usually
787 the easiest thing, you can just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them
788 for example).
789 .Sp
790 Note that certain global state, such as signal state (and installed signal
791 handlers), will not be freed by this function, and related watchers (such
792 as signal and child watchers) would need to be stopped manually.
793 .Sp
794 This function is normally used on loop objects allocated by
795 \&\f(CW\*(C`ev_loop_new\*(C'\fR, but it can also be used on the default loop returned by
796 \&\f(CW\*(C`ev_default_loop\*(C'\fR, in which case it is not thread-safe.
797 .Sp
798 Note that it is not advisable to call this function on the default loop
799 except in the rare occasion where you really need to free its resources.
800 If you need dynamically allocated loops it is better to use \f(CW\*(C`ev_loop_new\*(C'\fR
801 and \f(CW\*(C`ev_loop_destroy\*(C'\fR.
802 .IP "ev_loop_fork (loop)" 4
803 .IX Item "ev_loop_fork (loop)"
804 This function sets a flag that causes subsequent \f(CW\*(C`ev_run\*(C'\fR iterations to
805 reinitialise the kernel state for backends that have one. Despite the
806 name, you can call it anytime, but it makes most sense after forking, in
807 the child process. You \fImust\fR call it (or use \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR) in the
808 child before resuming or calling \f(CW\*(C`ev_run\*(C'\fR.
809 .Sp
810 Again, you \fIhave\fR to call it on \fIany\fR loop that you want to re-use after
811 a fork, \fIeven if you do not plan to use the loop in the parent\fR. This is
812 because some kernel interfaces *cough* \fIkqueue\fR *cough* do funny things
813 during fork.
814 .Sp
815 On the other hand, you only need to call this function in the child
816 process if and only if you want to use the event loop in the child. If
817 you just fork+exec or create a new loop in the child, you don't have to
818 call it at all (in fact, \f(CW\*(C`epoll\*(C'\fR is so badly broken that it makes a
819 difference, but libev will usually detect this case on its own and do a
820 costly reset of the backend).
821 .Sp
822 The function itself is quite fast and it's usually not a problem to call
823 it just in case after a fork.
824 .Sp
825 Example: Automate calling \f(CW\*(C`ev_loop_fork\*(C'\fR on the default loop when
826 using pthreads.
827 .Sp
828 .Vb 5
829 \& static void
830 \& post_fork_child (void)
831 \& {
832 \& ev_loop_fork (EV_DEFAULT);
833 \& }
834 \&
835 \& ...
836 \& pthread_atfork (0, 0, post_fork_child);
837 .Ve
838 .IP "int ev_is_default_loop (loop)" 4
839 .IX Item "int ev_is_default_loop (loop)"
840 Returns true when the given loop is, in fact, the default loop, and false
841 otherwise.
842 .IP "unsigned int ev_iteration (loop)" 4
843 .IX Item "unsigned int ev_iteration (loop)"
844 Returns the current iteration count for the event loop, which is identical
845 to the number of times libev did poll for new events. It starts at \f(CW0\fR
846 and happily wraps around with enough iterations.
847 .Sp
848 This value can sometimes be useful as a generation counter of sorts (it
849 \&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with
850 \&\f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR calls \- and is incremented between the
851 prepare and check phases.
852 .IP "unsigned int ev_depth (loop)" 4
853 .IX Item "unsigned int ev_depth (loop)"
854 Returns the number of times \f(CW\*(C`ev_run\*(C'\fR was entered minus the number of
855 times \f(CW\*(C`ev_run\*(C'\fR was exited normally, in other words, the recursion depth.
856 .Sp
857 Outside \f(CW\*(C`ev_run\*(C'\fR, this number is zero. In a callback, this number is
858 \&\f(CW1\fR, unless \f(CW\*(C`ev_run\*(C'\fR was invoked recursively (or from another thread),
859 in which case it is higher.
860 .Sp
861 Leaving \f(CW\*(C`ev_run\*(C'\fR abnormally (setjmp/longjmp, cancelling the thread,
862 throwing an exception etc.), doesn't count as \*(L"exit\*(R" \- consider this
863 as a hint to avoid such ungentleman-like behaviour unless it's really
864 convenient, in which case it is fully supported.
865 .IP "unsigned int ev_backend (loop)" 4
866 .IX Item "unsigned int ev_backend (loop)"
867 Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
868 use.
869 .IP "ev_tstamp ev_now (loop)" 4
870 .IX Item "ev_tstamp ev_now (loop)"
871 Returns the current \*(L"event loop time\*(R", which is the time the event loop
872 received events and started processing them. This timestamp does not
873 change as long as callbacks are being processed, and this is also the base
874 time used for relative timers. You can treat it as the timestamp of the
875 event occurring (or more correctly, libev finding out about it).
876 .IP "ev_now_update (loop)" 4
877 .IX Item "ev_now_update (loop)"
878 Establishes the current time by querying the kernel, updating the time
879 returned by \f(CW\*(C`ev_now ()\*(C'\fR in the progress. This is a costly operation and
880 is usually done automatically within \f(CW\*(C`ev_run ()\*(C'\fR.
881 .Sp
882 This function is rarely useful, but when some event callback runs for a
883 very long time without entering the event loop, updating libev's idea of
884 the current time is a good idea.
885 .Sp
886 See also \*(L"The special problem of time updates\*(R" in the \f(CW\*(C`ev_timer\*(C'\fR section.
887 .IP "ev_suspend (loop)" 4
888 .IX Item "ev_suspend (loop)"
889 .PD 0
890 .IP "ev_resume (loop)" 4
891 .IX Item "ev_resume (loop)"
892 .PD
893 These two functions suspend and resume an event loop, for use when the
894 loop is not used for a while and timeouts should not be processed.
895 .Sp
896 A typical use case would be an interactive program such as a game: When
897 the user presses \f(CW\*(C`^Z\*(C'\fR to suspend the game and resumes it an hour later it
898 would be best to handle timeouts as if no time had actually passed while
899 the program was suspended. This can be achieved by calling \f(CW\*(C`ev_suspend\*(C'\fR
900 in your \f(CW\*(C`SIGTSTP\*(C'\fR handler, sending yourself a \f(CW\*(C`SIGSTOP\*(C'\fR and calling
901 \&\f(CW\*(C`ev_resume\*(C'\fR directly afterwards to resume timer processing.
902 .Sp
903 Effectively, all \f(CW\*(C`ev_timer\*(C'\fR watchers will be delayed by the time spend
904 between \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
905 will be rescheduled (that is, they will lose any events that would have
906 occurred while suspended).
907 .Sp
908 After calling \f(CW\*(C`ev_suspend\*(C'\fR you \fBmust not\fR call \fIany\fR function on the
909 given loop other than \f(CW\*(C`ev_resume\*(C'\fR, and you \fBmust not\fR call \f(CW\*(C`ev_resume\*(C'\fR
910 without a previous call to \f(CW\*(C`ev_suspend\*(C'\fR.
911 .Sp
912 Calling \f(CW\*(C`ev_suspend\*(C'\fR/\f(CW\*(C`ev_resume\*(C'\fR has the side effect of updating the
913 event loop time (see \f(CW\*(C`ev_now_update\*(C'\fR).
914 .IP "bool ev_run (loop, int flags)" 4
915 .IX Item "bool ev_run (loop, int flags)"
916 Finally, this is it, the event handler. This function usually is called
917 after you have initialised all your watchers and you want to start
918 handling events. It will ask the operating system for any new events, call
919 the watcher callbacks, and then repeat the whole process indefinitely: This
920 is why event loops are called \fIloops\fR.
921 .Sp
922 If the flags argument is specified as \f(CW0\fR, it will keep handling events
923 until either no event watchers are active anymore or \f(CW\*(C`ev_break\*(C'\fR was
924 called.
925 .Sp
926 The return value is false if there are no more active watchers (which
927 usually means \*(L"all jobs done\*(R" or \*(L"deadlock\*(R"), and true in all other cases
928 (which usually means " you should call \f(CW\*(C`ev_run\*(C'\fR again").
929 .Sp
930 Please note that an explicit \f(CW\*(C`ev_break\*(C'\fR is usually better than
931 relying on all watchers to be stopped when deciding when a program has
932 finished (especially in interactive programs), but having a program
933 that automatically loops as long as it has to and no longer by virtue
934 of relying on its watchers stopping correctly, that is truly a thing of
935 beauty.
936 .Sp
937 This function is \fImostly\fR exception-safe \- you can break out of a
938 \&\f(CW\*(C`ev_run\*(C'\fR call by calling \f(CW\*(C`longjmp\*(C'\fR in a callback, throwing a \*(C+
939 exception and so on. This does not decrement the \f(CW\*(C`ev_depth\*(C'\fR value, nor
940 will it clear any outstanding \f(CW\*(C`EVBREAK_ONE\*(C'\fR breaks.
941 .Sp
942 A flags value of \f(CW\*(C`EVRUN_NOWAIT\*(C'\fR will look for new events, will handle
943 those events and any already outstanding ones, but will not wait and
944 block your process in case there are no events and will return after one
945 iteration of the loop. This is sometimes useful to poll and handle new
946 events while doing lengthy calculations, to keep the program responsive.
947 .Sp
948 A flags value of \f(CW\*(C`EVRUN_ONCE\*(C'\fR will look for new events (waiting if
949 necessary) and will handle those and any already outstanding ones. It
950 will block your process until at least one new event arrives (which could
951 be an event internal to libev itself, so there is no guarantee that a
952 user-registered callback will be called), and will return after one
953 iteration of the loop.
954 .Sp
955 This is useful if you are waiting for some external event in conjunction
956 with something not expressible using other libev watchers (i.e. "roll your
957 own \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
958 usually a better approach for this kind of thing.
959 .Sp
960 Here are the gory details of what \f(CW\*(C`ev_run\*(C'\fR does (this is for your
961 understanding, not a guarantee that things will work exactly like this in
962 future versions):
963 .Sp
964 .Vb 10
965 \& \- Increment loop depth.
966 \& \- Reset the ev_break status.
967 \& \- Before the first iteration, call any pending watchers.
968 \& LOOP:
969 \& \- If EVFLAG_FORKCHECK was used, check for a fork.
970 \& \- If a fork was detected (by any means), queue and call all fork watchers.
971 \& \- Queue and call all prepare watchers.
972 \& \- If ev_break was called, goto FINISH.
973 \& \- If we have been forked, detach and recreate the kernel state
974 \& as to not disturb the other process.
975 \& \- Update the kernel state with all outstanding changes.
976 \& \- Update the "event loop time" (ev_now ()).
977 \& \- Calculate for how long to sleep or block, if at all
978 \& (active idle watchers, EVRUN_NOWAIT or not having
979 \& any active watchers at all will result in not sleeping).
980 \& \- Sleep if the I/O and timer collect interval say so.
981 \& \- Increment loop iteration counter.
982 \& \- Block the process, waiting for any events.
983 \& \- Queue all outstanding I/O (fd) events.
984 \& \- Update the "event loop time" (ev_now ()), and do time jump adjustments.
985 \& \- Queue all expired timers.
986 \& \- Queue all expired periodics.
987 \& \- Queue all idle watchers with priority higher than that of pending events.
988 \& \- Queue all check watchers.
989 \& \- Call all queued watchers in reverse order (i.e. check watchers first).
990 \& Signals and child watchers are implemented as I/O watchers, and will
991 \& be handled here by queueing them when their watcher gets executed.
992 \& \- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
993 \& were used, or there are no active watchers, goto FINISH, otherwise
994 \& continue with step LOOP.
995 \& FINISH:
996 \& \- Reset the ev_break status iff it was EVBREAK_ONE.
997 \& \- Decrement the loop depth.
998 \& \- Return.
999 .Ve
1000 .Sp
1001 Example: Queue some jobs and then loop until no events are outstanding
1002 anymore.
1003 .Sp
1004 .Vb 4
1005 \& ... queue jobs here, make sure they register event watchers as long
1006 \& ... as they still have work to do (even an idle watcher will do..)
1007 \& ev_run (my_loop, 0);
1008 \& ... jobs done or somebody called break. yeah!
1009 .Ve
1010 .IP "ev_break (loop, how)" 4
1011 .IX Item "ev_break (loop, how)"
1012 Can be used to make a call to \f(CW\*(C`ev_run\*(C'\fR return early (but only after it
1013 has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either
1014 \&\f(CW\*(C`EVBREAK_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_run\*(C'\fR call return, or
1015 \&\f(CW\*(C`EVBREAK_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_run\*(C'\fR calls return.
1016 .Sp
1017 This \*(L"break state\*(R" will be cleared on the next call to \f(CW\*(C`ev_run\*(C'\fR.
1018 .Sp
1019 It is safe to call \f(CW\*(C`ev_break\*(C'\fR from outside any \f(CW\*(C`ev_run\*(C'\fR calls, too, in
1020 which case it will have no effect.
1021 .IP "ev_ref (loop)" 4
1022 .IX Item "ev_ref (loop)"
1023 .PD 0
1024 .IP "ev_unref (loop)" 4
1025 .IX Item "ev_unref (loop)"
1026 .PD
1027 Ref/unref can be used to add or remove a reference count on the event
1028 loop: Every watcher keeps one reference, and as long as the reference
1029 count is nonzero, \f(CW\*(C`ev_run\*(C'\fR will not return on its own.
1030 .Sp
1031 This is useful when you have a watcher that you never intend to
1032 unregister, but that nevertheless should not keep \f(CW\*(C`ev_run\*(C'\fR from
1033 returning. In such a case, call \f(CW\*(C`ev_unref\*(C'\fR after starting, and \f(CW\*(C`ev_ref\*(C'\fR
1034 before stopping it.
1035 .Sp
1036 As an example, libev itself uses this for its internal signal pipe: It
1037 is not visible to the libev user and should not keep \f(CW\*(C`ev_run\*(C'\fR from
1038 exiting if no event watchers registered by it are active. It is also an
1039 excellent way to do this for generic recurring timers or from within
1040 third-party libraries. Just remember to \fIunref after start\fR and \fIref
1041 before stop\fR (but only if the watcher wasn't active before, or was active
1042 before, respectively. Note also that libev might stop watchers itself
1043 (e.g. non-repeating timers) in which case you have to \f(CW\*(C`ev_ref\*(C'\fR
1044 in the callback).
1045 .Sp
1046 Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_run\*(C'\fR
1047 running when nothing else is active.
1048 .Sp
1049 .Vb 4
1050 \& ev_signal exitsig;
1051 \& ev_signal_init (&exitsig, sig_cb, SIGINT);
1052 \& ev_signal_start (loop, &exitsig);
1053 \& ev_unref (loop);
1054 .Ve
1055 .Sp
1056 Example: For some weird reason, unregister the above signal handler again.
1057 .Sp
1058 .Vb 2
1059 \& ev_ref (loop);
1060 \& ev_signal_stop (loop, &exitsig);
1061 .Ve
1062 .IP "ev_set_io_collect_interval (loop, ev_tstamp interval)" 4
1063 .IX Item "ev_set_io_collect_interval (loop, ev_tstamp interval)"
1064 .PD 0
1065 .IP "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 4
1066 .IX Item "ev_set_timeout_collect_interval (loop, ev_tstamp interval)"
1067 .PD
1068 These advanced functions influence the time that libev will spend waiting
1069 for events. Both time intervals are by default \f(CW0\fR, meaning that libev
1070 will try to invoke timer/periodic callbacks and I/O callbacks with minimum
1071 latency.
1072 .Sp
1073 Setting these to a higher value (the \f(CW\*(C`interval\*(C'\fR \fImust\fR be >= \f(CW0\fR)
1074 allows libev to delay invocation of I/O and timer/periodic callbacks
1075 to increase efficiency of loop iterations (or to increase power-saving
1076 opportunities).
1077 .Sp
1078 The idea is that sometimes your program runs just fast enough to handle
1079 one (or very few) event(s) per loop iteration. While this makes the
1080 program responsive, it also wastes a lot of \s-1CPU\s0 time to poll for new
1081 events, especially with backends like \f(CW\*(C`select ()\*(C'\fR which have a high
1082 overhead for the actual polling but can deliver many events at once.
1083 .Sp
1084 By setting a higher \fIio collect interval\fR you allow libev to spend more
1085 time collecting I/O events, so you can handle more events per iteration,
1086 at the cost of increasing latency. Timeouts (both \f(CW\*(C`ev_periodic\*(C'\fR and
1087 \&\f(CW\*(C`ev_timer\*(C'\fR) will not be affected. Setting this to a non-null value will
1088 introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations. The
1089 sleep time ensures that libev will not poll for I/O events more often then
1090 once per this interval, on average (as long as the host time resolution is
1091 good enough).
1092 .Sp
1093 Likewise, by setting a higher \fItimeout collect interval\fR you allow libev
1094 to spend more time collecting timeouts, at the expense of increased
1095 latency/jitter/inexactness (the watcher callback will be called
1096 later). \f(CW\*(C`ev_io\*(C'\fR watchers will not be affected. Setting this to a non-null
1097 value will not introduce any overhead in libev.
1098 .Sp
1099 Many (busy) programs can usually benefit by setting the I/O collect
1100 interval to a value near \f(CW0.1\fR or so, which is often enough for
1101 interactive servers (of course not for games), likewise for timeouts. It
1102 usually doesn't make much sense to set it to a lower value than \f(CW0.01\fR,
1103 as this approaches the timing granularity of most systems. Note that if
1104 you do transactions with the outside world and you can't increase the
1105 parallelity, then this setting will limit your transaction rate (if you
1106 need to poll once per transaction and the I/O collect interval is 0.01,
1107 then you can't do more than 100 transactions per second).
1108 .Sp
1109 Setting the \fItimeout collect interval\fR can improve the opportunity for
1110 saving power, as the program will \*(L"bundle\*(R" timer callback invocations that
1111 are \*(L"near\*(R" in time together, by delaying some, thus reducing the number of
1112 times the process sleeps and wakes up again. Another useful technique to
1113 reduce iterations/wake\-ups is to use \f(CW\*(C`ev_periodic\*(C'\fR watchers and make sure
1114 they fire on, say, one-second boundaries only.
1115 .Sp
1116 Example: we only need 0.1s timeout granularity, and we wish not to poll
1117 more often than 100 times per second:
1118 .Sp
1119 .Vb 2
1120 \& ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
1121 \& ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
1122 .Ve
1123 .IP "ev_invoke_pending (loop)" 4
1124 .IX Item "ev_invoke_pending (loop)"
1125 This call will simply invoke all pending watchers while resetting their
1126 pending state. Normally, \f(CW\*(C`ev_run\*(C'\fR does this automatically when required,
1127 but when overriding the invoke callback this call comes handy. This
1128 function can be invoked from a watcher \- this can be useful for example
1129 when you want to do some lengthy calculation and want to pass further
1130 event handling to another thread (you still have to make sure only one
1131 thread executes within \f(CW\*(C`ev_invoke_pending\*(C'\fR or \f(CW\*(C`ev_run\*(C'\fR of course).
1132 .IP "int ev_pending_count (loop)" 4
1133 .IX Item "int ev_pending_count (loop)"
1134 Returns the number of pending watchers \- zero indicates that no watchers
1135 are pending.
1136 .IP "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(\s-1EV_P\s0))" 4
1137 .IX Item "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))"
1138 This overrides the invoke pending functionality of the loop: Instead of
1139 invoking all pending watchers when there are any, \f(CW\*(C`ev_run\*(C'\fR will call
1140 this callback instead. This is useful, for example, when you want to
1141 invoke the actual watchers inside another context (another thread etc.).
1142 .Sp
1143 If you want to reset the callback, use \f(CW\*(C`ev_invoke_pending\*(C'\fR as new
1144 callback.
1145 .IP "ev_set_loop_release_cb (loop, void (*release)(\s-1EV_P\s0) throw (), void (*acquire)(\s-1EV_P\s0) throw ())" 4
1146 .IX Item "ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())"
1147 Sometimes you want to share the same loop between multiple threads. This
1148 can be done relatively simply by putting mutex_lock/unlock calls around
1149 each call to a libev function.
1150 .Sp
1151 However, \f(CW\*(C`ev_run\*(C'\fR can run an indefinite time, so it is not feasible
1152 to wait for it to return. One way around this is to wake up the event
1153 loop via \f(CW\*(C`ev_break\*(C'\fR and \f(CW\*(C`ev_async_send\*(C'\fR, another way is to set these
1154 \&\fIrelease\fR and \fIacquire\fR callbacks on the loop.
1155 .Sp
1156 When set, then \f(CW\*(C`release\*(C'\fR will be called just before the thread is
1157 suspended waiting for new events, and \f(CW\*(C`acquire\*(C'\fR is called just
1158 afterwards.
1159 .Sp
1160 Ideally, \f(CW\*(C`release\*(C'\fR will just call your mutex_unlock function, and
1161 \&\f(CW\*(C`acquire\*(C'\fR will just call the mutex_lock function again.
1162 .Sp
1163 While event loop modifications are allowed between invocations of
1164 \&\f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR (that's their only purpose after all), no
1165 modifications done will affect the event loop, i.e. adding watchers will
1166 have no effect on the set of file descriptors being watched, or the time
1167 waited. Use an \f(CW\*(C`ev_async\*(C'\fR watcher to wake up \f(CW\*(C`ev_run\*(C'\fR when you want it
1168 to take note of any changes you made.
1169 .Sp
1170 In theory, threads executing \f(CW\*(C`ev_run\*(C'\fR will be async-cancel safe between
1171 invocations of \f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR.
1172 .Sp
1173 See also the locking example in the \f(CW\*(C`THREADS\*(C'\fR section later in this
1174 document.
1175 .IP "ev_set_userdata (loop, void *data)" 4
1176 .IX Item "ev_set_userdata (loop, void *data)"
1177 .PD 0
1178 .IP "void *ev_userdata (loop)" 4
1179 .IX Item "void *ev_userdata (loop)"
1180 .PD
1181 Set and retrieve a single \f(CW\*(C`void *\*(C'\fR associated with a loop. When
1182 \&\f(CW\*(C`ev_set_userdata\*(C'\fR has never been called, then \f(CW\*(C`ev_userdata\*(C'\fR returns
1183 \&\f(CW0\fR.
1184 .Sp
1185 These two functions can be used to associate arbitrary data with a loop,
1186 and are intended solely for the \f(CW\*(C`invoke_pending_cb\*(C'\fR, \f(CW\*(C`release\*(C'\fR and
1187 \&\f(CW\*(C`acquire\*(C'\fR callbacks described above, but of course can be (ab\-)used for
1188 any other purpose as well.
1189 .IP "ev_verify (loop)" 4
1190 .IX Item "ev_verify (loop)"
1191 This function only does something when \f(CW\*(C`EV_VERIFY\*(C'\fR support has been
1192 compiled in, which is the default for non-minimal builds. It tries to go
1193 through all internal structures and checks them for validity. If anything
1194 is found to be inconsistent, it will print an error message to standard
1195 error and call \f(CW\*(C`abort ()\*(C'\fR.
1196 .Sp
1197 This can be used to catch bugs inside libev itself: under normal
1198 circumstances, this function will never abort as of course libev keeps its
1199 data structures consistent.
1200 .SH "ANATOMY OF A WATCHER"
1201 .IX Header "ANATOMY OF A WATCHER"
1202 In the following description, uppercase \f(CW\*(C`TYPE\*(C'\fR in names stands for the
1203 watcher type, e.g. \f(CW\*(C`ev_TYPE_start\*(C'\fR can mean \f(CW\*(C`ev_timer_start\*(C'\fR for timer
1204 watchers and \f(CW\*(C`ev_io_start\*(C'\fR for I/O watchers.
1205 .PP
1206 A watcher is an opaque structure that you allocate and register to record
1207 your interest in some event. To make a concrete example, imagine you want
1208 to wait for \s-1STDIN\s0 to become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher
1209 for that:
1210 .PP
1211 .Vb 5
1212 \& static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
1213 \& {
1214 \& ev_io_stop (w);
1215 \& ev_break (loop, EVBREAK_ALL);
1216 \& }
1217 \&
1218 \& struct ev_loop *loop = ev_default_loop (0);
1219 \&
1220 \& ev_io stdin_watcher;
1221 \&
1222 \& ev_init (&stdin_watcher, my_cb);
1223 \& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
1224 \& ev_io_start (loop, &stdin_watcher);
1225 \&
1226 \& ev_run (loop, 0);
1227 .Ve
1228 .PP
1229 As you can see, you are responsible for allocating the memory for your
1230 watcher structures (and it is \fIusually\fR a bad idea to do this on the
1231 stack).
1232 .PP
1233 Each watcher has an associated watcher structure (called \f(CW\*(C`struct ev_TYPE\*(C'\fR
1234 or simply \f(CW\*(C`ev_TYPE\*(C'\fR, as typedefs are provided for all watcher structs).
1235 .PP
1236 Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init (watcher
1237 *, callback)\*(C'\fR, which expects a callback to be provided. This callback is
1238 invoked each time the event occurs (or, in the case of I/O watchers, each
1239 time the event loop detects that the file descriptor given is readable
1240 and/or writable).
1241 .PP
1242 Each watcher type further has its own \f(CW\*(C`ev_TYPE_set (watcher *, ...)\*(C'\fR
1243 macro to configure it, with arguments specific to the watcher type. There
1244 is also a macro to combine initialisation and setting in one call: \f(CW\*(C`ev_TYPE_init (watcher *, callback, ...)\*(C'\fR.
1245 .PP
1246 To make the watcher actually watch out for events, you have to start it
1247 with a watcher-specific start function (\f(CW\*(C`ev_TYPE_start (loop, watcher
1248 *)\*(C'\fR), and you can stop watching for events at any time by calling the
1249 corresponding stop function (\f(CW\*(C`ev_TYPE_stop (loop, watcher *)\*(C'\fR.
1250 .PP
1251 As long as your watcher is active (has been started but not stopped) you
1252 must not touch the values stored in it. Most specifically you must never
1253 reinitialise it or call its \f(CW\*(C`ev_TYPE_set\*(C'\fR macro.
1254 .PP
1255 Each and every callback receives the event loop pointer as first, the
1256 registered watcher structure as second, and a bitset of received events as
1257 third argument.
1258 .PP
1259 The received events usually include a single bit per event type received
1260 (you can receive multiple events at the same time). The possible bit masks
1261 are:
1262 .ie n .IP """EV_READ""" 4
1263 .el .IP "\f(CWEV_READ\fR" 4
1264 .IX Item "EV_READ"
1265 .PD 0
1266 .ie n .IP """EV_WRITE""" 4
1267 .el .IP "\f(CWEV_WRITE\fR" 4
1268 .IX Item "EV_WRITE"
1269 .PD
1270 The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or
1271 writable.
1272 .ie n .IP """EV_TIMER""" 4
1273 .el .IP "\f(CWEV_TIMER\fR" 4
1274 .IX Item "EV_TIMER"
1275 The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out.
1276 .ie n .IP """EV_PERIODIC""" 4
1277 .el .IP "\f(CWEV_PERIODIC\fR" 4
1278 .IX Item "EV_PERIODIC"
1279 The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out.
1280 .ie n .IP """EV_SIGNAL""" 4
1281 .el .IP "\f(CWEV_SIGNAL\fR" 4
1282 .IX Item "EV_SIGNAL"
1283 The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread.
1284 .ie n .IP """EV_CHILD""" 4
1285 .el .IP "\f(CWEV_CHILD\fR" 4
1286 .IX Item "EV_CHILD"
1287 The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change.
1288 .ie n .IP """EV_STAT""" 4
1289 .el .IP "\f(CWEV_STAT\fR" 4
1290 .IX Item "EV_STAT"
1291 The path specified in the \f(CW\*(C`ev_stat\*(C'\fR watcher changed its attributes somehow.
1292 .ie n .IP """EV_IDLE""" 4
1293 .el .IP "\f(CWEV_IDLE\fR" 4
1294 .IX Item "EV_IDLE"
1295 The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do.
1296 .ie n .IP """EV_PREPARE""" 4
1297 .el .IP "\f(CWEV_PREPARE\fR" 4
1298 .IX Item "EV_PREPARE"
1299 .PD 0
1300 .ie n .IP """EV_CHECK""" 4
1301 .el .IP "\f(CWEV_CHECK\fR" 4
1302 .IX Item "EV_CHECK"
1303 .PD
1304 All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_run\*(C'\fR starts to
1305 gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are queued (not invoked)
1306 just after \f(CW\*(C`ev_run\*(C'\fR has gathered them, but before it queues any callbacks
1307 for any received events. That means \f(CW\*(C`ev_prepare\*(C'\fR watchers are the last
1308 watchers invoked before the event loop sleeps or polls for new events, and
1309 \&\f(CW\*(C`ev_check\*(C'\fR watchers will be invoked before any other watchers of the same
1310 or lower priority within an event loop iteration.
1311 .Sp
1312 Callbacks of both watcher types can start and stop as many watchers as
1313 they want, and all of them will be taken into account (for example, a
1314 \&\f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep \f(CW\*(C`ev_run\*(C'\fR from
1315 blocking).
1316 .ie n .IP """EV_EMBED""" 4
1317 .el .IP "\f(CWEV_EMBED\fR" 4
1318 .IX Item "EV_EMBED"
1319 The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention.
1320 .ie n .IP """EV_FORK""" 4
1321 .el .IP "\f(CWEV_FORK\fR" 4
1322 .IX Item "EV_FORK"
1323 The event loop has been resumed in the child process after fork (see
1324 \&\f(CW\*(C`ev_fork\*(C'\fR).
1325 .ie n .IP """EV_CLEANUP""" 4
1326 .el .IP "\f(CWEV_CLEANUP\fR" 4
1327 .IX Item "EV_CLEANUP"
1328 The event loop is about to be destroyed (see \f(CW\*(C`ev_cleanup\*(C'\fR).
1329 .ie n .IP """EV_ASYNC""" 4
1330 .el .IP "\f(CWEV_ASYNC\fR" 4
1331 .IX Item "EV_ASYNC"
1332 The given async watcher has been asynchronously notified (see \f(CW\*(C`ev_async\*(C'\fR).
1333 .ie n .IP """EV_CUSTOM""" 4
1334 .el .IP "\f(CWEV_CUSTOM\fR" 4
1335 .IX Item "EV_CUSTOM"
1336 Not ever sent (or otherwise used) by libev itself, but can be freely used
1337 by libev users to signal watchers (e.g. via \f(CW\*(C`ev_feed_event\*(C'\fR).
1338 .ie n .IP """EV_ERROR""" 4
1339 .el .IP "\f(CWEV_ERROR\fR" 4
1340 .IX Item "EV_ERROR"
1341 An unspecified error has occurred, the watcher has been stopped. This might
1342 happen because the watcher could not be properly started because libev
1343 ran out of memory, a file descriptor was found to be closed or any other
1344 problem. Libev considers these application bugs.
1345 .Sp
1346 You best act on it by reporting the problem and somehow coping with the
1347 watcher being stopped. Note that well-written programs should not receive
1348 an error ever, so when your watcher receives it, this usually indicates a
1349 bug in your program.
1350 .Sp
1351 Libev will usually signal a few \*(L"dummy\*(R" events together with an error, for
1352 example it might indicate that a fd is readable or writable, and if your
1353 callbacks is well-written it can just attempt the operation and cope with
1354 the error from \fIread()\fR or \fIwrite()\fR. This will not work in multi-threaded
1355 programs, though, as the fd could already be closed and reused for another
1356 thing, so beware.
1357 .SS "\s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0"
1358 .IX Subsection "GENERIC WATCHER FUNCTIONS"
1359 .ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4
1360 .el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4
1361 .IX Item "ev_init (ev_TYPE *watcher, callback)"
1362 This macro initialises the generic portion of a watcher. The contents
1363 of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only
1364 the generic parts of the watcher are initialised, you \fIneed\fR to call
1365 the type-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR macro afterwards to initialise the
1366 type-specific parts. For each type there is also a \f(CW\*(C`ev_TYPE_init\*(C'\fR macro
1367 which rolls both calls into one.
1368 .Sp
1369 You can reinitialise a watcher at any time as long as it has been stopped
1370 (or never started) and there are no pending events outstanding.
1371 .Sp
1372 The callback is always of type \f(CW\*(C`void (*)(struct ev_loop *loop, ev_TYPE *watcher,
1373 int revents)\*(C'\fR.
1374 .Sp
1375 Example: Initialise an \f(CW\*(C`ev_io\*(C'\fR watcher in two steps.
1376 .Sp
1377 .Vb 3
1378 \& ev_io w;
1379 \& ev_init (&w, my_cb);
1380 \& ev_io_set (&w, STDIN_FILENO, EV_READ);
1381 .Ve
1382 .ie n .IP """ev_TYPE_set"" (ev_TYPE *watcher, [args])" 4
1383 .el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *watcher, [args])" 4
1384 .IX Item "ev_TYPE_set (ev_TYPE *watcher, [args])"
1385 This macro initialises the type-specific parts of a watcher. You need to
1386 call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can
1387 call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this
1388 macro on a watcher that is active (it can be pending, however, which is a
1389 difference to the \f(CW\*(C`ev_init\*(C'\fR macro).
1390 .Sp
1391 Although some watcher types do not have type-specific arguments
1392 (e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro.
1393 .Sp
1394 See \f(CW\*(C`ev_init\*(C'\fR, above, for an example.
1395 .ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4
1396 .el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4
1397 .IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])"
1398 This convenience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro
1399 calls into a single call. This is the most convenient method to initialise
1400 a watcher. The same limitations apply, of course.
1401 .Sp
1402 Example: Initialise and set an \f(CW\*(C`ev_io\*(C'\fR watcher in one step.
1403 .Sp
1404 .Vb 1
1405 \& ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1406 .Ve
1407 .ie n .IP """ev_TYPE_start"" (loop, ev_TYPE *watcher)" 4
1408 .el .IP "\f(CWev_TYPE_start\fR (loop, ev_TYPE *watcher)" 4
1409 .IX Item "ev_TYPE_start (loop, ev_TYPE *watcher)"
1410 Starts (activates) the given watcher. Only active watchers will receive
1411 events. If the watcher is already active nothing will happen.
1412 .Sp
1413 Example: Start the \f(CW\*(C`ev_io\*(C'\fR watcher that is being abused as example in this
1414 whole section.
1415 .Sp
1416 .Vb 1
1417 \& ev_io_start (EV_DEFAULT_UC, &w);
1418 .Ve
1419 .ie n .IP """ev_TYPE_stop"" (loop, ev_TYPE *watcher)" 4
1420 .el .IP "\f(CWev_TYPE_stop\fR (loop, ev_TYPE *watcher)" 4
1421 .IX Item "ev_TYPE_stop (loop, ev_TYPE *watcher)"
1422 Stops the given watcher if active, and clears the pending status (whether
1423 the watcher was active or not).
1424 .Sp
1425 It is possible that stopped watchers are pending \- for example,
1426 non-repeating timers are being stopped when they become pending \- but
1427 calling \f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor
1428 pending. If you want to free or reuse the memory used by the watcher it is
1429 therefore a good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function.
1430 .IP "bool ev_is_active (ev_TYPE *watcher)" 4
1431 .IX Item "bool ev_is_active (ev_TYPE *watcher)"
1432 Returns a true value iff the watcher is active (i.e. it has been started
1433 and not yet been stopped). As long as a watcher is active you must not modify
1434 it.
1435 .IP "bool ev_is_pending (ev_TYPE *watcher)" 4
1436 .IX Item "bool ev_is_pending (ev_TYPE *watcher)"
1437 Returns a true value iff the watcher is pending, (i.e. it has outstanding
1438 events but its callback has not yet been invoked). As long as a watcher
1439 is pending (but not active) you must not call an init function on it (but
1440 \&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe), you must not change its priority, and you must
1441 make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR
1442 it).
1443 .IP "callback ev_cb (ev_TYPE *watcher)" 4
1444 .IX Item "callback ev_cb (ev_TYPE *watcher)"
1445 Returns the callback currently set on the watcher.
1446 .IP "ev_set_cb (ev_TYPE *watcher, callback)" 4
1447 .IX Item "ev_set_cb (ev_TYPE *watcher, callback)"
1448 Change the callback. You can change the callback at virtually any time
1449 (modulo threads).
1450 .IP "ev_set_priority (ev_TYPE *watcher, int priority)" 4
1451 .IX Item "ev_set_priority (ev_TYPE *watcher, int priority)"
1452 .PD 0
1453 .IP "int ev_priority (ev_TYPE *watcher)" 4
1454 .IX Item "int ev_priority (ev_TYPE *watcher)"
1455 .PD
1456 Set and query the priority of the watcher. The priority is a small
1457 integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR
1458 (default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked
1459 before watchers with lower priority, but priority will not keep watchers
1460 from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers).
1461 .Sp
1462 If you need to suppress invocation when higher priority events are pending
1463 you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality.
1464 .Sp
1465 You \fImust not\fR change the priority of a watcher as long as it is active or
1466 pending.
1467 .Sp
1468 Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is
1469 fine, as long as you do not mind that the priority value you query might
1470 or might not have been clamped to the valid range.
1471 .Sp
1472 The default priority used by watchers when no priority has been set is
1473 always \f(CW0\fR, which is supposed to not be too high and not be too low :).
1474 .Sp
1475 See \*(L"\s-1WATCHER\s0 \s-1PRIORITY\s0 \s-1MODELS\s0\*(R", below, for a more thorough treatment of
1476 priorities.
1477 .IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4
1478 .IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)"
1479 Invoke the \f(CW\*(C`watcher\*(C'\fR with the given \f(CW\*(C`loop\*(C'\fR and \f(CW\*(C`revents\*(C'\fR. Neither
1480 \&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback
1481 can deal with that fact, as both are simply passed through to the
1482 callback.
1483 .IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4
1484 .IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)"
1485 If the watcher is pending, this function clears its pending status and
1486 returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the
1487 watcher isn't pending it does nothing and returns \f(CW0\fR.
1488 .Sp
1489 Sometimes it can be useful to \*(L"poll\*(R" a watcher instead of waiting for its
1490 callback to be invoked, which can be accomplished with this function.
1491 .IP "ev_feed_event (loop, ev_TYPE *watcher, int revents)" 4
1492 .IX Item "ev_feed_event (loop, ev_TYPE *watcher, int revents)"
1493 Feeds the given event set into the event loop, as if the specified event
1494 had happened for the specified watcher (which must be a pointer to an
1495 initialised but not necessarily started event watcher). Obviously you must
1496 not free the watcher as long as it has pending events.
1497 .Sp
1498 Stopping the watcher, letting libev invoke it, or calling
1499 \&\f(CW\*(C`ev_clear_pending\*(C'\fR will clear the pending event, even if the watcher was
1500 not started in the first place.
1501 .Sp
1502 See also \f(CW\*(C`ev_feed_fd_event\*(C'\fR and \f(CW\*(C`ev_feed_signal_event\*(C'\fR for related
1503 functions that do not need a watcher.
1504 .PP
1505 See also the \*(L"\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0\*(R" and \*(L"\s-1BUILDING\s0 \s-1YOUR\s0
1506 \&\s-1OWN\s0 \s-1COMPOSITE\s0 \s-1WATCHERS\s0\*(R" idioms.
1507 .SS "\s-1WATCHER\s0 \s-1STATES\s0"
1508 .IX Subsection "WATCHER STATES"
1509 There are various watcher states mentioned throughout this manual \-
1510 active, pending and so on. In this section these states and the rules to
1511 transition between them will be described in more detail \- and while these
1512 rules might look complicated, they usually do \*(L"the right thing\*(R".
1513 .IP "initialised" 4
1514 .IX Item "initialised"
1515 Before a watcher can be registered with the event loop it has to be
1516 initialised. This can be done with a call to \f(CW\*(C`ev_TYPE_init\*(C'\fR, or calls to
1517 \&\f(CW\*(C`ev_init\*(C'\fR followed by the watcher-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR function.
1518 .Sp
1519 In this state it is simply some block of memory that is suitable for
1520 use in an event loop. It can be moved around, freed, reused etc. at
1521 will \- as long as you either keep the memory contents intact, or call
1522 \&\f(CW\*(C`ev_TYPE_init\*(C'\fR again.
1523 .IP "started/running/active" 4
1524 .IX Item "started/running/active"
1525 Once a watcher has been started with a call to \f(CW\*(C`ev_TYPE_start\*(C'\fR it becomes
1526 property of the event loop, and is actively waiting for events. While in
1527 this state it cannot be accessed (except in a few documented ways), moved,
1528 freed or anything else \- the only legal thing is to keep a pointer to it,
1529 and call libev functions on it that are documented to work on active watchers.
1530 .IP "pending" 4
1531 .IX Item "pending"
1532 If a watcher is active and libev determines that an event it is interested
1533 in has occurred (such as a timer expiring), it will become pending. It will
1534 stay in this pending state until either it is stopped or its callback is
1535 about to be invoked, so it is not normally pending inside the watcher
1536 callback.
1537 .Sp
1538 The watcher might or might not be active while it is pending (for example,
1539 an expired non-repeating timer can be pending but no longer active). If it
1540 is stopped, it can be freely accessed (e.g. by calling \f(CW\*(C`ev_TYPE_set\*(C'\fR),
1541 but it is still property of the event loop at this time, so cannot be
1542 moved, freed or reused. And if it is active the rules described in the
1543 previous item still apply.
1544 .Sp
1545 It is also possible to feed an event on a watcher that is not active (e.g.
1546 via \f(CW\*(C`ev_feed_event\*(C'\fR), in which case it becomes pending without being
1547 active.
1548 .IP "stopped" 4
1549 .IX Item "stopped"
1550 A watcher can be stopped implicitly by libev (in which case it might still
1551 be pending), or explicitly by calling its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function. The
1552 latter will clear any pending state the watcher might be in, regardless
1553 of whether it was active or not, so stopping a watcher explicitly before
1554 freeing it is often a good idea.
1555 .Sp
1556 While stopped (and not pending) the watcher is essentially in the
1557 initialised state, that is, it can be reused, moved, modified in any way
1558 you wish (but when you trash the memory block, you need to \f(CW\*(C`ev_TYPE_init\*(C'\fR
1559 it again).
1560 .SS "\s-1WATCHER\s0 \s-1PRIORITY\s0 \s-1MODELS\s0"
1561 .IX Subsection "WATCHER PRIORITY MODELS"
1562 Many event loops support \fIwatcher priorities\fR, which are usually small
1563 integers that influence the ordering of event callback invocation
1564 between watchers in some way, all else being equal.
1565 .PP
1566 In libev, Watcher priorities can be set using \f(CW\*(C`ev_set_priority\*(C'\fR. See its
1567 description for the more technical details such as the actual priority
1568 range.
1569 .PP
1570 There are two common ways how these these priorities are being interpreted
1571 by event loops:
1572 .PP
1573 In the more common lock-out model, higher priorities \*(L"lock out\*(R" invocation
1574 of lower priority watchers, which means as long as higher priority
1575 watchers receive events, lower priority watchers are not being invoked.
1576 .PP
1577 The less common only-for-ordering model uses priorities solely to order
1578 callback invocation within a single event loop iteration: Higher priority
1579 watchers are invoked before lower priority ones, but they all get invoked
1580 before polling for new events.
1581 .PP
1582 Libev uses the second (only-for-ordering) model for all its watchers
1583 except for idle watchers (which use the lock-out model).
1584 .PP
1585 The rationale behind this is that implementing the lock-out model for
1586 watchers is not well supported by most kernel interfaces, and most event
1587 libraries will just poll for the same events again and again as long as
1588 their callbacks have not been executed, which is very inefficient in the
1589 common case of one high-priority watcher locking out a mass of lower
1590 priority ones.
1591 .PP
1592 Static (ordering) priorities are most useful when you have two or more
1593 watchers handling the same resource: a typical usage example is having an
1594 \&\f(CW\*(C`ev_io\*(C'\fR watcher to receive data, and an associated \f(CW\*(C`ev_timer\*(C'\fR to handle
1595 timeouts. Under load, data might be received while the program handles
1596 other jobs, but since timers normally get invoked first, the timeout
1597 handler will be executed before checking for data. In that case, giving
1598 the timer a lower priority than the I/O watcher ensures that I/O will be
1599 handled first even under adverse conditions (which is usually, but not
1600 always, what you want).
1601 .PP
1602 Since idle watchers use the \*(L"lock-out\*(R" model, meaning that idle watchers
1603 will only be executed when no same or higher priority watchers have
1604 received events, they can be used to implement the \*(L"lock-out\*(R" model when
1605 required.
1606 .PP
1607 For example, to emulate how many other event libraries handle priorities,
1608 you can associate an \f(CW\*(C`ev_idle\*(C'\fR watcher to each such watcher, and in
1609 the normal watcher callback, you just start the idle watcher. The real
1610 processing is done in the idle watcher callback. This causes libev to
1611 continuously poll and process kernel event data for the watcher, but when
1612 the lock-out case is known to be rare (which in turn is rare :), this is
1613 workable.
1614 .PP
1615 Usually, however, the lock-out model implemented that way will perform
1616 miserably under the type of load it was designed to handle. In that case,
1617 it might be preferable to stop the real watcher before starting the
1618 idle watcher, so the kernel will not have to process the event in case
1619 the actual processing will be delayed for considerable time.
1620 .PP
1621 Here is an example of an I/O watcher that should run at a strictly lower
1622 priority than the default, and which should only process data when no
1623 other events are pending:
1624 .PP
1625 .Vb 2
1626 \& ev_idle idle; // actual processing watcher
1627 \& ev_io io; // actual event watcher
1628 \&
1629 \& static void
1630 \& io_cb (EV_P_ ev_io *w, int revents)
1631 \& {
1632 \& // stop the I/O watcher, we received the event, but
1633 \& // are not yet ready to handle it.
1634 \& ev_io_stop (EV_A_ w);
1635 \&
1636 \& // start the idle watcher to handle the actual event.
1637 \& // it will not be executed as long as other watchers
1638 \& // with the default priority are receiving events.
1639 \& ev_idle_start (EV_A_ &idle);
1640 \& }
1641 \&
1642 \& static void
1643 \& idle_cb (EV_P_ ev_idle *w, int revents)
1644 \& {
1645 \& // actual processing
1646 \& read (STDIN_FILENO, ...);
1647 \&
1648 \& // have to start the I/O watcher again, as
1649 \& // we have handled the event
1650 \& ev_io_start (EV_P_ &io);
1651 \& }
1652 \&
1653 \& // initialisation
1654 \& ev_idle_init (&idle, idle_cb);
1655 \& ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
1656 \& ev_io_start (EV_DEFAULT_ &io);
1657 .Ve
1658 .PP
1659 In the \*(L"real\*(R" world, it might also be beneficial to start a timer, so that
1660 low-priority connections can not be locked out forever under load. This
1661 enables your program to keep a lower latency for important connections
1662 during short periods of high load, while not completely locking out less
1663 important ones.
1664 .SH "WATCHER TYPES"
1665 .IX Header "WATCHER TYPES"
1666 This section describes each watcher in detail, but will not repeat
1667 information given in the last section. Any initialisation/set macros,
1668 functions and members specific to the watcher type are explained.
1669 .PP
1670 Members are additionally marked with either \fI[read\-only]\fR, meaning that,
1671 while the watcher is active, you can look at the member and expect some
1672 sensible content, but you must not modify it (you can modify it while the
1673 watcher is stopped to your hearts content), or \fI[read\-write]\fR, which
1674 means you can expect it to have some sensible content while the watcher
1675 is active, but you can also modify it. Modifying it may not do something
1676 sensible or take immediate effect (or do anything at all), but libev will
1677 not crash or malfunction in any way.
1678 .ie n .SS """ev_io"" \- is this file descriptor readable or writable?"
1679 .el .SS "\f(CWev_io\fP \- is this file descriptor readable or writable?"
1680 .IX Subsection "ev_io - is this file descriptor readable or writable?"
1681 I/O watchers check whether a file descriptor is readable or writable
1682 in each iteration of the event loop, or, more precisely, when reading
1683 would not block the process and writing would at least be able to write
1684 some data. This behaviour is called level-triggering because you keep
1685 receiving events as long as the condition persists. Remember you can stop
1686 the watcher if you don't want to act on the event and neither want to
1687 receive future events.
1688 .PP
1689 In general you can register as many read and/or write event watchers per
1690 fd as you want (as long as you don't confuse yourself). Setting all file
1691 descriptors to non-blocking mode is also usually a good idea (but not
1692 required if you know what you are doing).
1693 .PP
1694 Another thing you have to watch out for is that it is quite easy to
1695 receive \*(L"spurious\*(R" readiness notifications, that is, your callback might
1696 be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block
1697 because there is no data. It is very easy to get into this situation even
1698 with a relatively standard program structure. Thus it is best to always
1699 use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning \f(CW\*(C`EAGAIN\*(C'\fR is far
1700 preferable to a program hanging until some data arrives.
1701 .PP
1702 If you cannot run the fd in non-blocking mode (for example you should
1703 not play around with an Xlib connection), then you have to separately
1704 re-test whether a file descriptor is really ready with a known-to-be good
1705 interface such as poll (fortunately in the case of Xlib, it already does
1706 this on its own, so its quite safe to use). Some people additionally
1707 use \f(CW\*(C`SIGALRM\*(C'\fR and an interval timer, just to be sure you won't block
1708 indefinitely.
1709 .PP
1710 But really, best use non-blocking mode.
1711 .PP
1712 \fIThe special problem of disappearing file descriptors\fR
1713 .IX Subsection "The special problem of disappearing file descriptors"
1714 .PP
1715 Some backends (e.g. kqueue, epoll) need to be told about closing a file
1716 descriptor (either due to calling \f(CW\*(C`close\*(C'\fR explicitly or any other means,
1717 such as \f(CW\*(C`dup2\*(C'\fR). The reason is that you register interest in some file
1718 descriptor, but when it goes away, the operating system will silently drop
1719 this interest. If another file descriptor with the same number then is
1720 registered with libev, there is no efficient way to see that this is, in
1721 fact, a different file descriptor.
1722 .PP
1723 To avoid having to explicitly tell libev about such cases, libev follows
1724 the following policy: Each time \f(CW\*(C`ev_io_set\*(C'\fR is being called, libev
1725 will assume that this is potentially a new file descriptor, otherwise
1726 it is assumed that the file descriptor stays the same. That means that
1727 you \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
1728 descriptor even if the file descriptor number itself did not change.
1729 .PP
1730 This is how one would do it normally anyway, the important point is that
1731 the libev application should not optimise around libev but should leave
1732 optimisations to libev.
1733 .PP
1734 \fIThe special problem of dup'ed file descriptors\fR
1735 .IX Subsection "The special problem of dup'ed file descriptors"
1736 .PP
1737 Some backends (e.g. epoll), cannot register events for file descriptors,
1738 but only events for the underlying file descriptions. That means when you
1739 have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or weirder constellations, and register
1740 events for them, only one file descriptor might actually receive events.
1741 .PP
1742 There is no workaround possible except not registering events
1743 for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors, or to resort to
1744 \&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1745 .PP
1746 \fIThe special problem of files\fR
1747 .IX Subsection "The special problem of files"
1748 .PP
1749 Many people try to use \f(CW\*(C`select\*(C'\fR (or libev) on file descriptors
1750 representing files, and expect it to become ready when their program
1751 doesn't block on disk accesses (which can take a long time on their own).
1752 .PP
1753 However, this cannot ever work in the \*(L"expected\*(R" way \- you get a readiness
1754 notification as soon as the kernel knows whether and how much data is
1755 there, and in the case of open files, that's always the case, so you
1756 always get a readiness notification instantly, and your read (or possibly
1757 write) will still block on the disk I/O.
1758 .PP
1759 Another way to view it is that in the case of sockets, pipes, character
1760 devices and so on, there is another party (the sender) that delivers data
1761 on its own, but in the case of files, there is no such thing: the disk
1762 will not send data on its own, simply because it doesn't know what you
1763 wish to read \- you would first have to request some data.
1764 .PP
1765 Since files are typically not-so-well supported by advanced notification
1766 mechanism, libev tries hard to emulate \s-1POSIX\s0 behaviour with respect
1767 to files, even though you should not use it. The reason for this is
1768 convenience: sometimes you want to watch \s-1STDIN\s0 or \s-1STDOUT\s0, which is
1769 usually a tty, often a pipe, but also sometimes files or special devices
1770 (for example, \f(CW\*(C`epoll\*(C'\fR on Linux works with \fI/dev/random\fR but not with
1771 \&\fI/dev/urandom\fR), and even though the file might better be served with
1772 asynchronous I/O instead of with non-blocking I/O, it is still useful when
1773 it \*(L"just works\*(R" instead of freezing.
1774 .PP
1775 So avoid file descriptors pointing to files when you know it (e.g. use
1776 libeio), but use them when it is convenient, e.g. for \s-1STDIN/STDOUT\s0, or
1777 when you rarely read from a file instead of from a socket, and want to
1778 reuse the same code path.
1779 .PP
1780 \fIThe special problem of fork\fR
1781 .IX Subsection "The special problem of fork"
1782 .PP
1783 Some backends (epoll, kqueue) do not support \f(CW\*(C`fork ()\*(C'\fR at all or exhibit
1784 useless behaviour. Libev fully supports fork, but needs to be told about
1785 it in the child if you want to continue to use it in the child.
1786 .PP
1787 To support fork in your child processes, you have to call \f(CW\*(C`ev_loop_fork
1788 ()\*(C'\fR after a fork in the child, enable \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR, or resort to
1789 \&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1790 .PP
1791 \fIThe special problem of \s-1SIGPIPE\s0\fR
1792 .IX Subsection "The special problem of SIGPIPE"
1793 .PP
1794 While not really specific to libev, it is easy to forget about \f(CW\*(C`SIGPIPE\*(C'\fR:
1795 when writing to a pipe whose other end has been closed, your program gets
1796 sent a \s-1SIGPIPE\s0, which, by default, aborts your program. For most programs
1797 this is sensible behaviour, for daemons, this is usually undesirable.
1798 .PP
1799 So when you encounter spurious, unexplained daemon exits, make sure you
1800 ignore \s-1SIGPIPE\s0 (and maybe make sure you log the exit status of your daemon
1801 somewhere, as that would have given you a big clue).
1802 .PP
1803 \fIThe special problem of \fIaccept()\fIing when you can't\fR
1804 .IX Subsection "The special problem of accept()ing when you can't"
1805 .PP
1806 Many implementations of the \s-1POSIX\s0 \f(CW\*(C`accept\*(C'\fR function (for example,
1807 found in post\-2004 Linux) have the peculiar behaviour of not removing a
1808 connection from the pending queue in all error cases.
1809 .PP
1810 For example, larger servers often run out of file descriptors (because
1811 of resource limits), causing \f(CW\*(C`accept\*(C'\fR to fail with \f(CW\*(C`ENFILE\*(C'\fR but not
1812 rejecting the connection, leading to libev signalling readiness on
1813 the next iteration again (the connection still exists after all), and
1814 typically causing the program to loop at 100% \s-1CPU\s0 usage.
1815 .PP
1816 Unfortunately, the set of errors that cause this issue differs between
1817 operating systems, there is usually little the app can do to remedy the
1818 situation, and no known thread-safe method of removing the connection to
1819 cope with overload is known (to me).
1820 .PP
1821 One of the easiest ways to handle this situation is to just ignore it
1822 \&\- when the program encounters an overload, it will just loop until the
1823 situation is over. While this is a form of busy waiting, no \s-1OS\s0 offers an
1824 event-based way to handle this situation, so it's the best one can do.
1825 .PP
1826 A better way to handle the situation is to log any errors other than
1827 \&\f(CW\*(C`EAGAIN\*(C'\fR and \f(CW\*(C`EWOULDBLOCK\*(C'\fR, making sure not to flood the log with such
1828 messages, and continue as usual, which at least gives the user an idea of
1829 what could be wrong (\*(L"raise the ulimit!\*(R"). For extra points one could stop
1830 the \f(CW\*(C`ev_io\*(C'\fR watcher on the listening fd \*(L"for a while\*(R", which reduces \s-1CPU\s0
1831 usage.
1832 .PP
1833 If your program is single-threaded, then you could also keep a dummy file
1834 descriptor for overload situations (e.g. by opening \fI/dev/null\fR), and
1835 when 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,
1836 close that fd, and create a new dummy fd. This will gracefully refuse
1837 clients under typical overload conditions.
1838 .PP
1839 The last way to handle it is to simply log the error and \f(CW\*(C`exit\*(C'\fR, as
1840 is often done with \f(CW\*(C`malloc\*(C'\fR failures, but this results in an easy
1841 opportunity for a DoS attack.
1842 .PP
1843 \fIWatcher-Specific Functions\fR
1844 .IX Subsection "Watcher-Specific Functions"
1845 .IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
1846 .IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
1847 .PD 0
1848 .IP "ev_io_set (ev_io *, int fd, int events)" 4
1849 .IX Item "ev_io_set (ev_io *, int fd, int events)"
1850 .PD
1851 Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to
1852 receive 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
1853 \&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR, to express the desire to receive the given events.
1854 .IP "int fd [read\-only]" 4
1855 .IX Item "int fd [read-only]"
1856 The file descriptor being watched.
1857 .IP "int events [read\-only]" 4
1858 .IX Item "int events [read-only]"
1859 The events being watched.
1860 .PP
1861 \fIExamples\fR
1862 .IX Subsection "Examples"
1863 .PP
1864 Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well
1865 readable, but only once. Since it is likely line-buffered, you could
1866 attempt to read a whole line in the callback.
1867 .PP
1868 .Vb 6
1869 \& static void
1870 \& stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1871 \& {
1872 \& ev_io_stop (loop, w);
1873 \& .. read from stdin here (or from w\->fd) and handle any I/O errors
1874 \& }
1875 \&
1876 \& ...
1877 \& struct ev_loop *loop = ev_default_init (0);
1878 \& ev_io stdin_readable;
1879 \& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1880 \& ev_io_start (loop, &stdin_readable);
1881 \& ev_run (loop, 0);
1882 .Ve
1883 .ie n .SS """ev_timer"" \- relative and optionally repeating timeouts"
1884 .el .SS "\f(CWev_timer\fP \- relative and optionally repeating timeouts"
1885 .IX Subsection "ev_timer - relative and optionally repeating timeouts"
1886 Timer watchers are simple relative timers that generate an event after a
1887 given time, and optionally repeating in regular intervals after that.
1888 .PP
1889 The timers are based on real time, that is, if you register an event that
1890 times out after an hour and you reset your system clock to January last
1891 year, it will still time out after (roughly) one hour. \*(L"Roughly\*(R" because
1892 detecting time jumps is hard, and some inaccuracies are unavoidable (the
1893 monotonic clock option helps a lot here).
1894 .PP
1895 The callback is guaranteed to be invoked only \fIafter\fR its timeout has
1896 passed (not \fIat\fR, so on systems with very low-resolution clocks this
1897 might introduce a small delay, see \*(L"the special problem of being too
1898 early\*(R", below). If multiple timers become ready during the same loop
1899 iteration then the ones with earlier time-out values are invoked before
1900 ones of the same priority with later time-out values (but this is no
1901 longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
1902 .PP
1903 \fIBe smart about timeouts\fR
1904 .IX Subsection "Be smart about timeouts"
1905 .PP
1906 Many real-world problems involve some kind of timeout, usually for error
1907 recovery. A typical example is an \s-1HTTP\s0 request \- if the other side hangs,
1908 you want to raise some error after a while.
1909 .PP
1910 What follows are some ways to handle this problem, from obvious and
1911 inefficient to smart and efficient.
1912 .PP
1913 In the following, a 60 second activity timeout is assumed \- a timeout that
1914 gets reset to 60 seconds each time there is activity (e.g. each time some
1915 data or other life sign was received).
1916 .IP "1. Use a timer and stop, reinitialise and start it on activity." 4
1917 .IX Item "1. Use a timer and stop, reinitialise and start it on activity."
1918 This is the most obvious, but not the most simple way: In the beginning,
1919 start the watcher:
1920 .Sp
1921 .Vb 2
1922 \& ev_timer_init (timer, callback, 60., 0.);
1923 \& ev_timer_start (loop, timer);
1924 .Ve
1925 .Sp
1926 Then, each time there is some activity, \f(CW\*(C`ev_timer_stop\*(C'\fR it, initialise it
1927 and start it again:
1928 .Sp
1929 .Vb 3
1930 \& ev_timer_stop (loop, timer);
1931 \& ev_timer_set (timer, 60., 0.);
1932 \& ev_timer_start (loop, timer);
1933 .Ve
1934 .Sp
1935 This is relatively simple to implement, but means that each time there is
1936 some activity, libev will first have to remove the timer from its internal
1937 data structure and then add it again. Libev tries to be fast, but it's
1938 still not a constant-time operation.
1939 .ie n .IP "2. Use a timer and re-start it with ""ev_timer_again"" inactivity." 4
1940 .el .IP "2. Use a timer and re-start it with \f(CWev_timer_again\fR inactivity." 4
1941 .IX Item "2. Use a timer and re-start it with ev_timer_again inactivity."
1942 This is the easiest way, and involves using \f(CW\*(C`ev_timer_again\*(C'\fR instead of
1943 \&\f(CW\*(C`ev_timer_start\*(C'\fR.
1944 .Sp
1945 To implement this, configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value
1946 of \f(CW60\fR and then call \f(CW\*(C`ev_timer_again\*(C'\fR at start and each time you
1947 successfully read or write some data. If you go into an idle state where
1948 you do not expect data to travel on the socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR
1949 the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will automatically restart it if need be.
1950 .Sp
1951 That means you can ignore both the \f(CW\*(C`ev_timer_start\*(C'\fR function and the
1952 \&\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
1953 member and \f(CW\*(C`ev_timer_again\*(C'\fR.
1954 .Sp
1955 At start:
1956 .Sp
1957 .Vb 3
1958 \& ev_init (timer, callback);
1959 \& timer\->repeat = 60.;
1960 \& ev_timer_again (loop, timer);
1961 .Ve
1962 .Sp
1963 Each time there is some activity:
1964 .Sp
1965 .Vb 1
1966 \& ev_timer_again (loop, timer);
1967 .Ve
1968 .Sp
1969 It is even possible to change the time-out on the fly, regardless of
1970 whether the watcher is active or not:
1971 .Sp
1972 .Vb 2
1973 \& timer\->repeat = 30.;
1974 \& ev_timer_again (loop, timer);
1975 .Ve
1976 .Sp
1977 This is slightly more efficient then stopping/starting the timer each time
1978 you want to modify its timeout value, as libev does not have to completely
1979 remove and re-insert the timer from/into its internal data structure.
1980 .Sp
1981 It is, however, even simpler than the \*(L"obvious\*(R" way to do it.
1982 .IP "3. Let the timer time out, but then re-arm it as required." 4
1983 .IX Item "3. Let the timer time out, but then re-arm it as required."
1984 This method is more tricky, but usually most efficient: Most timeouts are
1985 relatively long compared to the intervals between other activity \- in
1986 our example, within 60 seconds, there are usually many I/O events with
1987 associated activity resets.
1988 .Sp
1989 In this case, it would be more efficient to leave the \f(CW\*(C`ev_timer\*(C'\fR alone,
1990 but remember the time of last activity, and check for a real timeout only
1991 within the callback:
1992 .Sp
1993 .Vb 3
1994 \& ev_tstamp timeout = 60.;
1995 \& ev_tstamp last_activity; // time of last activity
1996 \& ev_timer timer;
1997 \&
1998 \& static void
1999 \& callback (EV_P_ ev_timer *w, int revents)
2000 \& {
2001 \& // calculate when the timeout would happen
2002 \& ev_tstamp after = last_activity \- ev_now (EV_A) + timeout;
2003 \&
2004 \& // if negative, it means we the timeout already occurred
2005 \& if (after < 0.)
2006 \& {
2007 \& // timeout occurred, take action
2008 \& }
2009 \& else
2010 \& {
2011 \& // callback was invoked, but there was some recent
2012 \& // activity. simply restart the timer to time out
2013 \& // after "after" seconds, which is the earliest time
2014 \& // the timeout can occur.
2015 \& ev_timer_set (w, after, 0.);
2016 \& ev_timer_start (EV_A_ w);
2017 \& }
2018 \& }
2019 .Ve
2020 .Sp
2021 To summarise the callback: first calculate in how many seconds the
2022 timeout will occur (by calculating the absolute time when it would occur,
2023 \&\f(CW\*(C`last_activity + timeout\*(C'\fR, and subtracting the current time, \f(CW\*(C`ev_now
2024 (EV_A)\*(C'\fR from that).
2025 .Sp
2026 If this value is negative, then we are already past the timeout, i.e. we
2027 timed out, and need to do whatever is needed in this case.
2028 .Sp
2029 Otherwise, we now the earliest time at which the timeout would trigger,
2030 and simply start the timer with this timeout value.
2031 .Sp
2032 In other words, each time the callback is invoked it will check whether
2033 the timeout occurred. If not, it will simply reschedule itself to check
2034 again at the earliest time it could time out. Rinse. Repeat.
2035 .Sp
2036 This scheme causes more callback invocations (about one every 60 seconds
2037 minus half the average time between activity), but virtually no calls to
2038 libev to change the timeout.
2039 .Sp
2040 To start the machinery, simply initialise the watcher and set
2041 \&\f(CW\*(C`last_activity\*(C'\fR to the current time (meaning there was some activity just
2042 now), then call the callback, which will \*(L"do the right thing\*(R" and start
2043 the timer:
2044 .Sp
2045 .Vb 3
2046 \& last_activity = ev_now (EV_A);
2047 \& ev_init (&timer, callback);
2048 \& callback (EV_A_ &timer, 0);
2049 .Ve
2050 .Sp
2051 When there is some activity, simply store the current time in
2052 \&\f(CW\*(C`last_activity\*(C'\fR, no libev calls at all:
2053 .Sp
2054 .Vb 2
2055 \& if (activity detected)
2056 \& last_activity = ev_now (EV_A);
2057 .Ve
2058 .Sp
2059 When your timeout value changes, then the timeout can be changed by simply
2060 providing a new value, stopping the timer and calling the callback, which
2061 will again do the right thing (for example, time out immediately :).
2062 .Sp
2063 .Vb 3
2064 \& timeout = new_value;
2065 \& ev_timer_stop (EV_A_ &timer);
2066 \& callback (EV_A_ &timer, 0);
2067 .Ve
2068 .Sp
2069 This technique is slightly more complex, but in most cases where the
2070 time-out is unlikely to be triggered, much more efficient.
2071 .IP "4. Wee, just use a double-linked list for your timeouts." 4
2072 .IX Item "4. Wee, just use a double-linked list for your timeouts."
2073 If there is not one request, but many thousands (millions...), all
2074 employing some kind of timeout with the same timeout value, then one can
2075 do even better:
2076 .Sp
2077 When starting the timeout, calculate the timeout value and put the timeout
2078 at the \fIend\fR of the list.
2079 .Sp
2080 Then use an \f(CW\*(C`ev_timer\*(C'\fR to fire when the timeout at the \fIbeginning\fR of
2081 the list is expected to fire (for example, using the technique #3).
2082 .Sp
2083 When there is some activity, remove the timer from the list, recalculate
2084 the timeout, append it to the end of the list again, and make sure to
2085 update the \f(CW\*(C`ev_timer\*(C'\fR if it was taken from the beginning of the list.
2086 .Sp
2087 This way, one can manage an unlimited number of timeouts in O(1) time for
2088 starting, stopping and updating the timers, at the expense of a major
2089 complication, and having to use a constant timeout. The constant timeout
2090 ensures that the list stays sorted.
2091 .PP
2092 So which method the best?
2093 .PP
2094 Method #2 is a simple no-brain-required solution that is adequate in most
2095 situations. Method #3 requires a bit more thinking, but handles many cases
2096 better, and isn't very complicated either. In most case, choosing either
2097 one is fine, with #3 being better in typical situations.
2098 .PP
2099 Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
2100 rather complicated, but extremely efficient, something that really pays
2101 off after the first million or so of active timers, i.e. it's usually
2102 overkill :)
2103 .PP
2104 \fIThe special problem of being too early\fR
2105 .IX Subsection "The special problem of being too early"
2106 .PP
2107 If you ask a timer to call your callback after three seconds, then
2108 you expect it to be invoked after three seconds \- but of course, this
2109 cannot be guaranteed to infinite precision. Less obviously, it cannot be
2110 guaranteed to any precision by libev \- imagine somebody suspending the
2111 process with a \s-1STOP\s0 signal for a few hours for example.
2112 .PP
2113 So, libev tries to invoke your callback as soon as possible \fIafter\fR the
2114 delay has occurred, but cannot guarantee this.
2115 .PP
2116 A less obvious failure mode is calling your callback too early: many event
2117 loops compare timestamps with a \*(L"elapsed delay >= requested delay\*(R", but
2118 this can cause your callback to be invoked much earlier than you would
2119 expect.
2120 .PP
2121 To see why, imagine a system with a clock that only offers full second
2122 resolution (think windows if you can't come up with a broken enough \s-1OS\s0
2123 yourself). If you schedule a one-second timer at the time 500.9, then the
2124 event loop will schedule your timeout to elapse at a system time of 500
2125 (500.9 truncated to the resolution) + 1, or 501.
2126 .PP
2127 If an event library looks at the timeout 0.1s later, it will see \*(L"501 >=
2128 501\*(R" and invoke the callback 0.1s after it was started, even though a
2129 one-second delay was requested \- this is being \*(L"too early\*(R", despite best
2130 intentions.
2131 .PP
2132 This is the reason why libev will never invoke the callback if the elapsed
2133 delay equals the requested delay, but only when the elapsed delay is
2134 larger than the requested delay. In the example above, libev would only invoke
2135 the callback at system time 502, or 1.1s after the timer was started.
2136 .PP
2137 So, while libev cannot guarantee that your callback will be invoked
2138 exactly when requested, it \fIcan\fR and \fIdoes\fR guarantee that the requested
2139 delay has actually elapsed, or in other words, it always errs on the \*(L"too
2140 late\*(R" side of things.
2141 .PP
2142 \fIThe special problem of time updates\fR
2143 .IX Subsection "The special problem of time updates"
2144 .PP
2145 Establishing the current time is a costly operation (it usually takes
2146 at least one system call): \s-1EV\s0 therefore updates its idea of the current
2147 time only before and after \f(CW\*(C`ev_run\*(C'\fR collects new events, which causes a
2148 growing difference between \f(CW\*(C`ev_now ()\*(C'\fR and \f(CW\*(C`ev_time ()\*(C'\fR when handling
2149 lots of events in one iteration.
2150 .PP
2151 The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
2152 time. This is usually the right thing as this timestamp refers to the time
2153 of the event triggering whatever timeout you are modifying/starting. If
2154 you suspect event processing to be delayed and you \fIneed\fR to base the
2155 timeout on the current time, use something like this to adjust for this:
2156 .PP
2157 .Vb 1
2158 \& ev_timer_set (&timer, after + ev_now () \- ev_time (), 0.);
2159 .Ve
2160 .PP
2161 If the event loop is suspended for a long time, you can also force an
2162 update of the time returned by \f(CW\*(C`ev_now ()\*(C'\fR by calling \f(CW\*(C`ev_now_update
2163 ()\*(C'\fR.
2164 .PP
2165 \fIThe special problem of unsynchronised clocks\fR
2166 .IX Subsection "The special problem of unsynchronised clocks"
2167 .PP
2168 Modern systems have a variety of clocks \- libev itself uses the normal
2169 \&\*(L"wall clock\*(R" clock and, if available, the monotonic clock (to avoid time
2170 jumps).
2171 .PP
2172 Neither of these clocks is synchronised with each other or any other clock
2173 on the system, so \f(CW\*(C`ev_time ()\*(C'\fR might return a considerably different time
2174 than \f(CW\*(C`gettimeofday ()\*(C'\fR or \f(CW\*(C`time ()\*(C'\fR. On a GNU/Linux system, for example,
2175 a call to \f(CW\*(C`gettimeofday\*(C'\fR might return a second count that is one higher
2176 than a directly following call to \f(CW\*(C`time\*(C'\fR.
2177 .PP
2178 The moral of this is to only compare libev-related timestamps with
2179 \&\f(CW\*(C`ev_time ()\*(C'\fR and \f(CW\*(C`ev_now ()\*(C'\fR, at least if you want better precision than
2180 a second or so.
2181 .PP
2182 One more problem arises due to this lack of synchronisation: if libev uses
2183 the system monotonic clock and you compare timestamps from \f(CW\*(C`ev_time\*(C'\fR
2184 or \f(CW\*(C`ev_now\*(C'\fR from when you started your timer and when your callback is
2185 invoked, you will find that sometimes the callback is a bit \*(L"early\*(R".
2186 .PP
2187 This is because \f(CW\*(C`ev_timer\*(C'\fRs work in real time, not wall clock time, so
2188 libev makes sure your callback is not invoked before the delay happened,
2189 \&\fImeasured according to the real time\fR, not the system clock.
2190 .PP
2191 If your timeouts are based on a physical timescale (e.g. \*(L"time out this
2192 connection after 100 seconds\*(R") then this shouldn't bother you as it is
2193 exactly the right behaviour.
2194 .PP
2195 If you want to compare wall clock/system timestamps to your timers, then
2196 you need to use \f(CW\*(C`ev_periodic\*(C'\fRs, as these are based on the wall clock
2197 time, where your comparisons will always generate correct results.
2198 .PP
2199 \fIThe special problems of suspended animation\fR
2200 .IX Subsection "The special problems of suspended animation"
2201 .PP
2202 When you leave the server world it is quite customary to hit machines that
2203 can suspend/hibernate \- what happens to the clocks during such a suspend?
2204 .PP
2205 Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
2206 all processes, while the clocks (\f(CW\*(C`times\*(C'\fR, \f(CW\*(C`CLOCK_MONOTONIC\*(C'\fR) continue
2207 to run until the system is suspended, but they will not advance while the
2208 system is suspended. That means, on resume, it will be as if the program
2209 was frozen for a few seconds, but the suspend time will not be counted
2210 towards \f(CW\*(C`ev_timer\*(C'\fR when a monotonic clock source is used. The real time
2211 clock advanced as expected, but if it is used as sole clocksource, then a
2212 long suspend would be detected as a time jump by libev, and timers would
2213 be adjusted accordingly.
2214 .PP
2215 I would not be surprised to see different behaviour in different between
2216 operating systems, \s-1OS\s0 versions or even different hardware.
2217 .PP
2218 The other form of suspend (job control, or sending a \s-1SIGSTOP\s0) will see a
2219 time jump in the monotonic clocks and the realtime clock. If the program
2220 is suspended for a very long time, and monotonic clock sources are in use,
2221 then you can expect \f(CW\*(C`ev_timer\*(C'\fRs to expire as the full suspension time
2222 will be counted towards the timers. When no monotonic clock source is in
2223 use, then libev will again assume a timejump and adjust accordingly.
2224 .PP
2225 It might be beneficial for this latter case to call \f(CW\*(C`ev_suspend\*(C'\fR
2226 and \f(CW\*(C`ev_resume\*(C'\fR in code that handles \f(CW\*(C`SIGTSTP\*(C'\fR, to at least get
2227 deterministic behaviour in this case (you can do nothing against
2228 \&\f(CW\*(C`SIGSTOP\*(C'\fR).
2229 .PP
2230 \fIWatcher-Specific Functions and Data Members\fR
2231 .IX Subsection "Watcher-Specific Functions and Data Members"
2232 .IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
2233 .IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
2234 .PD 0
2235 .IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
2236 .IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
2237 .PD
2238 Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR
2239 is \f(CW0.\fR, then it will automatically be stopped once the timeout is
2240 reached. If it is positive, then the timer will automatically be
2241 configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds later, again, and again,
2242 until stopped manually.
2243 .Sp
2244 The timer itself will do a best-effort at avoiding drift, that is, if
2245 you configure a timer to trigger every 10 seconds, then it will normally
2246 trigger at exactly 10 second intervals. If, however, your program cannot
2247 keep up with the timer (because it takes longer than those 10 seconds to
2248 do stuff) the timer will not fire more than once per event loop iteration.
2249 .IP "ev_timer_again (loop, ev_timer *)" 4
2250 .IX Item "ev_timer_again (loop, ev_timer *)"
2251 This will act as if the timer timed out, and restarts it again if it is
2252 repeating. It basically works like calling \f(CW\*(C`ev_timer_stop\*(C'\fR, updating the
2253 timeout to the \f(CW\*(C`repeat\*(C'\fR value and calling \f(CW\*(C`ev_timer_start\*(C'\fR.
2254 .Sp
2255 The exact semantics are as in the following rules, all of which will be
2256 applied to the watcher:
2257 .RS 4
2258 .IP "If the timer is pending, the pending status is always cleared." 4
2259 .IX Item "If the timer is pending, the pending status is always cleared."
2260 .PD 0
2261 .IP "If the timer is started but non-repeating, stop it (as if it timed out, without invoking it)." 4
2262 .IX Item "If the timer is started but non-repeating, stop it (as if it timed out, without invoking it)."
2263 .ie n .IP "If the timer is repeating, make the ""repeat"" value the new timeout and start the timer, if necessary." 4
2264 .el .IP "If the timer is repeating, make the \f(CWrepeat\fR value the new timeout and start the timer, if necessary." 4
2265 .IX Item "If the timer is repeating, make the repeat value the new timeout and start the timer, if necessary."
2266 .RE
2267 .RS 4
2268 .PD
2269 .Sp
2270 This sounds a bit complicated, see \*(L"Be smart about timeouts\*(R", above, for a
2271 usage example.
2272 .RE
2273 .IP "ev_tstamp ev_timer_remaining (loop, ev_timer *)" 4
2274 .IX Item "ev_tstamp ev_timer_remaining (loop, ev_timer *)"
2275 Returns the remaining time until a timer fires. If the timer is active,
2276 then this time is relative to the current event loop time, otherwise it's
2277 the timeout value currently configured.
2278 .Sp
2279 That is, after an \f(CW\*(C`ev_timer_set (w, 5, 7)\*(C'\fR, \f(CW\*(C`ev_timer_remaining\*(C'\fR returns
2280 \&\f(CW5\fR. When the timer is started and one second passes, \f(CW\*(C`ev_timer_remaining\*(C'\fR
2281 will return \f(CW4\fR. When the timer expires and is restarted, it will return
2282 roughly \f(CW7\fR (likely slightly less as callback invocation takes some time,
2283 too), and so on.
2284 .IP "ev_tstamp repeat [read\-write]" 4
2285 .IX Item "ev_tstamp repeat [read-write]"
2286 The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out
2287 or \f(CW\*(C`ev_timer_again\*(C'\fR is called, and determines the next timeout (if any),
2288 which is also when any modifications are taken into account.
2289 .PP
2290 \fIExamples\fR
2291 .IX Subsection "Examples"
2292 .PP
2293 Example: Create a timer that fires after 60 seconds.
2294 .PP
2295 .Vb 5
2296 \& static void
2297 \& one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
2298 \& {
2299 \& .. one minute over, w is actually stopped right here
2300 \& }
2301 \&
2302 \& ev_timer mytimer;
2303 \& ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
2304 \& ev_timer_start (loop, &mytimer);
2305 .Ve
2306 .PP
2307 Example: Create a timeout timer that times out after 10 seconds of
2308 inactivity.
2309 .PP
2310 .Vb 5
2311 \& static void
2312 \& timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
2313 \& {
2314 \& .. ten seconds without any activity
2315 \& }
2316 \&
2317 \& ev_timer mytimer;
2318 \& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
2319 \& ev_timer_again (&mytimer); /* start timer */
2320 \& ev_run (loop, 0);
2321 \&
2322 \& // and in some piece of code that gets executed on any "activity":
2323 \& // reset the timeout to start ticking again at 10 seconds
2324 \& ev_timer_again (&mytimer);
2325 .Ve
2326 .ie n .SS """ev_periodic"" \- to cron or not to cron?"
2327 .el .SS "\f(CWev_periodic\fP \- to cron or not to cron?"
2328 .IX Subsection "ev_periodic - to cron or not to cron?"
2329 Periodic watchers are also timers of a kind, but they are very versatile
2330 (and unfortunately a bit complex).
2331 .PP
2332 Unlike \f(CW\*(C`ev_timer\*(C'\fR, periodic watchers are not based on real time (or
2333 relative time, the physical time that passes) but on wall clock time
2334 (absolute time, the thing you can read on your calender or clock). The
2335 difference is that wall clock time can run faster or slower than real
2336 time, and time jumps are not uncommon (e.g. when you adjust your
2337 wrist-watch).
2338 .PP
2339 You can tell a periodic watcher to trigger after some specific point
2340 in time: for example, if you tell a periodic watcher to trigger \*(L"in 10
2341 seconds\*(R" (by specifying e.g. \f(CW\*(C`ev_now () + 10.\*(C'\fR, that is, an absolute time
2342 not a delay) and then reset your system clock to January of the previous
2343 year, then it will take a year or more to trigger the event (unlike an
2344 \&\f(CW\*(C`ev_timer\*(C'\fR, which would still trigger roughly 10 seconds after starting
2345 it, as it uses a relative timeout).
2346 .PP
2347 \&\f(CW\*(C`ev_periodic\*(C'\fR watchers can also be used to implement vastly more complex
2348 timers, such as triggering an event on each \*(L"midnight, local time\*(R", or
2349 other complicated rules. This cannot be done with \f(CW\*(C`ev_timer\*(C'\fR watchers, as
2350 those cannot react to time jumps.
2351 .PP
2352 As with timers, the callback is guaranteed to be invoked only when the
2353 point in time where it is supposed to trigger has passed. If multiple
2354 timers become ready during the same loop iteration then the ones with
2355 earlier time-out values are invoked before ones with later time-out values
2356 (but this is no longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
2357 .PP
2358 \fIWatcher-Specific Functions and Data Members\fR
2359 .IX Subsection "Watcher-Specific Functions and Data Members"
2360 .IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
2361 .IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
2362 .PD 0
2363 .IP "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
2364 .IX Item "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
2365 .PD
2366 Lots of arguments, let's sort it out... There are basically three modes of
2367 operation, and we will explain them from simplest to most complex:
2368 .RS 4
2369 .IP "\(bu" 4
2370 absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
2371 .Sp
2372 In this configuration the watcher triggers an event after the wall clock
2373 time \f(CW\*(C`offset\*(C'\fR has passed. It will not repeat and will not adjust when a
2374 time jump occurs, that is, if it is to be run at January 1st 2011 then it
2375 will be stopped and invoked when the system clock reaches or surpasses
2376 this point in time.
2377 .IP "\(bu" 4
2378 repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
2379 .Sp
2380 In this mode the watcher will always be scheduled to time out at the next
2381 \&\f(CW\*(C`offset + N * interval\*(C'\fR time (for some integer N, which can also be
2382 negative) and then repeat, regardless of any time jumps. The \f(CW\*(C`offset\*(C'\fR
2383 argument is merely an offset into the \f(CW\*(C`interval\*(C'\fR periods.
2384 .Sp
2385 This can be used to create timers that do not drift with respect to the
2386 system clock, for example, here is an \f(CW\*(C`ev_periodic\*(C'\fR that triggers each
2387 hour, on the hour (with respect to \s-1UTC\s0):
2388 .Sp
2389 .Vb 1
2390 \& ev_periodic_set (&periodic, 0., 3600., 0);
2391 .Ve
2392 .Sp
2393 This doesn't mean there will always be 3600 seconds in between triggers,
2394 but only that the callback will be called when the system time shows a
2395 full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
2396 by 3600.
2397 .Sp
2398 Another way to think about it (for the mathematically inclined) is that
2399 \&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
2400 time where \f(CW\*(C`time = offset (mod interval)\*(C'\fR, regardless of any time jumps.
2401 .Sp
2402 The \f(CW\*(C`interval\*(C'\fR \fI\s-1MUST\s0\fR be positive, and for numerical stability, the
2403 interval value should be higher than \f(CW\*(C`1/8192\*(C'\fR (which is around 100
2404 microseconds) and \f(CW\*(C`offset\*(C'\fR should be higher than \f(CW0\fR and should have
2405 at most a similar magnitude as the current time (say, within a factor of
2406 ten). Typical values for offset are, in fact, \f(CW0\fR or something between
2407 \&\f(CW0\fR and \f(CW\*(C`interval\*(C'\fR, which is also the recommended range.
2408 .Sp
2409 Note also that there is an upper limit to how often a timer can fire (\s-1CPU\s0
2410 speed for example), so if \f(CW\*(C`interval\*(C'\fR is very small then timing stability
2411 will of course deteriorate. Libev itself tries to be exact to be about one
2412 millisecond (if the \s-1OS\s0 supports it and the machine is fast enough).
2413 .IP "\(bu" 4
2414 manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
2415 .Sp
2416 In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`offset\*(C'\fR are both being
2417 ignored. Instead, each time the periodic watcher gets scheduled, the
2418 reschedule callback will be called with the watcher as first, and the
2419 current time as second argument.
2420 .Sp
2421 \&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, ever,
2422 or make \s-1ANY\s0 other event loop modifications whatsoever, unless explicitly
2423 allowed by documentation here\fR.
2424 .Sp
2425 If you need to stop it, return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop
2426 it afterwards (e.g. by starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is the
2427 only event loop modification you are allowed to do).
2428 .Sp
2429 The callback prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(ev_periodic
2430 *w, ev_tstamp now)\*(C'\fR, e.g.:
2431 .Sp
2432 .Vb 5
2433 \& static ev_tstamp
2434 \& my_rescheduler (ev_periodic *w, ev_tstamp now)
2435 \& {
2436 \& return now + 60.;
2437 \& }
2438 .Ve
2439 .Sp
2440 It must return the next time to trigger, based on the passed time value
2441 (that is, the lowest time value larger than to the second argument). It
2442 will usually be called just before the callback will be triggered, but
2443 might be called at other times, too.
2444 .Sp
2445 \&\s-1NOTE:\s0 \fIThis callback must always return a time that is higher than or
2446 equal to the passed \f(CI\*(C`now\*(C'\fI value\fR.
2447 .Sp
2448 This can be used to create very complex timers, such as a timer that
2449 triggers on \*(L"next midnight, local time\*(R". To do this, you would calculate the
2450 next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How
2451 you do this is, again, up to you (but it is not trivial, which is the main
2452 reason I omitted it as an example).
2453 .RE
2454 .RS 4
2455 .RE
2456 .IP "ev_periodic_again (loop, ev_periodic *)" 4
2457 .IX Item "ev_periodic_again (loop, ev_periodic *)"
2458 Simply stops and restarts the periodic watcher again. This is only useful
2459 when you changed some parameters or the reschedule callback would return
2460 a different time than the last time it was called (e.g. in a crond like
2461 program when the crontabs have changed).
2462 .IP "ev_tstamp ev_periodic_at (ev_periodic *)" 4
2463 .IX Item "ev_tstamp ev_periodic_at (ev_periodic *)"
2464 When active, returns the absolute time that the watcher is supposed
2465 to trigger next. This is not the same as the \f(CW\*(C`offset\*(C'\fR argument to
2466 \&\f(CW\*(C`ev_periodic_set\*(C'\fR, but indeed works even in interval and manual
2467 rescheduling modes.
2468 .IP "ev_tstamp offset [read\-write]" 4
2469 .IX Item "ev_tstamp offset [read-write]"
2470 When repeating, this contains the offset value, otherwise this is the
2471 absolute point in time (the \f(CW\*(C`offset\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR,
2472 although libev might modify this value for better numerical stability).
2473 .Sp
2474 Can be modified any time, but changes only take effect when the periodic
2475 timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
2476 .IP "ev_tstamp interval [read\-write]" 4
2477 .IX Item "ev_tstamp interval [read-write]"
2478 The current interval value. Can be modified any time, but changes only
2479 take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being
2480 called.
2481 .IP "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read\-write]" 4
2482 .IX Item "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]"
2483 The current reschedule callback, or \f(CW0\fR, if this functionality is
2484 switched off. Can be changed any time, but changes only take effect when
2485 the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
2486 .PP
2487 \fIExamples\fR
2488 .IX Subsection "Examples"
2489 .PP
2490 Example: Call a callback every hour, or, more precisely, whenever the
2491 system time is divisible by 3600. The callback invocation times have
2492 potentially a lot of jitter, but good long-term stability.
2493 .PP
2494 .Vb 5
2495 \& static void
2496 \& clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
2497 \& {
2498 \& ... its now a full hour (UTC, or TAI or whatever your clock follows)
2499 \& }
2500 \&
2501 \& ev_periodic hourly_tick;
2502 \& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
2503 \& ev_periodic_start (loop, &hourly_tick);
2504 .Ve
2505 .PP
2506 Example: The same as above, but use a reschedule callback to do it:
2507 .PP
2508 .Vb 1
2509 \& #include <math.h>
2510 \&
2511 \& static ev_tstamp
2512 \& my_scheduler_cb (ev_periodic *w, ev_tstamp now)
2513 \& {
2514 \& return now + (3600. \- fmod (now, 3600.));
2515 \& }
2516 \&
2517 \& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
2518 .Ve
2519 .PP
2520 Example: Call a callback every hour, starting now:
2521 .PP
2522 .Vb 4
2523 \& ev_periodic hourly_tick;
2524 \& ev_periodic_init (&hourly_tick, clock_cb,
2525 \& fmod (ev_now (loop), 3600.), 3600., 0);
2526 \& ev_periodic_start (loop, &hourly_tick);
2527 .Ve
2528 .ie n .SS """ev_signal"" \- signal me when a signal gets signalled!"
2529 .el .SS "\f(CWev_signal\fP \- signal me when a signal gets signalled!"
2530 .IX Subsection "ev_signal - signal me when a signal gets signalled!"
2531 Signal watchers will trigger an event when the process receives a specific
2532 signal one or more times. Even though signals are very asynchronous, libev
2533 will try its best to deliver signals synchronously, i.e. as part of the
2534 normal event processing, like any other event.
2535 .PP
2536 If you want signals to be delivered truly asynchronously, just use
2537 \&\f(CW\*(C`sigaction\*(C'\fR as you would do without libev and forget about sharing
2538 the signal. You can even use \f(CW\*(C`ev_async\*(C'\fR from a signal handler to
2539 synchronously wake up an event loop.
2540 .PP
2541 You can configure as many watchers as you like for the same signal, but
2542 only within the same loop, i.e. you can watch for \f(CW\*(C`SIGINT\*(C'\fR in your
2543 default loop and for \f(CW\*(C`SIGIO\*(C'\fR in another loop, but you cannot watch for
2544 \&\f(CW\*(C`SIGINT\*(C'\fR in both the default loop and another loop at the same time. At
2545 the moment, \f(CW\*(C`SIGCHLD\*(C'\fR is permanently tied to the default loop.
2546 .PP
2547 When the first watcher gets started will libev actually register something
2548 with the kernel (thus it coexists with your own signal handlers as long as
2549 you don't register any with libev for the same signal).
2550 .PP
2551 If possible and supported, libev will install its handlers with
2552 \&\f(CW\*(C`SA_RESTART\*(C'\fR (or equivalent) behaviour enabled, so system calls should
2553 not be unduly interrupted. If you have a problem with system calls getting
2554 interrupted by signals you can block all signals in an \f(CW\*(C`ev_check\*(C'\fR watcher
2555 and unblock them in an \f(CW\*(C`ev_prepare\*(C'\fR watcher.
2556 .PP
2557 \fIThe special problem of inheritance over fork/execve/pthread_create\fR
2558 .IX Subsection "The special problem of inheritance over fork/execve/pthread_create"
2559 .PP
2560 Both the signal mask (\f(CW\*(C`sigprocmask\*(C'\fR) and the signal disposition
2561 (\f(CW\*(C`sigaction\*(C'\fR) are unspecified after starting a signal watcher (and after
2562 stopping it again), that is, libev might or might not block the signal,
2563 and might or might not set or restore the installed signal handler (but
2564 see \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR).
2565 .PP
2566 While this does not matter for the signal disposition (libev never
2567 sets signals to \f(CW\*(C`SIG_IGN\*(C'\fR, so handlers will be reset to \f(CW\*(C`SIG_DFL\*(C'\fR on
2568 \&\f(CW\*(C`execve\*(C'\fR), this matters for the signal mask: many programs do not expect
2569 certain signals to be blocked.
2570 .PP
2571 This means that before calling \f(CW\*(C`exec\*(C'\fR (from the child) you should reset
2572 the signal mask to whatever \*(L"default\*(R" you expect (all clear is a good
2573 choice usually).
2574 .PP
2575 The simplest way to ensure that the signal mask is reset in the child is
2576 to install a fork handler with \f(CW\*(C`pthread_atfork\*(C'\fR that resets it. That will
2577 catch fork calls done by libraries (such as the libc) as well.
2578 .PP
2579 In current versions of libev, the signal will not be blocked indefinitely
2580 unless you use the \f(CW\*(C`signalfd\*(C'\fR \s-1API\s0 (\f(CW\*(C`EV_SIGNALFD\*(C'\fR). While this reduces
2581 the window of opportunity for problems, it will not go away, as libev
2582 \&\fIhas\fR to modify the signal mask, at least temporarily.
2583 .PP
2584 So I can't stress this enough: \fIIf you do not reset your signal mask when
2585 you expect it to be empty, you have a race condition in your code\fR. This
2586 is not a libev-specific thing, this is true for most event libraries.
2587 .PP
2588 \fIThe special problem of threads signal handling\fR
2589 .IX Subsection "The special problem of threads signal handling"
2590 .PP
2591 \&\s-1POSIX\s0 threads has problematic signal handling semantics, specifically,
2592 a lot of functionality (sigfd, sigwait etc.) only really works if all
2593 threads in a process block signals, which is hard to achieve.
2594 .PP
2595 When you want to use sigwait (or mix libev signal handling with your own
2596 for the same signals), you can tackle this problem by globally blocking
2597 all signals before creating any threads (or creating them with a fully set
2598 sigprocmask) and also specifying the \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR when creating
2599 loops. Then designate one thread as \*(L"signal receiver thread\*(R" which handles
2600 these signals. You can pass on any signals that libev might be interested
2601 in by calling \f(CW\*(C`ev_feed_signal\*(C'\fR.
2602 .PP
2603 \fIWatcher-Specific Functions and Data Members\fR
2604 .IX Subsection "Watcher-Specific Functions and Data Members"
2605 .IP "ev_signal_init (ev_signal *, callback, int signum)" 4
2606 .IX Item "ev_signal_init (ev_signal *, callback, int signum)"
2607 .PD 0
2608 .IP "ev_signal_set (ev_signal *, int signum)" 4
2609 .IX Item "ev_signal_set (ev_signal *, int signum)"
2610 .PD
2611 Configures the watcher to trigger on the given signal number (usually one
2612 of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
2613 .IP "int signum [read\-only]" 4
2614 .IX Item "int signum [read-only]"
2615 The signal the watcher watches out for.
2616 .PP
2617 \fIExamples\fR
2618 .IX Subsection "Examples"
2619 .PP
2620 Example: Try to exit cleanly on \s-1SIGINT\s0.
2621 .PP
2622 .Vb 5
2623 \& static void
2624 \& sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
2625 \& {
2626 \& ev_break (loop, EVBREAK_ALL);
2627 \& }
2628 \&
2629 \& ev_signal signal_watcher;
2630 \& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
2631 \& ev_signal_start (loop, &signal_watcher);
2632 .Ve
2633 .ie n .SS """ev_child"" \- watch out for process status changes"
2634 .el .SS "\f(CWev_child\fP \- watch out for process status changes"
2635 .IX Subsection "ev_child - watch out for process status changes"
2636 Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
2637 some child status changes (most typically when a child of yours dies or
2638 exits). It is permissible to install a child watcher \fIafter\fR the child
2639 has been forked (which implies it might have already exited), as long
2640 as the event loop isn't entered (or is continued from a watcher), i.e.,
2641 forking and then immediately registering a watcher for the child is fine,
2642 but forking and registering a watcher a few event loop iterations later or
2643 in the next callback invocation is not.
2644 .PP
2645 Only the default event loop is capable of handling signals, and therefore
2646 you can only register child watchers in the default event loop.
2647 .PP
2648 Due to some design glitches inside libev, child watchers will always be
2649 handled at maximum priority (their priority is set to \f(CW\*(C`EV_MAXPRI\*(C'\fR by
2650 libev)
2651 .PP
2652 \fIProcess Interaction\fR
2653 .IX Subsection "Process Interaction"
2654 .PP
2655 Libev grabs \f(CW\*(C`SIGCHLD\*(C'\fR as soon as the default event loop is
2656 initialised. This is necessary to guarantee proper behaviour even if the
2657 first child watcher is started after the child exits. The occurrence
2658 of \f(CW\*(C`SIGCHLD\*(C'\fR is recorded asynchronously, but child reaping is done
2659 synchronously as part of the event loop processing. Libev always reaps all
2660 children, even ones not watched.
2661 .PP
2662 \fIOverriding the Built-In Processing\fR
2663 .IX Subsection "Overriding the Built-In Processing"
2664 .PP
2665 Libev offers no special support for overriding the built-in child
2666 processing, but if your application collides with libev's default child
2667 handler, you can override it easily by installing your own handler for
2668 \&\f(CW\*(C`SIGCHLD\*(C'\fR after initialising the default loop, and making sure the
2669 default loop never gets destroyed. You are encouraged, however, to use an
2670 event-based approach to child reaping and thus use libev's support for
2671 that, so other libev users can use \f(CW\*(C`ev_child\*(C'\fR watchers freely.
2672 .PP
2673 \fIStopping the Child Watcher\fR
2674 .IX Subsection "Stopping the Child Watcher"
2675 .PP
2676 Currently, the child watcher never gets stopped, even when the
2677 child terminates, so normally one needs to stop the watcher in the
2678 callback. Future versions of libev might stop the watcher automatically
2679 when a child exit is detected (calling \f(CW\*(C`ev_child_stop\*(C'\fR twice is not a
2680 problem).
2681 .PP
2682 \fIWatcher-Specific Functions and Data Members\fR
2683 .IX Subsection "Watcher-Specific Functions and Data Members"
2684 .IP "ev_child_init (ev_child *, callback, int pid, int trace)" 4
2685 .IX Item "ev_child_init (ev_child *, callback, int pid, int trace)"
2686 .PD 0
2687 .IP "ev_child_set (ev_child *, int pid, int trace)" 4
2688 .IX Item "ev_child_set (ev_child *, int pid, int trace)"
2689 .PD
2690 Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
2691 \&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
2692 at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
2693 the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
2694 \&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
2695 process causing the status change. \f(CW\*(C`trace\*(C'\fR must be either \f(CW0\fR (only
2696 activate the watcher when the process terminates) or \f(CW1\fR (additionally
2697 activate the watcher when the process is stopped or continued).
2698 .IP "int pid [read\-only]" 4
2699 .IX Item "int pid [read-only]"
2700 The process id this watcher watches out for, or \f(CW0\fR, meaning any process id.
2701 .IP "int rpid [read\-write]" 4
2702 .IX Item "int rpid [read-write]"
2703 The process id that detected a status change.
2704 .IP "int rstatus [read\-write]" 4
2705 .IX Item "int rstatus [read-write]"
2706 The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems
2707 \&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details).
2708 .PP
2709 \fIExamples\fR
2710 .IX Subsection "Examples"
2711 .PP
2712 Example: \f(CW\*(C`fork()\*(C'\fR a new process and install a child handler to wait for
2713 its completion.
2714 .PP
2715 .Vb 1
2716 \& ev_child cw;
2717 \&
2718 \& static void
2719 \& child_cb (EV_P_ ev_child *w, int revents)
2720 \& {
2721 \& ev_child_stop (EV_A_ w);
2722 \& printf ("process %d exited with status %x\en", w\->rpid, w\->rstatus);
2723 \& }
2724 \&
2725 \& pid_t pid = fork ();
2726 \&
2727 \& if (pid < 0)
2728 \& // error
2729 \& else if (pid == 0)
2730 \& {
2731 \& // the forked child executes here
2732 \& exit (1);
2733 \& }
2734 \& else
2735 \& {
2736 \& ev_child_init (&cw, child_cb, pid, 0);
2737 \& ev_child_start (EV_DEFAULT_ &cw);
2738 \& }
2739 .Ve
2740 .ie n .SS """ev_stat"" \- did the file attributes just change?"
2741 .el .SS "\f(CWev_stat\fP \- did the file attributes just change?"
2742 .IX Subsection "ev_stat - did the file attributes just change?"
2743 This watches a file system path for attribute changes. That is, it calls
2744 \&\f(CW\*(C`stat\*(C'\fR on that path in regular intervals (or when the \s-1OS\s0 says it changed)
2745 and sees if it changed compared to the last time, invoking the callback
2746 if it did. Starting the watcher \f(CW\*(C`stat\*(C'\fR's the file, so only changes that
2747 happen after the watcher has been started will be reported.
2748 .PP
2749 The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does
2750 not exist\*(R" is a status change like any other. The condition \*(L"path does not
2751 exist\*(R" (or more correctly \*(L"path cannot be stat'ed\*(R") is signified by the
2752 \&\f(CW\*(C`st_nlink\*(C'\fR field being zero (which is otherwise always forced to be at
2753 least one) and all the other fields of the stat buffer having unspecified
2754 contents.
2755 .PP
2756 The path \fImust not\fR end in a slash or contain special components such as
2757 \&\f(CW\*(C`.\*(C'\fR or \f(CW\*(C`..\*(C'\fR. The path \fIshould\fR be absolute: If it is relative and
2758 your working directory changes, then the behaviour is undefined.
2759 .PP
2760 Since there is no portable change notification interface available, the
2761 portable implementation simply calls \f(CWstat(2)\fR regularly on the path
2762 to see if it changed somehow. You can specify a recommended polling
2763 interval for this case. If you specify a polling interval of \f(CW0\fR (highly
2764 recommended!) then a \fIsuitable, unspecified default\fR value will be used
2765 (which you can expect to be around five seconds, although this might
2766 change dynamically). Libev will also impose a minimum interval which is
2767 currently around \f(CW0.1\fR, but that's usually overkill.
2768 .PP
2769 This watcher type is not meant for massive numbers of stat watchers,
2770 as even with OS-supported change notifications, this can be
2771 resource-intensive.
2772 .PP
2773 At the time of this writing, the only OS-specific interface implemented
2774 is the Linux inotify interface (implementing kqueue support is left as an
2775 exercise for the reader. Note, however, that the author sees no way of
2776 implementing \f(CW\*(C`ev_stat\*(C'\fR semantics with kqueue, except as a hint).
2777 .PP
2778 \fI\s-1ABI\s0 Issues (Largefile Support)\fR
2779 .IX Subsection "ABI Issues (Largefile Support)"
2780 .PP
2781 Libev by default (unless the user overrides this) uses the default
2782 compilation environment, which means that on systems with large file
2783 support disabled by default, you get the 32 bit version of the stat
2784 structure. When using the library from programs that change the \s-1ABI\s0 to
2785 use 64 bit file offsets the programs will fail. In that case you have to
2786 compile libev with the same flags to get binary compatibility. This is
2787 obviously the case with any flags that change the \s-1ABI\s0, but the problem is
2788 most noticeably displayed with ev_stat and large file support.
2789 .PP
2790 The solution for this is to lobby your distribution maker to make large
2791 file interfaces available by default (as e.g. FreeBSD does) and not
2792 optional. Libev cannot simply switch on large file support because it has
2793 to exchange stat structures with application programs compiled using the
2794 default compilation environment.
2795 .PP
2796 \fIInotify and Kqueue\fR
2797 .IX Subsection "Inotify and Kqueue"
2798 .PP
2799 When \f(CW\*(C`inotify (7)\*(C'\fR support has been compiled into libev and present at
2800 runtime, it will be used to speed up change detection where possible. The
2801 inotify descriptor will be created lazily when the first \f(CW\*(C`ev_stat\*(C'\fR
2802 watcher is being started.
2803 .PP
2804 Inotify presence does not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers
2805 except that changes might be detected earlier, and in some cases, to avoid
2806 making regular \f(CW\*(C`stat\*(C'\fR calls. Even in the presence of inotify support
2807 there are many cases where libev has to resort to regular \f(CW\*(C`stat\*(C'\fR polling,
2808 but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
2809 many bugs), the path exists (i.e. stat succeeds), and the path resides on
2810 a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
2811 xfs are fully working) libev usually gets away without polling.
2812 .PP
2813 There is no support for kqueue, as apparently it cannot be used to
2814 implement this functionality, due to the requirement of having a file
2815 descriptor open on the object at all times, and detecting renames, unlinks
2816 etc. is difficult.
2817 .PP
2818 \fI\f(CI\*(C`stat ()\*(C'\fI is a synchronous operation\fR
2819 .IX Subsection "stat () is a synchronous operation"
2820 .PP
2821 Libev doesn't normally do any kind of I/O itself, and so is not blocking
2822 the process. The exception are \f(CW\*(C`ev_stat\*(C'\fR watchers \- those call \f(CW\*(C`stat
2823 ()\*(C'\fR, which is a synchronous operation.
2824 .PP
2825 For local paths, this usually doesn't matter: unless the system is very
2826 busy or the intervals between stat's are large, a stat call will be fast,
2827 as the path data is usually in memory already (except when starting the
2828 watcher).
2829 .PP
2830 For networked file systems, calling \f(CW\*(C`stat ()\*(C'\fR can block an indefinite
2831 time due to network issues, and even under good conditions, a stat call
2832 often takes multiple milliseconds.
2833 .PP
2834 Therefore, it is best to avoid using \f(CW\*(C`ev_stat\*(C'\fR watchers on networked
2835 paths, although this is fully supported by libev.
2836 .PP
2837 \fIThe special problem of stat time resolution\fR
2838 .IX Subsection "The special problem of stat time resolution"
2839 .PP
2840 The \f(CW\*(C`stat ()\*(C'\fR system call only supports full-second resolution portably,
2841 and even on systems where the resolution is higher, most file systems
2842 still only support whole seconds.
2843 .PP
2844 That means that, if the time is the only thing that changes, you can
2845 easily miss updates: on the first update, \f(CW\*(C`ev_stat\*(C'\fR detects a change and
2846 calls your callback, which does something. When there is another update
2847 within the same second, \f(CW\*(C`ev_stat\*(C'\fR will be unable to detect unless the
2848 stat data does change in other ways (e.g. file size).
2849 .PP
2850 The solution to this is to delay acting on a change for slightly more
2851 than a second (or till slightly after the next full second boundary), using
2852 a roughly one-second-delay \f(CW\*(C`ev_timer\*(C'\fR (e.g. \f(CW\*(C`ev_timer_set (w, 0., 1.02);
2853 ev_timer_again (loop, w)\*(C'\fR).
2854 .PP
2855 The \f(CW.02\fR offset is added to work around small timing inconsistencies
2856 of some operating systems (where the second counter of the current time
2857 might be be delayed. One such system is the Linux kernel, where a call to
2858 \&\f(CW\*(C`gettimeofday\*(C'\fR might return a timestamp with a full second later than
2859 a subsequent \f(CW\*(C`time\*(C'\fR call \- if the equivalent of \f(CW\*(C`time ()\*(C'\fR is used to
2860 update file times then there will be a small window where the kernel uses
2861 the previous second to update file times but libev might already execute
2862 the timer callback).
2863 .PP
2864 \fIWatcher-Specific Functions and Data Members\fR
2865 .IX Subsection "Watcher-Specific Functions and Data Members"
2866 .IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4
2867 .IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)"
2868 .PD 0
2869 .IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4
2870 .IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)"
2871 .PD
2872 Configures the watcher to wait for status changes of the given
2873 \&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to
2874 be detected and should normally be specified as \f(CW0\fR to let libev choose
2875 a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same
2876 path for as long as the watcher is active.
2877 .Sp
2878 The callback will receive an \f(CW\*(C`EV_STAT\*(C'\fR event when a change was detected,
2879 relative to the attributes at the time the watcher was started (or the
2880 last change was detected).
2881 .IP "ev_stat_stat (loop, ev_stat *)" 4
2882 .IX Item "ev_stat_stat (loop, ev_stat *)"
2883 Updates the stat buffer immediately with new values. If you change the
2884 watched path in your callback, you could call this function to avoid
2885 detecting this change (while introducing a race condition if you are not
2886 the only one changing the path). Can also be useful simply to find out the
2887 new values.
2888 .IP "ev_statdata attr [read\-only]" 4
2889 .IX Item "ev_statdata attr [read-only]"
2890 The most-recently detected attributes of the file. Although the type is
2891 \&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types
2892 suitable for your system, but you can only rely on the POSIX-standardised
2893 members to be present. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there was
2894 some error while \f(CW\*(C`stat\*(C'\fRing the file.
2895 .IP "ev_statdata prev [read\-only]" 4
2896 .IX Item "ev_statdata prev [read-only]"
2897 The previous attributes of the file. The callback gets invoked whenever
2898 \&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR, or, more precisely, one or more of these members
2899 differ: \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,
2900 \&\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.
2901 .IP "ev_tstamp interval [read\-only]" 4
2902 .IX Item "ev_tstamp interval [read-only]"
2903 The specified interval.
2904 .IP "const char *path [read\-only]" 4
2905 .IX Item "const char *path [read-only]"
2906 The file system path that is being watched.
2907 .PP
2908 \fIExamples\fR
2909 .IX Subsection "Examples"
2910 .PP
2911 Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes.
2912 .PP
2913 .Vb 10
2914 \& static void
2915 \& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
2916 \& {
2917 \& /* /etc/passwd changed in some way */
2918 \& if (w\->attr.st_nlink)
2919 \& {
2920 \& printf ("passwd current size %ld\en", (long)w\->attr.st_size);
2921 \& printf ("passwd current atime %ld\en", (long)w\->attr.st_mtime);
2922 \& printf ("passwd current mtime %ld\en", (long)w\->attr.st_mtime);
2923 \& }
2924 \& else
2925 \& /* you shalt not abuse printf for puts */
2926 \& puts ("wow, /etc/passwd is not there, expect problems. "
2927 \& "if this is windows, they already arrived\en");
2928 \& }
2929 \&
2930 \& ...
2931 \& ev_stat passwd;
2932 \&
2933 \& ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
2934 \& ev_stat_start (loop, &passwd);
2935 .Ve
2936 .PP
2937 Example: Like above, but additionally use a one-second delay so we do not
2938 miss updates (however, frequent updates will delay processing, too, so
2939 one might do the work both on \f(CW\*(C`ev_stat\*(C'\fR callback invocation \fIand\fR on
2940 \&\f(CW\*(C`ev_timer\*(C'\fR callback invocation).
2941 .PP
2942 .Vb 2
2943 \& static ev_stat passwd;
2944 \& static ev_timer timer;
2945 \&
2946 \& static void
2947 \& timer_cb (EV_P_ ev_timer *w, int revents)
2948 \& {
2949 \& ev_timer_stop (EV_A_ w);
2950 \&
2951 \& /* now it\*(Aqs one second after the most recent passwd change */
2952 \& }
2953 \&
2954 \& static void
2955 \& stat_cb (EV_P_ ev_stat *w, int revents)
2956 \& {
2957 \& /* reset the one\-second timer */
2958 \& ev_timer_again (EV_A_ &timer);
2959 \& }
2960 \&
2961 \& ...
2962 \& ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
2963 \& ev_stat_start (loop, &passwd);
2964 \& ev_timer_init (&timer, timer_cb, 0., 1.02);
2965 .Ve
2966 .ie n .SS """ev_idle"" \- when you've got nothing better to do..."
2967 .el .SS "\f(CWev_idle\fP \- when you've got nothing better to do..."
2968 .IX Subsection "ev_idle - when you've got nothing better to do..."
2969 Idle watchers trigger events when no other events of the same or higher
2970 priority are pending (prepare, check and other idle watchers do not count
2971 as receiving \*(L"events\*(R").
2972 .PP
2973 That is, as long as your process is busy handling sockets or timeouts
2974 (or even signals, imagine) of the same or higher priority it will not be
2975 triggered. But when your process is idle (or only lower-priority watchers
2976 are pending), the idle watchers are being called once per event loop
2977 iteration \- until stopped, that is, or your process receives more events
2978 and becomes busy again with higher priority stuff.
2979 .PP
2980 The most noteworthy effect is that as long as any idle watchers are
2981 active, the process will not block when waiting for new events.
2982 .PP
2983 Apart from keeping your process non-blocking (which is a useful
2984 effect on its own sometimes), idle watchers are a good place to do
2985 \&\*(L"pseudo-background processing\*(R", or delay processing stuff to after the
2986 event loop has handled all outstanding events.
2987 .PP
2988 \fIAbusing an \f(CI\*(C`ev_idle\*(C'\fI watcher for its side-effect\fR
2989 .IX Subsection "Abusing an ev_idle watcher for its side-effect"
2990 .PP
2991 As long as there is at least one active idle watcher, libev will never
2992 sleep unnecessarily. Or in other words, it will loop as fast as possible.
2993 For this to work, the idle watcher doesn't need to be invoked at all \- the
2994 lowest priority will do.
2995 .PP
2996 This mode of operation can be useful together with an \f(CW\*(C`ev_check\*(C'\fR watcher,
2997 to do something on each event loop iteration \- for example to balance load
2998 between different connections.
2999 .PP
3000 See \*(L"Abusing an ev_check watcher for its side-effect\*(R" for a longer
3001 example.
3002 .PP
3003 \fIWatcher-Specific Functions and Data Members\fR
3004 .IX Subsection "Watcher-Specific Functions and Data Members"
3005 .IP "ev_idle_init (ev_idle *, callback)" 4
3006 .IX Item "ev_idle_init (ev_idle *, callback)"
3007 Initialises and configures the idle watcher \- it has no parameters of any
3008 kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
3009 believe me.
3010 .PP
3011 \fIExamples\fR
3012 .IX Subsection "Examples"
3013 .PP
3014 Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the
3015 callback, free it. Also, use no error checking, as usual.
3016 .PP
3017 .Vb 5
3018 \& static void
3019 \& idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
3020 \& {
3021 \& // stop the watcher
3022 \& ev_idle_stop (loop, w);
3023 \&
3024 \& // now we can free it
3025 \& free (w);
3026 \&
3027 \& // now do something you wanted to do when the program has
3028 \& // no longer anything immediate to do.
3029 \& }
3030 \&
3031 \& ev_idle *idle_watcher = malloc (sizeof (ev_idle));
3032 \& ev_idle_init (idle_watcher, idle_cb);
3033 \& ev_idle_start (loop, idle_watcher);
3034 .Ve
3035 .ie n .SS """ev_prepare"" and ""ev_check"" \- customise your event loop!"
3036 .el .SS "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!"
3037 .IX Subsection "ev_prepare and ev_check - customise your event loop!"
3038 Prepare and check watchers are often (but not always) used in pairs:
3039 prepare watchers get invoked before the process blocks and check watchers
3040 afterwards.
3041 .PP
3042 You \fImust not\fR call \f(CW\*(C`ev_run\*(C'\fR or similar functions that enter
3043 the current event loop from either \f(CW\*(C`ev_prepare\*(C'\fR or \f(CW\*(C`ev_check\*(C'\fR
3044 watchers. Other loops than the current one are fine, however. The
3045 rationale behind this is that you do not need to check for recursion in
3046 those watchers, i.e. the sequence will always be \f(CW\*(C`ev_prepare\*(C'\fR, blocking,
3047 \&\f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each kind they will always be
3048 called in pairs bracketing the blocking call.
3049 .PP
3050 Their main purpose is to integrate other event mechanisms into libev and
3051 their use is somewhat advanced. They could be used, for example, to track
3052 variable changes, implement your own watchers, integrate net-snmp or a
3053 coroutine library and lots more. They are also occasionally useful if
3054 you cache some data and want to flush it before blocking (for example,
3055 in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR
3056 watcher).
3057 .PP
3058 This is done by examining in each prepare call which file descriptors
3059 need to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers
3060 for them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many
3061 libraries provide exactly this functionality). Then, in the check watcher,
3062 you check for any events that occurred (by checking the pending status
3063 of all watchers and stopping them) and call back into the library. The
3064 I/O and timer callbacks will never actually be called (but must be valid
3065 nevertheless, because you never know, you know?).
3066 .PP
3067 As another example, the Perl Coro module uses these hooks to integrate
3068 coroutines into libev programs, by yielding to other active coroutines
3069 during each prepare and only letting the process block if no coroutines
3070 are ready to run (it's actually more complicated: it only runs coroutines
3071 with priority higher than or equal to the event loop and one coroutine
3072 of lower priority, but only once, using idle watchers to keep the event
3073 loop from blocking if lower-priority coroutines are active, thus mapping
3074 low-priority coroutines to idle/background tasks).
3075 .PP
3076 When used for this purpose, it is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers
3077 highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR) priority, to ensure that they are being run before
3078 any other watchers after the poll (this doesn't matter for \f(CW\*(C`ev_prepare\*(C'\fR
3079 watchers).
3080 .PP
3081 Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers, too) should not
3082 activate (\*(L"feed\*(R") events into libev. While libev fully supports this, they
3083 might get executed before other \f(CW\*(C`ev_check\*(C'\fR watchers did their job. As
3084 \&\f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other (non-libev) event
3085 loops those other event loops might be in an unusable state until their
3086 \&\f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to coexist peacefully with
3087 others).
3088 .PP
3089 \fIAbusing an \f(CI\*(C`ev_check\*(C'\fI watcher for its side-effect\fR
3090 .IX Subsection "Abusing an ev_check watcher for its side-effect"
3091 .PP
3092 \&\f(CW\*(C`ev_check\*(C'\fR (and less often also \f(CW\*(C`ev_prepare\*(C'\fR) watchers can also be
3093 useful because they are called once per event loop iteration. For
3094 example, if you want to handle a large number of connections fairly, you
3095 normally only do a bit of work for each active connection, and if there
3096 is more work to do, you wait for the next event loop iteration, so other
3097 connections have a chance of making progress.
3098 .PP
3099 Using an \f(CW\*(C`ev_check\*(C'\fR watcher is almost enough: it will be called on the
3100 next event loop iteration. However, that isn't as soon as possible \-
3101 without external events, your \f(CW\*(C`ev_check\*(C'\fR watcher will not be invoked.
3102 .PP
3103 This is where \f(CW\*(C`ev_idle\*(C'\fR watchers come in handy \- all you need is a
3104 single global idle watcher that is active as long as you have one active
3105 \&\f(CW\*(C`ev_check\*(C'\fR watcher. The \f(CW\*(C`ev_idle\*(C'\fR watcher makes sure the event loop
3106 will not sleep, and the \f(CW\*(C`ev_check\*(C'\fR watcher makes sure a callback gets
3107 invoked. Neither watcher alone can do that.
3108 .PP
3109 \fIWatcher-Specific Functions and Data Members\fR
3110 .IX Subsection "Watcher-Specific Functions and Data Members"
3111 .IP "ev_prepare_init (ev_prepare *, callback)" 4
3112 .IX Item "ev_prepare_init (ev_prepare *, callback)"
3113 .PD 0
3114 .IP "ev_check_init (ev_check *, callback)" 4
3115 .IX Item "ev_check_init (ev_check *, callback)"
3116 .PD
3117 Initialises and configures the prepare or check watcher \- they have no
3118 parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
3119 macros, but using them is utterly, utterly, utterly and completely
3120 pointless.
3121 .PP
3122 \fIExamples\fR
3123 .IX Subsection "Examples"
3124 .PP
3125 There are a number of principal ways to embed other event loops or modules
3126 into libev. Here are some ideas on how to include libadns into libev
3127 (there is a Perl module named \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could
3128 use as a working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR embeds a
3129 Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0 into the
3130 Glib event loop).
3131 .PP
3132 Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler,
3133 and in a check watcher, destroy them and call into libadns. What follows
3134 is pseudo-code only of course. This requires you to either use a low
3135 priority for the check watcher or use \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as
3136 the callbacks for the IO/timeout watchers might not have been called yet.
3137 .PP
3138 .Vb 2
3139 \& static ev_io iow [nfd];
3140 \& static ev_timer tw;
3141 \&
3142 \& static void
3143 \& io_cb (struct ev_loop *loop, ev_io *w, int revents)
3144 \& {
3145 \& }
3146 \&
3147 \& // create io watchers for each fd and a timer before blocking
3148 \& static void
3149 \& adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
3150 \& {
3151 \& int timeout = 3600000;
3152 \& struct pollfd fds [nfd];
3153 \& // actual code will need to loop here and realloc etc.
3154 \& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
3155 \&
3156 \& /* the callback is illegal, but won\*(Aqt be called as we stop during check */
3157 \& ev_timer_init (&tw, 0, timeout * 1e\-3, 0.);
3158 \& ev_timer_start (loop, &tw);
3159 \&
3160 \& // create one ev_io per pollfd
3161 \& for (int i = 0; i < nfd; ++i)
3162 \& {
3163 \& ev_io_init (iow + i, io_cb, fds [i].fd,
3164 \& ((fds [i].events & POLLIN ? EV_READ : 0)
3165 \& | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
3166 \&
3167 \& fds [i].revents = 0;
3168 \& ev_io_start (loop, iow + i);
3169 \& }
3170 \& }
3171 \&
3172 \& // stop all watchers after blocking
3173 \& static void
3174 \& adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
3175 \& {
3176 \& ev_timer_stop (loop, &tw);
3177 \&
3178 \& for (int i = 0; i < nfd; ++i)
3179 \& {
3180 \& // set the relevant poll flags
3181 \& // could also call adns_processreadable etc. here
3182 \& struct pollfd *fd = fds + i;
3183 \& int revents = ev_clear_pending (iow + i);
3184 \& if (revents & EV_READ ) fd\->revents |= fd\->events & POLLIN;
3185 \& if (revents & EV_WRITE) fd\->revents |= fd\->events & POLLOUT;
3186 \&
3187 \& // now stop the watcher
3188 \& ev_io_stop (loop, iow + i);
3189 \& }
3190 \&
3191 \& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
3192 \& }
3193 .Ve
3194 .PP
3195 Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR
3196 in the prepare watcher and would dispose of the check watcher.
3197 .PP
3198 Method 3: If the module to be embedded supports explicit event
3199 notification (libadns does), you can also make use of the actual watcher
3200 callbacks, and only destroy/create the watchers in the prepare watcher.
3201 .PP
3202 .Vb 5
3203 \& static void
3204 \& timer_cb (EV_P_ ev_timer *w, int revents)
3205 \& {
3206 \& adns_state ads = (adns_state)w\->data;
3207 \& update_now (EV_A);
3208 \&
3209 \& adns_processtimeouts (ads, &tv_now);
3210 \& }
3211 \&
3212 \& static void
3213 \& io_cb (EV_P_ ev_io *w, int revents)
3214 \& {
3215 \& adns_state ads = (adns_state)w\->data;
3216 \& update_now (EV_A);
3217 \&
3218 \& if (revents & EV_READ ) adns_processreadable (ads, w\->fd, &tv_now);
3219 \& if (revents & EV_WRITE) adns_processwriteable (ads, w\->fd, &tv_now);
3220 \& }
3221 \&
3222 \& // do not ever call adns_afterpoll
3223 .Ve
3224 .PP
3225 Method 4: Do not use a prepare or check watcher because the module you
3226 want to embed is not flexible enough to support it. Instead, you can
3227 override their poll function. The drawback with this solution is that the
3228 main loop is now no longer controllable by \s-1EV\s0. The \f(CW\*(C`Glib::EV\*(C'\fR module uses
3229 this approach, effectively embedding \s-1EV\s0 as a client into the horrible
3230 libglib event loop.
3231 .PP
3232 .Vb 4
3233 \& static gint
3234 \& event_poll_func (GPollFD *fds, guint nfds, gint timeout)
3235 \& {
3236 \& int got_events = 0;
3237 \&
3238 \& for (n = 0; n < nfds; ++n)
3239 \& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
3240 \&
3241 \& if (timeout >= 0)
3242 \& // create/start timer
3243 \&
3244 \& // poll
3245 \& ev_run (EV_A_ 0);
3246 \&
3247 \& // stop timer again
3248 \& if (timeout >= 0)
3249 \& ev_timer_stop (EV_A_ &to);
3250 \&
3251 \& // stop io watchers again \- their callbacks should have set
3252 \& for (n = 0; n < nfds; ++n)
3253 \& ev_io_stop (EV_A_ iow [n]);
3254 \&
3255 \& return got_events;
3256 \& }
3257 .Ve
3258 .ie n .SS """ev_embed"" \- when one backend isn't enough..."
3259 .el .SS "\f(CWev_embed\fP \- when one backend isn't enough..."
3260 .IX Subsection "ev_embed - when one backend isn't enough..."
3261 This is a rather advanced watcher type that lets you embed one event loop
3262 into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded
3263 loop, other types of watchers might be handled in a delayed or incorrect
3264 fashion and must not be used).
3265 .PP
3266 There are primarily two reasons you would want that: work around bugs and
3267 prioritise I/O.
3268 .PP
3269 As an example for a bug workaround, the kqueue backend might only support
3270 sockets on some platform, so it is unusable as generic backend, but you
3271 still want to make use of it because you have many sockets and it scales
3272 so nicely. In this case, you would create a kqueue-based loop and embed
3273 it into your default loop (which might use e.g. poll). Overall operation
3274 will be a bit slower because first libev has to call \f(CW\*(C`poll\*(C'\fR and then
3275 \&\f(CW\*(C`kevent\*(C'\fR, but at least you can use both mechanisms for what they are
3276 best: \f(CW\*(C`kqueue\*(C'\fR for scalable sockets and \f(CW\*(C`poll\*(C'\fR if you want it to work :)
3277 .PP
3278 As for prioritising I/O: under rare circumstances you have the case where
3279 some fds have to be watched and handled very quickly (with low latency),
3280 and even priorities and idle watchers might have too much overhead. In
3281 this case you would put all the high priority stuff in one loop and all
3282 the rest in a second one, and embed the second one in the first.
3283 .PP
3284 As long as the watcher is active, the callback will be invoked every
3285 time there might be events pending in the embedded loop. The callback
3286 must then call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single
3287 sweep and invoke their callbacks (the callback doesn't need to invoke the
3288 \&\f(CW\*(C`ev_embed_sweep\*(C'\fR function directly, it could also start an idle watcher
3289 to give the embedded loop strictly lower priority for example).
3290 .PP
3291 You can also set the callback to \f(CW0\fR, in which case the embed watcher
3292 will automatically execute the embedded loop sweep whenever necessary.
3293 .PP
3294 Fork detection will be handled transparently while the \f(CW\*(C`ev_embed\*(C'\fR watcher
3295 is active, i.e., the embedded loop will automatically be forked when the
3296 embedding loop forks. In other cases, the user is responsible for calling
3297 \&\f(CW\*(C`ev_loop_fork\*(C'\fR on the embedded loop.
3298 .PP
3299 Unfortunately, not all backends are embeddable: only the ones returned by
3300 \&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any
3301 portable one.
3302 .PP
3303 So when you want to use this feature you will always have to be prepared
3304 that you cannot get an embeddable loop. The recommended way to get around
3305 this is to have a separate variables for your embeddable loop, try to
3306 create it, and if that fails, use the normal loop for everything.
3307 .PP
3308 \fI\f(CI\*(C`ev_embed\*(C'\fI and fork\fR
3309 .IX Subsection "ev_embed and fork"
3310 .PP
3311 While the \f(CW\*(C`ev_embed\*(C'\fR watcher is running, forks in the embedding loop will
3312 automatically be applied to the embedded loop as well, so no special
3313 fork handling is required in that case. When the watcher is not running,
3314 however, it is still the task of the libev user to call \f(CW\*(C`ev_loop_fork ()\*(C'\fR
3315 as applicable.
3316 .PP
3317 \fIWatcher-Specific Functions and Data Members\fR
3318 .IX Subsection "Watcher-Specific Functions and Data Members"
3319 .IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
3320 .IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)"
3321 .PD 0
3322 .IP "ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)" 4
3323 .IX Item "ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)"
3324 .PD
3325 Configures the watcher to embed the given loop, which must be
3326 embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be
3327 invoked automatically, otherwise it is the responsibility of the callback
3328 to invoke it (it will continue to be called until the sweep has been done,
3329 if you do not want that, you need to temporarily stop the embed watcher).
3330 .IP "ev_embed_sweep (loop, ev_embed *)" 4
3331 .IX Item "ev_embed_sweep (loop, ev_embed *)"
3332 Make a single, non-blocking sweep over the embedded loop. This works
3333 similarly to \f(CW\*(C`ev_run (embedded_loop, EVRUN_NOWAIT)\*(C'\fR, but in the most
3334 appropriate way for embedded loops.
3335 .IP "struct ev_loop *other [read\-only]" 4
3336 .IX Item "struct ev_loop *other [read-only]"
3337 The embedded event loop.
3338 .PP
3339 \fIExamples\fR
3340 .IX Subsection "Examples"
3341 .PP
3342 Example: Try to get an embeddable event loop and embed it into the default
3343 event loop. If that is not possible, use the default loop. The default
3344 loop is stored in \f(CW\*(C`loop_hi\*(C'\fR, while the embeddable loop is stored in
3345 \&\f(CW\*(C`loop_lo\*(C'\fR (which is \f(CW\*(C`loop_hi\*(C'\fR in the case no embeddable loop can be
3346 used).
3347 .PP
3348 .Vb 3
3349 \& struct ev_loop *loop_hi = ev_default_init (0);
3350 \& struct ev_loop *loop_lo = 0;
3351 \& ev_embed embed;
3352 \&
3353 \& // see if there is a chance of getting one that works
3354 \& // (remember that a flags value of 0 means autodetection)
3355 \& loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3356 \& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3357 \& : 0;
3358 \&
3359 \& // if we got one, then embed it, otherwise default to loop_hi
3360 \& if (loop_lo)
3361 \& {
3362 \& ev_embed_init (&embed, 0, loop_lo);
3363 \& ev_embed_start (loop_hi, &embed);
3364 \& }
3365 \& else
3366 \& loop_lo = loop_hi;
3367 .Ve
3368 .PP
3369 Example: Check if kqueue is available but not recommended and create
3370 a kqueue backend for use with sockets (which usually work with any
3371 kqueue implementation). Store the kqueue/socket\-only event loop in
3372 \&\f(CW\*(C`loop_socket\*(C'\fR. (One might optionally use \f(CW\*(C`EVFLAG_NOENV\*(C'\fR, too).
3373 .PP
3374 .Vb 3
3375 \& struct ev_loop *loop = ev_default_init (0);
3376 \& struct ev_loop *loop_socket = 0;
3377 \& ev_embed embed;
3378 \&
3379 \& if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3380 \& if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3381 \& {
3382 \& ev_embed_init (&embed, 0, loop_socket);
3383 \& ev_embed_start (loop, &embed);
3384 \& }
3385 \&
3386 \& if (!loop_socket)
3387 \& loop_socket = loop;
3388 \&
3389 \& // now use loop_socket for all sockets, and loop for everything else
3390 .Ve
3391 .ie n .SS """ev_fork"" \- the audacity to resume the event loop after a fork"
3392 .el .SS "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork"
3393 .IX Subsection "ev_fork - the audacity to resume the event loop after a fork"
3394 Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because
3395 whoever is a good citizen cared to tell libev about it by calling
3396 \&\f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the event loop blocks next
3397 and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called, and only in the child
3398 after the fork. If whoever good citizen calling \f(CW\*(C`ev_default_fork\*(C'\fR cheats
3399 and calls it in the wrong process, the fork handlers will be invoked, too,
3400 of course.
3401 .PP
3402 \fIThe special problem of life after fork \- how is it possible?\fR
3403 .IX Subsection "The special problem of life after fork - how is it possible?"
3404 .PP
3405 Most uses of \f(CW\*(C`fork()\*(C'\fR consist of forking, then some simple calls to set
3406 up/change the process environment, followed by a call to \f(CW\*(C`exec()\*(C'\fR. This
3407 sequence should be handled by libev without any problems.
3408 .PP
3409 This changes when the application actually wants to do event handling
3410 in the child, or both parent in child, in effect \*(L"continuing\*(R" after the
3411 fork.
3412 .PP
3413 The default mode of operation (for libev, with application help to detect
3414 forks) is to duplicate all the state in the child, as would be expected
3415 when \fIeither\fR the parent \fIor\fR the child process continues.
3416 .PP
3417 When both processes want to continue using libev, then this is usually the
3418 wrong result. In that case, usually one process (typically the parent) is
3419 supposed to continue with all watchers in place as before, while the other
3420 process typically wants to start fresh, i.e. without any active watchers.
3421 .PP
3422 The cleanest and most efficient way to achieve that with libev is to
3423 simply create a new event loop, which of course will be \*(L"empty\*(R", and
3424 use that for new watchers. This has the advantage of not touching more
3425 memory than necessary, and thus avoiding the copy-on-write, and the
3426 disadvantage of having to use multiple event loops (which do not support
3427 signal watchers).
3428 .PP
3429 When this is not possible, or you want to use the default loop for
3430 other reasons, then in the process that wants to start \*(L"fresh\*(R", call
3431 \&\f(CW\*(C`ev_loop_destroy (EV_DEFAULT)\*(C'\fR followed by \f(CW\*(C`ev_default_loop (...)\*(C'\fR.
3432 Destroying the default loop will \*(L"orphan\*(R" (not stop) all registered
3433 watchers, so you have to be careful not to execute code that modifies
3434 those watchers. Note also that in that case, you have to re-register any
3435 signal watchers.
3436 .PP
3437 \fIWatcher-Specific Functions and Data Members\fR
3438 .IX Subsection "Watcher-Specific Functions and Data Members"
3439 .IP "ev_fork_init (ev_fork *, callback)" 4
3440 .IX Item "ev_fork_init (ev_fork *, callback)"
3441 Initialises and configures the fork watcher \- it has no parameters of any
3442 kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless,
3443 really.
3444 .ie n .SS """ev_cleanup"" \- even the best things end"
3445 .el .SS "\f(CWev_cleanup\fP \- even the best things end"
3446 .IX Subsection "ev_cleanup - even the best things end"
3447 Cleanup watchers are called just before the event loop is being destroyed
3448 by a call to \f(CW\*(C`ev_loop_destroy\*(C'\fR.
3449 .PP
3450 While there is no guarantee that the event loop gets destroyed, cleanup
3451 watchers provide a convenient method to install cleanup hooks for your
3452 program, worker threads and so on \- you just to make sure to destroy the
3453 loop when you want them to be invoked.
3454 .PP
3455 Cleanup watchers are invoked in the same way as any other watcher. Unlike
3456 all other watchers, they do not keep a reference to the event loop (which
3457 makes a lot of sense if you think about it). Like all other watchers, you
3458 can call libev functions in the callback, except \f(CW\*(C`ev_cleanup_start\*(C'\fR.
3459 .PP
3460 \fIWatcher-Specific Functions and Data Members\fR
3461 .IX Subsection "Watcher-Specific Functions and Data Members"
3462 .IP "ev_cleanup_init (ev_cleanup *, callback)" 4
3463 .IX Item "ev_cleanup_init (ev_cleanup *, callback)"
3464 Initialises and configures the cleanup watcher \- it has no parameters of
3465 any kind. There is a \f(CW\*(C`ev_cleanup_set\*(C'\fR macro, but using it is utterly
3466 pointless, I assure you.
3467 .PP
3468 Example: Register an atexit handler to destroy the default loop, so any
3469 cleanup functions are called.
3470 .PP
3471 .Vb 5
3472 \& static void
3473 \& program_exits (void)
3474 \& {
3475 \& ev_loop_destroy (EV_DEFAULT_UC);
3476 \& }
3477 \&
3478 \& ...
3479 \& atexit (program_exits);
3480 .Ve
3481 .ie n .SS """ev_async"" \- how to wake up an event loop"
3482 .el .SS "\f(CWev_async\fP \- how to wake up an event loop"
3483 .IX Subsection "ev_async - how to wake up an event loop"
3484 In general, you cannot use an \f(CW\*(C`ev_loop\*(C'\fR from multiple threads or other
3485 asynchronous sources such as signal handlers (as opposed to multiple event
3486 loops \- those are of course safe to use in different threads).
3487 .PP
3488 Sometimes, however, you need to wake up an event loop you do not control,
3489 for example because it belongs to another thread. This is what \f(CW\*(C`ev_async\*(C'\fR
3490 watchers do: as long as the \f(CW\*(C`ev_async\*(C'\fR watcher is active, you can signal
3491 it by calling \f(CW\*(C`ev_async_send\*(C'\fR, which is thread\- and signal safe.
3492 .PP
3493 This functionality is very similar to \f(CW\*(C`ev_signal\*(C'\fR watchers, as signals,
3494 too, are asynchronous in nature, and signals, too, will be compressed
3495 (i.e. the number of callback invocations may be less than the number of
3496 \&\f(CW\*(C`ev_async_send\*(C'\fR calls). In fact, you could use signal watchers as a kind
3497 of \*(L"global async watchers\*(R" by using a watcher on an otherwise unused
3498 signal, and \f(CW\*(C`ev_feed_signal\*(C'\fR to signal this watcher from another thread,
3499 even without knowing which loop owns the signal.
3500 .PP
3501 \fIQueueing\fR
3502 .IX Subsection "Queueing"
3503 .PP
3504 \&\f(CW\*(C`ev_async\*(C'\fR does not support queueing of data in any way. The reason
3505 is that the author does not know of a simple (or any) algorithm for a
3506 multiple-writer-single-reader queue that works in all cases and doesn't
3507 need elaborate support such as pthreads or unportable memory access
3508 semantics.
3509 .PP
3510 That means that if you want to queue data, you have to provide your own
3511 queue. But at least I can tell you how to implement locking around your
3512 queue:
3513 .IP "queueing from a signal handler context" 4
3514 .IX Item "queueing from a signal handler context"
3515 To implement race-free queueing, you simply add to the queue in the signal
3516 handler but you block the signal handler in the watcher callback. Here is
3517 an example that does that for some fictitious \s-1SIGUSR1\s0 handler:
3518 .Sp
3519 .Vb 1
3520 \& static ev_async mysig;
3521 \&
3522 \& static void
3523 \& sigusr1_handler (void)
3524 \& {
3525 \& sometype data;
3526 \&
3527 \& // no locking etc.
3528 \& queue_put (data);
3529 \& ev_async_send (EV_DEFAULT_ &mysig);
3530 \& }
3531 \&
3532 \& static void
3533 \& mysig_cb (EV_P_ ev_async *w, int revents)
3534 \& {
3535 \& sometype data;
3536 \& sigset_t block, prev;
3537 \&
3538 \& sigemptyset (&block);
3539 \& sigaddset (&block, SIGUSR1);
3540 \& sigprocmask (SIG_BLOCK, &block, &prev);
3541 \&
3542 \& while (queue_get (&data))
3543 \& process (data);
3544 \&
3545 \& if (sigismember (&prev, SIGUSR1)
3546 \& sigprocmask (SIG_UNBLOCK, &block, 0);
3547 \& }
3548 .Ve
3549 .Sp
3550 (Note: pthreads in theory requires you to use \f(CW\*(C`pthread_setmask\*(C'\fR
3551 instead of \f(CW\*(C`sigprocmask\*(C'\fR when you use threads, but libev doesn't do it
3552 either...).
3553 .IP "queueing from a thread context" 4
3554 .IX Item "queueing from a thread context"
3555 The strategy for threads is different, as you cannot (easily) block
3556 threads but you can easily preempt them, so to queue safely you need to
3557 employ a traditional mutex lock, such as in this pthread example:
3558 .Sp
3559 .Vb 2
3560 \& static ev_async mysig;
3561 \& static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
3562 \&
3563 \& static void
3564 \& otherthread (void)
3565 \& {
3566 \& // only need to lock the actual queueing operation
3567 \& pthread_mutex_lock (&mymutex);
3568 \& queue_put (data);
3569 \& pthread_mutex_unlock (&mymutex);
3570 \&
3571 \& ev_async_send (EV_DEFAULT_ &mysig);
3572 \& }
3573 \&
3574 \& static void
3575 \& mysig_cb (EV_P_ ev_async *w, int revents)
3576 \& {
3577 \& pthread_mutex_lock (&mymutex);
3578 \&
3579 \& while (queue_get (&data))
3580 \& process (data);
3581 \&
3582 \& pthread_mutex_unlock (&mymutex);
3583 \& }
3584 .Ve
3585 .PP
3586 \fIWatcher-Specific Functions and Data Members\fR
3587 .IX Subsection "Watcher-Specific Functions and Data Members"
3588 .IP "ev_async_init (ev_async *, callback)" 4
3589 .IX Item "ev_async_init (ev_async *, callback)"
3590 Initialises and configures the async watcher \- it has no parameters of any
3591 kind. There is a \f(CW\*(C`ev_async_set\*(C'\fR macro, but using it is utterly pointless,
3592 trust me.
3593 .IP "ev_async_send (loop, ev_async *)" 4
3594 .IX Item "ev_async_send (loop, ev_async *)"
3595 Sends/signals/activates the given \f(CW\*(C`ev_async\*(C'\fR watcher, that is, feeds
3596 an \f(CW\*(C`EV_ASYNC\*(C'\fR event on the watcher into the event loop, and instantly
3597 returns.
3598 .Sp
3599 Unlike \f(CW\*(C`ev_feed_event\*(C'\fR, this call is safe to do from other threads,
3600 signal or similar contexts (see the discussion of \f(CW\*(C`EV_ATOMIC_T\*(C'\fR in the
3601 embedding section below on what exactly this means).
3602 .Sp
3603 Note that, as with other watchers in libev, multiple events might get
3604 compressed into a single callback invocation (another way to look at
3605 this is that \f(CW\*(C`ev_async\*(C'\fR watchers are level-triggered: they are set on
3606 \&\f(CW\*(C`ev_async_send\*(C'\fR, reset when the event loop detects that).
3607 .Sp
3608 This call incurs the overhead of at most one extra system call per event
3609 loop iteration, if the event loop is blocked, and no syscall at all if
3610 the event loop (or your program) is processing events. That means that
3611 repeated calls are basically free (there is no need to avoid calls for
3612 performance reasons) and that the overhead becomes smaller (typically
3613 zero) under load.
3614 .IP "bool = ev_async_pending (ev_async *)" 4
3615 .IX Item "bool = ev_async_pending (ev_async *)"
3616 Returns a non-zero value when \f(CW\*(C`ev_async_send\*(C'\fR has been called on the
3617 watcher but the event has not yet been processed (or even noted) by the
3618 event loop.
3619 .Sp
3620 \&\f(CW\*(C`ev_async_send\*(C'\fR sets a flag in the watcher and wakes up the loop. When
3621 the loop iterates next and checks for the watcher to have become active,
3622 it will reset the flag again. \f(CW\*(C`ev_async_pending\*(C'\fR can be used to very
3623 quickly check whether invoking the loop might be a good idea.
3624 .Sp
3625 Not that this does \fInot\fR check whether the watcher itself is pending,
3626 only whether it has been requested to make this watcher pending: there
3627 is a time window between the event loop checking and resetting the async
3628 notification, and the callback being invoked.
3629 .SH "OTHER FUNCTIONS"
3630 .IX Header "OTHER FUNCTIONS"
3631 There are some other functions of possible interest. Described. Here. Now.
3632 .IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4
3633 .IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)"
3634 This function combines a simple timer and an I/O watcher, calls your
3635 callback on whichever event happens first and automatically stops both
3636 watchers. This is useful if you want to wait for a single event on an fd
3637 or timeout without having to allocate/configure/start/stop/free one or
3638 more watchers yourself.
3639 .Sp
3640 If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and the
3641 \&\f(CW\*(C`events\*(C'\fR argument is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for
3642 the given \f(CW\*(C`fd\*(C'\fR and \f(CW\*(C`events\*(C'\fR set will be created and started.
3643 .Sp
3644 If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be
3645 started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and
3646 repeat = 0) will be started. \f(CW0\fR is a valid timeout.
3647 .Sp
3648 The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and is
3649 passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of
3650 \&\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
3651 value passed to \f(CW\*(C`ev_once\*(C'\fR. Note that it is possible to receive \fIboth\fR
3652 a timeout and an io event at the same time \- you probably should give io
3653 events precedence.
3654 .Sp
3655 Example: wait up to ten seconds for data to appear on \s-1STDIN_FILENO\s0.
3656 .Sp
3657 .Vb 7
3658 \& static void stdin_ready (int revents, void *arg)
3659 \& {
3660 \& if (revents & EV_READ)
3661 \& /* stdin might have data for us, joy! */;
3662 \& else if (revents & EV_TIMER)
3663 \& /* doh, nothing entered */;
3664 \& }
3665 \&
3666 \& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3667 .Ve
3668 .IP "ev_feed_fd_event (loop, int fd, int revents)" 4
3669 .IX Item "ev_feed_fd_event (loop, int fd, int revents)"
3670 Feed an event on the given fd, as if a file descriptor backend detected
3671 the given events.
3672 .IP "ev_feed_signal_event (loop, int signum)" 4
3673 .IX Item "ev_feed_signal_event (loop, int signum)"
3674 Feed an event as if the given signal occurred. See also \f(CW\*(C`ev_feed_signal\*(C'\fR,
3675 which is async-safe.
3676 .SH "COMMON OR USEFUL IDIOMS (OR BOTH)"
3677 .IX Header "COMMON OR USEFUL IDIOMS (OR BOTH)"
3678 This section explains some common idioms that are not immediately
3679 obvious. Note that examples are sprinkled over the whole manual, and this
3680 section only contains stuff that wouldn't fit anywhere else.
3681 .SS "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0"
3682 .IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"
3683 Each watcher has, by default, a \f(CW\*(C`void *data\*(C'\fR member that you can read
3684 or modify at any time: libev will completely ignore it. This can be used
3685 to associate arbitrary data with your watcher. If you need more data and
3686 don't want to allocate memory separately and store a pointer to it in that
3687 data member, you can also \*(L"subclass\*(R" the watcher type and provide your own
3688 data:
3689 .PP
3690 .Vb 7
3691 \& struct my_io
3692 \& {
3693 \& ev_io io;
3694 \& int otherfd;
3695 \& void *somedata;
3696 \& struct whatever *mostinteresting;
3697 \& };
3698 \&
3699 \& ...
3700 \& struct my_io w;
3701 \& ev_io_init (&w.io, my_cb, fd, EV_READ);
3702 .Ve
3703 .PP
3704 And since your callback will be called with a pointer to the watcher, you
3705 can cast it back to your own type:
3706 .PP
3707 .Vb 5
3708 \& static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
3709 \& {
3710 \& struct my_io *w = (struct my_io *)w_;
3711 \& ...
3712 \& }
3713 .Ve
3714 .PP
3715 More interesting and less C\-conformant ways of casting your callback
3716 function type instead have been omitted.
3717 .SS "\s-1BUILDING\s0 \s-1YOUR\s0 \s-1OWN\s0 \s-1COMPOSITE\s0 \s-1WATCHERS\s0"
3718 .IX Subsection "BUILDING YOUR OWN COMPOSITE WATCHERS"
3719 Another common scenario is to use some data structure with multiple
3720 embedded watchers, in effect creating your own watcher that combines
3721 multiple libev event sources into one \*(L"super-watcher\*(R":
3722 .PP
3723 .Vb 6
3724 \& struct my_biggy
3725 \& {
3726 \& int some_data;
3727 \& ev_timer t1;
3728 \& ev_timer t2;
3729 \& }
3730 .Ve
3731 .PP
3732 In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more
3733 complicated: Either you store the address of your \f(CW\*(C`my_biggy\*(C'\fR struct in
3734 the \f(CW\*(C`data\*(C'\fR member of the watcher (for woozies or \*(C+ coders), or you need
3735 to use some pointer arithmetic using \f(CW\*(C`offsetof\*(C'\fR inside your watchers (for
3736 real programmers):
3737 .PP
3738 .Vb 1
3739 \& #include <stddef.h>
3740 \&
3741 \& static void
3742 \& t1_cb (EV_P_ ev_timer *w, int revents)
3743 \& {
3744 \& struct my_biggy big = (struct my_biggy *)
3745 \& (((char *)w) \- offsetof (struct my_biggy, t1));
3746 \& }
3747 \&
3748 \& static void
3749 \& t2_cb (EV_P_ ev_timer *w, int revents)
3750 \& {
3751 \& struct my_biggy big = (struct my_biggy *)
3752 \& (((char *)w) \- offsetof (struct my_biggy, t2));
3753 \& }
3754 .Ve
3755 .SS "\s-1AVOIDING\s0 \s-1FINISHING\s0 \s-1BEFORE\s0 \s-1RETURNING\s0"
3756 .IX Subsection "AVOIDING FINISHING BEFORE RETURNING"
3757 Often you have structures like this in event-based programs:
3758 .PP
3759 .Vb 4
3760 \& callback ()
3761 \& {
3762 \& free (request);
3763 \& }
3764 \&
3765 \& request = start_new_request (..., callback);
3766 .Ve
3767 .PP
3768 The intent is to start some \*(L"lengthy\*(R" operation. The \f(CW\*(C`request\*(C'\fR could be
3769 used to cancel the operation, or do other things with it.
3770 .PP
3771 It's not uncommon to have code paths in \f(CW\*(C`start_new_request\*(C'\fR that
3772 immediately invoke the callback, for example, to report errors. Or you add
3773 some caching layer that finds that it can skip the lengthy aspects of the
3774 operation and simply invoke the callback with the result.
3775 .PP
3776 The problem here is that this will happen \fIbefore\fR \f(CW\*(C`start_new_request\*(C'\fR
3777 has returned, so \f(CW\*(C`request\*(C'\fR is not set.
3778 .PP
3779 Even if you pass the request by some safer means to the callback, you
3780 might want to do something to the request after starting it, such as
3781 canceling it, which probably isn't working so well when the callback has
3782 already been invoked.
3783 .PP
3784 A common way around all these issues is to make sure that
3785 \&\f(CW\*(C`start_new_request\*(C'\fR \fIalways\fR returns before the callback is invoked. If
3786 \&\f(CW\*(C`start_new_request\*(C'\fR immediately knows the result, it can artificially
3787 delay invoking the callback by using a \f(CW\*(C`prepare\*(C'\fR or \f(CW\*(C`idle\*(C'\fR watcher for
3788 example, or more sneakily, by reusing an existing (stopped) watcher and
3789 pushing it into the pending queue:
3790 .PP
3791 .Vb 2
3792 \& ev_set_cb (watcher, callback);
3793 \& ev_feed_event (EV_A_ watcher, 0);
3794 .Ve
3795 .PP
3796 This way, \f(CW\*(C`start_new_request\*(C'\fR can safely return before the callback is
3797 invoked, while not delaying callback invocation too much.
3798 .SS "\s-1MODEL/NESTED\s0 \s-1EVENT\s0 \s-1LOOP\s0 \s-1INVOCATIONS\s0 \s-1AND\s0 \s-1EXIT\s0 \s-1CONDITIONS\s0"
3799 .IX Subsection "MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS"
3800 Often (especially in \s-1GUI\s0 toolkits) there are places where you have
3801 \&\fImodal\fR interaction, which is most easily implemented by recursively
3802 invoking \f(CW\*(C`ev_run\*(C'\fR.
3803 .PP
3804 This brings the problem of exiting \- a callback might want to finish the
3805 main \f(CW\*(C`ev_run\*(C'\fR call, but not the nested one (e.g. user clicked \*(L"Quit\*(R", but
3806 a modal \*(L"Are you sure?\*(R" dialog is still waiting), or just the nested one
3807 and not the main one (e.g. user clocked \*(L"Ok\*(R" in a modal dialog), or some
3808 other combination: In these cases, a simple \f(CW\*(C`ev_break\*(C'\fR will not work.
3809 .PP
3810 The solution is to maintain \*(L"break this loop\*(R" variable for each \f(CW\*(C`ev_run\*(C'\fR
3811 invocation, and use a loop around \f(CW\*(C`ev_run\*(C'\fR until the condition is
3812 triggered, using \f(CW\*(C`EVRUN_ONCE\*(C'\fR:
3813 .PP
3814 .Vb 2
3815 \& // main loop
3816 \& int exit_main_loop = 0;
3817 \&
3818 \& while (!exit_main_loop)
3819 \& ev_run (EV_DEFAULT_ EVRUN_ONCE);
3820 \&
3821 \& // in a modal watcher
3822 \& int exit_nested_loop = 0;
3823 \&
3824 \& while (!exit_nested_loop)
3825 \& ev_run (EV_A_ EVRUN_ONCE);
3826 .Ve
3827 .PP
3828 To exit from any of these loops, just set the corresponding exit variable:
3829 .PP
3830 .Vb 2
3831 \& // exit modal loop
3832 \& exit_nested_loop = 1;
3833 \&
3834 \& // exit main program, after modal loop is finished
3835 \& exit_main_loop = 1;
3836 \&
3837 \& // exit both
3838 \& exit_main_loop = exit_nested_loop = 1;
3839 .Ve
3840 .SS "\s-1THREAD\s0 \s-1LOCKING\s0 \s-1EXAMPLE\s0"
3841 .IX Subsection "THREAD LOCKING EXAMPLE"
3842 Here is a fictitious example of how to run an event loop in a different
3843 thread from where callbacks are being invoked and watchers are
3844 created/added/removed.
3845 .PP
3846 For a real-world example, see the \f(CW\*(C`EV::Loop::Async\*(C'\fR perl module,
3847 which uses exactly this technique (which is suited for many high-level
3848 languages).
3849 .PP
3850 The example uses a pthread mutex to protect the loop data, a condition
3851 variable to wait for callback invocations, an async watcher to notify the
3852 event loop thread and an unspecified mechanism to wake up the main thread.
3853 .PP
3854 First, you need to associate some data with the event loop:
3855 .PP
3856 .Vb 6
3857 \& typedef struct {
3858 \& mutex_t lock; /* global loop lock */
3859 \& ev_async async_w;
3860 \& thread_t tid;
3861 \& cond_t invoke_cv;
3862 \& } userdata;
3863 \&
3864 \& void prepare_loop (EV_P)
3865 \& {
3866 \& // for simplicity, we use a static userdata struct.
3867 \& static userdata u;
3868 \&
3869 \& ev_async_init (&u\->async_w, async_cb);
3870 \& ev_async_start (EV_A_ &u\->async_w);
3871 \&
3872 \& pthread_mutex_init (&u\->lock, 0);
3873 \& pthread_cond_init (&u\->invoke_cv, 0);
3874 \&
3875 \& // now associate this with the loop
3876 \& ev_set_userdata (EV_A_ u);
3877 \& ev_set_invoke_pending_cb (EV_A_ l_invoke);
3878 \& ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
3879 \&
3880 \& // then create the thread running ev_run
3881 \& pthread_create (&u\->tid, 0, l_run, EV_A);
3882 \& }
3883 .Ve
3884 .PP
3885 The callback for the \f(CW\*(C`ev_async\*(C'\fR watcher does nothing: the watcher is used
3886 solely to wake up the event loop so it takes notice of any new watchers
3887 that might have been added:
3888 .PP
3889 .Vb 5
3890 \& static void
3891 \& async_cb (EV_P_ ev_async *w, int revents)
3892 \& {
3893 \& // just used for the side effects
3894 \& }
3895 .Ve
3896 .PP
3897 The \f(CW\*(C`l_release\*(C'\fR and \f(CW\*(C`l_acquire\*(C'\fR callbacks simply unlock/lock the mutex
3898 protecting the loop data, respectively.
3899 .PP
3900 .Vb 6
3901 \& static void
3902 \& l_release (EV_P)
3903 \& {
3904 \& userdata *u = ev_userdata (EV_A);
3905 \& pthread_mutex_unlock (&u\->lock);
3906 \& }
3907 \&
3908 \& static void
3909 \& l_acquire (EV_P)
3910 \& {
3911 \& userdata *u = ev_userdata (EV_A);
3912 \& pthread_mutex_lock (&u\->lock);
3913 \& }
3914 .Ve
3915 .PP
3916 The event loop thread first acquires the mutex, and then jumps straight
3917 into \f(CW\*(C`ev_run\*(C'\fR:
3918 .PP
3919 .Vb 4
3920 \& void *
3921 \& l_run (void *thr_arg)
3922 \& {
3923 \& struct ev_loop *loop = (struct ev_loop *)thr_arg;
3924 \&
3925 \& l_acquire (EV_A);
3926 \& pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
3927 \& ev_run (EV_A_ 0);
3928 \& l_release (EV_A);
3929 \&
3930 \& return 0;
3931 \& }
3932 .Ve
3933 .PP
3934 Instead of invoking all pending watchers, the \f(CW\*(C`l_invoke\*(C'\fR callback will
3935 signal the main thread via some unspecified mechanism (signals? pipe
3936 writes? \f(CW\*(C`Async::Interrupt\*(C'\fR?) and then waits until all pending watchers
3937 have been called (in a while loop because a) spurious wakeups are possible
3938 and b) skipping inter-thread-communication when there are no pending
3939 watchers is very beneficial):
3940 .PP
3941 .Vb 4
3942 \& static void
3943 \& l_invoke (EV_P)
3944 \& {
3945 \& userdata *u = ev_userdata (EV_A);
3946 \&
3947 \& while (ev_pending_count (EV_A))
3948 \& {
3949 \& wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
3950 \& pthread_cond_wait (&u\->invoke_cv, &u\->lock);
3951 \& }
3952 \& }
3953 .Ve
3954 .PP
3955 Now, whenever the main thread gets told to invoke pending watchers, it
3956 will grab the lock, call \f(CW\*(C`ev_invoke_pending\*(C'\fR and then signal the loop
3957 thread to continue:
3958 .PP
3959 .Vb 4
3960 \& static void
3961 \& real_invoke_pending (EV_P)
3962 \& {
3963 \& userdata *u = ev_userdata (EV_A);
3964 \&
3965 \& pthread_mutex_lock (&u\->lock);
3966 \& ev_invoke_pending (EV_A);
3967 \& pthread_cond_signal (&u\->invoke_cv);
3968 \& pthread_mutex_unlock (&u\->lock);
3969 \& }
3970 .Ve
3971 .PP
3972 Whenever you want to start/stop a watcher or do other modifications to an
3973 event loop, you will now have to lock:
3974 .PP
3975 .Vb 2
3976 \& ev_timer timeout_watcher;
3977 \& userdata *u = ev_userdata (EV_A);
3978 \&
3979 \& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
3980 \&
3981 \& pthread_mutex_lock (&u\->lock);
3982 \& ev_timer_start (EV_A_ &timeout_watcher);
3983 \& ev_async_send (EV_A_ &u\->async_w);
3984 \& pthread_mutex_unlock (&u\->lock);
3985 .Ve
3986 .PP
3987 Note that sending the \f(CW\*(C`ev_async\*(C'\fR watcher is required because otherwise
3988 an event loop currently blocking in the kernel will have no knowledge
3989 about the newly added timer. By waking up the loop it will pick up any new
3990 watchers in the next event loop iteration.
3991 .SS "\s-1THREADS\s0, \s-1COROUTINES\s0, \s-1CONTINUATIONS\s0, \s-1QUEUES\s0... \s-1INSTEAD\s0 \s-1OF\s0 \s-1CALLBACKS\s0"
3992 .IX Subsection "THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS"
3993 While the overhead of a callback that e.g. schedules a thread is small, it
3994 is still an overhead. If you embed libev, and your main usage is with some
3995 kind of threads or coroutines, you might want to customise libev so that
3996 doesn't need callbacks anymore.
3997 .PP
3998 Imagine you have coroutines that you can switch to using a function
3999 \&\f(CW\*(C`switch_to (coro)\*(C'\fR, that libev runs in a coroutine called \f(CW\*(C`libev_coro\*(C'\fR
4000 and that due to some magic, the currently active coroutine is stored in a
4001 global called \f(CW\*(C`current_coro\*(C'\fR. Then you can build your own \*(L"wait for libev
4002 event\*(R" primitive by changing \f(CW\*(C`EV_CB_DECLARE\*(C'\fR and \f(CW\*(C`EV_CB_INVOKE\*(C'\fR (note
4003 the differing \f(CW\*(C`;\*(C'\fR conventions):
4004 .PP
4005 .Vb 2
4006 \& #define EV_CB_DECLARE(type) struct my_coro *cb;
4007 \& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb)
4008 .Ve
4009 .PP
4010 That means instead of having a C callback function, you store the
4011 coroutine to switch to in each watcher, and instead of having libev call
4012 your callback, you instead have it switch to that coroutine.
4013 .PP
4014 A coroutine might now wait for an event with a function called
4015 \&\f(CW\*(C`wait_for_event\*(C'\fR. (the watcher needs to be started, as always, but it doesn't
4016 matter when, or whether the watcher is active or not when this function is
4017 called):
4018 .PP
4019 .Vb 6
4020 \& void
4021 \& wait_for_event (ev_watcher *w)
4022 \& {
4023 \& ev_set_cb (w, current_coro);
4024 \& switch_to (libev_coro);
4025 \& }
4026 .Ve
4027 .PP
4028 That basically suspends the coroutine inside \f(CW\*(C`wait_for_event\*(C'\fR and
4029 continues the libev coroutine, which, when appropriate, switches back to
4030 this or any other coroutine.
4031 .PP
4032 You can do similar tricks if you have, say, threads with an event queue \-
4033 instead of storing a coroutine, you store the queue object and instead of
4034 switching to a coroutine, you push the watcher onto the queue and notify
4035 any waiters.
4036 .PP
4037 To embed libev, see \*(L"\s-1EMBEDDING\s0\*(R", but in short, it's easiest to create two
4038 files, \fImy_ev.h\fR and \fImy_ev.c\fR that include the respective libev files:
4039 .PP
4040 .Vb 4
4041 \& // my_ev.h
4042 \& #define EV_CB_DECLARE(type) struct my_coro *cb;
4043 \& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb);
4044 \& #include "../libev/ev.h"
4045 \&
4046 \& // my_ev.c
4047 \& #define EV_H "my_ev.h"
4048 \& #include "../libev/ev.c"
4049 .Ve
4050 .PP
4051 And then use \fImy_ev.h\fR when you would normally use \fIev.h\fR, and compile
4052 \&\fImy_ev.c\fR into your project. When properly specifying include paths, you
4053 can even use \fIev.h\fR as header file name directly.
4054 .SH "LIBEVENT EMULATION"
4055 .IX Header "LIBEVENT EMULATION"
4056 Libev offers a compatibility emulation layer for libevent. It cannot
4057 emulate the internals of libevent, so here are some usage hints:
4058 .IP "\(bu" 4
4059 Only the libevent\-1.4.1\-beta \s-1API\s0 is being emulated.
4060 .Sp
4061 This was the newest libevent version available when libev was implemented,
4062 and is still mostly unchanged in 2010.
4063 .IP "\(bu" 4
4064 Use it by including <event.h>, as usual.
4065 .IP "\(bu" 4
4066 The following members are fully supported: ev_base, ev_callback,
4067 ev_arg, ev_fd, ev_res, ev_events.
4068 .IP "\(bu" 4
4069 Avoid using ev_flags and the EVLIST_*\-macros, while it is
4070 maintained by libev, it does not work exactly the same way as in libevent (consider
4071 it a private \s-1API\s0).
4072 .IP "\(bu" 4
4073 Priorities are not currently supported. Initialising priorities
4074 will fail and all watchers will have the same priority, even though there
4075 is an ev_pri field.
4076 .IP "\(bu" 4
4077 In libevent, the last base created gets the signals, in libev, the
4078 base that registered the signal gets the signals.
4079 .IP "\(bu" 4
4080 Other members are not supported.
4081 .IP "\(bu" 4
4082 The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need
4083 to use the libev header file and library.
4084 .SH "\*(C+ SUPPORT"
4085 .IX Header " SUPPORT"
4086 .SS "C \s-1API\s0"
4087 .IX Subsection "C API"
4088 The normal C \s-1API\s0 should work fine when used from \*(C+: both ev.h and the
4089 libev sources can be compiled as \*(C+. Therefore, code that uses the C \s-1API\s0
4090 will work fine.
4091 .PP
4092 Proper exception specifications might have to be added to callbacks passed
4093 to libev: exceptions may be thrown only from watcher callbacks, all
4094 other callbacks (allocator, syserr, loop acquire/release and periodic
4095 reschedule callbacks) must not throw exceptions, and might need a \f(CW\*(C`throw
4096 ()\*(C'\fR specification. If you have code that needs to be compiled as both C
4097 and \*(C+ you can use the \f(CW\*(C`EV_THROW\*(C'\fR macro for this:
4098 .PP
4099 .Vb 6
4100 \& static void
4101 \& fatal_error (const char *msg) EV_THROW
4102 \& {
4103 \& perror (msg);
4104 \& abort ();
4105 \& }
4106 \&
4107 \& ...
4108 \& ev_set_syserr_cb (fatal_error);
4109 .Ve
4110 .PP
4111 The only \s-1API\s0 functions that can currently throw exceptions are \f(CW\*(C`ev_run\*(C'\fR,
4112 \&\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
4113 because it runs cleanup watchers).
4114 .PP
4115 Throwing exceptions in watcher callbacks is only supported if libev itself
4116 is compiled with a \*(C+ compiler or your C and \*(C+ environments allow
4117 throwing exceptions through C libraries (most do).
4118 .SS "\*(C+ \s-1API\s0"
4119 .IX Subsection " API"
4120 Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow
4121 you to use some convenience methods to start/stop watchers and also change
4122 the callback model to a model using method callbacks on objects.
4123 .PP
4124 To use it,
4125 .PP
4126 .Vb 1
4127 \& #include <ev++.h>
4128 .Ve
4129 .PP
4130 This automatically includes \fIev.h\fR and puts all of its definitions (many
4131 of them macros) into the global namespace. All \*(C+ specific things are
4132 put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding
4133 options as \fIev.h\fR, most notably \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR.
4134 .PP
4135 Care has been taken to keep the overhead low. The only data member the \*(C+
4136 classes add (compared to plain C\-style watchers) is the event loop pointer
4137 that the watcher is associated with (or no additional members at all if
4138 you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev).
4139 .PP
4140 Currently, functions, static and non-static member functions and classes
4141 with \f(CW\*(C`operator ()\*(C'\fR can be used as callbacks. Other types should be easy
4142 to add as long as they only need one additional pointer for context. If
4143 you need support for other types of functors please contact the author
4144 (preferably after implementing it).
4145 .PP
4146 For all this to work, your \*(C+ compiler either has to use the same calling
4147 conventions as your C compiler (for static member functions), or you have
4148 to embed libev and compile libev itself as \*(C+.
4149 .PP
4150 Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace:
4151 .ie n .IP """ev::READ"", ""ev::WRITE"" etc." 4
4152 .el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4
4153 .IX Item "ev::READ, ev::WRITE etc."
4154 These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc.
4155 macros from \fIev.h\fR.
4156 .ie n .IP """ev::tstamp"", ""ev::now""" 4
4157 .el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4
4158 .IX Item "ev::tstamp, ev::now"
4159 Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix.
4160 .ie n .IP """ev::io"", ""ev::timer"", ""ev::periodic"", ""ev::idle"", ""ev::sig"" etc." 4
4161 .el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4
4162 .IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc."
4163 For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of
4164 the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR
4165 which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro
4166 defined by many implementations.
4167 .Sp
4168 All of those classes have these methods:
4169 .RS 4
4170 .IP "ev::TYPE::TYPE ()" 4
4171 .IX Item "ev::TYPE::TYPE ()"
4172 .PD 0
4173 .IP "ev::TYPE::TYPE (loop)" 4
4174 .IX Item "ev::TYPE::TYPE (loop)"
4175 .IP "ev::TYPE::~TYPE" 4
4176 .IX Item "ev::TYPE::~TYPE"
4177 .PD
4178 The constructor (optionally) takes an event loop to associate the watcher
4179 with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR.
4180 .Sp
4181 The constructor calls \f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the
4182 \&\f(CW\*(C`set\*(C'\fR method before starting it.
4183 .Sp
4184 It will not set a callback, however: You have to call the templated \f(CW\*(C`set\*(C'\fR
4185 method to set a callback before you can start the watcher.
4186 .Sp
4187 (The reason why you have to use a method is a limitation in \*(C+ which does
4188 not allow explicit template arguments for constructors).
4189 .Sp
4190 The destructor automatically stops the watcher if it is active.
4191 .IP "w\->set<class, &class::method> (object *)" 4
4192 .IX Item "w->set<class, &class::method> (object *)"
4193 This method sets the callback method to call. The method has to have a
4194 signature of \f(CW\*(C`void (*)(ev_TYPE &, int)\*(C'\fR, it receives the watcher as
4195 first argument and the \f(CW\*(C`revents\*(C'\fR as second. The object must be given as
4196 parameter and is stored in the \f(CW\*(C`data\*(C'\fR member of the watcher.
4197 .Sp
4198 This method synthesizes efficient thunking code to call your method from
4199 the C callback that libev requires. If your compiler can inline your
4200 callback (i.e. it is visible to it at the place of the \f(CW\*(C`set\*(C'\fR call and
4201 your compiler is good :), then the method will be fully inlined into the
4202 thunking function, making it as fast as a direct C callback.
4203 .Sp
4204 Example: simple class declaration and watcher initialisation
4205 .Sp
4206 .Vb 4
4207 \& struct myclass
4208 \& {
4209 \& void io_cb (ev::io &w, int revents) { }
4210 \& }
4211 \&
4212 \& myclass obj;
4213 \& ev::io iow;
4214 \& iow.set <myclass, &myclass::io_cb> (&obj);
4215 .Ve
4216 .IP "w\->set (object *)" 4
4217 .IX Item "w->set (object *)"
4218 This is a variation of a method callback \- leaving out the method to call
4219 will default the method to \f(CW\*(C`operator ()\*(C'\fR, which makes it possible to use
4220 functor objects without having to manually specify the \f(CW\*(C`operator ()\*(C'\fR all
4221 the time. Incidentally, you can then also leave out the template argument
4222 list.
4223 .Sp
4224 The \f(CW\*(C`operator ()\*(C'\fR method prototype must be \f(CW\*(C`void operator ()(watcher &w,
4225 int revents)\*(C'\fR.
4226 .Sp
4227 See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
4228 .Sp
4229 Example: use a functor object as callback.
4230 .Sp
4231 .Vb 7
4232 \& struct myfunctor
4233 \& {
4234 \& void operator() (ev::io &w, int revents)
4235 \& {
4236 \& ...
4237 \& }
4238 \& }
4239 \&
4240 \& myfunctor f;
4241 \&
4242 \& ev::io w;
4243 \& w.set (&f);
4244 .Ve
4245 .IP "w\->set<function> (void *data = 0)" 4
4246 .IX Item "w->set<function> (void *data = 0)"
4247 Also sets a callback, but uses a static method or plain function as
4248 callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's
4249 \&\f(CW\*(C`data\*(C'\fR member and is free for you to use.
4250 .Sp
4251 The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR.
4252 .Sp
4253 See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
4254 .Sp
4255 Example: Use a plain function as callback.
4256 .Sp
4257 .Vb 2
4258 \& static void io_cb (ev::io &w, int revents) { }
4259 \& iow.set <io_cb> ();
4260 .Ve
4261 .IP "w\->set (loop)" 4
4262 .IX Item "w->set (loop)"
4263 Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only
4264 do this when the watcher is inactive (and not pending either).
4265 .IP "w\->set ([arguments])" 4
4266 .IX Item "w->set ([arguments])"
4267 Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR (except for \f(CW\*(C`ev::embed\*(C'\fR watchers>),
4268 with the same arguments. Either this method or a suitable start method
4269 must be called at least once. Unlike the C counterpart, an active watcher
4270 gets automatically stopped and restarted when reconfiguring it with this
4271 method.
4272 .Sp
4273 For \f(CW\*(C`ev::embed\*(C'\fR watchers this method is called \f(CW\*(C`set_embed\*(C'\fR, to avoid
4274 clashing with the \f(CW\*(C`set (loop)\*(C'\fR method.
4275 .IP "w\->start ()" 4
4276 .IX Item "w->start ()"
4277 Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the
4278 constructor already stores the event loop.
4279 .IP "w\->start ([arguments])" 4
4280 .IX Item "w->start ([arguments])"
4281 Instead of calling \f(CW\*(C`set\*(C'\fR and \f(CW\*(C`start\*(C'\fR methods separately, it is often
4282 convenient to wrap them in one call. Uses the same type of arguments as
4283 the configure \f(CW\*(C`set\*(C'\fR method of the watcher.
4284 .IP "w\->stop ()" 4
4285 .IX Item "w->stop ()"
4286 Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument.
4287 .ie n .IP "w\->again () (""ev::timer"", ""ev::periodic"" only)" 4
4288 .el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4
4289 .IX Item "w->again () (ev::timer, ev::periodic only)"
4290 For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding
4291 \&\f(CW\*(C`ev_TYPE_again\*(C'\fR function.
4292 .ie n .IP "w\->sweep () (""ev::embed"" only)" 4
4293 .el .IP "w\->sweep () (\f(CWev::embed\fR only)" 4
4294 .IX Item "w->sweep () (ev::embed only)"
4295 Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR.
4296 .ie n .IP "w\->update () (""ev::stat"" only)" 4
4297 .el .IP "w\->update () (\f(CWev::stat\fR only)" 4
4298 .IX Item "w->update () (ev::stat only)"
4299 Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR.
4300 .RE
4301 .RS 4
4302 .RE
4303 .PP
4304 Example: Define a class with two I/O and idle watchers, start the I/O
4305 watchers in the constructor.
4306 .PP
4307 .Vb 5
4308 \& class myclass
4309 \& {
4310 \& ev::io io ; void io_cb (ev::io &w, int revents);
4311 \& ev::io io2 ; void io2_cb (ev::io &w, int revents);
4312 \& ev::idle idle; void idle_cb (ev::idle &w, int revents);
4313 \&
4314 \& myclass (int fd)
4315 \& {
4316 \& io .set <myclass, &myclass::io_cb > (this);
4317 \& io2 .set <myclass, &myclass::io2_cb > (this);
4318 \& idle.set <myclass, &myclass::idle_cb> (this);
4319 \&
4320 \& io.set (fd, ev::WRITE); // configure the watcher
4321 \& io.start (); // start it whenever convenient
4322 \&
4323 \& io2.start (fd, ev::READ); // set + start in one call
4324 \& }
4325 \& };
4326 .Ve
4327 .SH "OTHER LANGUAGE BINDINGS"
4328 .IX Header "OTHER LANGUAGE BINDINGS"
4329 Libev does not offer other language bindings itself, but bindings for a
4330 number of languages exist in the form of third-party packages. If you know
4331 any interesting language binding in addition to the ones listed here, drop
4332 me a note.
4333 .IP "Perl" 4
4334 .IX Item "Perl"
4335 The \s-1EV\s0 module implements the full libev \s-1API\s0 and is actually used to test
4336 libev. \s-1EV\s0 is developed together with libev. Apart from the \s-1EV\s0 core module,
4337 there are additional modules that implement libev-compatible interfaces
4338 to \f(CW\*(C`libadns\*(C'\fR (\f(CW\*(C`EV::ADNS\*(C'\fR, but \f(CW\*(C`AnyEvent::DNS\*(C'\fR is preferred nowadays),
4339 \&\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
4340 and \f(CW\*(C`EV::Glib\*(C'\fR).
4341 .Sp
4342 It can be found and installed via \s-1CPAN\s0, its homepage is at
4343 <http://software.schmorp.de/pkg/EV>.
4344 .IP "Python" 4
4345 .IX Item "Python"
4346 Python bindings can be found at <http://code.google.com/p/pyev/>. It
4347 seems to be quite complete and well-documented.
4348 .IP "Ruby" 4
4349 .IX Item "Ruby"
4350 Tony Arcieri has written a ruby extension that offers access to a subset
4351 of the libev \s-1API\s0 and adds file handle abstractions, asynchronous \s-1DNS\s0 and
4352 more on top of it. It can be found via gem servers. Its homepage is at
4353 <http://rev.rubyforge.org/>.
4354 .Sp
4355 Roger Pack reports that using the link order \f(CW\*(C`\-lws2_32 \-lmsvcrt\-ruby\-190\*(C'\fR
4356 makes rev work even on mingw.
4357 .IP "Haskell" 4
4358 .IX Item "Haskell"
4359 A haskell binding to libev is available at
4360 http://hackage.haskell.org/cgi\-bin/hackage\-scripts/package/hlibev <http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
4361 .IP "D" 4
4362 .IX Item "D"
4363 Leandro Lucarella has written a D language binding (\fIev.d\fR) for libev, to
4364 be found at <http://www.llucax.com.ar/proj/ev.d/index.html>.
4365 .IP "Ocaml" 4
4366 .IX Item "Ocaml"
4367 Erkki Seppala has written Ocaml bindings for libev, to be found at
4368 http://modeemi.cs.tut.fi/~flux/software/ocaml\-ev/ <http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
4369 .IP "Lua" 4
4370 .IX Item "Lua"
4371 Brian Maher has written a partial interface to libev for lua (at the
4372 time of this writing, only \f(CW\*(C`ev_io\*(C'\fR and \f(CW\*(C`ev_timer\*(C'\fR), to be found at
4373 http://github.com/brimworks/lua\-ev <http://github.com/brimworks/lua-ev>.
4374 .IP "Javascript" 4
4375 .IX Item "Javascript"
4376 Node.js (<http://nodejs.org>) uses libev as the underlying event library.
4377 .IP "Others" 4
4378 .IX Item "Others"
4379 There are others, and I stopped counting.
4380 .SH "MACRO MAGIC"
4381 .IX Header "MACRO MAGIC"
4382 Libev can be compiled with a variety of options, the most fundamental
4383 of which is \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most)
4384 functions and callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument.
4385 .PP
4386 To make it easier to write programs that cope with either variant, the
4387 following macros are defined:
4388 .ie n .IP """EV_A"", ""EV_A_""" 4
4389 .el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4
4390 .IX Item "EV_A, EV_A_"
4391 This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev
4392 loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument,
4393 \&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example:
4394 .Sp
4395 .Vb 3
4396 \& ev_unref (EV_A);
4397 \& ev_timer_add (EV_A_ watcher);
4398 \& ev_run (EV_A_ 0);
4399 .Ve
4400 .Sp
4401 It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope,
4402 which is often provided by the following macro.
4403 .ie n .IP """EV_P"", ""EV_P_""" 4
4404 .el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4
4405 .IX Item "EV_P, EV_P_"
4406 This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev
4407 loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter,
4408 \&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example:
4409 .Sp
4410 .Vb 2
4411 \& // this is how ev_unref is being declared
4412 \& static void ev_unref (EV_P);
4413 \&
4414 \& // this is how you can declare your typical callback
4415 \& static void cb (EV_P_ ev_timer *w, int revents)
4416 .Ve
4417 .Sp
4418 It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite
4419 suitable for use with \f(CW\*(C`EV_A\*(C'\fR.
4420 .ie n .IP """EV_DEFAULT"", ""EV_DEFAULT_""" 4
4421 .el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4
4422 .IX Item "EV_DEFAULT, EV_DEFAULT_"
4423 Similar to the other two macros, this gives you the value of the default
4424 loop, if multiple loops are supported (\*(L"ev loop default\*(R"). The default loop
4425 will be initialised if it isn't already initialised.
4426 .Sp
4427 For non-multiplicity builds, these macros do nothing, so you always have
4428 to initialise the loop somewhere.
4429 .ie n .IP """EV_DEFAULT_UC"", ""EV_DEFAULT_UC_""" 4
4430 .el .IP "\f(CWEV_DEFAULT_UC\fR, \f(CWEV_DEFAULT_UC_\fR" 4
4431 .IX Item "EV_DEFAULT_UC, EV_DEFAULT_UC_"
4432 Usage identical to \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR, but requires that the
4433 default loop has been initialised (\f(CW\*(C`UC\*(C'\fR == unchecked). Their behaviour
4434 is undefined when the default loop has not been initialised by a previous
4435 execution of \f(CW\*(C`EV_DEFAULT\*(C'\fR, \f(CW\*(C`EV_DEFAULT_\*(C'\fR or \f(CW\*(C`ev_default_init (...)\*(C'\fR.
4436 .Sp
4437 It is often prudent to use \f(CW\*(C`EV_DEFAULT\*(C'\fR when initialising the first
4438 watcher in a function but use \f(CW\*(C`EV_DEFAULT_UC\*(C'\fR afterwards.
4439 .PP
4440 Example: Declare and initialise a check watcher, utilising the above
4441 macros so it will work regardless of whether multiple loops are supported
4442 or not.
4443 .PP
4444 .Vb 5
4445 \& static void
4446 \& check_cb (EV_P_ ev_timer *w, int revents)
4447 \& {
4448 \& ev_check_stop (EV_A_ w);
4449 \& }
4450 \&
4451 \& ev_check check;
4452 \& ev_check_init (&check, check_cb);
4453 \& ev_check_start (EV_DEFAULT_ &check);
4454 \& ev_run (EV_DEFAULT_ 0);
4455 .Ve
4456 .SH "EMBEDDING"
4457 .IX Header "EMBEDDING"
4458 Libev can (and often is) directly embedded into host
4459 applications. Examples of applications that embed it include the Deliantra
4460 Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe)
4461 and rxvt-unicode.
4462 .PP
4463 The goal is to enable you to just copy the necessary files into your
4464 source directory without having to change even a single line in them, so
4465 you can easily upgrade by simply copying (or having a checked-out copy of
4466 libev somewhere in your source tree).
4467 .SS "\s-1FILESETS\s0"
4468 .IX Subsection "FILESETS"
4469 Depending on what features you need you need to include one or more sets of files
4470 in your application.
4471 .PP
4472 \fI\s-1CORE\s0 \s-1EVENT\s0 \s-1LOOP\s0\fR
4473 .IX Subsection "CORE EVENT LOOP"
4474 .PP
4475 To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual
4476 configuration (no autoconf):
4477 .PP
4478 .Vb 2
4479 \& #define EV_STANDALONE 1
4480 \& #include "ev.c"
4481 .Ve
4482 .PP
4483 This will automatically include \fIev.h\fR, too, and should be done in a
4484 single C source file only to provide the function implementations. To use
4485 it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best
4486 done by writing a wrapper around \fIev.h\fR that you can include instead and
4487 where you can put other configuration options):
4488 .PP
4489 .Vb 2
4490 \& #define EV_STANDALONE 1
4491 \& #include "ev.h"
4492 .Ve
4493 .PP
4494 Both header files and implementation files can be compiled with a \*(C+
4495 compiler (at least, that's a stated goal, and breakage will be treated
4496 as a bug).
4497 .PP
4498 You need the following files in your source tree, or in a directory
4499 in your include path (e.g. in libev/ when using \-Ilibev):
4500 .PP
4501 .Vb 4
4502 \& ev.h
4503 \& ev.c
4504 \& ev_vars.h
4505 \& ev_wrap.h
4506 \&
4507 \& ev_win32.c required on win32 platforms only
4508 \&
4509 \& ev_select.c only when select backend is enabled (which is enabled by default)
4510 \& ev_poll.c only when poll backend is enabled (disabled by default)
4511 \& ev_epoll.c only when the epoll backend is enabled (disabled by default)
4512 \& ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
4513 \& ev_port.c only when the solaris port backend is enabled (disabled by default)
4514 .Ve
4515 .PP
4516 \&\fIev.c\fR includes the backend files directly when enabled, so you only need
4517 to compile this single file.
4518 .PP
4519 \fI\s-1LIBEVENT\s0 \s-1COMPATIBILITY\s0 \s-1API\s0\fR
4520 .IX Subsection "LIBEVENT COMPATIBILITY API"
4521 .PP
4522 To include the libevent compatibility \s-1API\s0, also include:
4523 .PP
4524 .Vb 1
4525 \& #include "event.c"
4526 .Ve
4527 .PP
4528 in the file including \fIev.c\fR, and:
4529 .PP
4530 .Vb 1
4531 \& #include "event.h"
4532 .Ve
4533 .PP
4534 in the files that want to use the libevent \s-1API\s0. This also includes \fIev.h\fR.
4535 .PP
4536 You need the following additional files for this:
4537 .PP
4538 .Vb 2
4539 \& event.h
4540 \& event.c
4541 .Ve
4542 .PP
4543 \fI\s-1AUTOCONF\s0 \s-1SUPPORT\s0\fR
4544 .IX Subsection "AUTOCONF SUPPORT"
4545 .PP
4546 Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your configuration in
4547 whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your
4548 \&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then
4549 include \fIconfig.h\fR and configure itself accordingly.
4550 .PP
4551 For this of course you need the m4 file:
4552 .PP
4553 .Vb 1
4554 \& libev.m4
4555 .Ve
4556 .SS "\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0"
4557 .IX Subsection "PREPROCESSOR SYMBOLS/MACROS"
4558 Libev can be configured via a variety of preprocessor symbols you have to
4559 define before including (or compiling) any of its files. The default in
4560 the absence of autoconf is documented for every option.
4561 .PP
4562 Symbols marked with \*(L"(h)\*(R" do not change the \s-1ABI\s0, and can have different
4563 values when compiling libev vs. including \fIev.h\fR, so it is permissible
4564 to redefine them before including \fIev.h\fR without breaking compatibility
4565 to a compiled library. All other symbols change the \s-1ABI\s0, which means all
4566 users of libev and the libev code itself must be compiled with compatible
4567 settings.
4568 .IP "\s-1EV_COMPAT3\s0 (h)" 4
4569 .IX Item "EV_COMPAT3 (h)"
4570 Backwards compatibility is a major concern for libev. This is why this
4571 release of libev comes with wrappers for the functions and symbols that
4572 have been renamed between libev version 3 and 4.
4573 .Sp
4574 You can disable these wrappers (to test compatibility with future
4575 versions) by defining \f(CW\*(C`EV_COMPAT3\*(C'\fR to \f(CW0\fR when compiling your
4576 sources. This has the additional advantage that you can drop the \f(CW\*(C`struct\*(C'\fR
4577 from \f(CW\*(C`struct ev_loop\*(C'\fR declarations, as libev will provide an \f(CW\*(C`ev_loop\*(C'\fR
4578 typedef in that case.
4579 .Sp
4580 In some future version, the default for \f(CW\*(C`EV_COMPAT3\*(C'\fR will become \f(CW0\fR,
4581 and in some even more future version the compatibility code will be
4582 removed completely.
4583 .IP "\s-1EV_STANDALONE\s0 (h)" 4
4584 .IX Item "EV_STANDALONE (h)"
4585 Must always be \f(CW1\fR if you do not use autoconf configuration, which
4586 keeps libev from including \fIconfig.h\fR, and it also defines dummy
4587 implementations for some libevent functions (such as logging, which is not
4588 supported). It will also not define any of the structs usually found in
4589 \&\fIevent.h\fR that are not directly supported by the libev core alone.
4590 .Sp
4591 In standalone mode, libev will still try to automatically deduce the
4592 configuration, but has to be more conservative.
4593 .IP "\s-1EV_USE_FLOOR\s0" 4
4594 .IX Item "EV_USE_FLOOR"
4595 If defined to be \f(CW1\fR, libev will use the \f(CW\*(C`floor ()\*(C'\fR function for its
4596 periodic reschedule calculations, otherwise libev will fall back on a
4597 portable (slower) implementation. If you enable this, you usually have to
4598 link against libm or something equivalent. Enabling this when the \f(CW\*(C`floor\*(C'\fR
4599 function is not available will fail, so the safe default is to not enable
4600 this.
4601 .IP "\s-1EV_USE_MONOTONIC\s0" 4
4602 .IX Item "EV_USE_MONOTONIC"
4603 If defined to be \f(CW1\fR, libev will try to detect the availability of the
4604 monotonic clock option at both compile time and runtime. Otherwise no
4605 use of the monotonic clock option will be attempted. If you enable this,
4606 you usually have to link against librt or something similar. Enabling it
4607 when the functionality isn't available is safe, though, although you have
4608 to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR
4609 function is hiding in (often \fI\-lrt\fR). See also \f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
4610 .IP "\s-1EV_USE_REALTIME\s0" 4
4611 .IX Item "EV_USE_REALTIME"
4612 If defined to be \f(CW1\fR, libev will try to detect the availability of the
4613 real-time clock option at compile time (and assume its availability
4614 at runtime if successful). Otherwise no use of the real-time clock
4615 option will be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR
4616 by \f(CW\*(C`clock_get (CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect
4617 correctness. See the note about libraries in the description of
4618 \&\f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. Defaults to the opposite value of
4619 \&\f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
4620 .IP "\s-1EV_USE_CLOCK_SYSCALL\s0" 4
4621 .IX Item "EV_USE_CLOCK_SYSCALL"
4622 If defined to be \f(CW1\fR, libev will try to use a direct syscall instead
4623 of calling the system-provided \f(CW\*(C`clock_gettime\*(C'\fR function. This option
4624 exists 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
4625 unconditionally pulls in \f(CW\*(C`libpthread\*(C'\fR, slowing down single-threaded
4626 programs needlessly. Using a direct syscall is slightly slower (in
4627 theory), because no optimised vdso implementation can be used, but avoids
4628 the pthread dependency. Defaults to \f(CW1\fR on GNU/Linux with glibc 2.x or
4629 higher, as it simplifies linking (no need for \f(CW\*(C`\-lrt\*(C'\fR).
4630 .IP "\s-1EV_USE_NANOSLEEP\s0" 4
4631 .IX Item "EV_USE_NANOSLEEP"
4632 If defined to be \f(CW1\fR, libev will assume that \f(CW\*(C`nanosleep ()\*(C'\fR is available
4633 and will use it for delays. Otherwise it will use \f(CW\*(C`select ()\*(C'\fR.
4634 .IP "\s-1EV_USE_EVENTFD\s0" 4
4635 .IX Item "EV_USE_EVENTFD"
4636 If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is
4637 available and will probe for kernel support at runtime. This will improve
4638 \&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption.
4639 If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
4640 2.7 or newer, otherwise disabled.
4641 .IP "\s-1EV_USE_SELECT\s0" 4
4642 .IX Item "EV_USE_SELECT"
4643 If undefined or defined to be \f(CW1\fR, libev will compile in support for the
4644 \&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at auto-detection will be done: if no
4645 other method takes over, select will be it. Otherwise the select backend
4646 will not be compiled in.
4647 .IP "\s-1EV_SELECT_USE_FD_SET\s0" 4
4648 .IX Item "EV_SELECT_USE_FD_SET"
4649 If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR
4650 structure. This is useful if libev doesn't compile due to a missing
4651 \&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it mis-guesses the bitset layout
4652 on exotic systems. This usually limits the range of file descriptors to
4653 some low limit such as 1024 or might have other limitations (winsocket
4654 only allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation,
4655 configures the maximum size of the \f(CW\*(C`fd_set\*(C'\fR.
4656 .IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4
4657 .IX Item "EV_SELECT_IS_WINSOCKET"
4658 When defined to \f(CW1\fR, the select backend will assume that
4659 select/socket/connect etc. don't understand file descriptors but
4660 wants osf handles on win32 (this is the case when the select to
4661 be used is the winsock select). This means that it will call
4662 \&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise,
4663 it is assumed that all these functions actually work on fds, even
4664 on win32. Should not be defined on non\-win32 platforms.
4665 .IP "\s-1EV_FD_TO_WIN32_HANDLE\s0(fd)" 4
4666 .IX Item "EV_FD_TO_WIN32_HANDLE(fd)"
4667 If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR is enabled, then libev needs a way to map
4668 file descriptors to socket handles. When not defining this symbol (the
4669 default), then libev will call \f(CW\*(C`_get_osfhandle\*(C'\fR, which is usually
4670 correct. In some cases, programs use their own file descriptor management,
4671 in which case they can provide this function to map fds to socket handles.
4672 .IP "\s-1EV_WIN32_HANDLE_TO_FD\s0(handle)" 4
4673 .IX Item "EV_WIN32_HANDLE_TO_FD(handle)"
4674 If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR then libev maps handles to file descriptors
4675 using the standard \f(CW\*(C`_open_osfhandle\*(C'\fR function. For programs implementing
4676 their own fd to handle mapping, overwriting this function makes it easier
4677 to do so. This can be done by defining this macro to an appropriate value.
4678 .IP "\s-1EV_WIN32_CLOSE_FD\s0(fd)" 4
4679 .IX Item "EV_WIN32_CLOSE_FD(fd)"
4680 If programs implement their own fd to handle mapping on win32, then this
4681 macro can be used to override the \f(CW\*(C`close\*(C'\fR function, useful to unregister
4682 file descriptors again. Note that the replacement function has to close
4683 the underlying \s-1OS\s0 handle.
4684 .IP "\s-1EV_USE_WSASOCKET\s0" 4
4685 .IX Item "EV_USE_WSASOCKET"
4686 If defined to be \f(CW1\fR, libev will use \f(CW\*(C`WSASocket\*(C'\fR to create its internal
4687 communication socket, which works better in some environments. Otherwise,
4688 the normal \f(CW\*(C`socket\*(C'\fR function will be used, which works better in other
4689 environments.
4690 .IP "\s-1EV_USE_POLL\s0" 4
4691 .IX Item "EV_USE_POLL"
4692 If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2)
4693 backend. Otherwise it will be enabled on non\-win32 platforms. It
4694 takes precedence over select.
4695 .IP "\s-1EV_USE_EPOLL\s0" 4
4696 .IX Item "EV_USE_EPOLL"
4697 If defined to be \f(CW1\fR, libev will compile in support for the Linux
4698 \&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime,
4699 otherwise another method will be used as fallback. This is the preferred
4700 backend for GNU/Linux systems. If undefined, it will be enabled if the
4701 headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4702 .IP "\s-1EV_USE_KQUEUE\s0" 4
4703 .IX Item "EV_USE_KQUEUE"
4704 If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style
4705 \&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime,
4706 otherwise another method will be used as fallback. This is the preferred
4707 backend for \s-1BSD\s0 and BSD-like systems, although on most BSDs kqueue only
4708 supports some types of fds correctly (the only platform we found that
4709 supports ptys for example was NetBSD), so kqueue might be compiled in, but
4710 not be used unless explicitly requested. The best way to use it is to find
4711 out whether kqueue supports your type of fd properly and use an embedded
4712 kqueue loop.
4713 .IP "\s-1EV_USE_PORT\s0" 4
4714 .IX Item "EV_USE_PORT"
4715 If defined to be \f(CW1\fR, libev will compile in support for the Solaris
4716 10 port style backend. Its availability will be detected at runtime,
4717 otherwise another method will be used as fallback. This is the preferred
4718 backend for Solaris 10 systems.
4719 .IP "\s-1EV_USE_DEVPOLL\s0" 4
4720 .IX Item "EV_USE_DEVPOLL"
4721 Reserved for future expansion, works like the \s-1USE\s0 symbols above.
4722 .IP "\s-1EV_USE_INOTIFY\s0" 4
4723 .IX Item "EV_USE_INOTIFY"
4724 If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify
4725 interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will
4726 be detected at runtime. If undefined, it will be enabled if the headers
4727 indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4728 .IP "\s-1EV_NO_SMP\s0" 4
4729 .IX Item "EV_NO_SMP"
4730 If defined to be \f(CW1\fR, libev will assume that memory is always coherent
4731 between threads, that is, threads can be used, but threads never run on
4732 different cpus (or different cpu cores). This reduces dependencies
4733 and makes libev faster.
4734 .IP "\s-1EV_NO_THREADS\s0" 4
4735 .IX Item "EV_NO_THREADS"
4736 If defined to be \f(CW1\fR, libev will assume that it will never be called from
4737 different threads (that includes signal handlers), which is a stronger
4738 assumption than \f(CW\*(C`EV_NO_SMP\*(C'\fR, above. This reduces dependencies and makes
4739 libev faster.
4740 .IP "\s-1EV_ATOMIC_T\s0" 4
4741 .IX Item "EV_ATOMIC_T"
4742 Libev requires an integer type (suitable for storing \f(CW0\fR or \f(CW1\fR) whose
4743 access is atomic with respect to other threads or signal contexts. No
4744 such type is easily found in the C language, so you can provide your own
4745 type that you know is safe for your purposes. It is used both for signal
4746 handler \*(L"locking\*(R" as well as for signal and thread safety in \f(CW\*(C`ev_async\*(C'\fR
4747 watchers.
4748 .Sp
4749 In the absence of this define, libev will use \f(CW\*(C`sig_atomic_t volatile\*(C'\fR
4750 (from \fIsignal.h\fR), which is usually good enough on most platforms.
4751 .IP "\s-1EV_H\s0 (h)" 4
4752 .IX Item "EV_H (h)"
4753 The name of the \fIev.h\fR header file used to include it. The default if
4754 undefined is \f(CW"ev.h"\fR in \fIevent.h\fR, \fIev.c\fR and \fIev++.h\fR. This can be
4755 used to virtually rename the \fIev.h\fR header file in case of conflicts.
4756 .IP "\s-1EV_CONFIG_H\s0 (h)" 4
4757 .IX Item "EV_CONFIG_H (h)"
4758 If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override
4759 \&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to
4760 \&\f(CW\*(C`EV_H\*(C'\fR, above.
4761 .IP "\s-1EV_EVENT_H\s0 (h)" 4
4762 .IX Item "EV_EVENT_H (h)"
4763 Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea
4764 of how the \fIevent.h\fR header can be found, the default is \f(CW"event.h"\fR.
4765 .IP "\s-1EV_PROTOTYPES\s0 (h)" 4
4766 .IX Item "EV_PROTOTYPES (h)"
4767 If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function
4768 prototypes, but still define all the structs and other symbols. This is
4769 occasionally useful if you want to p