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129 .\" ========================================================================
131 .IX Title ""<STANDARD INPUT>" 1"
132 .TH "<STANDARD INPUT>" 1 "2007-11-24" "perl v5.8.8" "User Contributed Perl Documentation"
134 libev \- a high performance full\-featured event loop written in C
136 .IX Header "SYNOPSIS"
141 .IX Header "DESCRIPTION"
142 Libev is an event loop: you register interest in certain events (such as a
143 file descriptor being readable or a timeout occuring), and it will manage
144 these event sources and provide your program with events.
146 To do this, it must take more or less complete control over your process
147 (or thread) by executing the \fIevent loop\fR handler, and will then
148 communicate events via a callback mechanism.
150 You register interest in certain events by registering so-called \fIevent
151 watchers\fR, which are relatively small C structures you initialise with the
152 details of the event, and then hand it over to libev by \fIstarting\fR the
155 .IX Header "FEATURES"
156 Libev supports select, poll, the linux-specific epoll and the bsd-specific
157 kqueue mechanisms for file descriptor events, relative timers, absolute
158 timers with customised rescheduling, signal events, process status change
159 events (related to \s-1SIGCHLD\s0), and event watchers dealing with the event
160 loop mechanism itself (idle, prepare and check watchers). It also is quite
161 fast (see this benchmark comparing
162 it to libevent for example).
164 .IX Header "CONVENTIONS"
165 Libev is very configurable. In this manual the default configuration
166 will be described, which supports multiple event loops. For more info
167 about various configuration options please have a look at the file
168 \&\fI\s-1README\s0.embed\fR in the libev distribution. If libev was configured without
169 support for multiple event loops, then all functions taking an initial
170 argument of name \f(CW\*(C`loop\*(C'\fR (which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR)
171 will not have this argument.
172 .SH "TIME REPRESENTATION"
173 .IX Header "TIME REPRESENTATION"
174 Libev represents time as a single floating point number, representing the
175 (fractional) number of seconds since the (\s-1POSIX\s0) epoch (somewhere near
176 the beginning of 1970, details are complicated, don't ask). This type is
177 called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use too. It usually aliases
178 to the \f(CW\*(C`double\*(C'\fR type in C, and when you need to do any calculations on
179 it, you should treat it as such.
180 .SH "GLOBAL FUNCTIONS"
181 .IX Header "GLOBAL FUNCTIONS"
182 These functions can be called anytime, even before initialising the
184 .IP "ev_tstamp ev_time ()" 4
185 .IX Item "ev_tstamp ev_time ()"
186 Returns the current time as libev would use it. Please note that the
187 \&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp
188 you actually want to know.
189 .IP "int ev_version_major ()" 4
190 .IX Item "int ev_version_major ()"
192 .IP "int ev_version_minor ()" 4
193 .IX Item "int ev_version_minor ()"
195 You can find out the major and minor version numbers of the library
196 you linked against by calling the functions \f(CW\*(C`ev_version_major\*(C'\fR and
197 \&\f(CW\*(C`ev_version_minor\*(C'\fR. If you want, you can compare against the global
198 symbols \f(CW\*(C`EV_VERSION_MAJOR\*(C'\fR and \f(CW\*(C`EV_VERSION_MINOR\*(C'\fR, which specify the
199 version of the library your program was compiled against.
201 Usually, it's a good idea to terminate if the major versions mismatch,
202 as this indicates an incompatible change. Minor versions are usually
203 compatible to older versions, so a larger minor version alone is usually
206 Example: make sure we haven't accidentally been linked against the wrong
210 \& assert (("libev version mismatch",
211 \& ev_version_major () == EV_VERSION_MAJOR
212 \& && ev_version_minor () >= EV_VERSION_MINOR));
214 .IP "unsigned int ev_supported_backends ()" 4
215 .IX Item "unsigned int ev_supported_backends ()"
216 Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR
217 value) compiled into this binary of libev (independent of their
218 availability on the system you are running on). See \f(CW\*(C`ev_default_loop\*(C'\fR for
219 a description of the set values.
221 Example: make sure we have the epoll method, because yeah this is cool and
222 a must have and can we have a torrent of it please!!!11
225 \& assert (("sorry, no epoll, no sex",
226 \& ev_supported_backends () & EVBACKEND_EPOLL));
228 .IP "unsigned int ev_recommended_backends ()" 4
229 .IX Item "unsigned int ev_recommended_backends ()"
230 Return the set of all backends compiled into this binary of libev and also
231 recommended for this platform. This set is often smaller than the one
232 returned by \f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on
233 most BSDs and will not be autodetected unless you explicitly request it
234 (assuming you know what you are doing). This is the set of backends that
235 libev will probe for if you specify no backends explicitly.
236 .IP "unsigned int ev_embeddable_backends ()" 4
237 .IX Item "unsigned int ev_embeddable_backends ()"
238 Returns the set of backends that are embeddable in other event loops. This
239 is the theoretical, all\-platform, value. To find which backends
240 might be supported on the current system, you would need to look at
241 \&\f(CW\*(C`ev_embeddable_backends () & ev_supported_backends ()\*(C'\fR, likewise for
244 See the description of \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
245 .IP "ev_set_allocator (void *(*cb)(void *ptr, long size))" 4
246 .IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size))"
247 Sets the allocation function to use (the prototype is similar to the
248 realloc C function, the semantics are identical). It is used to allocate
249 and free memory (no surprises here). If it returns zero when memory
250 needs to be allocated, the library might abort or take some potentially
251 destructive action. The default is your system realloc function.
253 You could override this function in high-availability programs to, say,
254 free some memory if it cannot allocate memory, to use a special allocator,
255 or even to sleep a while and retry until some memory is available.
257 Example: replace the libev allocator with one that waits a bit and then
258 retries: better than mine).
262 \& persistent_realloc (void *ptr, long size)
266 \& void *newptr = realloc (ptr, size);
282 \& ev_set_allocator (persistent_realloc);
284 .IP "ev_set_syserr_cb (void (*cb)(const char *msg));" 4
285 .IX Item "ev_set_syserr_cb (void (*cb)(const char *msg));"
286 Set the callback function to call on a retryable syscall error (such
287 as failed select, poll, epoll_wait). The message is a printable string
288 indicating the system call or subsystem causing the problem. If this
289 callback is set, then libev will expect it to remedy the sitution, no
290 matter what, when it returns. That is, libev will generally retry the
291 requested operation, or, if the condition doesn't go away, do bad stuff
294 Example: do the same thing as libev does internally:
298 \& fatal_error (const char *msg)
307 \& ev_set_syserr_cb (fatal_error);
309 .SH "FUNCTIONS CONTROLLING THE EVENT LOOP"
310 .IX Header "FUNCTIONS CONTROLLING THE EVENT LOOP"
311 An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR. The library knows two
312 types of such loops, the \fIdefault\fR loop, which supports signals and child
313 events, and dynamically created loops which do not.
315 If you use threads, a common model is to run the default event loop
316 in your main thread (or in a separate thread) and for each thread you
317 create, you also create another event loop. Libev itself does no locking
318 whatsoever, so if you mix calls to the same event loop in different
319 threads, make sure you lock (this is usually a bad idea, though, even if
320 done correctly, because it's hideous and inefficient).
321 .IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
322 .IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
323 This will initialise the default event loop if it hasn't been initialised
324 yet and return it. If the default loop could not be initialised, returns
325 false. If it already was initialised it simply returns it (and ignores the
326 flags. If that is troubling you, check \f(CW\*(C`ev_backend ()\*(C'\fR afterwards).
328 If you don't know what event loop to use, use the one returned from this
331 The flags argument can be used to specify special behaviour or specific
332 backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR).
334 The following flags are supported:
336 .ie n .IP """EVFLAG_AUTO""" 4
337 .el .IP "\f(CWEVFLAG_AUTO\fR" 4
338 .IX Item "EVFLAG_AUTO"
339 The default flags value. Use this if you have no clue (it's the right
341 .ie n .IP """EVFLAG_NOENV""" 4
342 .el .IP "\f(CWEVFLAG_NOENV\fR" 4
343 .IX Item "EVFLAG_NOENV"
344 If this flag bit is ored into the flag value (or the program runs setuid
345 or setgid) then libev will \fInot\fR look at the environment variable
346 \&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will
347 override the flags completely if it is found in the environment. This is
348 useful to try out specific backends to test their performance, or to work
350 .ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4
351 .el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4
352 .IX Item "EVBACKEND_SELECT (value 1, portable select backend)"
353 This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as
354 libev tries to roll its own fd_set with no limits on the number of fds,
355 but if that fails, expect a fairly low limit on the number of fds when
356 using this backend. It doesn't scale too well (O(highest_fd)), but its usually
357 the fastest backend for a low number of fds.
358 .ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4
359 .el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4
360 .IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)"
361 And this is your standard \fIpoll\fR\|(2) backend. It's more complicated than
362 select, but handles sparse fds better and has no artificial limit on the
363 number of fds you can use (except it will slow down considerably with a
364 lot of inactive fds). It scales similarly to select, i.e. O(total_fds).
365 .ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
366 .el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
367 .IX Item "EVBACKEND_EPOLL (value 4, Linux)"
368 For few fds, this backend is a bit little slower than poll and select,
369 but it scales phenomenally better. While poll and select usually scale like
370 O(total_fds) where n is the total number of fds (or the highest fd), epoll scales
371 either O(1) or O(active_fds).
373 While stopping and starting an I/O watcher in the same iteration will
374 result in some caching, there is still a syscall per such incident
375 (because the fd could point to a different file description now), so its
376 best to avoid that. Also, \fIdup()\fRed file descriptors might not work very
377 well if you register events for both fds.
379 Please note that epoll sometimes generates spurious notifications, so you
380 need to use non-blocking I/O or other means to avoid blocking when no data
381 (or space) is available.
382 .ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4
383 .el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
384 .IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
385 Kqueue deserves special mention, as at the time of this writing, it
386 was broken on all BSDs except NetBSD (usually it doesn't work with
387 anything but sockets and pipes, except on Darwin, where of course its
388 completely useless). For this reason its not being \*(L"autodetected\*(R"
389 unless you explicitly specify it explicitly in the flags (i.e. using
390 \&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR).
392 It scales in the same way as the epoll backend, but the interface to the
393 kernel is more efficient (which says nothing about its actual speed, of
394 course). While starting and stopping an I/O watcher does not cause an
395 extra syscall as with epoll, it still adds up to four event changes per
396 incident, so its best to avoid that.
397 .ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
398 .el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
399 .IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
400 This is not implemented yet (and might never be).
401 .ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
402 .el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
403 .IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
404 This uses the Solaris 10 port mechanism. As with everything on Solaris,
405 it's really slow, but it still scales very well (O(active_fds)).
407 Please note that solaris ports can result in a lot of spurious
408 notifications, so you need to use non-blocking I/O or other means to avoid
409 blocking when no data (or space) is available.
410 .ie n .IP """EVBACKEND_ALL""" 4
411 .el .IP "\f(CWEVBACKEND_ALL\fR" 4
412 .IX Item "EVBACKEND_ALL"
413 Try all backends (even potentially broken ones that wouldn't be tried
414 with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as
415 \&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR.
419 If one or more of these are ored into the flags value, then only these
420 backends will be tried (in the reverse order as given here). If none are
421 specified, most compiled-in backend will be tried, usually in reverse
422 order of their flag values :)
424 The most typical usage is like this:
427 \& if (!ev_default_loop (0))
428 \& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
431 Restrict libev to the select and poll backends, and do not allow
432 environment settings to be taken into account:
435 \& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
438 Use whatever libev has to offer, but make sure that kqueue is used if
439 available (warning, breaks stuff, best use only with your own private
440 event loop and only if you know the \s-1OS\s0 supports your types of fds):
443 \& ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
446 .IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
447 .IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
448 Similar to \f(CW\*(C`ev_default_loop\*(C'\fR, but always creates a new event loop that is
449 always distinct from the default loop. Unlike the default loop, it cannot
450 handle signal and child watchers, and attempts to do so will be greeted by
451 undefined behaviour (or a failed assertion if assertions are enabled).
453 Example: try to create a event loop that uses epoll and nothing else.
456 \& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
458 \& fatal ("no epoll found here, maybe it hides under your chair");
460 .IP "ev_default_destroy ()" 4
461 .IX Item "ev_default_destroy ()"
462 Destroys the default loop again (frees all memory and kernel state
463 etc.). This stops all registered event watchers (by not touching them in
464 any way whatsoever, although you cannot rely on this :).
465 .IP "ev_loop_destroy (loop)" 4
466 .IX Item "ev_loop_destroy (loop)"
467 Like \f(CW\*(C`ev_default_destroy\*(C'\fR, but destroys an event loop created by an
468 earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR.
469 .IP "ev_default_fork ()" 4
470 .IX Item "ev_default_fork ()"
471 This function reinitialises the kernel state for backends that have
472 one. Despite the name, you can call it anytime, but it makes most sense
473 after forking, in either the parent or child process (or both, but that
474 again makes little sense).
476 You \fImust\fR call this function in the child process after forking if and
477 only if you want to use the event library in both processes. If you just
478 fork+exec, you don't have to call it.
480 The function itself is quite fast and it's usually not a problem to call
481 it just in case after a fork. To make this easy, the function will fit in
482 quite nicely into a call to \f(CW\*(C`pthread_atfork\*(C'\fR:
485 \& pthread_atfork (0, 0, ev_default_fork);
488 At the moment, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and \f(CW\*(C`EVBACKEND_POLL\*(C'\fR are safe to use
489 without calling this function, so if you force one of those backends you
491 .IP "ev_loop_fork (loop)" 4
492 .IX Item "ev_loop_fork (loop)"
493 Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by
494 \&\f(CW\*(C`ev_loop_new\*(C'\fR. Yes, you have to call this on every allocated event loop
495 after fork, and how you do this is entirely your own problem.
496 .IP "unsigned int ev_backend (loop)" 4
497 .IX Item "unsigned int ev_backend (loop)"
498 Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
500 .IP "ev_tstamp ev_now (loop)" 4
501 .IX Item "ev_tstamp ev_now (loop)"
502 Returns the current \*(L"event loop time\*(R", which is the time the event loop
503 received events and started processing them. This timestamp does not
504 change as long as callbacks are being processed, and this is also the base
505 time used for relative timers. You can treat it as the timestamp of the
506 event occuring (or more correctly, libev finding out about it).
507 .IP "ev_loop (loop, int flags)" 4
508 .IX Item "ev_loop (loop, int flags)"
509 Finally, this is it, the event handler. This function usually is called
510 after you initialised all your watchers and you want to start handling
513 If the flags argument is specified as \f(CW0\fR, it will not return until
514 either no event watchers are active anymore or \f(CW\*(C`ev_unloop\*(C'\fR was called.
516 Please note that an explicit \f(CW\*(C`ev_unloop\*(C'\fR is usually better than
517 relying on all watchers to be stopped when deciding when a program has
518 finished (especially in interactive programs), but having a program that
519 automatically loops as long as it has to and no longer by virtue of
520 relying on its watchers stopping correctly is a thing of beauty.
522 A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle
523 those events and any outstanding ones, but will not block your process in
524 case there are no events and will return after one iteration of the loop.
526 A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if
527 neccessary) and will handle those and any outstanding ones. It will block
528 your process until at least one new event arrives, and will return after
529 one iteration of the loop. This is useful if you are waiting for some
530 external event in conjunction with something not expressible using other
531 libev watchers. However, a pair of \f(CW\*(C`ev_prepare\*(C'\fR/\f(CW\*(C`ev_check\*(C'\fR watchers is
532 usually a better approach for this kind of thing.
534 Here are the gory details of what \f(CW\*(C`ev_loop\*(C'\fR does:
537 \& * If there are no active watchers (reference count is zero), return.
538 \& - Queue prepare watchers and then call all outstanding watchers.
539 \& - If we have been forked, recreate the kernel state.
540 \& - Update the kernel state with all outstanding changes.
541 \& - Update the "event loop time".
542 \& - Calculate for how long to block.
543 \& - Block the process, waiting for any events.
544 \& - Queue all outstanding I/O (fd) events.
545 \& - Update the "event loop time" and do time jump handling.
546 \& - Queue all outstanding timers.
547 \& - Queue all outstanding periodics.
548 \& - If no events are pending now, queue all idle watchers.
549 \& - Queue all check watchers.
550 \& - Call all queued watchers in reverse order (i.e. check watchers first).
551 \& Signals and child watchers are implemented as I/O watchers, and will
552 \& be handled here by queueing them when their watcher gets executed.
553 \& - If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
554 \& were used, return, otherwise continue with step *.
557 Example: queue some jobs and then loop until no events are outsanding
561 \& ... queue jobs here, make sure they register event watchers as long
562 \& ... as they still have work to do (even an idle watcher will do..)
563 \& ev_loop (my_loop, 0);
564 \& ... jobs done. yeah!
566 .IP "ev_unloop (loop, how)" 4
567 .IX Item "ev_unloop (loop, how)"
568 Can be used to make a call to \f(CW\*(C`ev_loop\*(C'\fR return early (but only after it
569 has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either
570 \&\f(CW\*(C`EVUNLOOP_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_loop\*(C'\fR call return, or
571 \&\f(CW\*(C`EVUNLOOP_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_loop\*(C'\fR calls return.
572 .IP "ev_ref (loop)" 4
573 .IX Item "ev_ref (loop)"
575 .IP "ev_unref (loop)" 4
576 .IX Item "ev_unref (loop)"
578 Ref/unref can be used to add or remove a reference count on the event
579 loop: Every watcher keeps one reference, and as long as the reference
580 count is nonzero, \f(CW\*(C`ev_loop\*(C'\fR will not return on its own. If you have
581 a watcher you never unregister that should not keep \f(CW\*(C`ev_loop\*(C'\fR from
582 returning, \fIev_unref()\fR after starting, and \fIev_ref()\fR before stopping it. For
583 example, libev itself uses this for its internal signal pipe: It is not
584 visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from exiting if
585 no event watchers registered by it are active. It is also an excellent
586 way to do this for generic recurring timers or from within third-party
587 libraries. Just remember to \fIunref after start\fR and \fIref before stop\fR.
589 Example: create a signal watcher, but keep it from keeping \f(CW\*(C`ev_loop\*(C'\fR
590 running when nothing else is active.
593 \& struct dv_signal exitsig;
594 \& ev_signal_init (&exitsig, sig_cb, SIGINT);
595 \& ev_signal_start (myloop, &exitsig);
596 \& evf_unref (myloop);
599 Example: for some weird reason, unregister the above signal handler again.
603 \& ev_signal_stop (myloop, &exitsig);
605 .SH "ANATOMY OF A WATCHER"
606 .IX Header "ANATOMY OF A WATCHER"
607 A watcher is a structure that you create and register to record your
608 interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to
609 become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher for that:
612 \& static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
615 \& ev_unloop (loop, EVUNLOOP_ALL);
620 \& struct ev_loop *loop = ev_default_loop (0);
621 \& struct ev_io stdin_watcher;
622 \& ev_init (&stdin_watcher, my_cb);
623 \& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
624 \& ev_io_start (loop, &stdin_watcher);
625 \& ev_loop (loop, 0);
628 As you can see, you are responsible for allocating the memory for your
629 watcher structures (and it is usually a bad idea to do this on the stack,
630 although this can sometimes be quite valid).
632 Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init
633 (watcher *, callback)\*(C'\fR, which expects a callback to be provided. This
634 callback gets invoked each time the event occurs (or, in the case of io
635 watchers, each time the event loop detects that the file descriptor given
636 is readable and/or writable).
638 Each watcher type has its own \f(CW\*(C`ev_<type>_set (watcher *, ...)\*(C'\fR macro
639 with arguments specific to this watcher type. There is also a macro
640 to combine initialisation and setting in one call: \f(CW\*(C`ev_<type>_init
641 (watcher *, callback, ...)\*(C'\fR.
643 To make the watcher actually watch out for events, you have to start it
644 with a watcher-specific start function (\f(CW\*(C`ev_<type>_start (loop, watcher
645 *)\*(C'\fR), and you can stop watching for events at any time by calling the
646 corresponding stop function (\f(CW\*(C`ev_<type>_stop (loop, watcher *)\*(C'\fR.
648 As long as your watcher is active (has been started but not stopped) you
649 must not touch the values stored in it. Most specifically you must never
650 reinitialise it or call its \f(CW\*(C`set\*(C'\fR macro.
652 Each and every callback receives the event loop pointer as first, the
653 registered watcher structure as second, and a bitset of received events as
656 The received events usually include a single bit per event type received
657 (you can receive multiple events at the same time). The possible bit masks
659 .ie n .IP """EV_READ""" 4
660 .el .IP "\f(CWEV_READ\fR" 4
663 .ie n .IP """EV_WRITE""" 4
664 .el .IP "\f(CWEV_WRITE\fR" 4
667 The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or
669 .ie n .IP """EV_TIMEOUT""" 4
670 .el .IP "\f(CWEV_TIMEOUT\fR" 4
671 .IX Item "EV_TIMEOUT"
672 The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out.
673 .ie n .IP """EV_PERIODIC""" 4
674 .el .IP "\f(CWEV_PERIODIC\fR" 4
675 .IX Item "EV_PERIODIC"
676 The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out.
677 .ie n .IP """EV_SIGNAL""" 4
678 .el .IP "\f(CWEV_SIGNAL\fR" 4
680 The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread.
681 .ie n .IP """EV_CHILD""" 4
682 .el .IP "\f(CWEV_CHILD\fR" 4
684 The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change.
685 .ie n .IP """EV_IDLE""" 4
686 .el .IP "\f(CWEV_IDLE\fR" 4
688 The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do.
689 .ie n .IP """EV_PREPARE""" 4
690 .el .IP "\f(CWEV_PREPARE\fR" 4
691 .IX Item "EV_PREPARE"
693 .ie n .IP """EV_CHECK""" 4
694 .el .IP "\f(CWEV_CHECK\fR" 4
697 All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_loop\*(C'\fR starts
698 to gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are invoked just after
699 \&\f(CW\*(C`ev_loop\*(C'\fR has gathered them, but before it invokes any callbacks for any
700 received events. Callbacks of both watcher types can start and stop as
701 many watchers as they want, and all of them will be taken into account
702 (for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep
703 \&\f(CW\*(C`ev_loop\*(C'\fR from blocking).
704 .ie n .IP """EV_ERROR""" 4
705 .el .IP "\f(CWEV_ERROR\fR" 4
707 An unspecified error has occured, the watcher has been stopped. This might
708 happen because the watcher could not be properly started because libev
709 ran out of memory, a file descriptor was found to be closed or any other
710 problem. You best act on it by reporting the problem and somehow coping
711 with the watcher being stopped.
713 Libev will usually signal a few \*(L"dummy\*(R" events together with an error,
714 for example it might indicate that a fd is readable or writable, and if
715 your callbacks is well-written it can just attempt the operation and cope
716 with the error from \fIread()\fR or \fIwrite()\fR. This will not work in multithreaded
717 programs, though, so beware.
718 .Sh "\s-1SUMMARY\s0 \s-1OF\s0 \s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0"
719 .IX Subsection "SUMMARY OF GENERIC WATCHER FUNCTIONS"
720 In the following description, \f(CW\*(C`TYPE\*(C'\fR stands for the watcher type,
721 e.g. \f(CW\*(C`timer\*(C'\fR for \f(CW\*(C`ev_timer\*(C'\fR watchers and \f(CW\*(C`io\*(C'\fR for \f(CW\*(C`ev_io\*(C'\fR watchers.
722 .ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4
723 .el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4
724 .IX Item "ev_init (ev_TYPE *watcher, callback)"
725 This macro initialises the generic portion of a watcher. The contents
726 of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only
727 the generic parts of the watcher are initialised, you \fIneed\fR to call
728 the type-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR macro afterwards to initialise the
729 type-specific parts. For each type there is also a \f(CW\*(C`ev_TYPE_init\*(C'\fR macro
730 which rolls both calls into one.
732 You can reinitialise a watcher at any time as long as it has been stopped
733 (or never started) and there are no pending events outstanding.
735 The callbakc is always of type \f(CW\*(C`void (*)(ev_loop *loop, ev_TYPE *watcher,
736 int revents)\*(C'\fR.
737 .ie n .IP """ev_TYPE_set"" (ev_TYPE *, [args])" 4
738 .el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *, [args])" 4
739 .IX Item "ev_TYPE_set (ev_TYPE *, [args])"
740 This macro initialises the type-specific parts of a watcher. You need to
741 call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can
742 call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this
743 macro on a watcher that is active (it can be pending, however, which is a
744 difference to the \f(CW\*(C`ev_init\*(C'\fR macro).
746 Although some watcher types do not have type-specific arguments
747 (e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro.
748 .ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4
749 .el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4
750 .IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])"
751 This convinience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro
752 calls into a single call. This is the most convinient method to initialise
753 a watcher. The same limitations apply, of course.
754 .ie n .IP """ev_TYPE_start"" (loop *, ev_TYPE *watcher)" 4
755 .el .IP "\f(CWev_TYPE_start\fR (loop *, ev_TYPE *watcher)" 4
756 .IX Item "ev_TYPE_start (loop *, ev_TYPE *watcher)"
757 Starts (activates) the given watcher. Only active watchers will receive
758 events. If the watcher is already active nothing will happen.
759 .ie n .IP """ev_TYPE_stop"" (loop *, ev_TYPE *watcher)" 4
760 .el .IP "\f(CWev_TYPE_stop\fR (loop *, ev_TYPE *watcher)" 4
761 .IX Item "ev_TYPE_stop (loop *, ev_TYPE *watcher)"
762 Stops the given watcher again (if active) and clears the pending
763 status. It is possible that stopped watchers are pending (for example,
764 non-repeating timers are being stopped when they become pending), but
765 \&\f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor pending. If
766 you want to free or reuse the memory used by the watcher it is therefore a
767 good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function.
768 .IP "bool ev_is_active (ev_TYPE *watcher)" 4
769 .IX Item "bool ev_is_active (ev_TYPE *watcher)"
770 Returns a true value iff the watcher is active (i.e. it has been started
771 and not yet been stopped). As long as a watcher is active you must not modify
773 .IP "bool ev_is_pending (ev_TYPE *watcher)" 4
774 .IX Item "bool ev_is_pending (ev_TYPE *watcher)"
775 Returns a true value iff the watcher is pending, (i.e. it has outstanding
776 events but its callback has not yet been invoked). As long as a watcher
777 is pending (but not active) you must not call an init function on it (but
778 \&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe) and you must make sure the watcher is available to
779 libev (e.g. you cnanot \f(CW\*(C`free ()\*(C'\fR it).
780 .IP "callback = ev_cb (ev_TYPE *watcher)" 4
781 .IX Item "callback = ev_cb (ev_TYPE *watcher)"
782 Returns the callback currently set on the watcher.
783 .IP "ev_cb_set (ev_TYPE *watcher, callback)" 4
784 .IX Item "ev_cb_set (ev_TYPE *watcher, callback)"
785 Change the callback. You can change the callback at virtually any time
787 .Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0"
788 .IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"
789 Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change
790 and read at any time, libev will completely ignore it. This can be used
791 to associate arbitrary data with your watcher. If you need more data and
792 don't want to allocate memory and store a pointer to it in that data
793 member, you can also \*(L"subclass\*(R" the watcher type and provide your own
802 \& struct whatever *mostinteresting;
806 And since your callback will be called with a pointer to the watcher, you
807 can cast it back to your own type:
810 \& static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
812 \& struct my_io *w = (struct my_io *)w_;
817 More interesting and less C\-conformant ways of catsing your callback type
818 have been omitted....
820 .IX Header "WATCHER TYPES"
821 This section describes each watcher in detail, but will not repeat
822 information given in the last section.
823 .ie n .Sh """ev_io"" \- is this file descriptor readable or writable"
824 .el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable"
825 .IX Subsection "ev_io - is this file descriptor readable or writable"
826 I/O watchers check whether a file descriptor is readable or writable
827 in each iteration of the event loop (This behaviour is called
828 level-triggering because you keep receiving events as long as the
829 condition persists. Remember you can stop the watcher if you don't want to
830 act on the event and neither want to receive future events).
832 In general you can register as many read and/or write event watchers per
833 fd as you want (as long as you don't confuse yourself). Setting all file
834 descriptors to non-blocking mode is also usually a good idea (but not
835 required if you know what you are doing).
837 You have to be careful with dup'ed file descriptors, though. Some backends
838 (the linux epoll backend is a notable example) cannot handle dup'ed file
839 descriptors correctly if you register interest in two or more fds pointing
840 to the same underlying file/socket etc. description (that is, they share
841 the same underlying \*(L"file open\*(R").
843 If you must do this, then force the use of a known-to-be-good backend
844 (at the time of this writing, this includes only \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and
845 \&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR).
846 .IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
847 .IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
849 .IP "ev_io_set (ev_io *, int fd, int events)" 4
850 .IX Item "ev_io_set (ev_io *, int fd, int events)"
852 Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The fd is the file descriptor to rceeive
853 events for and events is either \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or \f(CW\*(C`EV_READ |
854 EV_WRITE\*(C'\fR to receive the given events.
856 Please note that most of the more scalable backend mechanisms (for example
857 epoll and solaris ports) can result in spurious readyness notifications
858 for file descriptors, so you practically need to use non-blocking I/O (and
859 treat callback invocation as hint only), or retest separately with a safe
860 interface before doing I/O (XLib can do this), or force the use of either
861 \&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR, which don't suffer from this
862 problem. Also note that it is quite easy to have your callback invoked
863 when the readyness condition is no longer valid even when employing
864 typical ways of handling events, so its a good idea to use non-blocking
867 Example: call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well
868 readable, but only once. Since it is likely line\-buffered, you could
869 attempt to read a whole line in the callback:
873 \& stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
875 \& ev_io_stop (loop, w);
876 \& .. read from stdin here (or from w->fd) and haqndle any I/O errors
882 \& struct ev_loop *loop = ev_default_init (0);
883 \& struct ev_io stdin_readable;
884 \& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
885 \& ev_io_start (loop, &stdin_readable);
886 \& ev_loop (loop, 0);
888 .ie n .Sh """ev_timer"" \- relative and optionally recurring timeouts"
889 .el .Sh "\f(CWev_timer\fP \- relative and optionally recurring timeouts"
890 .IX Subsection "ev_timer - relative and optionally recurring timeouts"
891 Timer watchers are simple relative timers that generate an event after a
892 given time, and optionally repeating in regular intervals after that.
894 The timers are based on real time, that is, if you register an event that
895 times out after an hour and you reset your system clock to last years
896 time, it will still time out after (roughly) and hour. \*(L"Roughly\*(R" because
897 detecting time jumps is hard, and some inaccuracies are unavoidable (the
898 monotonic clock option helps a lot here).
900 The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
901 time. This is usually the right thing as this timestamp refers to the time
902 of the event triggering whatever timeout you are modifying/starting. If
903 you suspect event processing to be delayed and you \fIneed\fR to base the timeout
904 on the current time, use something like this to adjust for this:
907 \& ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
910 The callback is guarenteed to be invoked only when its timeout has passed,
911 but if multiple timers become ready during the same loop iteration then
912 order of execution is undefined.
913 .IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
914 .IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
916 .IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
917 .IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
919 Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR is
920 \&\f(CW0.\fR, then it will automatically be stopped. If it is positive, then the
921 timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds
922 later, again, and again, until stopped manually.
924 The timer itself will do a best-effort at avoiding drift, that is, if you
925 configure a timer to trigger every 10 seconds, then it will trigger at
926 exactly 10 second intervals. If, however, your program cannot keep up with
927 the timer (because it takes longer than those 10 seconds to do stuff) the
928 timer will not fire more than once per event loop iteration.
929 .IP "ev_timer_again (loop)" 4
930 .IX Item "ev_timer_again (loop)"
931 This will act as if the timer timed out and restart it again if it is
932 repeating. The exact semantics are:
934 If the timer is started but nonrepeating, stop it.
936 If the timer is repeating, either start it if necessary (with the repeat
937 value), or reset the running timer to the repeat value.
939 This sounds a bit complicated, but here is a useful and typical
940 example: Imagine you have a tcp connection and you want a so-called idle
941 timeout, that is, you want to be called when there have been, say, 60
942 seconds of inactivity on the socket. The easiest way to do this is to
943 configure an \f(CW\*(C`ev_timer\*(C'\fR with after=repeat=60 and calling ev_timer_again each
944 time you successfully read or write some data. If you go into an idle
945 state where you do not expect data to travel on the socket, you can stop
946 the timer, and again will automatically restart it if need be.
948 Example: create a timer that fires after 60 seconds.
952 \& one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
954 \& .. one minute over, w is actually stopped right here
959 \& struct ev_timer mytimer;
960 \& ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
961 \& ev_timer_start (loop, &mytimer);
964 Example: create a timeout timer that times out after 10 seconds of
969 \& timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
971 \& .. ten seconds without any activity
976 \& struct ev_timer mytimer;
977 \& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
978 \& ev_timer_again (&mytimer); /* start timer */
979 \& ev_loop (loop, 0);
983 \& // and in some piece of code that gets executed on any "activity":
984 \& // reset the timeout to start ticking again at 10 seconds
985 \& ev_timer_again (&mytimer);
987 .ie n .Sh """ev_periodic"" \- to cron or not to cron"
988 .el .Sh "\f(CWev_periodic\fP \- to cron or not to cron"
989 .IX Subsection "ev_periodic - to cron or not to cron"
990 Periodic watchers are also timers of a kind, but they are very versatile
991 (and unfortunately a bit complex).
993 Unlike \f(CW\*(C`ev_timer\*(C'\fR's, they are not based on real time (or relative time)
994 but on wallclock time (absolute time). You can tell a periodic watcher
995 to trigger \*(L"at\*(R" some specific point in time. For example, if you tell a
996 periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()
997 + 10.>) and then reset your system clock to the last year, then it will
998 take a year to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would trigger
999 roughly 10 seconds later and of course not if you reset your system time
1002 They can also be used to implement vastly more complex timers, such as
1003 triggering an event on eahc midnight, local time.
1005 As with timers, the callback is guarenteed to be invoked only when the
1006 time (\f(CW\*(C`at\*(C'\fR) has been passed, but if multiple periodic timers become ready
1007 during the same loop iteration then order of execution is undefined.
1008 .IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 4
1009 .IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)"
1011 .IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4
1012 .IX Item "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)"
1014 Lots of arguments, lets sort it out... There are basically three modes of
1015 operation, and we will explain them from simplest to complex:
1017 .IP "* absolute timer (interval = reschedule_cb = 0)" 4
1018 .IX Item "absolute timer (interval = reschedule_cb = 0)"
1019 In this configuration the watcher triggers an event at the wallclock time
1020 \&\f(CW\*(C`at\*(C'\fR and doesn't repeat. It will not adjust when a time jump occurs,
1021 that is, if it is to be run at January 1st 2011 then it will run when the
1022 system time reaches or surpasses this time.
1023 .IP "* non-repeating interval timer (interval > 0, reschedule_cb = 0)" 4
1024 .IX Item "non-repeating interval timer (interval > 0, reschedule_cb = 0)"
1025 In this mode the watcher will always be scheduled to time out at the next
1026 \&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N) and then repeat, regardless
1029 This can be used to create timers that do not drift with respect to system
1033 \& ev_periodic_set (&periodic, 0., 3600., 0);
1036 This doesn't mean there will always be 3600 seconds in between triggers,
1037 but only that the the callback will be called when the system time shows a
1038 full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
1041 Another way to think about it (for the mathematically inclined) is that
1042 \&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
1043 time where \f(CW\*(C`time = at (mod interval)\*(C'\fR, regardless of any time jumps.
1044 .IP "* manual reschedule mode (reschedule_cb = callback)" 4
1045 .IX Item "manual reschedule mode (reschedule_cb = callback)"
1046 In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being
1047 ignored. Instead, each time the periodic watcher gets scheduled, the
1048 reschedule callback will be called with the watcher as first, and the
1049 current time as second argument.
1051 \&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher,
1052 ever, or make any event loop modifications\fR. If you need to stop it,
1053 return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop it afterwards (e.g. by
1054 starting a prepare watcher).
1056 Its prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
1057 ev_tstamp now)\*(C'\fR, e.g.:
1060 \& static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
1062 \& return now + 60.;
1066 It must return the next time to trigger, based on the passed time value
1067 (that is, the lowest time value larger than to the second argument). It
1068 will usually be called just before the callback will be triggered, but
1069 might be called at other times, too.
1071 \&\s-1NOTE:\s0 \fIThis callback must always return a time that is later than the
1072 passed \f(CI\*(C`now\*(C'\fI value\fR. Not even \f(CW\*(C`now\*(C'\fR itself will do, it \fImust\fR be larger.
1074 This can be used to create very complex timers, such as a timer that
1075 triggers on each midnight, local time. To do this, you would calculate the
1076 next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How
1077 you do this is, again, up to you (but it is not trivial, which is the main
1078 reason I omitted it as an example).
1082 .IP "ev_periodic_again (loop, ev_periodic *)" 4
1083 .IX Item "ev_periodic_again (loop, ev_periodic *)"
1084 Simply stops and restarts the periodic watcher again. This is only useful
1085 when you changed some parameters or the reschedule callback would return
1086 a different time than the last time it was called (e.g. in a crond like
1087 program when the crontabs have changed).
1089 Example: call a callback every hour, or, more precisely, whenever the
1090 system clock is divisible by 3600. The callback invocation times have
1091 potentially a lot of jittering, but good long-term stability.
1095 \& clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
1097 \& ... its now a full hour (UTC, or TAI or whatever your clock follows)
1102 \& struct ev_periodic hourly_tick;
1103 \& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1104 \& ev_periodic_start (loop, &hourly_tick);
1107 Example: the same as above, but use a reschedule callback to do it:
1110 \& #include <math.h>
1115 \& my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
1117 \& return fmod (now, 3600.) + 3600.;
1122 \& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1125 Example: call a callback every hour, starting now:
1128 \& struct ev_periodic hourly_tick;
1129 \& ev_periodic_init (&hourly_tick, clock_cb,
1130 \& fmod (ev_now (loop), 3600.), 3600., 0);
1131 \& ev_periodic_start (loop, &hourly_tick);
1133 .ie n .Sh """ev_signal"" \- signal me when a signal gets signalled"
1134 .el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled"
1135 .IX Subsection "ev_signal - signal me when a signal gets signalled"
1136 Signal watchers will trigger an event when the process receives a specific
1137 signal one or more times. Even though signals are very asynchronous, libev
1138 will try it's best to deliver signals synchronously, i.e. as part of the
1139 normal event processing, like any other event.
1141 You can configure as many watchers as you like per signal. Only when the
1142 first watcher gets started will libev actually register a signal watcher
1143 with the kernel (thus it coexists with your own signal handlers as long
1144 as you don't register any with libev). Similarly, when the last signal
1145 watcher for a signal is stopped libev will reset the signal handler to
1146 \&\s-1SIG_DFL\s0 (regardless of what it was set to before).
1147 .IP "ev_signal_init (ev_signal *, callback, int signum)" 4
1148 .IX Item "ev_signal_init (ev_signal *, callback, int signum)"
1150 .IP "ev_signal_set (ev_signal *, int signum)" 4
1151 .IX Item "ev_signal_set (ev_signal *, int signum)"
1153 Configures the watcher to trigger on the given signal number (usually one
1154 of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
1155 .ie n .Sh """ev_child"" \- wait for pid status changes"
1156 .el .Sh "\f(CWev_child\fP \- wait for pid status changes"
1157 .IX Subsection "ev_child - wait for pid status changes"
1158 Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
1159 some child status changes (most typically when a child of yours dies).
1160 .IP "ev_child_init (ev_child *, callback, int pid)" 4
1161 .IX Item "ev_child_init (ev_child *, callback, int pid)"
1163 .IP "ev_child_set (ev_child *, int pid)" 4
1164 .IX Item "ev_child_set (ev_child *, int pid)"
1166 Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
1167 \&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
1168 at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
1169 the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
1170 \&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
1171 process causing the status change.
1173 Example: try to exit cleanly on \s-1SIGINT\s0 and \s-1SIGTERM\s0.
1177 \& sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
1179 \& ev_unloop (loop, EVUNLOOP_ALL);
1184 \& struct ev_signal signal_watcher;
1185 \& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1186 \& ev_signal_start (loop, &sigint_cb);
1188 .ie n .Sh """ev_idle"" \- when you've got nothing better to do"
1189 .el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do"
1190 .IX Subsection "ev_idle - when you've got nothing better to do"
1191 Idle watchers trigger events when there are no other events are pending
1192 (prepare, check and other idle watchers do not count). That is, as long
1193 as your process is busy handling sockets or timeouts (or even signals,
1194 imagine) it will not be triggered. But when your process is idle all idle
1195 watchers are being called again and again, once per event loop iteration \-
1196 until stopped, that is, or your process receives more events and becomes
1199 The most noteworthy effect is that as long as any idle watchers are
1200 active, the process will not block when waiting for new events.
1202 Apart from keeping your process non-blocking (which is a useful
1203 effect on its own sometimes), idle watchers are a good place to do
1204 \&\*(L"pseudo\-background processing\*(R", or delay processing stuff to after the
1205 event loop has handled all outstanding events.
1206 .IP "ev_idle_init (ev_signal *, callback)" 4
1207 .IX Item "ev_idle_init (ev_signal *, callback)"
1208 Initialises and configures the idle watcher \- it has no parameters of any
1209 kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
1212 Example: dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR, start it, and in the
1213 callback, free it. Alos, use no error checking, as usual.
1217 \& idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
1220 \& // now do something you wanted to do when the program has
1221 \& // no longer asnything immediate to do.
1226 \& struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
1227 \& ev_idle_init (idle_watcher, idle_cb);
1228 \& ev_idle_start (loop, idle_cb);
1230 .ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop"
1231 .el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop"
1232 .IX Subsection "ev_prepare and ev_check - customise your event loop"
1233 Prepare and check watchers are usually (but not always) used in tandem:
1234 prepare watchers get invoked before the process blocks and check watchers
1237 Their main purpose is to integrate other event mechanisms into libev and
1238 their use is somewhat advanced. This could be used, for example, to track
1239 variable changes, implement your own watchers, integrate net-snmp or a
1240 coroutine library and lots more.
1242 This is done by examining in each prepare call which file descriptors need
1243 to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers for
1244 them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many libraries
1245 provide just this functionality). Then, in the check watcher you check for
1246 any events that occured (by checking the pending status of all watchers
1247 and stopping them) and call back into the library. The I/O and timer
1248 callbacks will never actually be called (but must be valid nevertheless,
1249 because you never know, you know?).
1251 As another example, the Perl Coro module uses these hooks to integrate
1252 coroutines into libev programs, by yielding to other active coroutines
1253 during each prepare and only letting the process block if no coroutines
1254 are ready to run (it's actually more complicated: it only runs coroutines
1255 with priority higher than or equal to the event loop and one coroutine
1256 of lower priority, but only once, using idle watchers to keep the event
1257 loop from blocking if lower-priority coroutines are active, thus mapping
1258 low-priority coroutines to idle/background tasks).
1259 .IP "ev_prepare_init (ev_prepare *, callback)" 4
1260 .IX Item "ev_prepare_init (ev_prepare *, callback)"
1262 .IP "ev_check_init (ev_check *, callback)" 4
1263 .IX Item "ev_check_init (ev_check *, callback)"
1265 Initialises and configures the prepare or check watcher \- they have no
1266 parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
1267 macros, but using them is utterly, utterly and completely pointless.
1270 .ie n .Sh """ev_embed"" \- when one backend isn't enough"
1271 .el .Sh "\f(CWev_embed\fP \- when one backend isn't enough"
1272 .IX Subsection "ev_embed - when one backend isn't enough"
1273 This is a rather advanced watcher type that lets you embed one event loop
1274 into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded
1275 loop, other types of watchers might be handled in a delayed or incorrect
1276 fashion and must not be used).
1278 There are primarily two reasons you would want that: work around bugs and
1281 As an example for a bug workaround, the kqueue backend might only support
1282 sockets on some platform, so it is unusable as generic backend, but you
1283 still want to make use of it because you have many sockets and it scales
1284 so nicely. In this case, you would create a kqueue-based loop and embed it
1285 into your default loop (which might use e.g. poll). Overall operation will
1286 be a bit slower because first libev has to poll and then call kevent, but
1287 at least you can use both at what they are best.
1289 As for prioritising I/O: rarely you have the case where some fds have
1290 to be watched and handled very quickly (with low latency), and even
1291 priorities and idle watchers might have too much overhead. In this case
1292 you would put all the high priority stuff in one loop and all the rest in
1293 a second one, and embed the second one in the first.
1295 As long as the watcher is active, the callback will be invoked every time
1296 there might be events pending in the embedded loop. The callback must then
1297 call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single sweep and invoke
1298 their callbacks (you could also start an idle watcher to give the embedded
1299 loop strictly lower priority for example). You can also set the callback
1300 to \f(CW0\fR, in which case the embed watcher will automatically execute the
1301 embedded loop sweep.
1303 As long as the watcher is started it will automatically handle events. The
1304 callback will be invoked whenever some events have been handled. You can
1305 set the callback to \f(CW0\fR to avoid having to specify one if you are not
1308 Also, there have not currently been made special provisions for forking:
1309 when you fork, you not only have to call \f(CW\*(C`ev_loop_fork\*(C'\fR on both loops,
1310 but you will also have to stop and restart any \f(CW\*(C`ev_embed\*(C'\fR watchers
1313 Unfortunately, not all backends are embeddable, only the ones returned by
1314 \&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any
1317 So when you want to use this feature you will always have to be prepared
1318 that you cannot get an embeddable loop. The recommended way to get around
1319 this is to have a separate variables for your embeddable loop, try to
1320 create it, and if that fails, use the normal loop for everything:
1323 \& struct ev_loop *loop_hi = ev_default_init (0);
1324 \& struct ev_loop *loop_lo = 0;
1325 \& struct ev_embed embed;
1329 \& // see if there is a chance of getting one that works
1330 \& // (remember that a flags value of 0 means autodetection)
1331 \& loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1332 \& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1337 \& // if we got one, then embed it, otherwise default to loop_hi
1340 \& ev_embed_init (&embed, 0, loop_lo);
1341 \& ev_embed_start (loop_hi, &embed);
1344 \& loop_lo = loop_hi;
1346 .IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
1347 .IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)"
1349 .IP "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
1350 .IX Item "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)"
1352 Configures the watcher to embed the given loop, which must be
1353 embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be
1354 invoked automatically, otherwise it is the responsibility of the callback
1355 to invoke it (it will continue to be called until the sweep has been done,
1356 if you do not want thta, you need to temporarily stop the embed watcher).
1357 .IP "ev_embed_sweep (loop, ev_embed *)" 4
1358 .IX Item "ev_embed_sweep (loop, ev_embed *)"
1359 Make a single, non-blocking sweep over the embedded loop. This works
1360 similarly to \f(CW\*(C`ev_loop (embedded_loop, EVLOOP_NONBLOCK)\*(C'\fR, but in the most
1361 apropriate way for embedded loops.
1362 .SH "OTHER FUNCTIONS"
1363 .IX Header "OTHER FUNCTIONS"
1364 There are some other functions of possible interest. Described. Here. Now.
1365 .IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4
1366 .IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)"
1367 This function combines a simple timer and an I/O watcher, calls your
1368 callback on whichever event happens first and automatically stop both
1369 watchers. This is useful if you want to wait for a single event on an fd
1370 or timeout without having to allocate/configure/start/stop/free one or
1371 more watchers yourself.
1373 If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and events
1374 is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for the given \f(CW\*(C`fd\*(C'\fR and
1375 \&\f(CW\*(C`events\*(C'\fR set will be craeted and started.
1377 If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be
1378 started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and
1379 repeat = 0) will be started. While \f(CW0\fR is a valid timeout, it is of
1382 The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and gets
1383 passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of
1384 \&\f(CW\*(C`EV_ERROR\*(C'\fR, \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or \f(CW\*(C`EV_TIMEOUT\*(C'\fR) and the \f(CW\*(C`arg\*(C'\fR
1385 value passed to \f(CW\*(C`ev_once\*(C'\fR:
1388 \& static void stdin_ready (int revents, void *arg)
1390 \& if (revents & EV_TIMEOUT)
1391 \& /* doh, nothing entered */;
1392 \& else if (revents & EV_READ)
1393 \& /* stdin might have data for us, joy! */;
1398 \& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1400 .IP "ev_feed_event (ev_loop *, watcher *, int revents)" 4
1401 .IX Item "ev_feed_event (ev_loop *, watcher *, int revents)"
1402 Feeds the given event set into the event loop, as if the specified event
1403 had happened for the specified watcher (which must be a pointer to an
1404 initialised but not necessarily started event watcher).
1405 .IP "ev_feed_fd_event (ev_loop *, int fd, int revents)" 4
1406 .IX Item "ev_feed_fd_event (ev_loop *, int fd, int revents)"
1407 Feed an event on the given fd, as if a file descriptor backend detected
1408 the given events it.
1409 .IP "ev_feed_signal_event (ev_loop *loop, int signum)" 4
1410 .IX Item "ev_feed_signal_event (ev_loop *loop, int signum)"
1411 Feed an event as if the given signal occured (\f(CW\*(C`loop\*(C'\fR must be the default
1413 .SH "LIBEVENT EMULATION"
1414 .IX Header "LIBEVENT EMULATION"
1415 Libev offers a compatibility emulation layer for libevent. It cannot
1416 emulate the internals of libevent, so here are some usage hints:
1417 .IP "* Use it by including <event.h>, as usual." 4
1418 .IX Item "Use it by including <event.h>, as usual."
1420 .IP "* The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4
1421 .IX Item "The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events."
1422 .IP "* Avoid using ev_flags and the EVLIST_*\-macros, while it is maintained by libev, it does not work exactly the same way as in libevent (consider it a private \s-1API\s0)." 4
1423 .IX Item "Avoid using ev_flags and the EVLIST_*-macros, while it is maintained by libev, it does not work exactly the same way as in libevent (consider it a private API)."
1424 .IP "* Priorities are not currently supported. Initialising priorities will fail and all watchers will have the same priority, even though there is an ev_pri field." 4
1425 .IX Item "Priorities are not currently supported. Initialising priorities will fail and all watchers will have the same priority, even though there is an ev_pri field."
1426 .IP "* Other members are not supported." 4
1427 .IX Item "Other members are not supported."
1428 .IP "* The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need to use the libev header file and library." 4
1429 .IX Item "The libev emulation is not ABI compatible to libevent, you need to use the libev header file and library."
1432 .IX Header " SUPPORT"
1436 Marc Lehmann <libev@schmorp.de>.
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