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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.). None of the active event watchers will be stopped in the normal
464 sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your
465 responsibility to either stop all watchers cleanly yoursef \fIbefore\fR
466 calling this function, or cope with the fact afterwards (which is usually
467 the easiest thing, youc na just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them
469 .IP "ev_loop_destroy (loop)" 4
470 .IX Item "ev_loop_destroy (loop)"
471 Like \f(CW\*(C`ev_default_destroy\*(C'\fR, but destroys an event loop created by an
472 earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR.
473 .IP "ev_default_fork ()" 4
474 .IX Item "ev_default_fork ()"
475 This function reinitialises the kernel state for backends that have
476 one. Despite the name, you can call it anytime, but it makes most sense
477 after forking, in either the parent or child process (or both, but that
478 again makes little sense).
480 You \fImust\fR call this function in the child process after forking if and
481 only if you want to use the event library in both processes. If you just
482 fork+exec, you don't have to call it.
484 The function itself is quite fast and it's usually not a problem to call
485 it just in case after a fork. To make this easy, the function will fit in
486 quite nicely into a call to \f(CW\*(C`pthread_atfork\*(C'\fR:
489 \& pthread_atfork (0, 0, ev_default_fork);
492 At the moment, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and \f(CW\*(C`EVBACKEND_POLL\*(C'\fR are safe to use
493 without calling this function, so if you force one of those backends you
495 .IP "ev_loop_fork (loop)" 4
496 .IX Item "ev_loop_fork (loop)"
497 Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by
498 \&\f(CW\*(C`ev_loop_new\*(C'\fR. Yes, you have to call this on every allocated event loop
499 after fork, and how you do this is entirely your own problem.
500 .IP "unsigned int ev_backend (loop)" 4
501 .IX Item "unsigned int ev_backend (loop)"
502 Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
504 .IP "ev_tstamp ev_now (loop)" 4
505 .IX Item "ev_tstamp ev_now (loop)"
506 Returns the current \*(L"event loop time\*(R", which is the time the event loop
507 received events and started processing them. This timestamp does not
508 change as long as callbacks are being processed, and this is also the base
509 time used for relative timers. You can treat it as the timestamp of the
510 event occuring (or more correctly, libev finding out about it).
511 .IP "ev_loop (loop, int flags)" 4
512 .IX Item "ev_loop (loop, int flags)"
513 Finally, this is it, the event handler. This function usually is called
514 after you initialised all your watchers and you want to start handling
517 If the flags argument is specified as \f(CW0\fR, it will not return until
518 either no event watchers are active anymore or \f(CW\*(C`ev_unloop\*(C'\fR was called.
520 Please note that an explicit \f(CW\*(C`ev_unloop\*(C'\fR is usually better than
521 relying on all watchers to be stopped when deciding when a program has
522 finished (especially in interactive programs), but having a program that
523 automatically loops as long as it has to and no longer by virtue of
524 relying on its watchers stopping correctly is a thing of beauty.
526 A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle
527 those events and any outstanding ones, but will not block your process in
528 case there are no events and will return after one iteration of the loop.
530 A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if
531 neccessary) and will handle those and any outstanding ones. It will block
532 your process until at least one new event arrives, and will return after
533 one iteration of the loop. This is useful if you are waiting for some
534 external event in conjunction with something not expressible using other
535 libev watchers. However, a pair of \f(CW\*(C`ev_prepare\*(C'\fR/\f(CW\*(C`ev_check\*(C'\fR watchers is
536 usually a better approach for this kind of thing.
538 Here are the gory details of what \f(CW\*(C`ev_loop\*(C'\fR does:
541 \& * If there are no active watchers (reference count is zero), return.
542 \& - Queue prepare watchers and then call all outstanding watchers.
543 \& - If we have been forked, recreate the kernel state.
544 \& - Update the kernel state with all outstanding changes.
545 \& - Update the "event loop time".
546 \& - Calculate for how long to block.
547 \& - Block the process, waiting for any events.
548 \& - Queue all outstanding I/O (fd) events.
549 \& - Update the "event loop time" and do time jump handling.
550 \& - Queue all outstanding timers.
551 \& - Queue all outstanding periodics.
552 \& - If no events are pending now, queue all idle watchers.
553 \& - Queue all check watchers.
554 \& - Call all queued watchers in reverse order (i.e. check watchers first).
555 \& Signals and child watchers are implemented as I/O watchers, and will
556 \& be handled here by queueing them when their watcher gets executed.
557 \& - If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
558 \& were used, return, otherwise continue with step *.
561 Example: queue some jobs and then loop until no events are outsanding
565 \& ... queue jobs here, make sure they register event watchers as long
566 \& ... as they still have work to do (even an idle watcher will do..)
567 \& ev_loop (my_loop, 0);
568 \& ... jobs done. yeah!
570 .IP "ev_unloop (loop, how)" 4
571 .IX Item "ev_unloop (loop, how)"
572 Can be used to make a call to \f(CW\*(C`ev_loop\*(C'\fR return early (but only after it
573 has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either
574 \&\f(CW\*(C`EVUNLOOP_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_loop\*(C'\fR call return, or
575 \&\f(CW\*(C`EVUNLOOP_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_loop\*(C'\fR calls return.
576 .IP "ev_ref (loop)" 4
577 .IX Item "ev_ref (loop)"
579 .IP "ev_unref (loop)" 4
580 .IX Item "ev_unref (loop)"
582 Ref/unref can be used to add or remove a reference count on the event
583 loop: Every watcher keeps one reference, and as long as the reference
584 count is nonzero, \f(CW\*(C`ev_loop\*(C'\fR will not return on its own. If you have
585 a watcher you never unregister that should not keep \f(CW\*(C`ev_loop\*(C'\fR from
586 returning, \fIev_unref()\fR after starting, and \fIev_ref()\fR before stopping it. For
587 example, libev itself uses this for its internal signal pipe: It is not
588 visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from exiting if
589 no event watchers registered by it are active. It is also an excellent
590 way to do this for generic recurring timers or from within third-party
591 libraries. Just remember to \fIunref after start\fR and \fIref before stop\fR.
593 Example: create a signal watcher, but keep it from keeping \f(CW\*(C`ev_loop\*(C'\fR
594 running when nothing else is active.
597 \& struct dv_signal exitsig;
598 \& ev_signal_init (&exitsig, sig_cb, SIGINT);
599 \& ev_signal_start (myloop, &exitsig);
600 \& evf_unref (myloop);
603 Example: for some weird reason, unregister the above signal handler again.
607 \& ev_signal_stop (myloop, &exitsig);
609 .SH "ANATOMY OF A WATCHER"
610 .IX Header "ANATOMY OF A WATCHER"
611 A watcher is a structure that you create and register to record your
612 interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to
613 become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher for that:
616 \& static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
619 \& ev_unloop (loop, EVUNLOOP_ALL);
624 \& struct ev_loop *loop = ev_default_loop (0);
625 \& struct ev_io stdin_watcher;
626 \& ev_init (&stdin_watcher, my_cb);
627 \& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
628 \& ev_io_start (loop, &stdin_watcher);
629 \& ev_loop (loop, 0);
632 As you can see, you are responsible for allocating the memory for your
633 watcher structures (and it is usually a bad idea to do this on the stack,
634 although this can sometimes be quite valid).
636 Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init
637 (watcher *, callback)\*(C'\fR, which expects a callback to be provided. This
638 callback gets invoked each time the event occurs (or, in the case of io
639 watchers, each time the event loop detects that the file descriptor given
640 is readable and/or writable).
642 Each watcher type has its own \f(CW\*(C`ev_<type>_set (watcher *, ...)\*(C'\fR macro
643 with arguments specific to this watcher type. There is also a macro
644 to combine initialisation and setting in one call: \f(CW\*(C`ev_<type>_init
645 (watcher *, callback, ...)\*(C'\fR.
647 To make the watcher actually watch out for events, you have to start it
648 with a watcher-specific start function (\f(CW\*(C`ev_<type>_start (loop, watcher
649 *)\*(C'\fR), and you can stop watching for events at any time by calling the
650 corresponding stop function (\f(CW\*(C`ev_<type>_stop (loop, watcher *)\*(C'\fR.
652 As long as your watcher is active (has been started but not stopped) you
653 must not touch the values stored in it. Most specifically you must never
654 reinitialise it or call its \f(CW\*(C`set\*(C'\fR macro.
656 Each and every callback receives the event loop pointer as first, the
657 registered watcher structure as second, and a bitset of received events as
660 The received events usually include a single bit per event type received
661 (you can receive multiple events at the same time). The possible bit masks
663 .ie n .IP """EV_READ""" 4
664 .el .IP "\f(CWEV_READ\fR" 4
667 .ie n .IP """EV_WRITE""" 4
668 .el .IP "\f(CWEV_WRITE\fR" 4
671 The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or
673 .ie n .IP """EV_TIMEOUT""" 4
674 .el .IP "\f(CWEV_TIMEOUT\fR" 4
675 .IX Item "EV_TIMEOUT"
676 The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out.
677 .ie n .IP """EV_PERIODIC""" 4
678 .el .IP "\f(CWEV_PERIODIC\fR" 4
679 .IX Item "EV_PERIODIC"
680 The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out.
681 .ie n .IP """EV_SIGNAL""" 4
682 .el .IP "\f(CWEV_SIGNAL\fR" 4
684 The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread.
685 .ie n .IP """EV_CHILD""" 4
686 .el .IP "\f(CWEV_CHILD\fR" 4
688 The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change.
689 .ie n .IP """EV_IDLE""" 4
690 .el .IP "\f(CWEV_IDLE\fR" 4
692 The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do.
693 .ie n .IP """EV_PREPARE""" 4
694 .el .IP "\f(CWEV_PREPARE\fR" 4
695 .IX Item "EV_PREPARE"
697 .ie n .IP """EV_CHECK""" 4
698 .el .IP "\f(CWEV_CHECK\fR" 4
701 All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_loop\*(C'\fR starts
702 to gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are invoked just after
703 \&\f(CW\*(C`ev_loop\*(C'\fR has gathered them, but before it invokes any callbacks for any
704 received events. Callbacks of both watcher types can start and stop as
705 many watchers as they want, and all of them will be taken into account
706 (for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep
707 \&\f(CW\*(C`ev_loop\*(C'\fR from blocking).
708 .ie n .IP """EV_ERROR""" 4
709 .el .IP "\f(CWEV_ERROR\fR" 4
711 An unspecified error has occured, the watcher has been stopped. This might
712 happen because the watcher could not be properly started because libev
713 ran out of memory, a file descriptor was found to be closed or any other
714 problem. You best act on it by reporting the problem and somehow coping
715 with the watcher being stopped.
717 Libev will usually signal a few \*(L"dummy\*(R" events together with an error,
718 for example it might indicate that a fd is readable or writable, and if
719 your callbacks is well-written it can just attempt the operation and cope
720 with the error from \fIread()\fR or \fIwrite()\fR. This will not work in multithreaded
721 programs, though, so beware.
722 .Sh "\s-1SUMMARY\s0 \s-1OF\s0 \s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0"
723 .IX Subsection "SUMMARY OF GENERIC WATCHER FUNCTIONS"
724 In the following description, \f(CW\*(C`TYPE\*(C'\fR stands for the watcher type,
725 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.
726 .ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4
727 .el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4
728 .IX Item "ev_init (ev_TYPE *watcher, callback)"
729 This macro initialises the generic portion of a watcher. The contents
730 of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only
731 the generic parts of the watcher are initialised, you \fIneed\fR to call
732 the type-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR macro afterwards to initialise the
733 type-specific parts. For each type there is also a \f(CW\*(C`ev_TYPE_init\*(C'\fR macro
734 which rolls both calls into one.
736 You can reinitialise a watcher at any time as long as it has been stopped
737 (or never started) and there are no pending events outstanding.
739 The callbakc is always of type \f(CW\*(C`void (*)(ev_loop *loop, ev_TYPE *watcher,
740 int revents)\*(C'\fR.
741 .ie n .IP """ev_TYPE_set"" (ev_TYPE *, [args])" 4
742 .el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *, [args])" 4
743 .IX Item "ev_TYPE_set (ev_TYPE *, [args])"
744 This macro initialises the type-specific parts of a watcher. You need to
745 call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can
746 call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this
747 macro on a watcher that is active (it can be pending, however, which is a
748 difference to the \f(CW\*(C`ev_init\*(C'\fR macro).
750 Although some watcher types do not have type-specific arguments
751 (e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro.
752 .ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4
753 .el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4
754 .IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])"
755 This convinience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro
756 calls into a single call. This is the most convinient method to initialise
757 a watcher. The same limitations apply, of course.
758 .ie n .IP """ev_TYPE_start"" (loop *, ev_TYPE *watcher)" 4
759 .el .IP "\f(CWev_TYPE_start\fR (loop *, ev_TYPE *watcher)" 4
760 .IX Item "ev_TYPE_start (loop *, ev_TYPE *watcher)"
761 Starts (activates) the given watcher. Only active watchers will receive
762 events. If the watcher is already active nothing will happen.
763 .ie n .IP """ev_TYPE_stop"" (loop *, ev_TYPE *watcher)" 4
764 .el .IP "\f(CWev_TYPE_stop\fR (loop *, ev_TYPE *watcher)" 4
765 .IX Item "ev_TYPE_stop (loop *, ev_TYPE *watcher)"
766 Stops the given watcher again (if active) and clears the pending
767 status. It is possible that stopped watchers are pending (for example,
768 non-repeating timers are being stopped when they become pending), but
769 \&\f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor pending. If
770 you want to free or reuse the memory used by the watcher it is therefore a
771 good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function.
772 .IP "bool ev_is_active (ev_TYPE *watcher)" 4
773 .IX Item "bool ev_is_active (ev_TYPE *watcher)"
774 Returns a true value iff the watcher is active (i.e. it has been started
775 and not yet been stopped). As long as a watcher is active you must not modify
777 .IP "bool ev_is_pending (ev_TYPE *watcher)" 4
778 .IX Item "bool ev_is_pending (ev_TYPE *watcher)"
779 Returns a true value iff the watcher is pending, (i.e. it has outstanding
780 events but its callback has not yet been invoked). As long as a watcher
781 is pending (but not active) you must not call an init function on it (but
782 \&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe) and you must make sure the watcher is available to
783 libev (e.g. you cnanot \f(CW\*(C`free ()\*(C'\fR it).
784 .IP "callback = ev_cb (ev_TYPE *watcher)" 4
785 .IX Item "callback = ev_cb (ev_TYPE *watcher)"
786 Returns the callback currently set on the watcher.
787 .IP "ev_cb_set (ev_TYPE *watcher, callback)" 4
788 .IX Item "ev_cb_set (ev_TYPE *watcher, callback)"
789 Change the callback. You can change the callback at virtually any time
791 .Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0"
792 .IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"
793 Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change
794 and read at any time, libev will completely ignore it. This can be used
795 to associate arbitrary data with your watcher. If you need more data and
796 don't want to allocate memory and store a pointer to it in that data
797 member, you can also \*(L"subclass\*(R" the watcher type and provide your own
806 \& struct whatever *mostinteresting;
810 And since your callback will be called with a pointer to the watcher, you
811 can cast it back to your own type:
814 \& static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
816 \& struct my_io *w = (struct my_io *)w_;
821 More interesting and less C\-conformant ways of catsing your callback type
822 have been omitted....
824 .IX Header "WATCHER TYPES"
825 This section describes each watcher in detail, but will not repeat
826 information given in the last section.
827 .ie n .Sh """ev_io"" \- is this file descriptor readable or writable"
828 .el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable"
829 .IX Subsection "ev_io - is this file descriptor readable or writable"
830 I/O watchers check whether a file descriptor is readable or writable
831 in each iteration of the event loop (This behaviour is called
832 level-triggering because you keep receiving events as long as the
833 condition persists. Remember you can stop the watcher if you don't want to
834 act on the event and neither want to receive future events).
836 In general you can register as many read and/or write event watchers per
837 fd as you want (as long as you don't confuse yourself). Setting all file
838 descriptors to non-blocking mode is also usually a good idea (but not
839 required if you know what you are doing).
841 You have to be careful with dup'ed file descriptors, though. Some backends
842 (the linux epoll backend is a notable example) cannot handle dup'ed file
843 descriptors correctly if you register interest in two or more fds pointing
844 to the same underlying file/socket etc. description (that is, they share
845 the same underlying \*(L"file open\*(R").
847 If you must do this, then force the use of a known-to-be-good backend
848 (at the time of this writing, this includes only \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and
849 \&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR).
850 .IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
851 .IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
853 .IP "ev_io_set (ev_io *, int fd, int events)" 4
854 .IX Item "ev_io_set (ev_io *, int fd, int events)"
856 Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The fd is the file descriptor to rceeive
857 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 |
858 EV_WRITE\*(C'\fR to receive the given events.
860 Please note that most of the more scalable backend mechanisms (for example
861 epoll and solaris ports) can result in spurious readyness notifications
862 for file descriptors, so you practically need to use non-blocking I/O (and
863 treat callback invocation as hint only), or retest separately with a safe
864 interface before doing I/O (XLib can do this), or force the use of either
865 \&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR, which don't suffer from this
866 problem. Also note that it is quite easy to have your callback invoked
867 when the readyness condition is no longer valid even when employing
868 typical ways of handling events, so its a good idea to use non-blocking
871 Example: call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well
872 readable, but only once. Since it is likely line\-buffered, you could
873 attempt to read a whole line in the callback:
877 \& stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
879 \& ev_io_stop (loop, w);
880 \& .. read from stdin here (or from w->fd) and haqndle any I/O errors
886 \& struct ev_loop *loop = ev_default_init (0);
887 \& struct ev_io stdin_readable;
888 \& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
889 \& ev_io_start (loop, &stdin_readable);
890 \& ev_loop (loop, 0);
892 .ie n .Sh """ev_timer"" \- relative and optionally recurring timeouts"
893 .el .Sh "\f(CWev_timer\fP \- relative and optionally recurring timeouts"
894 .IX Subsection "ev_timer - relative and optionally recurring timeouts"
895 Timer watchers are simple relative timers that generate an event after a
896 given time, and optionally repeating in regular intervals after that.
898 The timers are based on real time, that is, if you register an event that
899 times out after an hour and you reset your system clock to last years
900 time, it will still time out after (roughly) and hour. \*(L"Roughly\*(R" because
901 detecting time jumps is hard, and some inaccuracies are unavoidable (the
902 monotonic clock option helps a lot here).
904 The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
905 time. This is usually the right thing as this timestamp refers to the time
906 of the event triggering whatever timeout you are modifying/starting. If
907 you suspect event processing to be delayed and you \fIneed\fR to base the timeout
908 on the current time, use something like this to adjust for this:
911 \& ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
914 The callback is guarenteed to be invoked only when its timeout has passed,
915 but if multiple timers become ready during the same loop iteration then
916 order of execution is undefined.
917 .IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
918 .IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
920 .IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
921 .IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
923 Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR is
924 \&\f(CW0.\fR, then it will automatically be stopped. If it is positive, then the
925 timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds
926 later, again, and again, until stopped manually.
928 The timer itself will do a best-effort at avoiding drift, that is, if you
929 configure a timer to trigger every 10 seconds, then it will trigger at
930 exactly 10 second intervals. If, however, your program cannot keep up with
931 the timer (because it takes longer than those 10 seconds to do stuff) the
932 timer will not fire more than once per event loop iteration.
933 .IP "ev_timer_again (loop)" 4
934 .IX Item "ev_timer_again (loop)"
935 This will act as if the timer timed out and restart it again if it is
936 repeating. The exact semantics are:
938 If the timer is started but nonrepeating, stop it.
940 If the timer is repeating, either start it if necessary (with the repeat
941 value), or reset the running timer to the repeat value.
943 This sounds a bit complicated, but here is a useful and typical
944 example: Imagine you have a tcp connection and you want a so-called idle
945 timeout, that is, you want to be called when there have been, say, 60
946 seconds of inactivity on the socket. The easiest way to do this is to
947 configure an \f(CW\*(C`ev_timer\*(C'\fR with after=repeat=60 and calling ev_timer_again each
948 time you successfully read or write some data. If you go into an idle
949 state where you do not expect data to travel on the socket, you can stop
950 the timer, and again will automatically restart it if need be.
952 Example: create a timer that fires after 60 seconds.
956 \& one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
958 \& .. one minute over, w is actually stopped right here
963 \& struct ev_timer mytimer;
964 \& ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
965 \& ev_timer_start (loop, &mytimer);
968 Example: create a timeout timer that times out after 10 seconds of
973 \& timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
975 \& .. ten seconds without any activity
980 \& struct ev_timer mytimer;
981 \& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
982 \& ev_timer_again (&mytimer); /* start timer */
983 \& ev_loop (loop, 0);
987 \& // and in some piece of code that gets executed on any "activity":
988 \& // reset the timeout to start ticking again at 10 seconds
989 \& ev_timer_again (&mytimer);
991 .ie n .Sh """ev_periodic"" \- to cron or not to cron"
992 .el .Sh "\f(CWev_periodic\fP \- to cron or not to cron"
993 .IX Subsection "ev_periodic - to cron or not to cron"
994 Periodic watchers are also timers of a kind, but they are very versatile
995 (and unfortunately a bit complex).
997 Unlike \f(CW\*(C`ev_timer\*(C'\fR's, they are not based on real time (or relative time)
998 but on wallclock time (absolute time). You can tell a periodic watcher
999 to trigger \*(L"at\*(R" some specific point in time. For example, if you tell a
1000 periodic watcher to trigger in 10 seconds (by specifiying e.g. \f(CW\*(C`ev_now ()
1001 + 10.\*(C'\fR) and then reset your system clock to the last year, then it will
1002 take a year to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would trigger
1003 roughly 10 seconds later and of course not if you reset your system time
1006 They can also be used to implement vastly more complex timers, such as
1007 triggering an event on eahc midnight, local time.
1009 As with timers, the callback is guarenteed to be invoked only when the
1010 time (\f(CW\*(C`at\*(C'\fR) has been passed, but if multiple periodic timers become ready
1011 during the same loop iteration then order of execution is undefined.
1012 .IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 4
1013 .IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)"
1015 .IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4
1016 .IX Item "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)"
1018 Lots of arguments, lets sort it out... There are basically three modes of
1019 operation, and we will explain them from simplest to complex:
1021 .IP "* absolute timer (interval = reschedule_cb = 0)" 4
1022 .IX Item "absolute timer (interval = reschedule_cb = 0)"
1023 In this configuration the watcher triggers an event at the wallclock time
1024 \&\f(CW\*(C`at\*(C'\fR and doesn't repeat. It will not adjust when a time jump occurs,
1025 that is, if it is to be run at January 1st 2011 then it will run when the
1026 system time reaches or surpasses this time.
1027 .IP "* non-repeating interval timer (interval > 0, reschedule_cb = 0)" 4
1028 .IX Item "non-repeating interval timer (interval > 0, reschedule_cb = 0)"
1029 In this mode the watcher will always be scheduled to time out at the next
1030 \&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N) and then repeat, regardless
1033 This can be used to create timers that do not drift with respect to system
1037 \& ev_periodic_set (&periodic, 0., 3600., 0);
1040 This doesn't mean there will always be 3600 seconds in between triggers,
1041 but only that the the callback will be called when the system time shows a
1042 full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
1045 Another way to think about it (for the mathematically inclined) is that
1046 \&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
1047 time where \f(CW\*(C`time = at (mod interval)\*(C'\fR, regardless of any time jumps.
1048 .IP "* manual reschedule mode (reschedule_cb = callback)" 4
1049 .IX Item "manual reschedule mode (reschedule_cb = callback)"
1050 In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being
1051 ignored. Instead, each time the periodic watcher gets scheduled, the
1052 reschedule callback will be called with the watcher as first, and the
1053 current time as second argument.
1055 \&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher,
1056 ever, or make any event loop modifications\fR. If you need to stop it,
1057 return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop it afterwards (e.g. by
1058 starting a prepare watcher).
1060 Its prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
1061 ev_tstamp now)\*(C'\fR, e.g.:
1064 \& static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
1066 \& return now + 60.;
1070 It must return the next time to trigger, based on the passed time value
1071 (that is, the lowest time value larger than to the second argument). It
1072 will usually be called just before the callback will be triggered, but
1073 might be called at other times, too.
1075 \&\s-1NOTE:\s0 \fIThis callback must always return a time that is later than the
1076 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.
1078 This can be used to create very complex timers, such as a timer that
1079 triggers on each midnight, local time. To do this, you would calculate the
1080 next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How
1081 you do this is, again, up to you (but it is not trivial, which is the main
1082 reason I omitted it as an example).
1086 .IP "ev_periodic_again (loop, ev_periodic *)" 4
1087 .IX Item "ev_periodic_again (loop, ev_periodic *)"
1088 Simply stops and restarts the periodic watcher again. This is only useful
1089 when you changed some parameters or the reschedule callback would return
1090 a different time than the last time it was called (e.g. in a crond like
1091 program when the crontabs have changed).
1093 Example: call a callback every hour, or, more precisely, whenever the
1094 system clock is divisible by 3600. The callback invocation times have
1095 potentially a lot of jittering, but good long-term stability.
1099 \& clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
1101 \& ... its now a full hour (UTC, or TAI or whatever your clock follows)
1106 \& struct ev_periodic hourly_tick;
1107 \& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1108 \& ev_periodic_start (loop, &hourly_tick);
1111 Example: the same as above, but use a reschedule callback to do it:
1114 \& #include <math.h>
1119 \& my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
1121 \& return fmod (now, 3600.) + 3600.;
1126 \& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1129 Example: call a callback every hour, starting now:
1132 \& struct ev_periodic hourly_tick;
1133 \& ev_periodic_init (&hourly_tick, clock_cb,
1134 \& fmod (ev_now (loop), 3600.), 3600., 0);
1135 \& ev_periodic_start (loop, &hourly_tick);
1137 .ie n .Sh """ev_signal"" \- signal me when a signal gets signalled"
1138 .el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled"
1139 .IX Subsection "ev_signal - signal me when a signal gets signalled"
1140 Signal watchers will trigger an event when the process receives a specific
1141 signal one or more times. Even though signals are very asynchronous, libev
1142 will try it's best to deliver signals synchronously, i.e. as part of the
1143 normal event processing, like any other event.
1145 You can configure as many watchers as you like per signal. Only when the
1146 first watcher gets started will libev actually register a signal watcher
1147 with the kernel (thus it coexists with your own signal handlers as long
1148 as you don't register any with libev). Similarly, when the last signal
1149 watcher for a signal is stopped libev will reset the signal handler to
1150 \&\s-1SIG_DFL\s0 (regardless of what it was set to before).
1151 .IP "ev_signal_init (ev_signal *, callback, int signum)" 4
1152 .IX Item "ev_signal_init (ev_signal *, callback, int signum)"
1154 .IP "ev_signal_set (ev_signal *, int signum)" 4
1155 .IX Item "ev_signal_set (ev_signal *, int signum)"
1157 Configures the watcher to trigger on the given signal number (usually one
1158 of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
1159 .ie n .Sh """ev_child"" \- wait for pid status changes"
1160 .el .Sh "\f(CWev_child\fP \- wait for pid status changes"
1161 .IX Subsection "ev_child - wait for pid status changes"
1162 Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
1163 some child status changes (most typically when a child of yours dies).
1164 .IP "ev_child_init (ev_child *, callback, int pid)" 4
1165 .IX Item "ev_child_init (ev_child *, callback, int pid)"
1167 .IP "ev_child_set (ev_child *, int pid)" 4
1168 .IX Item "ev_child_set (ev_child *, int pid)"
1170 Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
1171 \&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
1172 at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
1173 the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
1174 \&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
1175 process causing the status change.
1177 Example: try to exit cleanly on \s-1SIGINT\s0 and \s-1SIGTERM\s0.
1181 \& sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
1183 \& ev_unloop (loop, EVUNLOOP_ALL);
1188 \& struct ev_signal signal_watcher;
1189 \& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1190 \& ev_signal_start (loop, &sigint_cb);
1192 .ie n .Sh """ev_idle"" \- when you've got nothing better to do"
1193 .el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do"
1194 .IX Subsection "ev_idle - when you've got nothing better to do"
1195 Idle watchers trigger events when there are no other events are pending
1196 (prepare, check and other idle watchers do not count). That is, as long
1197 as your process is busy handling sockets or timeouts (or even signals,
1198 imagine) it will not be triggered. But when your process is idle all idle
1199 watchers are being called again and again, once per event loop iteration \-
1200 until stopped, that is, or your process receives more events and becomes
1203 The most noteworthy effect is that as long as any idle watchers are
1204 active, the process will not block when waiting for new events.
1206 Apart from keeping your process non-blocking (which is a useful
1207 effect on its own sometimes), idle watchers are a good place to do
1208 \&\*(L"pseudo\-background processing\*(R", or delay processing stuff to after the
1209 event loop has handled all outstanding events.
1210 .IP "ev_idle_init (ev_signal *, callback)" 4
1211 .IX Item "ev_idle_init (ev_signal *, callback)"
1212 Initialises and configures the idle watcher \- it has no parameters of any
1213 kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
1216 Example: dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR, start it, and in the
1217 callback, free it. Alos, use no error checking, as usual.
1221 \& idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
1224 \& // now do something you wanted to do when the program has
1225 \& // no longer asnything immediate to do.
1230 \& struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
1231 \& ev_idle_init (idle_watcher, idle_cb);
1232 \& ev_idle_start (loop, idle_cb);
1234 .ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop"
1235 .el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop"
1236 .IX Subsection "ev_prepare and ev_check - customise your event loop"
1237 Prepare and check watchers are usually (but not always) used in tandem:
1238 prepare watchers get invoked before the process blocks and check watchers
1241 Their main purpose is to integrate other event mechanisms into libev and
1242 their use is somewhat advanced. This could be used, for example, to track
1243 variable changes, implement your own watchers, integrate net-snmp or a
1244 coroutine library and lots more.
1246 This is done by examining in each prepare call which file descriptors need
1247 to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers for
1248 them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many libraries
1249 provide just this functionality). Then, in the check watcher you check for
1250 any events that occured (by checking the pending status of all watchers
1251 and stopping them) and call back into the library. The I/O and timer
1252 callbacks will never actually be called (but must be valid nevertheless,
1253 because you never know, you know?).
1255 As another example, the Perl Coro module uses these hooks to integrate
1256 coroutines into libev programs, by yielding to other active coroutines
1257 during each prepare and only letting the process block if no coroutines
1258 are ready to run (it's actually more complicated: it only runs coroutines
1259 with priority higher than or equal to the event loop and one coroutine
1260 of lower priority, but only once, using idle watchers to keep the event
1261 loop from blocking if lower-priority coroutines are active, thus mapping
1262 low-priority coroutines to idle/background tasks).
1263 .IP "ev_prepare_init (ev_prepare *, callback)" 4
1264 .IX Item "ev_prepare_init (ev_prepare *, callback)"
1266 .IP "ev_check_init (ev_check *, callback)" 4
1267 .IX Item "ev_check_init (ev_check *, callback)"
1269 Initialises and configures the prepare or check watcher \- they have no
1270 parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
1271 macros, but using them is utterly, utterly and completely pointless.
1274 .ie n .Sh """ev_embed"" \- when one backend isn't enough"
1275 .el .Sh "\f(CWev_embed\fP \- when one backend isn't enough"
1276 .IX Subsection "ev_embed - when one backend isn't enough"
1277 This is a rather advanced watcher type that lets you embed one event loop
1278 into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded
1279 loop, other types of watchers might be handled in a delayed or incorrect
1280 fashion and must not be used).
1282 There are primarily two reasons you would want that: work around bugs and
1285 As an example for a bug workaround, the kqueue backend might only support
1286 sockets on some platform, so it is unusable as generic backend, but you
1287 still want to make use of it because you have many sockets and it scales
1288 so nicely. In this case, you would create a kqueue-based loop and embed it
1289 into your default loop (which might use e.g. poll). Overall operation will
1290 be a bit slower because first libev has to poll and then call kevent, but
1291 at least you can use both at what they are best.
1293 As for prioritising I/O: rarely you have the case where some fds have
1294 to be watched and handled very quickly (with low latency), and even
1295 priorities and idle watchers might have too much overhead. In this case
1296 you would put all the high priority stuff in one loop and all the rest in
1297 a second one, and embed the second one in the first.
1299 As long as the watcher is active, the callback will be invoked every time
1300 there might be events pending in the embedded loop. The callback must then
1301 call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single sweep and invoke
1302 their callbacks (you could also start an idle watcher to give the embedded
1303 loop strictly lower priority for example). You can also set the callback
1304 to \f(CW0\fR, in which case the embed watcher will automatically execute the
1305 embedded loop sweep.
1307 As long as the watcher is started it will automatically handle events. The
1308 callback will be invoked whenever some events have been handled. You can
1309 set the callback to \f(CW0\fR to avoid having to specify one if you are not
1312 Also, there have not currently been made special provisions for forking:
1313 when you fork, you not only have to call \f(CW\*(C`ev_loop_fork\*(C'\fR on both loops,
1314 but you will also have to stop and restart any \f(CW\*(C`ev_embed\*(C'\fR watchers
1317 Unfortunately, not all backends are embeddable, only the ones returned by
1318 \&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any
1321 So when you want to use this feature you will always have to be prepared
1322 that you cannot get an embeddable loop. The recommended way to get around
1323 this is to have a separate variables for your embeddable loop, try to
1324 create it, and if that fails, use the normal loop for everything:
1327 \& struct ev_loop *loop_hi = ev_default_init (0);
1328 \& struct ev_loop *loop_lo = 0;
1329 \& struct ev_embed embed;
1333 \& // see if there is a chance of getting one that works
1334 \& // (remember that a flags value of 0 means autodetection)
1335 \& loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1336 \& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1341 \& // if we got one, then embed it, otherwise default to loop_hi
1344 \& ev_embed_init (&embed, 0, loop_lo);
1345 \& ev_embed_start (loop_hi, &embed);
1348 \& loop_lo = loop_hi;
1350 .IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
1351 .IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)"
1353 .IP "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
1354 .IX Item "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)"
1356 Configures the watcher to embed the given loop, which must be
1357 embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be
1358 invoked automatically, otherwise it is the responsibility of the callback
1359 to invoke it (it will continue to be called until the sweep has been done,
1360 if you do not want thta, you need to temporarily stop the embed watcher).
1361 .IP "ev_embed_sweep (loop, ev_embed *)" 4
1362 .IX Item "ev_embed_sweep (loop, ev_embed *)"
1363 Make a single, non-blocking sweep over the embedded loop. This works
1364 similarly to \f(CW\*(C`ev_loop (embedded_loop, EVLOOP_NONBLOCK)\*(C'\fR, but in the most
1365 apropriate way for embedded loops.
1366 .SH "OTHER FUNCTIONS"
1367 .IX Header "OTHER FUNCTIONS"
1368 There are some other functions of possible interest. Described. Here. Now.
1369 .IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4
1370 .IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)"
1371 This function combines a simple timer and an I/O watcher, calls your
1372 callback on whichever event happens first and automatically stop both
1373 watchers. This is useful if you want to wait for a single event on an fd
1374 or timeout without having to allocate/configure/start/stop/free one or
1375 more watchers yourself.
1377 If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and events
1378 is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for the given \f(CW\*(C`fd\*(C'\fR and
1379 \&\f(CW\*(C`events\*(C'\fR set will be craeted and started.
1381 If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be
1382 started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and
1383 repeat = 0) will be started. While \f(CW0\fR is a valid timeout, it is of
1386 The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and gets
1387 passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of
1388 \&\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
1389 value passed to \f(CW\*(C`ev_once\*(C'\fR:
1392 \& static void stdin_ready (int revents, void *arg)
1394 \& if (revents & EV_TIMEOUT)
1395 \& /* doh, nothing entered */;
1396 \& else if (revents & EV_READ)
1397 \& /* stdin might have data for us, joy! */;
1402 \& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1404 .IP "ev_feed_event (ev_loop *, watcher *, int revents)" 4
1405 .IX Item "ev_feed_event (ev_loop *, watcher *, int revents)"
1406 Feeds the given event set into the event loop, as if the specified event
1407 had happened for the specified watcher (which must be a pointer to an
1408 initialised but not necessarily started event watcher).
1409 .IP "ev_feed_fd_event (ev_loop *, int fd, int revents)" 4
1410 .IX Item "ev_feed_fd_event (ev_loop *, int fd, int revents)"
1411 Feed an event on the given fd, as if a file descriptor backend detected
1412 the given events it.
1413 .IP "ev_feed_signal_event (ev_loop *loop, int signum)" 4
1414 .IX Item "ev_feed_signal_event (ev_loop *loop, int signum)"
1415 Feed an event as if the given signal occured (\f(CW\*(C`loop\*(C'\fR must be the default
1417 .SH "LIBEVENT EMULATION"
1418 .IX Header "LIBEVENT EMULATION"
1419 Libev offers a compatibility emulation layer for libevent. It cannot
1420 emulate the internals of libevent, so here are some usage hints:
1421 .IP "* Use it by including <event.h>, as usual." 4
1422 .IX Item "Use it by including <event.h>, as usual."
1424 .IP "* The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4
1425 .IX Item "The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events."
1426 .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
1427 .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)."
1428 .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
1429 .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."
1430 .IP "* Other members are not supported." 4
1431 .IX Item "Other members are not supported."
1432 .IP "* The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need to use the libev header file and library." 4
1433 .IX Item "The libev emulation is not ABI compatible to libevent, you need to use the libev header file and library."
1436 .IX Header " SUPPORT"
1437 Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow
1438 you to use some convinience methods to start/stop watchers and also change
1439 the callback model to a model using method callbacks on objects.
1444 \& #include <ev++.h>
1447 (it is not installed by default). This automatically includes \fIev.h\fR
1448 and puts all of its definitions (many of them macros) into the global
1449 namespace. All \*(C+ specific things are put into the \f(CW\*(C`ev\*(C'\fR namespace.
1451 It should support all the same embedding options as \fIev.h\fR, most notably
1452 \&\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR.
1454 Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace:
1455 .ie n .IP """ev::READ""\fR, \f(CW""ev::WRITE"" etc." 4
1456 .el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4
1457 .IX Item "ev::READ, ev::WRITE etc."
1458 These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc.
1459 macros from \fIev.h\fR.
1460 .ie n .IP """ev::tstamp""\fR, \f(CW""ev::now""" 4
1461 .el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4
1462 .IX Item "ev::tstamp, ev::now"
1463 Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix.
1464 .ie n .IP """ev::io""\fR, \f(CW""ev::timer""\fR, \f(CW""ev::periodic""\fR, \f(CW""ev::idle""\fR, \f(CW""ev::sig"" etc." 4
1465 .el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4
1466 .IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc."
1467 For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of
1468 the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR
1469 which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro
1470 defines by many implementations.
1472 All of those classes have these methods:
1474 .IP "ev::TYPE::TYPE (object *, object::method *)" 4
1475 .IX Item "ev::TYPE::TYPE (object *, object::method *)"
1477 .IP "ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)" 4
1478 .IX Item "ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)"
1479 .IP "ev::TYPE::~TYPE" 4
1480 .IX Item "ev::TYPE::~TYPE"
1482 The constructor takes a pointer to an object and a method pointer to
1483 the event handler callback to call in this class. The constructor calls
1484 \&\f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the \f(CW\*(C`set\*(C'\fR method
1485 before starting it. If you do not specify a loop then the constructor
1486 automatically associates the default loop with this watcher.
1488 The destructor automatically stops the watcher if it is active.
1489 .IP "w\->set (struct ev_loop *)" 4
1490 .IX Item "w->set (struct ev_loop *)"
1491 Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only
1492 do this when the watcher is inactive (and not pending either).
1493 .IP "w\->set ([args])" 4
1494 .IX Item "w->set ([args])"
1495 Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR, with the same args. Must be
1496 called at least once. Unlike the C counterpart, an active watcher gets
1497 automatically stopped and restarted.
1498 .IP "w\->start ()" 4
1499 .IX Item "w->start ()"
1500 Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument as the
1501 constructor already takes the loop.
1503 .IX Item "w->stop ()"
1504 Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument.
1505 .ie n .IP "w\->again () ""ev::timer""\fR, \f(CW""ev::periodic"" only" 4
1506 .el .IP "w\->again () \f(CWev::timer\fR, \f(CWev::periodic\fR only" 4
1507 .IX Item "w->again () ev::timer, ev::periodic only"
1508 For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding
1509 \&\f(CW\*(C`ev_TYPE_again\*(C'\fR function.
1510 .ie n .IP "w\->sweep () ""ev::embed"" only" 4
1511 .el .IP "w\->sweep () \f(CWev::embed\fR only" 4
1512 .IX Item "w->sweep () ev::embed only"
1513 Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR.
1518 Example: Define a class with an \s-1IO\s0 and idle watcher, start one of them in
1524 \& ev_io io; void io_cb (ev::io &w, int revents);
1525 \& ev_idle idle void idle_cb (ev::idle &w, int revents);
1534 \& myclass::myclass (int fd)
1535 \& : io (this, &myclass::io_cb),
1536 \& idle (this, &myclass::idle_cb)
1538 \& io.start (fd, ev::READ);
1543 Marc Lehmann <libev@schmorp.de>.
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