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131 .IX Title ""<STANDARD INPUT>" 1"
132 .TH "<STANDARD INPUT>" 1 "2007-11-27" "perl v5.8.8" "User Contributed Perl Documentation"
134 libev \- a high performance full\-featured event loop written in C
136 .IX Header "SYNOPSIS"
140 .SH "EXAMPLE PROGRAM"
141 .IX Header "EXAMPLE PROGRAM"
147 \& ev_io stdin_watcher;
148 \& ev_timer timeout_watcher;
152 \& /* called when data readable on stdin */
154 \& stdin_cb (EV_P_ struct ev_io *w, int revents)
156 \& /* puts ("stdin ready"); */
157 \& ev_io_stop (EV_A_ w); /* just a syntax example */
158 \& ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */
164 \& timeout_cb (EV_P_ struct ev_timer *w, int revents)
166 \& /* puts ("timeout"); */
167 \& ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */
175 \& struct ev_loop *loop = ev_default_loop (0);
179 \& /* initialise an io watcher, then start it */
180 \& ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
181 \& ev_io_start (loop, &stdin_watcher);
185 \& /* simple non-repeating 5.5 second timeout */
186 \& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
187 \& ev_timer_start (loop, &timeout_watcher);
191 \& /* loop till timeout or data ready */
192 \& ev_loop (loop, 0);
200 .IX Header "DESCRIPTION"
201 Libev is an event loop: you register interest in certain events (such as a
202 file descriptor being readable or a timeout occuring), and it will manage
203 these event sources and provide your program with events.
205 To do this, it must take more or less complete control over your process
206 (or thread) by executing the \fIevent loop\fR handler, and will then
207 communicate events via a callback mechanism.
209 You register interest in certain events by registering so-called \fIevent
210 watchers\fR, which are relatively small C structures you initialise with the
211 details of the event, and then hand it over to libev by \fIstarting\fR the
214 .IX Header "FEATURES"
215 Libev supports \f(CW\*(C`select\*(C'\fR, \f(CW\*(C`poll\*(C'\fR, the linux-specific \f(CW\*(C`epoll\*(C'\fR, the
216 bsd-specific \f(CW\*(C`kqueue\*(C'\fR and the solaris-specific event port mechanisms
217 for file descriptor events (\f(CW\*(C`ev_io\*(C'\fR), relative timers (\f(CW\*(C`ev_timer\*(C'\fR),
218 absolute timers with customised rescheduling (\f(CW\*(C`ev_periodic\*(C'\fR), synchronous
219 signals (\f(CW\*(C`ev_signal\*(C'\fR), process status change events (\f(CW\*(C`ev_child\*(C'\fR), and
220 event watchers dealing with the event loop mechanism itself (\f(CW\*(C`ev_idle\*(C'\fR,
221 \&\f(CW\*(C`ev_embed\*(C'\fR, \f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR watchers) as well as
222 file watchers (\f(CW\*(C`ev_stat\*(C'\fR) and even limited support for fork events
223 (\f(CW\*(C`ev_fork\*(C'\fR).
225 It also is quite fast (see this
226 benchmark comparing it to libevent
229 .IX Header "CONVENTIONS"
230 Libev is very configurable. In this manual the default configuration will
231 be described, which supports multiple event loops. For more info about
232 various configuration options please have a look at \fB\s-1EMBED\s0\fR section in
233 this manual. If libev was configured without support for multiple event
234 loops, then all functions taking an initial argument of name \f(CW\*(C`loop\*(C'\fR
235 (which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) will not have this argument.
236 .SH "TIME REPRESENTATION"
237 .IX Header "TIME REPRESENTATION"
238 Libev represents time as a single floating point number, representing the
239 (fractional) number of seconds since the (\s-1POSIX\s0) epoch (somewhere near
240 the beginning of 1970, details are complicated, don't ask). This type is
241 called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use too. It usually aliases
242 to the \f(CW\*(C`double\*(C'\fR type in C, and when you need to do any calculations on
243 it, you should treat it as such.
244 .SH "GLOBAL FUNCTIONS"
245 .IX Header "GLOBAL FUNCTIONS"
246 These functions can be called anytime, even before initialising the
248 .IP "ev_tstamp ev_time ()" 4
249 .IX Item "ev_tstamp ev_time ()"
250 Returns the current time as libev would use it. Please note that the
251 \&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp
252 you actually want to know.
253 .IP "int ev_version_major ()" 4
254 .IX Item "int ev_version_major ()"
256 .IP "int ev_version_minor ()" 4
257 .IX Item "int ev_version_minor ()"
259 You can find out the major and minor version numbers of the library
260 you linked against by calling the functions \f(CW\*(C`ev_version_major\*(C'\fR and
261 \&\f(CW\*(C`ev_version_minor\*(C'\fR. If you want, you can compare against the global
262 symbols \f(CW\*(C`EV_VERSION_MAJOR\*(C'\fR and \f(CW\*(C`EV_VERSION_MINOR\*(C'\fR, which specify the
263 version of the library your program was compiled against.
265 Usually, it's a good idea to terminate if the major versions mismatch,
266 as this indicates an incompatible change. Minor versions are usually
267 compatible to older versions, so a larger minor version alone is usually
270 Example: Make sure we haven't accidentally been linked against the wrong
274 \& assert (("libev version mismatch",
275 \& ev_version_major () == EV_VERSION_MAJOR
276 \& && ev_version_minor () >= EV_VERSION_MINOR));
278 .IP "unsigned int ev_supported_backends ()" 4
279 .IX Item "unsigned int ev_supported_backends ()"
280 Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR
281 value) compiled into this binary of libev (independent of their
282 availability on the system you are running on). See \f(CW\*(C`ev_default_loop\*(C'\fR for
283 a description of the set values.
285 Example: make sure we have the epoll method, because yeah this is cool and
286 a must have and can we have a torrent of it please!!!11
289 \& assert (("sorry, no epoll, no sex",
290 \& ev_supported_backends () & EVBACKEND_EPOLL));
292 .IP "unsigned int ev_recommended_backends ()" 4
293 .IX Item "unsigned int ev_recommended_backends ()"
294 Return the set of all backends compiled into this binary of libev and also
295 recommended for this platform. This set is often smaller than the one
296 returned by \f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on
297 most BSDs and will not be autodetected unless you explicitly request it
298 (assuming you know what you are doing). This is the set of backends that
299 libev will probe for if you specify no backends explicitly.
300 .IP "unsigned int ev_embeddable_backends ()" 4
301 .IX Item "unsigned int ev_embeddable_backends ()"
302 Returns the set of backends that are embeddable in other event loops. This
303 is the theoretical, all\-platform, value. To find which backends
304 might be supported on the current system, you would need to look at
305 \&\f(CW\*(C`ev_embeddable_backends () & ev_supported_backends ()\*(C'\fR, likewise for
308 See the description of \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
309 .IP "ev_set_allocator (void *(*cb)(void *ptr, size_t size))" 4
310 .IX Item "ev_set_allocator (void *(*cb)(void *ptr, size_t size))"
311 Sets the allocation function to use (the prototype and semantics are
312 identical to the realloc C function). It is used to allocate and free
313 memory (no surprises here). If it returns zero when memory needs to be
314 allocated, the library might abort or take some potentially destructive
315 action. The default is your system realloc function.
317 You could override this function in high-availability programs to, say,
318 free some memory if it cannot allocate memory, to use a special allocator,
319 or even to sleep a while and retry until some memory is available.
321 Example: Replace the libev allocator with one that waits a bit and then
326 \& persistent_realloc (void *ptr, size_t size)
330 \& void *newptr = realloc (ptr, size);
346 \& ev_set_allocator (persistent_realloc);
348 .IP "ev_set_syserr_cb (void (*cb)(const char *msg));" 4
349 .IX Item "ev_set_syserr_cb (void (*cb)(const char *msg));"
350 Set the callback function to call on a retryable syscall error (such
351 as failed select, poll, epoll_wait). The message is a printable string
352 indicating the system call or subsystem causing the problem. If this
353 callback is set, then libev will expect it to remedy the sitution, no
354 matter what, when it returns. That is, libev will generally retry the
355 requested operation, or, if the condition doesn't go away, do bad stuff
358 Example: This is basically the same thing that libev does internally, too.
362 \& fatal_error (const char *msg)
371 \& ev_set_syserr_cb (fatal_error);
373 .SH "FUNCTIONS CONTROLLING THE EVENT LOOP"
374 .IX Header "FUNCTIONS CONTROLLING THE EVENT LOOP"
375 An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR. The library knows two
376 types of such loops, the \fIdefault\fR loop, which supports signals and child
377 events, and dynamically created loops which do not.
379 If you use threads, a common model is to run the default event loop
380 in your main thread (or in a separate thread) and for each thread you
381 create, you also create another event loop. Libev itself does no locking
382 whatsoever, so if you mix calls to the same event loop in different
383 threads, make sure you lock (this is usually a bad idea, though, even if
384 done correctly, because it's hideous and inefficient).
385 .IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
386 .IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
387 This will initialise the default event loop if it hasn't been initialised
388 yet and return it. If the default loop could not be initialised, returns
389 false. If it already was initialised it simply returns it (and ignores the
390 flags. If that is troubling you, check \f(CW\*(C`ev_backend ()\*(C'\fR afterwards).
392 If you don't know what event loop to use, use the one returned from this
395 The flags argument can be used to specify special behaviour or specific
396 backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR).
398 The following flags are supported:
400 .ie n .IP """EVFLAG_AUTO""" 4
401 .el .IP "\f(CWEVFLAG_AUTO\fR" 4
402 .IX Item "EVFLAG_AUTO"
403 The default flags value. Use this if you have no clue (it's the right
405 .ie n .IP """EVFLAG_NOENV""" 4
406 .el .IP "\f(CWEVFLAG_NOENV\fR" 4
407 .IX Item "EVFLAG_NOENV"
408 If this flag bit is ored into the flag value (or the program runs setuid
409 or setgid) then libev will \fInot\fR look at the environment variable
410 \&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will
411 override the flags completely if it is found in the environment. This is
412 useful to try out specific backends to test their performance, or to work
414 .ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4
415 .el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4
416 .IX Item "EVBACKEND_SELECT (value 1, portable select backend)"
417 This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as
418 libev tries to roll its own fd_set with no limits on the number of fds,
419 but if that fails, expect a fairly low limit on the number of fds when
420 using this backend. It doesn't scale too well (O(highest_fd)), but its usually
421 the fastest backend for a low number of fds.
422 .ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4
423 .el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4
424 .IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)"
425 And this is your standard \fIpoll\fR\|(2) backend. It's more complicated than
426 select, but handles sparse fds better and has no artificial limit on the
427 number of fds you can use (except it will slow down considerably with a
428 lot of inactive fds). It scales similarly to select, i.e. O(total_fds).
429 .ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
430 .el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
431 .IX Item "EVBACKEND_EPOLL (value 4, Linux)"
432 For few fds, this backend is a bit little slower than poll and select,
433 but it scales phenomenally better. While poll and select usually scale like
434 O(total_fds) where n is the total number of fds (or the highest fd), epoll scales
435 either O(1) or O(active_fds).
437 While stopping and starting an I/O watcher in the same iteration will
438 result in some caching, there is still a syscall per such incident
439 (because the fd could point to a different file description now), so its
440 best to avoid that. Also, \fIdup()\fRed file descriptors might not work very
441 well if you register events for both fds.
443 Please note that epoll sometimes generates spurious notifications, so you
444 need to use non-blocking I/O or other means to avoid blocking when no data
445 (or space) is available.
446 .ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4
447 .el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
448 .IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
449 Kqueue deserves special mention, as at the time of this writing, it
450 was broken on all BSDs except NetBSD (usually it doesn't work with
451 anything but sockets and pipes, except on Darwin, where of course its
452 completely useless). For this reason its not being \*(L"autodetected\*(R"
453 unless you explicitly specify it explicitly in the flags (i.e. using
454 \&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR).
456 It scales in the same way as the epoll backend, but the interface to the
457 kernel is more efficient (which says nothing about its actual speed, of
458 course). While starting and stopping an I/O watcher does not cause an
459 extra syscall as with epoll, it still adds up to four event changes per
460 incident, so its best to avoid that.
461 .ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
462 .el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
463 .IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
464 This is not implemented yet (and might never be).
465 .ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
466 .el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
467 .IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
468 This uses the Solaris 10 port mechanism. As with everything on Solaris,
469 it's really slow, but it still scales very well (O(active_fds)).
471 Please note that solaris ports can result in a lot of spurious
472 notifications, so you need to use non-blocking I/O or other means to avoid
473 blocking when no data (or space) is available.
474 .ie n .IP """EVBACKEND_ALL""" 4
475 .el .IP "\f(CWEVBACKEND_ALL\fR" 4
476 .IX Item "EVBACKEND_ALL"
477 Try all backends (even potentially broken ones that wouldn't be tried
478 with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as
479 \&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR.
483 If one or more of these are ored into the flags value, then only these
484 backends will be tried (in the reverse order as given here). If none are
485 specified, most compiled-in backend will be tried, usually in reverse
486 order of their flag values :)
488 The most typical usage is like this:
491 \& if (!ev_default_loop (0))
492 \& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
495 Restrict libev to the select and poll backends, and do not allow
496 environment settings to be taken into account:
499 \& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
502 Use whatever libev has to offer, but make sure that kqueue is used if
503 available (warning, breaks stuff, best use only with your own private
504 event loop and only if you know the \s-1OS\s0 supports your types of fds):
507 \& ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
510 .IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
511 .IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
512 Similar to \f(CW\*(C`ev_default_loop\*(C'\fR, but always creates a new event loop that is
513 always distinct from the default loop. Unlike the default loop, it cannot
514 handle signal and child watchers, and attempts to do so will be greeted by
515 undefined behaviour (or a failed assertion if assertions are enabled).
517 Example: Try to create a event loop that uses epoll and nothing else.
520 \& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
522 \& fatal ("no epoll found here, maybe it hides under your chair");
524 .IP "ev_default_destroy ()" 4
525 .IX Item "ev_default_destroy ()"
526 Destroys the default loop again (frees all memory and kernel state
527 etc.). None of the active event watchers will be stopped in the normal
528 sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your
529 responsibility to either stop all watchers cleanly yoursef \fIbefore\fR
530 calling this function, or cope with the fact afterwards (which is usually
531 the easiest thing, youc na just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them
533 .IP "ev_loop_destroy (loop)" 4
534 .IX Item "ev_loop_destroy (loop)"
535 Like \f(CW\*(C`ev_default_destroy\*(C'\fR, but destroys an event loop created by an
536 earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR.
537 .IP "ev_default_fork ()" 4
538 .IX Item "ev_default_fork ()"
539 This function reinitialises the kernel state for backends that have
540 one. Despite the name, you can call it anytime, but it makes most sense
541 after forking, in either the parent or child process (or both, but that
542 again makes little sense).
544 You \fImust\fR call this function in the child process after forking if and
545 only if you want to use the event library in both processes. If you just
546 fork+exec, you don't have to call it.
548 The function itself is quite fast and it's usually not a problem to call
549 it just in case after a fork. To make this easy, the function will fit in
550 quite nicely into a call to \f(CW\*(C`pthread_atfork\*(C'\fR:
553 \& pthread_atfork (0, 0, ev_default_fork);
556 At the moment, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and \f(CW\*(C`EVBACKEND_POLL\*(C'\fR are safe to use
557 without calling this function, so if you force one of those backends you
559 .IP "ev_loop_fork (loop)" 4
560 .IX Item "ev_loop_fork (loop)"
561 Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by
562 \&\f(CW\*(C`ev_loop_new\*(C'\fR. Yes, you have to call this on every allocated event loop
563 after fork, and how you do this is entirely your own problem.
564 .IP "unsigned int ev_backend (loop)" 4
565 .IX Item "unsigned int ev_backend (loop)"
566 Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
568 .IP "ev_tstamp ev_now (loop)" 4
569 .IX Item "ev_tstamp ev_now (loop)"
570 Returns the current \*(L"event loop time\*(R", which is the time the event loop
571 received events and started processing them. This timestamp does not
572 change as long as callbacks are being processed, and this is also the base
573 time used for relative timers. You can treat it as the timestamp of the
574 event occuring (or more correctly, libev finding out about it).
575 .IP "ev_loop (loop, int flags)" 4
576 .IX Item "ev_loop (loop, int flags)"
577 Finally, this is it, the event handler. This function usually is called
578 after you initialised all your watchers and you want to start handling
581 If the flags argument is specified as \f(CW0\fR, it will not return until
582 either no event watchers are active anymore or \f(CW\*(C`ev_unloop\*(C'\fR was called.
584 Please note that an explicit \f(CW\*(C`ev_unloop\*(C'\fR is usually better than
585 relying on all watchers to be stopped when deciding when a program has
586 finished (especially in interactive programs), but having a program that
587 automatically loops as long as it has to and no longer by virtue of
588 relying on its watchers stopping correctly is a thing of beauty.
590 A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle
591 those events and any outstanding ones, but will not block your process in
592 case there are no events and will return after one iteration of the loop.
594 A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if
595 neccessary) and will handle those and any outstanding ones. It will block
596 your process until at least one new event arrives, and will return after
597 one iteration of the loop. This is useful if you are waiting for some
598 external event in conjunction with something not expressible using other
599 libev watchers. However, a pair of \f(CW\*(C`ev_prepare\*(C'\fR/\f(CW\*(C`ev_check\*(C'\fR watchers is
600 usually a better approach for this kind of thing.
602 Here are the gory details of what \f(CW\*(C`ev_loop\*(C'\fR does:
605 \& * If there are no active watchers (reference count is zero), return.
606 \& - Queue prepare watchers and then call all outstanding watchers.
607 \& - If we have been forked, recreate the kernel state.
608 \& - Update the kernel state with all outstanding changes.
609 \& - Update the "event loop time".
610 \& - Calculate for how long to block.
611 \& - Block the process, waiting for any events.
612 \& - Queue all outstanding I/O (fd) events.
613 \& - Update the "event loop time" and do time jump handling.
614 \& - Queue all outstanding timers.
615 \& - Queue all outstanding periodics.
616 \& - If no events are pending now, queue all idle watchers.
617 \& - Queue all check watchers.
618 \& - Call all queued watchers in reverse order (i.e. check watchers first).
619 \& Signals and child watchers are implemented as I/O watchers, and will
620 \& be handled here by queueing them when their watcher gets executed.
621 \& - If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
622 \& were used, return, otherwise continue with step *.
625 Example: Queue some jobs and then loop until no events are outsanding
629 \& ... queue jobs here, make sure they register event watchers as long
630 \& ... as they still have work to do (even an idle watcher will do..)
631 \& ev_loop (my_loop, 0);
632 \& ... jobs done. yeah!
634 .IP "ev_unloop (loop, how)" 4
635 .IX Item "ev_unloop (loop, how)"
636 Can be used to make a call to \f(CW\*(C`ev_loop\*(C'\fR return early (but only after it
637 has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either
638 \&\f(CW\*(C`EVUNLOOP_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_loop\*(C'\fR call return, or
639 \&\f(CW\*(C`EVUNLOOP_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_loop\*(C'\fR calls return.
640 .IP "ev_ref (loop)" 4
641 .IX Item "ev_ref (loop)"
643 .IP "ev_unref (loop)" 4
644 .IX Item "ev_unref (loop)"
646 Ref/unref can be used to add or remove a reference count on the event
647 loop: Every watcher keeps one reference, and as long as the reference
648 count is nonzero, \f(CW\*(C`ev_loop\*(C'\fR will not return on its own. If you have
649 a watcher you never unregister that should not keep \f(CW\*(C`ev_loop\*(C'\fR from
650 returning, \fIev_unref()\fR after starting, and \fIev_ref()\fR before stopping it. For
651 example, libev itself uses this for its internal signal pipe: It is not
652 visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from exiting if
653 no event watchers registered by it are active. It is also an excellent
654 way to do this for generic recurring timers or from within third-party
655 libraries. Just remember to \fIunref after start\fR and \fIref before stop\fR.
657 Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_loop\*(C'\fR
658 running when nothing else is active.
661 \& struct ev_signal exitsig;
662 \& ev_signal_init (&exitsig, sig_cb, SIGINT);
663 \& ev_signal_start (loop, &exitsig);
667 Example: For some weird reason, unregister the above signal handler again.
671 \& ev_signal_stop (loop, &exitsig);
673 .SH "ANATOMY OF A WATCHER"
674 .IX Header "ANATOMY OF A WATCHER"
675 A watcher is a structure that you create and register to record your
676 interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to
677 become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher for that:
680 \& static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
683 \& ev_unloop (loop, EVUNLOOP_ALL);
688 \& struct ev_loop *loop = ev_default_loop (0);
689 \& struct ev_io stdin_watcher;
690 \& ev_init (&stdin_watcher, my_cb);
691 \& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
692 \& ev_io_start (loop, &stdin_watcher);
693 \& ev_loop (loop, 0);
696 As you can see, you are responsible for allocating the memory for your
697 watcher structures (and it is usually a bad idea to do this on the stack,
698 although this can sometimes be quite valid).
700 Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init
701 (watcher *, callback)\*(C'\fR, which expects a callback to be provided. This
702 callback gets invoked each time the event occurs (or, in the case of io
703 watchers, each time the event loop detects that the file descriptor given
704 is readable and/or writable).
706 Each watcher type has its own \f(CW\*(C`ev_<type>_set (watcher *, ...)\*(C'\fR macro
707 with arguments specific to this watcher type. There is also a macro
708 to combine initialisation and setting in one call: \f(CW\*(C`ev_<type>_init
709 (watcher *, callback, ...)\*(C'\fR.
711 To make the watcher actually watch out for events, you have to start it
712 with a watcher-specific start function (\f(CW\*(C`ev_<type>_start (loop, watcher
713 *)\*(C'\fR), and you can stop watching for events at any time by calling the
714 corresponding stop function (\f(CW\*(C`ev_<type>_stop (loop, watcher *)\*(C'\fR.
716 As long as your watcher is active (has been started but not stopped) you
717 must not touch the values stored in it. Most specifically you must never
718 reinitialise it or call its \f(CW\*(C`set\*(C'\fR macro.
720 Each and every callback receives the event loop pointer as first, the
721 registered watcher structure as second, and a bitset of received events as
724 The received events usually include a single bit per event type received
725 (you can receive multiple events at the same time). The possible bit masks
727 .ie n .IP """EV_READ""" 4
728 .el .IP "\f(CWEV_READ\fR" 4
731 .ie n .IP """EV_WRITE""" 4
732 .el .IP "\f(CWEV_WRITE\fR" 4
735 The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or
737 .ie n .IP """EV_TIMEOUT""" 4
738 .el .IP "\f(CWEV_TIMEOUT\fR" 4
739 .IX Item "EV_TIMEOUT"
740 The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out.
741 .ie n .IP """EV_PERIODIC""" 4
742 .el .IP "\f(CWEV_PERIODIC\fR" 4
743 .IX Item "EV_PERIODIC"
744 The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out.
745 .ie n .IP """EV_SIGNAL""" 4
746 .el .IP "\f(CWEV_SIGNAL\fR" 4
748 The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread.
749 .ie n .IP """EV_CHILD""" 4
750 .el .IP "\f(CWEV_CHILD\fR" 4
752 The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change.
753 .ie n .IP """EV_STAT""" 4
754 .el .IP "\f(CWEV_STAT\fR" 4
756 The path specified in the \f(CW\*(C`ev_stat\*(C'\fR watcher changed its attributes somehow.
757 .ie n .IP """EV_IDLE""" 4
758 .el .IP "\f(CWEV_IDLE\fR" 4
760 The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do.
761 .ie n .IP """EV_PREPARE""" 4
762 .el .IP "\f(CWEV_PREPARE\fR" 4
763 .IX Item "EV_PREPARE"
765 .ie n .IP """EV_CHECK""" 4
766 .el .IP "\f(CWEV_CHECK\fR" 4
769 All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_loop\*(C'\fR starts
770 to gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are invoked just after
771 \&\f(CW\*(C`ev_loop\*(C'\fR has gathered them, but before it invokes any callbacks for any
772 received events. Callbacks of both watcher types can start and stop as
773 many watchers as they want, and all of them will be taken into account
774 (for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep
775 \&\f(CW\*(C`ev_loop\*(C'\fR from blocking).
776 .ie n .IP """EV_EMBED""" 4
777 .el .IP "\f(CWEV_EMBED\fR" 4
779 The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention.
780 .ie n .IP """EV_FORK""" 4
781 .el .IP "\f(CWEV_FORK\fR" 4
783 The event loop has been resumed in the child process after fork (see
784 \&\f(CW\*(C`ev_fork\*(C'\fR).
785 .ie n .IP """EV_ERROR""" 4
786 .el .IP "\f(CWEV_ERROR\fR" 4
788 An unspecified error has occured, the watcher has been stopped. This might
789 happen because the watcher could not be properly started because libev
790 ran out of memory, a file descriptor was found to be closed or any other
791 problem. You best act on it by reporting the problem and somehow coping
792 with the watcher being stopped.
794 Libev will usually signal a few \*(L"dummy\*(R" events together with an error,
795 for example it might indicate that a fd is readable or writable, and if
796 your callbacks is well-written it can just attempt the operation and cope
797 with the error from \fIread()\fR or \fIwrite()\fR. This will not work in multithreaded
798 programs, though, so beware.
799 .Sh "\s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0"
800 .IX Subsection "GENERIC WATCHER FUNCTIONS"
801 In the following description, \f(CW\*(C`TYPE\*(C'\fR stands for the watcher type,
802 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.
803 .ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4
804 .el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4
805 .IX Item "ev_init (ev_TYPE *watcher, callback)"
806 This macro initialises the generic portion of a watcher. The contents
807 of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only
808 the generic parts of the watcher are initialised, you \fIneed\fR to call
809 the type-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR macro afterwards to initialise the
810 type-specific parts. For each type there is also a \f(CW\*(C`ev_TYPE_init\*(C'\fR macro
811 which rolls both calls into one.
813 You can reinitialise a watcher at any time as long as it has been stopped
814 (or never started) and there are no pending events outstanding.
816 The callback is always of type \f(CW\*(C`void (*)(ev_loop *loop, ev_TYPE *watcher,
817 int revents)\*(C'\fR.
818 .ie n .IP """ev_TYPE_set"" (ev_TYPE *, [args])" 4
819 .el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *, [args])" 4
820 .IX Item "ev_TYPE_set (ev_TYPE *, [args])"
821 This macro initialises the type-specific parts of a watcher. You need to
822 call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can
823 call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this
824 macro on a watcher that is active (it can be pending, however, which is a
825 difference to the \f(CW\*(C`ev_init\*(C'\fR macro).
827 Although some watcher types do not have type-specific arguments
828 (e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro.
829 .ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4
830 .el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4
831 .IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])"
832 This convinience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro
833 calls into a single call. This is the most convinient method to initialise
834 a watcher. The same limitations apply, of course.
835 .ie n .IP """ev_TYPE_start"" (loop *, ev_TYPE *watcher)" 4
836 .el .IP "\f(CWev_TYPE_start\fR (loop *, ev_TYPE *watcher)" 4
837 .IX Item "ev_TYPE_start (loop *, ev_TYPE *watcher)"
838 Starts (activates) the given watcher. Only active watchers will receive
839 events. If the watcher is already active nothing will happen.
840 .ie n .IP """ev_TYPE_stop"" (loop *, ev_TYPE *watcher)" 4
841 .el .IP "\f(CWev_TYPE_stop\fR (loop *, ev_TYPE *watcher)" 4
842 .IX Item "ev_TYPE_stop (loop *, ev_TYPE *watcher)"
843 Stops the given watcher again (if active) and clears the pending
844 status. It is possible that stopped watchers are pending (for example,
845 non-repeating timers are being stopped when they become pending), but
846 \&\f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor pending. If
847 you want to free or reuse the memory used by the watcher it is therefore a
848 good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function.
849 .IP "bool ev_is_active (ev_TYPE *watcher)" 4
850 .IX Item "bool ev_is_active (ev_TYPE *watcher)"
851 Returns a true value iff the watcher is active (i.e. it has been started
852 and not yet been stopped). As long as a watcher is active you must not modify
854 .IP "bool ev_is_pending (ev_TYPE *watcher)" 4
855 .IX Item "bool ev_is_pending (ev_TYPE *watcher)"
856 Returns a true value iff the watcher is pending, (i.e. it has outstanding
857 events but its callback has not yet been invoked). As long as a watcher
858 is pending (but not active) you must not call an init function on it (but
859 \&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe) and you must make sure the watcher is available to
860 libev (e.g. you cnanot \f(CW\*(C`free ()\*(C'\fR it).
861 .IP "callback ev_cb (ev_TYPE *watcher)" 4
862 .IX Item "callback ev_cb (ev_TYPE *watcher)"
863 Returns the callback currently set on the watcher.
864 .IP "ev_cb_set (ev_TYPE *watcher, callback)" 4
865 .IX Item "ev_cb_set (ev_TYPE *watcher, callback)"
866 Change the callback. You can change the callback at virtually any time
868 .Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0"
869 .IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"
870 Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change
871 and read at any time, libev will completely ignore it. This can be used
872 to associate arbitrary data with your watcher. If you need more data and
873 don't want to allocate memory and store a pointer to it in that data
874 member, you can also \*(L"subclass\*(R" the watcher type and provide your own
883 \& struct whatever *mostinteresting;
887 And since your callback will be called with a pointer to the watcher, you
888 can cast it back to your own type:
891 \& static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
893 \& struct my_io *w = (struct my_io *)w_;
898 More interesting and less C\-conformant ways of casting your callback type
899 instead have been omitted.
901 Another common scenario is having some data structure with multiple
913 In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more complicated,
914 you need to use \f(CW\*(C`offsetof\*(C'\fR:
917 \& #include <stddef.h>
922 \& t1_cb (EV_P_ struct ev_timer *w, int revents)
924 \& struct my_biggy big = (struct my_biggy *
925 \& (((char *)w) - offsetof (struct my_biggy, t1));
931 \& t2_cb (EV_P_ struct ev_timer *w, int revents)
933 \& struct my_biggy big = (struct my_biggy *
934 \& (((char *)w) - offsetof (struct my_biggy, t2));
938 .IX Header "WATCHER TYPES"
939 This section describes each watcher in detail, but will not repeat
940 information given in the last section. Any initialisation/set macros,
941 functions and members specific to the watcher type are explained.
943 Members are additionally marked with either \fI[read\-only]\fR, meaning that,
944 while the watcher is active, you can look at the member and expect some
945 sensible content, but you must not modify it (you can modify it while the
946 watcher is stopped to your hearts content), or \fI[read\-write]\fR, which
947 means you can expect it to have some sensible content while the watcher
948 is active, but you can also modify it. Modifying it may not do something
949 sensible or take immediate effect (or do anything at all), but libev will
950 not crash or malfunction in any way.
951 .ie n .Sh """ev_io"" \- is this file descriptor readable or writable?"
952 .el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable?"
953 .IX Subsection "ev_io - is this file descriptor readable or writable?"
954 I/O watchers check whether a file descriptor is readable or writable
955 in each iteration of the event loop, or, more precisely, when reading
956 would not block the process and writing would at least be able to write
957 some data. This behaviour is called level-triggering because you keep
958 receiving events as long as the condition persists. Remember you can stop
959 the watcher if you don't want to act on the event and neither want to
960 receive future events.
962 In general you can register as many read and/or write event watchers per
963 fd as you want (as long as you don't confuse yourself). Setting all file
964 descriptors to non-blocking mode is also usually a good idea (but not
965 required if you know what you are doing).
967 You have to be careful with dup'ed file descriptors, though. Some backends
968 (the linux epoll backend is a notable example) cannot handle dup'ed file
969 descriptors correctly if you register interest in two or more fds pointing
970 to the same underlying file/socket/etc. description (that is, they share
971 the same underlying \*(L"file open\*(R").
973 If you must do this, then force the use of a known-to-be-good backend
974 (at the time of this writing, this includes only \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and
975 \&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR).
977 Another thing you have to watch out for is that it is quite easy to
978 receive \*(L"spurious\*(R" readyness notifications, that is your callback might
979 be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block
980 because there is no data. Not only are some backends known to create a
981 lot of those (for example solaris ports), it is very easy to get into
982 this situation even with a relatively standard program structure. Thus
983 it is best to always use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning
984 \&\f(CW\*(C`EAGAIN\*(C'\fR is far preferable to a program hanging until some data arrives.
986 If you cannot run the fd in non-blocking mode (for example you should not
987 play around with an Xlib connection), then you have to seperately re-test
988 wether a file descriptor is really ready with a known-to-be good interface
989 such as poll (fortunately in our Xlib example, Xlib already does this on
990 its own, so its quite safe to use).
991 .IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
992 .IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
994 .IP "ev_io_set (ev_io *, int fd, int events)" 4
995 .IX Item "ev_io_set (ev_io *, int fd, int events)"
997 Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to
998 rceeive events for and events is either \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or
999 \&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR to receive the given events.
1000 .IP "int fd [read\-only]" 4
1001 .IX Item "int fd [read-only]"
1002 The file descriptor being watched.
1003 .IP "int events [read\-only]" 4
1004 .IX Item "int events [read-only]"
1005 The events being watched.
1007 Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well
1008 readable, but only once. Since it is likely line\-buffered, you could
1009 attempt to read a whole line in the callback.
1013 \& stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
1015 \& ev_io_stop (loop, w);
1016 \& .. read from stdin here (or from w->fd) and haqndle any I/O errors
1022 \& struct ev_loop *loop = ev_default_init (0);
1023 \& struct ev_io stdin_readable;
1024 \& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1025 \& ev_io_start (loop, &stdin_readable);
1026 \& ev_loop (loop, 0);
1028 .ie n .Sh """ev_timer"" \- relative and optionally repeating timeouts"
1029 .el .Sh "\f(CWev_timer\fP \- relative and optionally repeating timeouts"
1030 .IX Subsection "ev_timer - relative and optionally repeating timeouts"
1031 Timer watchers are simple relative timers that generate an event after a
1032 given time, and optionally repeating in regular intervals after that.
1034 The timers are based on real time, that is, if you register an event that
1035 times out after an hour and you reset your system clock to last years
1036 time, it will still time out after (roughly) and hour. \*(L"Roughly\*(R" because
1037 detecting time jumps is hard, and some inaccuracies are unavoidable (the
1038 monotonic clock option helps a lot here).
1040 The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
1041 time. This is usually the right thing as this timestamp refers to the time
1042 of the event triggering whatever timeout you are modifying/starting. If
1043 you suspect event processing to be delayed and you \fIneed\fR to base the timeout
1044 on the current time, use something like this to adjust for this:
1047 \& ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1050 The callback is guarenteed to be invoked only when its timeout has passed,
1051 but if multiple timers become ready during the same loop iteration then
1052 order of execution is undefined.
1053 .IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
1054 .IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
1056 .IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
1057 .IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
1059 Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR is
1060 \&\f(CW0.\fR, then it will automatically be stopped. If it is positive, then the
1061 timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds
1062 later, again, and again, until stopped manually.
1064 The timer itself will do a best-effort at avoiding drift, that is, if you
1065 configure a timer to trigger every 10 seconds, then it will trigger at
1066 exactly 10 second intervals. If, however, your program cannot keep up with
1067 the timer (because it takes longer than those 10 seconds to do stuff) the
1068 timer will not fire more than once per event loop iteration.
1069 .IP "ev_timer_again (loop)" 4
1070 .IX Item "ev_timer_again (loop)"
1071 This will act as if the timer timed out and restart it again if it is
1072 repeating. The exact semantics are:
1074 If the timer is started but nonrepeating, stop it.
1076 If the timer is repeating, either start it if necessary (with the repeat
1077 value), or reset the running timer to the repeat value.
1079 This sounds a bit complicated, but here is a useful and typical
1080 example: Imagine you have a tcp connection and you want a so-called
1081 idle timeout, that is, you want to be called when there have been,
1082 say, 60 seconds of inactivity on the socket. The easiest way to do
1083 this is to configure an \f(CW\*(C`ev_timer\*(C'\fR with \f(CW\*(C`after\*(C'\fR=\f(CW\*(C`repeat\*(C'\fR=\f(CW60\fR and calling
1084 \&\f(CW\*(C`ev_timer_again\*(C'\fR each time you successfully read or write some data. If
1085 you go into an idle state where you do not expect data to travel on the
1086 socket, you can stop the timer, and again will automatically restart it if
1089 You can also ignore the \f(CW\*(C`after\*(C'\fR value and \f(CW\*(C`ev_timer_start\*(C'\fR altogether
1090 and only ever use the \f(CW\*(C`repeat\*(C'\fR value:
1093 \& ev_timer_init (timer, callback, 0., 5.);
1094 \& ev_timer_again (loop, timer);
1096 \& timer->again = 17.;
1097 \& ev_timer_again (loop, timer);
1099 \& timer->again = 10.;
1100 \& ev_timer_again (loop, timer);
1103 This is more efficient then stopping/starting the timer eahc time you want
1104 to modify its timeout value.
1105 .IP "ev_tstamp repeat [read\-write]" 4
1106 .IX Item "ev_tstamp repeat [read-write]"
1107 The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out
1108 or \f(CW\*(C`ev_timer_again\*(C'\fR is called and determines the next timeout (if any),
1109 which is also when any modifications are taken into account.
1111 Example: Create a timer that fires after 60 seconds.
1115 \& one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
1117 \& .. one minute over, w is actually stopped right here
1122 \& struct ev_timer mytimer;
1123 \& ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1124 \& ev_timer_start (loop, &mytimer);
1127 Example: Create a timeout timer that times out after 10 seconds of
1132 \& timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
1134 \& .. ten seconds without any activity
1139 \& struct ev_timer mytimer;
1140 \& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1141 \& ev_timer_again (&mytimer); /* start timer */
1142 \& ev_loop (loop, 0);
1146 \& // and in some piece of code that gets executed on any "activity":
1147 \& // reset the timeout to start ticking again at 10 seconds
1148 \& ev_timer_again (&mytimer);
1150 .ie n .Sh """ev_periodic"" \- to cron or not to cron?"
1151 .el .Sh "\f(CWev_periodic\fP \- to cron or not to cron?"
1152 .IX Subsection "ev_periodic - to cron or not to cron?"
1153 Periodic watchers are also timers of a kind, but they are very versatile
1154 (and unfortunately a bit complex).
1156 Unlike \f(CW\*(C`ev_timer\*(C'\fR's, they are not based on real time (or relative time)
1157 but on wallclock time (absolute time). You can tell a periodic watcher
1158 to trigger \*(L"at\*(R" some specific point in time. For example, if you tell a
1159 periodic watcher to trigger in 10 seconds (by specifiying e.g. \f(CW\*(C`ev_now ()
1160 + 10.\*(C'\fR) and then reset your system clock to the last year, then it will
1161 take a year to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would trigger
1162 roughly 10 seconds later and of course not if you reset your system time
1165 They can also be used to implement vastly more complex timers, such as
1166 triggering an event on eahc midnight, local time.
1168 As with timers, the callback is guarenteed to be invoked only when the
1169 time (\f(CW\*(C`at\*(C'\fR) has been passed, but if multiple periodic timers become ready
1170 during the same loop iteration then order of execution is undefined.
1171 .IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 4
1172 .IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)"
1174 .IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4
1175 .IX Item "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)"
1177 Lots of arguments, lets sort it out... There are basically three modes of
1178 operation, and we will explain them from simplest to complex:
1180 .IP "* absolute timer (interval = reschedule_cb = 0)" 4
1181 .IX Item "absolute timer (interval = reschedule_cb = 0)"
1182 In this configuration the watcher triggers an event at the wallclock time
1183 \&\f(CW\*(C`at\*(C'\fR and doesn't repeat. It will not adjust when a time jump occurs,
1184 that is, if it is to be run at January 1st 2011 then it will run when the
1185 system time reaches or surpasses this time.
1186 .IP "* non-repeating interval timer (interval > 0, reschedule_cb = 0)" 4
1187 .IX Item "non-repeating interval timer (interval > 0, reschedule_cb = 0)"
1188 In this mode the watcher will always be scheduled to time out at the next
1189 \&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N) and then repeat, regardless
1192 This can be used to create timers that do not drift with respect to system
1196 \& ev_periodic_set (&periodic, 0., 3600., 0);
1199 This doesn't mean there will always be 3600 seconds in between triggers,
1200 but only that the the callback will be called when the system time shows a
1201 full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
1204 Another way to think about it (for the mathematically inclined) is that
1205 \&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
1206 time where \f(CW\*(C`time = at (mod interval)\*(C'\fR, regardless of any time jumps.
1207 .IP "* manual reschedule mode (reschedule_cb = callback)" 4
1208 .IX Item "manual reschedule mode (reschedule_cb = callback)"
1209 In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being
1210 ignored. Instead, each time the periodic watcher gets scheduled, the
1211 reschedule callback will be called with the watcher as first, and the
1212 current time as second argument.
1214 \&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher,
1215 ever, or make any event loop modifications\fR. If you need to stop it,
1216 return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop it afterwards (e.g. by
1217 starting a prepare watcher).
1219 Its prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
1220 ev_tstamp now)\*(C'\fR, e.g.:
1223 \& static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
1225 \& return now + 60.;
1229 It must return the next time to trigger, based on the passed time value
1230 (that is, the lowest time value larger than to the second argument). It
1231 will usually be called just before the callback will be triggered, but
1232 might be called at other times, too.
1234 \&\s-1NOTE:\s0 \fIThis callback must always return a time that is later than the
1235 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.
1237 This can be used to create very complex timers, such as a timer that
1238 triggers on each midnight, local time. To do this, you would calculate the
1239 next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How
1240 you do this is, again, up to you (but it is not trivial, which is the main
1241 reason I omitted it as an example).
1245 .IP "ev_periodic_again (loop, ev_periodic *)" 4
1246 .IX Item "ev_periodic_again (loop, ev_periodic *)"
1247 Simply stops and restarts the periodic watcher again. This is only useful
1248 when you changed some parameters or the reschedule callback would return
1249 a different time than the last time it was called (e.g. in a crond like
1250 program when the crontabs have changed).
1251 .IP "ev_tstamp interval [read\-write]" 4
1252 .IX Item "ev_tstamp interval [read-write]"
1253 The current interval value. Can be modified any time, but changes only
1254 take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being
1256 .IP "ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read\-write]" 4
1257 .IX Item "ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]"
1258 The current reschedule callback, or \f(CW0\fR, if this functionality is
1259 switched off. Can be changed any time, but changes only take effect when
1260 the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
1262 Example: Call a callback every hour, or, more precisely, whenever the
1263 system clock is divisible by 3600. The callback invocation times have
1264 potentially a lot of jittering, but good long-term stability.
1268 \& clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
1270 \& ... its now a full hour (UTC, or TAI or whatever your clock follows)
1275 \& struct ev_periodic hourly_tick;
1276 \& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1277 \& ev_periodic_start (loop, &hourly_tick);
1280 Example: The same as above, but use a reschedule callback to do it:
1283 \& #include <math.h>
1288 \& my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
1290 \& return fmod (now, 3600.) + 3600.;
1295 \& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1298 Example: Call a callback every hour, starting now:
1301 \& struct ev_periodic hourly_tick;
1302 \& ev_periodic_init (&hourly_tick, clock_cb,
1303 \& fmod (ev_now (loop), 3600.), 3600., 0);
1304 \& ev_periodic_start (loop, &hourly_tick);
1306 .ie n .Sh """ev_signal"" \- signal me when a signal gets signalled!"
1307 .el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled!"
1308 .IX Subsection "ev_signal - signal me when a signal gets signalled!"
1309 Signal watchers will trigger an event when the process receives a specific
1310 signal one or more times. Even though signals are very asynchronous, libev
1311 will try it's best to deliver signals synchronously, i.e. as part of the
1312 normal event processing, like any other event.
1314 You can configure as many watchers as you like per signal. Only when the
1315 first watcher gets started will libev actually register a signal watcher
1316 with the kernel (thus it coexists with your own signal handlers as long
1317 as you don't register any with libev). Similarly, when the last signal
1318 watcher for a signal is stopped libev will reset the signal handler to
1319 \&\s-1SIG_DFL\s0 (regardless of what it was set to before).
1320 .IP "ev_signal_init (ev_signal *, callback, int signum)" 4
1321 .IX Item "ev_signal_init (ev_signal *, callback, int signum)"
1323 .IP "ev_signal_set (ev_signal *, int signum)" 4
1324 .IX Item "ev_signal_set (ev_signal *, int signum)"
1326 Configures the watcher to trigger on the given signal number (usually one
1327 of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
1328 .IP "int signum [read\-only]" 4
1329 .IX Item "int signum [read-only]"
1330 The signal the watcher watches out for.
1331 .ie n .Sh """ev_child"" \- watch out for process status changes"
1332 .el .Sh "\f(CWev_child\fP \- watch out for process status changes"
1333 .IX Subsection "ev_child - watch out for process status changes"
1334 Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
1335 some child status changes (most typically when a child of yours dies).
1336 .IP "ev_child_init (ev_child *, callback, int pid)" 4
1337 .IX Item "ev_child_init (ev_child *, callback, int pid)"
1339 .IP "ev_child_set (ev_child *, int pid)" 4
1340 .IX Item "ev_child_set (ev_child *, int pid)"
1342 Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
1343 \&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
1344 at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
1345 the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
1346 \&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
1347 process causing the status change.
1348 .IP "int pid [read\-only]" 4
1349 .IX Item "int pid [read-only]"
1350 The process id this watcher watches out for, or \f(CW0\fR, meaning any process id.
1351 .IP "int rpid [read\-write]" 4
1352 .IX Item "int rpid [read-write]"
1353 The process id that detected a status change.
1354 .IP "int rstatus [read\-write]" 4
1355 .IX Item "int rstatus [read-write]"
1356 The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems
1357 \&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details).
1359 Example: Try to exit cleanly on \s-1SIGINT\s0 and \s-1SIGTERM\s0.
1363 \& sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
1365 \& ev_unloop (loop, EVUNLOOP_ALL);
1370 \& struct ev_signal signal_watcher;
1371 \& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1372 \& ev_signal_start (loop, &sigint_cb);
1374 .ie n .Sh """ev_stat"" \- did the file attributes just change?"
1375 .el .Sh "\f(CWev_stat\fP \- did the file attributes just change?"
1376 .IX Subsection "ev_stat - did the file attributes just change?"
1377 This watches a filesystem path for attribute changes. That is, it calls
1378 \&\f(CW\*(C`stat\*(C'\fR regularly (or when the \s-1OS\s0 says it changed) and sees if it changed
1379 compared to the last time, invoking the callback if it did.
1381 The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does
1382 not exist\*(R" is a status change like any other. The condition \*(L"path does
1383 not exist\*(R" is signified by the \f(CW\*(C`st_nlink\*(C'\fR field being zero (which is
1384 otherwise always forced to be at least one) and all the other fields of
1385 the stat buffer having unspecified contents.
1387 Since there is no standard to do this, the portable implementation simply
1388 calls \f(CW\*(C`stat (2)\*(C'\fR regulalry on the path to see if it changed somehow. You
1389 can specify a recommended polling interval for this case. If you specify
1390 a polling interval of \f(CW0\fR (highly recommended!) then a \fIsuitable,
1391 unspecified default\fR value will be used (which you can expect to be around
1392 five seconds, although this might change dynamically). Libev will also
1393 impose a minimum interval which is currently around \f(CW0.1\fR, but thats
1396 This watcher type is not meant for massive numbers of stat watchers,
1397 as even with OS-supported change notifications, this can be
1398 resource\-intensive.
1400 At the time of this writing, no specific \s-1OS\s0 backends are implemented, but
1401 if demand increases, at least a kqueue and inotify backend will be added.
1402 .IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4
1403 .IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)"
1405 .IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4
1406 .IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)"
1408 Configures the watcher to wait for status changes of the given
1409 \&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to
1410 be detected and should normally be specified as \f(CW0\fR to let libev choose
1411 a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same
1412 path for as long as the watcher is active.
1414 The callback will be receive \f(CW\*(C`EV_STAT\*(C'\fR when a change was detected,
1415 relative to the attributes at the time the watcher was started (or the
1416 last change was detected).
1417 .IP "ev_stat_stat (ev_stat *)" 4
1418 .IX Item "ev_stat_stat (ev_stat *)"
1419 Updates the stat buffer immediately with new values. If you change the
1420 watched path in your callback, you could call this fucntion to avoid
1421 detecting this change (while introducing a race condition). Can also be
1422 useful simply to find out the new values.
1423 .IP "ev_statdata attr [read\-only]" 4
1424 .IX Item "ev_statdata attr [read-only]"
1425 The most-recently detected attributes of the file. Although the type is of
1426 \&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types
1427 suitable for your system. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there
1428 was some error while \f(CW\*(C`stat\*(C'\fRing the file.
1429 .IP "ev_statdata prev [read\-only]" 4
1430 .IX Item "ev_statdata prev [read-only]"
1431 The previous attributes of the file. The callback gets invoked whenever
1432 \&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR.
1433 .IP "ev_tstamp interval [read\-only]" 4
1434 .IX Item "ev_tstamp interval [read-only]"
1435 The specified interval.
1436 .IP "const char *path [read\-only]" 4
1437 .IX Item "const char *path [read-only]"
1438 The filesystem path that is being watched.
1440 Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes.
1444 \& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1446 \& /* /etc/passwd changed in some way */
1447 \& if (w->attr.st_nlink)
1449 \& printf ("passwd current size %ld\en", (long)w->attr.st_size);
1450 \& printf ("passwd current atime %ld\en", (long)w->attr.st_mtime);
1451 \& printf ("passwd current mtime %ld\en", (long)w->attr.st_mtime);
1454 \& /* you shalt not abuse printf for puts */
1455 \& puts ("wow, /etc/passwd is not there, expect problems. "
1456 \& "if this is windows, they already arrived\en");
1466 \& ev_stat_init (&passwd, passwd_cb, "/etc/passwd");
1467 \& ev_stat_start (loop, &passwd);
1469 .ie n .Sh """ev_idle"" \- when you've got nothing better to do..."
1470 .el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do..."
1471 .IX Subsection "ev_idle - when you've got nothing better to do..."
1472 Idle watchers trigger events when there are no other events are pending
1473 (prepare, check and other idle watchers do not count). That is, as long
1474 as your process is busy handling sockets or timeouts (or even signals,
1475 imagine) it will not be triggered. But when your process is idle all idle
1476 watchers are being called again and again, once per event loop iteration \-
1477 until stopped, that is, or your process receives more events and becomes
1480 The most noteworthy effect is that as long as any idle watchers are
1481 active, the process will not block when waiting for new events.
1483 Apart from keeping your process non-blocking (which is a useful
1484 effect on its own sometimes), idle watchers are a good place to do
1485 \&\*(L"pseudo\-background processing\*(R", or delay processing stuff to after the
1486 event loop has handled all outstanding events.
1487 .IP "ev_idle_init (ev_signal *, callback)" 4
1488 .IX Item "ev_idle_init (ev_signal *, callback)"
1489 Initialises and configures the idle watcher \- it has no parameters of any
1490 kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
1493 Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the
1494 callback, free it. Also, use no error checking, as usual.
1498 \& idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
1501 \& // now do something you wanted to do when the program has
1502 \& // no longer asnything immediate to do.
1507 \& struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
1508 \& ev_idle_init (idle_watcher, idle_cb);
1509 \& ev_idle_start (loop, idle_cb);
1511 .ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop!"
1512 .el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!"
1513 .IX Subsection "ev_prepare and ev_check - customise your event loop!"
1514 Prepare and check watchers are usually (but not always) used in tandem:
1515 prepare watchers get invoked before the process blocks and check watchers
1518 You \fImust not\fR call \f(CW\*(C`ev_loop\*(C'\fR or similar functions that enter
1519 the current event loop from either \f(CW\*(C`ev_prepare\*(C'\fR or \f(CW\*(C`ev_check\*(C'\fR
1520 watchers. Other loops than the current one are fine, however. The
1521 rationale behind this is that you do not need to check for recursion in
1522 those watchers, i.e. the sequence will always be \f(CW\*(C`ev_prepare\*(C'\fR, blocking,
1523 \&\f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each kind they will always be
1524 called in pairs bracketing the blocking call.
1526 Their main purpose is to integrate other event mechanisms into libev and
1527 their use is somewhat advanced. This could be used, for example, to track
1528 variable changes, implement your own watchers, integrate net-snmp or a
1529 coroutine library and lots more. They are also occasionally useful if
1530 you cache some data and want to flush it before blocking (for example,
1531 in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR
1534 This is done by examining in each prepare call which file descriptors need
1535 to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers for
1536 them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many libraries
1537 provide just this functionality). Then, in the check watcher you check for
1538 any events that occured (by checking the pending status of all watchers
1539 and stopping them) and call back into the library. The I/O and timer
1540 callbacks will never actually be called (but must be valid nevertheless,
1541 because you never know, you know?).
1543 As another example, the Perl Coro module uses these hooks to integrate
1544 coroutines into libev programs, by yielding to other active coroutines
1545 during each prepare and only letting the process block if no coroutines
1546 are ready to run (it's actually more complicated: it only runs coroutines
1547 with priority higher than or equal to the event loop and one coroutine
1548 of lower priority, but only once, using idle watchers to keep the event
1549 loop from blocking if lower-priority coroutines are active, thus mapping
1550 low-priority coroutines to idle/background tasks).
1551 .IP "ev_prepare_init (ev_prepare *, callback)" 4
1552 .IX Item "ev_prepare_init (ev_prepare *, callback)"
1554 .IP "ev_check_init (ev_check *, callback)" 4
1555 .IX Item "ev_check_init (ev_check *, callback)"
1557 Initialises and configures the prepare or check watcher \- they have no
1558 parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
1559 macros, but using them is utterly, utterly and completely pointless.
1561 Example: To include a library such as adns, you would add \s-1IO\s0 watchers
1562 and a timeout watcher in a prepare handler, as required by libadns, and
1563 in a check watcher, destroy them and call into libadns. What follows is
1564 pseudo-code only of course:
1567 \& static ev_io iow [nfd];
1568 \& static ev_timer tw;
1573 \& io_cb (ev_loop *loop, ev_io *w, int revents)
1575 \& // set the relevant poll flags
1576 \& // could also call adns_processreadable etc. here
1577 \& struct pollfd *fd = (struct pollfd *)w->data;
1578 \& if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1579 \& if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1584 \& // create io watchers for each fd and a timer before blocking
1586 \& adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
1588 \& int timeout = 3600000;truct pollfd fds [nfd];
1589 \& // actual code will need to loop here and realloc etc.
1590 \& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1594 \& /* the callback is illegal, but won't be called as we stop during check */
1595 \& ev_timer_init (&tw, 0, timeout * 1e-3);
1596 \& ev_timer_start (loop, &tw);
1600 \& // create on ev_io per pollfd
1601 \& for (int i = 0; i < nfd; ++i)
1603 \& ev_io_init (iow + i, io_cb, fds [i].fd,
1604 \& ((fds [i].events & POLLIN ? EV_READ : 0)
1605 \& | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1609 \& fds [i].revents = 0;
1610 \& iow [i].data = fds + i;
1611 \& ev_io_start (loop, iow + i);
1617 \& // stop all watchers after blocking
1619 \& adns_check_cb (ev_loop *loop, ev_check *w, int revents)
1621 \& ev_timer_stop (loop, &tw);
1625 \& for (int i = 0; i < nfd; ++i)
1626 \& ev_io_stop (loop, iow + i);
1630 \& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1633 .ie n .Sh """ev_embed"" \- when one backend isn't enough..."
1634 .el .Sh "\f(CWev_embed\fP \- when one backend isn't enough..."
1635 .IX Subsection "ev_embed - when one backend isn't enough..."
1636 This is a rather advanced watcher type that lets you embed one event loop
1637 into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded
1638 loop, other types of watchers might be handled in a delayed or incorrect
1639 fashion and must not be used).
1641 There are primarily two reasons you would want that: work around bugs and
1644 As an example for a bug workaround, the kqueue backend might only support
1645 sockets on some platform, so it is unusable as generic backend, but you
1646 still want to make use of it because you have many sockets and it scales
1647 so nicely. In this case, you would create a kqueue-based loop and embed it
1648 into your default loop (which might use e.g. poll). Overall operation will
1649 be a bit slower because first libev has to poll and then call kevent, but
1650 at least you can use both at what they are best.
1652 As for prioritising I/O: rarely you have the case where some fds have
1653 to be watched and handled very quickly (with low latency), and even
1654 priorities and idle watchers might have too much overhead. In this case
1655 you would put all the high priority stuff in one loop and all the rest in
1656 a second one, and embed the second one in the first.
1658 As long as the watcher is active, the callback will be invoked every time
1659 there might be events pending in the embedded loop. The callback must then
1660 call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single sweep and invoke
1661 their callbacks (you could also start an idle watcher to give the embedded
1662 loop strictly lower priority for example). You can also set the callback
1663 to \f(CW0\fR, in which case the embed watcher will automatically execute the
1664 embedded loop sweep.
1666 As long as the watcher is started it will automatically handle events. The
1667 callback will be invoked whenever some events have been handled. You can
1668 set the callback to \f(CW0\fR to avoid having to specify one if you are not
1671 Also, there have not currently been made special provisions for forking:
1672 when you fork, you not only have to call \f(CW\*(C`ev_loop_fork\*(C'\fR on both loops,
1673 but you will also have to stop and restart any \f(CW\*(C`ev_embed\*(C'\fR watchers
1676 Unfortunately, not all backends are embeddable, only the ones returned by
1677 \&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any
1680 So when you want to use this feature you will always have to be prepared
1681 that you cannot get an embeddable loop. The recommended way to get around
1682 this is to have a separate variables for your embeddable loop, try to
1683 create it, and if that fails, use the normal loop for everything:
1686 \& struct ev_loop *loop_hi = ev_default_init (0);
1687 \& struct ev_loop *loop_lo = 0;
1688 \& struct ev_embed embed;
1692 \& // see if there is a chance of getting one that works
1693 \& // (remember that a flags value of 0 means autodetection)
1694 \& loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1695 \& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1700 \& // if we got one, then embed it, otherwise default to loop_hi
1703 \& ev_embed_init (&embed, 0, loop_lo);
1704 \& ev_embed_start (loop_hi, &embed);
1707 \& loop_lo = loop_hi;
1709 .IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
1710 .IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)"
1712 .IP "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
1713 .IX Item "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)"
1715 Configures the watcher to embed the given loop, which must be
1716 embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be
1717 invoked automatically, otherwise it is the responsibility of the callback
1718 to invoke it (it will continue to be called until the sweep has been done,
1719 if you do not want thta, you need to temporarily stop the embed watcher).
1720 .IP "ev_embed_sweep (loop, ev_embed *)" 4
1721 .IX Item "ev_embed_sweep (loop, ev_embed *)"
1722 Make a single, non-blocking sweep over the embedded loop. This works
1723 similarly to \f(CW\*(C`ev_loop (embedded_loop, EVLOOP_NONBLOCK)\*(C'\fR, but in the most
1724 apropriate way for embedded loops.
1725 .IP "struct ev_loop *loop [read\-only]" 4
1726 .IX Item "struct ev_loop *loop [read-only]"
1727 The embedded event loop.
1728 .ie n .Sh """ev_fork"" \- the audacity to resume the event loop after a fork"
1729 .el .Sh "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork"
1730 .IX Subsection "ev_fork - the audacity to resume the event loop after a fork"
1731 Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because
1732 whoever is a good citizen cared to tell libev about it by calling
1733 \&\f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the
1734 event loop blocks next and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called,
1735 and only in the child after the fork. If whoever good citizen calling
1736 \&\f(CW\*(C`ev_default_fork\*(C'\fR cheats and calls it in the wrong process, the fork
1737 handlers will be invoked, too, of course.
1738 .IP "ev_fork_init (ev_signal *, callback)" 4
1739 .IX Item "ev_fork_init (ev_signal *, callback)"
1740 Initialises and configures the fork watcher \- it has no parameters of any
1741 kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless,
1743 .SH "OTHER FUNCTIONS"
1744 .IX Header "OTHER FUNCTIONS"
1745 There are some other functions of possible interest. Described. Here. Now.
1746 .IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4
1747 .IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)"
1748 This function combines a simple timer and an I/O watcher, calls your
1749 callback on whichever event happens first and automatically stop both
1750 watchers. This is useful if you want to wait for a single event on an fd
1751 or timeout without having to allocate/configure/start/stop/free one or
1752 more watchers yourself.
1754 If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and events
1755 is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for the given \f(CW\*(C`fd\*(C'\fR and
1756 \&\f(CW\*(C`events\*(C'\fR set will be craeted and started.
1758 If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be
1759 started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and
1760 repeat = 0) will be started. While \f(CW0\fR is a valid timeout, it is of
1763 The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and gets
1764 passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of
1765 \&\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
1766 value passed to \f(CW\*(C`ev_once\*(C'\fR:
1769 \& static void stdin_ready (int revents, void *arg)
1771 \& if (revents & EV_TIMEOUT)
1772 \& /* doh, nothing entered */;
1773 \& else if (revents & EV_READ)
1774 \& /* stdin might have data for us, joy! */;
1779 \& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1781 .IP "ev_feed_event (ev_loop *, watcher *, int revents)" 4
1782 .IX Item "ev_feed_event (ev_loop *, watcher *, int revents)"
1783 Feeds the given event set into the event loop, as if the specified event
1784 had happened for the specified watcher (which must be a pointer to an
1785 initialised but not necessarily started event watcher).
1786 .IP "ev_feed_fd_event (ev_loop *, int fd, int revents)" 4
1787 .IX Item "ev_feed_fd_event (ev_loop *, int fd, int revents)"
1788 Feed an event on the given fd, as if a file descriptor backend detected
1789 the given events it.
1790 .IP "ev_feed_signal_event (ev_loop *loop, int signum)" 4
1791 .IX Item "ev_feed_signal_event (ev_loop *loop, int signum)"
1792 Feed an event as if the given signal occured (\f(CW\*(C`loop\*(C'\fR must be the default
1794 .SH "LIBEVENT EMULATION"
1795 .IX Header "LIBEVENT EMULATION"
1796 Libev offers a compatibility emulation layer for libevent. It cannot
1797 emulate the internals of libevent, so here are some usage hints:
1798 .IP "* Use it by including <event.h>, as usual." 4
1799 .IX Item "Use it by including <event.h>, as usual."
1801 .IP "* The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4
1802 .IX Item "The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events."
1803 .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
1804 .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)."
1805 .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
1806 .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."
1807 .IP "* Other members are not supported." 4
1808 .IX Item "Other members are not supported."
1809 .IP "* The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need to use the libev header file and library." 4
1810 .IX Item "The libev emulation is not ABI compatible to libevent, you need to use the libev header file and library."
1813 .IX Header " SUPPORT"
1814 Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow
1815 you to use some convinience methods to start/stop watchers and also change
1816 the callback model to a model using method callbacks on objects.
1821 \& #include <ev++.h>
1824 (it is not installed by default). This automatically includes \fIev.h\fR
1825 and puts all of its definitions (many of them macros) into the global
1826 namespace. All \*(C+ specific things are put into the \f(CW\*(C`ev\*(C'\fR namespace.
1828 It should support all the same embedding options as \fIev.h\fR, most notably
1829 \&\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR.
1831 Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace:
1832 .ie n .IP """ev::READ""\fR, \f(CW""ev::WRITE"" etc." 4
1833 .el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4
1834 .IX Item "ev::READ, ev::WRITE etc."
1835 These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc.
1836 macros from \fIev.h\fR.
1837 .ie n .IP """ev::tstamp""\fR, \f(CW""ev::now""" 4
1838 .el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4
1839 .IX Item "ev::tstamp, ev::now"
1840 Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix.
1841 .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
1842 .el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4
1843 .IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc."
1844 For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of
1845 the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR
1846 which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro
1847 defines by many implementations.
1849 All of those classes have these methods:
1851 .IP "ev::TYPE::TYPE (object *, object::method *)" 4
1852 .IX Item "ev::TYPE::TYPE (object *, object::method *)"
1854 .IP "ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)" 4
1855 .IX Item "ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)"
1856 .IP "ev::TYPE::~TYPE" 4
1857 .IX Item "ev::TYPE::~TYPE"
1859 The constructor takes a pointer to an object and a method pointer to
1860 the event handler callback to call in this class. The constructor calls
1861 \&\f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the \f(CW\*(C`set\*(C'\fR method
1862 before starting it. If you do not specify a loop then the constructor
1863 automatically associates the default loop with this watcher.
1865 The destructor automatically stops the watcher if it is active.
1866 .IP "w\->set (struct ev_loop *)" 4
1867 .IX Item "w->set (struct ev_loop *)"
1868 Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only
1869 do this when the watcher is inactive (and not pending either).
1870 .IP "w\->set ([args])" 4
1871 .IX Item "w->set ([args])"
1872 Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR, with the same args. Must be
1873 called at least once. Unlike the C counterpart, an active watcher gets
1874 automatically stopped and restarted.
1875 .IP "w\->start ()" 4
1876 .IX Item "w->start ()"
1877 Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument as the
1878 constructor already takes the loop.
1880 .IX Item "w->stop ()"
1881 Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument.
1882 .ie n .IP "w\->again () ""ev::timer""\fR, \f(CW""ev::periodic"" only" 4
1883 .el .IP "w\->again () \f(CWev::timer\fR, \f(CWev::periodic\fR only" 4
1884 .IX Item "w->again () ev::timer, ev::periodic only"
1885 For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding
1886 \&\f(CW\*(C`ev_TYPE_again\*(C'\fR function.
1887 .ie n .IP "w\->sweep () ""ev::embed"" only" 4
1888 .el .IP "w\->sweep () \f(CWev::embed\fR only" 4
1889 .IX Item "w->sweep () ev::embed only"
1890 Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR.
1891 .ie n .IP "w\->update () ""ev::stat"" only" 4
1892 .el .IP "w\->update () \f(CWev::stat\fR only" 4
1893 .IX Item "w->update () ev::stat only"
1894 Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR.
1899 Example: Define a class with an \s-1IO\s0 and idle watcher, start one of them in
1905 \& ev_io io; void io_cb (ev::io &w, int revents);
1906 \& ev_idle idle void idle_cb (ev::idle &w, int revents);
1915 \& myclass::myclass (int fd)
1916 \& : io (this, &myclass::io_cb),
1917 \& idle (this, &myclass::idle_cb)
1919 \& io.start (fd, ev::READ);
1923 .IX Header "MACRO MAGIC"
1924 Libev can be compiled with a variety of options, the most fundemantal is
1925 \&\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines wether (most) functions and
1926 callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument.
1928 To make it easier to write programs that cope with either variant, the
1929 following macros are defined:
1930 .ie n .IP """EV_A""\fR, \f(CW""EV_A_""" 4
1931 .el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4
1932 .IX Item "EV_A, EV_A_"
1933 This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev
1934 loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument,
1935 \&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example:
1939 \& ev_timer_add (EV_A_ watcher);
1940 \& ev_loop (EV_A_ 0);
1943 It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope,
1944 which is often provided by the following macro.
1945 .ie n .IP """EV_P""\fR, \f(CW""EV_P_""" 4
1946 .el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4
1947 .IX Item "EV_P, EV_P_"
1948 This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev
1949 loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter,
1950 \&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example:
1953 \& // this is how ev_unref is being declared
1954 \& static void ev_unref (EV_P);
1958 \& // this is how you can declare your typical callback
1959 \& static void cb (EV_P_ ev_timer *w, int revents)
1962 It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite
1963 suitable for use with \f(CW\*(C`EV_A\*(C'\fR.
1964 .ie n .IP """EV_DEFAULT""\fR, \f(CW""EV_DEFAULT_""" 4
1965 .el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4
1966 .IX Item "EV_DEFAULT, EV_DEFAULT_"
1967 Similar to the other two macros, this gives you the value of the default
1968 loop, if multiple loops are supported (\*(L"ev loop default\*(R").
1970 Example: Declare and initialise a check watcher, working regardless of
1971 wether multiple loops are supported or not.
1975 \& check_cb (EV_P_ ev_timer *w, int revents)
1977 \& ev_check_stop (EV_A_ w);
1983 \& ev_check_init (&check, check_cb);
1984 \& ev_check_start (EV_DEFAULT_ &check);
1985 \& ev_loop (EV_DEFAULT_ 0);
1988 .IX Header "EMBEDDING"
1989 Libev can (and often is) directly embedded into host
1990 applications. Examples of applications that embed it include the Deliantra
1991 Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe)
1994 The goal is to enable you to just copy the neecssary files into your
1995 source directory without having to change even a single line in them, so
1996 you can easily upgrade by simply copying (or having a checked-out copy of
1997 libev somewhere in your source tree).
1998 .Sh "\s-1FILESETS\s0"
1999 .IX Subsection "FILESETS"
2000 Depending on what features you need you need to include one or more sets of files
2003 \fI\s-1CORE\s0 \s-1EVENT\s0 \s-1LOOP\s0\fR
2004 .IX Subsection "CORE EVENT LOOP"
2006 To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual
2007 configuration (no autoconf):
2010 \& #define EV_STANDALONE 1
2014 This will automatically include \fIev.h\fR, too, and should be done in a
2015 single C source file only to provide the function implementations. To use
2016 it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best
2017 done by writing a wrapper around \fIev.h\fR that you can include instead and
2018 where you can put other configuration options):
2021 \& #define EV_STANDALONE 1
2025 Both header files and implementation files can be compiled with a \*(C+
2026 compiler (at least, thats a stated goal, and breakage will be treated
2029 You need the following files in your source tree, or in a directory
2030 in your include path (e.g. in libev/ when using \-Ilibev):
2040 \& ev_win32.c required on win32 platforms only
2044 \& ev_select.c only when select backend is enabled (which is by default)
2045 \& ev_poll.c only when poll backend is enabled (disabled by default)
2046 \& ev_epoll.c only when the epoll backend is enabled (disabled by default)
2047 \& ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2048 \& ev_port.c only when the solaris port backend is enabled (disabled by default)
2051 \&\fIev.c\fR includes the backend files directly when enabled, so you only need
2052 to compile this single file.
2054 \fI\s-1LIBEVENT\s0 \s-1COMPATIBILITY\s0 \s-1API\s0\fR
2055 .IX Subsection "LIBEVENT COMPATIBILITY API"
2057 To include the libevent compatibility \s-1API\s0, also include:
2060 \& #include "event.c"
2063 in the file including \fIev.c\fR, and:
2066 \& #include "event.h"
2069 in the files that want to use the libevent \s-1API\s0. This also includes \fIev.h\fR.
2071 You need the following additional files for this:
2078 \fI\s-1AUTOCONF\s0 \s-1SUPPORT\s0\fR
2079 .IX Subsection "AUTOCONF SUPPORT"
2081 Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your config in
2082 whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your
2083 \&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then
2084 include \fIconfig.h\fR and configure itself accordingly.
2086 For this of course you need the m4 file:
2091 .Sh "\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0"
2092 .IX Subsection "PREPROCESSOR SYMBOLS/MACROS"
2093 Libev can be configured via a variety of preprocessor symbols you have to define
2094 before including any of its files. The default is not to build for multiplicity
2095 and only include the select backend.
2096 .IP "\s-1EV_STANDALONE\s0" 4
2097 .IX Item "EV_STANDALONE"
2098 Must always be \f(CW1\fR if you do not use autoconf configuration, which
2099 keeps libev from including \fIconfig.h\fR, and it also defines dummy
2100 implementations for some libevent functions (such as logging, which is not
2101 supported). It will also not define any of the structs usually found in
2102 \&\fIevent.h\fR that are not directly supported by the libev core alone.
2103 .IP "\s-1EV_USE_MONOTONIC\s0" 4
2104 .IX Item "EV_USE_MONOTONIC"
2105 If defined to be \f(CW1\fR, libev will try to detect the availability of the
2106 monotonic clock option at both compiletime and runtime. Otherwise no use
2107 of the monotonic clock option will be attempted. If you enable this, you
2108 usually have to link against librt or something similar. Enabling it when
2109 the functionality isn't available is safe, though, althoguh you have
2110 to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR
2111 function is hiding in (often \fI\-lrt\fR).
2112 .IP "\s-1EV_USE_REALTIME\s0" 4
2113 .IX Item "EV_USE_REALTIME"
2114 If defined to be \f(CW1\fR, libev will try to detect the availability of the
2115 realtime clock option at compiletime (and assume its availability at
2116 runtime if successful). Otherwise no use of the realtime clock option will
2117 be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR by \f(CW\*(C`clock_get
2118 (CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect correctness. See tzhe note about libraries
2119 in the description of \f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though.
2120 .IP "\s-1EV_USE_SELECT\s0" 4
2121 .IX Item "EV_USE_SELECT"
2122 If undefined or defined to be \f(CW1\fR, libev will compile in support for the
2123 \&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at autodetection will be done: if no
2124 other method takes over, select will be it. Otherwise the select backend
2125 will not be compiled in.
2126 .IP "\s-1EV_SELECT_USE_FD_SET\s0" 4
2127 .IX Item "EV_SELECT_USE_FD_SET"
2128 If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR
2129 structure. This is useful if libev doesn't compile due to a missing
2130 \&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it misguesses the bitset layout on
2131 exotic systems. This usually limits the range of file descriptors to some
2132 low limit such as 1024 or might have other limitations (winsocket only
2133 allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation, might
2134 influence the size of the \f(CW\*(C`fd_set\*(C'\fR used.
2135 .IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4
2136 .IX Item "EV_SELECT_IS_WINSOCKET"
2137 When defined to \f(CW1\fR, the select backend will assume that
2138 select/socket/connect etc. don't understand file descriptors but
2139 wants osf handles on win32 (this is the case when the select to
2140 be used is the winsock select). This means that it will call
2141 \&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise,
2142 it is assumed that all these functions actually work on fds, even
2143 on win32. Should not be defined on non\-win32 platforms.
2144 .IP "\s-1EV_USE_POLL\s0" 4
2145 .IX Item "EV_USE_POLL"
2146 If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2)
2147 backend. Otherwise it will be enabled on non\-win32 platforms. It
2148 takes precedence over select.
2149 .IP "\s-1EV_USE_EPOLL\s0" 4
2150 .IX Item "EV_USE_EPOLL"
2151 If defined to be \f(CW1\fR, libev will compile in support for the Linux
2152 \&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime,
2153 otherwise another method will be used as fallback. This is the
2154 preferred backend for GNU/Linux systems.
2155 .IP "\s-1EV_USE_KQUEUE\s0" 4
2156 .IX Item "EV_USE_KQUEUE"
2157 If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style
2158 \&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime,
2159 otherwise another method will be used as fallback. This is the preferred
2160 backend for \s-1BSD\s0 and BSD-like systems, although on most BSDs kqueue only
2161 supports some types of fds correctly (the only platform we found that
2162 supports ptys for example was NetBSD), so kqueue might be compiled in, but
2163 not be used unless explicitly requested. The best way to use it is to find
2164 out whether kqueue supports your type of fd properly and use an embedded
2166 .IP "\s-1EV_USE_PORT\s0" 4
2167 .IX Item "EV_USE_PORT"
2168 If defined to be \f(CW1\fR, libev will compile in support for the Solaris
2169 10 port style backend. Its availability will be detected at runtime,
2170 otherwise another method will be used as fallback. This is the preferred
2171 backend for Solaris 10 systems.
2172 .IP "\s-1EV_USE_DEVPOLL\s0" 4
2173 .IX Item "EV_USE_DEVPOLL"
2174 reserved for future expansion, works like the \s-1USE\s0 symbols above.
2177 The name of the \fIev.h\fR header file used to include it. The default if
2178 undefined is \f(CW\*(C`<ev.h>\*(C'\fR in \fIevent.h\fR and \f(CW"ev.h"\fR in \fIev.c\fR. This
2179 can be used to virtually rename the \fIev.h\fR header file in case of conflicts.
2180 .IP "\s-1EV_CONFIG_H\s0" 4
2181 .IX Item "EV_CONFIG_H"
2182 If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override
2183 \&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to
2184 \&\f(CW\*(C`EV_H\*(C'\fR, above.
2185 .IP "\s-1EV_EVENT_H\s0" 4
2186 .IX Item "EV_EVENT_H"
2187 Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea
2188 of how the \fIevent.h\fR header can be found.
2189 .IP "\s-1EV_PROTOTYPES\s0" 4
2190 .IX Item "EV_PROTOTYPES"
2191 If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function
2192 prototypes, but still define all the structs and other symbols. This is
2193 occasionally useful if you want to provide your own wrapper functions
2194 around libev functions.
2195 .IP "\s-1EV_MULTIPLICITY\s0" 4
2196 .IX Item "EV_MULTIPLICITY"
2197 If undefined or defined to \f(CW1\fR, then all event-loop-specific functions
2198 will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create
2199 additional independent event loops. Otherwise there will be no support
2200 for multiple event loops and there is no first event loop pointer
2201 argument. Instead, all functions act on the single default loop.
2202 .IP "\s-1EV_PERIODIC_ENABLE\s0" 4
2203 .IX Item "EV_PERIODIC_ENABLE"
2204 If undefined or defined to be \f(CW1\fR, then periodic timers are supported. If
2205 defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of
2207 .IP "\s-1EV_EMBED_ENABLE\s0" 4
2208 .IX Item "EV_EMBED_ENABLE"
2209 If undefined or defined to be \f(CW1\fR, then embed watchers are supported. If
2210 defined to be \f(CW0\fR, then they are not.
2211 .IP "\s-1EV_STAT_ENABLE\s0" 4
2212 .IX Item "EV_STAT_ENABLE"
2213 If undefined or defined to be \f(CW1\fR, then stat watchers are supported. If
2214 defined to be \f(CW0\fR, then they are not.
2215 .IP "\s-1EV_FORK_ENABLE\s0" 4
2216 .IX Item "EV_FORK_ENABLE"
2217 If undefined or defined to be \f(CW1\fR, then fork watchers are supported. If
2218 defined to be \f(CW0\fR, then they are not.
2219 .IP "\s-1EV_MINIMAL\s0" 4
2220 .IX Item "EV_MINIMAL"
2221 If you need to shave off some kilobytes of code at the expense of some
2222 speed, define this symbol to \f(CW1\fR. Currently only used for gcc to override
2223 some inlining decisions, saves roughly 30% codesize of amd64.
2224 .IP "\s-1EV_PID_HASHSIZE\s0" 4
2225 .IX Item "EV_PID_HASHSIZE"
2226 \&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by
2227 pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR), usually more
2228 than enough. If you need to manage thousands of children you might want to
2229 increase this value.
2230 .IP "\s-1EV_COMMON\s0" 4
2231 .IX Item "EV_COMMON"
2232 By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining
2233 this macro to a something else you can include more and other types of
2234 members. You have to define it each time you include one of the files,
2235 though, and it must be identical each time.
2237 For example, the perl \s-1EV\s0 module uses something like this:
2240 \& #define EV_COMMON \e
2241 \& SV *self; /* contains this struct */ \e
2242 \& SV *cb_sv, *fh /* note no trailing ";" */
2244 .IP "\s-1EV_CB_DECLARE\s0 (type)" 4
2245 .IX Item "EV_CB_DECLARE (type)"
2247 .IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4
2248 .IX Item "EV_CB_INVOKE (watcher, revents)"
2249 .IP "ev_set_cb (ev, cb)" 4
2250 .IX Item "ev_set_cb (ev, cb)"
2252 Can be used to change the callback member declaration in each watcher,
2253 and the way callbacks are invoked and set. Must expand to a struct member
2254 definition and a statement, respectively. See the \fIev.v\fR header file for
2255 their default definitions. One possible use for overriding these is to
2256 avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use
2257 method calls instead of plain function calls in \*(C+.
2258 .Sh "\s-1EXAMPLES\s0"
2259 .IX Subsection "EXAMPLES"
2260 For a real-world example of a program the includes libev
2261 verbatim, you can have a look at the \s-1EV\s0 perl module
2262 (<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
2263 the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public
2264 interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file
2265 will be compiled. It is pretty complex because it provides its own header
2268 The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file
2269 that everybody includes and which overrides some autoconf choices:
2272 \& #define EV_USE_POLL 0
2273 \& #define EV_MULTIPLICITY 0
2274 \& #define EV_PERIODICS 0
2275 \& #define EV_CONFIG_H <config.h>
2279 \& #include "ev++.h"
2282 And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled:
2285 \& #include "ev_cpp.h"
2289 .IX Header "COMPLEXITIES"
2290 In this section the complexities of (many of) the algorithms used inside
2291 libev will be explained. For complexity discussions about backends see the
2292 documentation for \f(CW\*(C`ev_default_init\*(C'\fR.
2294 .IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4
2295 .IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)"
2297 .IP "Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)" 4
2298 .IX Item "Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)"
2299 .IP "Starting io/check/prepare/idle/signal/child watchers: O(1)" 4
2300 .IX Item "Starting io/check/prepare/idle/signal/child watchers: O(1)"
2301 .IP "Stopping check/prepare/idle watchers: O(1)" 4
2302 .IX Item "Stopping check/prepare/idle watchers: O(1)"
2303 .IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % 16))" 4
2304 .IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % 16))"
2305 .IP "Finding the next timer per loop iteration: O(1)" 4
2306 .IX Item "Finding the next timer per loop iteration: O(1)"
2307 .IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4
2308 .IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)"
2309 .IP "Activating one watcher: O(1)" 4
2310 .IX Item "Activating one watcher: O(1)"
2316 Marc Lehmann <libev@schmorp.de>.
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