3 libev - a high performance full-featured event loop written in C
14 ev_timer timeout_watcher;
16 /* called when data readable on stdin */
18 stdin_cb (EV_P_ struct ev_io *w, int revents)
20 /* puts ("stdin ready"); */
21 ev_io_stop (EV_A_ w); /* just a syntax example */
22 ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */
26 timeout_cb (EV_P_ struct ev_timer *w, int revents)
28 /* puts ("timeout"); */
29 ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */
35 struct ev_loop *loop = ev_default_loop (0);
37 /* initialise an io watcher, then start it */
38 ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
39 ev_io_start (loop, &stdin_watcher);
41 /* simple non-repeating 5.5 second timeout */
42 ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
43 ev_timer_start (loop, &timeout_watcher);
45 /* loop till timeout or data ready */
53 The newest version of this document is also available as a html-formatted
54 web page you might find easier to navigate when reading it for the first
55 time: L<http://cvs.schmorp.de/libev/ev.html>.
57 Libev is an event loop: you register interest in certain events (such as a
58 file descriptor being readable or a timeout occuring), and it will manage
59 these event sources and provide your program with events.
61 To do this, it must take more or less complete control over your process
62 (or thread) by executing the I<event loop> handler, and will then
63 communicate events via a callback mechanism.
65 You register interest in certain events by registering so-called I<event
66 watchers>, which are relatively small C structures you initialise with the
67 details of the event, and then hand it over to libev by I<starting> the
72 Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
73 BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
74 for file descriptor events (C<ev_io>), the Linux C<inotify> interface
75 (for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
76 with customised rescheduling (C<ev_periodic>), synchronous signals
77 (C<ev_signal>), process status change events (C<ev_child>), and event
78 watchers dealing with the event loop mechanism itself (C<ev_idle>,
79 C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as
80 file watchers (C<ev_stat>) and even limited support for fork events
83 It also is quite fast (see this
84 L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
89 Libev is very configurable. In this manual the default configuration will
90 be described, which supports multiple event loops. For more info about
91 various configuration options please have a look at B<EMBED> section in
92 this manual. If libev was configured without support for multiple event
93 loops, then all functions taking an initial argument of name C<loop>
94 (which is always of type C<struct ev_loop *>) will not have this argument.
96 =head1 TIME REPRESENTATION
98 Libev represents time as a single floating point number, representing the
99 (fractional) number of seconds since the (POSIX) epoch (somewhere near
100 the beginning of 1970, details are complicated, don't ask). This type is
101 called C<ev_tstamp>, which is what you should use too. It usually aliases
102 to the C<double> type in C, and when you need to do any calculations on
103 it, you should treat it as some floatingpoint value. Unlike the name
104 component C<stamp> might indicate, it is also used for time differences
107 =head1 GLOBAL FUNCTIONS
109 These functions can be called anytime, even before initialising the
114 =item ev_tstamp ev_time ()
116 Returns the current time as libev would use it. Please note that the
117 C<ev_now> function is usually faster and also often returns the timestamp
118 you actually want to know.
120 =item int ev_version_major ()
122 =item int ev_version_minor ()
124 You can find out the major and minor ABI version numbers of the library
125 you linked against by calling the functions C<ev_version_major> and
126 C<ev_version_minor>. If you want, you can compare against the global
127 symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
128 version of the library your program was compiled against.
130 These version numbers refer to the ABI version of the library, not the
133 Usually, it's a good idea to terminate if the major versions mismatch,
134 as this indicates an incompatible change. Minor versions are usually
135 compatible to older versions, so a larger minor version alone is usually
138 Example: Make sure we haven't accidentally been linked against the wrong
141 assert (("libev version mismatch",
142 ev_version_major () == EV_VERSION_MAJOR
143 && ev_version_minor () >= EV_VERSION_MINOR));
145 =item unsigned int ev_supported_backends ()
147 Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
148 value) compiled into this binary of libev (independent of their
149 availability on the system you are running on). See C<ev_default_loop> for
150 a description of the set values.
152 Example: make sure we have the epoll method, because yeah this is cool and
153 a must have and can we have a torrent of it please!!!11
155 assert (("sorry, no epoll, no sex",
156 ev_supported_backends () & EVBACKEND_EPOLL));
158 =item unsigned int ev_recommended_backends ()
160 Return the set of all backends compiled into this binary of libev and also
161 recommended for this platform. This set is often smaller than the one
162 returned by C<ev_supported_backends>, as for example kqueue is broken on
163 most BSDs and will not be autodetected unless you explicitly request it
164 (assuming you know what you are doing). This is the set of backends that
165 libev will probe for if you specify no backends explicitly.
167 =item unsigned int ev_embeddable_backends ()
169 Returns the set of backends that are embeddable in other event loops. This
170 is the theoretical, all-platform, value. To find which backends
171 might be supported on the current system, you would need to look at
172 C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
175 See the description of C<ev_embed> watchers for more info.
177 =item ev_set_allocator (void *(*cb)(void *ptr, long size))
179 Sets the allocation function to use (the prototype is similar - the
180 semantics is identical - to the realloc C function). It is used to
181 allocate and free memory (no surprises here). If it returns zero when
182 memory needs to be allocated, the library might abort or take some
183 potentially destructive action. The default is your system realloc
186 You could override this function in high-availability programs to, say,
187 free some memory if it cannot allocate memory, to use a special allocator,
188 or even to sleep a while and retry until some memory is available.
190 Example: Replace the libev allocator with one that waits a bit and then
194 persistent_realloc (void *ptr, size_t size)
198 void *newptr = realloc (ptr, size);
208 ev_set_allocator (persistent_realloc);
210 =item ev_set_syserr_cb (void (*cb)(const char *msg));
212 Set the callback function to call on a retryable syscall error (such
213 as failed select, poll, epoll_wait). The message is a printable string
214 indicating the system call or subsystem causing the problem. If this
215 callback is set, then libev will expect it to remedy the sitution, no
216 matter what, when it returns. That is, libev will generally retry the
217 requested operation, or, if the condition doesn't go away, do bad stuff
220 Example: This is basically the same thing that libev does internally, too.
223 fatal_error (const char *msg)
230 ev_set_syserr_cb (fatal_error);
234 =head1 FUNCTIONS CONTROLLING THE EVENT LOOP
236 An event loop is described by a C<struct ev_loop *>. The library knows two
237 types of such loops, the I<default> loop, which supports signals and child
238 events, and dynamically created loops which do not.
240 If you use threads, a common model is to run the default event loop
241 in your main thread (or in a separate thread) and for each thread you
242 create, you also create another event loop. Libev itself does no locking
243 whatsoever, so if you mix calls to the same event loop in different
244 threads, make sure you lock (this is usually a bad idea, though, even if
245 done correctly, because it's hideous and inefficient).
249 =item struct ev_loop *ev_default_loop (unsigned int flags)
251 This will initialise the default event loop if it hasn't been initialised
252 yet and return it. If the default loop could not be initialised, returns
253 false. If it already was initialised it simply returns it (and ignores the
254 flags. If that is troubling you, check C<ev_backend ()> afterwards).
256 If you don't know what event loop to use, use the one returned from this
259 The flags argument can be used to specify special behaviour or specific
260 backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
262 The following flags are supported:
268 The default flags value. Use this if you have no clue (it's the right
271 =item C<EVFLAG_NOENV>
273 If this flag bit is ored into the flag value (or the program runs setuid
274 or setgid) then libev will I<not> look at the environment variable
275 C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
276 override the flags completely if it is found in the environment. This is
277 useful to try out specific backends to test their performance, or to work
280 =item C<EVFLAG_FORKCHECK>
282 Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after
283 a fork, you can also make libev check for a fork in each iteration by
286 This works by calling C<getpid ()> on every iteration of the loop,
287 and thus this might slow down your event loop if you do a lot of loop
288 iterations and little real work, but is usually not noticeable (on my
289 Linux system for example, C<getpid> is actually a simple 5-insn sequence
290 without a syscall and thus I<very> fast, but my Linux system also has
291 C<pthread_atfork> which is even faster).
293 The big advantage of this flag is that you can forget about fork (and
294 forget about forgetting to tell libev about forking) when you use this
297 This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>
298 environment variable.
300 =item C<EVBACKEND_SELECT> (value 1, portable select backend)
302 This is your standard select(2) backend. Not I<completely> standard, as
303 libev tries to roll its own fd_set with no limits on the number of fds,
304 but if that fails, expect a fairly low limit on the number of fds when
305 using this backend. It doesn't scale too well (O(highest_fd)), but its usually
306 the fastest backend for a low number of fds.
308 =item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
310 And this is your standard poll(2) backend. It's more complicated than
311 select, but handles sparse fds better and has no artificial limit on the
312 number of fds you can use (except it will slow down considerably with a
313 lot of inactive fds). It scales similarly to select, i.e. O(total_fds).
315 =item C<EVBACKEND_EPOLL> (value 4, Linux)
317 For few fds, this backend is a bit little slower than poll and select,
318 but it scales phenomenally better. While poll and select usually scale like
319 O(total_fds) where n is the total number of fds (or the highest fd), epoll scales
320 either O(1) or O(active_fds).
322 While stopping and starting an I/O watcher in the same iteration will
323 result in some caching, there is still a syscall per such incident
324 (because the fd could point to a different file description now), so its
325 best to avoid that. Also, dup()ed file descriptors might not work very
326 well if you register events for both fds.
328 Please note that epoll sometimes generates spurious notifications, so you
329 need to use non-blocking I/O or other means to avoid blocking when no data
330 (or space) is available.
332 =item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
334 Kqueue deserves special mention, as at the time of this writing, it
335 was broken on all BSDs except NetBSD (usually it doesn't work with
336 anything but sockets and pipes, except on Darwin, where of course it's
337 completely useless). For this reason it's not being "autodetected"
338 unless you explicitly specify it explicitly in the flags (i.e. using
339 C<EVBACKEND_KQUEUE>).
341 It scales in the same way as the epoll backend, but the interface to the
342 kernel is more efficient (which says nothing about its actual speed, of
343 course). While starting and stopping an I/O watcher does not cause an
344 extra syscall as with epoll, it still adds up to four event changes per
345 incident, so its best to avoid that.
347 =item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
349 This is not implemented yet (and might never be).
351 =item C<EVBACKEND_PORT> (value 32, Solaris 10)
353 This uses the Solaris 10 port mechanism. As with everything on Solaris,
354 it's really slow, but it still scales very well (O(active_fds)).
356 Please note that solaris ports can result in a lot of spurious
357 notifications, so you need to use non-blocking I/O or other means to avoid
358 blocking when no data (or space) is available.
360 =item C<EVBACKEND_ALL>
362 Try all backends (even potentially broken ones that wouldn't be tried
363 with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
364 C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
368 If one or more of these are ored into the flags value, then only these
369 backends will be tried (in the reverse order as given here). If none are
370 specified, most compiled-in backend will be tried, usually in reverse
371 order of their flag values :)
373 The most typical usage is like this:
375 if (!ev_default_loop (0))
376 fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
378 Restrict libev to the select and poll backends, and do not allow
379 environment settings to be taken into account:
381 ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
383 Use whatever libev has to offer, but make sure that kqueue is used if
384 available (warning, breaks stuff, best use only with your own private
385 event loop and only if you know the OS supports your types of fds):
387 ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
389 =item struct ev_loop *ev_loop_new (unsigned int flags)
391 Similar to C<ev_default_loop>, but always creates a new event loop that is
392 always distinct from the default loop. Unlike the default loop, it cannot
393 handle signal and child watchers, and attempts to do so will be greeted by
394 undefined behaviour (or a failed assertion if assertions are enabled).
396 Example: Try to create a event loop that uses epoll and nothing else.
398 struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
400 fatal ("no epoll found here, maybe it hides under your chair");
402 =item ev_default_destroy ()
404 Destroys the default loop again (frees all memory and kernel state
405 etc.). None of the active event watchers will be stopped in the normal
406 sense, so e.g. C<ev_is_active> might still return true. It is your
407 responsibility to either stop all watchers cleanly yoursef I<before>
408 calling this function, or cope with the fact afterwards (which is usually
409 the easiest thing, you can just ignore the watchers and/or C<free ()> them
412 Note that certain global state, such as signal state, will not be freed by
413 this function, and related watchers (such as signal and child watchers)
414 would need to be stopped manually.
416 In general it is not advisable to call this function except in the
417 rare occasion where you really need to free e.g. the signal handling
418 pipe fds. If you need dynamically allocated loops it is better to use
419 C<ev_loop_new> and C<ev_loop_destroy>).
421 =item ev_loop_destroy (loop)
423 Like C<ev_default_destroy>, but destroys an event loop created by an
424 earlier call to C<ev_loop_new>.
426 =item ev_default_fork ()
428 This function reinitialises the kernel state for backends that have
429 one. Despite the name, you can call it anytime, but it makes most sense
430 after forking, in either the parent or child process (or both, but that
431 again makes little sense).
433 You I<must> call this function in the child process after forking if and
434 only if you want to use the event library in both processes. If you just
435 fork+exec, you don't have to call it.
437 The function itself is quite fast and it's usually not a problem to call
438 it just in case after a fork. To make this easy, the function will fit in
439 quite nicely into a call to C<pthread_atfork>:
441 pthread_atfork (0, 0, ev_default_fork);
443 At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
444 without calling this function, so if you force one of those backends you
447 =item ev_loop_fork (loop)
449 Like C<ev_default_fork>, but acts on an event loop created by
450 C<ev_loop_new>. Yes, you have to call this on every allocated event loop
451 after fork, and how you do this is entirely your own problem.
453 =item unsigned int ev_loop_count (loop)
455 Returns the count of loop iterations for the loop, which is identical to
456 the number of times libev did poll for new events. It starts at C<0> and
457 happily wraps around with enough iterations.
459 This value can sometimes be useful as a generation counter of sorts (it
460 "ticks" the number of loop iterations), as it roughly corresponds with
461 C<ev_prepare> and C<ev_check> calls.
463 =item unsigned int ev_backend (loop)
465 Returns one of the C<EVBACKEND_*> flags indicating the event backend in
468 =item ev_tstamp ev_now (loop)
470 Returns the current "event loop time", which is the time the event loop
471 received events and started processing them. This timestamp does not
472 change as long as callbacks are being processed, and this is also the base
473 time used for relative timers. You can treat it as the timestamp of the
474 event occuring (or more correctly, libev finding out about it).
476 =item ev_loop (loop, int flags)
478 Finally, this is it, the event handler. This function usually is called
479 after you initialised all your watchers and you want to start handling
482 If the flags argument is specified as C<0>, it will not return until
483 either no event watchers are active anymore or C<ev_unloop> was called.
485 Please note that an explicit C<ev_unloop> is usually better than
486 relying on all watchers to be stopped when deciding when a program has
487 finished (especially in interactive programs), but having a program that
488 automatically loops as long as it has to and no longer by virtue of
489 relying on its watchers stopping correctly is a thing of beauty.
491 A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
492 those events and any outstanding ones, but will not block your process in
493 case there are no events and will return after one iteration of the loop.
495 A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
496 neccessary) and will handle those and any outstanding ones. It will block
497 your process until at least one new event arrives, and will return after
498 one iteration of the loop. This is useful if you are waiting for some
499 external event in conjunction with something not expressible using other
500 libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is
501 usually a better approach for this kind of thing.
503 Here are the gory details of what C<ev_loop> does:
505 - Before the first iteration, call any pending watchers.
506 * If there are no active watchers (reference count is zero), return.
507 - Queue all prepare watchers and then call all outstanding watchers.
508 - If we have been forked, recreate the kernel state.
509 - Update the kernel state with all outstanding changes.
510 - Update the "event loop time".
511 - Calculate for how long to block.
512 - Block the process, waiting for any events.
513 - Queue all outstanding I/O (fd) events.
514 - Update the "event loop time" and do time jump handling.
515 - Queue all outstanding timers.
516 - Queue all outstanding periodics.
517 - If no events are pending now, queue all idle watchers.
518 - Queue all check watchers.
519 - Call all queued watchers in reverse order (i.e. check watchers first).
520 Signals and child watchers are implemented as I/O watchers, and will
521 be handled here by queueing them when their watcher gets executed.
522 - If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
523 were used, return, otherwise continue with step *.
525 Example: Queue some jobs and then loop until no events are outsanding
528 ... queue jobs here, make sure they register event watchers as long
529 ... as they still have work to do (even an idle watcher will do..)
530 ev_loop (my_loop, 0);
533 =item ev_unloop (loop, how)
535 Can be used to make a call to C<ev_loop> return early (but only after it
536 has processed all outstanding events). The C<how> argument must be either
537 C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
538 C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
542 =item ev_unref (loop)
544 Ref/unref can be used to add or remove a reference count on the event
545 loop: Every watcher keeps one reference, and as long as the reference
546 count is nonzero, C<ev_loop> will not return on its own. If you have
547 a watcher you never unregister that should not keep C<ev_loop> from
548 returning, ev_unref() after starting, and ev_ref() before stopping it. For
549 example, libev itself uses this for its internal signal pipe: It is not
550 visible to the libev user and should not keep C<ev_loop> from exiting if
551 no event watchers registered by it are active. It is also an excellent
552 way to do this for generic recurring timers or from within third-party
553 libraries. Just remember to I<unref after start> and I<ref before stop>.
555 Example: Create a signal watcher, but keep it from keeping C<ev_loop>
556 running when nothing else is active.
558 struct ev_signal exitsig;
559 ev_signal_init (&exitsig, sig_cb, SIGINT);
560 ev_signal_start (loop, &exitsig);
563 Example: For some weird reason, unregister the above signal handler again.
566 ev_signal_stop (loop, &exitsig);
571 =head1 ANATOMY OF A WATCHER
573 A watcher is a structure that you create and register to record your
574 interest in some event. For instance, if you want to wait for STDIN to
575 become readable, you would create an C<ev_io> watcher for that:
577 static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
580 ev_unloop (loop, EVUNLOOP_ALL);
583 struct ev_loop *loop = ev_default_loop (0);
584 struct ev_io stdin_watcher;
585 ev_init (&stdin_watcher, my_cb);
586 ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
587 ev_io_start (loop, &stdin_watcher);
590 As you can see, you are responsible for allocating the memory for your
591 watcher structures (and it is usually a bad idea to do this on the stack,
592 although this can sometimes be quite valid).
594 Each watcher structure must be initialised by a call to C<ev_init
595 (watcher *, callback)>, which expects a callback to be provided. This
596 callback gets invoked each time the event occurs (or, in the case of io
597 watchers, each time the event loop detects that the file descriptor given
598 is readable and/or writable).
600 Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro
601 with arguments specific to this watcher type. There is also a macro
602 to combine initialisation and setting in one call: C<< ev_<type>_init
603 (watcher *, callback, ...) >>.
605 To make the watcher actually watch out for events, you have to start it
606 with a watcher-specific start function (C<< ev_<type>_start (loop, watcher
607 *) >>), and you can stop watching for events at any time by calling the
608 corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.
610 As long as your watcher is active (has been started but not stopped) you
611 must not touch the values stored in it. Most specifically you must never
612 reinitialise it or call its C<set> macro.
614 Each and every callback receives the event loop pointer as first, the
615 registered watcher structure as second, and a bitset of received events as
618 The received events usually include a single bit per event type received
619 (you can receive multiple events at the same time). The possible bit masks
628 The file descriptor in the C<ev_io> watcher has become readable and/or
633 The C<ev_timer> watcher has timed out.
637 The C<ev_periodic> watcher has timed out.
641 The signal specified in the C<ev_signal> watcher has been received by a thread.
645 The pid specified in the C<ev_child> watcher has received a status change.
649 The path specified in the C<ev_stat> watcher changed its attributes somehow.
653 The C<ev_idle> watcher has determined that you have nothing better to do.
659 All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts
660 to gather new events, and all C<ev_check> watchers are invoked just after
661 C<ev_loop> has gathered them, but before it invokes any callbacks for any
662 received events. Callbacks of both watcher types can start and stop as
663 many watchers as they want, and all of them will be taken into account
664 (for example, a C<ev_prepare> watcher might start an idle watcher to keep
665 C<ev_loop> from blocking).
669 The embedded event loop specified in the C<ev_embed> watcher needs attention.
673 The event loop has been resumed in the child process after fork (see
678 An unspecified error has occured, the watcher has been stopped. This might
679 happen because the watcher could not be properly started because libev
680 ran out of memory, a file descriptor was found to be closed or any other
681 problem. You best act on it by reporting the problem and somehow coping
682 with the watcher being stopped.
684 Libev will usually signal a few "dummy" events together with an error,
685 for example it might indicate that a fd is readable or writable, and if
686 your callbacks is well-written it can just attempt the operation and cope
687 with the error from read() or write(). This will not work in multithreaded
688 programs, though, so beware.
692 =head2 GENERIC WATCHER FUNCTIONS
694 In the following description, C<TYPE> stands for the watcher type,
695 e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
699 =item C<ev_init> (ev_TYPE *watcher, callback)
701 This macro initialises the generic portion of a watcher. The contents
702 of the watcher object can be arbitrary (so C<malloc> will do). Only
703 the generic parts of the watcher are initialised, you I<need> to call
704 the type-specific C<ev_TYPE_set> macro afterwards to initialise the
705 type-specific parts. For each type there is also a C<ev_TYPE_init> macro
706 which rolls both calls into one.
708 You can reinitialise a watcher at any time as long as it has been stopped
709 (or never started) and there are no pending events outstanding.
711 The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,
714 =item C<ev_TYPE_set> (ev_TYPE *, [args])
716 This macro initialises the type-specific parts of a watcher. You need to
717 call C<ev_init> at least once before you call this macro, but you can
718 call C<ev_TYPE_set> any number of times. You must not, however, call this
719 macro on a watcher that is active (it can be pending, however, which is a
720 difference to the C<ev_init> macro).
722 Although some watcher types do not have type-specific arguments
723 (e.g. C<ev_prepare>) you still need to call its C<set> macro.
725 =item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
727 This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
728 calls into a single call. This is the most convinient method to initialise
729 a watcher. The same limitations apply, of course.
731 =item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
733 Starts (activates) the given watcher. Only active watchers will receive
734 events. If the watcher is already active nothing will happen.
736 =item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
738 Stops the given watcher again (if active) and clears the pending
739 status. It is possible that stopped watchers are pending (for example,
740 non-repeating timers are being stopped when they become pending), but
741 C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If
742 you want to free or reuse the memory used by the watcher it is therefore a
743 good idea to always call its C<ev_TYPE_stop> function.
745 =item bool ev_is_active (ev_TYPE *watcher)
747 Returns a true value iff the watcher is active (i.e. it has been started
748 and not yet been stopped). As long as a watcher is active you must not modify
751 =item bool ev_is_pending (ev_TYPE *watcher)
753 Returns a true value iff the watcher is pending, (i.e. it has outstanding
754 events but its callback has not yet been invoked). As long as a watcher
755 is pending (but not active) you must not call an init function on it (but
756 C<ev_TYPE_set> is safe), you must not change its priority, and you must
757 make sure the watcher is available to libev (e.g. you cannot C<free ()>
760 =item callback ev_cb (ev_TYPE *watcher)
762 Returns the callback currently set on the watcher.
764 =item ev_cb_set (ev_TYPE *watcher, callback)
766 Change the callback. You can change the callback at virtually any time
769 =item ev_set_priority (ev_TYPE *watcher, priority)
771 =item int ev_priority (ev_TYPE *watcher)
773 Set and query the priority of the watcher. The priority is a small
774 integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
775 (default: C<-2>). Pending watchers with higher priority will be invoked
776 before watchers with lower priority, but priority will not keep watchers
777 from being executed (except for C<ev_idle> watchers).
779 This means that priorities are I<only> used for ordering callback
780 invocation after new events have been received. This is useful, for
781 example, to reduce latency after idling, or more often, to bind two
782 watchers on the same event and make sure one is called first.
784 If you need to suppress invocation when higher priority events are pending
785 you need to look at C<ev_idle> watchers, which provide this functionality.
787 You I<must not> change the priority of a watcher as long as it is active or
790 The default priority used by watchers when no priority has been set is
791 always C<0>, which is supposed to not be too high and not be too low :).
793 Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
794 fine, as long as you do not mind that the priority value you query might
795 or might not have been adjusted to be within valid range.
797 =item ev_invoke (loop, ev_TYPE *watcher, int revents)
799 Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
800 C<loop> nor C<revents> need to be valid as long as the watcher callback
801 can deal with that fact.
803 =item int ev_clear_pending (loop, ev_TYPE *watcher)
805 If the watcher is pending, this function returns clears its pending status
806 and returns its C<revents> bitset (as if its callback was invoked). If the
807 watcher isn't pending it does nothing and returns C<0>.
812 =head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
814 Each watcher has, by default, a member C<void *data> that you can change
815 and read at any time, libev will completely ignore it. This can be used
816 to associate arbitrary data with your watcher. If you need more data and
817 don't want to allocate memory and store a pointer to it in that data
818 member, you can also "subclass" the watcher type and provide your own
826 struct whatever *mostinteresting;
829 And since your callback will be called with a pointer to the watcher, you
830 can cast it back to your own type:
832 static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
834 struct my_io *w = (struct my_io *)w_;
838 More interesting and less C-conformant ways of casting your callback type
839 instead have been omitted.
841 Another common scenario is having some data structure with multiple
851 In this case getting the pointer to C<my_biggy> is a bit more complicated,
852 you need to use C<offsetof>:
857 t1_cb (EV_P_ struct ev_timer *w, int revents)
859 struct my_biggy big = (struct my_biggy *
860 (((char *)w) - offsetof (struct my_biggy, t1));
864 t2_cb (EV_P_ struct ev_timer *w, int revents)
866 struct my_biggy big = (struct my_biggy *
867 (((char *)w) - offsetof (struct my_biggy, t2));
873 This section describes each watcher in detail, but will not repeat
874 information given in the last section. Any initialisation/set macros,
875 functions and members specific to the watcher type are explained.
877 Members are additionally marked with either I<[read-only]>, meaning that,
878 while the watcher is active, you can look at the member and expect some
879 sensible content, but you must not modify it (you can modify it while the
880 watcher is stopped to your hearts content), or I<[read-write]>, which
881 means you can expect it to have some sensible content while the watcher
882 is active, but you can also modify it. Modifying it may not do something
883 sensible or take immediate effect (or do anything at all), but libev will
884 not crash or malfunction in any way.
887 =head2 C<ev_io> - is this file descriptor readable or writable?
889 I/O watchers check whether a file descriptor is readable or writable
890 in each iteration of the event loop, or, more precisely, when reading
891 would not block the process and writing would at least be able to write
892 some data. This behaviour is called level-triggering because you keep
893 receiving events as long as the condition persists. Remember you can stop
894 the watcher if you don't want to act on the event and neither want to
895 receive future events.
897 In general you can register as many read and/or write event watchers per
898 fd as you want (as long as you don't confuse yourself). Setting all file
899 descriptors to non-blocking mode is also usually a good idea (but not
900 required if you know what you are doing).
902 You have to be careful with dup'ed file descriptors, though. Some backends
903 (the linux epoll backend is a notable example) cannot handle dup'ed file
904 descriptors correctly if you register interest in two or more fds pointing
905 to the same underlying file/socket/etc. description (that is, they share
906 the same underlying "file open").
908 If you must do this, then force the use of a known-to-be-good backend
909 (at the time of this writing, this includes only C<EVBACKEND_SELECT> and
912 Another thing you have to watch out for is that it is quite easy to
913 receive "spurious" readyness notifications, that is your callback might
914 be called with C<EV_READ> but a subsequent C<read>(2) will actually block
915 because there is no data. Not only are some backends known to create a
916 lot of those (for example solaris ports), it is very easy to get into
917 this situation even with a relatively standard program structure. Thus
918 it is best to always use non-blocking I/O: An extra C<read>(2) returning
919 C<EAGAIN> is far preferable to a program hanging until some data arrives.
921 If you cannot run the fd in non-blocking mode (for example you should not
922 play around with an Xlib connection), then you have to seperately re-test
923 whether a file descriptor is really ready with a known-to-be good interface
924 such as poll (fortunately in our Xlib example, Xlib already does this on
925 its own, so its quite safe to use).
927 =head3 The special problem of disappearing file descriptors
929 Some backends (e.g kqueue, epoll) need to be told about closing a file
930 descriptor (either by calling C<close> explicitly or by any other means,
931 such as C<dup>). The reason is that you register interest in some file
932 descriptor, but when it goes away, the operating system will silently drop
933 this interest. If another file descriptor with the same number then is
934 registered with libev, there is no efficient way to see that this is, in
935 fact, a different file descriptor.
937 To avoid having to explicitly tell libev about such cases, libev follows
938 the following policy: Each time C<ev_io_set> is being called, libev
939 will assume that this is potentially a new file descriptor, otherwise
940 it is assumed that the file descriptor stays the same. That means that
941 you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
942 descriptor even if the file descriptor number itself did not change.
944 This is how one would do it normally anyway, the important point is that
945 the libev application should not optimise around libev but should leave
946 optimisations to libev.
949 =head3 Watcher-Specific Functions
953 =item ev_io_init (ev_io *, callback, int fd, int events)
955 =item ev_io_set (ev_io *, int fd, int events)
957 Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
958 rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or
959 C<EV_READ | EV_WRITE> to receive the given events.
961 =item int fd [read-only]
963 The file descriptor being watched.
965 =item int events [read-only]
967 The events being watched.
971 Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
972 readable, but only once. Since it is likely line-buffered, you could
973 attempt to read a whole line in the callback.
976 stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
978 ev_io_stop (loop, w);
979 .. read from stdin here (or from w->fd) and haqndle any I/O errors
983 struct ev_loop *loop = ev_default_init (0);
984 struct ev_io stdin_readable;
985 ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
986 ev_io_start (loop, &stdin_readable);
990 =head2 C<ev_timer> - relative and optionally repeating timeouts
992 Timer watchers are simple relative timers that generate an event after a
993 given time, and optionally repeating in regular intervals after that.
995 The timers are based on real time, that is, if you register an event that
996 times out after an hour and you reset your system clock to last years
997 time, it will still time out after (roughly) and hour. "Roughly" because
998 detecting time jumps is hard, and some inaccuracies are unavoidable (the
999 monotonic clock option helps a lot here).
1001 The relative timeouts are calculated relative to the C<ev_now ()>
1002 time. This is usually the right thing as this timestamp refers to the time
1003 of the event triggering whatever timeout you are modifying/starting. If
1004 you suspect event processing to be delayed and you I<need> to base the timeout
1005 on the current time, use something like this to adjust for this:
1007 ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1009 The callback is guarenteed to be invoked only when its timeout has passed,
1010 but if multiple timers become ready during the same loop iteration then
1011 order of execution is undefined.
1013 =head3 Watcher-Specific Functions and Data Members
1017 =item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1019 =item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1021 Configure the timer to trigger after C<after> seconds. If C<repeat> is
1022 C<0.>, then it will automatically be stopped. If it is positive, then the
1023 timer will automatically be configured to trigger again C<repeat> seconds
1024 later, again, and again, until stopped manually.
1026 The timer itself will do a best-effort at avoiding drift, that is, if you
1027 configure a timer to trigger every 10 seconds, then it will trigger at
1028 exactly 10 second intervals. If, however, your program cannot keep up with
1029 the timer (because it takes longer than those 10 seconds to do stuff) the
1030 timer will not fire more than once per event loop iteration.
1032 =item ev_timer_again (loop)
1034 This will act as if the timer timed out and restart it again if it is
1035 repeating. The exact semantics are:
1037 If the timer is pending, its pending status is cleared.
1039 If the timer is started but nonrepeating, stop it (as if it timed out).
1041 If the timer is repeating, either start it if necessary (with the
1042 C<repeat> value), or reset the running timer to the C<repeat> value.
1044 This sounds a bit complicated, but here is a useful and typical
1045 example: Imagine you have a tcp connection and you want a so-called idle
1046 timeout, that is, you want to be called when there have been, say, 60
1047 seconds of inactivity on the socket. The easiest way to do this is to
1048 configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1049 C<ev_timer_again> each time you successfully read or write some data. If
1050 you go into an idle state where you do not expect data to travel on the
1051 socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1052 automatically restart it if need be.
1054 That means you can ignore the C<after> value and C<ev_timer_start>
1055 altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1057 ev_timer_init (timer, callback, 0., 5.);
1058 ev_timer_again (loop, timer);
1061 ev_timer_again (loop, timer);
1064 ev_timer_again (loop, timer);
1066 This is more slightly efficient then stopping/starting the timer each time
1067 you want to modify its timeout value.
1069 =item ev_tstamp repeat [read-write]
1071 The current C<repeat> value. Will be used each time the watcher times out
1072 or C<ev_timer_again> is called and determines the next timeout (if any),
1073 which is also when any modifications are taken into account.
1077 Example: Create a timer that fires after 60 seconds.
1080 one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
1082 .. one minute over, w is actually stopped right here
1085 struct ev_timer mytimer;
1086 ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1087 ev_timer_start (loop, &mytimer);
1089 Example: Create a timeout timer that times out after 10 seconds of
1093 timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
1095 .. ten seconds without any activity
1098 struct ev_timer mytimer;
1099 ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1100 ev_timer_again (&mytimer); /* start timer */
1103 // and in some piece of code that gets executed on any "activity":
1104 // reset the timeout to start ticking again at 10 seconds
1105 ev_timer_again (&mytimer);
1108 =head2 C<ev_periodic> - to cron or not to cron?
1110 Periodic watchers are also timers of a kind, but they are very versatile
1111 (and unfortunately a bit complex).
1113 Unlike C<ev_timer>'s, they are not based on real time (or relative time)
1114 but on wallclock time (absolute time). You can tell a periodic watcher
1115 to trigger "at" some specific point in time. For example, if you tell a
1116 periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()
1117 + 10.>) and then reset your system clock to the last year, then it will
1118 take a year to trigger the event (unlike an C<ev_timer>, which would trigger
1119 roughly 10 seconds later).
1121 They can also be used to implement vastly more complex timers, such as
1122 triggering an event on each midnight, local time or other, complicated,
1125 As with timers, the callback is guarenteed to be invoked only when the
1126 time (C<at>) has been passed, but if multiple periodic timers become ready
1127 during the same loop iteration then order of execution is undefined.
1129 =head3 Watcher-Specific Functions and Data Members
1133 =item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
1135 =item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)
1137 Lots of arguments, lets sort it out... There are basically three modes of
1138 operation, and we will explain them from simplest to complex:
1142 =item * absolute timer (at = time, interval = reschedule_cb = 0)
1144 In this configuration the watcher triggers an event at the wallclock time
1145 C<at> and doesn't repeat. It will not adjust when a time jump occurs,
1146 that is, if it is to be run at January 1st 2011 then it will run when the
1147 system time reaches or surpasses this time.
1149 =item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
1151 In this mode the watcher will always be scheduled to time out at the next
1152 C<at + N * interval> time (for some integer N, which can also be negative)
1153 and then repeat, regardless of any time jumps.
1155 This can be used to create timers that do not drift with respect to system
1158 ev_periodic_set (&periodic, 0., 3600., 0);
1160 This doesn't mean there will always be 3600 seconds in between triggers,
1161 but only that the the callback will be called when the system time shows a
1162 full hour (UTC), or more correctly, when the system time is evenly divisible
1165 Another way to think about it (for the mathematically inclined) is that
1166 C<ev_periodic> will try to run the callback in this mode at the next possible
1167 time where C<time = at (mod interval)>, regardless of any time jumps.
1169 For numerical stability it is preferable that the C<at> value is near
1170 C<ev_now ()> (the current time), but there is no range requirement for
1173 =item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
1175 In this mode the values for C<interval> and C<at> are both being
1176 ignored. Instead, each time the periodic watcher gets scheduled, the
1177 reschedule callback will be called with the watcher as first, and the
1178 current time as second argument.
1180 NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
1181 ever, or make any event loop modifications>. If you need to stop it,
1182 return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by
1183 starting an C<ev_prepare> watcher, which is legal).
1185 Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
1186 ev_tstamp now)>, e.g.:
1188 static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
1193 It must return the next time to trigger, based on the passed time value
1194 (that is, the lowest time value larger than to the second argument). It
1195 will usually be called just before the callback will be triggered, but
1196 might be called at other times, too.
1198 NOTE: I<< This callback must always return a time that is later than the
1199 passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.
1201 This can be used to create very complex timers, such as a timer that
1202 triggers on each midnight, local time. To do this, you would calculate the
1203 next midnight after C<now> and return the timestamp value for this. How
1204 you do this is, again, up to you (but it is not trivial, which is the main
1205 reason I omitted it as an example).
1209 =item ev_periodic_again (loop, ev_periodic *)
1211 Simply stops and restarts the periodic watcher again. This is only useful
1212 when you changed some parameters or the reschedule callback would return
1213 a different time than the last time it was called (e.g. in a crond like
1214 program when the crontabs have changed).
1216 =item ev_tstamp offset [read-write]
1218 When repeating, this contains the offset value, otherwise this is the
1219 absolute point in time (the C<at> value passed to C<ev_periodic_set>).
1221 Can be modified any time, but changes only take effect when the periodic
1222 timer fires or C<ev_periodic_again> is being called.
1224 =item ev_tstamp interval [read-write]
1226 The current interval value. Can be modified any time, but changes only
1227 take effect when the periodic timer fires or C<ev_periodic_again> is being
1230 =item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]
1232 The current reschedule callback, or C<0>, if this functionality is
1233 switched off. Can be changed any time, but changes only take effect when
1234 the periodic timer fires or C<ev_periodic_again> is being called.
1236 =item ev_tstamp at [read-only]
1238 When active, contains the absolute time that the watcher is supposed to
1243 Example: Call a callback every hour, or, more precisely, whenever the
1244 system clock is divisible by 3600. The callback invocation times have
1245 potentially a lot of jittering, but good long-term stability.
1248 clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
1250 ... its now a full hour (UTC, or TAI or whatever your clock follows)
1253 struct ev_periodic hourly_tick;
1254 ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1255 ev_periodic_start (loop, &hourly_tick);
1257 Example: The same as above, but use a reschedule callback to do it:
1262 my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
1264 return fmod (now, 3600.) + 3600.;
1267 ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1269 Example: Call a callback every hour, starting now:
1271 struct ev_periodic hourly_tick;
1272 ev_periodic_init (&hourly_tick, clock_cb,
1273 fmod (ev_now (loop), 3600.), 3600., 0);
1274 ev_periodic_start (loop, &hourly_tick);
1277 =head2 C<ev_signal> - signal me when a signal gets signalled!
1279 Signal watchers will trigger an event when the process receives a specific
1280 signal one or more times. Even though signals are very asynchronous, libev
1281 will try it's best to deliver signals synchronously, i.e. as part of the
1282 normal event processing, like any other event.
1284 You can configure as many watchers as you like per signal. Only when the
1285 first watcher gets started will libev actually register a signal watcher
1286 with the kernel (thus it coexists with your own signal handlers as long
1287 as you don't register any with libev). Similarly, when the last signal
1288 watcher for a signal is stopped libev will reset the signal handler to
1289 SIG_DFL (regardless of what it was set to before).
1291 =head3 Watcher-Specific Functions and Data Members
1295 =item ev_signal_init (ev_signal *, callback, int signum)
1297 =item ev_signal_set (ev_signal *, int signum)
1299 Configures the watcher to trigger on the given signal number (usually one
1300 of the C<SIGxxx> constants).
1302 =item int signum [read-only]
1304 The signal the watcher watches out for.
1309 =head2 C<ev_child> - watch out for process status changes
1311 Child watchers trigger when your process receives a SIGCHLD in response to
1312 some child status changes (most typically when a child of yours dies).
1314 =head3 Watcher-Specific Functions and Data Members
1318 =item ev_child_init (ev_child *, callback, int pid)
1320 =item ev_child_set (ev_child *, int pid)
1322 Configures the watcher to wait for status changes of process C<pid> (or
1323 I<any> process if C<pid> is specified as C<0>). The callback can look
1324 at the C<rstatus> member of the C<ev_child> watcher structure to see
1325 the status word (use the macros from C<sys/wait.h> and see your systems
1326 C<waitpid> documentation). The C<rpid> member contains the pid of the
1327 process causing the status change.
1329 =item int pid [read-only]
1331 The process id this watcher watches out for, or C<0>, meaning any process id.
1333 =item int rpid [read-write]
1335 The process id that detected a status change.
1337 =item int rstatus [read-write]
1339 The process exit/trace status caused by C<rpid> (see your systems
1340 C<waitpid> and C<sys/wait.h> documentation for details).
1344 Example: Try to exit cleanly on SIGINT and SIGTERM.
1347 sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
1349 ev_unloop (loop, EVUNLOOP_ALL);
1352 struct ev_signal signal_watcher;
1353 ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1354 ev_signal_start (loop, &sigint_cb);
1357 =head2 C<ev_stat> - did the file attributes just change?
1359 This watches a filesystem path for attribute changes. That is, it calls
1360 C<stat> regularly (or when the OS says it changed) and sees if it changed
1361 compared to the last time, invoking the callback if it did.
1363 The path does not need to exist: changing from "path exists" to "path does
1364 not exist" is a status change like any other. The condition "path does
1365 not exist" is signified by the C<st_nlink> field being zero (which is
1366 otherwise always forced to be at least one) and all the other fields of
1367 the stat buffer having unspecified contents.
1369 The path I<should> be absolute and I<must not> end in a slash. If it is
1370 relative and your working directory changes, the behaviour is undefined.
1372 Since there is no standard to do this, the portable implementation simply
1373 calls C<stat (2)> regularly on the path to see if it changed somehow. You
1374 can specify a recommended polling interval for this case. If you specify
1375 a polling interval of C<0> (highly recommended!) then a I<suitable,
1376 unspecified default> value will be used (which you can expect to be around
1377 five seconds, although this might change dynamically). Libev will also
1378 impose a minimum interval which is currently around C<0.1>, but thats
1381 This watcher type is not meant for massive numbers of stat watchers,
1382 as even with OS-supported change notifications, this can be
1385 At the time of this writing, only the Linux inotify interface is
1386 implemented (implementing kqueue support is left as an exercise for the
1387 reader). Inotify will be used to give hints only and should not change the
1388 semantics of C<ev_stat> watchers, which means that libev sometimes needs
1389 to fall back to regular polling again even with inotify, but changes are
1390 usually detected immediately, and if the file exists there will be no
1393 =head3 Watcher-Specific Functions and Data Members
1397 =item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
1399 =item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
1401 Configures the watcher to wait for status changes of the given
1402 C<path>. The C<interval> is a hint on how quickly a change is expected to
1403 be detected and should normally be specified as C<0> to let libev choose
1404 a suitable value. The memory pointed to by C<path> must point to the same
1405 path for as long as the watcher is active.
1407 The callback will be receive C<EV_STAT> when a change was detected,
1408 relative to the attributes at the time the watcher was started (or the
1409 last change was detected).
1411 =item ev_stat_stat (ev_stat *)
1413 Updates the stat buffer immediately with new values. If you change the
1414 watched path in your callback, you could call this fucntion to avoid
1415 detecting this change (while introducing a race condition). Can also be
1416 useful simply to find out the new values.
1418 =item ev_statdata attr [read-only]
1420 The most-recently detected attributes of the file. Although the type is of
1421 C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1422 suitable for your system. If the C<st_nlink> member is C<0>, then there
1423 was some error while C<stat>ing the file.
1425 =item ev_statdata prev [read-only]
1427 The previous attributes of the file. The callback gets invoked whenever
1430 =item ev_tstamp interval [read-only]
1432 The specified interval.
1434 =item const char *path [read-only]
1436 The filesystem path that is being watched.
1440 Example: Watch C</etc/passwd> for attribute changes.
1443 passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1445 /* /etc/passwd changed in some way */
1446 if (w->attr.st_nlink)
1448 printf ("passwd current size %ld\n", (long)w->attr.st_size);
1449 printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1450 printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1453 /* you shalt not abuse printf for puts */
1454 puts ("wow, /etc/passwd is not there, expect problems. "
1455 "if this is windows, they already arrived\n");
1461 ev_stat_init (&passwd, passwd_cb, "/etc/passwd");
1462 ev_stat_start (loop, &passwd);
1465 =head2 C<ev_idle> - when you've got nothing better to do...
1467 Idle watchers trigger events when no other events of the same or higher
1468 priority are pending (prepare, check and other idle watchers do not
1471 That is, as long as your process is busy handling sockets or timeouts
1472 (or even signals, imagine) of the same or higher priority it will not be
1473 triggered. But when your process is idle (or only lower-priority watchers
1474 are pending), the idle watchers are being called once per event loop
1475 iteration - until stopped, that is, or your process receives more events
1476 and becomes busy again with higher priority stuff.
1478 The most noteworthy effect is that as long as any idle watchers are
1479 active, the process will not block when waiting for new events.
1481 Apart from keeping your process non-blocking (which is a useful
1482 effect on its own sometimes), idle watchers are a good place to do
1483 "pseudo-background processing", or delay processing stuff to after the
1484 event loop has handled all outstanding events.
1486 =head3 Watcher-Specific Functions and Data Members
1490 =item ev_idle_init (ev_signal *, callback)
1492 Initialises and configures the idle watcher - it has no parameters of any
1493 kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1498 Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1499 callback, free it. Also, use no error checking, as usual.
1502 idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
1505 // now do something you wanted to do when the program has
1506 // no longer asnything immediate to do.
1509 struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
1510 ev_idle_init (idle_watcher, idle_cb);
1511 ev_idle_start (loop, idle_cb);
1514 =head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1516 Prepare and check watchers are usually (but not always) used in tandem:
1517 prepare watchers get invoked before the process blocks and check watchers
1520 You I<must not> call C<ev_loop> or similar functions that enter
1521 the current event loop from either C<ev_prepare> or C<ev_check>
1522 watchers. Other loops than the current one are fine, however. The
1523 rationale behind this is that you do not need to check for recursion in
1524 those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1525 C<ev_check> so if you have one watcher of each kind they will always be
1526 called in pairs bracketing the blocking call.
1528 Their main purpose is to integrate other event mechanisms into libev and
1529 their use is somewhat advanced. This could be used, for example, to track
1530 variable changes, implement your own watchers, integrate net-snmp or a
1531 coroutine library and lots more. They are also occasionally useful if
1532 you cache some data and want to flush it before blocking (for example,
1533 in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1536 This is done by examining in each prepare call which file descriptors need
1537 to be watched by the other library, registering C<ev_io> watchers for
1538 them and starting an C<ev_timer> watcher for any timeouts (many libraries
1539 provide just this functionality). Then, in the check watcher you check for
1540 any events that occured (by checking the pending status of all watchers
1541 and stopping them) and call back into the library. The I/O and timer
1542 callbacks will never actually be called (but must be valid nevertheless,
1543 because you never know, you know?).
1545 As another example, the Perl Coro module uses these hooks to integrate
1546 coroutines into libev programs, by yielding to other active coroutines
1547 during each prepare and only letting the process block if no coroutines
1548 are ready to run (it's actually more complicated: it only runs coroutines
1549 with priority higher than or equal to the event loop and one coroutine
1550 of lower priority, but only once, using idle watchers to keep the event
1551 loop from blocking if lower-priority coroutines are active, thus mapping
1552 low-priority coroutines to idle/background tasks).
1554 It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1555 priority, to ensure that they are being run before any other watchers
1556 after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,
1557 too) should not activate ("feed") events into libev. While libev fully
1558 supports this, they will be called before other C<ev_check> watchers did
1559 their job. As C<ev_check> watchers are often used to embed other event
1560 loops those other event loops might be in an unusable state until their
1561 C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1564 =head3 Watcher-Specific Functions and Data Members
1568 =item ev_prepare_init (ev_prepare *, callback)
1570 =item ev_check_init (ev_check *, callback)
1572 Initialises and configures the prepare or check watcher - they have no
1573 parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1574 macros, but using them is utterly, utterly and completely pointless.
1578 There are a number of principal ways to embed other event loops or modules
1579 into libev. Here are some ideas on how to include libadns into libev
1580 (there is a Perl module named C<EV::ADNS> that does this, which you could
1581 use for an actually working example. Another Perl module named C<EV::Glib>
1582 embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV
1583 into the Glib event loop).
1585 Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1586 and in a check watcher, destroy them and call into libadns. What follows
1587 is pseudo-code only of course. This requires you to either use a low
1588 priority for the check watcher or use C<ev_clear_pending> explicitly, as
1589 the callbacks for the IO/timeout watchers might not have been called yet.
1591 static ev_io iow [nfd];
1595 io_cb (ev_loop *loop, ev_io *w, int revents)
1599 // create io watchers for each fd and a timer before blocking
1601 adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
1603 int timeout = 3600000;
1604 struct pollfd fds [nfd];
1605 // actual code will need to loop here and realloc etc.
1606 adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1608 /* the callback is illegal, but won't be called as we stop during check */
1609 ev_timer_init (&tw, 0, timeout * 1e-3);
1610 ev_timer_start (loop, &tw);
1612 // create one ev_io per pollfd
1613 for (int i = 0; i < nfd; ++i)
1615 ev_io_init (iow + i, io_cb, fds [i].fd,
1616 ((fds [i].events & POLLIN ? EV_READ : 0)
1617 | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1619 fds [i].revents = 0;
1620 ev_io_start (loop, iow + i);
1624 // stop all watchers after blocking
1626 adns_check_cb (ev_loop *loop, ev_check *w, int revents)
1628 ev_timer_stop (loop, &tw);
1630 for (int i = 0; i < nfd; ++i)
1632 // set the relevant poll flags
1633 // could also call adns_processreadable etc. here
1634 struct pollfd *fd = fds + i;
1635 int revents = ev_clear_pending (iow + i);
1636 if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1637 if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1639 // now stop the watcher
1640 ev_io_stop (loop, iow + i);
1643 adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1646 Method 2: This would be just like method 1, but you run C<adns_afterpoll>
1647 in the prepare watcher and would dispose of the check watcher.
1649 Method 3: If the module to be embedded supports explicit event
1650 notification (adns does), you can also make use of the actual watcher
1651 callbacks, and only destroy/create the watchers in the prepare watcher.
1654 timer_cb (EV_P_ ev_timer *w, int revents)
1656 adns_state ads = (adns_state)w->data;
1659 adns_processtimeouts (ads, &tv_now);
1663 io_cb (EV_P_ ev_io *w, int revents)
1665 adns_state ads = (adns_state)w->data;
1668 if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1669 if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1672 // do not ever call adns_afterpoll
1674 Method 4: Do not use a prepare or check watcher because the module you
1675 want to embed is too inflexible to support it. Instead, youc na override
1676 their poll function. The drawback with this solution is that the main
1677 loop is now no longer controllable by EV. The C<Glib::EV> module does
1681 event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1685 for (n = 0; n < nfds; ++n)
1686 // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1689 // create/start timer
1696 ev_timer_stop (EV_A_ &to);
1698 // stop io watchers again - their callbacks should have set
1699 for (n = 0; n < nfds; ++n)
1700 ev_io_stop (EV_A_ iow [n]);
1706 =head2 C<ev_embed> - when one backend isn't enough...
1708 This is a rather advanced watcher type that lets you embed one event loop
1709 into another (currently only C<ev_io> events are supported in the embedded
1710 loop, other types of watchers might be handled in a delayed or incorrect
1711 fashion and must not be used).
1713 There are primarily two reasons you would want that: work around bugs and
1716 As an example for a bug workaround, the kqueue backend might only support
1717 sockets on some platform, so it is unusable as generic backend, but you
1718 still want to make use of it because you have many sockets and it scales
1719 so nicely. In this case, you would create a kqueue-based loop and embed it
1720 into your default loop (which might use e.g. poll). Overall operation will
1721 be a bit slower because first libev has to poll and then call kevent, but
1722 at least you can use both at what they are best.
1724 As for prioritising I/O: rarely you have the case where some fds have
1725 to be watched and handled very quickly (with low latency), and even
1726 priorities and idle watchers might have too much overhead. In this case
1727 you would put all the high priority stuff in one loop and all the rest in
1728 a second one, and embed the second one in the first.
1730 As long as the watcher is active, the callback will be invoked every time
1731 there might be events pending in the embedded loop. The callback must then
1732 call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke
1733 their callbacks (you could also start an idle watcher to give the embedded
1734 loop strictly lower priority for example). You can also set the callback
1735 to C<0>, in which case the embed watcher will automatically execute the
1736 embedded loop sweep.
1738 As long as the watcher is started it will automatically handle events. The
1739 callback will be invoked whenever some events have been handled. You can
1740 set the callback to C<0> to avoid having to specify one if you are not
1743 Also, there have not currently been made special provisions for forking:
1744 when you fork, you not only have to call C<ev_loop_fork> on both loops,
1745 but you will also have to stop and restart any C<ev_embed> watchers
1748 Unfortunately, not all backends are embeddable, only the ones returned by
1749 C<ev_embeddable_backends> are, which, unfortunately, does not include any
1752 So when you want to use this feature you will always have to be prepared
1753 that you cannot get an embeddable loop. The recommended way to get around
1754 this is to have a separate variables for your embeddable loop, try to
1755 create it, and if that fails, use the normal loop for everything:
1757 struct ev_loop *loop_hi = ev_default_init (0);
1758 struct ev_loop *loop_lo = 0;
1759 struct ev_embed embed;
1761 // see if there is a chance of getting one that works
1762 // (remember that a flags value of 0 means autodetection)
1763 loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1764 ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1767 // if we got one, then embed it, otherwise default to loop_hi
1770 ev_embed_init (&embed, 0, loop_lo);
1771 ev_embed_start (loop_hi, &embed);
1776 =head3 Watcher-Specific Functions and Data Members
1780 =item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1782 =item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
1784 Configures the watcher to embed the given loop, which must be
1785 embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1786 invoked automatically, otherwise it is the responsibility of the callback
1787 to invoke it (it will continue to be called until the sweep has been done,
1788 if you do not want thta, you need to temporarily stop the embed watcher).
1790 =item ev_embed_sweep (loop, ev_embed *)
1792 Make a single, non-blocking sweep over the embedded loop. This works
1793 similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
1794 apropriate way for embedded loops.
1796 =item struct ev_loop *loop [read-only]
1798 The embedded event loop.
1803 =head2 C<ev_fork> - the audacity to resume the event loop after a fork
1805 Fork watchers are called when a C<fork ()> was detected (usually because
1806 whoever is a good citizen cared to tell libev about it by calling
1807 C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
1808 event loop blocks next and before C<ev_check> watchers are being called,
1809 and only in the child after the fork. If whoever good citizen calling
1810 C<ev_default_fork> cheats and calls it in the wrong process, the fork
1811 handlers will be invoked, too, of course.
1813 =head3 Watcher-Specific Functions and Data Members
1817 =item ev_fork_init (ev_signal *, callback)
1819 Initialises and configures the fork watcher - it has no parameters of any
1820 kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
1826 =head1 OTHER FUNCTIONS
1828 There are some other functions of possible interest. Described. Here. Now.
1832 =item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1834 This function combines a simple timer and an I/O watcher, calls your
1835 callback on whichever event happens first and automatically stop both
1836 watchers. This is useful if you want to wait for a single event on an fd
1837 or timeout without having to allocate/configure/start/stop/free one or
1838 more watchers yourself.
1840 If C<fd> is less than 0, then no I/O watcher will be started and events
1841 is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and
1842 C<events> set will be craeted and started.
1844 If C<timeout> is less than 0, then no timeout watcher will be
1845 started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1846 repeat = 0) will be started. While C<0> is a valid timeout, it is of
1849 The callback has the type C<void (*cb)(int revents, void *arg)> and gets
1850 passed an C<revents> set like normal event callbacks (a combination of
1851 C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
1852 value passed to C<ev_once>:
1854 static void stdin_ready (int revents, void *arg)
1856 if (revents & EV_TIMEOUT)
1857 /* doh, nothing entered */;
1858 else if (revents & EV_READ)
1859 /* stdin might have data for us, joy! */;
1862 ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1864 =item ev_feed_event (ev_loop *, watcher *, int revents)
1866 Feeds the given event set into the event loop, as if the specified event
1867 had happened for the specified watcher (which must be a pointer to an
1868 initialised but not necessarily started event watcher).
1870 =item ev_feed_fd_event (ev_loop *, int fd, int revents)
1872 Feed an event on the given fd, as if a file descriptor backend detected
1873 the given events it.
1875 =item ev_feed_signal_event (ev_loop *loop, int signum)
1877 Feed an event as if the given signal occured (C<loop> must be the default
1883 =head1 LIBEVENT EMULATION
1885 Libev offers a compatibility emulation layer for libevent. It cannot
1886 emulate the internals of libevent, so here are some usage hints:
1890 =item * Use it by including <event.h>, as usual.
1892 =item * The following members are fully supported: ev_base, ev_callback,
1893 ev_arg, ev_fd, ev_res, ev_events.
1895 =item * Avoid using ev_flags and the EVLIST_*-macros, while it is
1896 maintained by libev, it does not work exactly the same way as in libevent (consider
1899 =item * Priorities are not currently supported. Initialising priorities
1900 will fail and all watchers will have the same priority, even though there
1903 =item * Other members are not supported.
1905 =item * The libev emulation is I<not> ABI compatible to libevent, you need
1906 to use the libev header file and library.
1912 Libev comes with some simplistic wrapper classes for C++ that mainly allow
1913 you to use some convinience methods to start/stop watchers and also change
1914 the callback model to a model using method callbacks on objects.
1920 This automatically includes F<ev.h> and puts all of its definitions (many
1921 of them macros) into the global namespace. All C++ specific things are
1922 put into the C<ev> namespace. It should support all the same embedding
1923 options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
1925 Care has been taken to keep the overhead low. The only data member the C++
1926 classes add (compared to plain C-style watchers) is the event loop pointer
1927 that the watcher is associated with (or no additional members at all if
1928 you disable C<EV_MULTIPLICITY> when embedding libev).
1930 Currently, functions, and static and non-static member functions can be
1931 used as callbacks. Other types should be easy to add as long as they only
1932 need one additional pointer for context. If you need support for other
1933 types of functors please contact the author (preferably after implementing
1936 Here is a list of things available in the C<ev> namespace:
1940 =item C<ev::READ>, C<ev::WRITE> etc.
1942 These are just enum values with the same values as the C<EV_READ> etc.
1943 macros from F<ev.h>.
1945 =item C<ev::tstamp>, C<ev::now>
1947 Aliases to the same types/functions as with the C<ev_> prefix.
1949 =item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
1951 For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
1952 the same name in the C<ev> namespace, with the exception of C<ev_signal>
1953 which is called C<ev::sig> to avoid clashes with the C<signal> macro
1954 defines by many implementations.
1956 All of those classes have these methods:
1960 =item ev::TYPE::TYPE ()
1962 =item ev::TYPE::TYPE (struct ev_loop *)
1964 =item ev::TYPE::~TYPE
1966 The constructor (optionally) takes an event loop to associate the watcher
1967 with. If it is omitted, it will use C<EV_DEFAULT>.
1969 The constructor calls C<ev_init> for you, which means you have to call the
1970 C<set> method before starting it.
1972 It will not set a callback, however: You have to call the templated C<set>
1973 method to set a callback before you can start the watcher.
1975 (The reason why you have to use a method is a limitation in C++ which does
1976 not allow explicit template arguments for constructors).
1978 The destructor automatically stops the watcher if it is active.
1980 =item w->set<class, &class::method> (object *)
1982 This method sets the callback method to call. The method has to have a
1983 signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
1984 first argument and the C<revents> as second. The object must be given as
1985 parameter and is stored in the C<data> member of the watcher.
1987 This method synthesizes efficient thunking code to call your method from
1988 the C callback that libev requires. If your compiler can inline your
1989 callback (i.e. it is visible to it at the place of the C<set> call and
1990 your compiler is good :), then the method will be fully inlined into the
1991 thunking function, making it as fast as a direct C callback.
1993 Example: simple class declaration and watcher initialisation
1997 void io_cb (ev::io &w, int revents) { }
2002 iow.set <myclass, &myclass::io_cb> (&obj);
2004 =item w->set<function> (void *data = 0)
2006 Also sets a callback, but uses a static method or plain function as
2007 callback. The optional C<data> argument will be stored in the watcher's
2008 C<data> member and is free for you to use.
2010 The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2012 See the method-C<set> above for more details.
2016 static void io_cb (ev::io &w, int revents) { }
2019 =item w->set (struct ev_loop *)
2021 Associates a different C<struct ev_loop> with this watcher. You can only
2022 do this when the watcher is inactive (and not pending either).
2024 =item w->set ([args])
2026 Basically the same as C<ev_TYPE_set>, with the same args. Must be
2027 called at least once. Unlike the C counterpart, an active watcher gets
2028 automatically stopped and restarted when reconfiguring it with this
2033 Starts the watcher. Note that there is no C<loop> argument, as the
2034 constructor already stores the event loop.
2038 Stops the watcher if it is active. Again, no C<loop> argument.
2040 =item w->again () (C<ev::timer>, C<ev::periodic> only)
2042 For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
2043 C<ev_TYPE_again> function.
2045 =item w->sweep () (C<ev::embed> only)
2047 Invokes C<ev_embed_sweep>.
2049 =item w->update () (C<ev::stat> only)
2051 Invokes C<ev_stat_stat>.
2057 Example: Define a class with an IO and idle watcher, start one of them in
2062 ev_io io; void io_cb (ev::io &w, int revents);
2063 ev_idle idle void idle_cb (ev::idle &w, int revents);
2068 myclass::myclass (int fd)
2070 io .set <myclass, &myclass::io_cb > (this);
2071 idle.set <myclass, &myclass::idle_cb> (this);
2073 io.start (fd, ev::READ);
2079 Libev can be compiled with a variety of options, the most fundamantal
2080 of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2081 functions and callbacks have an initial C<struct ev_loop *> argument.
2083 To make it easier to write programs that cope with either variant, the
2084 following macros are defined:
2088 =item C<EV_A>, C<EV_A_>
2090 This provides the loop I<argument> for functions, if one is required ("ev
2091 loop argument"). The C<EV_A> form is used when this is the sole argument,
2092 C<EV_A_> is used when other arguments are following. Example:
2095 ev_timer_add (EV_A_ watcher);
2098 It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2099 which is often provided by the following macro.
2101 =item C<EV_P>, C<EV_P_>
2103 This provides the loop I<parameter> for functions, if one is required ("ev
2104 loop parameter"). The C<EV_P> form is used when this is the sole parameter,
2105 C<EV_P_> is used when other parameters are following. Example:
2107 // this is how ev_unref is being declared
2108 static void ev_unref (EV_P);
2110 // this is how you can declare your typical callback
2111 static void cb (EV_P_ ev_timer *w, int revents)
2113 It declares a parameter C<loop> of type C<struct ev_loop *>, quite
2114 suitable for use with C<EV_A>.
2116 =item C<EV_DEFAULT>, C<EV_DEFAULT_>
2118 Similar to the other two macros, this gives you the value of the default
2119 loop, if multiple loops are supported ("ev loop default").
2123 Example: Declare and initialise a check watcher, utilising the above
2124 macros so it will work regardless of whether multiple loops are supported
2128 check_cb (EV_P_ ev_timer *w, int revents)
2130 ev_check_stop (EV_A_ w);
2134 ev_check_init (&check, check_cb);
2135 ev_check_start (EV_DEFAULT_ &check);
2136 ev_loop (EV_DEFAULT_ 0);
2140 Libev can (and often is) directly embedded into host
2141 applications. Examples of applications that embed it include the Deliantra
2142 Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
2145 The goal is to enable you to just copy the neecssary files into your
2146 source directory without having to change even a single line in them, so
2147 you can easily upgrade by simply copying (or having a checked-out copy of
2148 libev somewhere in your source tree).
2152 Depending on what features you need you need to include one or more sets of files
2155 =head3 CORE EVENT LOOP
2157 To include only the libev core (all the C<ev_*> functions), with manual
2158 configuration (no autoconf):
2160 #define EV_STANDALONE 1
2163 This will automatically include F<ev.h>, too, and should be done in a
2164 single C source file only to provide the function implementations. To use
2165 it, do the same for F<ev.h> in all files wishing to use this API (best
2166 done by writing a wrapper around F<ev.h> that you can include instead and
2167 where you can put other configuration options):
2169 #define EV_STANDALONE 1
2172 Both header files and implementation files can be compiled with a C++
2173 compiler (at least, thats a stated goal, and breakage will be treated
2176 You need the following files in your source tree, or in a directory
2177 in your include path (e.g. in libev/ when using -Ilibev):
2184 ev_win32.c required on win32 platforms only
2186 ev_select.c only when select backend is enabled (which is enabled by default)
2187 ev_poll.c only when poll backend is enabled (disabled by default)
2188 ev_epoll.c only when the epoll backend is enabled (disabled by default)
2189 ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2190 ev_port.c only when the solaris port backend is enabled (disabled by default)
2192 F<ev.c> includes the backend files directly when enabled, so you only need
2193 to compile this single file.
2195 =head3 LIBEVENT COMPATIBILITY API
2197 To include the libevent compatibility API, also include:
2201 in the file including F<ev.c>, and:
2205 in the files that want to use the libevent API. This also includes F<ev.h>.
2207 You need the following additional files for this:
2212 =head3 AUTOCONF SUPPORT
2214 Instead of using C<EV_STANDALONE=1> and providing your config in
2215 whatever way you want, you can also C<m4_include([libev.m4])> in your
2216 F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2217 include F<config.h> and configure itself accordingly.
2219 For this of course you need the m4 file:
2223 =head2 PREPROCESSOR SYMBOLS/MACROS
2225 Libev can be configured via a variety of preprocessor symbols you have to define
2226 before including any of its files. The default is not to build for multiplicity
2227 and only include the select backend.
2233 Must always be C<1> if you do not use autoconf configuration, which
2234 keeps libev from including F<config.h>, and it also defines dummy
2235 implementations for some libevent functions (such as logging, which is not
2236 supported). It will also not define any of the structs usually found in
2237 F<event.h> that are not directly supported by the libev core alone.
2239 =item EV_USE_MONOTONIC
2241 If defined to be C<1>, libev will try to detect the availability of the
2242 monotonic clock option at both compiletime and runtime. Otherwise no use
2243 of the monotonic clock option will be attempted. If you enable this, you
2244 usually have to link against librt or something similar. Enabling it when
2245 the functionality isn't available is safe, though, althoguh you have
2246 to make sure you link against any libraries where the C<clock_gettime>
2247 function is hiding in (often F<-lrt>).
2249 =item EV_USE_REALTIME
2251 If defined to be C<1>, libev will try to detect the availability of the
2252 realtime clock option at compiletime (and assume its availability at
2253 runtime if successful). Otherwise no use of the realtime clock option will
2254 be attempted. This effectively replaces C<gettimeofday> by C<clock_get
2255 (CLOCK_REALTIME, ...)> and will not normally affect correctness. See the
2256 note about libraries in the description of C<EV_USE_MONOTONIC>, though.
2260 If undefined or defined to be C<1>, libev will compile in support for the
2261 C<select>(2) backend. No attempt at autodetection will be done: if no
2262 other method takes over, select will be it. Otherwise the select backend
2263 will not be compiled in.
2265 =item EV_SELECT_USE_FD_SET
2267 If defined to C<1>, then the select backend will use the system C<fd_set>
2268 structure. This is useful if libev doesn't compile due to a missing
2269 C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on
2270 exotic systems. This usually limits the range of file descriptors to some
2271 low limit such as 1024 or might have other limitations (winsocket only
2272 allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might
2273 influence the size of the C<fd_set> used.
2275 =item EV_SELECT_IS_WINSOCKET
2277 When defined to C<1>, the select backend will assume that
2278 select/socket/connect etc. don't understand file descriptors but
2279 wants osf handles on win32 (this is the case when the select to
2280 be used is the winsock select). This means that it will call
2281 C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2282 it is assumed that all these functions actually work on fds, even
2283 on win32. Should not be defined on non-win32 platforms.
2287 If defined to be C<1>, libev will compile in support for the C<poll>(2)
2288 backend. Otherwise it will be enabled on non-win32 platforms. It
2289 takes precedence over select.
2293 If defined to be C<1>, libev will compile in support for the Linux
2294 C<epoll>(7) backend. Its availability will be detected at runtime,
2295 otherwise another method will be used as fallback. This is the
2296 preferred backend for GNU/Linux systems.
2300 If defined to be C<1>, libev will compile in support for the BSD style
2301 C<kqueue>(2) backend. Its actual availability will be detected at runtime,
2302 otherwise another method will be used as fallback. This is the preferred
2303 backend for BSD and BSD-like systems, although on most BSDs kqueue only
2304 supports some types of fds correctly (the only platform we found that
2305 supports ptys for example was NetBSD), so kqueue might be compiled in, but
2306 not be used unless explicitly requested. The best way to use it is to find
2307 out whether kqueue supports your type of fd properly and use an embedded
2312 If defined to be C<1>, libev will compile in support for the Solaris
2313 10 port style backend. Its availability will be detected at runtime,
2314 otherwise another method will be used as fallback. This is the preferred
2315 backend for Solaris 10 systems.
2317 =item EV_USE_DEVPOLL
2319 reserved for future expansion, works like the USE symbols above.
2321 =item EV_USE_INOTIFY
2323 If defined to be C<1>, libev will compile in support for the Linux inotify
2324 interface to speed up C<ev_stat> watchers. Its actual availability will
2325 be detected at runtime.
2329 The name of the F<ev.h> header file used to include it. The default if
2330 undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This
2331 can be used to virtually rename the F<ev.h> header file in case of conflicts.
2335 If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2336 F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2341 Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2342 of how the F<event.h> header can be found.
2346 If defined to be C<0>, then F<ev.h> will not define any function
2347 prototypes, but still define all the structs and other symbols. This is
2348 occasionally useful if you want to provide your own wrapper functions
2349 around libev functions.
2351 =item EV_MULTIPLICITY
2353 If undefined or defined to C<1>, then all event-loop-specific functions
2354 will have the C<struct ev_loop *> as first argument, and you can create
2355 additional independent event loops. Otherwise there will be no support
2356 for multiple event loops and there is no first event loop pointer
2357 argument. Instead, all functions act on the single default loop.
2363 The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
2364 C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
2365 provide for more priorities by overriding those symbols (usually defined
2366 to be C<-2> and C<2>, respectively).
2368 When doing priority-based operations, libev usually has to linearly search
2369 all the priorities, so having many of them (hundreds) uses a lot of space
2370 and time, so using the defaults of five priorities (-2 .. +2) is usually
2373 If your embedding app does not need any priorities, defining these both to
2374 C<0> will save some memory and cpu.
2376 =item EV_PERIODIC_ENABLE
2378 If undefined or defined to be C<1>, then periodic timers are supported. If
2379 defined to be C<0>, then they are not. Disabling them saves a few kB of
2382 =item EV_IDLE_ENABLE
2384 If undefined or defined to be C<1>, then idle watchers are supported. If
2385 defined to be C<0>, then they are not. Disabling them saves a few kB of
2388 =item EV_EMBED_ENABLE
2390 If undefined or defined to be C<1>, then embed watchers are supported. If
2391 defined to be C<0>, then they are not.
2393 =item EV_STAT_ENABLE
2395 If undefined or defined to be C<1>, then stat watchers are supported. If
2396 defined to be C<0>, then they are not.
2398 =item EV_FORK_ENABLE
2400 If undefined or defined to be C<1>, then fork watchers are supported. If
2401 defined to be C<0>, then they are not.
2405 If you need to shave off some kilobytes of code at the expense of some
2406 speed, define this symbol to C<1>. Currently only used for gcc to override
2407 some inlining decisions, saves roughly 30% codesize of amd64.
2409 =item EV_PID_HASHSIZE
2411 C<ev_child> watchers use a small hash table to distribute workload by
2412 pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
2413 than enough. If you need to manage thousands of children you might want to
2414 increase this value (I<must> be a power of two).
2416 =item EV_INOTIFY_HASHSIZE
2418 C<ev_staz> watchers use a small hash table to distribute workload by
2419 inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
2420 usually more than enough. If you need to manage thousands of C<ev_stat>
2421 watchers you might want to increase this value (I<must> be a power of
2426 By default, all watchers have a C<void *data> member. By redefining
2427 this macro to a something else you can include more and other types of
2428 members. You have to define it each time you include one of the files,
2429 though, and it must be identical each time.
2431 For example, the perl EV module uses something like this:
2434 SV *self; /* contains this struct */ \
2435 SV *cb_sv, *fh /* note no trailing ";" */
2437 =item EV_CB_DECLARE (type)
2439 =item EV_CB_INVOKE (watcher, revents)
2441 =item ev_set_cb (ev, cb)
2443 Can be used to change the callback member declaration in each watcher,
2444 and the way callbacks are invoked and set. Must expand to a struct member
2445 definition and a statement, respectively. See the F<ev.v> header file for
2446 their default definitions. One possible use for overriding these is to
2447 avoid the C<struct ev_loop *> as first argument in all cases, or to use
2448 method calls instead of plain function calls in C++.
2450 =head2 EXPORTED API SYMBOLS
2452 If you need to re-export the API (e.g. via a dll) and you need a list of
2453 exported symbols, you can use the provided F<Symbol.*> files which list
2454 all public symbols, one per line:
2456 Symbols.ev for libev proper
2457 Symbols.event for the libevent emulation
2459 This can also be used to rename all public symbols to avoid clashes with
2460 multiple versions of libev linked together (which is obviously bad in
2461 itself, but sometimes it is inconvinient to avoid this).
2463 A sed comamnd like this will create wrapper C<#define>'s that you need to
2464 include before including F<ev.h>:
2466 <Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
2468 This would create a file F<wrap.h> which essentially looks like this:
2470 #define ev_backend myprefix_ev_backend
2471 #define ev_check_start myprefix_ev_check_start
2472 #define ev_check_stop myprefix_ev_check_stop
2477 For a real-world example of a program the includes libev
2478 verbatim, you can have a look at the EV perl module
2479 (L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
2480 the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
2481 interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
2482 will be compiled. It is pretty complex because it provides its own header
2485 The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2486 that everybody includes and which overrides some configure choices:
2488 #define EV_MINIMAL 1
2489 #define EV_USE_POLL 0
2490 #define EV_MULTIPLICITY 0
2491 #define EV_PERIODIC_ENABLE 0
2492 #define EV_STAT_ENABLE 0
2493 #define EV_FORK_ENABLE 0
2494 #define EV_CONFIG_H <config.h>
2500 And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2508 In this section the complexities of (many of) the algorithms used inside
2509 libev will be explained. For complexity discussions about backends see the
2510 documentation for C<ev_default_init>.
2512 All of the following are about amortised time: If an array needs to be
2513 extended, libev needs to realloc and move the whole array, but this
2514 happens asymptotically never with higher number of elements, so O(1) might
2515 mean it might do a lengthy realloc operation in rare cases, but on average
2516 it is much faster and asymptotically approaches constant time.
2520 =item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2522 This means that, when you have a watcher that triggers in one hour and
2523 there are 100 watchers that would trigger before that then inserting will
2524 have to skip those 100 watchers.
2526 =item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)
2528 That means that for changing a timer costs less than removing/adding them
2529 as only the relative motion in the event queue has to be paid for.
2531 =item Starting io/check/prepare/idle/signal/child watchers: O(1)
2533 These just add the watcher into an array or at the head of a list.
2534 =item Stopping check/prepare/idle watchers: O(1)
2536 =item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2538 These watchers are stored in lists then need to be walked to find the
2539 correct watcher to remove. The lists are usually short (you don't usually
2540 have many watchers waiting for the same fd or signal).
2542 =item Finding the next timer per loop iteration: O(1)
2544 =item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2546 A change means an I/O watcher gets started or stopped, which requires
2547 libev to recalculate its status (and possibly tell the kernel).
2549 =item Activating one watcher: O(1)
2551 =item Priority handling: O(number_of_priorities)
2553 Priorities are implemented by allocating some space for each
2554 priority. When doing priority-based operations, libev usually has to
2555 linearly search all the priorities.
2562 Marc Lehmann <libev@schmorp.de>.