ViewVC Help

View File | Revision Log | Show Annotations | Download File

/cvs/libev/ev.pod

Comparing libev/ev.pod (file contents):
Revision 1.338 by root, Sun Oct 31 21:16:26 2010 UTC vs.
Revision 1.456 by root, Tue Jul 2 06:07:54 2019 UTC

		1	=encoding utf-8
		2
1	=head1 NAME	3	=head1 NAME
2		4
3	libev - a high performance full-featured event loop written in C	5	libev - a high performance full-featured event loop written in C
4		6
5	=head1 SYNOPSIS	7	=head1 SYNOPSIS
…		…
58	ev_timer_start (loop, &timeout_watcher);	60	ev_timer_start (loop, &timeout_watcher);
59		61
60	// now wait for events to arrive	62	// now wait for events to arrive
61	ev_run (loop, 0);	63	ev_run (loop, 0);
62		64
63	// unloop was called, so exit	65	// break was called, so exit
64	return 0;	66	return 0;
65	}	67	}
66		68
67	=head1 ABOUT THIS DOCUMENT	69	=head1 ABOUT THIS DOCUMENT
68		70
…		…
82		84
83	=head1 WHAT TO READ WHEN IN A HURRY	85	=head1 WHAT TO READ WHEN IN A HURRY
84		86
85	This manual tries to be very detailed, but unfortunately, this also makes	87	This manual tries to be very detailed, but unfortunately, this also makes
86	it very long. If you just want to know the basics of libev, I suggest	88	it very long. If you just want to know the basics of libev, I suggest
87	reading L<ANATOMY OF A WATCHER>, then the L<EXAMPLE PROGRAM> above and	89	reading L</ANATOMY OF A WATCHER>, then the L</EXAMPLE PROGRAM> above and
88	look up the missing functions in L<GLOBAL FUNCTIONS> and the C<ev_io> and	90	look up the missing functions in L</GLOBAL FUNCTIONS> and the C<ev_io> and
89	C<ev_timer> sections in L<WATCHER TYPES>.	91	C<ev_timer> sections in L</WATCHER TYPES>.
90		92
91	=head1 ABOUT LIBEV	93	=head1 ABOUT LIBEV
92		94
93	Libev is an event loop: you register interest in certain events (such as a	95	Libev is an event loop: you register interest in certain events (such as a
94	file descriptor being readable or a timeout occurring), and it will manage	96	file descriptor being readable or a timeout occurring), and it will manage
…		…
103	details of the event, and then hand it over to libev by I<starting> the	105	details of the event, and then hand it over to libev by I<starting> the
104	watcher.	106	watcher.
105		107
106	=head2 FEATURES	108	=head2 FEATURES
107		109
108	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	110	Libev supports C<select>, C<poll>, the Linux-specific aio and C<epoll>
109	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	111	interfaces, the BSD-specific C<kqueue> and the Solaris-specific event port
110	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	112	mechanisms for file descriptor events (C<ev_io>), the Linux C<inotify>
111	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner	113	interface (for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
112	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative	114	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
113	timers (C<ev_timer>), absolute timers with customised rescheduling	115	timers (C<ev_timer>), absolute timers with customised rescheduling
114	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status	116	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
115	change events (C<ev_child>), and event watchers dealing with the event	117	change events (C<ev_child>), and event watchers dealing with the event
116	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and	118	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
…		…
157	When libev detects a usage error such as a negative timer interval, then	159	When libev detects a usage error such as a negative timer interval, then
158	it will print a diagnostic message and abort (via the C<assert> mechanism,	160	it will print a diagnostic message and abort (via the C<assert> mechanism,
159	so C<NDEBUG> will disable this checking): these are programming errors in	161	so C<NDEBUG> will disable this checking): these are programming errors in
160	the libev caller and need to be fixed there.	162	the libev caller and need to be fixed there.
161		163
		164	Via the C<EV_FREQUENT> macro you can compile in and/or enable extensive
		165	consistency checking code inside libev that can be used to check for
		166	internal inconsistencies, suually caused by application bugs.
		167
162	Libev also has a few internal error-checking C<assert>ions, and also has	168	Libev also has a few internal error-checking C<assert>ions. These do not
163	extensive consistency checking code. These do not trigger under normal
164	circumstances, as they indicate either a bug in libev or worse.	169	trigger under normal circumstances, as they indicate either a bug in libev
		170	or worse.
165		171
166		172
167	=head1 GLOBAL FUNCTIONS	173	=head1 GLOBAL FUNCTIONS
168		174
169	These functions can be called anytime, even before initialising the	175	These functions can be called anytime, even before initialising the
…		…
174	=item ev_tstamp ev_time ()	180	=item ev_tstamp ev_time ()
175		181
176	Returns the current time as libev would use it. Please note that the	182	Returns the current time as libev would use it. Please note that the
177	C<ev_now> function is usually faster and also often returns the timestamp	183	C<ev_now> function is usually faster and also often returns the timestamp
178	you actually want to know. Also interesting is the combination of	184	you actually want to know. Also interesting is the combination of
179	C<ev_update_now> and C<ev_now>.	185	C<ev_now_update> and C<ev_now>.
180		186
181	=item ev_sleep (ev_tstamp interval)	187	=item ev_sleep (ev_tstamp interval)
182		188
183	Sleep for the given interval: The current thread will be blocked until	189	Sleep for the given interval: The current thread will be blocked
184	either it is interrupted or the given time interval has passed. Basically	190	until either it is interrupted or the given time interval has
		191	passed (approximately - it might return a bit earlier even if not
		192	interrupted). Returns immediately if C<< interval <= 0 >>.
		193
185	this is a sub-second-resolution C<sleep ()>.	194	Basically this is a sub-second-resolution C<sleep ()>.
		195
		196	The range of the C<interval> is limited - libev only guarantees to work
		197	with sleep times of up to one day (C<< interval <= 86400 >>).
186		198
187	=item int ev_version_major ()	199	=item int ev_version_major ()
188		200
189	=item int ev_version_minor ()	201	=item int ev_version_minor ()
190		202
…		…
241	the current system, you would need to look at C<ev_embeddable_backends ()	253	the current system, you would need to look at C<ev_embeddable_backends ()
242	& ev_supported_backends ()>, likewise for recommended ones.	254	& ev_supported_backends ()>, likewise for recommended ones.
243		255
244	See the description of C<ev_embed> watchers for more info.	256	See the description of C<ev_embed> watchers for more info.
245		257
246	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]	258	=item ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())
247		259
248	Sets the allocation function to use (the prototype is similar - the	260	Sets the allocation function to use (the prototype is similar - the
249	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is	261	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
250	used to allocate and free memory (no surprises here). If it returns zero	262	used to allocate and free memory (no surprises here). If it returns zero
251	when memory needs to be allocated (C<size != 0>), the library might abort	263	when memory needs to be allocated (C<size != 0>), the library might abort
…		…
257		269
258	You could override this function in high-availability programs to, say,	270	You could override this function in high-availability programs to, say,
259	free some memory if it cannot allocate memory, to use a special allocator,	271	free some memory if it cannot allocate memory, to use a special allocator,
260	or even to sleep a while and retry until some memory is available.	272	or even to sleep a while and retry until some memory is available.
261		273
		274	Example: The following is the C<realloc> function that libev itself uses
		275	which should work with C<realloc> and C<free> functions of all kinds and
		276	is probably a good basis for your own implementation.
		277
		278	static void *
		279	ev_realloc_emul (void *ptr, long size) EV_NOEXCEPT
		280	{
		281	if (size)
		282	return realloc (ptr, size);
		283
		284	free (ptr);
		285	return 0;
		286	}
		287
262	Example: Replace the libev allocator with one that waits a bit and then	288	Example: Replace the libev allocator with one that waits a bit and then
263	retries (example requires a standards-compliant C<realloc>).	289	retries.
264		290
265	static void *	291	static void *
266	persistent_realloc (void *ptr, size_t size)	292	persistent_realloc (void *ptr, size_t size)
267	{	293	{
		294	if (!size)
		295	{
		296	free (ptr);
		297	return 0;
		298	}
		299
268	for (;;)	300	for (;;)
269	{	301	{
270	void *newptr = realloc (ptr, size);	302	void *newptr = realloc (ptr, size);
271		303
272	if (newptr)	304	if (newptr)
…		…
277	}	309	}
278		310
279	...	311	...
280	ev_set_allocator (persistent_realloc);	312	ev_set_allocator (persistent_realloc);
281		313
282	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]	314	=item ev_set_syserr_cb (void (*cb)(const char *msg) throw ())
283		315
284	Set the callback function to call on a retryable system call error (such	316	Set the callback function to call on a retryable system call error (such
285	as failed select, poll, epoll_wait). The message is a printable string	317	as failed select, poll, epoll_wait). The message is a printable string
286	indicating the system call or subsystem causing the problem. If this	318	indicating the system call or subsystem causing the problem. If this
287	callback is set, then libev will expect it to remedy the situation, no	319	callback is set, then libev will expect it to remedy the situation, no
…		…
299	}	331	}
300		332
301	...	333	...
302	ev_set_syserr_cb (fatal_error);	334	ev_set_syserr_cb (fatal_error);
303		335
		336	=item ev_feed_signal (int signum)
		337
		338	This function can be used to "simulate" a signal receive. It is completely
		339	safe to call this function at any time, from any context, including signal
		340	handlers or random threads.
		341
		342	Its main use is to customise signal handling in your process, especially
		343	in the presence of threads. For example, you could block signals
		344	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		345	creating any loops), and in one thread, use C<sigwait> or any other
		346	mechanism to wait for signals, then "deliver" them to libev by calling
		347	C<ev_feed_signal>.
		348
304	=back	349	=back
305		350
306	=head1 FUNCTIONS CONTROLLING EVENT LOOPS	351	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
307		352
308	An event loop is described by a C<struct ev_loop *> (the C<struct> is	353	An event loop is described by a C<struct ev_loop *> (the C<struct> is
…		…
355	=item struct ev_loop *ev_loop_new (unsigned int flags)	400	=item struct ev_loop *ev_loop_new (unsigned int flags)
356		401
357	This will create and initialise a new event loop object. If the loop	402	This will create and initialise a new event loop object. If the loop
358	could not be initialised, returns false.	403	could not be initialised, returns false.
359		404
360	Note that this function I<is> thread-safe, and one common way to use	405	This function is thread-safe, and one common way to use libev with
361	libev with threads is indeed to create one loop per thread, and using the	406	threads is indeed to create one loop per thread, and using the default
362	default loop in the "main" or "initial" thread.	407	loop in the "main" or "initial" thread.
363		408
364	The flags argument can be used to specify special behaviour or specific	409	The flags argument can be used to specify special behaviour or specific
365	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	410	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
366		411
367	The following flags are supported:	412	The following flags are supported:
…		…
377		422
378	If this flag bit is or'ed into the flag value (or the program runs setuid	423	If this flag bit is or'ed into the flag value (or the program runs setuid
379	or setgid) then libev will I<not> look at the environment variable	424	or setgid) then libev will I<not> look at the environment variable
380	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	425	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
381	override the flags completely if it is found in the environment. This is	426	override the flags completely if it is found in the environment. This is
382	useful to try out specific backends to test their performance, or to work	427	useful to try out specific backends to test their performance, to work
383	around bugs.	428	around bugs, or to make libev threadsafe (accessing environment variables
		429	cannot be done in a threadsafe way, but usually it works if no other
		430	thread modifies them).
384		431
385	=item C<EVFLAG_FORKCHECK>	432	=item C<EVFLAG_FORKCHECK>
386		433
387	Instead of calling C<ev_loop_fork> manually after a fork, you can also	434	Instead of calling C<ev_loop_fork> manually after a fork, you can also
388	make libev check for a fork in each iteration by enabling this flag.	435	make libev check for a fork in each iteration by enabling this flag.
389		436
390	This works by calling C<getpid ()> on every iteration of the loop,	437	This works by calling C<getpid ()> on every iteration of the loop,
391	and thus this might slow down your event loop if you do a lot of loop	438	and thus this might slow down your event loop if you do a lot of loop
392	iterations and little real work, but is usually not noticeable (on my	439	iterations and little real work, but is usually not noticeable (on my
393	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence	440	GNU/Linux system for example, C<getpid> is actually a simple 5-insn
394	without a system call and thus I<very> fast, but my GNU/Linux system also has	441	sequence without a system call and thus I<very> fast, but my GNU/Linux
395	C<pthread_atfork> which is even faster).	442	system also has C<pthread_atfork> which is even faster). (Update: glibc
		443	versions 2.25 apparently removed the C<getpid> optimisation again).
396		444
397	The big advantage of this flag is that you can forget about fork (and	445	The big advantage of this flag is that you can forget about fork (and
398	forget about forgetting to tell libev about forking) when you use this	446	forget about forgetting to tell libev about forking, although you still
399	flag.	447	have to ignore C<SIGPIPE>) when you use this flag.
400		448
401	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>	449	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
402	environment variable.	450	environment variable.
403		451
404	=item C<EVFLAG_NOINOTIFY>	452	=item C<EVFLAG_NOINOTIFY>
405		453
406	When this flag is specified, then libev will not attempt to use the	454	When this flag is specified, then libev will not attempt to use the
407	I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and	455	I<inotify> API for its C<ev_stat> watchers. Apart from debugging and
408	testing, this flag can be useful to conserve inotify file descriptors, as	456	testing, this flag can be useful to conserve inotify file descriptors, as
409	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.	457	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
410		458
411	=item C<EVFLAG_SIGNALFD>	459	=item C<EVFLAG_SIGNALFD>
412		460
413	When this flag is specified, then libev will attempt to use the	461	When this flag is specified, then libev will attempt to use the
414	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This API	462	I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API
415	delivers signals synchronously, which makes it both faster and might make	463	delivers signals synchronously, which makes it both faster and might make
416	it possible to get the queued signal data. It can also simplify signal	464	it possible to get the queued signal data. It can also simplify signal
417	handling with threads, as long as you properly block signals in your	465	handling with threads, as long as you properly block signals in your
418	threads that are not interested in handling them.	466	threads that are not interested in handling them.
419		467
420	Signalfd will not be used by default as this changes your signal mask, and	468	Signalfd will not be used by default as this changes your signal mask, and
421	there are a lot of shoddy libraries and programs (glib's threadpool for	469	there are a lot of shoddy libraries and programs (glib's threadpool for
422	example) that can't properly initialise their signal masks.	470	example) that can't properly initialise their signal masks.
		471
		472	=item C<EVFLAG_NOSIGMASK>
		473
		474	When this flag is specified, then libev will avoid to modify the signal
		475	mask. Specifically, this means you have to make sure signals are unblocked
		476	when you want to receive them.
		477
		478	This behaviour is useful when you want to do your own signal handling, or
		479	want to handle signals only in specific threads and want to avoid libev
		480	unblocking the signals.
		481
		482	It's also required by POSIX in a threaded program, as libev calls
		483	C<sigprocmask>, whose behaviour is officially unspecified.
		484
		485	This flag's behaviour will become the default in future versions of libev.
423		486
424	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	487	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
425		488
426	This is your standard select(2) backend. Not I<completely> standard, as	489	This is your standard select(2) backend. Not I<completely> standard, as
427	libev tries to roll its own fd_set with no limits on the number of fds,	490	libev tries to roll its own fd_set with no limits on the number of fds,
…		…
452	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and	515	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
453	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.	516	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
454		517
455	=item C<EVBACKEND_EPOLL> (value 4, Linux)	518	=item C<EVBACKEND_EPOLL> (value 4, Linux)
456		519
457	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9	520	Use the Linux-specific epoll(7) interface (for both pre- and post-2.6.9
458	kernels).	521	kernels).
459		522
460	For few fds, this backend is a bit little slower than poll and select,	523	For few fds, this backend is a bit little slower than poll and select, but
461	but it scales phenomenally better. While poll and select usually scale	524	it scales phenomenally better. While poll and select usually scale like
462	like O(total_fds) where n is the total number of fds (or the highest fd),	525	O(total_fds) where total_fds is the total number of fds (or the highest
463	epoll scales either O(1) or O(active_fds).	526	fd), epoll scales either O(1) or O(active_fds).
464		527
465	The epoll mechanism deserves honorable mention as the most misdesigned	528	The epoll mechanism deserves honorable mention as the most misdesigned
466	of the more advanced event mechanisms: mere annoyances include silently	529	of the more advanced event mechanisms: mere annoyances include silently
467	dropping file descriptors, requiring a system call per change per file	530	dropping file descriptors, requiring a system call per change per file
468	descriptor (and unnecessary guessing of parameters), problems with dup,	531	descriptor (and unnecessary guessing of parameters), problems with dup,
…		…
471	0.1ms) and so on. The biggest issue is fork races, however - if a program	534	0.1ms) and so on. The biggest issue is fork races, however - if a program
472	forks then I<both> parent and child process have to recreate the epoll	535	forks then I<both> parent and child process have to recreate the epoll
473	set, which can take considerable time (one syscall per file descriptor)	536	set, which can take considerable time (one syscall per file descriptor)
474	and is of course hard to detect.	537	and is of course hard to detect.
475		538
476	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but	539	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
477	of course I<doesn't>, and epoll just loves to report events for totally	540	but of course I<doesn't>, and epoll just loves to report events for
478	I<different> file descriptors (even already closed ones, so one cannot	541	totally I<different> file descriptors (even already closed ones, so
479	even remove them from the set) than registered in the set (especially	542	one cannot even remove them from the set) than registered in the set
480	on SMP systems). Libev tries to counter these spurious notifications by	543	(especially on SMP systems). Libev tries to counter these spurious
481	employing an additional generation counter and comparing that against the	544	notifications by employing an additional generation counter and comparing
482	events to filter out spurious ones, recreating the set when required. Last	545	that against the events to filter out spurious ones, recreating the set
		546	when required. Epoll also erroneously rounds down timeouts, but gives you
		547	no way to know when and by how much, so sometimes you have to busy-wait
		548	because epoll returns immediately despite a nonzero timeout. And last
483	not least, it also refuses to work with some file descriptors which work	549	not least, it also refuses to work with some file descriptors which work
484	perfectly fine with C<select> (files, many character devices...).	550	perfectly fine with C<select> (files, many character devices...).
485		551
486	Epoll is truly the train wreck analog among event poll mechanisms.	552	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		553	cobbled together in a hurry, no thought to design or interaction with
		554	others. Oh, the pain, will it ever stop...
487		555
488	While stopping, setting and starting an I/O watcher in the same iteration	556	While stopping, setting and starting an I/O watcher in the same iteration
489	will result in some caching, there is still a system call per such	557	will result in some caching, there is still a system call per such
490	incident (because the same I<file descriptor> could point to a different	558	incident (because the same I<file descriptor> could point to a different
491	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed	559	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
…		…
503	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or	571	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
504	faster than epoll for maybe up to a hundred file descriptors, depending on	572	faster than epoll for maybe up to a hundred file descriptors, depending on
505	the usage. So sad.	573	the usage. So sad.
506		574
507	While nominally embeddable in other event loops, this feature is broken in	575	While nominally embeddable in other event loops, this feature is broken in
508	all kernel versions tested so far.	576	a lot of kernel revisions, but probably(!) works in current versions.
509		577
510	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	578	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
511	C<EVBACKEND_POLL>.	579	C<EVBACKEND_POLL>.
512		580
		581	=item C<EVBACKEND_LINUXAIO> (value 64, Linux)
		582
		583	Use the Linux-specific Linux AIO (I<not> C<< aio(7) >> but C<<
		584	io_submit(2) >>) event interface available in post-4.18 kernels (but libev
		585	only tries to use it in 4.19+).
		586
		587	This is another Linux train wreck of an event interface.
		588
		589	If this backend works for you (as of this writing, it was very
		590	experimental), it is the best event interface available on Linux and might
		591	be well worth enabling it - if it isn't available in your kernel this will
		592	be detected and this backend will be skipped.
		593
		594	This backend can batch oneshot requests and supports a user-space ring
		595	buffer to receive events. It also doesn't suffer from most of the design
		596	problems of epoll (such as not being able to remove event sources from
		597	the epoll set), and generally sounds too good to be true. Because, this
		598	being the Linux kernel, of course it suffers from a whole new set of
		599	limitations, forcing you to fall back to epoll, inheriting all its design
		600	issues.
		601
		602	For one, it is not easily embeddable (but probably could be done using
		603	an event fd at some extra overhead). It also is subject to a system wide
		604	limit that can be configured in F</proc/sys/fs/aio-max-nr>. If no AIO
		605	requests are left, this backend will be skipped during initialisation, and
		606	will switch to epoll when the loop is active.
		607
		608	Most problematic in practice, however, is that not all file descriptors
		609	work with it. For example, in Linux 5.1, TCP sockets, pipes, event fds,
		610	files, F</dev/null> and many others are supported, but ttys do not work
		611	properly (a known bug that the kernel developers don't care about, see
		612	L<https://lore.kernel.org/patchwork/patch/1047453/>), so this is not
		613	(yet?) a generic event polling interface.
		614
		615	Overall, it seems the Linux developers just don't want it to have a
		616	generic event handling mechanism other than C<select> or C<poll>.
		617
		618	To work around all these problem, the current version of libev uses its
		619	epoll backend as a fallback for file descriptor types that do not work. Or
		620	falls back completely to epoll if the kernel acts up.
		621
		622	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		623	C<EVBACKEND_POLL>.
		624
513	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	625	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
514		626
515	Kqueue deserves special mention, as at the time of this writing, it	627	Kqueue deserves special mention, as at the time this backend was
516	was broken on all BSDs except NetBSD (usually it doesn't work reliably	628	implemented, it was broken on all BSDs except NetBSD (usually it doesn't
517	with anything but sockets and pipes, except on Darwin, where of course	629	work reliably with anything but sockets and pipes, except on Darwin,
518	it's completely useless). Unlike epoll, however, whose brokenness	630	where of course it's completely useless). Unlike epoll, however, whose
519	is by design, these kqueue bugs can (and eventually will) be fixed	631	brokenness is by design, these kqueue bugs can be (and mostly have been)
520	without API changes to existing programs. For this reason it's not being	632	fixed without API changes to existing programs. For this reason it's not
521	"auto-detected" unless you explicitly specify it in the flags (i.e. using	633	being "auto-detected" on all platforms unless you explicitly specify it
522	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)	634	in the flags (i.e. using C<EVBACKEND_KQUEUE>) or libev was compiled on a
523	system like NetBSD.	635	known-to-be-good (-enough) system like NetBSD.
524		636
525	You still can embed kqueue into a normal poll or select backend and use it	637	You still can embed kqueue into a normal poll or select backend and use it
526	only for sockets (after having made sure that sockets work with kqueue on	638	only for sockets (after having made sure that sockets work with kqueue on
527	the target platform). See C<ev_embed> watchers for more info.	639	the target platform). See C<ev_embed> watchers for more info.
528		640
529	It scales in the same way as the epoll backend, but the interface to the	641	It scales in the same way as the epoll backend, but the interface to the
530	kernel is more efficient (which says nothing about its actual speed, of	642	kernel is more efficient (which says nothing about its actual speed, of
531	course). While stopping, setting and starting an I/O watcher does never	643	course). While stopping, setting and starting an I/O watcher does never
532	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to	644	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
533	two event changes per incident. Support for C<fork ()> is very bad (but	645	two event changes per incident. Support for C<fork ()> is very bad (you
534	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect	646	might have to leak fds on fork, but it's more sane than epoll) and it
535	cases	647	drops fds silently in similarly hard-to-detect cases.
536		648
537	This backend usually performs well under most conditions.	649	This backend usually performs well under most conditions.
538		650
539	While nominally embeddable in other event loops, this doesn't work	651	While nominally embeddable in other event loops, this doesn't work
540	everywhere, so you might need to test for this. And since it is broken	652	everywhere, so you might need to test for this. And since it is broken
…		…
557	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	669	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
558		670
559	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	671	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
560	it's really slow, but it still scales very well (O(active_fds)).	672	it's really slow, but it still scales very well (O(active_fds)).
561		673
562	Please note that Solaris event ports can deliver a lot of spurious
563	notifications, so you need to use non-blocking I/O or other means to avoid
564	blocking when no data (or space) is available.
565
566	While this backend scales well, it requires one system call per active	674	While this backend scales well, it requires one system call per active
567	file descriptor per loop iteration. For small and medium numbers of file	675	file descriptor per loop iteration. For small and medium numbers of file
568	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	676	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
569	might perform better.	677	might perform better.
570		678
571	On the positive side, with the exception of the spurious readiness	679	On the positive side, this backend actually performed fully to
572	notifications, this backend actually performed fully to specification
573	in all tests and is fully embeddable, which is a rare feat among the	680	specification in all tests and is fully embeddable, which is a rare feat
574	OS-specific backends (I vastly prefer correctness over speed hacks).	681	among the OS-specific backends (I vastly prefer correctness over speed
		682	hacks).
		683
		684	On the negative side, the interface is I<bizarre> - so bizarre that
		685	even sun itself gets it wrong in their code examples: The event polling
		686	function sometimes returns events to the caller even though an error
		687	occurred, but with no indication whether it has done so or not (yes, it's
		688	even documented that way) - deadly for edge-triggered interfaces where you
		689	absolutely have to know whether an event occurred or not because you have
		690	to re-arm the watcher.
		691
		692	Fortunately libev seems to be able to work around these idiocies.
575		693
576	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	694	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
577	C<EVBACKEND_POLL>.	695	C<EVBACKEND_POLL>.
578		696
579	=item C<EVBACKEND_ALL>	697	=item C<EVBACKEND_ALL>
580		698
581	Try all backends (even potentially broken ones that wouldn't be tried	699	Try all backends (even potentially broken ones that wouldn't be tried
582	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	700	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
583	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	701	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
584		702
585	It is definitely not recommended to use this flag.	703	It is definitely not recommended to use this flag, use whatever
		704	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		705	at all.
		706
		707	=item C<EVBACKEND_MASK>
		708
		709	Not a backend at all, but a mask to select all backend bits from a
		710	C<flags> value, in case you want to mask out any backends from a flags
		711	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
586		712
587	=back	713	=back
588		714
589	If one or more of the backend flags are or'ed into the flags value,	715	If one or more of the backend flags are or'ed into the flags value,
590	then only these backends will be tried (in the reverse order as listed	716	then only these backends will be tried (in the reverse order as listed
…		…
599		725
600	Example: Use whatever libev has to offer, but make sure that kqueue is	726	Example: Use whatever libev has to offer, but make sure that kqueue is
601	used if available.	727	used if available.
602		728
603	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);	729	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		730
		731	Example: Similarly, on linux, you mgiht want to take advantage of the
		732	linux aio backend if possible, but fall back to something else if that
		733	isn't available.
		734
		735	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_LINUXAIO);
604		736
605	=item ev_loop_destroy (loop)	737	=item ev_loop_destroy (loop)
606		738
607	Destroys an event loop object (frees all memory and kernel state	739	Destroys an event loop object (frees all memory and kernel state
608	etc.). None of the active event watchers will be stopped in the normal	740	etc.). None of the active event watchers will be stopped in the normal
…		…
619	This function is normally used on loop objects allocated by	751	This function is normally used on loop objects allocated by
620	C<ev_loop_new>, but it can also be used on the default loop returned by	752	C<ev_loop_new>, but it can also be used on the default loop returned by
621	C<ev_default_loop>, in which case it is not thread-safe.	753	C<ev_default_loop>, in which case it is not thread-safe.
622		754
623	Note that it is not advisable to call this function on the default loop	755	Note that it is not advisable to call this function on the default loop
624	except in the rare occasion where you really need to free it's resources.	756	except in the rare occasion where you really need to free its resources.
625	If you need dynamically allocated loops it is better to use C<ev_loop_new>	757	If you need dynamically allocated loops it is better to use C<ev_loop_new>
626	and C<ev_loop_destroy>.	758	and C<ev_loop_destroy>.
627		759
628	=item ev_loop_fork (loop)	760	=item ev_loop_fork (loop)
629		761
630	This function sets a flag that causes subsequent C<ev_run> iterations to	762	This function sets a flag that causes subsequent C<ev_run> iterations
631	reinitialise the kernel state for backends that have one. Despite the	763	to reinitialise the kernel state for backends that have one. Despite
632	name, you can call it anytime, but it makes most sense after forking, in	764	the name, you can call it anytime you are allowed to start or stop
633	the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the	765	watchers (except inside an C<ev_prepare> callback), but it makes most
		766	sense after forking, in the child process. You I<must> call it (or use
634	child before resuming or calling C<ev_run>.	767	C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.
635		768
		769	In addition, if you want to reuse a loop (via this function or
		770	C<EVFLAG_FORKCHECK>), you I<also> have to ignore C<SIGPIPE>.
		771
636	Again, you I<have> to call it on I<any> loop that you want to re-use after	772	Again, you I<have> to call it on I<any> loop that you want to re-use after
637	a fork, I<even if you do not plan to use the loop in the parent>. This is	773	a fork, I<even if you do not plan to use the loop in the parent>. This is
638	because some kernel interfaces *cough* I<kqueue> *cough* do funny things	774	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
639	during fork.	775	during fork.
640		776
641	On the other hand, you only need to call this function in the child	777	On the other hand, you only need to call this function in the child
…		…
677	prepare and check phases.	813	prepare and check phases.
678		814
679	=item unsigned int ev_depth (loop)	815	=item unsigned int ev_depth (loop)
680		816
681	Returns the number of times C<ev_run> was entered minus the number of	817	Returns the number of times C<ev_run> was entered minus the number of
682	times C<ev_run> was exited, in other words, the recursion depth.	818	times C<ev_run> was exited normally, in other words, the recursion depth.
683		819
684	Outside C<ev_run>, this number is zero. In a callback, this number is	820	Outside C<ev_run>, this number is zero. In a callback, this number is
685	C<1>, unless C<ev_run> was invoked recursively (or from another thread),	821	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
686	in which case it is higher.	822	in which case it is higher.
687		823
688	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread	824	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
689	etc.), doesn't count as "exit" - consider this as a hint to avoid such	825	throwing an exception etc.), doesn't count as "exit" - consider this
690	ungentleman-like behaviour unless it's really convenient.	826	as a hint to avoid such ungentleman-like behaviour unless it's really
		827	convenient, in which case it is fully supported.
691		828
692	=item unsigned int ev_backend (loop)	829	=item unsigned int ev_backend (loop)
693		830
694	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	831	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
695	use.	832	use.
…		…
710		847
711	This function is rarely useful, but when some event callback runs for a	848	This function is rarely useful, but when some event callback runs for a
712	very long time without entering the event loop, updating libev's idea of	849	very long time without entering the event loop, updating libev's idea of
713	the current time is a good idea.	850	the current time is a good idea.
714		851
715	See also L<The special problem of time updates> in the C<ev_timer> section.	852	See also L</The special problem of time updates> in the C<ev_timer> section.
716		853
717	=item ev_suspend (loop)	854	=item ev_suspend (loop)
718		855
719	=item ev_resume (loop)	856	=item ev_resume (loop)
720		857
…		…
738	without a previous call to C<ev_suspend>.	875	without a previous call to C<ev_suspend>.
739		876
740	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the	877	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
741	event loop time (see C<ev_now_update>).	878	event loop time (see C<ev_now_update>).
742		879
743	=item ev_run (loop, int flags)	880	=item bool ev_run (loop, int flags)
744		881
745	Finally, this is it, the event handler. This function usually is called	882	Finally, this is it, the event handler. This function usually is called
746	after you have initialised all your watchers and you want to start	883	after you have initialised all your watchers and you want to start
747	handling events. It will ask the operating system for any new events, call	884	handling events. It will ask the operating system for any new events, call
748	the watcher callbacks, an then repeat the whole process indefinitely: This	885	the watcher callbacks, and then repeat the whole process indefinitely: This
749	is why event loops are called I<loops>.	886	is why event loops are called I<loops>.
750		887
751	If the flags argument is specified as C<0>, it will keep handling events	888	If the flags argument is specified as C<0>, it will keep handling events
752	until either no event watchers are active anymore or C<ev_break> was	889	until either no event watchers are active anymore or C<ev_break> was
753	called.	890	called.
		891
		892	The return value is false if there are no more active watchers (which
		893	usually means "all jobs done" or "deadlock"), and true in all other cases
		894	(which usually means " you should call C<ev_run> again").
754		895
755	Please note that an explicit C<ev_break> is usually better than	896	Please note that an explicit C<ev_break> is usually better than
756	relying on all watchers to be stopped when deciding when a program has	897	relying on all watchers to be stopped when deciding when a program has
757	finished (especially in interactive programs), but having a program	898	finished (especially in interactive programs), but having a program
758	that automatically loops as long as it has to and no longer by virtue	899	that automatically loops as long as it has to and no longer by virtue
759	of relying on its watchers stopping correctly, that is truly a thing of	900	of relying on its watchers stopping correctly, that is truly a thing of
760	beauty.	901	beauty.
761		902
		903	This function is I<mostly> exception-safe - you can break out of a
		904	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		905	exception and so on. This does not decrement the C<ev_depth> value, nor
		906	will it clear any outstanding C<EVBREAK_ONE> breaks.
		907
762	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle	908	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
763	those events and any already outstanding ones, but will not wait and	909	those events and any already outstanding ones, but will not wait and
764	block your process in case there are no events and will return after one	910	block your process in case there are no events and will return after one
765	iteration of the loop. This is sometimes useful to poll and handle new	911	iteration of the loop. This is sometimes useful to poll and handle new
766	events while doing lengthy calculations, to keep the program responsive.	912	events while doing lengthy calculations, to keep the program responsive.
…		…
775	This is useful if you are waiting for some external event in conjunction	921	This is useful if you are waiting for some external event in conjunction
776	with something not expressible using other libev watchers (i.e. "roll your	922	with something not expressible using other libev watchers (i.e. "roll your
777	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is	923	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
778	usually a better approach for this kind of thing.	924	usually a better approach for this kind of thing.
779		925
780	Here are the gory details of what C<ev_run> does:	926	Here are the gory details of what C<ev_run> does (this is for your
		927	understanding, not a guarantee that things will work exactly like this in
		928	future versions):
781		929
782	- Increment loop depth.	930	- Increment loop depth.
783	- Reset the ev_break status.	931	- Reset the ev_break status.
784	- Before the first iteration, call any pending watchers.	932	- Before the first iteration, call any pending watchers.
785	LOOP:	933	LOOP:
…		…
818	anymore.	966	anymore.
819		967
820	... queue jobs here, make sure they register event watchers as long	968	... queue jobs here, make sure they register event watchers as long
821	... as they still have work to do (even an idle watcher will do..)	969	... as they still have work to do (even an idle watcher will do..)
822	ev_run (my_loop, 0);	970	ev_run (my_loop, 0);
823	... jobs done or somebody called unloop. yeah!	971	... jobs done or somebody called break. yeah!
824		972
825	=item ev_break (loop, how)	973	=item ev_break (loop, how)
826		974
827	Can be used to make a call to C<ev_run> return early (but only after it	975	Can be used to make a call to C<ev_run> return early (but only after it
828	has processed all outstanding events). The C<how> argument must be either	976	has processed all outstanding events). The C<how> argument must be either
829	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or	977	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
830	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.	978	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
831		979
832	This "break state" will be cleared when entering C<ev_run> again.	980	This "break state" will be cleared on the next call to C<ev_run>.
833		981
834	It is safe to call C<ev_break> from outside any C<ev_run> calls, too.	982	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		983	which case it will have no effect.
835		984
836	=item ev_ref (loop)	985	=item ev_ref (loop)
837		986
838	=item ev_unref (loop)	987	=item ev_unref (loop)
839		988
…		…
860	running when nothing else is active.	1009	running when nothing else is active.
861		1010
862	ev_signal exitsig;	1011	ev_signal exitsig;
863	ev_signal_init (&exitsig, sig_cb, SIGINT);	1012	ev_signal_init (&exitsig, sig_cb, SIGINT);
864	ev_signal_start (loop, &exitsig);	1013	ev_signal_start (loop, &exitsig);
865	evf_unref (loop);	1014	ev_unref (loop);
866		1015
867	Example: For some weird reason, unregister the above signal handler again.	1016	Example: For some weird reason, unregister the above signal handler again.
868		1017
869	ev_ref (loop);	1018	ev_ref (loop);
870	ev_signal_stop (loop, &exitsig);	1019	ev_signal_stop (loop, &exitsig);
…		…
890	overhead for the actual polling but can deliver many events at once.	1039	overhead for the actual polling but can deliver many events at once.
891		1040
892	By setting a higher I<io collect interval> you allow libev to spend more	1041	By setting a higher I<io collect interval> you allow libev to spend more
893	time collecting I/O events, so you can handle more events per iteration,	1042	time collecting I/O events, so you can handle more events per iteration,
894	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	1043	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
895	C<ev_timer>) will be not affected. Setting this to a non-null value will	1044	C<ev_timer>) will not be affected. Setting this to a non-null value will
896	introduce an additional C<ev_sleep ()> call into most loop iterations. The	1045	introduce an additional C<ev_sleep ()> call into most loop iterations. The
897	sleep time ensures that libev will not poll for I/O events more often then	1046	sleep time ensures that libev will not poll for I/O events more often then
898	once per this interval, on average.	1047	once per this interval, on average (as long as the host time resolution is
		1048	good enough).
899		1049
900	Likewise, by setting a higher I<timeout collect interval> you allow libev	1050	Likewise, by setting a higher I<timeout collect interval> you allow libev
901	to spend more time collecting timeouts, at the expense of increased	1051	to spend more time collecting timeouts, at the expense of increased
902	latency/jitter/inexactness (the watcher callback will be called	1052	latency/jitter/inexactness (the watcher callback will be called
903	later). C<ev_io> watchers will not be affected. Setting this to a non-null	1053	later). C<ev_io> watchers will not be affected. Setting this to a non-null
…		…
949	invoke the actual watchers inside another context (another thread etc.).	1099	invoke the actual watchers inside another context (another thread etc.).
950		1100
951	If you want to reset the callback, use C<ev_invoke_pending> as new	1101	If you want to reset the callback, use C<ev_invoke_pending> as new
952	callback.	1102	callback.
953		1103
954	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))	1104	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
955		1105
956	Sometimes you want to share the same loop between multiple threads. This	1106	Sometimes you want to share the same loop between multiple threads. This
957	can be done relatively simply by putting mutex_lock/unlock calls around	1107	can be done relatively simply by putting mutex_lock/unlock calls around
958	each call to a libev function.	1108	each call to a libev function.
959		1109
960	However, C<ev_run> can run an indefinite time, so it is not feasible	1110	However, C<ev_run> can run an indefinite time, so it is not feasible
961	to wait for it to return. One way around this is to wake up the event	1111	to wait for it to return. One way around this is to wake up the event
962	loop via C<ev_break> and C<av_async_send>, another way is to set these	1112	loop via C<ev_break> and C<ev_async_send>, another way is to set these
963	I<release> and I<acquire> callbacks on the loop.	1113	I<release> and I<acquire> callbacks on the loop.
964		1114
965	When set, then C<release> will be called just before the thread is	1115	When set, then C<release> will be called just before the thread is
966	suspended waiting for new events, and C<acquire> is called just	1116	suspended waiting for new events, and C<acquire> is called just
967	afterwards.	1117	afterwards.
…		…
982	See also the locking example in the C<THREADS> section later in this	1132	See also the locking example in the C<THREADS> section later in this
983	document.	1133	document.
984		1134
985	=item ev_set_userdata (loop, void *data)	1135	=item ev_set_userdata (loop, void *data)
986		1136
987	=item ev_userdata (loop)	1137	=item void *ev_userdata (loop)
988		1138
989	Set and retrieve a single C<void *> associated with a loop. When	1139	Set and retrieve a single C<void *> associated with a loop. When
990	C<ev_set_userdata> has never been called, then C<ev_userdata> returns	1140	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
991	C<0.>	1141	C<0>.
992		1142
993	These two functions can be used to associate arbitrary data with a loop,	1143	These two functions can be used to associate arbitrary data with a loop,
994	and are intended solely for the C<invoke_pending_cb>, C<release> and	1144	and are intended solely for the C<invoke_pending_cb>, C<release> and
995	C<acquire> callbacks described above, but of course can be (ab-)used for	1145	C<acquire> callbacks described above, but of course can be (ab-)used for
996	any other purpose as well.	1146	any other purpose as well.
…		…
1107		1257
1108	=item C<EV_PREPARE>	1258	=item C<EV_PREPARE>
1109		1259
1110	=item C<EV_CHECK>	1260	=item C<EV_CHECK>
1111		1261
1112	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts	1262	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts to
1113	to gather new events, and all C<ev_check> watchers are invoked just after	1263	gather new events, and all C<ev_check> watchers are queued (not invoked)
1114	C<ev_run> has gathered them, but before it invokes any callbacks for any	1264	just after C<ev_run> has gathered them, but before it queues any callbacks
		1265	for any received events. That means C<ev_prepare> watchers are the last
		1266	watchers invoked before the event loop sleeps or polls for new events, and
		1267	C<ev_check> watchers will be invoked before any other watchers of the same
		1268	or lower priority within an event loop iteration.
		1269
1115	received events. Callbacks of both watcher types can start and stop as	1270	Callbacks of both watcher types can start and stop as many watchers as
1116	many watchers as they want, and all of them will be taken into account	1271	they want, and all of them will be taken into account (for example, a
1117	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1272	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
1118	C<ev_run> from blocking).	1273	blocking).
1119		1274
1120	=item C<EV_EMBED>	1275	=item C<EV_EMBED>
1121		1276
1122	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1277	The embedded event loop specified in the C<ev_embed> watcher needs attention.
1123		1278
…		…
1246		1401
1247	=item callback ev_cb (ev_TYPE *watcher)	1402	=item callback ev_cb (ev_TYPE *watcher)
1248		1403
1249	Returns the callback currently set on the watcher.	1404	Returns the callback currently set on the watcher.
1250		1405
1251	=item ev_cb_set (ev_TYPE *watcher, callback)	1406	=item ev_set_cb (ev_TYPE *watcher, callback)
1252		1407
1253	Change the callback. You can change the callback at virtually any time	1408	Change the callback. You can change the callback at virtually any time
1254	(modulo threads).	1409	(modulo threads).
1255		1410
1256	=item ev_set_priority (ev_TYPE *watcher, int priority)	1411	=item ev_set_priority (ev_TYPE *watcher, int priority)
…		…
1274	or might not have been clamped to the valid range.	1429	or might not have been clamped to the valid range.
1275		1430
1276	The default priority used by watchers when no priority has been set is	1431	The default priority used by watchers when no priority has been set is
1277	always C<0>, which is supposed to not be too high and not be too low :).	1432	always C<0>, which is supposed to not be too high and not be too low :).
1278		1433
1279	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of	1434	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1280	priorities.	1435	priorities.
1281		1436
1282	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1437	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1283		1438
1284	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1439	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
…		…
1309	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related	1464	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1310	functions that do not need a watcher.	1465	functions that do not need a watcher.
1311		1466
1312	=back	1467	=back
1313		1468
1314	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1469	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
1315		1470	OWN COMPOSITE WATCHERS> idioms.
1316	Each watcher has, by default, a member C<void *data> that you can change
1317	and read at any time: libev will completely ignore it. This can be used
1318	to associate arbitrary data with your watcher. If you need more data and
1319	don't want to allocate memory and store a pointer to it in that data
1320	member, you can also "subclass" the watcher type and provide your own
1321	data:
1322
1323	struct my_io
1324	{
1325	ev_io io;
1326	int otherfd;
1327	void *somedata;
1328	struct whatever *mostinteresting;
1329	};
1330
1331	...
1332	struct my_io w;
1333	ev_io_init (&w.io, my_cb, fd, EV_READ);
1334
1335	And since your callback will be called with a pointer to the watcher, you
1336	can cast it back to your own type:
1337
1338	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1339	{
1340	struct my_io *w = (struct my_io *)w_;
1341	...
1342	}
1343
1344	More interesting and less C-conformant ways of casting your callback type
1345	instead have been omitted.
1346
1347	Another common scenario is to use some data structure with multiple
1348	embedded watchers:
1349
1350	struct my_biggy
1351	{
1352	int some_data;
1353	ev_timer t1;
1354	ev_timer t2;
1355	}
1356
1357	In this case getting the pointer to C<my_biggy> is a bit more
1358	complicated: Either you store the address of your C<my_biggy> struct
1359	in the C<data> member of the watcher (for woozies), or you need to use
1360	some pointer arithmetic using C<offsetof> inside your watchers (for real
1361	programmers):
1362
1363	#include <stddef.h>
1364
1365	static void
1366	t1_cb (EV_P_ ev_timer *w, int revents)
1367	{
1368	struct my_biggy big = (struct my_biggy *)
1369	(((char *)w) - offsetof (struct my_biggy, t1));
1370	}
1371
1372	static void
1373	t2_cb (EV_P_ ev_timer *w, int revents)
1374	{
1375	struct my_biggy big = (struct my_biggy *)
1376	(((char *)w) - offsetof (struct my_biggy, t2));
1377	}
1378		1471
1379	=head2 WATCHER STATES	1472	=head2 WATCHER STATES
1380		1473
1381	There are various watcher states mentioned throughout this manual -	1474	There are various watcher states mentioned throughout this manual -
1382	active, pending and so on. In this section these states and the rules to	1475	active, pending and so on. In this section these states and the rules to
1383	transition between them will be described in more detail - and while these	1476	transition between them will be described in more detail - and while these
1384	rules might look complicated, they usually do "the right thing".	1477	rules might look complicated, they usually do "the right thing".
1385		1478
1386	=over 4	1479	=over 4
1387		1480
1388	=item initialiased	1481	=item initialised
1389		1482
1390	Before a watcher can be registered with the event looop it has to be	1483	Before a watcher can be registered with the event loop it has to be
1391	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to	1484	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
1392	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.	1485	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1393		1486
1394	In this state it is simply some block of memory that is suitable for use	1487	In this state it is simply some block of memory that is suitable for
1395	in an event loop. It can be moved around, freed, reused etc. at will.	1488	use in an event loop. It can be moved around, freed, reused etc. at
		1489	will - as long as you either keep the memory contents intact, or call
		1490	C<ev_TYPE_init> again.
1396		1491
1397	=item started/running/active	1492	=item started/running/active
1398		1493
1399	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes	1494	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
1400	property of the event loop, and is actively waiting for events. While in	1495	property of the event loop, and is actively waiting for events. While in
…		…
1428	latter will clear any pending state the watcher might be in, regardless	1523	latter will clear any pending state the watcher might be in, regardless
1429	of whether it was active or not, so stopping a watcher explicitly before	1524	of whether it was active or not, so stopping a watcher explicitly before
1430	freeing it is often a good idea.	1525	freeing it is often a good idea.
1431		1526
1432	While stopped (and not pending) the watcher is essentially in the	1527	While stopped (and not pending) the watcher is essentially in the
1433	initialised state, that is it can be reused, moved, modified in any way	1528	initialised state, that is, it can be reused, moved, modified in any way
1434	you wish.	1529	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1530	it again).
1435		1531
1436	=back	1532	=back
1437		1533
1438	=head2 WATCHER PRIORITY MODELS	1534	=head2 WATCHER PRIORITY MODELS
1439		1535
…		…
1568	In general you can register as many read and/or write event watchers per	1664	In general you can register as many read and/or write event watchers per
1569	fd as you want (as long as you don't confuse yourself). Setting all file	1665	fd as you want (as long as you don't confuse yourself). Setting all file
1570	descriptors to non-blocking mode is also usually a good idea (but not	1666	descriptors to non-blocking mode is also usually a good idea (but not
1571	required if you know what you are doing).	1667	required if you know what you are doing).
1572		1668
1573	If you cannot use non-blocking mode, then force the use of a
1574	known-to-be-good backend (at the time of this writing, this includes only
1575	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
1576	descriptors for which non-blocking operation makes no sense (such as
1577	files) - libev doesn't guarantee any specific behaviour in that case.
1578
1579	Another thing you have to watch out for is that it is quite easy to	1669	Another thing you have to watch out for is that it is quite easy to
1580	receive "spurious" readiness notifications, that is your callback might	1670	receive "spurious" readiness notifications, that is, your callback might
1581	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1671	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1582	because there is no data. Not only are some backends known to create a	1672	because there is no data. It is very easy to get into this situation even
1583	lot of those (for example Solaris ports), it is very easy to get into	1673	with a relatively standard program structure. Thus it is best to always
1584	this situation even with a relatively standard program structure. Thus	1674	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1585	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1586	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1675	preferable to a program hanging until some data arrives.
1587		1676
1588	If you cannot run the fd in non-blocking mode (for example you should	1677	If you cannot run the fd in non-blocking mode (for example you should
1589	not play around with an Xlib connection), then you have to separately	1678	not play around with an Xlib connection), then you have to separately
1590	re-test whether a file descriptor is really ready with a known-to-be good	1679	re-test whether a file descriptor is really ready with a known-to-be good
1591	interface such as poll (fortunately in our Xlib example, Xlib already	1680	interface such as poll (fortunately in the case of Xlib, it already does
1592	does this on its own, so its quite safe to use). Some people additionally	1681	this on its own, so its quite safe to use). Some people additionally
1593	use C<SIGALRM> and an interval timer, just to be sure you won't block	1682	use C<SIGALRM> and an interval timer, just to be sure you won't block
1594	indefinitely.	1683	indefinitely.
1595		1684
1596	But really, best use non-blocking mode.	1685	But really, best use non-blocking mode.
1597		1686
1598	=head3 The special problem of disappearing file descriptors	1687	=head3 The special problem of disappearing file descriptors
1599		1688
1600	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1689	Some backends (e.g. kqueue, epoll, linuxaio) need to be told about closing
1601	descriptor (either due to calling C<close> explicitly or any other means,	1690	a file descriptor (either due to calling C<close> explicitly or any other
1602	such as C<dup2>). The reason is that you register interest in some file	1691	means, such as C<dup2>). The reason is that you register interest in some
1603	descriptor, but when it goes away, the operating system will silently drop	1692	file descriptor, but when it goes away, the operating system will silently
1604	this interest. If another file descriptor with the same number then is	1693	drop this interest. If another file descriptor with the same number then
1605	registered with libev, there is no efficient way to see that this is, in	1694	is registered with libev, there is no efficient way to see that this is,
1606	fact, a different file descriptor.	1695	in fact, a different file descriptor.
1607		1696
1608	To avoid having to explicitly tell libev about such cases, libev follows	1697	To avoid having to explicitly tell libev about such cases, libev follows
1609	the following policy: Each time C<ev_io_set> is being called, libev	1698	the following policy: Each time C<ev_io_set> is being called, libev
1610	will assume that this is potentially a new file descriptor, otherwise	1699	will assume that this is potentially a new file descriptor, otherwise
1611	it is assumed that the file descriptor stays the same. That means that	1700	it is assumed that the file descriptor stays the same. That means that
…		…
1625		1714
1626	There is no workaround possible except not registering events	1715	There is no workaround possible except not registering events
1627	for potentially C<dup ()>'ed file descriptors, or to resort to	1716	for potentially C<dup ()>'ed file descriptors, or to resort to
1628	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1717	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1629		1718
		1719	=head3 The special problem of files
		1720
		1721	Many people try to use C<select> (or libev) on file descriptors
		1722	representing files, and expect it to become ready when their program
		1723	doesn't block on disk accesses (which can take a long time on their own).
		1724
		1725	However, this cannot ever work in the "expected" way - you get a readiness
		1726	notification as soon as the kernel knows whether and how much data is
		1727	there, and in the case of open files, that's always the case, so you
		1728	always get a readiness notification instantly, and your read (or possibly
		1729	write) will still block on the disk I/O.
		1730
		1731	Another way to view it is that in the case of sockets, pipes, character
		1732	devices and so on, there is another party (the sender) that delivers data
		1733	on its own, but in the case of files, there is no such thing: the disk
		1734	will not send data on its own, simply because it doesn't know what you
		1735	wish to read - you would first have to request some data.
		1736
		1737	Since files are typically not-so-well supported by advanced notification
		1738	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1739	to files, even though you should not use it. The reason for this is
		1740	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1741	usually a tty, often a pipe, but also sometimes files or special devices
		1742	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1743	F</dev/urandom>), and even though the file might better be served with
		1744	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1745	it "just works" instead of freezing.
		1746
		1747	So avoid file descriptors pointing to files when you know it (e.g. use
		1748	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1749	when you rarely read from a file instead of from a socket, and want to
		1750	reuse the same code path.
		1751
1630	=head3 The special problem of fork	1752	=head3 The special problem of fork
1631		1753
1632	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1754	Some backends (epoll, kqueue, linuxaio, iouring) do not support C<fork ()>
1633	useless behaviour. Libev fully supports fork, but needs to be told about	1755	at all or exhibit useless behaviour. Libev fully supports fork, but needs
1634	it in the child.	1756	to be told about it in the child if you want to continue to use it in the
		1757	child.
1635		1758
1636	To support fork in your programs, you either have to call	1759	To support fork in your child processes, you have to call C<ev_loop_fork
1637	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1760	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1638	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1761	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1639	C<EVBACKEND_POLL>.
1640		1762
1641	=head3 The special problem of SIGPIPE	1763	=head3 The special problem of SIGPIPE
1642		1764
1643	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1765	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1644	when writing to a pipe whose other end has been closed, your program gets	1766	when writing to a pipe whose other end has been closed, your program gets
…		…
1742	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1864	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1743	monotonic clock option helps a lot here).	1865	monotonic clock option helps a lot here).
1744		1866
1745	The callback is guaranteed to be invoked only I<after> its timeout has	1867	The callback is guaranteed to be invoked only I<after> its timeout has
1746	passed (not I<at>, so on systems with very low-resolution clocks this	1868	passed (not I<at>, so on systems with very low-resolution clocks this
1747	might introduce a small delay). If multiple timers become ready during the	1869	might introduce a small delay, see "the special problem of being too
		1870	early", below). If multiple timers become ready during the same loop
1748	same loop iteration then the ones with earlier time-out values are invoked	1871	iteration then the ones with earlier time-out values are invoked before
1749	before ones of the same priority with later time-out values (but this is	1872	ones of the same priority with later time-out values (but this is no
1750	no longer true when a callback calls C<ev_run> recursively).	1873	longer true when a callback calls C<ev_run> recursively).
1751		1874
1752	=head3 Be smart about timeouts	1875	=head3 Be smart about timeouts
1753		1876
1754	Many real-world problems involve some kind of timeout, usually for error	1877	Many real-world problems involve some kind of timeout, usually for error
1755	recovery. A typical example is an HTTP request - if the other side hangs,	1878	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1830		1953
1831	In this case, it would be more efficient to leave the C<ev_timer> alone,	1954	In this case, it would be more efficient to leave the C<ev_timer> alone,
1832	but remember the time of last activity, and check for a real timeout only	1955	but remember the time of last activity, and check for a real timeout only
1833	within the callback:	1956	within the callback:
1834		1957
		1958	ev_tstamp timeout = 60.;
1835	ev_tstamp last_activity; // time of last activity	1959	ev_tstamp last_activity; // time of last activity
		1960	ev_timer timer;
1836		1961
1837	static void	1962	static void
1838	callback (EV_P_ ev_timer *w, int revents)	1963	callback (EV_P_ ev_timer *w, int revents)
1839	{	1964	{
1840	ev_tstamp now = ev_now (EV_A);	1965	// calculate when the timeout would happen
1841	ev_tstamp timeout = last_activity + 60.;	1966	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
1842		1967
1843	// if last_activity + 60. is older than now, we did time out	1968	// if negative, it means we the timeout already occurred
1844	if (timeout < now)	1969	if (after < 0.)
1845	{	1970	{
1846	// timeout occurred, take action	1971	// timeout occurred, take action
1847	}	1972	}
1848	else	1973	else
1849	{	1974	{
1850	// callback was invoked, but there was some activity, re-arm	1975	// callback was invoked, but there was some recent
1851	// the watcher to fire in last_activity + 60, which is	1976	// activity. simply restart the timer to time out
1852	// guaranteed to be in the future, so "again" is positive:	1977	// after "after" seconds, which is the earliest time
1853	w->repeat = timeout - now;	1978	// the timeout can occur.
		1979	ev_timer_set (w, after, 0.);
1854	ev_timer_again (EV_A_ w);	1980	ev_timer_start (EV_A_ w);
1855	}	1981	}
1856	}	1982	}
1857		1983
1858	To summarise the callback: first calculate the real timeout (defined	1984	To summarise the callback: first calculate in how many seconds the
1859	as "60 seconds after the last activity"), then check if that time has	1985	timeout will occur (by calculating the absolute time when it would occur,
1860	been reached, which means something I<did>, in fact, time out. Otherwise	1986	C<last_activity + timeout>, and subtracting the current time, C<ev_now
1861	the callback was invoked too early (C<timeout> is in the future), so	1987	(EV_A)> from that).
1862	re-schedule the timer to fire at that future time, to see if maybe we have
1863	a timeout then.
1864		1988
1865	Note how C<ev_timer_again> is used, taking advantage of the	1989	If this value is negative, then we are already past the timeout, i.e. we
1866	C<ev_timer_again> optimisation when the timer is already running.	1990	timed out, and need to do whatever is needed in this case.
		1991
		1992	Otherwise, we now the earliest time at which the timeout would trigger,
		1993	and simply start the timer with this timeout value.
		1994
		1995	In other words, each time the callback is invoked it will check whether
		1996	the timeout occurred. If not, it will simply reschedule itself to check
		1997	again at the earliest time it could time out. Rinse. Repeat.
1867		1998
1868	This scheme causes more callback invocations (about one every 60 seconds	1999	This scheme causes more callback invocations (about one every 60 seconds
1869	minus half the average time between activity), but virtually no calls to	2000	minus half the average time between activity), but virtually no calls to
1870	libev to change the timeout.	2001	libev to change the timeout.
1871		2002
1872	To start the timer, simply initialise the watcher and set C<last_activity>	2003	To start the machinery, simply initialise the watcher and set
1873	to the current time (meaning we just have some activity :), then call the	2004	C<last_activity> to the current time (meaning there was some activity just
1874	callback, which will "do the right thing" and start the timer:	2005	now), then call the callback, which will "do the right thing" and start
		2006	the timer:
1875		2007
		2008	last_activity = ev_now (EV_A);
1876	ev_init (timer, callback);	2009	ev_init (&timer, callback);
1877	last_activity = ev_now (loop);	2010	callback (EV_A_ &timer, 0);
1878	callback (loop, timer, EV_TIMER);
1879		2011
1880	And when there is some activity, simply store the current time in	2012	When there is some activity, simply store the current time in
1881	C<last_activity>, no libev calls at all:	2013	C<last_activity>, no libev calls at all:
1882		2014
		2015	if (activity detected)
1883	last_activity = ev_now (loop);	2016	last_activity = ev_now (EV_A);
		2017
		2018	When your timeout value changes, then the timeout can be changed by simply
		2019	providing a new value, stopping the timer and calling the callback, which
		2020	will again do the right thing (for example, time out immediately :).
		2021
		2022	timeout = new_value;
		2023	ev_timer_stop (EV_A_ &timer);
		2024	callback (EV_A_ &timer, 0);
1884		2025
1885	This technique is slightly more complex, but in most cases where the	2026	This technique is slightly more complex, but in most cases where the
1886	time-out is unlikely to be triggered, much more efficient.	2027	time-out is unlikely to be triggered, much more efficient.
1887
1888	Changing the timeout is trivial as well (if it isn't hard-coded in the
1889	callback :) - just change the timeout and invoke the callback, which will
1890	fix things for you.
1891		2028
1892	=item 4. Wee, just use a double-linked list for your timeouts.	2029	=item 4. Wee, just use a double-linked list for your timeouts.
1893		2030
1894	If there is not one request, but many thousands (millions...), all	2031	If there is not one request, but many thousands (millions...), all
1895	employing some kind of timeout with the same timeout value, then one can	2032	employing some kind of timeout with the same timeout value, then one can
…		…
1922	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is	2059	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
1923	rather complicated, but extremely efficient, something that really pays	2060	rather complicated, but extremely efficient, something that really pays
1924	off after the first million or so of active timers, i.e. it's usually	2061	off after the first million or so of active timers, i.e. it's usually
1925	overkill :)	2062	overkill :)
1926		2063
		2064	=head3 The special problem of being too early
		2065
		2066	If you ask a timer to call your callback after three seconds, then
		2067	you expect it to be invoked after three seconds - but of course, this
		2068	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		2069	guaranteed to any precision by libev - imagine somebody suspending the
		2070	process with a STOP signal for a few hours for example.
		2071
		2072	So, libev tries to invoke your callback as soon as possible I<after> the
		2073	delay has occurred, but cannot guarantee this.
		2074
		2075	A less obvious failure mode is calling your callback too early: many event
		2076	loops compare timestamps with a "elapsed delay >= requested delay", but
		2077	this can cause your callback to be invoked much earlier than you would
		2078	expect.
		2079
		2080	To see why, imagine a system with a clock that only offers full second
		2081	resolution (think windows if you can't come up with a broken enough OS
		2082	yourself). If you schedule a one-second timer at the time 500.9, then the
		2083	event loop will schedule your timeout to elapse at a system time of 500
		2084	(500.9 truncated to the resolution) + 1, or 501.
		2085
		2086	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2087	501" and invoke the callback 0.1s after it was started, even though a
		2088	one-second delay was requested - this is being "too early", despite best
		2089	intentions.
		2090
		2091	This is the reason why libev will never invoke the callback if the elapsed
		2092	delay equals the requested delay, but only when the elapsed delay is
		2093	larger than the requested delay. In the example above, libev would only invoke
		2094	the callback at system time 502, or 1.1s after the timer was started.
		2095
		2096	So, while libev cannot guarantee that your callback will be invoked
		2097	exactly when requested, it I<can> and I<does> guarantee that the requested
		2098	delay has actually elapsed, or in other words, it always errs on the "too
		2099	late" side of things.
		2100
1927	=head3 The special problem of time updates	2101	=head3 The special problem of time updates
1928		2102
1929	Establishing the current time is a costly operation (it usually takes at	2103	Establishing the current time is a costly operation (it usually takes
1930	least two system calls): EV therefore updates its idea of the current	2104	at least one system call): EV therefore updates its idea of the current
1931	time only before and after C<ev_run> collects new events, which causes a	2105	time only before and after C<ev_run> collects new events, which causes a
1932	growing difference between C<ev_now ()> and C<ev_time ()> when handling	2106	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1933	lots of events in one iteration.	2107	lots of events in one iteration.
1934		2108
1935	The relative timeouts are calculated relative to the C<ev_now ()>	2109	The relative timeouts are calculated relative to the C<ev_now ()>
1936	time. This is usually the right thing as this timestamp refers to the time	2110	time. This is usually the right thing as this timestamp refers to the time
1937	of the event triggering whatever timeout you are modifying/starting. If	2111	of the event triggering whatever timeout you are modifying/starting. If
1938	you suspect event processing to be delayed and you I<need> to base the	2112	you suspect event processing to be delayed and you I<need> to base the
1939	timeout on the current time, use something like this to adjust for this:	2113	timeout on the current time, use something like the following to adjust
		2114	for it:
1940		2115
1941	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2116	ev_timer_set (&timer, after + (ev_time () - ev_now ()), 0.);
1942		2117
1943	If the event loop is suspended for a long time, you can also force an	2118	If the event loop is suspended for a long time, you can also force an
1944	update of the time returned by C<ev_now ()> by calling C<ev_now_update	2119	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1945	()>.	2120	()>, although that will push the event time of all outstanding events
		2121	further into the future.
		2122
		2123	=head3 The special problem of unsynchronised clocks
		2124
		2125	Modern systems have a variety of clocks - libev itself uses the normal
		2126	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2127	jumps).
		2128
		2129	Neither of these clocks is synchronised with each other or any other clock
		2130	on the system, so C<ev_time ()> might return a considerably different time
		2131	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2132	a call to C<gettimeofday> might return a second count that is one higher
		2133	than a directly following call to C<time>.
		2134
		2135	The moral of this is to only compare libev-related timestamps with
		2136	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2137	a second or so.
		2138
		2139	One more problem arises due to this lack of synchronisation: if libev uses
		2140	the system monotonic clock and you compare timestamps from C<ev_time>
		2141	or C<ev_now> from when you started your timer and when your callback is
		2142	invoked, you will find that sometimes the callback is a bit "early".
		2143
		2144	This is because C<ev_timer>s work in real time, not wall clock time, so
		2145	libev makes sure your callback is not invoked before the delay happened,
		2146	I<measured according to the real time>, not the system clock.
		2147
		2148	If your timeouts are based on a physical timescale (e.g. "time out this
		2149	connection after 100 seconds") then this shouldn't bother you as it is
		2150	exactly the right behaviour.
		2151
		2152	If you want to compare wall clock/system timestamps to your timers, then
		2153	you need to use C<ev_periodic>s, as these are based on the wall clock
		2154	time, where your comparisons will always generate correct results.
1946		2155
1947	=head3 The special problems of suspended animation	2156	=head3 The special problems of suspended animation
1948		2157
1949	When you leave the server world it is quite customary to hit machines that	2158	When you leave the server world it is quite customary to hit machines that
1950	can suspend/hibernate - what happens to the clocks during such a suspend?	2159	can suspend/hibernate - what happens to the clocks during such a suspend?
…		…
1980		2189
1981	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2190	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1982		2191
1983	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2192	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1984		2193
1985	Configure the timer to trigger after C<after> seconds. If C<repeat>	2194	Configure the timer to trigger after C<after> seconds (fractional and
1986	is C<0.>, then it will automatically be stopped once the timeout is	2195	negative values are supported). If C<repeat> is C<0.>, then it will
1987	reached. If it is positive, then the timer will automatically be	2196	automatically be stopped once the timeout is reached. If it is positive,
1988	configured to trigger again C<repeat> seconds later, again, and again,	2197	then the timer will automatically be configured to trigger again C<repeat>
1989	until stopped manually.	2198	seconds later, again, and again, until stopped manually.
1990		2199
1991	The timer itself will do a best-effort at avoiding drift, that is, if	2200	The timer itself will do a best-effort at avoiding drift, that is, if
1992	you configure a timer to trigger every 10 seconds, then it will normally	2201	you configure a timer to trigger every 10 seconds, then it will normally
1993	trigger at exactly 10 second intervals. If, however, your program cannot	2202	trigger at exactly 10 second intervals. If, however, your program cannot
1994	keep up with the timer (because it takes longer than those 10 seconds to	2203	keep up with the timer (because it takes longer than those 10 seconds to
1995	do stuff) the timer will not fire more than once per event loop iteration.	2204	do stuff) the timer will not fire more than once per event loop iteration.
1996		2205
1997	=item ev_timer_again (loop, ev_timer *)	2206	=item ev_timer_again (loop, ev_timer *)
1998		2207
1999	This will act as if the timer timed out and restart it again if it is	2208	This will act as if the timer timed out, and restarts it again if it is
2000	repeating. The exact semantics are:	2209	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2210	timeout to the C<repeat> value and calling C<ev_timer_start>.
2001		2211
		2212	The exact semantics are as in the following rules, all of which will be
		2213	applied to the watcher:
		2214
		2215	=over 4
		2216
2002	If the timer is pending, its pending status is cleared.	2217	=item If the timer is pending, the pending status is always cleared.
2003		2218
2004	If the timer is started but non-repeating, stop it (as if it timed out).	2219	=item If the timer is started but non-repeating, stop it (as if it timed
		2220	out, without invoking it).
2005		2221
2006	If the timer is repeating, either start it if necessary (with the	2222	=item If the timer is repeating, make the C<repeat> value the new timeout
2007	C<repeat> value), or reset the running timer to the C<repeat> value.	2223	and start the timer, if necessary.
2008		2224
		2225	=back
		2226
2009	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a	2227	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
2010	usage example.	2228	usage example.
2011		2229
2012	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)	2230	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
2013		2231
2014	Returns the remaining time until a timer fires. If the timer is active,	2232	Returns the remaining time until a timer fires. If the timer is active,
…		…
2067	Periodic watchers are also timers of a kind, but they are very versatile	2285	Periodic watchers are also timers of a kind, but they are very versatile
2068	(and unfortunately a bit complex).	2286	(and unfortunately a bit complex).
2069		2287
2070	Unlike C<ev_timer>, periodic watchers are not based on real time (or	2288	Unlike C<ev_timer>, periodic watchers are not based on real time (or
2071	relative time, the physical time that passes) but on wall clock time	2289	relative time, the physical time that passes) but on wall clock time
2072	(absolute time, the thing you can read on your calender or clock). The	2290	(absolute time, the thing you can read on your calendar or clock). The
2073	difference is that wall clock time can run faster or slower than real	2291	difference is that wall clock time can run faster or slower than real
2074	time, and time jumps are not uncommon (e.g. when you adjust your	2292	time, and time jumps are not uncommon (e.g. when you adjust your
2075	wrist-watch).	2293	wrist-watch).
2076		2294
2077	You can tell a periodic watcher to trigger after some specific point	2295	You can tell a periodic watcher to trigger after some specific point
…		…
2082	C<ev_timer>, which would still trigger roughly 10 seconds after starting	2300	C<ev_timer>, which would still trigger roughly 10 seconds after starting
2083	it, as it uses a relative timeout).	2301	it, as it uses a relative timeout).
2084		2302
2085	C<ev_periodic> watchers can also be used to implement vastly more complex	2303	C<ev_periodic> watchers can also be used to implement vastly more complex
2086	timers, such as triggering an event on each "midnight, local time", or	2304	timers, such as triggering an event on each "midnight, local time", or
2087	other complicated rules. This cannot be done with C<ev_timer> watchers, as	2305	other complicated rules. This cannot easily be done with C<ev_timer>
2088	those cannot react to time jumps.	2306	watchers, as those cannot react to time jumps.
2089		2307
2090	As with timers, the callback is guaranteed to be invoked only when the	2308	As with timers, the callback is guaranteed to be invoked only when the
2091	point in time where it is supposed to trigger has passed. If multiple	2309	point in time where it is supposed to trigger has passed. If multiple
2092	timers become ready during the same loop iteration then the ones with	2310	timers become ready during the same loop iteration then the ones with
2093	earlier time-out values are invoked before ones with later time-out values	2311	earlier time-out values are invoked before ones with later time-out values
…		…
2134		2352
2135	Another way to think about it (for the mathematically inclined) is that	2353	Another way to think about it (for the mathematically inclined) is that
2136	C<ev_periodic> will try to run the callback in this mode at the next possible	2354	C<ev_periodic> will try to run the callback in this mode at the next possible
2137	time where C<time = offset (mod interval)>, regardless of any time jumps.	2355	time where C<time = offset (mod interval)>, regardless of any time jumps.
2138		2356
2139	For numerical stability it is preferable that the C<offset> value is near	2357	The C<interval> I<MUST> be positive, and for numerical stability, the
2140	C<ev_now ()> (the current time), but there is no range requirement for	2358	interval value should be higher than C<1/8192> (which is around 100
2141	this value, and in fact is often specified as zero.	2359	microseconds) and C<offset> should be higher than C<0> and should have
		2360	at most a similar magnitude as the current time (say, within a factor of
		2361	ten). Typical values for offset are, in fact, C<0> or something between
		2362	C<0> and C<interval>, which is also the recommended range.
2142		2363
2143	Note also that there is an upper limit to how often a timer can fire (CPU	2364	Note also that there is an upper limit to how often a timer can fire (CPU
2144	speed for example), so if C<interval> is very small then timing stability	2365	speed for example), so if C<interval> is very small then timing stability
2145	will of course deteriorate. Libev itself tries to be exact to be about one	2366	will of course deteriorate. Libev itself tries to be exact to be about one
2146	millisecond (if the OS supports it and the machine is fast enough).	2367	millisecond (if the OS supports it and the machine is fast enough).
…		…
2176		2397
2177	NOTE: I<< This callback must always return a time that is higher than or	2398	NOTE: I<< This callback must always return a time that is higher than or
2178	equal to the passed C<now> value >>.	2399	equal to the passed C<now> value >>.
2179		2400
2180	This can be used to create very complex timers, such as a timer that	2401	This can be used to create very complex timers, such as a timer that
2181	triggers on "next midnight, local time". To do this, you would calculate the	2402	triggers on "next midnight, local time". To do this, you would calculate
2182	next midnight after C<now> and return the timestamp value for this. How	2403	the next midnight after C<now> and return the timestamp value for
2183	you do this is, again, up to you (but it is not trivial, which is the main	2404	this. Here is a (completely untested, no error checking) example on how to
2184	reason I omitted it as an example).	2405	do this:
		2406
		2407	#include <time.h>
		2408
		2409	static ev_tstamp
		2410	my_rescheduler (ev_periodic *w, ev_tstamp now)
		2411	{
		2412	time_t tnow = (time_t)now;
		2413	struct tm tm;
		2414	localtime_r (&tnow, &tm);
		2415
		2416	tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
		2417	++tm.tm_mday; // midnight next day
		2418
		2419	return mktime (&tm);
		2420	}
		2421
		2422	Note: this code might run into trouble on days that have more then two
		2423	midnights (beginning and end).
2185		2424
2186	=back	2425	=back
2187		2426
2188	=item ev_periodic_again (loop, ev_periodic *)	2427	=item ev_periodic_again (loop, ev_periodic *)
2189		2428
…		…
2254		2493
2255	ev_periodic hourly_tick;	2494	ev_periodic hourly_tick;
2256	ev_periodic_init (&hourly_tick, clock_cb,	2495	ev_periodic_init (&hourly_tick, clock_cb,
2257	fmod (ev_now (loop), 3600.), 3600., 0);	2496	fmod (ev_now (loop), 3600.), 3600., 0);
2258	ev_periodic_start (loop, &hourly_tick);	2497	ev_periodic_start (loop, &hourly_tick);
2259		2498
2260		2499
2261	=head2 C<ev_signal> - signal me when a signal gets signalled!	2500	=head2 C<ev_signal> - signal me when a signal gets signalled!
2262		2501
2263	Signal watchers will trigger an event when the process receives a specific	2502	Signal watchers will trigger an event when the process receives a specific
2264	signal one or more times. Even though signals are very asynchronous, libev	2503	signal one or more times. Even though signals are very asynchronous, libev
2265	will try it's best to deliver signals synchronously, i.e. as part of the	2504	will try its best to deliver signals synchronously, i.e. as part of the
2266	normal event processing, like any other event.	2505	normal event processing, like any other event.
2267		2506
2268	If you want signals to be delivered truly asynchronously, just use	2507	If you want signals to be delivered truly asynchronously, just use
2269	C<sigaction> as you would do without libev and forget about sharing	2508	C<sigaction> as you would do without libev and forget about sharing
2270	the signal. You can even use C<ev_async> from a signal handler to	2509	the signal. You can even use C<ev_async> from a signal handler to
…		…
2274	only within the same loop, i.e. you can watch for C<SIGINT> in your	2513	only within the same loop, i.e. you can watch for C<SIGINT> in your
2275	default loop and for C<SIGIO> in another loop, but you cannot watch for	2514	default loop and for C<SIGIO> in another loop, but you cannot watch for
2276	C<SIGINT> in both the default loop and another loop at the same time. At	2515	C<SIGINT> in both the default loop and another loop at the same time. At
2277	the moment, C<SIGCHLD> is permanently tied to the default loop.	2516	the moment, C<SIGCHLD> is permanently tied to the default loop.
2278		2517
2279	When the first watcher gets started will libev actually register something	2518	Only after the first watcher for a signal is started will libev actually
2280	with the kernel (thus it coexists with your own signal handlers as long as	2519	register something with the kernel. It thus coexists with your own signal
2281	you don't register any with libev for the same signal).	2520	handlers as long as you don't register any with libev for the same signal.
2282		2521
2283	If possible and supported, libev will install its handlers with	2522	If possible and supported, libev will install its handlers with
2284	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should	2523	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
2285	not be unduly interrupted. If you have a problem with system calls getting	2524	not be unduly interrupted. If you have a problem with system calls getting
2286	interrupted by signals you can block all signals in an C<ev_check> watcher	2525	interrupted by signals you can block all signals in an C<ev_check> watcher
…		…
2289	=head3 The special problem of inheritance over fork/execve/pthread_create	2528	=head3 The special problem of inheritance over fork/execve/pthread_create
2290		2529
2291	Both the signal mask (C<sigprocmask>) and the signal disposition	2530	Both the signal mask (C<sigprocmask>) and the signal disposition
2292	(C<sigaction>) are unspecified after starting a signal watcher (and after	2531	(C<sigaction>) are unspecified after starting a signal watcher (and after
2293	stopping it again), that is, libev might or might not block the signal,	2532	stopping it again), that is, libev might or might not block the signal,
2294	and might or might not set or restore the installed signal handler.	2533	and might or might not set or restore the installed signal handler (but
		2534	see C<EVFLAG_NOSIGMASK>).
2295		2535
2296	While this does not matter for the signal disposition (libev never	2536	While this does not matter for the signal disposition (libev never
2297	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on	2537	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
2298	C<execve>), this matters for the signal mask: many programs do not expect	2538	C<execve>), this matters for the signal mask: many programs do not expect
2299	certain signals to be blocked.	2539	certain signals to be blocked.
…		…
2312	I<has> to modify the signal mask, at least temporarily.	2552	I<has> to modify the signal mask, at least temporarily.
2313		2553
2314	So I can't stress this enough: I<If you do not reset your signal mask when	2554	So I can't stress this enough: I<If you do not reset your signal mask when
2315	you expect it to be empty, you have a race condition in your code>. This	2555	you expect it to be empty, you have a race condition in your code>. This
2316	is not a libev-specific thing, this is true for most event libraries.	2556	is not a libev-specific thing, this is true for most event libraries.
		2557
		2558	=head3 The special problem of threads signal handling
		2559
		2560	POSIX threads has problematic signal handling semantics, specifically,
		2561	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2562	threads in a process block signals, which is hard to achieve.
		2563
		2564	When you want to use sigwait (or mix libev signal handling with your own
		2565	for the same signals), you can tackle this problem by globally blocking
		2566	all signals before creating any threads (or creating them with a fully set
		2567	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2568	loops. Then designate one thread as "signal receiver thread" which handles
		2569	these signals. You can pass on any signals that libev might be interested
		2570	in by calling C<ev_feed_signal>.
2317		2571
2318	=head3 Watcher-Specific Functions and Data Members	2572	=head3 Watcher-Specific Functions and Data Members
2319		2573
2320	=over 4	2574	=over 4
2321		2575
…		…
2456		2710
2457	=head2 C<ev_stat> - did the file attributes just change?	2711	=head2 C<ev_stat> - did the file attributes just change?
2458		2712
2459	This watches a file system path for attribute changes. That is, it calls	2713	This watches a file system path for attribute changes. That is, it calls
2460	C<stat> on that path in regular intervals (or when the OS says it changed)	2714	C<stat> on that path in regular intervals (or when the OS says it changed)
2461	and sees if it changed compared to the last time, invoking the callback if	2715	and sees if it changed compared to the last time, invoking the callback
2462	it did.	2716	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2717	happen after the watcher has been started will be reported.
2463		2718
2464	The path does not need to exist: changing from "path exists" to "path does	2719	The path does not need to exist: changing from "path exists" to "path does
2465	not exist" is a status change like any other. The condition "path does not	2720	not exist" is a status change like any other. The condition "path does not
2466	exist" (or more correctly "path cannot be stat'ed") is signified by the	2721	exist" (or more correctly "path cannot be stat'ed") is signified by the
2467	C<st_nlink> field being zero (which is otherwise always forced to be at	2722	C<st_nlink> field being zero (which is otherwise always forced to be at
…		…
2697	Apart from keeping your process non-blocking (which is a useful	2952	Apart from keeping your process non-blocking (which is a useful
2698	effect on its own sometimes), idle watchers are a good place to do	2953	effect on its own sometimes), idle watchers are a good place to do
2699	"pseudo-background processing", or delay processing stuff to after the	2954	"pseudo-background processing", or delay processing stuff to after the
2700	event loop has handled all outstanding events.	2955	event loop has handled all outstanding events.
2701		2956
		2957	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2958
		2959	As long as there is at least one active idle watcher, libev will never
		2960	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2961	For this to work, the idle watcher doesn't need to be invoked at all - the
		2962	lowest priority will do.
		2963
		2964	This mode of operation can be useful together with an C<ev_check> watcher,
		2965	to do something on each event loop iteration - for example to balance load
		2966	between different connections.
		2967
		2968	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2969	example.
		2970
2702	=head3 Watcher-Specific Functions and Data Members	2971	=head3 Watcher-Specific Functions and Data Members
2703		2972
2704	=over 4	2973	=over 4
2705		2974
2706	=item ev_idle_init (ev_idle *, callback)	2975	=item ev_idle_init (ev_idle *, callback)
…		…
2717	callback, free it. Also, use no error checking, as usual.	2986	callback, free it. Also, use no error checking, as usual.
2718		2987
2719	static void	2988	static void
2720	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)	2989	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2721	{	2990	{
		2991	// stop the watcher
		2992	ev_idle_stop (loop, w);
		2993
		2994	// now we can free it
2722	free (w);	2995	free (w);
		2996
2723	// now do something you wanted to do when the program has	2997	// now do something you wanted to do when the program has
2724	// no longer anything immediate to do.	2998	// no longer anything immediate to do.
2725	}	2999	}
2726		3000
2727	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	3001	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
…		…
2729	ev_idle_start (loop, idle_watcher);	3003	ev_idle_start (loop, idle_watcher);
2730		3004
2731		3005
2732	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	3006	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2733		3007
2734	Prepare and check watchers are usually (but not always) used in pairs:	3008	Prepare and check watchers are often (but not always) used in pairs:
2735	prepare watchers get invoked before the process blocks and check watchers	3009	prepare watchers get invoked before the process blocks and check watchers
2736	afterwards.	3010	afterwards.
2737		3011
2738	You I<must not> call C<ev_run> or similar functions that enter	3012	You I<must not> call C<ev_run> (or similar functions that enter the
2739	the current event loop from either C<ev_prepare> or C<ev_check>	3013	current event loop) or C<ev_loop_fork> from either C<ev_prepare> or
2740	watchers. Other loops than the current one are fine, however. The	3014	C<ev_check> watchers. Other loops than the current one are fine,
2741	rationale behind this is that you do not need to check for recursion in	3015	however. The rationale behind this is that you do not need to check
2742	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	3016	for recursion in those watchers, i.e. the sequence will always be
2743	C<ev_check> so if you have one watcher of each kind they will always be	3017	C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
2744	called in pairs bracketing the blocking call.	3018	kind they will always be called in pairs bracketing the blocking call.
2745		3019
2746	Their main purpose is to integrate other event mechanisms into libev and	3020	Their main purpose is to integrate other event mechanisms into libev and
2747	their use is somewhat advanced. They could be used, for example, to track	3021	their use is somewhat advanced. They could be used, for example, to track
2748	variable changes, implement your own watchers, integrate net-snmp or a	3022	variable changes, implement your own watchers, integrate net-snmp or a
2749	coroutine library and lots more. They are also occasionally useful if	3023	coroutine library and lots more. They are also occasionally useful if
…		…
2767	with priority higher than or equal to the event loop and one coroutine	3041	with priority higher than or equal to the event loop and one coroutine
2768	of lower priority, but only once, using idle watchers to keep the event	3042	of lower priority, but only once, using idle watchers to keep the event
2769	loop from blocking if lower-priority coroutines are active, thus mapping	3043	loop from blocking if lower-priority coroutines are active, thus mapping
2770	low-priority coroutines to idle/background tasks).	3044	low-priority coroutines to idle/background tasks).
2771		3045
2772	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	3046	When used for this purpose, it is recommended to give C<ev_check> watchers
2773	priority, to ensure that they are being run before any other watchers	3047	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
2774	after the poll (this doesn't matter for C<ev_prepare> watchers).	3048	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		3049	watchers).
2775		3050
2776	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not	3051	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
2777	activate ("feed") events into libev. While libev fully supports this, they	3052	activate ("feed") events into libev. While libev fully supports this, they
2778	might get executed before other C<ev_check> watchers did their job. As	3053	might get executed before other C<ev_check> watchers did their job. As
2779	C<ev_check> watchers are often used to embed other (non-libev) event	3054	C<ev_check> watchers are often used to embed other (non-libev) event
2780	loops those other event loops might be in an unusable state until their	3055	loops those other event loops might be in an unusable state until their
2781	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	3056	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
2782	others).	3057	others).
		3058
		3059	=head3 Abusing an C<ev_check> watcher for its side-effect
		3060
		3061	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		3062	useful because they are called once per event loop iteration. For
		3063	example, if you want to handle a large number of connections fairly, you
		3064	normally only do a bit of work for each active connection, and if there
		3065	is more work to do, you wait for the next event loop iteration, so other
		3066	connections have a chance of making progress.
		3067
		3068	Using an C<ev_check> watcher is almost enough: it will be called on the
		3069	next event loop iteration. However, that isn't as soon as possible -
		3070	without external events, your C<ev_check> watcher will not be invoked.
		3071
		3072	This is where C<ev_idle> watchers come in handy - all you need is a
		3073	single global idle watcher that is active as long as you have one active
		3074	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		3075	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		3076	invoked. Neither watcher alone can do that.
2783		3077
2784	=head3 Watcher-Specific Functions and Data Members	3078	=head3 Watcher-Specific Functions and Data Members
2785		3079
2786	=over 4	3080	=over 4
2787		3081
…		…
2988		3282
2989	=over 4	3283	=over 4
2990		3284
2991	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3285	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
2992		3286
2993	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3287	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
2994		3288
2995	Configures the watcher to embed the given loop, which must be	3289	Configures the watcher to embed the given loop, which must be
2996	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3290	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
2997	invoked automatically, otherwise it is the responsibility of the callback	3291	invoked automatically, otherwise it is the responsibility of the callback
2998	to invoke it (it will continue to be called until the sweep has been done,	3292	to invoke it (it will continue to be called until the sweep has been done,
…		…
3019	used).	3313	used).
3020		3314
3021	struct ev_loop *loop_hi = ev_default_init (0);	3315	struct ev_loop *loop_hi = ev_default_init (0);
3022	struct ev_loop *loop_lo = 0;	3316	struct ev_loop *loop_lo = 0;
3023	ev_embed embed;	3317	ev_embed embed;
3024		3318
3025	// see if there is a chance of getting one that works	3319	// see if there is a chance of getting one that works
3026	// (remember that a flags value of 0 means autodetection)	3320	// (remember that a flags value of 0 means autodetection)
3027	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3321	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3028	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3322	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3029	: 0;	3323	: 0;
…		…
3043	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3337	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
3044		3338
3045	struct ev_loop *loop = ev_default_init (0);	3339	struct ev_loop *loop = ev_default_init (0);
3046	struct ev_loop *loop_socket = 0;	3340	struct ev_loop *loop_socket = 0;
3047	ev_embed embed;	3341	ev_embed embed;
3048		3342
3049	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3343	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3050	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3344	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3051	{	3345	{
3052	ev_embed_init (&embed, 0, loop_socket);	3346	ev_embed_init (&embed, 0, loop_socket);
3053	ev_embed_start (loop, &embed);	3347	ev_embed_start (loop, &embed);
…		…
3061		3355
3062	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3356	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
3063		3357
3064	Fork watchers are called when a C<fork ()> was detected (usually because	3358	Fork watchers are called when a C<fork ()> was detected (usually because
3065	whoever is a good citizen cared to tell libev about it by calling	3359	whoever is a good citizen cared to tell libev about it by calling
3066	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the	3360	C<ev_loop_fork>). The invocation is done before the event loop blocks next
3067	event loop blocks next and before C<ev_check> watchers are being called,	3361	and before C<ev_check> watchers are being called, and only in the child
3068	and only in the child after the fork. If whoever good citizen calling	3362	after the fork. If whoever good citizen calling C<ev_default_fork> cheats
3069	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3363	and calls it in the wrong process, the fork handlers will be invoked, too,
3070	handlers will be invoked, too, of course.	3364	of course.
3071		3365
3072	=head3 The special problem of life after fork - how is it possible?	3366	=head3 The special problem of life after fork - how is it possible?
3073		3367
3074	Most uses of C<fork()> consist of forking, then some simple calls to set	3368	Most uses of C<fork ()> consist of forking, then some simple calls to set
3075	up/change the process environment, followed by a call to C<exec()>. This	3369	up/change the process environment, followed by a call to C<exec()>. This
3076	sequence should be handled by libev without any problems.	3370	sequence should be handled by libev without any problems.
3077		3371
3078	This changes when the application actually wants to do event handling	3372	This changes when the application actually wants to do event handling
3079	in the child, or both parent in child, in effect "continuing" after the	3373	in the child, or both parent in child, in effect "continuing" after the
…		…
3156	atexit (program_exits);	3450	atexit (program_exits);
3157		3451
3158		3452
3159	=head2 C<ev_async> - how to wake up an event loop	3453	=head2 C<ev_async> - how to wake up an event loop
3160		3454
3161	In general, you cannot use an C<ev_run> from multiple threads or other	3455	In general, you cannot use an C<ev_loop> from multiple threads or other
3162	asynchronous sources such as signal handlers (as opposed to multiple event	3456	asynchronous sources such as signal handlers (as opposed to multiple event
3163	loops - those are of course safe to use in different threads).	3457	loops - those are of course safe to use in different threads).
3164		3458
3165	Sometimes, however, you need to wake up an event loop you do not control,	3459	Sometimes, however, you need to wake up an event loop you do not control,
3166	for example because it belongs to another thread. This is what C<ev_async>	3460	for example because it belongs to another thread. This is what C<ev_async>
…		…
3168	it by calling C<ev_async_send>, which is thread- and signal safe.	3462	it by calling C<ev_async_send>, which is thread- and signal safe.
3169		3463
3170	This functionality is very similar to C<ev_signal> watchers, as signals,	3464	This functionality is very similar to C<ev_signal> watchers, as signals,
3171	too, are asynchronous in nature, and signals, too, will be compressed	3465	too, are asynchronous in nature, and signals, too, will be compressed
3172	(i.e. the number of callback invocations may be less than the number of	3466	(i.e. the number of callback invocations may be less than the number of
3173	C<ev_async_sent> calls).	3467	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
3174		3468	of "global async watchers" by using a watcher on an otherwise unused
3175	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not	3469	signal, and C<ev_feed_signal> to signal this watcher from another thread,
3176	just the default loop.	3470	even without knowing which loop owns the signal.
3177		3471
3178	=head3 Queueing	3472	=head3 Queueing
3179		3473
3180	C<ev_async> does not support queueing of data in any way. The reason	3474	C<ev_async> does not support queueing of data in any way. The reason
3181	is that the author does not know of a simple (or any) algorithm for a	3475	is that the author does not know of a simple (or any) algorithm for a
…		…
3273	trust me.	3567	trust me.
3274		3568
3275	=item ev_async_send (loop, ev_async *)	3569	=item ev_async_send (loop, ev_async *)
3276		3570
3277	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3571	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
3278	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3572	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3573	returns.
		3574
3279	C<ev_feed_event>, this call is safe to do from other threads, signal or	3575	Unlike C<ev_feed_event>, this call is safe to do from other threads,
3280	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3576	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3281	section below on what exactly this means).	3577	embedding section below on what exactly this means).
3282		3578
3283	Note that, as with other watchers in libev, multiple events might get	3579	Note that, as with other watchers in libev, multiple events might get
3284	compressed into a single callback invocation (another way to look at this	3580	compressed into a single callback invocation (another way to look at
3285	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,	3581	this is that C<ev_async> watchers are level-triggered: they are set on
3286	reset when the event loop detects that).	3582	C<ev_async_send>, reset when the event loop detects that).
3287		3583
3288	This call incurs the overhead of a system call only once per event loop	3584	This call incurs the overhead of at most one extra system call per event
3289	iteration, so while the overhead might be noticeable, it doesn't apply to	3585	loop iteration, if the event loop is blocked, and no syscall at all if
3290	repeated calls to C<ev_async_send> for the same event loop.	3586	the event loop (or your program) is processing events. That means that
		3587	repeated calls are basically free (there is no need to avoid calls for
		3588	performance reasons) and that the overhead becomes smaller (typically
		3589	zero) under load.
3291		3590
3292	=item bool = ev_async_pending (ev_async *)	3591	=item bool = ev_async_pending (ev_async *)
3293		3592
3294	Returns a non-zero value when C<ev_async_send> has been called on the	3593	Returns a non-zero value when C<ev_async_send> has been called on the
3295	watcher but the event has not yet been processed (or even noted) by the	3594	watcher but the event has not yet been processed (or even noted) by the
…		…
3312		3611
3313	There are some other functions of possible interest. Described. Here. Now.	3612	There are some other functions of possible interest. Described. Here. Now.
3314		3613
3315	=over 4	3614	=over 4
3316		3615
3317	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3616	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)
3318		3617
3319	This function combines a simple timer and an I/O watcher, calls your	3618	This function combines a simple timer and an I/O watcher, calls your
3320	callback on whichever event happens first and automatically stops both	3619	callback on whichever event happens first and automatically stops both
3321	watchers. This is useful if you want to wait for a single event on an fd	3620	watchers. This is useful if you want to wait for a single event on an fd
3322	or timeout without having to allocate/configure/start/stop/free one or	3621	or timeout without having to allocate/configure/start/stop/free one or
…		…
3350	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3649	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3351		3650
3352	=item ev_feed_fd_event (loop, int fd, int revents)	3651	=item ev_feed_fd_event (loop, int fd, int revents)
3353		3652
3354	Feed an event on the given fd, as if a file descriptor backend detected	3653	Feed an event on the given fd, as if a file descriptor backend detected
3355	the given events it.	3654	the given events.
3356		3655
3357	=item ev_feed_signal_event (loop, int signum)	3656	=item ev_feed_signal_event (loop, int signum)
3358		3657
3359	Feed an event as if the given signal occurred (C<loop> must be the default	3658	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3360	loop!).	3659	which is async-safe.
3361		3660
3362	=back	3661	=back
		3662
		3663
		3664	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3665
		3666	This section explains some common idioms that are not immediately
		3667	obvious. Note that examples are sprinkled over the whole manual, and this
		3668	section only contains stuff that wouldn't fit anywhere else.
		3669
		3670	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3671
		3672	Each watcher has, by default, a C<void *data> member that you can read
		3673	or modify at any time: libev will completely ignore it. This can be used
		3674	to associate arbitrary data with your watcher. If you need more data and
		3675	don't want to allocate memory separately and store a pointer to it in that
		3676	data member, you can also "subclass" the watcher type and provide your own
		3677	data:
		3678
		3679	struct my_io
		3680	{
		3681	ev_io io;
		3682	int otherfd;
		3683	void *somedata;
		3684	struct whatever *mostinteresting;
		3685	};
		3686
		3687	...
		3688	struct my_io w;
		3689	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3690
		3691	And since your callback will be called with a pointer to the watcher, you
		3692	can cast it back to your own type:
		3693
		3694	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3695	{
		3696	struct my_io *w = (struct my_io *)w_;
		3697	...
		3698	}
		3699
		3700	More interesting and less C-conformant ways of casting your callback
		3701	function type instead have been omitted.
		3702
		3703	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3704
		3705	Another common scenario is to use some data structure with multiple
		3706	embedded watchers, in effect creating your own watcher that combines
		3707	multiple libev event sources into one "super-watcher":
		3708
		3709	struct my_biggy
		3710	{
		3711	int some_data;
		3712	ev_timer t1;
		3713	ev_timer t2;
		3714	}
		3715
		3716	In this case getting the pointer to C<my_biggy> is a bit more
		3717	complicated: Either you store the address of your C<my_biggy> struct in
		3718	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3719	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3720	real programmers):
		3721
		3722	#include <stddef.h>
		3723
		3724	static void
		3725	t1_cb (EV_P_ ev_timer *w, int revents)
		3726	{
		3727	struct my_biggy big = (struct my_biggy *)
		3728	(((char *)w) - offsetof (struct my_biggy, t1));
		3729	}
		3730
		3731	static void
		3732	t2_cb (EV_P_ ev_timer *w, int revents)
		3733	{
		3734	struct my_biggy big = (struct my_biggy *)
		3735	(((char *)w) - offsetof (struct my_biggy, t2));
		3736	}
		3737
		3738	=head2 AVOIDING FINISHING BEFORE RETURNING
		3739
		3740	Often you have structures like this in event-based programs:
		3741
		3742	callback ()
		3743	{
		3744	free (request);
		3745	}
		3746
		3747	request = start_new_request (..., callback);
		3748
		3749	The intent is to start some "lengthy" operation. The C<request> could be
		3750	used to cancel the operation, or do other things with it.
		3751
		3752	It's not uncommon to have code paths in C<start_new_request> that
		3753	immediately invoke the callback, for example, to report errors. Or you add
		3754	some caching layer that finds that it can skip the lengthy aspects of the
		3755	operation and simply invoke the callback with the result.
		3756
		3757	The problem here is that this will happen I<before> C<start_new_request>
		3758	has returned, so C<request> is not set.
		3759
		3760	Even if you pass the request by some safer means to the callback, you
		3761	might want to do something to the request after starting it, such as
		3762	canceling it, which probably isn't working so well when the callback has
		3763	already been invoked.
		3764
		3765	A common way around all these issues is to make sure that
		3766	C<start_new_request> I<always> returns before the callback is invoked. If
		3767	C<start_new_request> immediately knows the result, it can artificially
		3768	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3769	example, or more sneakily, by reusing an existing (stopped) watcher and
		3770	pushing it into the pending queue:
		3771
		3772	ev_set_cb (watcher, callback);
		3773	ev_feed_event (EV_A_ watcher, 0);
		3774
		3775	This way, C<start_new_request> can safely return before the callback is
		3776	invoked, while not delaying callback invocation too much.
		3777
		3778	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3779
		3780	Often (especially in GUI toolkits) there are places where you have
		3781	I<modal> interaction, which is most easily implemented by recursively
		3782	invoking C<ev_run>.
		3783
		3784	This brings the problem of exiting - a callback might want to finish the
		3785	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3786	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3787	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3788	other combination: In these cases, a simple C<ev_break> will not work.
		3789
		3790	The solution is to maintain "break this loop" variable for each C<ev_run>
		3791	invocation, and use a loop around C<ev_run> until the condition is
		3792	triggered, using C<EVRUN_ONCE>:
		3793
		3794	// main loop
		3795	int exit_main_loop = 0;
		3796
		3797	while (!exit_main_loop)
		3798	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3799
		3800	// in a modal watcher
		3801	int exit_nested_loop = 0;
		3802
		3803	while (!exit_nested_loop)
		3804	ev_run (EV_A_ EVRUN_ONCE);
		3805
		3806	To exit from any of these loops, just set the corresponding exit variable:
		3807
		3808	// exit modal loop
		3809	exit_nested_loop = 1;
		3810
		3811	// exit main program, after modal loop is finished
		3812	exit_main_loop = 1;
		3813
		3814	// exit both
		3815	exit_main_loop = exit_nested_loop = 1;
		3816
		3817	=head2 THREAD LOCKING EXAMPLE
		3818
		3819	Here is a fictitious example of how to run an event loop in a different
		3820	thread from where callbacks are being invoked and watchers are
		3821	created/added/removed.
		3822
		3823	For a real-world example, see the C<EV::Loop::Async> perl module,
		3824	which uses exactly this technique (which is suited for many high-level
		3825	languages).
		3826
		3827	The example uses a pthread mutex to protect the loop data, a condition
		3828	variable to wait for callback invocations, an async watcher to notify the
		3829	event loop thread and an unspecified mechanism to wake up the main thread.
		3830
		3831	First, you need to associate some data with the event loop:
		3832
		3833	typedef struct {
		3834	mutex_t lock; /* global loop lock */
		3835	ev_async async_w;
		3836	thread_t tid;
		3837	cond_t invoke_cv;
		3838	} userdata;
		3839
		3840	void prepare_loop (EV_P)
		3841	{
		3842	// for simplicity, we use a static userdata struct.
		3843	static userdata u;
		3844
		3845	ev_async_init (&u->async_w, async_cb);
		3846	ev_async_start (EV_A_ &u->async_w);
		3847
		3848	pthread_mutex_init (&u->lock, 0);
		3849	pthread_cond_init (&u->invoke_cv, 0);
		3850
		3851	// now associate this with the loop
		3852	ev_set_userdata (EV_A_ u);
		3853	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3854	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3855
		3856	// then create the thread running ev_run
		3857	pthread_create (&u->tid, 0, l_run, EV_A);
		3858	}
		3859
		3860	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3861	solely to wake up the event loop so it takes notice of any new watchers
		3862	that might have been added:
		3863
		3864	static void
		3865	async_cb (EV_P_ ev_async *w, int revents)
		3866	{
		3867	// just used for the side effects
		3868	}
		3869
		3870	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3871	protecting the loop data, respectively.
		3872
		3873	static void
		3874	l_release (EV_P)
		3875	{
		3876	userdata *u = ev_userdata (EV_A);
		3877	pthread_mutex_unlock (&u->lock);
		3878	}
		3879
		3880	static void
		3881	l_acquire (EV_P)
		3882	{
		3883	userdata *u = ev_userdata (EV_A);
		3884	pthread_mutex_lock (&u->lock);
		3885	}
		3886
		3887	The event loop thread first acquires the mutex, and then jumps straight
		3888	into C<ev_run>:
		3889
		3890	void *
		3891	l_run (void *thr_arg)
		3892	{
		3893	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3894
		3895	l_acquire (EV_A);
		3896	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3897	ev_run (EV_A_ 0);
		3898	l_release (EV_A);
		3899
		3900	return 0;
		3901	}
		3902
		3903	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3904	signal the main thread via some unspecified mechanism (signals? pipe
		3905	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3906	have been called (in a while loop because a) spurious wakeups are possible
		3907	and b) skipping inter-thread-communication when there are no pending
		3908	watchers is very beneficial):
		3909
		3910	static void
		3911	l_invoke (EV_P)
		3912	{
		3913	userdata *u = ev_userdata (EV_A);
		3914
		3915	while (ev_pending_count (EV_A))
		3916	{
		3917	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3918	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3919	}
		3920	}
		3921
		3922	Now, whenever the main thread gets told to invoke pending watchers, it
		3923	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3924	thread to continue:
		3925
		3926	static void
		3927	real_invoke_pending (EV_P)
		3928	{
		3929	userdata *u = ev_userdata (EV_A);
		3930
		3931	pthread_mutex_lock (&u->lock);
		3932	ev_invoke_pending (EV_A);
		3933	pthread_cond_signal (&u->invoke_cv);
		3934	pthread_mutex_unlock (&u->lock);
		3935	}
		3936
		3937	Whenever you want to start/stop a watcher or do other modifications to an
		3938	event loop, you will now have to lock:
		3939
		3940	ev_timer timeout_watcher;
		3941	userdata *u = ev_userdata (EV_A);
		3942
		3943	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3944
		3945	pthread_mutex_lock (&u->lock);
		3946	ev_timer_start (EV_A_ &timeout_watcher);
		3947	ev_async_send (EV_A_ &u->async_w);
		3948	pthread_mutex_unlock (&u->lock);
		3949
		3950	Note that sending the C<ev_async> watcher is required because otherwise
		3951	an event loop currently blocking in the kernel will have no knowledge
		3952	about the newly added timer. By waking up the loop it will pick up any new
		3953	watchers in the next event loop iteration.
		3954
		3955	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3956
		3957	While the overhead of a callback that e.g. schedules a thread is small, it
		3958	is still an overhead. If you embed libev, and your main usage is with some
		3959	kind of threads or coroutines, you might want to customise libev so that
		3960	doesn't need callbacks anymore.
		3961
		3962	Imagine you have coroutines that you can switch to using a function
		3963	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3964	and that due to some magic, the currently active coroutine is stored in a
		3965	global called C<current_coro>. Then you can build your own "wait for libev
		3966	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3967	the differing C<;> conventions):
		3968
		3969	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3970	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3971
		3972	That means instead of having a C callback function, you store the
		3973	coroutine to switch to in each watcher, and instead of having libev call
		3974	your callback, you instead have it switch to that coroutine.
		3975
		3976	A coroutine might now wait for an event with a function called
		3977	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3978	matter when, or whether the watcher is active or not when this function is
		3979	called):
		3980
		3981	void
		3982	wait_for_event (ev_watcher *w)
		3983	{
		3984	ev_set_cb (w, current_coro);
		3985	switch_to (libev_coro);
		3986	}
		3987
		3988	That basically suspends the coroutine inside C<wait_for_event> and
		3989	continues the libev coroutine, which, when appropriate, switches back to
		3990	this or any other coroutine.
		3991
		3992	You can do similar tricks if you have, say, threads with an event queue -
		3993	instead of storing a coroutine, you store the queue object and instead of
		3994	switching to a coroutine, you push the watcher onto the queue and notify
		3995	any waiters.
		3996
		3997	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		3998	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3999
		4000	// my_ev.h
		4001	#define EV_CB_DECLARE(type) struct my_coro *cb;
		4002	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		4003	#include "../libev/ev.h"
		4004
		4005	// my_ev.c
		4006	#define EV_H "my_ev.h"
		4007	#include "../libev/ev.c"
		4008
		4009	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		4010	F<my_ev.c> into your project. When properly specifying include paths, you
		4011	can even use F<ev.h> as header file name directly.
3363		4012
3364		4013
3365	=head1 LIBEVENT EMULATION	4014	=head1 LIBEVENT EMULATION
3366		4015
3367	Libev offers a compatibility emulation layer for libevent. It cannot	4016	Libev offers a compatibility emulation layer for libevent. It cannot
3368	emulate the internals of libevent, so here are some usage hints:	4017	emulate the internals of libevent, so here are some usage hints:
3369		4018
3370	=over 4	4019	=over 4
		4020
		4021	=item * Only the libevent-1.4.1-beta API is being emulated.
		4022
		4023	This was the newest libevent version available when libev was implemented,
		4024	and is still mostly unchanged in 2010.
3371		4025
3372	=item * Use it by including <event.h>, as usual.	4026	=item * Use it by including <event.h>, as usual.
3373		4027
3374	=item * The following members are fully supported: ev_base, ev_callback,	4028	=item * The following members are fully supported: ev_base, ev_callback,
3375	ev_arg, ev_fd, ev_res, ev_events.	4029	ev_arg, ev_fd, ev_res, ev_events.
…		…
3381	=item * Priorities are not currently supported. Initialising priorities	4035	=item * Priorities are not currently supported. Initialising priorities
3382	will fail and all watchers will have the same priority, even though there	4036	will fail and all watchers will have the same priority, even though there
3383	is an ev_pri field.	4037	is an ev_pri field.
3384		4038
3385	=item * In libevent, the last base created gets the signals, in libev, the	4039	=item * In libevent, the last base created gets the signals, in libev, the
3386	first base created (== the default loop) gets the signals.	4040	base that registered the signal gets the signals.
3387		4041
3388	=item * Other members are not supported.	4042	=item * Other members are not supported.
3389		4043
3390	=item * The libev emulation is I<not> ABI compatible to libevent, you need	4044	=item * The libev emulation is I<not> ABI compatible to libevent, you need
3391	to use the libev header file and library.	4045	to use the libev header file and library.
3392		4046
3393	=back	4047	=back
3394		4048
3395	=head1 C++ SUPPORT	4049	=head1 C++ SUPPORT
		4050
		4051	=head2 C API
		4052
		4053	The normal C API should work fine when used from C++: both ev.h and the
		4054	libev sources can be compiled as C++. Therefore, code that uses the C API
		4055	will work fine.
		4056
		4057	Proper exception specifications might have to be added to callbacks passed
		4058	to libev: exceptions may be thrown only from watcher callbacks, all other
		4059	callbacks (allocator, syserr, loop acquire/release and periodic reschedule
		4060	callbacks) must not throw exceptions, and might need a C<noexcept>
		4061	specification. If you have code that needs to be compiled as both C and
		4062	C++ you can use the C<EV_NOEXCEPT> macro for this:
		4063
		4064	static void
		4065	fatal_error (const char *msg) EV_NOEXCEPT
		4066	{
		4067	perror (msg);
		4068	abort ();
		4069	}
		4070
		4071	...
		4072	ev_set_syserr_cb (fatal_error);
		4073
		4074	The only API functions that can currently throw exceptions are C<ev_run>,
		4075	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		4076	because it runs cleanup watchers).
		4077
		4078	Throwing exceptions in watcher callbacks is only supported if libev itself
		4079	is compiled with a C++ compiler or your C and C++ environments allow
		4080	throwing exceptions through C libraries (most do).
		4081
		4082	=head2 C++ API
3396		4083
3397	Libev comes with some simplistic wrapper classes for C++ that mainly allow	4084	Libev comes with some simplistic wrapper classes for C++ that mainly allow
3398	you to use some convenience methods to start/stop watchers and also change	4085	you to use some convenience methods to start/stop watchers and also change
3399	the callback model to a model using method callbacks on objects.	4086	the callback model to a model using method callbacks on objects.
3400		4087
3401	To use it,	4088	To use it,
3402		4089
3403	#include <ev++.h>	4090	#include <ev++.h>
3404		4091
3405	This automatically includes F<ev.h> and puts all of its definitions (many	4092	This automatically includes F<ev.h> and puts all of its definitions (many
3406	of them macros) into the global namespace. All C++ specific things are	4093	of them macros) into the global namespace. All C++ specific things are
3407	put into the C<ev> namespace. It should support all the same embedding	4094	put into the C<ev> namespace. It should support all the same embedding
…		…
3410	Care has been taken to keep the overhead low. The only data member the C++	4097	Care has been taken to keep the overhead low. The only data member the C++
3411	classes add (compared to plain C-style watchers) is the event loop pointer	4098	classes add (compared to plain C-style watchers) is the event loop pointer
3412	that the watcher is associated with (or no additional members at all if	4099	that the watcher is associated with (or no additional members at all if
3413	you disable C<EV_MULTIPLICITY> when embedding libev).	4100	you disable C<EV_MULTIPLICITY> when embedding libev).
3414		4101
3415	Currently, functions, and static and non-static member functions can be	4102	Currently, functions, static and non-static member functions and classes
3416	used as callbacks. Other types should be easy to add as long as they only	4103	with C<operator ()> can be used as callbacks. Other types should be easy
3417	need one additional pointer for context. If you need support for other	4104	to add as long as they only need one additional pointer for context. If
3418	types of functors please contact the author (preferably after implementing	4105	you need support for other types of functors please contact the author
3419	it).	4106	(preferably after implementing it).
		4107
		4108	For all this to work, your C++ compiler either has to use the same calling
		4109	conventions as your C compiler (for static member functions), or you have
		4110	to embed libev and compile libev itself as C++.
3420		4111
3421	Here is a list of things available in the C<ev> namespace:	4112	Here is a list of things available in the C<ev> namespace:
3422		4113
3423	=over 4	4114	=over 4
3424		4115
…		…
3434	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4125	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
3435		4126
3436	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4127	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
3437	the same name in the C<ev> namespace, with the exception of C<ev_signal>	4128	the same name in the C<ev> namespace, with the exception of C<ev_signal>
3438	which is called C<ev::sig> to avoid clashes with the C<signal> macro	4129	which is called C<ev::sig> to avoid clashes with the C<signal> macro
3439	defines by many implementations.	4130	defined by many implementations.
3440		4131
3441	All of those classes have these methods:	4132	All of those classes have these methods:
3442		4133
3443	=over 4	4134	=over 4
3444		4135
…		…
3506	void operator() (ev::io &w, int revents)	4197	void operator() (ev::io &w, int revents)
3507	{	4198	{
3508	...	4199	...
3509	}	4200	}
3510	}	4201	}
3511		4202
3512	myfunctor f;	4203	myfunctor f;
3513		4204
3514	ev::io w;	4205	ev::io w;
3515	w.set (&f);	4206	w.set (&f);
3516		4207
…		…
3534	Associates a different C<struct ev_loop> with this watcher. You can only	4225	Associates a different C<struct ev_loop> with this watcher. You can only
3535	do this when the watcher is inactive (and not pending either).	4226	do this when the watcher is inactive (and not pending either).
3536		4227
3537	=item w->set ([arguments])	4228	=item w->set ([arguments])
3538		4229
3539	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this	4230	Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
3540	method or a suitable start method must be called at least once. Unlike the	4231	with the same arguments. Either this method or a suitable start method
3541	C counterpart, an active watcher gets automatically stopped and restarted	4232	must be called at least once. Unlike the C counterpart, an active watcher
3542	when reconfiguring it with this method.	4233	gets automatically stopped and restarted when reconfiguring it with this
		4234	method.
		4235
		4236	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4237	clashing with the C<set (loop)> method.
3543		4238
3544	=item w->start ()	4239	=item w->start ()
3545		4240
3546	Starts the watcher. Note that there is no C<loop> argument, as the	4241	Starts the watcher. Note that there is no C<loop> argument, as the
3547	constructor already stores the event loop.	4242	constructor already stores the event loop.
…		…
3577	watchers in the constructor.	4272	watchers in the constructor.
3578		4273
3579	class myclass	4274	class myclass
3580	{	4275	{
3581	ev::io io ; void io_cb (ev::io &w, int revents);	4276	ev::io io ; void io_cb (ev::io &w, int revents);
3582	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);	4277	ev::io io2 ; void io2_cb (ev::io &w, int revents);
3583	ev::idle idle; void idle_cb (ev::idle &w, int revents);	4278	ev::idle idle; void idle_cb (ev::idle &w, int revents);
3584		4279
3585	myclass (int fd)	4280	myclass (int fd)
3586	{	4281	{
3587	io .set <myclass, &myclass::io_cb > (this);	4282	io .set <myclass, &myclass::io_cb > (this);
…		…
3638	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.	4333	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3639		4334
3640	=item D	4335	=item D
3641		4336
3642	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4337	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
3643	be found at L<http://proj.llucax.com.ar/wiki/evd>.	4338	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
3644		4339
3645	=item Ocaml	4340	=item Ocaml
3646		4341
3647	Erkki Seppala has written Ocaml bindings for libev, to be found at	4342	Erkki Seppala has written Ocaml bindings for libev, to be found at
3648	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	4343	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
…		…
3651		4346
3652	Brian Maher has written a partial interface to libev for lua (at the	4347	Brian Maher has written a partial interface to libev for lua (at the
3653	time of this writing, only C<ev_io> and C<ev_timer>), to be found at	4348	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
3654	L<http://github.com/brimworks/lua-ev>.	4349	L<http://github.com/brimworks/lua-ev>.
3655		4350
		4351	=item Javascript
		4352
		4353	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4354
		4355	=item Others
		4356
		4357	There are others, and I stopped counting.
		4358
3656	=back	4359	=back
3657		4360
3658		4361
3659	=head1 MACRO MAGIC	4362	=head1 MACRO MAGIC
3660		4363
…		…
3696	suitable for use with C<EV_A>.	4399	suitable for use with C<EV_A>.
3697		4400
3698	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4401	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
3699		4402
3700	Similar to the other two macros, this gives you the value of the default	4403	Similar to the other two macros, this gives you the value of the default
3701	loop, if multiple loops are supported ("ev loop default").	4404	loop, if multiple loops are supported ("ev loop default"). The default loop
		4405	will be initialised if it isn't already initialised.
		4406
		4407	For non-multiplicity builds, these macros do nothing, so you always have
		4408	to initialise the loop somewhere.
3702		4409
3703	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4410	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
3704		4411
3705	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4412	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
3706	default loop has been initialised (C<UC> == unchecked). Their behaviour	4413	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
3773	ev_vars.h	4480	ev_vars.h
3774	ev_wrap.h	4481	ev_wrap.h
3775		4482
3776	ev_win32.c required on win32 platforms only	4483	ev_win32.c required on win32 platforms only
3777		4484
3778	ev_select.c only when select backend is enabled (which is enabled by default)	4485	ev_select.c only when select backend is enabled
3779	ev_poll.c only when poll backend is enabled (disabled by default)	4486	ev_poll.c only when poll backend is enabled
3780	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4487	ev_epoll.c only when the epoll backend is enabled
		4488	ev_linuxaio.c only when the linux aio backend is enabled
		4489	ev_iouring.c only when the linux io_uring backend is enabled
3781	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4490	ev_kqueue.c only when the kqueue backend is enabled
3782	ev_port.c only when the solaris port backend is enabled (disabled by default)	4491	ev_port.c only when the solaris port backend is enabled
3783		4492
3784	F<ev.c> includes the backend files directly when enabled, so you only need	4493	F<ev.c> includes the backend files directly when enabled, so you only need
3785	to compile this single file.	4494	to compile this single file.
3786		4495
3787	=head3 LIBEVENT COMPATIBILITY API	4496	=head3 LIBEVENT COMPATIBILITY API
…		…
3851	supported). It will also not define any of the structs usually found in	4560	supported). It will also not define any of the structs usually found in
3852	F<event.h> that are not directly supported by the libev core alone.	4561	F<event.h> that are not directly supported by the libev core alone.
3853		4562
3854	In standalone mode, libev will still try to automatically deduce the	4563	In standalone mode, libev will still try to automatically deduce the
3855	configuration, but has to be more conservative.	4564	configuration, but has to be more conservative.
		4565
		4566	=item EV_USE_FLOOR
		4567
		4568	If defined to be C<1>, libev will use the C<floor ()> function for its
		4569	periodic reschedule calculations, otherwise libev will fall back on a
		4570	portable (slower) implementation. If you enable this, you usually have to
		4571	link against libm or something equivalent. Enabling this when the C<floor>
		4572	function is not available will fail, so the safe default is to not enable
		4573	this.
3856		4574
3857	=item EV_USE_MONOTONIC	4575	=item EV_USE_MONOTONIC
3858		4576
3859	If defined to be C<1>, libev will try to detect the availability of the	4577	If defined to be C<1>, libev will try to detect the availability of the
3860	monotonic clock option at both compile time and runtime. Otherwise no	4578	monotonic clock option at both compile time and runtime. Otherwise no
…		…
3946	If programs implement their own fd to handle mapping on win32, then this	4664	If programs implement their own fd to handle mapping on win32, then this
3947	macro can be used to override the C<close> function, useful to unregister	4665	macro can be used to override the C<close> function, useful to unregister
3948	file descriptors again. Note that the replacement function has to close	4666	file descriptors again. Note that the replacement function has to close
3949	the underlying OS handle.	4667	the underlying OS handle.
3950		4668
		4669	=item EV_USE_WSASOCKET
		4670
		4671	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4672	communication socket, which works better in some environments. Otherwise,
		4673	the normal C<socket> function will be used, which works better in other
		4674	environments.
		4675
3951	=item EV_USE_POLL	4676	=item EV_USE_POLL
3952		4677
3953	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4678	If defined to be C<1>, libev will compile in support for the C<poll>(2)
3954	backend. Otherwise it will be enabled on non-win32 platforms. It	4679	backend. Otherwise it will be enabled on non-win32 platforms. It
3955	takes precedence over select.	4680	takes precedence over select.
…		…
3959	If defined to be C<1>, libev will compile in support for the Linux	4684	If defined to be C<1>, libev will compile in support for the Linux
3960	C<epoll>(7) backend. Its availability will be detected at runtime,	4685	C<epoll>(7) backend. Its availability will be detected at runtime,
3961	otherwise another method will be used as fallback. This is the preferred	4686	otherwise another method will be used as fallback. This is the preferred
3962	backend for GNU/Linux systems. If undefined, it will be enabled if the	4687	backend for GNU/Linux systems. If undefined, it will be enabled if the
3963	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4688	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4689
		4690	=item EV_USE_LINUXAIO
		4691
		4692	If defined to be C<1>, libev will compile in support for the Linux aio
		4693	backend (C<EV_USE_EPOLL> must also be enabled). If undefined, it will be
		4694	enabled on linux, otherwise disabled.
		4695
		4696	=item EV_USE_IOURING
		4697
		4698	If defined to be C<1>, libev will compile in support for the Linux
		4699	io_uring backend (C<EV_USE_EPOLL> must also be enabled). Due to it's
		4700	current limitations it has to be requested explicitly. If undefined, it
		4701	will be enabled on linux, otherwise disabled.
3964		4702
3965	=item EV_USE_KQUEUE	4703	=item EV_USE_KQUEUE
3966		4704
3967	If defined to be C<1>, libev will compile in support for the BSD style	4705	If defined to be C<1>, libev will compile in support for the BSD style
3968	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	4706	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
3990	If defined to be C<1>, libev will compile in support for the Linux inotify	4728	If defined to be C<1>, libev will compile in support for the Linux inotify
3991	interface to speed up C<ev_stat> watchers. Its actual availability will	4729	interface to speed up C<ev_stat> watchers. Its actual availability will
3992	be detected at runtime. If undefined, it will be enabled if the headers	4730	be detected at runtime. If undefined, it will be enabled if the headers
3993	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4731	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
3994		4732
		4733	=item EV_NO_SMP
		4734
		4735	If defined to be C<1>, libev will assume that memory is always coherent
		4736	between threads, that is, threads can be used, but threads never run on
		4737	different cpus (or different cpu cores). This reduces dependencies
		4738	and makes libev faster.
		4739
		4740	=item EV_NO_THREADS
		4741
		4742	If defined to be C<1>, libev will assume that it will never be called from
		4743	different threads (that includes signal handlers), which is a stronger
		4744	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4745	libev faster.
		4746
3995	=item EV_ATOMIC_T	4747	=item EV_ATOMIC_T
3996		4748
3997	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4749	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
3998	access is atomic with respect to other threads or signal contexts. No such	4750	access is atomic with respect to other threads or signal contexts. No
3999	type is easily found in the C language, so you can provide your own type	4751	such type is easily found in the C language, so you can provide your own
4000	that you know is safe for your purposes. It is used both for signal handler "locking"	4752	type that you know is safe for your purposes. It is used both for signal
4001	as well as for signal and thread safety in C<ev_async> watchers.	4753	handler "locking" as well as for signal and thread safety in C<ev_async>
		4754	watchers.
4002		4755
4003	In the absence of this define, libev will use C<sig_atomic_t volatile>	4756	In the absence of this define, libev will use C<sig_atomic_t volatile>
4004	(from F<signal.h>), which is usually good enough on most platforms.	4757	(from F<signal.h>), which is usually good enough on most platforms.
4005		4758
4006	=item EV_H (h)	4759	=item EV_H (h)
…		…
4033	will have the C<struct ev_loop *> as first argument, and you can create	4786	will have the C<struct ev_loop *> as first argument, and you can create
4034	additional independent event loops. Otherwise there will be no support	4787	additional independent event loops. Otherwise there will be no support
4035	for multiple event loops and there is no first event loop pointer	4788	for multiple event loops and there is no first event loop pointer
4036	argument. Instead, all functions act on the single default loop.	4789	argument. Instead, all functions act on the single default loop.
4037		4790
		4791	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4792	default loop when multiplicity is switched off - you always have to
		4793	initialise the loop manually in this case.
		4794
4038	=item EV_MINPRI	4795	=item EV_MINPRI
4039		4796
4040	=item EV_MAXPRI	4797	=item EV_MAXPRI
4041		4798
4042	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4799	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
4078	#define EV_USE_POLL 1	4835	#define EV_USE_POLL 1
4079	#define EV_CHILD_ENABLE 1	4836	#define EV_CHILD_ENABLE 1
4080	#define EV_ASYNC_ENABLE 1	4837	#define EV_ASYNC_ENABLE 1
4081		4838
4082	The actual value is a bitset, it can be a combination of the following	4839	The actual value is a bitset, it can be a combination of the following
4083	values:	4840	values (by default, all of these are enabled):
4084		4841
4085	=over 4	4842	=over 4
4086		4843
4087	=item C<1> - faster/larger code	4844	=item C<1> - faster/larger code
4088		4845
…		…
4092	code size by roughly 30% on amd64).	4849	code size by roughly 30% on amd64).
4093		4850
4094	When optimising for size, use of compiler flags such as C<-Os> with	4851	When optimising for size, use of compiler flags such as C<-Os> with
4095	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of	4852	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
4096	assertions.	4853	assertions.
		4854
		4855	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4856	(e.g. gcc with C<-Os>).
4097		4857
4098	=item C<2> - faster/larger data structures	4858	=item C<2> - faster/larger data structures
4099		4859
4100	Replaces the small 2-heap for timer management by a faster 4-heap, larger	4860	Replaces the small 2-heap for timer management by a faster 4-heap, larger
4101	hash table sizes and so on. This will usually further increase code size	4861	hash table sizes and so on. This will usually further increase code size
4102	and can additionally have an effect on the size of data structures at	4862	and can additionally have an effect on the size of data structures at
4103	runtime.	4863	runtime.
4104		4864
		4865	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4866	(e.g. gcc with C<-Os>).
		4867
4105	=item C<4> - full API configuration	4868	=item C<4> - full API configuration
4106		4869
4107	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and	4870	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
4108	enables multiplicity (C<EV_MULTIPLICITY>=1).	4871	enables multiplicity (C<EV_MULTIPLICITY>=1).
4109		4872
…		…
4139		4902
4140	With an intelligent-enough linker (gcc+binutils are intelligent enough	4903	With an intelligent-enough linker (gcc+binutils are intelligent enough
4141	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by	4904	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
4142	your program might be left out as well - a binary starting a timer and an	4905	your program might be left out as well - a binary starting a timer and an
4143	I/O watcher then might come out at only 5Kb.	4906	I/O watcher then might come out at only 5Kb.
		4907
		4908	=item EV_API_STATIC
		4909
		4910	If this symbol is defined (by default it is not), then all identifiers
		4911	will have static linkage. This means that libev will not export any
		4912	identifiers, and you cannot link against libev anymore. This can be useful
		4913	when you embed libev, only want to use libev functions in a single file,
		4914	and do not want its identifiers to be visible.
		4915
		4916	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4917	wants to use libev.
		4918
		4919	This option only works when libev is compiled with a C compiler, as C++
		4920	doesn't support the required declaration syntax.
4144		4921
4145	=item EV_AVOID_STDIO	4922	=item EV_AVOID_STDIO
4146		4923
4147	If this is set to C<1> at compiletime, then libev will avoid using stdio	4924	If this is set to C<1> at compiletime, then libev will avoid using stdio
4148	functions (printf, scanf, perror etc.). This will increase the code size	4925	functions (printf, scanf, perror etc.). This will increase the code size
…		…
4206	in. If set to C<1>, then verification code will be compiled in, but not	4983	in. If set to C<1>, then verification code will be compiled in, but not
4207	called. If set to C<2>, then the internal verification code will be	4984	called. If set to C<2>, then the internal verification code will be
4208	called once per loop, which can slow down libev. If set to C<3>, then the	4985	called once per loop, which can slow down libev. If set to C<3>, then the
4209	verification code will be called very frequently, which will slow down	4986	verification code will be called very frequently, which will slow down
4210	libev considerably.	4987	libev considerably.
		4988
		4989	Verification errors are reported via C's C<assert> mechanism, so if you
		4990	disable that (e.g. by defining C<NDEBUG>) then no errors will be reported.
4211		4991
4212	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it	4992	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
4213	will be C<0>.	4993	will be C<0>.
4214		4994
4215	=item EV_COMMON	4995	=item EV_COMMON
…		…
4292	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	5072	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4293		5073
4294	#include "ev_cpp.h"	5074	#include "ev_cpp.h"
4295	#include "ev.c"	5075	#include "ev.c"
4296		5076
4297	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	5077	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4298		5078
4299	=head2 THREADS AND COROUTINES	5079	=head2 THREADS AND COROUTINES
4300		5080
4301	=head3 THREADS	5081	=head3 THREADS
4302		5082
…		…
4353	default loop and triggering an C<ev_async> watcher from the default loop	5133	default loop and triggering an C<ev_async> watcher from the default loop
4354	watcher callback into the event loop interested in the signal.	5134	watcher callback into the event loop interested in the signal.
4355		5135
4356	=back	5136	=back
4357		5137
4358	=head4 THREAD LOCKING EXAMPLE	5138	See also L</THREAD LOCKING EXAMPLE>.
4359
4360	Here is a fictitious example of how to run an event loop in a different
4361	thread than where callbacks are being invoked and watchers are
4362	created/added/removed.
4363
4364	For a real-world example, see the C<EV::Loop::Async> perl module,
4365	which uses exactly this technique (which is suited for many high-level
4366	languages).
4367
4368	The example uses a pthread mutex to protect the loop data, a condition
4369	variable to wait for callback invocations, an async watcher to notify the
4370	event loop thread and an unspecified mechanism to wake up the main thread.
4371
4372	First, you need to associate some data with the event loop:
4373
4374	typedef struct {
4375	mutex_t lock; /* global loop lock */
4376	ev_async async_w;
4377	thread_t tid;
4378	cond_t invoke_cv;
4379	} userdata;
4380
4381	void prepare_loop (EV_P)
4382	{
4383	// for simplicity, we use a static userdata struct.
4384	static userdata u;
4385
4386	ev_async_init (&u->async_w, async_cb);
4387	ev_async_start (EV_A_ &u->async_w);
4388
4389	pthread_mutex_init (&u->lock, 0);
4390	pthread_cond_init (&u->invoke_cv, 0);
4391
4392	// now associate this with the loop
4393	ev_set_userdata (EV_A_ u);
4394	ev_set_invoke_pending_cb (EV_A_ l_invoke);
4395	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4396
4397	// then create the thread running ev_loop
4398	pthread_create (&u->tid, 0, l_run, EV_A);
4399	}
4400
4401	The callback for the C<ev_async> watcher does nothing: the watcher is used
4402	solely to wake up the event loop so it takes notice of any new watchers
4403	that might have been added:
4404
4405	static void
4406	async_cb (EV_P_ ev_async *w, int revents)
4407	{
4408	// just used for the side effects
4409	}
4410
4411	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
4412	protecting the loop data, respectively.
4413
4414	static void
4415	l_release (EV_P)
4416	{
4417	userdata *u = ev_userdata (EV_A);
4418	pthread_mutex_unlock (&u->lock);
4419	}
4420
4421	static void
4422	l_acquire (EV_P)
4423	{
4424	userdata *u = ev_userdata (EV_A);
4425	pthread_mutex_lock (&u->lock);
4426	}
4427
4428	The event loop thread first acquires the mutex, and then jumps straight
4429	into C<ev_run>:
4430
4431	void *
4432	l_run (void *thr_arg)
4433	{
4434	struct ev_loop *loop = (struct ev_loop *)thr_arg;
4435
4436	l_acquire (EV_A);
4437	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4438	ev_run (EV_A_ 0);
4439	l_release (EV_A);
4440
4441	return 0;
4442	}
4443
4444	Instead of invoking all pending watchers, the C<l_invoke> callback will
4445	signal the main thread via some unspecified mechanism (signals? pipe
4446	writes? C<Async::Interrupt>?) and then waits until all pending watchers
4447	have been called (in a while loop because a) spurious wakeups are possible
4448	and b) skipping inter-thread-communication when there are no pending
4449	watchers is very beneficial):
4450
4451	static void
4452	l_invoke (EV_P)
4453	{
4454	userdata *u = ev_userdata (EV_A);
4455
4456	while (ev_pending_count (EV_A))
4457	{
4458	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4459	pthread_cond_wait (&u->invoke_cv, &u->lock);
4460	}
4461	}
4462
4463	Now, whenever the main thread gets told to invoke pending watchers, it
4464	will grab the lock, call C<ev_invoke_pending> and then signal the loop
4465	thread to continue:
4466
4467	static void
4468	real_invoke_pending (EV_P)
4469	{
4470	userdata *u = ev_userdata (EV_A);
4471
4472	pthread_mutex_lock (&u->lock);
4473	ev_invoke_pending (EV_A);
4474	pthread_cond_signal (&u->invoke_cv);
4475	pthread_mutex_unlock (&u->lock);
4476	}
4477
4478	Whenever you want to start/stop a watcher or do other modifications to an
4479	event loop, you will now have to lock:
4480
4481	ev_timer timeout_watcher;
4482	userdata *u = ev_userdata (EV_A);
4483
4484	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4485
4486	pthread_mutex_lock (&u->lock);
4487	ev_timer_start (EV_A_ &timeout_watcher);
4488	ev_async_send (EV_A_ &u->async_w);
4489	pthread_mutex_unlock (&u->lock);
4490
4491	Note that sending the C<ev_async> watcher is required because otherwise
4492	an event loop currently blocking in the kernel will have no knowledge
4493	about the newly added timer. By waking up the loop it will pick up any new
4494	watchers in the next event loop iteration.
4495		5139
4496	=head3 COROUTINES	5140	=head3 COROUTINES
4497		5141
4498	Libev is very accommodating to coroutines ("cooperative threads"):	5142	Libev is very accommodating to coroutines ("cooperative threads"):
4499	libev fully supports nesting calls to its functions from different	5143	libev fully supports nesting calls to its functions from different
…		…
4664	requires, and its I/O model is fundamentally incompatible with the POSIX	5308	requires, and its I/O model is fundamentally incompatible with the POSIX
4665	model. Libev still offers limited functionality on this platform in	5309	model. Libev still offers limited functionality on this platform in
4666	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5310	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
4667	descriptors. This only applies when using Win32 natively, not when using	5311	descriptors. This only applies when using Win32 natively, not when using
4668	e.g. cygwin. Actually, it only applies to the microsofts own compilers,	5312	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4669	as every compielr comes with a slightly differently broken/incompatible	5313	as every compiler comes with a slightly differently broken/incompatible
4670	environment.	5314	environment.
4671		5315
4672	Lifting these limitations would basically require the full	5316	Lifting these limitations would basically require the full
4673	re-implementation of the I/O system. If you are into this kind of thing,	5317	re-implementation of the I/O system. If you are into this kind of thing,
4674	then note that glib does exactly that for you in a very portable way (note	5318	then note that glib does exactly that for you in a very portable way (note
…		…
4768	structure (guaranteed by POSIX but not by ISO C for example), but it also	5412	structure (guaranteed by POSIX but not by ISO C for example), but it also
4769	assumes that the same (machine) code can be used to call any watcher	5413	assumes that the same (machine) code can be used to call any watcher
4770	callback: The watcher callbacks have different type signatures, but libev	5414	callback: The watcher callbacks have different type signatures, but libev
4771	calls them using an C<ev_watcher *> internally.	5415	calls them using an C<ev_watcher *> internally.
4772		5416
		5417	=item null pointers and integer zero are represented by 0 bytes
		5418
		5419	Libev uses C<memset> to initialise structs and arrays to C<0> bytes, and
		5420	relies on this setting pointers and integers to null.
		5421
4773	=item pointer accesses must be thread-atomic	5422	=item pointer accesses must be thread-atomic
4774		5423
4775	Accessing a pointer value must be atomic, it must both be readable and	5424	Accessing a pointer value must be atomic, it must both be readable and
4776	writable in one piece - this is the case on all current architectures.	5425	writable in one piece - this is the case on all current architectures.
4777		5426
…		…
4790	thread" or will block signals process-wide, both behaviours would	5439	thread" or will block signals process-wide, both behaviours would
4791	be compatible with libev. Interaction between C<sigprocmask> and	5440	be compatible with libev. Interaction between C<sigprocmask> and
4792	C<pthread_sigmask> could complicate things, however.	5441	C<pthread_sigmask> could complicate things, however.
4793		5442
4794	The most portable way to handle signals is to block signals in all threads	5443	The most portable way to handle signals is to block signals in all threads
4795	except the initial one, and run the default loop in the initial thread as	5444	except the initial one, and run the signal handling loop in the initial
4796	well.	5445	thread as well.
4797		5446
4798	=item C<long> must be large enough for common memory allocation sizes	5447	=item C<long> must be large enough for common memory allocation sizes
4799		5448
4800	To improve portability and simplify its API, libev uses C<long> internally	5449	To improve portability and simplify its API, libev uses C<long> internally
4801	instead of C<size_t> when allocating its data structures. On non-POSIX	5450	instead of C<size_t> when allocating its data structures. On non-POSIX
…		…
4807		5456
4808	The type C<double> is used to represent timestamps. It is required to	5457	The type C<double> is used to represent timestamps. It is required to
4809	have at least 51 bits of mantissa (and 9 bits of exponent), which is	5458	have at least 51 bits of mantissa (and 9 bits of exponent), which is
4810	good enough for at least into the year 4000 with millisecond accuracy	5459	good enough for at least into the year 4000 with millisecond accuracy
4811	(the design goal for libev). This requirement is overfulfilled by	5460	(the design goal for libev). This requirement is overfulfilled by
4812	implementations using IEEE 754, which is basically all existing ones. With	5461	implementations using IEEE 754, which is basically all existing ones.
		5462
4813	IEEE 754 doubles, you get microsecond accuracy until at least 2200.	5463	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5464	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5465	is either obsolete or somebody patched it to use C<long double> or
		5466	something like that, just kidding).
4814		5467
4815	=back	5468	=back
4816		5469
4817	If you know of other additional requirements drop me a note.	5470	If you know of other additional requirements drop me a note.
4818		5471
…		…
4880	=item Processing ev_async_send: O(number_of_async_watchers)	5533	=item Processing ev_async_send: O(number_of_async_watchers)
4881		5534
4882	=item Processing signals: O(max_signal_number)	5535	=item Processing signals: O(max_signal_number)
4883		5536
4884	Sending involves a system call I<iff> there were no other C<ev_async_send>	5537	Sending involves a system call I<iff> there were no other C<ev_async_send>
4885	calls in the current loop iteration. Checking for async and signal events	5538	calls in the current loop iteration and the loop is currently
		5539	blocked. Checking for async and signal events involves iterating over all
4886	involves iterating over all running async watchers or all signal numbers.	5540	running async watchers or all signal numbers.
4887		5541
4888	=back	5542	=back
4889		5543
4890		5544
4891	=head1 PORTING FROM LIBEV 3.X TO 4.X	5545	=head1 PORTING FROM LIBEV 3.X TO 4.X
…		…
4900	=over 4	5554	=over 4
4901		5555
4902	=item C<EV_COMPAT3> backwards compatibility mechanism	5556	=item C<EV_COMPAT3> backwards compatibility mechanism
4903		5557
4904	The backward compatibility mechanism can be controlled by	5558	The backward compatibility mechanism can be controlled by
4905	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>	5559	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
4906	section.	5560	section.
4907		5561
4908	=item C<ev_default_destroy> and C<ev_default_fork> have been removed	5562	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
4909		5563
4910	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:	5564	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
…		…
4953	=over 4	5607	=over 4
4954		5608
4955	=item active	5609	=item active
4956		5610
4957	A watcher is active as long as it has been started and not yet stopped.	5611	A watcher is active as long as it has been started and not yet stopped.
4958	See L<WATCHER STATES> for details.	5612	See L</WATCHER STATES> for details.
4959		5613
4960	=item application	5614	=item application
4961		5615
4962	In this document, an application is whatever is using libev.	5616	In this document, an application is whatever is using libev.
4963		5617
…		…
4999	watchers and events.	5653	watchers and events.
5000		5654
5001	=item pending	5655	=item pending
5002		5656
5003	A watcher is pending as soon as the corresponding event has been	5657	A watcher is pending as soon as the corresponding event has been
5004	detected. See L<WATCHER STATES> for details.	5658	detected. See L</WATCHER STATES> for details.
5005		5659
5006	=item real time	5660	=item real time
5007		5661
5008	The physical time that is observed. It is apparently strictly monotonic :)	5662	The physical time that is observed. It is apparently strictly monotonic :)
5009		5663
5010	=item wall-clock time	5664	=item wall-clock time
5011		5665
5012	The time and date as shown on clocks. Unlike real time, it can actually	5666	The time and date as shown on clocks. Unlike real time, it can actually
5013	be wrong and jump forwards and backwards, e.g. when the you adjust your	5667	be wrong and jump forwards and backwards, e.g. when you adjust your
5014	clock.	5668	clock.
5015		5669
5016	=item watcher	5670	=item watcher
5017		5671
5018	A data structure that describes interest in certain events. Watchers need	5672	A data structure that describes interest in certain events. Watchers need
…		…
5021	=back	5675	=back
5022		5676
5023	=head1 AUTHOR	5677	=head1 AUTHOR
5024		5678
5025	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael	5679	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5026	Magnusson and Emanuele Giaquinta.	5680	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
5027		5681

Diff Legend

–	Removed lines
+	Added lines
<	Changed lines
>	Changed lines