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		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
…		…
78	with libev.	80	with libev.
79		81
80	Familiarity with event based programming techniques in general is assumed	82	Familiarity with event based programming techniques in general is assumed
81	throughout this document.	83	throughout this document.
82		84
		85	=head1 WHAT TO READ WHEN IN A HURRY
		86
		87	This manual tries to be very detailed, but unfortunately, this also makes
		88	it very long. If you just want to know the basics of libev, I suggest
		89	reading L</ANATOMY OF A WATCHER>, then the L</EXAMPLE PROGRAM> above and
		90	look up the missing functions in L</GLOBAL FUNCTIONS> and the C<ev_io> and
		91	C<ev_timer> sections in L</WATCHER TYPES>.
		92
83	=head1 ABOUT LIBEV	93	=head1 ABOUT LIBEV
84		94
85	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
86	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
87	these event sources and provide your program with events.	97	these event sources and provide your program with events.
…		…
95	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
96	watcher.	106	watcher.
97		107
98	=head2 FEATURES	108	=head2 FEATURES
99		109
100	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>
101	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	111	interfaces, the BSD-specific C<kqueue> and the Solaris-specific event port
102	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>
103	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner	113	interface (for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
104	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
105	timers (C<ev_timer>), absolute timers with customised rescheduling	115	timers (C<ev_timer>), absolute timers with customised rescheduling
106	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status	116	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
107	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
108	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
…		…
149	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
150	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,
151	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
152	the libev caller and need to be fixed there.	162	the libev caller and need to be fixed there.
153		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
154	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
155	extensive consistency checking code. These do not trigger under normal
156	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.
157		171
158		172
159	=head1 GLOBAL FUNCTIONS	173	=head1 GLOBAL FUNCTIONS
160		174
161	These functions can be called anytime, even before initialising the	175	These functions can be called anytime, even before initialising the
…		…
166	=item ev_tstamp ev_time ()	180	=item ev_tstamp ev_time ()
167		181
168	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
169	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
170	you actually want to know. Also interesting is the combination of	184	you actually want to know. Also interesting is the combination of
171	C<ev_update_now> and C<ev_now>.	185	C<ev_now_update> and C<ev_now>.
172		186
173	=item ev_sleep (ev_tstamp interval)	187	=item ev_sleep (ev_tstamp interval)
174		188
175	Sleep for the given interval: The current thread will be blocked until	189	Sleep for the given interval: The current thread will be blocked
176	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
177	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 >>).
178		198
179	=item int ev_version_major ()	199	=item int ev_version_major ()
180		200
181	=item int ev_version_minor ()	201	=item int ev_version_minor ()
182		202
…		…
233	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 ()
234	& ev_supported_backends ()>, likewise for recommended ones.	254	& ev_supported_backends ()>, likewise for recommended ones.
235		255
236	See the description of C<ev_embed> watchers for more info.	256	See the description of C<ev_embed> watchers for more info.
237		257
238	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]	258	=item ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())
239		259
240	Sets the allocation function to use (the prototype is similar - the	260	Sets the allocation function to use (the prototype is similar - the
241	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
242	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
243	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
…		…
249		269
250	You could override this function in high-availability programs to, say,	270	You could override this function in high-availability programs to, say,
251	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,
252	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.
253		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
254	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
255	retries (example requires a standards-compliant C<realloc>).	289	retries.
256		290
257	static void *	291	static void *
258	persistent_realloc (void *ptr, size_t size)	292	persistent_realloc (void *ptr, size_t size)
259	{	293	{
		294	if (!size)
		295	{
		296	free (ptr);
		297	return 0;
		298	}
		299
260	for (;;)	300	for (;;)
261	{	301	{
262	void *newptr = realloc (ptr, size);	302	void *newptr = realloc (ptr, size);
263		303
264	if (newptr)	304	if (newptr)
…		…
269	}	309	}
270		310
271	...	311	...
272	ev_set_allocator (persistent_realloc);	312	ev_set_allocator (persistent_realloc);
273		313
274	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]	314	=item ev_set_syserr_cb (void (*cb)(const char *msg) throw ())
275		315
276	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
277	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
278	indicating the system call or subsystem causing the problem. If this	318	indicating the system call or subsystem causing the problem. If this
279	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
…		…
291	}	331	}
292		332
293	...	333	...
294	ev_set_syserr_cb (fatal_error);	334	ev_set_syserr_cb (fatal_error);
295		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
296	=back	349	=back
297		350
298	=head1 FUNCTIONS CONTROLLING EVENT LOOPS	351	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
299		352
300	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
301	I<not> optional in this case unless libev 3 compatibility is disabled, as	354	I<not> optional in this case unless libev 3 compatibility is disabled, as
302	libev 3 had an C<ev_loop> function colliding with the struct name).	355	libev 3 had an C<ev_loop> function colliding with the struct name).
303		356
304	The library knows two types of such loops, the I<default> loop, which	357	The library knows two types of such loops, the I<default> loop, which
305	supports signals and child events, and dynamically created event loops	358	supports child process events, and dynamically created event loops which
306	which do not.	359	do not.
307		360
308	=over 4	361	=over 4
309		362
310	=item struct ev_loop *ev_default_loop (unsigned int flags)	363	=item struct ev_loop *ev_default_loop (unsigned int flags)
311		364
…		…
347	=item struct ev_loop *ev_loop_new (unsigned int flags)	400	=item struct ev_loop *ev_loop_new (unsigned int flags)
348		401
349	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
350	could not be initialised, returns false.	403	could not be initialised, returns false.
351		404
352	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
353	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
354	default loop in the "main" or "initial" thread.	407	loop in the "main" or "initial" thread.
355		408
356	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
357	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>).
358		411
359	The following flags are supported:	412	The following flags are supported:
…		…
369		422
370	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
371	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
372	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	425	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
373	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
374	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
375	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).
376		431
377	=item C<EVFLAG_FORKCHECK>	432	=item C<EVFLAG_FORKCHECK>
378		433
379	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
380	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.
381		436
382	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,
383	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
384	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
385	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
386	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
387	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).
388		444
389	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
390	forget about forgetting to tell libev about forking) when you use this	446	forget about forgetting to tell libev about forking, although you still
391	flag.	447	have to ignore C<SIGPIPE>) when you use this flag.
392		448
393	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>
394	environment variable.	450	environment variable.
395		451
396	=item C<EVFLAG_NOINOTIFY>	452	=item C<EVFLAG_NOINOTIFY>
397		453
398	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
399	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
400	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
401	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.
402		458
403	=item C<EVFLAG_SIGNALFD>	459	=item C<EVFLAG_SIGNALFD>
404		460
405	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
406	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
407	delivers signals synchronously, which makes it both faster and might make	463	delivers signals synchronously, which makes it both faster and might make
408	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
409	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
410	threads that are not interested in handling them.	466	threads that are not interested in handling them.
411		467
412	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
413	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
414	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	=item C<EVFLAG_NOTIMERFD>
		486
		487	When this flag is specified, the libev will avoid using a C<timerfd> to
		488	detect time jumps. It will still be able to detect time jumps, but takes
		489	longer and has a lower accuracy in doing so, but saves a file descriptor
		490	per loop.
		491
		492	The current implementation only tries to use a C<timerfd> when the first
		493	C<ev_periodic> watcher is started and falls back on other methods if it
		494	cannot be created, but this behaviour might change in the future.
415		495
416	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	496	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
417		497
418	This is your standard select(2) backend. Not I<completely> standard, as	498	This is your standard select(2) backend. Not I<completely> standard, as
419	libev tries to roll its own fd_set with no limits on the number of fds,	499	libev tries to roll its own fd_set with no limits on the number of fds,
…		…
444	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and	524	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
445	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.	525	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
446		526
447	=item C<EVBACKEND_EPOLL> (value 4, Linux)	527	=item C<EVBACKEND_EPOLL> (value 4, Linux)
448		528
449	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9	529	Use the Linux-specific epoll(7) interface (for both pre- and post-2.6.9
450	kernels).	530	kernels).
451		531
452	For few fds, this backend is a bit little slower than poll and select,	532	For few fds, this backend is a bit little slower than poll and select, but
453	but it scales phenomenally better. While poll and select usually scale	533	it scales phenomenally better. While poll and select usually scale like
454	like O(total_fds) where n is the total number of fds (or the highest fd),	534	O(total_fds) where total_fds is the total number of fds (or the highest
455	epoll scales either O(1) or O(active_fds).	535	fd), epoll scales either O(1) or O(active_fds).
456		536
457	The epoll mechanism deserves honorable mention as the most misdesigned	537	The epoll mechanism deserves honorable mention as the most misdesigned
458	of the more advanced event mechanisms: mere annoyances include silently	538	of the more advanced event mechanisms: mere annoyances include silently
459	dropping file descriptors, requiring a system call per change per file	539	dropping file descriptors, requiring a system call per change per file
460	descriptor (and unnecessary guessing of parameters), problems with dup and	540	descriptor (and unnecessary guessing of parameters), problems with dup,
		541	returning before the timeout value, resulting in additional iterations
		542	(and only giving 5ms accuracy while select on the same platform gives
461	so on. The biggest issue is fork races, however - if a program forks then	543	0.1ms) and so on. The biggest issue is fork races, however - if a program
462	I<both> parent and child process have to recreate the epoll set, which can	544	forks then I<both> parent and child process have to recreate the epoll
463	take considerable time (one syscall per file descriptor) and is of course	545	set, which can take considerable time (one syscall per file descriptor)
464	hard to detect.	546	and is of course hard to detect.
465		547
466	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but	548	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
467	of course I<doesn't>, and epoll just loves to report events for totally	549	but of course I<doesn't>, and epoll just loves to report events for
468	I<different> file descriptors (even already closed ones, so one cannot	550	totally I<different> file descriptors (even already closed ones, so
469	even remove them from the set) than registered in the set (especially	551	one cannot even remove them from the set) than registered in the set
470	on SMP systems). Libev tries to counter these spurious notifications by	552	(especially on SMP systems). Libev tries to counter these spurious
471	employing an additional generation counter and comparing that against the	553	notifications by employing an additional generation counter and comparing
472	events to filter out spurious ones, recreating the set when required. Last	554	that against the events to filter out spurious ones, recreating the set
		555	when required. Epoll also erroneously rounds down timeouts, but gives you
		556	no way to know when and by how much, so sometimes you have to busy-wait
		557	because epoll returns immediately despite a nonzero timeout. And last
473	not least, it also refuses to work with some file descriptors which work	558	not least, it also refuses to work with some file descriptors which work
474	perfectly fine with C<select> (files, many character devices...).	559	perfectly fine with C<select> (files, many character devices...).
		560
		561	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		562	cobbled together in a hurry, no thought to design or interaction with
		563	others. Oh, the pain, will it ever stop...
475		564
476	While stopping, setting and starting an I/O watcher in the same iteration	565	While stopping, setting and starting an I/O watcher in the same iteration
477	will result in some caching, there is still a system call per such	566	will result in some caching, there is still a system call per such
478	incident (because the same I<file descriptor> could point to a different	567	incident (because the same I<file descriptor> could point to a different
479	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed	568	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
…		…
491	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or	580	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
492	faster than epoll for maybe up to a hundred file descriptors, depending on	581	faster than epoll for maybe up to a hundred file descriptors, depending on
493	the usage. So sad.	582	the usage. So sad.
494		583
495	While nominally embeddable in other event loops, this feature is broken in	584	While nominally embeddable in other event loops, this feature is broken in
496	all kernel versions tested so far.	585	a lot of kernel revisions, but probably(!) works in current versions.
497		586
498	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	587	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
499	C<EVBACKEND_POLL>.	588	C<EVBACKEND_POLL>.
500		589
		590	=item C<EVBACKEND_LINUXAIO> (value 64, Linux)
		591
		592	Use the Linux-specific Linux AIO (I<not> C<< aio(7) >> but C<<
		593	io_submit(2) >>) event interface available in post-4.18 kernels (but libev
		594	only tries to use it in 4.19+).
		595
		596	This is another Linux train wreck of an event interface.
		597
		598	If this backend works for you (as of this writing, it was very
		599	experimental), it is the best event interface available on Linux and might
		600	be well worth enabling it - if it isn't available in your kernel this will
		601	be detected and this backend will be skipped.
		602
		603	This backend can batch oneshot requests and supports a user-space ring
		604	buffer to receive events. It also doesn't suffer from most of the design
		605	problems of epoll (such as not being able to remove event sources from
		606	the epoll set), and generally sounds too good to be true. Because, this
		607	being the Linux kernel, of course it suffers from a whole new set of
		608	limitations, forcing you to fall back to epoll, inheriting all its design
		609	issues.
		610
		611	For one, it is not easily embeddable (but probably could be done using
		612	an event fd at some extra overhead). It also is subject to a system wide
		613	limit that can be configured in F</proc/sys/fs/aio-max-nr>. If no AIO
		614	requests are left, this backend will be skipped during initialisation, and
		615	will switch to epoll when the loop is active.
		616
		617	Most problematic in practice, however, is that not all file descriptors
		618	work with it. For example, in Linux 5.1, TCP sockets, pipes, event fds,
		619	files, F</dev/null> and many others are supported, but ttys do not work
		620	properly (a known bug that the kernel developers don't care about, see
		621	L<https://lore.kernel.org/patchwork/patch/1047453/>), so this is not
		622	(yet?) a generic event polling interface.
		623
		624	Overall, it seems the Linux developers just don't want it to have a
		625	generic event handling mechanism other than C<select> or C<poll>.
		626
		627	To work around all these problem, the current version of libev uses its
		628	epoll backend as a fallback for file descriptor types that do not work. Or
		629	falls back completely to epoll if the kernel acts up.
		630
		631	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		632	C<EVBACKEND_POLL>.
		633
501	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	634	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
502		635
503	Kqueue deserves special mention, as at the time of this writing, it	636	Kqueue deserves special mention, as at the time this backend was
504	was broken on all BSDs except NetBSD (usually it doesn't work reliably	637	implemented, it was broken on all BSDs except NetBSD (usually it doesn't
505	with anything but sockets and pipes, except on Darwin, where of course	638	work reliably with anything but sockets and pipes, except on Darwin,
506	it's completely useless). Unlike epoll, however, whose brokenness	639	where of course it's completely useless). Unlike epoll, however, whose
507	is by design, these kqueue bugs can (and eventually will) be fixed	640	brokenness is by design, these kqueue bugs can be (and mostly have been)
508	without API changes to existing programs. For this reason it's not being	641	fixed without API changes to existing programs. For this reason it's not
509	"auto-detected" unless you explicitly specify it in the flags (i.e. using	642	being "auto-detected" on all platforms unless you explicitly specify it
510	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)	643	in the flags (i.e. using C<EVBACKEND_KQUEUE>) or libev was compiled on a
511	system like NetBSD.	644	known-to-be-good (-enough) system like NetBSD.
512		645
513	You still can embed kqueue into a normal poll or select backend and use it	646	You still can embed kqueue into a normal poll or select backend and use it
514	only for sockets (after having made sure that sockets work with kqueue on	647	only for sockets (after having made sure that sockets work with kqueue on
515	the target platform). See C<ev_embed> watchers for more info.	648	the target platform). See C<ev_embed> watchers for more info.
516		649
517	It scales in the same way as the epoll backend, but the interface to the	650	It scales in the same way as the epoll backend, but the interface to the
518	kernel is more efficient (which says nothing about its actual speed, of	651	kernel is more efficient (which says nothing about its actual speed, of
519	course). While stopping, setting and starting an I/O watcher does never	652	course). While stopping, setting and starting an I/O watcher does never
520	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to	653	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
521	two event changes per incident. Support for C<fork ()> is very bad (but	654	two event changes per incident. Support for C<fork ()> is very bad (you
522	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect	655	might have to leak fds on fork, but it's more sane than epoll) and it
523	cases	656	drops fds silently in similarly hard-to-detect cases.
524		657
525	This backend usually performs well under most conditions.	658	This backend usually performs well under most conditions.
526		659
527	While nominally embeddable in other event loops, this doesn't work	660	While nominally embeddable in other event loops, this doesn't work
528	everywhere, so you might need to test for this. And since it is broken	661	everywhere, so you might need to test for this. And since it is broken
…		…
545	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	678	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
546		679
547	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	680	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
548	it's really slow, but it still scales very well (O(active_fds)).	681	it's really slow, but it still scales very well (O(active_fds)).
549		682
550	Please note that Solaris event ports can deliver a lot of spurious
551	notifications, so you need to use non-blocking I/O or other means to avoid
552	blocking when no data (or space) is available.
553
554	While this backend scales well, it requires one system call per active	683	While this backend scales well, it requires one system call per active
555	file descriptor per loop iteration. For small and medium numbers of file	684	file descriptor per loop iteration. For small and medium numbers of file
556	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	685	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
557	might perform better.	686	might perform better.
558		687
559	On the positive side, with the exception of the spurious readiness	688	On the positive side, this backend actually performed fully to
560	notifications, this backend actually performed fully to specification
561	in all tests and is fully embeddable, which is a rare feat among the	689	specification in all tests and is fully embeddable, which is a rare feat
562	OS-specific backends (I vastly prefer correctness over speed hacks).	690	among the OS-specific backends (I vastly prefer correctness over speed
		691	hacks).
		692
		693	On the negative side, the interface is I<bizarre> - so bizarre that
		694	even sun itself gets it wrong in their code examples: The event polling
		695	function sometimes returns events to the caller even though an error
		696	occurred, but with no indication whether it has done so or not (yes, it's
		697	even documented that way) - deadly for edge-triggered interfaces where you
		698	absolutely have to know whether an event occurred or not because you have
		699	to re-arm the watcher.
		700
		701	Fortunately libev seems to be able to work around these idiocies.
563		702
564	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	703	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
565	C<EVBACKEND_POLL>.	704	C<EVBACKEND_POLL>.
566		705
567	=item C<EVBACKEND_ALL>	706	=item C<EVBACKEND_ALL>
568		707
569	Try all backends (even potentially broken ones that wouldn't be tried	708	Try all backends (even potentially broken ones that wouldn't be tried
570	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	709	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
571	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	710	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
572		711
573	It is definitely not recommended to use this flag.	712	It is definitely not recommended to use this flag, use whatever
		713	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		714	at all.
		715
		716	=item C<EVBACKEND_MASK>
		717
		718	Not a backend at all, but a mask to select all backend bits from a
		719	C<flags> value, in case you want to mask out any backends from a flags
		720	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
574		721
575	=back	722	=back
576		723
577	If one or more of the backend flags are or'ed into the flags value,	724	If one or more of the backend flags are or'ed into the flags value,
578	then only these backends will be tried (in the reverse order as listed	725	then only these backends will be tried (in the reverse order as listed
…		…
587		734
588	Example: Use whatever libev has to offer, but make sure that kqueue is	735	Example: Use whatever libev has to offer, but make sure that kqueue is
589	used if available.	736	used if available.
590		737
591	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);	738	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		739
		740	Example: Similarly, on linux, you mgiht want to take advantage of the
		741	linux aio backend if possible, but fall back to something else if that
		742	isn't available.
		743
		744	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_LINUXAIO);
592		745
593	=item ev_loop_destroy (loop)	746	=item ev_loop_destroy (loop)
594		747
595	Destroys an event loop object (frees all memory and kernel state	748	Destroys an event loop object (frees all memory and kernel state
596	etc.). None of the active event watchers will be stopped in the normal	749	etc.). None of the active event watchers will be stopped in the normal
…		…
607	This function is normally used on loop objects allocated by	760	This function is normally used on loop objects allocated by
608	C<ev_loop_new>, but it can also be used on the default loop returned by	761	C<ev_loop_new>, but it can also be used on the default loop returned by
609	C<ev_default_loop>, in which case it is not thread-safe.	762	C<ev_default_loop>, in which case it is not thread-safe.
610		763
611	Note that it is not advisable to call this function on the default loop	764	Note that it is not advisable to call this function on the default loop
612	except in the rare occasion where you really need to free it's resources.	765	except in the rare occasion where you really need to free its resources.
613	If you need dynamically allocated loops it is better to use C<ev_loop_new>	766	If you need dynamically allocated loops it is better to use C<ev_loop_new>
614	and C<ev_loop_destroy>.	767	and C<ev_loop_destroy>.
615		768
616	=item ev_loop_fork (loop)	769	=item ev_loop_fork (loop)
617		770
618	This function sets a flag that causes subsequent C<ev_run> iterations to	771	This function sets a flag that causes subsequent C<ev_run> iterations
619	reinitialise the kernel state for backends that have one. Despite the	772	to reinitialise the kernel state for backends that have one. Despite
620	name, you can call it anytime, but it makes most sense after forking, in	773	the name, you can call it anytime you are allowed to start or stop
621	the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the	774	watchers (except inside an C<ev_prepare> callback), but it makes most
		775	sense after forking, in the child process. You I<must> call it (or use
622	child before resuming or calling C<ev_run>.	776	C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.
623		777
		778	In addition, if you want to reuse a loop (via this function or
		779	C<EVFLAG_FORKCHECK>), you I<also> have to ignore C<SIGPIPE>.
		780
624	Again, you I<have> to call it on I<any> loop that you want to re-use after	781	Again, you I<have> to call it on I<any> loop that you want to re-use after
625	a fork, I<even if you do not plan to use the loop in the parent>. This is	782	a fork, I<even if you do not plan to use the loop in the parent>. This is
626	because some kernel interfaces *cough* I<kqueue> *cough* do funny things	783	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
627	during fork.	784	during fork.
628		785
629	On the other hand, you only need to call this function in the child	786	On the other hand, you only need to call this function in the child
…		…
665	prepare and check phases.	822	prepare and check phases.
666		823
667	=item unsigned int ev_depth (loop)	824	=item unsigned int ev_depth (loop)
668		825
669	Returns the number of times C<ev_run> was entered minus the number of	826	Returns the number of times C<ev_run> was entered minus the number of
670	times C<ev_run> was exited, in other words, the recursion depth.	827	times C<ev_run> was exited normally, in other words, the recursion depth.
671		828
672	Outside C<ev_run>, this number is zero. In a callback, this number is	829	Outside C<ev_run>, this number is zero. In a callback, this number is
673	C<1>, unless C<ev_run> was invoked recursively (or from another thread),	830	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
674	in which case it is higher.	831	in which case it is higher.
675		832
676	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread	833	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
677	etc.), doesn't count as "exit" - consider this as a hint to avoid such	834	throwing an exception etc.), doesn't count as "exit" - consider this
678	ungentleman-like behaviour unless it's really convenient.	835	as a hint to avoid such ungentleman-like behaviour unless it's really
		836	convenient, in which case it is fully supported.
679		837
680	=item unsigned int ev_backend (loop)	838	=item unsigned int ev_backend (loop)
681		839
682	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	840	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
683	use.	841	use.
…		…
698		856
699	This function is rarely useful, but when some event callback runs for a	857	This function is rarely useful, but when some event callback runs for a
700	very long time without entering the event loop, updating libev's idea of	858	very long time without entering the event loop, updating libev's idea of
701	the current time is a good idea.	859	the current time is a good idea.
702		860
703	See also L<The special problem of time updates> in the C<ev_timer> section.	861	See also L</The special problem of time updates> in the C<ev_timer> section.
704		862
705	=item ev_suspend (loop)	863	=item ev_suspend (loop)
706		864
707	=item ev_resume (loop)	865	=item ev_resume (loop)
708		866
…		…
726	without a previous call to C<ev_suspend>.	884	without a previous call to C<ev_suspend>.
727		885
728	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the	886	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
729	event loop time (see C<ev_now_update>).	887	event loop time (see C<ev_now_update>).
730		888
731	=item ev_run (loop, int flags)	889	=item bool ev_run (loop, int flags)
732		890
733	Finally, this is it, the event handler. This function usually is called	891	Finally, this is it, the event handler. This function usually is called
734	after you have initialised all your watchers and you want to start	892	after you have initialised all your watchers and you want to start
735	handling events. It will ask the operating system for any new events, call	893	handling events. It will ask the operating system for any new events, call
736	the watcher callbacks, an then repeat the whole process indefinitely: This	894	the watcher callbacks, and then repeat the whole process indefinitely: This
737	is why event loops are called I<loops>.	895	is why event loops are called I<loops>.
738		896
739	If the flags argument is specified as C<0>, it will keep handling events	897	If the flags argument is specified as C<0>, it will keep handling events
740	until either no event watchers are active anymore or C<ev_break> was	898	until either no event watchers are active anymore or C<ev_break> was
741	called.	899	called.
		900
		901	The return value is false if there are no more active watchers (which
		902	usually means "all jobs done" or "deadlock"), and true in all other cases
		903	(which usually means " you should call C<ev_run> again").
742		904
743	Please note that an explicit C<ev_break> is usually better than	905	Please note that an explicit C<ev_break> is usually better than
744	relying on all watchers to be stopped when deciding when a program has	906	relying on all watchers to be stopped when deciding when a program has
745	finished (especially in interactive programs), but having a program	907	finished (especially in interactive programs), but having a program
746	that automatically loops as long as it has to and no longer by virtue	908	that automatically loops as long as it has to and no longer by virtue
747	of relying on its watchers stopping correctly, that is truly a thing of	909	of relying on its watchers stopping correctly, that is truly a thing of
748	beauty.	910	beauty.
749		911
		912	This function is I<mostly> exception-safe - you can break out of a
		913	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		914	exception and so on. This does not decrement the C<ev_depth> value, nor
		915	will it clear any outstanding C<EVBREAK_ONE> breaks.
		916
750	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle	917	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
751	those events and any already outstanding ones, but will not wait and	918	those events and any already outstanding ones, but will not wait and
752	block your process in case there are no events and will return after one	919	block your process in case there are no events and will return after one
753	iteration of the loop. This is sometimes useful to poll and handle new	920	iteration of the loop. This is sometimes useful to poll and handle new
754	events while doing lengthy calculations, to keep the program responsive.	921	events while doing lengthy calculations, to keep the program responsive.
…		…
763	This is useful if you are waiting for some external event in conjunction	930	This is useful if you are waiting for some external event in conjunction
764	with something not expressible using other libev watchers (i.e. "roll your	931	with something not expressible using other libev watchers (i.e. "roll your
765	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is	932	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
766	usually a better approach for this kind of thing.	933	usually a better approach for this kind of thing.
767		934
768	Here are the gory details of what C<ev_run> does:	935	Here are the gory details of what C<ev_run> does (this is for your
		936	understanding, not a guarantee that things will work exactly like this in
		937	future versions):
769		938
770	- Increment loop depth.	939	- Increment loop depth.
771	- Reset the ev_break status.	940	- Reset the ev_break status.
772	- Before the first iteration, call any pending watchers.	941	- Before the first iteration, call any pending watchers.
773	LOOP:	942	LOOP:
…		…
806	anymore.	975	anymore.
807		976
808	... queue jobs here, make sure they register event watchers as long	977	... queue jobs here, make sure they register event watchers as long
809	... as they still have work to do (even an idle watcher will do..)	978	... as they still have work to do (even an idle watcher will do..)
810	ev_run (my_loop, 0);	979	ev_run (my_loop, 0);
811	... jobs done or somebody called unloop. yeah!	980	... jobs done or somebody called break. yeah!
812		981
813	=item ev_break (loop, how)	982	=item ev_break (loop, how)
814		983
815	Can be used to make a call to C<ev_run> return early (but only after it	984	Can be used to make a call to C<ev_run> return early (but only after it
816	has processed all outstanding events). The C<how> argument must be either	985	has processed all outstanding events). The C<how> argument must be either
817	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or	986	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
818	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.	987	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
819		988
820	This "unloop state" will be cleared when entering C<ev_run> again.	989	This "break state" will be cleared on the next call to C<ev_run>.
821		990
822	It is safe to call C<ev_break> from outside any C<ev_run> calls. ##TODO##	991	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		992	which case it will have no effect.
823		993
824	=item ev_ref (loop)	994	=item ev_ref (loop)
825		995
826	=item ev_unref (loop)	996	=item ev_unref (loop)
827		997
…		…
848	running when nothing else is active.	1018	running when nothing else is active.
849		1019
850	ev_signal exitsig;	1020	ev_signal exitsig;
851	ev_signal_init (&exitsig, sig_cb, SIGINT);	1021	ev_signal_init (&exitsig, sig_cb, SIGINT);
852	ev_signal_start (loop, &exitsig);	1022	ev_signal_start (loop, &exitsig);
853	evf_unref (loop);	1023	ev_unref (loop);
854		1024
855	Example: For some weird reason, unregister the above signal handler again.	1025	Example: For some weird reason, unregister the above signal handler again.
856		1026
857	ev_ref (loop);	1027	ev_ref (loop);
858	ev_signal_stop (loop, &exitsig);	1028	ev_signal_stop (loop, &exitsig);
…		…
878	overhead for the actual polling but can deliver many events at once.	1048	overhead for the actual polling but can deliver many events at once.
879		1049
880	By setting a higher I<io collect interval> you allow libev to spend more	1050	By setting a higher I<io collect interval> you allow libev to spend more
881	time collecting I/O events, so you can handle more events per iteration,	1051	time collecting I/O events, so you can handle more events per iteration,
882	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	1052	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
883	C<ev_timer>) will be not affected. Setting this to a non-null value will	1053	C<ev_timer>) will not be affected. Setting this to a non-null value will
884	introduce an additional C<ev_sleep ()> call into most loop iterations. The	1054	introduce an additional C<ev_sleep ()> call into most loop iterations. The
885	sleep time ensures that libev will not poll for I/O events more often then	1055	sleep time ensures that libev will not poll for I/O events more often then
886	once per this interval, on average.	1056	once per this interval, on average (as long as the host time resolution is
		1057	good enough).
887		1058
888	Likewise, by setting a higher I<timeout collect interval> you allow libev	1059	Likewise, by setting a higher I<timeout collect interval> you allow libev
889	to spend more time collecting timeouts, at the expense of increased	1060	to spend more time collecting timeouts, at the expense of increased
890	latency/jitter/inexactness (the watcher callback will be called	1061	latency/jitter/inexactness (the watcher callback will be called
891	later). C<ev_io> watchers will not be affected. Setting this to a non-null	1062	later). C<ev_io> watchers will not be affected. Setting this to a non-null
…		…
937	invoke the actual watchers inside another context (another thread etc.).	1108	invoke the actual watchers inside another context (another thread etc.).
938		1109
939	If you want to reset the callback, use C<ev_invoke_pending> as new	1110	If you want to reset the callback, use C<ev_invoke_pending> as new
940	callback.	1111	callback.
941		1112
942	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))	1113	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
943		1114
944	Sometimes you want to share the same loop between multiple threads. This	1115	Sometimes you want to share the same loop between multiple threads. This
945	can be done relatively simply by putting mutex_lock/unlock calls around	1116	can be done relatively simply by putting mutex_lock/unlock calls around
946	each call to a libev function.	1117	each call to a libev function.
947		1118
948	However, C<ev_run> can run an indefinite time, so it is not feasible	1119	However, C<ev_run> can run an indefinite time, so it is not feasible
949	to wait for it to return. One way around this is to wake up the event	1120	to wait for it to return. One way around this is to wake up the event
950	loop via C<ev_break> and C<av_async_send>, another way is to set these	1121	loop via C<ev_break> and C<ev_async_send>, another way is to set these
951	I<release> and I<acquire> callbacks on the loop.	1122	I<release> and I<acquire> callbacks on the loop.
952		1123
953	When set, then C<release> will be called just before the thread is	1124	When set, then C<release> will be called just before the thread is
954	suspended waiting for new events, and C<acquire> is called just	1125	suspended waiting for new events, and C<acquire> is called just
955	afterwards.	1126	afterwards.
…		…
970	See also the locking example in the C<THREADS> section later in this	1141	See also the locking example in the C<THREADS> section later in this
971	document.	1142	document.
972		1143
973	=item ev_set_userdata (loop, void *data)	1144	=item ev_set_userdata (loop, void *data)
974		1145
975	=item ev_userdata (loop)	1146	=item void *ev_userdata (loop)
976		1147
977	Set and retrieve a single C<void *> associated with a loop. When	1148	Set and retrieve a single C<void *> associated with a loop. When
978	C<ev_set_userdata> has never been called, then C<ev_userdata> returns	1149	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
979	C<0.>	1150	C<0>.
980		1151
981	These two functions can be used to associate arbitrary data with a loop,	1152	These two functions can be used to associate arbitrary data with a loop,
982	and are intended solely for the C<invoke_pending_cb>, C<release> and	1153	and are intended solely for the C<invoke_pending_cb>, C<release> and
983	C<acquire> callbacks described above, but of course can be (ab-)used for	1154	C<acquire> callbacks described above, but of course can be (ab-)used for
984	any other purpose as well.	1155	any other purpose as well.
…		…
1095		1266
1096	=item C<EV_PREPARE>	1267	=item C<EV_PREPARE>
1097		1268
1098	=item C<EV_CHECK>	1269	=item C<EV_CHECK>
1099		1270
1100	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts	1271	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts to
1101	to gather new events, and all C<ev_check> watchers are invoked just after	1272	gather new events, and all C<ev_check> watchers are queued (not invoked)
1102	C<ev_run> has gathered them, but before it invokes any callbacks for any	1273	just after C<ev_run> has gathered them, but before it queues any callbacks
		1274	for any received events. That means C<ev_prepare> watchers are the last
		1275	watchers invoked before the event loop sleeps or polls for new events, and
		1276	C<ev_check> watchers will be invoked before any other watchers of the same
		1277	or lower priority within an event loop iteration.
		1278
1103	received events. Callbacks of both watcher types can start and stop as	1279	Callbacks of both watcher types can start and stop as many watchers as
1104	many watchers as they want, and all of them will be taken into account	1280	they want, and all of them will be taken into account (for example, a
1105	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1281	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
1106	C<ev_run> from blocking).	1282	blocking).
1107		1283
1108	=item C<EV_EMBED>	1284	=item C<EV_EMBED>
1109		1285
1110	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1286	The embedded event loop specified in the C<ev_embed> watcher needs attention.
1111		1287
…		…
1114	The event loop has been resumed in the child process after fork (see	1290	The event loop has been resumed in the child process after fork (see
1115	C<ev_fork>).	1291	C<ev_fork>).
1116		1292
1117	=item C<EV_CLEANUP>	1293	=item C<EV_CLEANUP>
1118		1294
1119	The event loop is abotu to be destroyed (see C<ev_cleanup>).	1295	The event loop is about to be destroyed (see C<ev_cleanup>).
1120		1296
1121	=item C<EV_ASYNC>	1297	=item C<EV_ASYNC>
1122		1298
1123	The given async watcher has been asynchronously notified (see C<ev_async>).	1299	The given async watcher has been asynchronously notified (see C<ev_async>).
1124		1300
…		…
1146	programs, though, as the fd could already be closed and reused for another	1322	programs, though, as the fd could already be closed and reused for another
1147	thing, so beware.	1323	thing, so beware.
1148		1324
1149	=back	1325	=back
1150		1326
		1327	=head2 GENERIC WATCHER FUNCTIONS
		1328
		1329	=over 4
		1330
		1331	=item C<ev_init> (ev_TYPE *watcher, callback)
		1332
		1333	This macro initialises the generic portion of a watcher. The contents
		1334	of the watcher object can be arbitrary (so C<malloc> will do). Only
		1335	the generic parts of the watcher are initialised, you I<need> to call
		1336	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		1337	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		1338	which rolls both calls into one.
		1339
		1340	You can reinitialise a watcher at any time as long as it has been stopped
		1341	(or never started) and there are no pending events outstanding.
		1342
		1343	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
		1344	int revents)>.
		1345
		1346	Example: Initialise an C<ev_io> watcher in two steps.
		1347
		1348	ev_io w;
		1349	ev_init (&w, my_cb);
		1350	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1351
		1352	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
		1353
		1354	This macro initialises the type-specific parts of a watcher. You need to
		1355	call C<ev_init> at least once before you call this macro, but you can
		1356	call C<ev_TYPE_set> any number of times. You must not, however, call this
		1357	macro on a watcher that is active (it can be pending, however, which is a
		1358	difference to the C<ev_init> macro).
		1359
		1360	Although some watcher types do not have type-specific arguments
		1361	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		1362
		1363	See C<ev_init>, above, for an example.
		1364
		1365	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		1366
		1367	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		1368	calls into a single call. This is the most convenient method to initialise
		1369	a watcher. The same limitations apply, of course.
		1370
		1371	Example: Initialise and set an C<ev_io> watcher in one step.
		1372
		1373	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1374
		1375	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
		1376
		1377	Starts (activates) the given watcher. Only active watchers will receive
		1378	events. If the watcher is already active nothing will happen.
		1379
		1380	Example: Start the C<ev_io> watcher that is being abused as example in this
		1381	whole section.
		1382
		1383	ev_io_start (EV_DEFAULT_UC, &w);
		1384
		1385	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
		1386
		1387	Stops the given watcher if active, and clears the pending status (whether
		1388	the watcher was active or not).
		1389
		1390	It is possible that stopped watchers are pending - for example,
		1391	non-repeating timers are being stopped when they become pending - but
		1392	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
		1393	pending. If you want to free or reuse the memory used by the watcher it is
		1394	therefore a good idea to always call its C<ev_TYPE_stop> function.
		1395
		1396	=item bool ev_is_active (ev_TYPE *watcher)
		1397
		1398	Returns a true value iff the watcher is active (i.e. it has been started
		1399	and not yet been stopped). As long as a watcher is active you must not modify
		1400	it.
		1401
		1402	=item bool ev_is_pending (ev_TYPE *watcher)
		1403
		1404	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		1405	events but its callback has not yet been invoked). As long as a watcher
		1406	is pending (but not active) you must not call an init function on it (but
		1407	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		1408	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1409	it).
		1410
		1411	=item callback ev_cb (ev_TYPE *watcher)
		1412
		1413	Returns the callback currently set on the watcher.
		1414
		1415	=item ev_set_cb (ev_TYPE *watcher, callback)
		1416
		1417	Change the callback. You can change the callback at virtually any time
		1418	(modulo threads).
		1419
		1420	=item ev_set_priority (ev_TYPE *watcher, int priority)
		1421
		1422	=item int ev_priority (ev_TYPE *watcher)
		1423
		1424	Set and query the priority of the watcher. The priority is a small
		1425	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1426	(default: C<-2>). Pending watchers with higher priority will be invoked
		1427	before watchers with lower priority, but priority will not keep watchers
		1428	from being executed (except for C<ev_idle> watchers).
		1429
		1430	If you need to suppress invocation when higher priority events are pending
		1431	you need to look at C<ev_idle> watchers, which provide this functionality.
		1432
		1433	You I<must not> change the priority of a watcher as long as it is active or
		1434	pending.
		1435
		1436	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1437	fine, as long as you do not mind that the priority value you query might
		1438	or might not have been clamped to the valid range.
		1439
		1440	The default priority used by watchers when no priority has been set is
		1441	always C<0>, which is supposed to not be too high and not be too low :).
		1442
		1443	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1444	priorities.
		1445
		1446	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1447
		1448	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1449	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1450	can deal with that fact, as both are simply passed through to the
		1451	callback.
		1452
		1453	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1454
		1455	If the watcher is pending, this function clears its pending status and
		1456	returns its C<revents> bitset (as if its callback was invoked). If the
		1457	watcher isn't pending it does nothing and returns C<0>.
		1458
		1459	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1460	callback to be invoked, which can be accomplished with this function.
		1461
		1462	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1463
		1464	Feeds the given event set into the event loop, as if the specified event
		1465	had happened for the specified watcher (which must be a pointer to an
		1466	initialised but not necessarily started event watcher). Obviously you must
		1467	not free the watcher as long as it has pending events.
		1468
		1469	Stopping the watcher, letting libev invoke it, or calling
		1470	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1471	not started in the first place.
		1472
		1473	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1474	functions that do not need a watcher.
		1475
		1476	=back
		1477
		1478	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
		1479	OWN COMPOSITE WATCHERS> idioms.
		1480
1151	=head2 WATCHER STATES	1481	=head2 WATCHER STATES
1152		1482
1153	There are various watcher states mentioned throughout this manual -	1483	There are various watcher states mentioned throughout this manual -
1154	active, pending and so on. In this section these states and the rules to	1484	active, pending and so on. In this section these states and the rules to
1155	transition between them will be described in more detail - and while these	1485	transition between them will be described in more detail - and while these
1156	rules might look complicated, they usually do "the right thing".	1486	rules might look complicated, they usually do "the right thing".
1157		1487
1158	=over 4	1488	=over 4
1159		1489
1160	=item initialiased	1490	=item initialised
1161		1491
1162	Before a watcher can be registered with the event looop it has to be	1492	Before a watcher can be registered with the event loop it has to be
1163	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to	1493	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
1164	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.	1494	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1165		1495
1166	In this state it is simply some block of memory that is suitable for use	1496	In this state it is simply some block of memory that is suitable for
1167	in an event loop. It can be moved around, freed, reused etc. at will.	1497	use in an event loop. It can be moved around, freed, reused etc. at
		1498	will - as long as you either keep the memory contents intact, or call
		1499	C<ev_TYPE_init> again.
1168		1500
1169	=item started/running/active	1501	=item started/running/active
1170		1502
1171	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes	1503	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
1172	property of the event loop, and is actively waiting for events. While in	1504	property of the event loop, and is actively waiting for events. While in
…		…
1200	latter will clear any pending state the watcher might be in, regardless	1532	latter will clear any pending state the watcher might be in, regardless
1201	of whether it was active or not, so stopping a watcher explicitly before	1533	of whether it was active or not, so stopping a watcher explicitly before
1202	freeing it is often a good idea.	1534	freeing it is often a good idea.
1203		1535
1204	While stopped (and not pending) the watcher is essentially in the	1536	While stopped (and not pending) the watcher is essentially in the
1205	initialised state, that is it can be reused, moved, modified in any way	1537	initialised state, that is, it can be reused, moved, modified in any way
1206	you wish.	1538	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1539	it again).
1207		1540
1208	=back	1541	=back
1209
1210	=head2 GENERIC WATCHER FUNCTIONS
1211
1212	=over 4
1213
1214	=item C<ev_init> (ev_TYPE *watcher, callback)
1215
1216	This macro initialises the generic portion of a watcher. The contents
1217	of the watcher object can be arbitrary (so C<malloc> will do). Only
1218	the generic parts of the watcher are initialised, you I<need> to call
1219	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
1220	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
1221	which rolls both calls into one.
1222
1223	You can reinitialise a watcher at any time as long as it has been stopped
1224	(or never started) and there are no pending events outstanding.
1225
1226	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
1227	int revents)>.
1228
1229	Example: Initialise an C<ev_io> watcher in two steps.
1230
1231	ev_io w;
1232	ev_init (&w, my_cb);
1233	ev_io_set (&w, STDIN_FILENO, EV_READ);
1234
1235	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
1236
1237	This macro initialises the type-specific parts of a watcher. You need to
1238	call C<ev_init> at least once before you call this macro, but you can
1239	call C<ev_TYPE_set> any number of times. You must not, however, call this
1240	macro on a watcher that is active (it can be pending, however, which is a
1241	difference to the C<ev_init> macro).
1242
1243	Although some watcher types do not have type-specific arguments
1244	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
1245
1246	See C<ev_init>, above, for an example.
1247
1248	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
1249
1250	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
1251	calls into a single call. This is the most convenient method to initialise
1252	a watcher. The same limitations apply, of course.
1253
1254	Example: Initialise and set an C<ev_io> watcher in one step.
1255
1256	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1257
1258	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
1259
1260	Starts (activates) the given watcher. Only active watchers will receive
1261	events. If the watcher is already active nothing will happen.
1262
1263	Example: Start the C<ev_io> watcher that is being abused as example in this
1264	whole section.
1265
1266	ev_io_start (EV_DEFAULT_UC, &w);
1267
1268	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
1269
1270	Stops the given watcher if active, and clears the pending status (whether
1271	the watcher was active or not).
1272
1273	It is possible that stopped watchers are pending - for example,
1274	non-repeating timers are being stopped when they become pending - but
1275	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
1276	pending. If you want to free or reuse the memory used by the watcher it is
1277	therefore a good idea to always call its C<ev_TYPE_stop> function.
1278
1279	=item bool ev_is_active (ev_TYPE *watcher)
1280
1281	Returns a true value iff the watcher is active (i.e. it has been started
1282	and not yet been stopped). As long as a watcher is active you must not modify
1283	it.
1284
1285	=item bool ev_is_pending (ev_TYPE *watcher)
1286
1287	Returns a true value iff the watcher is pending, (i.e. it has outstanding
1288	events but its callback has not yet been invoked). As long as a watcher
1289	is pending (but not active) you must not call an init function on it (but
1290	C<ev_TYPE_set> is safe), you must not change its priority, and you must
1291	make sure the watcher is available to libev (e.g. you cannot C<free ()>
1292	it).
1293
1294	=item callback ev_cb (ev_TYPE *watcher)
1295
1296	Returns the callback currently set on the watcher.
1297
1298	=item ev_cb_set (ev_TYPE *watcher, callback)
1299
1300	Change the callback. You can change the callback at virtually any time
1301	(modulo threads).
1302
1303	=item ev_set_priority (ev_TYPE *watcher, int priority)
1304
1305	=item int ev_priority (ev_TYPE *watcher)
1306
1307	Set and query the priority of the watcher. The priority is a small
1308	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
1309	(default: C<-2>). Pending watchers with higher priority will be invoked
1310	before watchers with lower priority, but priority will not keep watchers
1311	from being executed (except for C<ev_idle> watchers).
1312
1313	If you need to suppress invocation when higher priority events are pending
1314	you need to look at C<ev_idle> watchers, which provide this functionality.
1315
1316	You I<must not> change the priority of a watcher as long as it is active or
1317	pending.
1318
1319	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
1320	fine, as long as you do not mind that the priority value you query might
1321	or might not have been clamped to the valid range.
1322
1323	The default priority used by watchers when no priority has been set is
1324	always C<0>, which is supposed to not be too high and not be too low :).
1325
1326	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1327	priorities.
1328
1329	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1330
1331	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
1332	C<loop> nor C<revents> need to be valid as long as the watcher callback
1333	can deal with that fact, as both are simply passed through to the
1334	callback.
1335
1336	=item int ev_clear_pending (loop, ev_TYPE *watcher)
1337
1338	If the watcher is pending, this function clears its pending status and
1339	returns its C<revents> bitset (as if its callback was invoked). If the
1340	watcher isn't pending it does nothing and returns C<0>.
1341
1342	Sometimes it can be useful to "poll" a watcher instead of waiting for its
1343	callback to be invoked, which can be accomplished with this function.
1344
1345	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
1346
1347	Feeds the given event set into the event loop, as if the specified event
1348	had happened for the specified watcher (which must be a pointer to an
1349	initialised but not necessarily started event watcher). Obviously you must
1350	not free the watcher as long as it has pending events.
1351
1352	Stopping the watcher, letting libev invoke it, or calling
1353	C<ev_clear_pending> will clear the pending event, even if the watcher was
1354	not started in the first place.
1355
1356	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1357	functions that do not need a watcher.
1358
1359	=back
1360
1361
1362	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
1363
1364	Each watcher has, by default, a member C<void *data> that you can change
1365	and read at any time: libev will completely ignore it. This can be used
1366	to associate arbitrary data with your watcher. If you need more data and
1367	don't want to allocate memory and store a pointer to it in that data
1368	member, you can also "subclass" the watcher type and provide your own
1369	data:
1370
1371	struct my_io
1372	{
1373	ev_io io;
1374	int otherfd;
1375	void *somedata;
1376	struct whatever *mostinteresting;
1377	};
1378
1379	...
1380	struct my_io w;
1381	ev_io_init (&w.io, my_cb, fd, EV_READ);
1382
1383	And since your callback will be called with a pointer to the watcher, you
1384	can cast it back to your own type:
1385
1386	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1387	{
1388	struct my_io *w = (struct my_io *)w_;
1389	...
1390	}
1391
1392	More interesting and less C-conformant ways of casting your callback type
1393	instead have been omitted.
1394
1395	Another common scenario is to use some data structure with multiple
1396	embedded watchers:
1397
1398	struct my_biggy
1399	{
1400	int some_data;
1401	ev_timer t1;
1402	ev_timer t2;
1403	}
1404
1405	In this case getting the pointer to C<my_biggy> is a bit more
1406	complicated: Either you store the address of your C<my_biggy> struct
1407	in the C<data> member of the watcher (for woozies), or you need to use
1408	some pointer arithmetic using C<offsetof> inside your watchers (for real
1409	programmers):
1410
1411	#include <stddef.h>
1412
1413	static void
1414	t1_cb (EV_P_ ev_timer *w, int revents)
1415	{
1416	struct my_biggy big = (struct my_biggy *)
1417	(((char *)w) - offsetof (struct my_biggy, t1));
1418	}
1419
1420	static void
1421	t2_cb (EV_P_ ev_timer *w, int revents)
1422	{
1423	struct my_biggy big = (struct my_biggy *)
1424	(((char *)w) - offsetof (struct my_biggy, t2));
1425	}
1426		1542
1427	=head2 WATCHER PRIORITY MODELS	1543	=head2 WATCHER PRIORITY MODELS
1428		1544
1429	Many event loops support I<watcher priorities>, which are usually small	1545	Many event loops support I<watcher priorities>, which are usually small
1430	integers that influence the ordering of event callback invocation	1546	integers that influence the ordering of event callback invocation
1431	between watchers in some way, all else being equal.	1547	between watchers in some way, all else being equal.
1432		1548
1433	In libev, Watcher priorities can be set using C<ev_set_priority>. See its	1549	In libev, watcher priorities can be set using C<ev_set_priority>. See its
1434	description for the more technical details such as the actual priority	1550	description for the more technical details such as the actual priority
1435	range.	1551	range.
1436		1552
1437	There are two common ways how these these priorities are being interpreted	1553	There are two common ways how these these priorities are being interpreted
1438	by event loops:	1554	by event loops:
…		…
1532		1648
1533	This section describes each watcher in detail, but will not repeat	1649	This section describes each watcher in detail, but will not repeat
1534	information given in the last section. Any initialisation/set macros,	1650	information given in the last section. Any initialisation/set macros,
1535	functions and members specific to the watcher type are explained.	1651	functions and members specific to the watcher type are explained.
1536		1652
1537	Members are additionally marked with either I<[read-only]>, meaning that,	1653	Most members are additionally marked with either I<[read-only]>, meaning
1538	while the watcher is active, you can look at the member and expect some	1654	that, while the watcher is active, you can look at the member and expect
1539	sensible content, but you must not modify it (you can modify it while the	1655	some sensible content, but you must not modify it (you can modify it while
1540	watcher is stopped to your hearts content), or I<[read-write]>, which	1656	the watcher is stopped to your hearts content), or I<[read-write]>, which
1541	means you can expect it to have some sensible content while the watcher	1657	means you can expect it to have some sensible content while the watcher
1542	is active, but you can also modify it. Modifying it may not do something	1658	is active, but you can also modify it. Modifying it may not do something
1543	sensible or take immediate effect (or do anything at all), but libev will	1659	sensible or take immediate effect (or do anything at all), but libev will
1544	not crash or malfunction in any way.	1660	not crash or malfunction in any way.
1545		1661
		1662	In any case, the documentation for each member will explain what the
		1663	effects are, and if there are any additional access restrictions.
1546		1664
1547	=head2 C<ev_io> - is this file descriptor readable or writable?	1665	=head2 C<ev_io> - is this file descriptor readable or writable?
1548		1666
1549	I/O watchers check whether a file descriptor is readable or writable	1667	I/O watchers check whether a file descriptor is readable or writable
1550	in each iteration of the event loop, or, more precisely, when reading	1668	in each iteration of the event loop, or, more precisely, when reading
…		…
1557	In general you can register as many read and/or write event watchers per	1675	In general you can register as many read and/or write event watchers per
1558	fd as you want (as long as you don't confuse yourself). Setting all file	1676	fd as you want (as long as you don't confuse yourself). Setting all file
1559	descriptors to non-blocking mode is also usually a good idea (but not	1677	descriptors to non-blocking mode is also usually a good idea (but not
1560	required if you know what you are doing).	1678	required if you know what you are doing).
1561		1679
1562	If you cannot use non-blocking mode, then force the use of a
1563	known-to-be-good backend (at the time of this writing, this includes only
1564	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
1565	descriptors for which non-blocking operation makes no sense (such as
1566	files) - libev doesn't guarantee any specific behaviour in that case.
1567
1568	Another thing you have to watch out for is that it is quite easy to	1680	Another thing you have to watch out for is that it is quite easy to
1569	receive "spurious" readiness notifications, that is your callback might	1681	receive "spurious" readiness notifications, that is, your callback might
1570	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1682	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1571	because there is no data. Not only are some backends known to create a	1683	because there is no data. It is very easy to get into this situation even
1572	lot of those (for example Solaris ports), it is very easy to get into	1684	with a relatively standard program structure. Thus it is best to always
1573	this situation even with a relatively standard program structure. Thus	1685	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1574	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1575	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1686	preferable to a program hanging until some data arrives.
1576		1687
1577	If you cannot run the fd in non-blocking mode (for example you should	1688	If you cannot run the fd in non-blocking mode (for example you should
1578	not play around with an Xlib connection), then you have to separately	1689	not play around with an Xlib connection), then you have to separately
1579	re-test whether a file descriptor is really ready with a known-to-be good	1690	re-test whether a file descriptor is really ready with a known-to-be good
1580	interface such as poll (fortunately in our Xlib example, Xlib already	1691	interface such as poll (fortunately in the case of Xlib, it already does
1581	does this on its own, so its quite safe to use). Some people additionally	1692	this on its own, so its quite safe to use). Some people additionally
1582	use C<SIGALRM> and an interval timer, just to be sure you won't block	1693	use C<SIGALRM> and an interval timer, just to be sure you won't block
1583	indefinitely.	1694	indefinitely.
1584		1695
1585	But really, best use non-blocking mode.	1696	But really, best use non-blocking mode.
1586		1697
1587	=head3 The special problem of disappearing file descriptors	1698	=head3 The special problem of disappearing file descriptors
1588		1699
1589	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1700	Some backends (e.g. kqueue, epoll, linuxaio) need to be told about closing
1590	descriptor (either due to calling C<close> explicitly or any other means,	1701	a file descriptor (either due to calling C<close> explicitly or any other
1591	such as C<dup2>). The reason is that you register interest in some file	1702	means, such as C<dup2>). The reason is that you register interest in some
1592	descriptor, but when it goes away, the operating system will silently drop	1703	file descriptor, but when it goes away, the operating system will silently
1593	this interest. If another file descriptor with the same number then is	1704	drop this interest. If another file descriptor with the same number then
1594	registered with libev, there is no efficient way to see that this is, in	1705	is registered with libev, there is no efficient way to see that this is,
1595	fact, a different file descriptor.	1706	in fact, a different file descriptor.
1596		1707
1597	To avoid having to explicitly tell libev about such cases, libev follows	1708	To avoid having to explicitly tell libev about such cases, libev follows
1598	the following policy: Each time C<ev_io_set> is being called, libev	1709	the following policy: Each time C<ev_io_set> is being called, libev
1599	will assume that this is potentially a new file descriptor, otherwise	1710	will assume that this is potentially a new file descriptor, otherwise
1600	it is assumed that the file descriptor stays the same. That means that	1711	it is assumed that the file descriptor stays the same. That means that
…		…
1614		1725
1615	There is no workaround possible except not registering events	1726	There is no workaround possible except not registering events
1616	for potentially C<dup ()>'ed file descriptors, or to resort to	1727	for potentially C<dup ()>'ed file descriptors, or to resort to
1617	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1728	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1618		1729
		1730	=head3 The special problem of files
		1731
		1732	Many people try to use C<select> (or libev) on file descriptors
		1733	representing files, and expect it to become ready when their program
		1734	doesn't block on disk accesses (which can take a long time on their own).
		1735
		1736	However, this cannot ever work in the "expected" way - you get a readiness
		1737	notification as soon as the kernel knows whether and how much data is
		1738	there, and in the case of open files, that's always the case, so you
		1739	always get a readiness notification instantly, and your read (or possibly
		1740	write) will still block on the disk I/O.
		1741
		1742	Another way to view it is that in the case of sockets, pipes, character
		1743	devices and so on, there is another party (the sender) that delivers data
		1744	on its own, but in the case of files, there is no such thing: the disk
		1745	will not send data on its own, simply because it doesn't know what you
		1746	wish to read - you would first have to request some data.
		1747
		1748	Since files are typically not-so-well supported by advanced notification
		1749	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1750	to files, even though you should not use it. The reason for this is
		1751	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1752	usually a tty, often a pipe, but also sometimes files or special devices
		1753	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1754	F</dev/urandom>), and even though the file might better be served with
		1755	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1756	it "just works" instead of freezing.
		1757
		1758	So avoid file descriptors pointing to files when you know it (e.g. use
		1759	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1760	when you rarely read from a file instead of from a socket, and want to
		1761	reuse the same code path.
		1762
1619	=head3 The special problem of fork	1763	=head3 The special problem of fork
1620		1764
1621	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1765	Some backends (epoll, kqueue, linuxaio, iouring) do not support C<fork ()>
1622	useless behaviour. Libev fully supports fork, but needs to be told about	1766	at all or exhibit useless behaviour. Libev fully supports fork, but needs
1623	it in the child.	1767	to be told about it in the child if you want to continue to use it in the
		1768	child.
1624		1769
1625	To support fork in your programs, you either have to call	1770	To support fork in your child processes, you have to call C<ev_loop_fork
1626	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1771	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1627	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1772	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1628	C<EVBACKEND_POLL>.
1629		1773
1630	=head3 The special problem of SIGPIPE	1774	=head3 The special problem of SIGPIPE
1631		1775
1632	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1776	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1633	when writing to a pipe whose other end has been closed, your program gets	1777	when writing to a pipe whose other end has been closed, your program gets
…		…
1687		1831
1688	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1832	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1689	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or	1833	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
1690	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.	1834	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1691		1835
1692	=item int fd [read-only]	1836	=item ev_io_modify (ev_io *, int events)
1693		1837
1694	The file descriptor being watched.	1838	Similar to C<ev_io_set>, but only changes the event mask. Using this might
		1839	be faster with some backends, as libev can assume that the C<fd> still
		1840	refers to the same underlying file description, something it cannot do
		1841	when using C<ev_io_set>.
1695		1842
		1843	=item int fd [no-modify]
		1844
		1845	The file descriptor being watched. While it can be read at any time, you
		1846	must not modify this member even when the watcher is stopped - always use
		1847	C<ev_io_set> for that.
		1848
1696	=item int events [read-only]	1849	=item int events [no-modify]
1697		1850
1698	The events being watched.	1851	The set of events being watched, among other flags. This field is a
		1852	bit set - to test for C<EV_READ>, use C<< w->events & EV_READ >>, and
		1853	similarly for C<EV_WRITE>.
		1854
		1855	As with C<fd>, you must not modify this member even when the watcher is
		1856	stopped, always use C<ev_io_set> or C<ev_io_modify> for that.
1699		1857
1700	=back	1858	=back
1701		1859
1702	=head3 Examples	1860	=head3 Examples
1703		1861
…		…
1731	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1889	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1732	monotonic clock option helps a lot here).	1890	monotonic clock option helps a lot here).
1733		1891
1734	The callback is guaranteed to be invoked only I<after> its timeout has	1892	The callback is guaranteed to be invoked only I<after> its timeout has
1735	passed (not I<at>, so on systems with very low-resolution clocks this	1893	passed (not I<at>, so on systems with very low-resolution clocks this
1736	might introduce a small delay). If multiple timers become ready during the	1894	might introduce a small delay, see "the special problem of being too
		1895	early", below). If multiple timers become ready during the same loop
1737	same loop iteration then the ones with earlier time-out values are invoked	1896	iteration then the ones with earlier time-out values are invoked before
1738	before ones of the same priority with later time-out values (but this is	1897	ones of the same priority with later time-out values (but this is no
1739	no longer true when a callback calls C<ev_run> recursively).	1898	longer true when a callback calls C<ev_run> recursively).
1740		1899
1741	=head3 Be smart about timeouts	1900	=head3 Be smart about timeouts
1742		1901
1743	Many real-world problems involve some kind of timeout, usually for error	1902	Many real-world problems involve some kind of timeout, usually for error
1744	recovery. A typical example is an HTTP request - if the other side hangs,	1903	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1819		1978
1820	In this case, it would be more efficient to leave the C<ev_timer> alone,	1979	In this case, it would be more efficient to leave the C<ev_timer> alone,
1821	but remember the time of last activity, and check for a real timeout only	1980	but remember the time of last activity, and check for a real timeout only
1822	within the callback:	1981	within the callback:
1823		1982
		1983	ev_tstamp timeout = 60.;
1824	ev_tstamp last_activity; // time of last activity	1984	ev_tstamp last_activity; // time of last activity
		1985	ev_timer timer;
1825		1986
1826	static void	1987	static void
1827	callback (EV_P_ ev_timer *w, int revents)	1988	callback (EV_P_ ev_timer *w, int revents)
1828	{	1989	{
1829	ev_tstamp now = ev_now (EV_A);	1990	// calculate when the timeout would happen
1830	ev_tstamp timeout = last_activity + 60.;	1991	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
1831		1992
1832	// if last_activity + 60. is older than now, we did time out	1993	// if negative, it means we the timeout already occurred
1833	if (timeout < now)	1994	if (after < 0.)
1834	{	1995	{
1835	// timeout occurred, take action	1996	// timeout occurred, take action
1836	}	1997	}
1837	else	1998	else
1838	{	1999	{
1839	// callback was invoked, but there was some activity, re-arm	2000	// callback was invoked, but there was some recent
1840	// the watcher to fire in last_activity + 60, which is	2001	// activity. simply restart the timer to time out
1841	// guaranteed to be in the future, so "again" is positive:	2002	// after "after" seconds, which is the earliest time
1842	w->repeat = timeout - now;	2003	// the timeout can occur.
		2004	ev_timer_set (w, after, 0.);
1843	ev_timer_again (EV_A_ w);	2005	ev_timer_start (EV_A_ w);
1844	}	2006	}
1845	}	2007	}
1846		2008
1847	To summarise the callback: first calculate the real timeout (defined	2009	To summarise the callback: first calculate in how many seconds the
1848	as "60 seconds after the last activity"), then check if that time has	2010	timeout will occur (by calculating the absolute time when it would occur,
1849	been reached, which means something I<did>, in fact, time out. Otherwise	2011	C<last_activity + timeout>, and subtracting the current time, C<ev_now
1850	the callback was invoked too early (C<timeout> is in the future), so	2012	(EV_A)> from that).
1851	re-schedule the timer to fire at that future time, to see if maybe we have
1852	a timeout then.
1853		2013
1854	Note how C<ev_timer_again> is used, taking advantage of the	2014	If this value is negative, then we are already past the timeout, i.e. we
1855	C<ev_timer_again> optimisation when the timer is already running.	2015	timed out, and need to do whatever is needed in this case.
		2016
		2017	Otherwise, we now the earliest time at which the timeout would trigger,
		2018	and simply start the timer with this timeout value.
		2019
		2020	In other words, each time the callback is invoked it will check whether
		2021	the timeout occurred. If not, it will simply reschedule itself to check
		2022	again at the earliest time it could time out. Rinse. Repeat.
1856		2023
1857	This scheme causes more callback invocations (about one every 60 seconds	2024	This scheme causes more callback invocations (about one every 60 seconds
1858	minus half the average time between activity), but virtually no calls to	2025	minus half the average time between activity), but virtually no calls to
1859	libev to change the timeout.	2026	libev to change the timeout.
1860		2027
1861	To start the timer, simply initialise the watcher and set C<last_activity>	2028	To start the machinery, simply initialise the watcher and set
1862	to the current time (meaning we just have some activity :), then call the	2029	C<last_activity> to the current time (meaning there was some activity just
1863	callback, which will "do the right thing" and start the timer:	2030	now), then call the callback, which will "do the right thing" and start
		2031	the timer:
1864		2032
		2033	last_activity = ev_now (EV_A);
1865	ev_init (timer, callback);	2034	ev_init (&timer, callback);
1866	last_activity = ev_now (loop);	2035	callback (EV_A_ &timer, 0);
1867	callback (loop, timer, EV_TIMER);
1868		2036
1869	And when there is some activity, simply store the current time in	2037	When there is some activity, simply store the current time in
1870	C<last_activity>, no libev calls at all:	2038	C<last_activity>, no libev calls at all:
1871		2039
		2040	if (activity detected)
1872	last_activity = ev_now (loop);	2041	last_activity = ev_now (EV_A);
		2042
		2043	When your timeout value changes, then the timeout can be changed by simply
		2044	providing a new value, stopping the timer and calling the callback, which
		2045	will again do the right thing (for example, time out immediately :).
		2046
		2047	timeout = new_value;
		2048	ev_timer_stop (EV_A_ &timer);
		2049	callback (EV_A_ &timer, 0);
1873		2050
1874	This technique is slightly more complex, but in most cases where the	2051	This technique is slightly more complex, but in most cases where the
1875	time-out is unlikely to be triggered, much more efficient.	2052	time-out is unlikely to be triggered, much more efficient.
1876
1877	Changing the timeout is trivial as well (if it isn't hard-coded in the
1878	callback :) - just change the timeout and invoke the callback, which will
1879	fix things for you.
1880		2053
1881	=item 4. Wee, just use a double-linked list for your timeouts.	2054	=item 4. Wee, just use a double-linked list for your timeouts.
1882		2055
1883	If there is not one request, but many thousands (millions...), all	2056	If there is not one request, but many thousands (millions...), all
1884	employing some kind of timeout with the same timeout value, then one can	2057	employing some kind of timeout with the same timeout value, then one can
…		…
1911	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is	2084	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
1912	rather complicated, but extremely efficient, something that really pays	2085	rather complicated, but extremely efficient, something that really pays
1913	off after the first million or so of active timers, i.e. it's usually	2086	off after the first million or so of active timers, i.e. it's usually
1914	overkill :)	2087	overkill :)
1915		2088
		2089	=head3 The special problem of being too early
		2090
		2091	If you ask a timer to call your callback after three seconds, then
		2092	you expect it to be invoked after three seconds - but of course, this
		2093	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		2094	guaranteed to any precision by libev - imagine somebody suspending the
		2095	process with a STOP signal for a few hours for example.
		2096
		2097	So, libev tries to invoke your callback as soon as possible I<after> the
		2098	delay has occurred, but cannot guarantee this.
		2099
		2100	A less obvious failure mode is calling your callback too early: many event
		2101	loops compare timestamps with a "elapsed delay >= requested delay", but
		2102	this can cause your callback to be invoked much earlier than you would
		2103	expect.
		2104
		2105	To see why, imagine a system with a clock that only offers full second
		2106	resolution (think windows if you can't come up with a broken enough OS
		2107	yourself). If you schedule a one-second timer at the time 500.9, then the
		2108	event loop will schedule your timeout to elapse at a system time of 500
		2109	(500.9 truncated to the resolution) + 1, or 501.
		2110
		2111	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2112	501" and invoke the callback 0.1s after it was started, even though a
		2113	one-second delay was requested - this is being "too early", despite best
		2114	intentions.
		2115
		2116	This is the reason why libev will never invoke the callback if the elapsed
		2117	delay equals the requested delay, but only when the elapsed delay is
		2118	larger than the requested delay. In the example above, libev would only invoke
		2119	the callback at system time 502, or 1.1s after the timer was started.
		2120
		2121	So, while libev cannot guarantee that your callback will be invoked
		2122	exactly when requested, it I<can> and I<does> guarantee that the requested
		2123	delay has actually elapsed, or in other words, it always errs on the "too
		2124	late" side of things.
		2125
1916	=head3 The special problem of time updates	2126	=head3 The special problem of time updates
1917		2127
1918	Establishing the current time is a costly operation (it usually takes at	2128	Establishing the current time is a costly operation (it usually takes
1919	least two system calls): EV therefore updates its idea of the current	2129	at least one system call): EV therefore updates its idea of the current
1920	time only before and after C<ev_run> collects new events, which causes a	2130	time only before and after C<ev_run> collects new events, which causes a
1921	growing difference between C<ev_now ()> and C<ev_time ()> when handling	2131	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1922	lots of events in one iteration.	2132	lots of events in one iteration.
1923		2133
1924	The relative timeouts are calculated relative to the C<ev_now ()>	2134	The relative timeouts are calculated relative to the C<ev_now ()>
1925	time. This is usually the right thing as this timestamp refers to the time	2135	time. This is usually the right thing as this timestamp refers to the time
1926	of the event triggering whatever timeout you are modifying/starting. If	2136	of the event triggering whatever timeout you are modifying/starting. If
1927	you suspect event processing to be delayed and you I<need> to base the	2137	you suspect event processing to be delayed and you I<need> to base the
1928	timeout on the current time, use something like this to adjust for this:	2138	timeout on the current time, use something like the following to adjust
		2139	for it:
1929		2140
1930	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2141	ev_timer_set (&timer, after + (ev_time () - ev_now ()), 0.);
1931		2142
1932	If the event loop is suspended for a long time, you can also force an	2143	If the event loop is suspended for a long time, you can also force an
1933	update of the time returned by C<ev_now ()> by calling C<ev_now_update	2144	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1934	()>.	2145	()>, although that will push the event time of all outstanding events
		2146	further into the future.
		2147
		2148	=head3 The special problem of unsynchronised clocks
		2149
		2150	Modern systems have a variety of clocks - libev itself uses the normal
		2151	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2152	jumps).
		2153
		2154	Neither of these clocks is synchronised with each other or any other clock
		2155	on the system, so C<ev_time ()> might return a considerably different time
		2156	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2157	a call to C<gettimeofday> might return a second count that is one higher
		2158	than a directly following call to C<time>.
		2159
		2160	The moral of this is to only compare libev-related timestamps with
		2161	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2162	a second or so.
		2163
		2164	One more problem arises due to this lack of synchronisation: if libev uses
		2165	the system monotonic clock and you compare timestamps from C<ev_time>
		2166	or C<ev_now> from when you started your timer and when your callback is
		2167	invoked, you will find that sometimes the callback is a bit "early".
		2168
		2169	This is because C<ev_timer>s work in real time, not wall clock time, so
		2170	libev makes sure your callback is not invoked before the delay happened,
		2171	I<measured according to the real time>, not the system clock.
		2172
		2173	If your timeouts are based on a physical timescale (e.g. "time out this
		2174	connection after 100 seconds") then this shouldn't bother you as it is
		2175	exactly the right behaviour.
		2176
		2177	If you want to compare wall clock/system timestamps to your timers, then
		2178	you need to use C<ev_periodic>s, as these are based on the wall clock
		2179	time, where your comparisons will always generate correct results.
1935		2180
1936	=head3 The special problems of suspended animation	2181	=head3 The special problems of suspended animation
1937		2182
1938	When you leave the server world it is quite customary to hit machines that	2183	When you leave the server world it is quite customary to hit machines that
1939	can suspend/hibernate - what happens to the clocks during such a suspend?	2184	can suspend/hibernate - what happens to the clocks during such a suspend?
…		…
1969		2214
1970	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2215	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1971		2216
1972	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2217	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1973		2218
1974	Configure the timer to trigger after C<after> seconds. If C<repeat>	2219	Configure the timer to trigger after C<after> seconds (fractional and
1975	is C<0.>, then it will automatically be stopped once the timeout is	2220	negative values are supported). If C<repeat> is C<0.>, then it will
1976	reached. If it is positive, then the timer will automatically be	2221	automatically be stopped once the timeout is reached. If it is positive,
1977	configured to trigger again C<repeat> seconds later, again, and again,	2222	then the timer will automatically be configured to trigger again C<repeat>
1978	until stopped manually.	2223	seconds later, again, and again, until stopped manually.
1979		2224
1980	The timer itself will do a best-effort at avoiding drift, that is, if	2225	The timer itself will do a best-effort at avoiding drift, that is, if
1981	you configure a timer to trigger every 10 seconds, then it will normally	2226	you configure a timer to trigger every 10 seconds, then it will normally
1982	trigger at exactly 10 second intervals. If, however, your program cannot	2227	trigger at exactly 10 second intervals. If, however, your program cannot
1983	keep up with the timer (because it takes longer than those 10 seconds to	2228	keep up with the timer (because it takes longer than those 10 seconds to
1984	do stuff) the timer will not fire more than once per event loop iteration.	2229	do stuff) the timer will not fire more than once per event loop iteration.
1985		2230
1986	=item ev_timer_again (loop, ev_timer *)	2231	=item ev_timer_again (loop, ev_timer *)
1987		2232
1988	This will act as if the timer timed out and restart it again if it is	2233	This will act as if the timer timed out, and restarts it again if it is
1989	repeating. The exact semantics are:	2234	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2235	timeout to the C<repeat> value and calling C<ev_timer_start>.
1990		2236
		2237	The exact semantics are as in the following rules, all of which will be
		2238	applied to the watcher:
		2239
		2240	=over 4
		2241
1991	If the timer is pending, its pending status is cleared.	2242	=item If the timer is pending, the pending status is always cleared.
1992		2243
1993	If the timer is started but non-repeating, stop it (as if it timed out).	2244	=item If the timer is started but non-repeating, stop it (as if it timed
		2245	out, without invoking it).
1994		2246
1995	If the timer is repeating, either start it if necessary (with the	2247	=item If the timer is repeating, make the C<repeat> value the new timeout
1996	C<repeat> value), or reset the running timer to the C<repeat> value.	2248	and start the timer, if necessary.
1997		2249
		2250	=back
		2251
1998	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a	2252	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
1999	usage example.	2253	usage example.
2000		2254
2001	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)	2255	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
2002		2256
2003	Returns the remaining time until a timer fires. If the timer is active,	2257	Returns the remaining time until a timer fires. If the timer is active,
…		…
2056	Periodic watchers are also timers of a kind, but they are very versatile	2310	Periodic watchers are also timers of a kind, but they are very versatile
2057	(and unfortunately a bit complex).	2311	(and unfortunately a bit complex).
2058		2312
2059	Unlike C<ev_timer>, periodic watchers are not based on real time (or	2313	Unlike C<ev_timer>, periodic watchers are not based on real time (or
2060	relative time, the physical time that passes) but on wall clock time	2314	relative time, the physical time that passes) but on wall clock time
2061	(absolute time, the thing you can read on your calender or clock). The	2315	(absolute time, the thing you can read on your calendar or clock). The
2062	difference is that wall clock time can run faster or slower than real	2316	difference is that wall clock time can run faster or slower than real
2063	time, and time jumps are not uncommon (e.g. when you adjust your	2317	time, and time jumps are not uncommon (e.g. when you adjust your
2064	wrist-watch).	2318	wrist-watch).
2065		2319
2066	You can tell a periodic watcher to trigger after some specific point	2320	You can tell a periodic watcher to trigger after some specific point
…		…
2071	C<ev_timer>, which would still trigger roughly 10 seconds after starting	2325	C<ev_timer>, which would still trigger roughly 10 seconds after starting
2072	it, as it uses a relative timeout).	2326	it, as it uses a relative timeout).
2073		2327
2074	C<ev_periodic> watchers can also be used to implement vastly more complex	2328	C<ev_periodic> watchers can also be used to implement vastly more complex
2075	timers, such as triggering an event on each "midnight, local time", or	2329	timers, such as triggering an event on each "midnight, local time", or
2076	other complicated rules. This cannot be done with C<ev_timer> watchers, as	2330	other complicated rules. This cannot easily be done with C<ev_timer>
2077	those cannot react to time jumps.	2331	watchers, as those cannot react to time jumps.
2078		2332
2079	As with timers, the callback is guaranteed to be invoked only when the	2333	As with timers, the callback is guaranteed to be invoked only when the
2080	point in time where it is supposed to trigger has passed. If multiple	2334	point in time where it is supposed to trigger has passed. If multiple
2081	timers become ready during the same loop iteration then the ones with	2335	timers become ready during the same loop iteration then the ones with
2082	earlier time-out values are invoked before ones with later time-out values	2336	earlier time-out values are invoked before ones with later time-out values
…		…
2123		2377
2124	Another way to think about it (for the mathematically inclined) is that	2378	Another way to think about it (for the mathematically inclined) is that
2125	C<ev_periodic> will try to run the callback in this mode at the next possible	2379	C<ev_periodic> will try to run the callback in this mode at the next possible
2126	time where C<time = offset (mod interval)>, regardless of any time jumps.	2380	time where C<time = offset (mod interval)>, regardless of any time jumps.
2127		2381
2128	For numerical stability it is preferable that the C<offset> value is near	2382	The C<interval> I<MUST> be positive, and for numerical stability, the
2129	C<ev_now ()> (the current time), but there is no range requirement for	2383	interval value should be higher than C<1/8192> (which is around 100
2130	this value, and in fact is often specified as zero.	2384	microseconds) and C<offset> should be higher than C<0> and should have
		2385	at most a similar magnitude as the current time (say, within a factor of
		2386	ten). Typical values for offset are, in fact, C<0> or something between
		2387	C<0> and C<interval>, which is also the recommended range.
2131		2388
2132	Note also that there is an upper limit to how often a timer can fire (CPU	2389	Note also that there is an upper limit to how often a timer can fire (CPU
2133	speed for example), so if C<interval> is very small then timing stability	2390	speed for example), so if C<interval> is very small then timing stability
2134	will of course deteriorate. Libev itself tries to be exact to be about one	2391	will of course deteriorate. Libev itself tries to be exact to be about one
2135	millisecond (if the OS supports it and the machine is fast enough).	2392	millisecond (if the OS supports it and the machine is fast enough).
…		…
2165		2422
2166	NOTE: I<< This callback must always return a time that is higher than or	2423	NOTE: I<< This callback must always return a time that is higher than or
2167	equal to the passed C<now> value >>.	2424	equal to the passed C<now> value >>.
2168		2425
2169	This can be used to create very complex timers, such as a timer that	2426	This can be used to create very complex timers, such as a timer that
2170	triggers on "next midnight, local time". To do this, you would calculate the	2427	triggers on "next midnight, local time". To do this, you would calculate
2171	next midnight after C<now> and return the timestamp value for this. How	2428	the next midnight after C<now> and return the timestamp value for
2172	you do this is, again, up to you (but it is not trivial, which is the main	2429	this. Here is a (completely untested, no error checking) example on how to
2173	reason I omitted it as an example).	2430	do this:
		2431
		2432	#include <time.h>
		2433
		2434	static ev_tstamp
		2435	my_rescheduler (ev_periodic *w, ev_tstamp now)
		2436	{
		2437	time_t tnow = (time_t)now;
		2438	struct tm tm;
		2439	localtime_r (&tnow, &tm);
		2440
		2441	tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
		2442	++tm.tm_mday; // midnight next day
		2443
		2444	return mktime (&tm);
		2445	}
		2446
		2447	Note: this code might run into trouble on days that have more then two
		2448	midnights (beginning and end).
2174		2449
2175	=back	2450	=back
2176		2451
2177	=item ev_periodic_again (loop, ev_periodic *)	2452	=item ev_periodic_again (loop, ev_periodic *)
2178		2453
…		…
2243		2518
2244	ev_periodic hourly_tick;	2519	ev_periodic hourly_tick;
2245	ev_periodic_init (&hourly_tick, clock_cb,	2520	ev_periodic_init (&hourly_tick, clock_cb,
2246	fmod (ev_now (loop), 3600.), 3600., 0);	2521	fmod (ev_now (loop), 3600.), 3600., 0);
2247	ev_periodic_start (loop, &hourly_tick);	2522	ev_periodic_start (loop, &hourly_tick);
2248		2523
2249		2524
2250	=head2 C<ev_signal> - signal me when a signal gets signalled!	2525	=head2 C<ev_signal> - signal me when a signal gets signalled!
2251		2526
2252	Signal watchers will trigger an event when the process receives a specific	2527	Signal watchers will trigger an event when the process receives a specific
2253	signal one or more times. Even though signals are very asynchronous, libev	2528	signal one or more times. Even though signals are very asynchronous, libev
2254	will try it's best to deliver signals synchronously, i.e. as part of the	2529	will try its best to deliver signals synchronously, i.e. as part of the
2255	normal event processing, like any other event.	2530	normal event processing, like any other event.
2256		2531
2257	If you want signals to be delivered truly asynchronously, just use	2532	If you want signals to be delivered truly asynchronously, just use
2258	C<sigaction> as you would do without libev and forget about sharing	2533	C<sigaction> as you would do without libev and forget about sharing
2259	the signal. You can even use C<ev_async> from a signal handler to	2534	the signal. You can even use C<ev_async> from a signal handler to
…		…
2263	only within the same loop, i.e. you can watch for C<SIGINT> in your	2538	only within the same loop, i.e. you can watch for C<SIGINT> in your
2264	default loop and for C<SIGIO> in another loop, but you cannot watch for	2539	default loop and for C<SIGIO> in another loop, but you cannot watch for
2265	C<SIGINT> in both the default loop and another loop at the same time. At	2540	C<SIGINT> in both the default loop and another loop at the same time. At
2266	the moment, C<SIGCHLD> is permanently tied to the default loop.	2541	the moment, C<SIGCHLD> is permanently tied to the default loop.
2267		2542
2268	When the first watcher gets started will libev actually register something	2543	Only after the first watcher for a signal is started will libev actually
2269	with the kernel (thus it coexists with your own signal handlers as long as	2544	register something with the kernel. It thus coexists with your own signal
2270	you don't register any with libev for the same signal).	2545	handlers as long as you don't register any with libev for the same signal.
2271		2546
2272	If possible and supported, libev will install its handlers with	2547	If possible and supported, libev will install its handlers with
2273	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should	2548	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
2274	not be unduly interrupted. If you have a problem with system calls getting	2549	not be unduly interrupted. If you have a problem with system calls getting
2275	interrupted by signals you can block all signals in an C<ev_check> watcher	2550	interrupted by signals you can block all signals in an C<ev_check> watcher
…		…
2278	=head3 The special problem of inheritance over fork/execve/pthread_create	2553	=head3 The special problem of inheritance over fork/execve/pthread_create
2279		2554
2280	Both the signal mask (C<sigprocmask>) and the signal disposition	2555	Both the signal mask (C<sigprocmask>) and the signal disposition
2281	(C<sigaction>) are unspecified after starting a signal watcher (and after	2556	(C<sigaction>) are unspecified after starting a signal watcher (and after
2282	stopping it again), that is, libev might or might not block the signal,	2557	stopping it again), that is, libev might or might not block the signal,
2283	and might or might not set or restore the installed signal handler.	2558	and might or might not set or restore the installed signal handler (but
		2559	see C<EVFLAG_NOSIGMASK>).
2284		2560
2285	While this does not matter for the signal disposition (libev never	2561	While this does not matter for the signal disposition (libev never
2286	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on	2562	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
2287	C<execve>), this matters for the signal mask: many programs do not expect	2563	C<execve>), this matters for the signal mask: many programs do not expect
2288	certain signals to be blocked.	2564	certain signals to be blocked.
…		…
2301	I<has> to modify the signal mask, at least temporarily.	2577	I<has> to modify the signal mask, at least temporarily.
2302		2578
2303	So I can't stress this enough: I<If you do not reset your signal mask when	2579	So I can't stress this enough: I<If you do not reset your signal mask when
2304	you expect it to be empty, you have a race condition in your code>. This	2580	you expect it to be empty, you have a race condition in your code>. This
2305	is not a libev-specific thing, this is true for most event libraries.	2581	is not a libev-specific thing, this is true for most event libraries.
		2582
		2583	=head3 The special problem of threads signal handling
		2584
		2585	POSIX threads has problematic signal handling semantics, specifically,
		2586	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2587	threads in a process block signals, which is hard to achieve.
		2588
		2589	When you want to use sigwait (or mix libev signal handling with your own
		2590	for the same signals), you can tackle this problem by globally blocking
		2591	all signals before creating any threads (or creating them with a fully set
		2592	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2593	loops. Then designate one thread as "signal receiver thread" which handles
		2594	these signals. You can pass on any signals that libev might be interested
		2595	in by calling C<ev_feed_signal>.
2306		2596
2307	=head3 Watcher-Specific Functions and Data Members	2597	=head3 Watcher-Specific Functions and Data Members
2308		2598
2309	=over 4	2599	=over 4
2310		2600
…		…
2445		2735
2446	=head2 C<ev_stat> - did the file attributes just change?	2736	=head2 C<ev_stat> - did the file attributes just change?
2447		2737
2448	This watches a file system path for attribute changes. That is, it calls	2738	This watches a file system path for attribute changes. That is, it calls
2449	C<stat> on that path in regular intervals (or when the OS says it changed)	2739	C<stat> on that path in regular intervals (or when the OS says it changed)
2450	and sees if it changed compared to the last time, invoking the callback if	2740	and sees if it changed compared to the last time, invoking the callback
2451	it did.	2741	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2742	happen after the watcher has been started will be reported.
2452		2743
2453	The path does not need to exist: changing from "path exists" to "path does	2744	The path does not need to exist: changing from "path exists" to "path does
2454	not exist" is a status change like any other. The condition "path does not	2745	not exist" is a status change like any other. The condition "path does not
2455	exist" (or more correctly "path cannot be stat'ed") is signified by the	2746	exist" (or more correctly "path cannot be stat'ed") is signified by the
2456	C<st_nlink> field being zero (which is otherwise always forced to be at	2747	C<st_nlink> field being zero (which is otherwise always forced to be at
…		…
2686	Apart from keeping your process non-blocking (which is a useful	2977	Apart from keeping your process non-blocking (which is a useful
2687	effect on its own sometimes), idle watchers are a good place to do	2978	effect on its own sometimes), idle watchers are a good place to do
2688	"pseudo-background processing", or delay processing stuff to after the	2979	"pseudo-background processing", or delay processing stuff to after the
2689	event loop has handled all outstanding events.	2980	event loop has handled all outstanding events.
2690		2981
		2982	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2983
		2984	As long as there is at least one active idle watcher, libev will never
		2985	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2986	For this to work, the idle watcher doesn't need to be invoked at all - the
		2987	lowest priority will do.
		2988
		2989	This mode of operation can be useful together with an C<ev_check> watcher,
		2990	to do something on each event loop iteration - for example to balance load
		2991	between different connections.
		2992
		2993	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2994	example.
		2995
2691	=head3 Watcher-Specific Functions and Data Members	2996	=head3 Watcher-Specific Functions and Data Members
2692		2997
2693	=over 4	2998	=over 4
2694		2999
2695	=item ev_idle_init (ev_idle *, callback)	3000	=item ev_idle_init (ev_idle *, callback)
…		…
2706	callback, free it. Also, use no error checking, as usual.	3011	callback, free it. Also, use no error checking, as usual.
2707		3012
2708	static void	3013	static void
2709	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)	3014	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2710	{	3015	{
		3016	// stop the watcher
		3017	ev_idle_stop (loop, w);
		3018
		3019	// now we can free it
2711	free (w);	3020	free (w);
		3021
2712	// now do something you wanted to do when the program has	3022	// now do something you wanted to do when the program has
2713	// no longer anything immediate to do.	3023	// no longer anything immediate to do.
2714	}	3024	}
2715		3025
2716	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	3026	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
…		…
2718	ev_idle_start (loop, idle_watcher);	3028	ev_idle_start (loop, idle_watcher);
2719		3029
2720		3030
2721	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	3031	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2722		3032
2723	Prepare and check watchers are usually (but not always) used in pairs:	3033	Prepare and check watchers are often (but not always) used in pairs:
2724	prepare watchers get invoked before the process blocks and check watchers	3034	prepare watchers get invoked before the process blocks and check watchers
2725	afterwards.	3035	afterwards.
2726		3036
2727	You I<must not> call C<ev_run> or similar functions that enter	3037	You I<must not> call C<ev_run> (or similar functions that enter the
2728	the current event loop from either C<ev_prepare> or C<ev_check>	3038	current event loop) or C<ev_loop_fork> from either C<ev_prepare> or
2729	watchers. Other loops than the current one are fine, however. The	3039	C<ev_check> watchers. Other loops than the current one are fine,
2730	rationale behind this is that you do not need to check for recursion in	3040	however. The rationale behind this is that you do not need to check
2731	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	3041	for recursion in those watchers, i.e. the sequence will always be
2732	C<ev_check> so if you have one watcher of each kind they will always be	3042	C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
2733	called in pairs bracketing the blocking call.	3043	kind they will always be called in pairs bracketing the blocking call.
2734		3044
2735	Their main purpose is to integrate other event mechanisms into libev and	3045	Their main purpose is to integrate other event mechanisms into libev and
2736	their use is somewhat advanced. They could be used, for example, to track	3046	their use is somewhat advanced. They could be used, for example, to track
2737	variable changes, implement your own watchers, integrate net-snmp or a	3047	variable changes, implement your own watchers, integrate net-snmp or a
2738	coroutine library and lots more. They are also occasionally useful if	3048	coroutine library and lots more. They are also occasionally useful if
…		…
2756	with priority higher than or equal to the event loop and one coroutine	3066	with priority higher than or equal to the event loop and one coroutine
2757	of lower priority, but only once, using idle watchers to keep the event	3067	of lower priority, but only once, using idle watchers to keep the event
2758	loop from blocking if lower-priority coroutines are active, thus mapping	3068	loop from blocking if lower-priority coroutines are active, thus mapping
2759	low-priority coroutines to idle/background tasks).	3069	low-priority coroutines to idle/background tasks).
2760		3070
2761	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	3071	When used for this purpose, it is recommended to give C<ev_check> watchers
2762	priority, to ensure that they are being run before any other watchers	3072	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
2763	after the poll (this doesn't matter for C<ev_prepare> watchers).	3073	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		3074	watchers).
2764		3075
2765	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not	3076	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
2766	activate ("feed") events into libev. While libev fully supports this, they	3077	activate ("feed") events into libev. While libev fully supports this, they
2767	might get executed before other C<ev_check> watchers did their job. As	3078	might get executed before other C<ev_check> watchers did their job. As
2768	C<ev_check> watchers are often used to embed other (non-libev) event	3079	C<ev_check> watchers are often used to embed other (non-libev) event
2769	loops those other event loops might be in an unusable state until their	3080	loops those other event loops might be in an unusable state until their
2770	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	3081	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
2771	others).	3082	others).
		3083
		3084	=head3 Abusing an C<ev_check> watcher for its side-effect
		3085
		3086	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		3087	useful because they are called once per event loop iteration. For
		3088	example, if you want to handle a large number of connections fairly, you
		3089	normally only do a bit of work for each active connection, and if there
		3090	is more work to do, you wait for the next event loop iteration, so other
		3091	connections have a chance of making progress.
		3092
		3093	Using an C<ev_check> watcher is almost enough: it will be called on the
		3094	next event loop iteration. However, that isn't as soon as possible -
		3095	without external events, your C<ev_check> watcher will not be invoked.
		3096
		3097	This is where C<ev_idle> watchers come in handy - all you need is a
		3098	single global idle watcher that is active as long as you have one active
		3099	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		3100	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		3101	invoked. Neither watcher alone can do that.
2772		3102
2773	=head3 Watcher-Specific Functions and Data Members	3103	=head3 Watcher-Specific Functions and Data Members
2774		3104
2775	=over 4	3105	=over 4
2776		3106
…		…
2977		3307
2978	=over 4	3308	=over 4
2979		3309
2980	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3310	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
2981		3311
2982	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3312	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
2983		3313
2984	Configures the watcher to embed the given loop, which must be	3314	Configures the watcher to embed the given loop, which must be
2985	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3315	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
2986	invoked automatically, otherwise it is the responsibility of the callback	3316	invoked automatically, otherwise it is the responsibility of the callback
2987	to invoke it (it will continue to be called until the sweep has been done,	3317	to invoke it (it will continue to be called until the sweep has been done,
…		…
3008	used).	3338	used).
3009		3339
3010	struct ev_loop *loop_hi = ev_default_init (0);	3340	struct ev_loop *loop_hi = ev_default_init (0);
3011	struct ev_loop *loop_lo = 0;	3341	struct ev_loop *loop_lo = 0;
3012	ev_embed embed;	3342	ev_embed embed;
3013		3343
3014	// see if there is a chance of getting one that works	3344	// see if there is a chance of getting one that works
3015	// (remember that a flags value of 0 means autodetection)	3345	// (remember that a flags value of 0 means autodetection)
3016	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3346	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3017	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3347	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3018	: 0;	3348	: 0;
…		…
3032	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3362	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
3033		3363
3034	struct ev_loop *loop = ev_default_init (0);	3364	struct ev_loop *loop = ev_default_init (0);
3035	struct ev_loop *loop_socket = 0;	3365	struct ev_loop *loop_socket = 0;
3036	ev_embed embed;	3366	ev_embed embed;
3037		3367
3038	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3368	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3039	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3369	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3040	{	3370	{
3041	ev_embed_init (&embed, 0, loop_socket);	3371	ev_embed_init (&embed, 0, loop_socket);
3042	ev_embed_start (loop, &embed);	3372	ev_embed_start (loop, &embed);
…		…
3050		3380
3051	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3381	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
3052		3382
3053	Fork watchers are called when a C<fork ()> was detected (usually because	3383	Fork watchers are called when a C<fork ()> was detected (usually because
3054	whoever is a good citizen cared to tell libev about it by calling	3384	whoever is a good citizen cared to tell libev about it by calling
3055	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the	3385	C<ev_loop_fork>). The invocation is done before the event loop blocks next
3056	event loop blocks next and before C<ev_check> watchers are being called,	3386	and before C<ev_check> watchers are being called, and only in the child
3057	and only in the child after the fork. If whoever good citizen calling	3387	after the fork. If whoever good citizen calling C<ev_default_fork> cheats
3058	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3388	and calls it in the wrong process, the fork handlers will be invoked, too,
3059	handlers will be invoked, too, of course.	3389	of course.
3060		3390
3061	=head3 The special problem of life after fork - how is it possible?	3391	=head3 The special problem of life after fork - how is it possible?
3062		3392
3063	Most uses of C<fork()> consist of forking, then some simple calls to set	3393	Most uses of C<fork ()> consist of forking, then some simple calls to set
3064	up/change the process environment, followed by a call to C<exec()>. This	3394	up/change the process environment, followed by a call to C<exec()>. This
3065	sequence should be handled by libev without any problems.	3395	sequence should be handled by libev without any problems.
3066		3396
3067	This changes when the application actually wants to do event handling	3397	This changes when the application actually wants to do event handling
3068	in the child, or both parent in child, in effect "continuing" after the	3398	in the child, or both parent in child, in effect "continuing" after the
…		…
3098		3428
3099	=item ev_fork_init (ev_fork *, callback)	3429	=item ev_fork_init (ev_fork *, callback)
3100		3430
3101	Initialises and configures the fork watcher - it has no parameters of any	3431	Initialises and configures the fork watcher - it has no parameters of any
3102	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,	3432	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
3103	believe me.	3433	really.
3104		3434
3105	=back	3435	=back
3106		3436
3107		3437
3108	=head2 C<ev_cleanup> - even the best things end	3438	=head2 C<ev_cleanup> - even the best things end
3109		3439
3110	Cleanup watchers are called just before the event loop they are registered	3440	Cleanup watchers are called just before the event loop is being destroyed
3111	with is being destroyed.	3441	by a call to C<ev_loop_destroy>.
3112		3442
3113	While there is no guarantee that the event loop gets destroyed, cleanup	3443	While there is no guarantee that the event loop gets destroyed, cleanup
3114	watchers provide a convenient method to install cleanup hooks for your	3444	watchers provide a convenient method to install cleanup hooks for your
3115	program, worker threads and so on - you just to make sure to destroy the	3445	program, worker threads and so on - you just to make sure to destroy the
3116	loop when you want them to be invoked.	3446	loop when you want them to be invoked.
…		…
3126		3456
3127	=item ev_cleanup_init (ev_cleanup *, callback)	3457	=item ev_cleanup_init (ev_cleanup *, callback)
3128		3458
3129	Initialises and configures the cleanup watcher - it has no parameters of	3459	Initialises and configures the cleanup watcher - it has no parameters of
3130	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly	3460	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
3131	pointless, believe me.	3461	pointless, I assure you.
3132		3462
3133	=back	3463	=back
3134		3464
3135	Example: Register an atexit handler to destroy the default loop, so any	3465	Example: Register an atexit handler to destroy the default loop, so any
3136	cleanup functions are called.	3466	cleanup functions are called.
…		…
3145	atexit (program_exits);	3475	atexit (program_exits);
3146		3476
3147		3477
3148	=head2 C<ev_async> - how to wake up an event loop	3478	=head2 C<ev_async> - how to wake up an event loop
3149		3479
3150	In general, you cannot use an C<ev_run> from multiple threads or other	3480	In general, you cannot use an C<ev_loop> from multiple threads or other
3151	asynchronous sources such as signal handlers (as opposed to multiple event	3481	asynchronous sources such as signal handlers (as opposed to multiple event
3152	loops - those are of course safe to use in different threads).	3482	loops - those are of course safe to use in different threads).
3153		3483
3154	Sometimes, however, you need to wake up an event loop you do not control,	3484	Sometimes, however, you need to wake up an event loop you do not control,
3155	for example because it belongs to another thread. This is what C<ev_async>	3485	for example because it belongs to another thread. This is what C<ev_async>
…		…
3157	it by calling C<ev_async_send>, which is thread- and signal safe.	3487	it by calling C<ev_async_send>, which is thread- and signal safe.
3158		3488
3159	This functionality is very similar to C<ev_signal> watchers, as signals,	3489	This functionality is very similar to C<ev_signal> watchers, as signals,
3160	too, are asynchronous in nature, and signals, too, will be compressed	3490	too, are asynchronous in nature, and signals, too, will be compressed
3161	(i.e. the number of callback invocations may be less than the number of	3491	(i.e. the number of callback invocations may be less than the number of
3162	C<ev_async_sent> calls).	3492	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
3163		3493	of "global async watchers" by using a watcher on an otherwise unused
3164	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not	3494	signal, and C<ev_feed_signal> to signal this watcher from another thread,
3165	just the default loop.	3495	even without knowing which loop owns the signal.
3166		3496
3167	=head3 Queueing	3497	=head3 Queueing
3168		3498
3169	C<ev_async> does not support queueing of data in any way. The reason	3499	C<ev_async> does not support queueing of data in any way. The reason
3170	is that the author does not know of a simple (or any) algorithm for a	3500	is that the author does not know of a simple (or any) algorithm for a
…		…
3262	trust me.	3592	trust me.
3263		3593
3264	=item ev_async_send (loop, ev_async *)	3594	=item ev_async_send (loop, ev_async *)
3265		3595
3266	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3596	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
3267	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3597	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3598	returns.
		3599
3268	C<ev_feed_event>, this call is safe to do from other threads, signal or	3600	Unlike C<ev_feed_event>, this call is safe to do from other threads,
3269	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3601	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3270	section below on what exactly this means).	3602	embedding section below on what exactly this means).
3271		3603
3272	Note that, as with other watchers in libev, multiple events might get	3604	Note that, as with other watchers in libev, multiple events might get
3273	compressed into a single callback invocation (another way to look at this	3605	compressed into a single callback invocation (another way to look at
3274	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,	3606	this is that C<ev_async> watchers are level-triggered: they are set on
3275	reset when the event loop detects that).	3607	C<ev_async_send>, reset when the event loop detects that).
3276		3608
3277	This call incurs the overhead of a system call only once per event loop	3609	This call incurs the overhead of at most one extra system call per event
3278	iteration, so while the overhead might be noticeable, it doesn't apply to	3610	loop iteration, if the event loop is blocked, and no syscall at all if
3279	repeated calls to C<ev_async_send> for the same event loop.	3611	the event loop (or your program) is processing events. That means that
		3612	repeated calls are basically free (there is no need to avoid calls for
		3613	performance reasons) and that the overhead becomes smaller (typically
		3614	zero) under load.
3280		3615
3281	=item bool = ev_async_pending (ev_async *)	3616	=item bool = ev_async_pending (ev_async *)
3282		3617
3283	Returns a non-zero value when C<ev_async_send> has been called on the	3618	Returns a non-zero value when C<ev_async_send> has been called on the
3284	watcher but the event has not yet been processed (or even noted) by the	3619	watcher but the event has not yet been processed (or even noted) by the
…		…
3301		3636
3302	There are some other functions of possible interest. Described. Here. Now.	3637	There are some other functions of possible interest. Described. Here. Now.
3303		3638
3304	=over 4	3639	=over 4
3305		3640
3306	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3641	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)
3307		3642
3308	This function combines a simple timer and an I/O watcher, calls your	3643	This function combines a simple timer and an I/O watcher, calls your
3309	callback on whichever event happens first and automatically stops both	3644	callback on whichever event happens first and automatically stops both
3310	watchers. This is useful if you want to wait for a single event on an fd	3645	watchers. This is useful if you want to wait for a single event on an fd
3311	or timeout without having to allocate/configure/start/stop/free one or	3646	or timeout without having to allocate/configure/start/stop/free one or
…		…
3339	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3674	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3340		3675
3341	=item ev_feed_fd_event (loop, int fd, int revents)	3676	=item ev_feed_fd_event (loop, int fd, int revents)
3342		3677
3343	Feed an event on the given fd, as if a file descriptor backend detected	3678	Feed an event on the given fd, as if a file descriptor backend detected
3344	the given events it.	3679	the given events.
3345		3680
3346	=item ev_feed_signal_event (loop, int signum)	3681	=item ev_feed_signal_event (loop, int signum)
3347		3682
3348	Feed an event as if the given signal occurred (C<loop> must be the default	3683	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3349	loop!).	3684	which is async-safe.
3350		3685
3351	=back	3686	=back
		3687
		3688
		3689	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3690
		3691	This section explains some common idioms that are not immediately
		3692	obvious. Note that examples are sprinkled over the whole manual, and this
		3693	section only contains stuff that wouldn't fit anywhere else.
		3694
		3695	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3696
		3697	Each watcher has, by default, a C<void *data> member that you can read
		3698	or modify at any time: libev will completely ignore it. This can be used
		3699	to associate arbitrary data with your watcher. If you need more data and
		3700	don't want to allocate memory separately and store a pointer to it in that
		3701	data member, you can also "subclass" the watcher type and provide your own
		3702	data:
		3703
		3704	struct my_io
		3705	{
		3706	ev_io io;
		3707	int otherfd;
		3708	void *somedata;
		3709	struct whatever *mostinteresting;
		3710	};
		3711
		3712	...
		3713	struct my_io w;
		3714	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3715
		3716	And since your callback will be called with a pointer to the watcher, you
		3717	can cast it back to your own type:
		3718
		3719	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3720	{
		3721	struct my_io *w = (struct my_io *)w_;
		3722	...
		3723	}
		3724
		3725	More interesting and less C-conformant ways of casting your callback
		3726	function type instead have been omitted.
		3727
		3728	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3729
		3730	Another common scenario is to use some data structure with multiple
		3731	embedded watchers, in effect creating your own watcher that combines
		3732	multiple libev event sources into one "super-watcher":
		3733
		3734	struct my_biggy
		3735	{
		3736	int some_data;
		3737	ev_timer t1;
		3738	ev_timer t2;
		3739	}
		3740
		3741	In this case getting the pointer to C<my_biggy> is a bit more
		3742	complicated: Either you store the address of your C<my_biggy> struct in
		3743	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3744	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3745	real programmers):
		3746
		3747	#include <stddef.h>
		3748
		3749	static void
		3750	t1_cb (EV_P_ ev_timer *w, int revents)
		3751	{
		3752	struct my_biggy big = (struct my_biggy *)
		3753	(((char *)w) - offsetof (struct my_biggy, t1));
		3754	}
		3755
		3756	static void
		3757	t2_cb (EV_P_ ev_timer *w, int revents)
		3758	{
		3759	struct my_biggy big = (struct my_biggy *)
		3760	(((char *)w) - offsetof (struct my_biggy, t2));
		3761	}
		3762
		3763	=head2 AVOIDING FINISHING BEFORE RETURNING
		3764
		3765	Often you have structures like this in event-based programs:
		3766
		3767	callback ()
		3768	{
		3769	free (request);
		3770	}
		3771
		3772	request = start_new_request (..., callback);
		3773
		3774	The intent is to start some "lengthy" operation. The C<request> could be
		3775	used to cancel the operation, or do other things with it.
		3776
		3777	It's not uncommon to have code paths in C<start_new_request> that
		3778	immediately invoke the callback, for example, to report errors. Or you add
		3779	some caching layer that finds that it can skip the lengthy aspects of the
		3780	operation and simply invoke the callback with the result.
		3781
		3782	The problem here is that this will happen I<before> C<start_new_request>
		3783	has returned, so C<request> is not set.
		3784
		3785	Even if you pass the request by some safer means to the callback, you
		3786	might want to do something to the request after starting it, such as
		3787	canceling it, which probably isn't working so well when the callback has
		3788	already been invoked.
		3789
		3790	A common way around all these issues is to make sure that
		3791	C<start_new_request> I<always> returns before the callback is invoked. If
		3792	C<start_new_request> immediately knows the result, it can artificially
		3793	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3794	example, or more sneakily, by reusing an existing (stopped) watcher and
		3795	pushing it into the pending queue:
		3796
		3797	ev_set_cb (watcher, callback);
		3798	ev_feed_event (EV_A_ watcher, 0);
		3799
		3800	This way, C<start_new_request> can safely return before the callback is
		3801	invoked, while not delaying callback invocation too much.
		3802
		3803	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3804
		3805	Often (especially in GUI toolkits) there are places where you have
		3806	I<modal> interaction, which is most easily implemented by recursively
		3807	invoking C<ev_run>.
		3808
		3809	This brings the problem of exiting - a callback might want to finish the
		3810	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3811	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3812	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3813	other combination: In these cases, a simple C<ev_break> will not work.
		3814
		3815	The solution is to maintain "break this loop" variable for each C<ev_run>
		3816	invocation, and use a loop around C<ev_run> until the condition is
		3817	triggered, using C<EVRUN_ONCE>:
		3818
		3819	// main loop
		3820	int exit_main_loop = 0;
		3821
		3822	while (!exit_main_loop)
		3823	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3824
		3825	// in a modal watcher
		3826	int exit_nested_loop = 0;
		3827
		3828	while (!exit_nested_loop)
		3829	ev_run (EV_A_ EVRUN_ONCE);
		3830
		3831	To exit from any of these loops, just set the corresponding exit variable:
		3832
		3833	// exit modal loop
		3834	exit_nested_loop = 1;
		3835
		3836	// exit main program, after modal loop is finished
		3837	exit_main_loop = 1;
		3838
		3839	// exit both
		3840	exit_main_loop = exit_nested_loop = 1;
		3841
		3842	=head2 THREAD LOCKING EXAMPLE
		3843
		3844	Here is a fictitious example of how to run an event loop in a different
		3845	thread from where callbacks are being invoked and watchers are
		3846	created/added/removed.
		3847
		3848	For a real-world example, see the C<EV::Loop::Async> perl module,
		3849	which uses exactly this technique (which is suited for many high-level
		3850	languages).
		3851
		3852	The example uses a pthread mutex to protect the loop data, a condition
		3853	variable to wait for callback invocations, an async watcher to notify the
		3854	event loop thread and an unspecified mechanism to wake up the main thread.
		3855
		3856	First, you need to associate some data with the event loop:
		3857
		3858	typedef struct {
		3859	mutex_t lock; /* global loop lock */
		3860	ev_async async_w;
		3861	thread_t tid;
		3862	cond_t invoke_cv;
		3863	} userdata;
		3864
		3865	void prepare_loop (EV_P)
		3866	{
		3867	// for simplicity, we use a static userdata struct.
		3868	static userdata u;
		3869
		3870	ev_async_init (&u->async_w, async_cb);
		3871	ev_async_start (EV_A_ &u->async_w);
		3872
		3873	pthread_mutex_init (&u->lock, 0);
		3874	pthread_cond_init (&u->invoke_cv, 0);
		3875
		3876	// now associate this with the loop
		3877	ev_set_userdata (EV_A_ u);
		3878	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3879	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3880
		3881	// then create the thread running ev_run
		3882	pthread_create (&u->tid, 0, l_run, EV_A);
		3883	}
		3884
		3885	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3886	solely to wake up the event loop so it takes notice of any new watchers
		3887	that might have been added:
		3888
		3889	static void
		3890	async_cb (EV_P_ ev_async *w, int revents)
		3891	{
		3892	// just used for the side effects
		3893	}
		3894
		3895	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3896	protecting the loop data, respectively.
		3897
		3898	static void
		3899	l_release (EV_P)
		3900	{
		3901	userdata *u = ev_userdata (EV_A);
		3902	pthread_mutex_unlock (&u->lock);
		3903	}
		3904
		3905	static void
		3906	l_acquire (EV_P)
		3907	{
		3908	userdata *u = ev_userdata (EV_A);
		3909	pthread_mutex_lock (&u->lock);
		3910	}
		3911
		3912	The event loop thread first acquires the mutex, and then jumps straight
		3913	into C<ev_run>:
		3914
		3915	void *
		3916	l_run (void *thr_arg)
		3917	{
		3918	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3919
		3920	l_acquire (EV_A);
		3921	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3922	ev_run (EV_A_ 0);
		3923	l_release (EV_A);
		3924
		3925	return 0;
		3926	}
		3927
		3928	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3929	signal the main thread via some unspecified mechanism (signals? pipe
		3930	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3931	have been called (in a while loop because a) spurious wakeups are possible
		3932	and b) skipping inter-thread-communication when there are no pending
		3933	watchers is very beneficial):
		3934
		3935	static void
		3936	l_invoke (EV_P)
		3937	{
		3938	userdata *u = ev_userdata (EV_A);
		3939
		3940	while (ev_pending_count (EV_A))
		3941	{
		3942	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3943	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3944	}
		3945	}
		3946
		3947	Now, whenever the main thread gets told to invoke pending watchers, it
		3948	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3949	thread to continue:
		3950
		3951	static void
		3952	real_invoke_pending (EV_P)
		3953	{
		3954	userdata *u = ev_userdata (EV_A);
		3955
		3956	pthread_mutex_lock (&u->lock);
		3957	ev_invoke_pending (EV_A);
		3958	pthread_cond_signal (&u->invoke_cv);
		3959	pthread_mutex_unlock (&u->lock);
		3960	}
		3961
		3962	Whenever you want to start/stop a watcher or do other modifications to an
		3963	event loop, you will now have to lock:
		3964
		3965	ev_timer timeout_watcher;
		3966	userdata *u = ev_userdata (EV_A);
		3967
		3968	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3969
		3970	pthread_mutex_lock (&u->lock);
		3971	ev_timer_start (EV_A_ &timeout_watcher);
		3972	ev_async_send (EV_A_ &u->async_w);
		3973	pthread_mutex_unlock (&u->lock);
		3974
		3975	Note that sending the C<ev_async> watcher is required because otherwise
		3976	an event loop currently blocking in the kernel will have no knowledge
		3977	about the newly added timer. By waking up the loop it will pick up any new
		3978	watchers in the next event loop iteration.
		3979
		3980	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3981
		3982	While the overhead of a callback that e.g. schedules a thread is small, it
		3983	is still an overhead. If you embed libev, and your main usage is with some
		3984	kind of threads or coroutines, you might want to customise libev so that
		3985	doesn't need callbacks anymore.
		3986
		3987	Imagine you have coroutines that you can switch to using a function
		3988	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3989	and that due to some magic, the currently active coroutine is stored in a
		3990	global called C<current_coro>. Then you can build your own "wait for libev
		3991	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3992	the differing C<;> conventions):
		3993
		3994	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3995	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3996
		3997	That means instead of having a C callback function, you store the
		3998	coroutine to switch to in each watcher, and instead of having libev call
		3999	your callback, you instead have it switch to that coroutine.
		4000
		4001	A coroutine might now wait for an event with a function called
		4002	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		4003	matter when, or whether the watcher is active or not when this function is
		4004	called):
		4005
		4006	void
		4007	wait_for_event (ev_watcher *w)
		4008	{
		4009	ev_set_cb (w, current_coro);
		4010	switch_to (libev_coro);
		4011	}
		4012
		4013	That basically suspends the coroutine inside C<wait_for_event> and
		4014	continues the libev coroutine, which, when appropriate, switches back to
		4015	this or any other coroutine.
		4016
		4017	You can do similar tricks if you have, say, threads with an event queue -
		4018	instead of storing a coroutine, you store the queue object and instead of
		4019	switching to a coroutine, you push the watcher onto the queue and notify
		4020	any waiters.
		4021
		4022	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		4023	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		4024
		4025	// my_ev.h
		4026	#define EV_CB_DECLARE(type) struct my_coro *cb;
		4027	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		4028	#include "../libev/ev.h"
		4029
		4030	// my_ev.c
		4031	#define EV_H "my_ev.h"
		4032	#include "../libev/ev.c"
		4033
		4034	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		4035	F<my_ev.c> into your project. When properly specifying include paths, you
		4036	can even use F<ev.h> as header file name directly.
3352		4037
3353		4038
3354	=head1 LIBEVENT EMULATION	4039	=head1 LIBEVENT EMULATION
3355		4040
3356	Libev offers a compatibility emulation layer for libevent. It cannot	4041	Libev offers a compatibility emulation layer for libevent. It cannot
3357	emulate the internals of libevent, so here are some usage hints:	4042	emulate the internals of libevent, so here are some usage hints:
3358		4043
3359	=over 4	4044	=over 4
		4045
		4046	=item * Only the libevent-1.4.1-beta API is being emulated.
		4047
		4048	This was the newest libevent version available when libev was implemented,
		4049	and is still mostly unchanged in 2010.
3360		4050
3361	=item * Use it by including <event.h>, as usual.	4051	=item * Use it by including <event.h>, as usual.
3362		4052
3363	=item * The following members are fully supported: ev_base, ev_callback,	4053	=item * The following members are fully supported: ev_base, ev_callback,
3364	ev_arg, ev_fd, ev_res, ev_events.	4054	ev_arg, ev_fd, ev_res, ev_events.
…		…
3370	=item * Priorities are not currently supported. Initialising priorities	4060	=item * Priorities are not currently supported. Initialising priorities
3371	will fail and all watchers will have the same priority, even though there	4061	will fail and all watchers will have the same priority, even though there
3372	is an ev_pri field.	4062	is an ev_pri field.
3373		4063
3374	=item * In libevent, the last base created gets the signals, in libev, the	4064	=item * In libevent, the last base created gets the signals, in libev, the
3375	first base created (== the default loop) gets the signals.	4065	base that registered the signal gets the signals.
3376		4066
3377	=item * Other members are not supported.	4067	=item * Other members are not supported.
3378		4068
3379	=item * The libev emulation is I<not> ABI compatible to libevent, you need	4069	=item * The libev emulation is I<not> ABI compatible to libevent, you need
3380	to use the libev header file and library.	4070	to use the libev header file and library.
3381		4071
3382	=back	4072	=back
3383		4073
3384	=head1 C++ SUPPORT	4074	=head1 C++ SUPPORT
		4075
		4076	=head2 C API
		4077
		4078	The normal C API should work fine when used from C++: both ev.h and the
		4079	libev sources can be compiled as C++. Therefore, code that uses the C API
		4080	will work fine.
		4081
		4082	Proper exception specifications might have to be added to callbacks passed
		4083	to libev: exceptions may be thrown only from watcher callbacks, all other
		4084	callbacks (allocator, syserr, loop acquire/release and periodic reschedule
		4085	callbacks) must not throw exceptions, and might need a C<noexcept>
		4086	specification. If you have code that needs to be compiled as both C and
		4087	C++ you can use the C<EV_NOEXCEPT> macro for this:
		4088
		4089	static void
		4090	fatal_error (const char *msg) EV_NOEXCEPT
		4091	{
		4092	perror (msg);
		4093	abort ();
		4094	}
		4095
		4096	...
		4097	ev_set_syserr_cb (fatal_error);
		4098
		4099	The only API functions that can currently throw exceptions are C<ev_run>,
		4100	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		4101	because it runs cleanup watchers).
		4102
		4103	Throwing exceptions in watcher callbacks is only supported if libev itself
		4104	is compiled with a C++ compiler or your C and C++ environments allow
		4105	throwing exceptions through C libraries (most do).
		4106
		4107	=head2 C++ API
3385		4108
3386	Libev comes with some simplistic wrapper classes for C++ that mainly allow	4109	Libev comes with some simplistic wrapper classes for C++ that mainly allow
3387	you to use some convenience methods to start/stop watchers and also change	4110	you to use some convenience methods to start/stop watchers and also change
3388	the callback model to a model using method callbacks on objects.	4111	the callback model to a model using method callbacks on objects.
3389		4112
3390	To use it,	4113	To use it,
3391		4114
3392	#include <ev++.h>	4115	#include <ev++.h>
3393		4116
3394	This automatically includes F<ev.h> and puts all of its definitions (many	4117	This automatically includes F<ev.h> and puts all of its definitions (many
3395	of them macros) into the global namespace. All C++ specific things are	4118	of them macros) into the global namespace. All C++ specific things are
3396	put into the C<ev> namespace. It should support all the same embedding	4119	put into the C<ev> namespace. It should support all the same embedding
…		…
3399	Care has been taken to keep the overhead low. The only data member the C++	4122	Care has been taken to keep the overhead low. The only data member the C++
3400	classes add (compared to plain C-style watchers) is the event loop pointer	4123	classes add (compared to plain C-style watchers) is the event loop pointer
3401	that the watcher is associated with (or no additional members at all if	4124	that the watcher is associated with (or no additional members at all if
3402	you disable C<EV_MULTIPLICITY> when embedding libev).	4125	you disable C<EV_MULTIPLICITY> when embedding libev).
3403		4126
3404	Currently, functions, and static and non-static member functions can be	4127	Currently, functions, static and non-static member functions and classes
3405	used as callbacks. Other types should be easy to add as long as they only	4128	with C<operator ()> can be used as callbacks. Other types should be easy
3406	need one additional pointer for context. If you need support for other	4129	to add as long as they only need one additional pointer for context. If
3407	types of functors please contact the author (preferably after implementing	4130	you need support for other types of functors please contact the author
3408	it).	4131	(preferably after implementing it).
		4132
		4133	For all this to work, your C++ compiler either has to use the same calling
		4134	conventions as your C compiler (for static member functions), or you have
		4135	to embed libev and compile libev itself as C++.
3409		4136
3410	Here is a list of things available in the C<ev> namespace:	4137	Here is a list of things available in the C<ev> namespace:
3411		4138
3412	=over 4	4139	=over 4
3413		4140
…		…
3423	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4150	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
3424		4151
3425	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4152	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
3426	the same name in the C<ev> namespace, with the exception of C<ev_signal>	4153	the same name in the C<ev> namespace, with the exception of C<ev_signal>
3427	which is called C<ev::sig> to avoid clashes with the C<signal> macro	4154	which is called C<ev::sig> to avoid clashes with the C<signal> macro
3428	defines by many implementations.	4155	defined by many implementations.
3429		4156
3430	All of those classes have these methods:	4157	All of those classes have these methods:
3431		4158
3432	=over 4	4159	=over 4
3433		4160
…		…
3495	void operator() (ev::io &w, int revents)	4222	void operator() (ev::io &w, int revents)
3496	{	4223	{
3497	...	4224	...
3498	}	4225	}
3499	}	4226	}
3500		4227
3501	myfunctor f;	4228	myfunctor f;
3502		4229
3503	ev::io w;	4230	ev::io w;
3504	w.set (&f);	4231	w.set (&f);
3505		4232
…		…
3523	Associates a different C<struct ev_loop> with this watcher. You can only	4250	Associates a different C<struct ev_loop> with this watcher. You can only
3524	do this when the watcher is inactive (and not pending either).	4251	do this when the watcher is inactive (and not pending either).
3525		4252
3526	=item w->set ([arguments])	4253	=item w->set ([arguments])
3527		4254
3528	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this	4255	Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
3529	method or a suitable start method must be called at least once. Unlike the	4256	with the same arguments. Either this method or a suitable start method
3530	C counterpart, an active watcher gets automatically stopped and restarted	4257	must be called at least once. Unlike the C counterpart, an active watcher
3531	when reconfiguring it with this method.	4258	gets automatically stopped and restarted when reconfiguring it with this
		4259	method.
		4260
		4261	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4262	clashing with the C<set (loop)> method.
3532		4263
3533	=item w->start ()	4264	=item w->start ()
3534		4265
3535	Starts the watcher. Note that there is no C<loop> argument, as the	4266	Starts the watcher. Note that there is no C<loop> argument, as the
3536	constructor already stores the event loop.	4267	constructor already stores the event loop.
…		…
3566	watchers in the constructor.	4297	watchers in the constructor.
3567		4298
3568	class myclass	4299	class myclass
3569	{	4300	{
3570	ev::io io ; void io_cb (ev::io &w, int revents);	4301	ev::io io ; void io_cb (ev::io &w, int revents);
3571	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);	4302	ev::io io2 ; void io2_cb (ev::io &w, int revents);
3572	ev::idle idle; void idle_cb (ev::idle &w, int revents);	4303	ev::idle idle; void idle_cb (ev::idle &w, int revents);
3573		4304
3574	myclass (int fd)	4305	myclass (int fd)
3575	{	4306	{
3576	io .set <myclass, &myclass::io_cb > (this);	4307	io .set <myclass, &myclass::io_cb > (this);
…		…
3627	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.	4358	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3628		4359
3629	=item D	4360	=item D
3630		4361
3631	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4362	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
3632	be found at L<http://proj.llucax.com.ar/wiki/evd>.	4363	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
3633		4364
3634	=item Ocaml	4365	=item Ocaml
3635		4366
3636	Erkki Seppala has written Ocaml bindings for libev, to be found at	4367	Erkki Seppala has written Ocaml bindings for libev, to be found at
3637	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	4368	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
…		…
3640		4371
3641	Brian Maher has written a partial interface to libev for lua (at the	4372	Brian Maher has written a partial interface to libev for lua (at the
3642	time of this writing, only C<ev_io> and C<ev_timer>), to be found at	4373	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
3643	L<http://github.com/brimworks/lua-ev>.	4374	L<http://github.com/brimworks/lua-ev>.
3644		4375
		4376	=item Javascript
		4377
		4378	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4379
		4380	=item Others
		4381
		4382	There are others, and I stopped counting.
		4383
3645	=back	4384	=back
3646		4385
3647		4386
3648	=head1 MACRO MAGIC	4387	=head1 MACRO MAGIC
3649		4388
…		…
3685	suitable for use with C<EV_A>.	4424	suitable for use with C<EV_A>.
3686		4425
3687	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4426	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
3688		4427
3689	Similar to the other two macros, this gives you the value of the default	4428	Similar to the other two macros, this gives you the value of the default
3690	loop, if multiple loops are supported ("ev loop default").	4429	loop, if multiple loops are supported ("ev loop default"). The default loop
		4430	will be initialised if it isn't already initialised.
		4431
		4432	For non-multiplicity builds, these macros do nothing, so you always have
		4433	to initialise the loop somewhere.
3691		4434
3692	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4435	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
3693		4436
3694	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4437	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
3695	default loop has been initialised (C<UC> == unchecked). Their behaviour	4438	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
3762	ev_vars.h	4505	ev_vars.h
3763	ev_wrap.h	4506	ev_wrap.h
3764		4507
3765	ev_win32.c required on win32 platforms only	4508	ev_win32.c required on win32 platforms only
3766		4509
3767	ev_select.c only when select backend is enabled (which is enabled by default)	4510	ev_select.c only when select backend is enabled
3768	ev_poll.c only when poll backend is enabled (disabled by default)	4511	ev_poll.c only when poll backend is enabled
3769	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4512	ev_epoll.c only when the epoll backend is enabled
		4513	ev_linuxaio.c only when the linux aio backend is enabled
		4514	ev_iouring.c only when the linux io_uring backend is enabled
3770	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4515	ev_kqueue.c only when the kqueue backend is enabled
3771	ev_port.c only when the solaris port backend is enabled (disabled by default)	4516	ev_port.c only when the solaris port backend is enabled
3772		4517
3773	F<ev.c> includes the backend files directly when enabled, so you only need	4518	F<ev.c> includes the backend files directly when enabled, so you only need
3774	to compile this single file.	4519	to compile this single file.
3775		4520
3776	=head3 LIBEVENT COMPATIBILITY API	4521	=head3 LIBEVENT COMPATIBILITY API
…		…
3840	supported). It will also not define any of the structs usually found in	4585	supported). It will also not define any of the structs usually found in
3841	F<event.h> that are not directly supported by the libev core alone.	4586	F<event.h> that are not directly supported by the libev core alone.
3842		4587
3843	In standalone mode, libev will still try to automatically deduce the	4588	In standalone mode, libev will still try to automatically deduce the
3844	configuration, but has to be more conservative.	4589	configuration, but has to be more conservative.
		4590
		4591	=item EV_USE_FLOOR
		4592
		4593	If defined to be C<1>, libev will use the C<floor ()> function for its
		4594	periodic reschedule calculations, otherwise libev will fall back on a
		4595	portable (slower) implementation. If you enable this, you usually have to
		4596	link against libm or something equivalent. Enabling this when the C<floor>
		4597	function is not available will fail, so the safe default is to not enable
		4598	this.
3845		4599
3846	=item EV_USE_MONOTONIC	4600	=item EV_USE_MONOTONIC
3847		4601
3848	If defined to be C<1>, libev will try to detect the availability of the	4602	If defined to be C<1>, libev will try to detect the availability of the
3849	monotonic clock option at both compile time and runtime. Otherwise no	4603	monotonic clock option at both compile time and runtime. Otherwise no
…		…
3886	available and will probe for kernel support at runtime. This will improve	4640	available and will probe for kernel support at runtime. This will improve
3887	C<ev_signal> and C<ev_async> performance and reduce resource consumption.	4641	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
3888	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc	4642	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
3889	2.7 or newer, otherwise disabled.	4643	2.7 or newer, otherwise disabled.
3890		4644
		4645	=item EV_USE_SIGNALFD
		4646
		4647	If defined to be C<1>, then libev will assume that C<signalfd ()> is
		4648	available and will probe for kernel support at runtime. This enables
		4649	the use of EVFLAG_SIGNALFD for faster and simpler signal handling. If
		4650	undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4651	2.7 or newer, otherwise disabled.
		4652
		4653	=item EV_USE_TIMERFD
		4654
		4655	If defined to be C<1>, then libev will assume that C<timerfd ()> is
		4656	available and will probe for kernel support at runtime. This allows
		4657	libev to detect time jumps accurately. If undefined, it will be enabled
		4658	if the headers indicate GNU/Linux + Glibc 2.8 or newer and define
		4659	C<TFD_TIMER_CANCEL_ON_SET>, otherwise disabled.
		4660
		4661	=item EV_USE_EVENTFD
		4662
		4663	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		4664	available and will probe for kernel support at runtime. This will improve
		4665	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		4666	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4667	2.7 or newer, otherwise disabled.
		4668
3891	=item EV_USE_SELECT	4669	=item EV_USE_SELECT
3892		4670
3893	If undefined or defined to be C<1>, libev will compile in support for the	4671	If undefined or defined to be C<1>, libev will compile in support for the
3894	C<select>(2) backend. No attempt at auto-detection will be done: if no	4672	C<select>(2) backend. No attempt at auto-detection will be done: if no
3895	other method takes over, select will be it. Otherwise the select backend	4673	other method takes over, select will be it. Otherwise the select backend
…		…
3935	If programs implement their own fd to handle mapping on win32, then this	4713	If programs implement their own fd to handle mapping on win32, then this
3936	macro can be used to override the C<close> function, useful to unregister	4714	macro can be used to override the C<close> function, useful to unregister
3937	file descriptors again. Note that the replacement function has to close	4715	file descriptors again. Note that the replacement function has to close
3938	the underlying OS handle.	4716	the underlying OS handle.
3939		4717
		4718	=item EV_USE_WSASOCKET
		4719
		4720	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4721	communication socket, which works better in some environments. Otherwise,
		4722	the normal C<socket> function will be used, which works better in other
		4723	environments.
		4724
3940	=item EV_USE_POLL	4725	=item EV_USE_POLL
3941		4726
3942	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4727	If defined to be C<1>, libev will compile in support for the C<poll>(2)
3943	backend. Otherwise it will be enabled on non-win32 platforms. It	4728	backend. Otherwise it will be enabled on non-win32 platforms. It
3944	takes precedence over select.	4729	takes precedence over select.
…		…
3948	If defined to be C<1>, libev will compile in support for the Linux	4733	If defined to be C<1>, libev will compile in support for the Linux
3949	C<epoll>(7) backend. Its availability will be detected at runtime,	4734	C<epoll>(7) backend. Its availability will be detected at runtime,
3950	otherwise another method will be used as fallback. This is the preferred	4735	otherwise another method will be used as fallback. This is the preferred
3951	backend for GNU/Linux systems. If undefined, it will be enabled if the	4736	backend for GNU/Linux systems. If undefined, it will be enabled if the
3952	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4737	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4738
		4739	=item EV_USE_LINUXAIO
		4740
		4741	If defined to be C<1>, libev will compile in support for the Linux aio
		4742	backend (C<EV_USE_EPOLL> must also be enabled). If undefined, it will be
		4743	enabled on linux, otherwise disabled.
		4744
		4745	=item EV_USE_IOURING
		4746
		4747	If defined to be C<1>, libev will compile in support for the Linux
		4748	io_uring backend (C<EV_USE_EPOLL> must also be enabled). Due to it's
		4749	current limitations it has to be requested explicitly. If undefined, it
		4750	will be enabled on linux, otherwise disabled.
3953		4751
3954	=item EV_USE_KQUEUE	4752	=item EV_USE_KQUEUE
3955		4753
3956	If defined to be C<1>, libev will compile in support for the BSD style	4754	If defined to be C<1>, libev will compile in support for the BSD style
3957	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	4755	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
3979	If defined to be C<1>, libev will compile in support for the Linux inotify	4777	If defined to be C<1>, libev will compile in support for the Linux inotify
3980	interface to speed up C<ev_stat> watchers. Its actual availability will	4778	interface to speed up C<ev_stat> watchers. Its actual availability will
3981	be detected at runtime. If undefined, it will be enabled if the headers	4779	be detected at runtime. If undefined, it will be enabled if the headers
3982	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4780	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
3983		4781
		4782	=item EV_NO_SMP
		4783
		4784	If defined to be C<1>, libev will assume that memory is always coherent
		4785	between threads, that is, threads can be used, but threads never run on
		4786	different cpus (or different cpu cores). This reduces dependencies
		4787	and makes libev faster.
		4788
		4789	=item EV_NO_THREADS
		4790
		4791	If defined to be C<1>, libev will assume that it will never be called from
		4792	different threads (that includes signal handlers), which is a stronger
		4793	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4794	libev faster.
		4795
3984	=item EV_ATOMIC_T	4796	=item EV_ATOMIC_T
3985		4797
3986	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4798	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
3987	access is atomic with respect to other threads or signal contexts. No such	4799	access is atomic with respect to other threads or signal contexts. No
3988	type is easily found in the C language, so you can provide your own type	4800	such type is easily found in the C language, so you can provide your own
3989	that you know is safe for your purposes. It is used both for signal handler "locking"	4801	type that you know is safe for your purposes. It is used both for signal
3990	as well as for signal and thread safety in C<ev_async> watchers.	4802	handler "locking" as well as for signal and thread safety in C<ev_async>
		4803	watchers.
3991		4804
3992	In the absence of this define, libev will use C<sig_atomic_t volatile>	4805	In the absence of this define, libev will use C<sig_atomic_t volatile>
3993	(from F<signal.h>), which is usually good enough on most platforms.	4806	(from F<signal.h>), which is usually good enough on most platforms.
3994		4807
3995	=item EV_H (h)	4808	=item EV_H (h)
…		…
4022	will have the C<struct ev_loop *> as first argument, and you can create	4835	will have the C<struct ev_loop *> as first argument, and you can create
4023	additional independent event loops. Otherwise there will be no support	4836	additional independent event loops. Otherwise there will be no support
4024	for multiple event loops and there is no first event loop pointer	4837	for multiple event loops and there is no first event loop pointer
4025	argument. Instead, all functions act on the single default loop.	4838	argument. Instead, all functions act on the single default loop.
4026		4839
		4840	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4841	default loop when multiplicity is switched off - you always have to
		4842	initialise the loop manually in this case.
		4843
4027	=item EV_MINPRI	4844	=item EV_MINPRI
4028		4845
4029	=item EV_MAXPRI	4846	=item EV_MAXPRI
4030		4847
4031	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4848	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
4067	#define EV_USE_POLL 1	4884	#define EV_USE_POLL 1
4068	#define EV_CHILD_ENABLE 1	4885	#define EV_CHILD_ENABLE 1
4069	#define EV_ASYNC_ENABLE 1	4886	#define EV_ASYNC_ENABLE 1
4070		4887
4071	The actual value is a bitset, it can be a combination of the following	4888	The actual value is a bitset, it can be a combination of the following
4072	values:	4889	values (by default, all of these are enabled):
4073		4890
4074	=over 4	4891	=over 4
4075		4892
4076	=item C<1> - faster/larger code	4893	=item C<1> - faster/larger code
4077		4894
…		…
4081	code size by roughly 30% on amd64).	4898	code size by roughly 30% on amd64).
4082		4899
4083	When optimising for size, use of compiler flags such as C<-Os> with	4900	When optimising for size, use of compiler flags such as C<-Os> with
4084	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of	4901	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
4085	assertions.	4902	assertions.
		4903
		4904	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4905	(e.g. gcc with C<-Os>).
4086		4906
4087	=item C<2> - faster/larger data structures	4907	=item C<2> - faster/larger data structures
4088		4908
4089	Replaces the small 2-heap for timer management by a faster 4-heap, larger	4909	Replaces the small 2-heap for timer management by a faster 4-heap, larger
4090	hash table sizes and so on. This will usually further increase code size	4910	hash table sizes and so on. This will usually further increase code size
4091	and can additionally have an effect on the size of data structures at	4911	and can additionally have an effect on the size of data structures at
4092	runtime.	4912	runtime.
4093		4913
		4914	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4915	(e.g. gcc with C<-Os>).
		4916
4094	=item C<4> - full API configuration	4917	=item C<4> - full API configuration
4095		4918
4096	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and	4919	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
4097	enables multiplicity (C<EV_MULTIPLICITY>=1).	4920	enables multiplicity (C<EV_MULTIPLICITY>=1).
4098		4921
…		…
4128		4951
4129	With an intelligent-enough linker (gcc+binutils are intelligent enough	4952	With an intelligent-enough linker (gcc+binutils are intelligent enough
4130	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by	4953	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
4131	your program might be left out as well - a binary starting a timer and an	4954	your program might be left out as well - a binary starting a timer and an
4132	I/O watcher then might come out at only 5Kb.	4955	I/O watcher then might come out at only 5Kb.
		4956
		4957	=item EV_API_STATIC
		4958
		4959	If this symbol is defined (by default it is not), then all identifiers
		4960	will have static linkage. This means that libev will not export any
		4961	identifiers, and you cannot link against libev anymore. This can be useful
		4962	when you embed libev, only want to use libev functions in a single file,
		4963	and do not want its identifiers to be visible.
		4964
		4965	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4966	wants to use libev.
		4967
		4968	This option only works when libev is compiled with a C compiler, as C++
		4969	doesn't support the required declaration syntax.
4133		4970
4134	=item EV_AVOID_STDIO	4971	=item EV_AVOID_STDIO
4135		4972
4136	If this is set to C<1> at compiletime, then libev will avoid using stdio	4973	If this is set to C<1> at compiletime, then libev will avoid using stdio
4137	functions (printf, scanf, perror etc.). This will increase the code size	4974	functions (printf, scanf, perror etc.). This will increase the code size
…		…
4195	in. If set to C<1>, then verification code will be compiled in, but not	5032	in. If set to C<1>, then verification code will be compiled in, but not
4196	called. If set to C<2>, then the internal verification code will be	5033	called. If set to C<2>, then the internal verification code will be
4197	called once per loop, which can slow down libev. If set to C<3>, then the	5034	called once per loop, which can slow down libev. If set to C<3>, then the
4198	verification code will be called very frequently, which will slow down	5035	verification code will be called very frequently, which will slow down
4199	libev considerably.	5036	libev considerably.
		5037
		5038	Verification errors are reported via C's C<assert> mechanism, so if you
		5039	disable that (e.g. by defining C<NDEBUG>) then no errors will be reported.
4200		5040
4201	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it	5041	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
4202	will be C<0>.	5042	will be C<0>.
4203		5043
4204	=item EV_COMMON	5044	=item EV_COMMON
…		…
4281	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	5121	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4282		5122
4283	#include "ev_cpp.h"	5123	#include "ev_cpp.h"
4284	#include "ev.c"	5124	#include "ev.c"
4285		5125
4286	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	5126	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4287		5127
4288	=head2 THREADS AND COROUTINES	5128	=head2 THREADS AND COROUTINES
4289		5129
4290	=head3 THREADS	5130	=head3 THREADS
4291		5131
…		…
4342	default loop and triggering an C<ev_async> watcher from the default loop	5182	default loop and triggering an C<ev_async> watcher from the default loop
4343	watcher callback into the event loop interested in the signal.	5183	watcher callback into the event loop interested in the signal.
4344		5184
4345	=back	5185	=back
4346		5186
4347	=head4 THREAD LOCKING EXAMPLE	5187	See also L</THREAD LOCKING EXAMPLE>.
4348
4349	Here is a fictitious example of how to run an event loop in a different
4350	thread than where callbacks are being invoked and watchers are
4351	created/added/removed.
4352
4353	For a real-world example, see the C<EV::Loop::Async> perl module,
4354	which uses exactly this technique (which is suited for many high-level
4355	languages).
4356
4357	The example uses a pthread mutex to protect the loop data, a condition
4358	variable to wait for callback invocations, an async watcher to notify the
4359	event loop thread and an unspecified mechanism to wake up the main thread.
4360
4361	First, you need to associate some data with the event loop:
4362
4363	typedef struct {
4364	mutex_t lock; /* global loop lock */
4365	ev_async async_w;
4366	thread_t tid;
4367	cond_t invoke_cv;
4368	} userdata;
4369
4370	void prepare_loop (EV_P)
4371	{
4372	// for simplicity, we use a static userdata struct.
4373	static userdata u;
4374
4375	ev_async_init (&u->async_w, async_cb);
4376	ev_async_start (EV_A_ &u->async_w);
4377
4378	pthread_mutex_init (&u->lock, 0);
4379	pthread_cond_init (&u->invoke_cv, 0);
4380
4381	// now associate this with the loop
4382	ev_set_userdata (EV_A_ u);
4383	ev_set_invoke_pending_cb (EV_A_ l_invoke);
4384	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4385
4386	// then create the thread running ev_loop
4387	pthread_create (&u->tid, 0, l_run, EV_A);
4388	}
4389
4390	The callback for the C<ev_async> watcher does nothing: the watcher is used
4391	solely to wake up the event loop so it takes notice of any new watchers
4392	that might have been added:
4393
4394	static void
4395	async_cb (EV_P_ ev_async *w, int revents)
4396	{
4397	// just used for the side effects
4398	}
4399
4400	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
4401	protecting the loop data, respectively.
4402
4403	static void
4404	l_release (EV_P)
4405	{
4406	userdata *u = ev_userdata (EV_A);
4407	pthread_mutex_unlock (&u->lock);
4408	}
4409
4410	static void
4411	l_acquire (EV_P)
4412	{
4413	userdata *u = ev_userdata (EV_A);
4414	pthread_mutex_lock (&u->lock);
4415	}
4416
4417	The event loop thread first acquires the mutex, and then jumps straight
4418	into C<ev_run>:
4419
4420	void *
4421	l_run (void *thr_arg)
4422	{
4423	struct ev_loop *loop = (struct ev_loop *)thr_arg;
4424
4425	l_acquire (EV_A);
4426	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4427	ev_run (EV_A_ 0);
4428	l_release (EV_A);
4429
4430	return 0;
4431	}
4432
4433	Instead of invoking all pending watchers, the C<l_invoke> callback will
4434	signal the main thread via some unspecified mechanism (signals? pipe
4435	writes? C<Async::Interrupt>?) and then waits until all pending watchers
4436	have been called (in a while loop because a) spurious wakeups are possible
4437	and b) skipping inter-thread-communication when there are no pending
4438	watchers is very beneficial):
4439
4440	static void
4441	l_invoke (EV_P)
4442	{
4443	userdata *u = ev_userdata (EV_A);
4444
4445	while (ev_pending_count (EV_A))
4446	{
4447	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4448	pthread_cond_wait (&u->invoke_cv, &u->lock);
4449	}
4450	}
4451
4452	Now, whenever the main thread gets told to invoke pending watchers, it
4453	will grab the lock, call C<ev_invoke_pending> and then signal the loop
4454	thread to continue:
4455
4456	static void
4457	real_invoke_pending (EV_P)
4458	{
4459	userdata *u = ev_userdata (EV_A);
4460
4461	pthread_mutex_lock (&u->lock);
4462	ev_invoke_pending (EV_A);
4463	pthread_cond_signal (&u->invoke_cv);
4464	pthread_mutex_unlock (&u->lock);
4465	}
4466
4467	Whenever you want to start/stop a watcher or do other modifications to an
4468	event loop, you will now have to lock:
4469
4470	ev_timer timeout_watcher;
4471	userdata *u = ev_userdata (EV_A);
4472
4473	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4474
4475	pthread_mutex_lock (&u->lock);
4476	ev_timer_start (EV_A_ &timeout_watcher);
4477	ev_async_send (EV_A_ &u->async_w);
4478	pthread_mutex_unlock (&u->lock);
4479
4480	Note that sending the C<ev_async> watcher is required because otherwise
4481	an event loop currently blocking in the kernel will have no knowledge
4482	about the newly added timer. By waking up the loop it will pick up any new
4483	watchers in the next event loop iteration.
4484		5188
4485	=head3 COROUTINES	5189	=head3 COROUTINES
4486		5190
4487	Libev is very accommodating to coroutines ("cooperative threads"):	5191	Libev is very accommodating to coroutines ("cooperative threads"):
4488	libev fully supports nesting calls to its functions from different	5192	libev fully supports nesting calls to its functions from different
…		…
4653	requires, and its I/O model is fundamentally incompatible with the POSIX	5357	requires, and its I/O model is fundamentally incompatible with the POSIX
4654	model. Libev still offers limited functionality on this platform in	5358	model. Libev still offers limited functionality on this platform in
4655	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5359	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
4656	descriptors. This only applies when using Win32 natively, not when using	5360	descriptors. This only applies when using Win32 natively, not when using
4657	e.g. cygwin. Actually, it only applies to the microsofts own compilers,	5361	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4658	as every compielr comes with a slightly differently broken/incompatible	5362	as every compiler comes with a slightly differently broken/incompatible
4659	environment.	5363	environment.
4660		5364
4661	Lifting these limitations would basically require the full	5365	Lifting these limitations would basically require the full
4662	re-implementation of the I/O system. If you are into this kind of thing,	5366	re-implementation of the I/O system. If you are into this kind of thing,
4663	then note that glib does exactly that for you in a very portable way (note	5367	then note that glib does exactly that for you in a very portable way (note
…		…
4757	structure (guaranteed by POSIX but not by ISO C for example), but it also	5461	structure (guaranteed by POSIX but not by ISO C for example), but it also
4758	assumes that the same (machine) code can be used to call any watcher	5462	assumes that the same (machine) code can be used to call any watcher
4759	callback: The watcher callbacks have different type signatures, but libev	5463	callback: The watcher callbacks have different type signatures, but libev
4760	calls them using an C<ev_watcher *> internally.	5464	calls them using an C<ev_watcher *> internally.
4761		5465
		5466	=item null pointers and integer zero are represented by 0 bytes
		5467
		5468	Libev uses C<memset> to initialise structs and arrays to C<0> bytes, and
		5469	relies on this setting pointers and integers to null.
		5470
		5471	=item pointer accesses must be thread-atomic
		5472
		5473	Accessing a pointer value must be atomic, it must both be readable and
		5474	writable in one piece - this is the case on all current architectures.
		5475
4762	=item C<sig_atomic_t volatile> must be thread-atomic as well	5476	=item C<sig_atomic_t volatile> must be thread-atomic as well
4763		5477
4764	The type C<sig_atomic_t volatile> (or whatever is defined as	5478	The type C<sig_atomic_t volatile> (or whatever is defined as
4765	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different	5479	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
4766	threads. This is not part of the specification for C<sig_atomic_t>, but is	5480	threads. This is not part of the specification for C<sig_atomic_t>, but is
…		…
4774	thread" or will block signals process-wide, both behaviours would	5488	thread" or will block signals process-wide, both behaviours would
4775	be compatible with libev. Interaction between C<sigprocmask> and	5489	be compatible with libev. Interaction between C<sigprocmask> and
4776	C<pthread_sigmask> could complicate things, however.	5490	C<pthread_sigmask> could complicate things, however.
4777		5491
4778	The most portable way to handle signals is to block signals in all threads	5492	The most portable way to handle signals is to block signals in all threads
4779	except the initial one, and run the default loop in the initial thread as	5493	except the initial one, and run the signal handling loop in the initial
4780	well.	5494	thread as well.
4781		5495
4782	=item C<long> must be large enough for common memory allocation sizes	5496	=item C<long> must be large enough for common memory allocation sizes
4783		5497
4784	To improve portability and simplify its API, libev uses C<long> internally	5498	To improve portability and simplify its API, libev uses C<long> internally
4785	instead of C<size_t> when allocating its data structures. On non-POSIX	5499	instead of C<size_t> when allocating its data structures. On non-POSIX
…		…
4791		5505
4792	The type C<double> is used to represent timestamps. It is required to	5506	The type C<double> is used to represent timestamps. It is required to
4793	have at least 51 bits of mantissa (and 9 bits of exponent), which is	5507	have at least 51 bits of mantissa (and 9 bits of exponent), which is
4794	good enough for at least into the year 4000 with millisecond accuracy	5508	good enough for at least into the year 4000 with millisecond accuracy
4795	(the design goal for libev). This requirement is overfulfilled by	5509	(the design goal for libev). This requirement is overfulfilled by
4796	implementations using IEEE 754, which is basically all existing ones. With	5510	implementations using IEEE 754, which is basically all existing ones.
		5511
4797	IEEE 754 doubles, you get microsecond accuracy until at least 2200.	5512	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5513	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5514	is either obsolete or somebody patched it to use C<long double> or
		5515	something like that, just kidding).
4798		5516
4799	=back	5517	=back
4800		5518
4801	If you know of other additional requirements drop me a note.	5519	If you know of other additional requirements drop me a note.
4802		5520
…		…
4864	=item Processing ev_async_send: O(number_of_async_watchers)	5582	=item Processing ev_async_send: O(number_of_async_watchers)
4865		5583
4866	=item Processing signals: O(max_signal_number)	5584	=item Processing signals: O(max_signal_number)
4867		5585
4868	Sending involves a system call I<iff> there were no other C<ev_async_send>	5586	Sending involves a system call I<iff> there were no other C<ev_async_send>
4869	calls in the current loop iteration. Checking for async and signal events	5587	calls in the current loop iteration and the loop is currently
		5588	blocked. Checking for async and signal events involves iterating over all
4870	involves iterating over all running async watchers or all signal numbers.	5589	running async watchers or all signal numbers.
4871		5590
4872	=back	5591	=back
4873		5592
4874		5593
4875	=head1 PORTING FROM LIBEV 3.X TO 4.X	5594	=head1 PORTING FROM LIBEV 3.X TO 4.X
4876		5595
4877	The major version 4 introduced some minor incompatible changes to the API.	5596	The major version 4 introduced some incompatible changes to the API.
4878		5597
4879	At the moment, the C<ev.h> header file tries to implement superficial	5598	At the moment, the C<ev.h> header file provides compatibility definitions
4880	compatibility, so most programs should still compile. Those might be	5599	for all changes, so most programs should still compile. The compatibility
4881	removed in later versions of libev, so better update early than late.	5600	layer might be removed in later versions of libev, so better update to the
		5601	new API early than late.
4882		5602
4883	=over 4	5603	=over 4
		5604
		5605	=item C<EV_COMPAT3> backwards compatibility mechanism
		5606
		5607	The backward compatibility mechanism can be controlled by
		5608	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
		5609	section.
4884		5610
4885	=item C<ev_default_destroy> and C<ev_default_fork> have been removed	5611	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
4886		5612
4887	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:	5613	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
4888		5614
…		…
4914	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme	5640	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
4915	as all other watcher types. Note that C<ev_loop_fork> is still called	5641	as all other watcher types. Note that C<ev_loop_fork> is still called
4916	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>	5642	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
4917	typedef.	5643	typedef.
4918		5644
4919	=item C<EV_COMPAT3> backwards compatibility mechanism
4920
4921	The backward compatibility mechanism can be controlled by
4922	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
4923	section.
4924
4925	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>	5645	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
4926		5646
4927	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different	5647	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
4928	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile	5648	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
4929	and work, but the library code will of course be larger.	5649	and work, but the library code will of course be larger.
…		…
4936	=over 4	5656	=over 4
4937		5657
4938	=item active	5658	=item active
4939		5659
4940	A watcher is active as long as it has been started and not yet stopped.	5660	A watcher is active as long as it has been started and not yet stopped.
4941	See L<WATCHER STATES> for details.	5661	See L</WATCHER STATES> for details.
4942		5662
4943	=item application	5663	=item application
4944		5664
4945	In this document, an application is whatever is using libev.	5665	In this document, an application is whatever is using libev.
4946		5666
…		…
4982	watchers and events.	5702	watchers and events.
4983		5703
4984	=item pending	5704	=item pending
4985		5705
4986	A watcher is pending as soon as the corresponding event has been	5706	A watcher is pending as soon as the corresponding event has been
4987	detected. See L<WATCHER STATES> for details.	5707	detected. See L</WATCHER STATES> for details.
4988		5708
4989	=item real time	5709	=item real time
4990		5710
4991	The physical time that is observed. It is apparently strictly monotonic :)	5711	The physical time that is observed. It is apparently strictly monotonic :)
4992		5712
4993	=item wall-clock time	5713	=item wall-clock time
4994		5714
4995	The time and date as shown on clocks. Unlike real time, it can actually	5715	The time and date as shown on clocks. Unlike real time, it can actually
4996	be wrong and jump forwards and backwards, e.g. when the you adjust your	5716	be wrong and jump forwards and backwards, e.g. when you adjust your
4997	clock.	5717	clock.
4998		5718
4999	=item watcher	5719	=item watcher
5000		5720
5001	A data structure that describes interest in certain events. Watchers need	5721	A data structure that describes interest in certain events. Watchers need
…		…
5003		5723
5004	=back	5724	=back
5005		5725
5006	=head1 AUTHOR	5726	=head1 AUTHOR
5007		5727
5008	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.	5728	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5729	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
5009		5730

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