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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
…		…
342	Example: Restrict libev to the select and poll backends, and do not allow	395	Example: Restrict libev to the select and poll backends, and do not allow
343	environment settings to be taken into account:	396	environment settings to be taken into account:
344		397
345	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	398	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
346		399
347	Example: Use whatever libev has to offer, but make sure that kqueue is
348	used if available (warning, breaks stuff, best use only with your own
349	private event loop and only if you know the OS supports your types of
350	fds):
351
352	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
353
354	=item struct ev_loop *ev_loop_new (unsigned int flags)	400	=item struct ev_loop *ev_loop_new (unsigned int flags)
355		401
356	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
357	could not be initialised, returns false.	403	could not be initialised, returns false.
358		404
359	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
360	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
361	default loop in the "main" or "initial" thread.	407	loop in the "main" or "initial" thread.
362		408
363	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
364	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>).
365		411
366	The following flags are supported:	412	The following flags are supported:
…		…
376		422
377	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
378	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
379	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	425	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
380	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
381	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
382	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).
383		431
384	=item C<EVFLAG_FORKCHECK>	432	=item C<EVFLAG_FORKCHECK>
385		433
386	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
387	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.
388		436
389	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,
390	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
391	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
392	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
393	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
394	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).
395		444
396	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
397	forget about forgetting to tell libev about forking) when you use this	446	forget about forgetting to tell libev about forking, although you still
398	flag.	447	have to ignore C<SIGPIPE>) when you use this flag.
399		448
400	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>
401	environment variable.	450	environment variable.
402		451
403	=item C<EVFLAG_NOINOTIFY>	452	=item C<EVFLAG_NOINOTIFY>
404		453
405	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
406	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
407	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
408	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.
409		458
410	=item C<EVFLAG_SIGNALFD>	459	=item C<EVFLAG_SIGNALFD>
411		460
412	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
413	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
414	delivers signals synchronously, which makes it both faster and might make	463	delivers signals synchronously, which makes it both faster and might make
415	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
416	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
417	threads that are not interested in handling them.	466	threads that are not interested in handling them.
418		467
419	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
420	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
421	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.
422		495
423	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	496	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
424		497
425	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
426	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,
…		…
451	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
452	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.	525	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
453		526
454	=item C<EVBACKEND_EPOLL> (value 4, Linux)	527	=item C<EVBACKEND_EPOLL> (value 4, Linux)
455		528
456	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
457	kernels).	530	kernels).
458		531
459	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
460	but it scales phenomenally better. While poll and select usually scale	533	it scales phenomenally better. While poll and select usually scale like
461	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
462	epoll scales either O(1) or O(active_fds).	535	fd), epoll scales either O(1) or O(active_fds).
463		536
464	The epoll mechanism deserves honorable mention as the most misdesigned	537	The epoll mechanism deserves honorable mention as the most misdesigned
465	of the more advanced event mechanisms: mere annoyances include silently	538	of the more advanced event mechanisms: mere annoyances include silently
466	dropping file descriptors, requiring a system call per change per file	539	dropping file descriptors, requiring a system call per change per file
467	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
468	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
469	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
470	take considerable time (one syscall per file descriptor) and is of course	545	set, which can take considerable time (one syscall per file descriptor)
471	hard to detect.	546	and is of course hard to detect.
472		547
473	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but	548	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
474	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
475	I<different> file descriptors (even already closed ones, so one cannot	550	totally I<different> file descriptors (even already closed ones, so
476	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
477	on SMP systems). Libev tries to counter these spurious notifications by	552	(especially on SMP systems). Libev tries to counter these spurious
478	employing an additional generation counter and comparing that against the	553	notifications by employing an additional generation counter and comparing
479	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
480	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
481	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...
482		564
483	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
484	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
485	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
486	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
…		…
498	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
499	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
500	the usage. So sad.	582	the usage. So sad.
501		583
502	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
503	all kernel versions tested so far.	585	a lot of kernel revisions, but probably(!) works in current versions.
504		586
505	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
506	C<EVBACKEND_POLL>.	588	C<EVBACKEND_POLL>.
507		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
508	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	634	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
509		635
510	Kqueue deserves special mention, as at the time of this writing, it	636	Kqueue deserves special mention, as at the time this backend was
511	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
512	with anything but sockets and pipes, except on Darwin, where of course	638	work reliably with anything but sockets and pipes, except on Darwin,
513	it's completely useless). Unlike epoll, however, whose brokenness	639	where of course it's completely useless). Unlike epoll, however, whose
514	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)
515	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
516	"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
517	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
518	system like NetBSD.	644	known-to-be-good (-enough) system like NetBSD.
519		645
520	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
521	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
522	the target platform). See C<ev_embed> watchers for more info.	648	the target platform). See C<ev_embed> watchers for more info.
523		649
524	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
525	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
526	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
527	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
528	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
529	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
530	cases	656	drops fds silently in similarly hard-to-detect cases.
531		657
532	This backend usually performs well under most conditions.	658	This backend usually performs well under most conditions.
533		659
534	While nominally embeddable in other event loops, this doesn't work	660	While nominally embeddable in other event loops, this doesn't work
535	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
…		…
552	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	678	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
553		679
554	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,
555	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)).
556		682
557	Please note that Solaris event ports can deliver a lot of spurious
558	notifications, so you need to use non-blocking I/O or other means to avoid
559	blocking when no data (or space) is available.
560
561	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
562	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
563	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	685	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
564	might perform better.	686	might perform better.
565		687
566	On the positive side, with the exception of the spurious readiness	688	On the positive side, this backend actually performed fully to
567	notifications, this backend actually performed fully to specification
568	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
569	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.
570		702
571	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
572	C<EVBACKEND_POLL>.	704	C<EVBACKEND_POLL>.
573		705
574	=item C<EVBACKEND_ALL>	706	=item C<EVBACKEND_ALL>
575		707
576	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
577	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
578	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	710	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
579		711
580	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).
581		721
582	=back	722	=back
583		723
584	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,
585	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
…		…
589	Example: Try to create a event loop that uses epoll and nothing else.	729	Example: Try to create a event loop that uses epoll and nothing else.
590		730
591	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	731	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
592	if (!epoller)	732	if (!epoller)
593	fatal ("no epoll found here, maybe it hides under your chair");	733	fatal ("no epoll found here, maybe it hides under your chair");
		734
		735	Example: Use whatever libev has to offer, but make sure that kqueue is
		736	used if available.
		737
		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);
594		745
595	=item ev_loop_destroy (loop)	746	=item ev_loop_destroy (loop)
596		747
597	Destroys an event loop object (frees all memory and kernel state	748	Destroys an event loop object (frees all memory and kernel state
598	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
…		…
609	This function is normally used on loop objects allocated by	760	This function is normally used on loop objects allocated by
610	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
611	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.
612		763
613	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
614	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.
615	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>
616	and C<ev_loop_destroy>.	767	and C<ev_loop_destroy>.
617		768
618	=item ev_loop_fork (loop)	769	=item ev_loop_fork (loop)
619		770
620	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
621	reinitialise the kernel state for backends that have one. Despite the	772	to reinitialise the kernel state for backends that have one. Despite
622	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
623	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
624	child before resuming or calling C<ev_run>.	776	C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.
625		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
626	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
627	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
628	because some kernel interfaces *cough* I<kqueue> *cough* do funny things	783	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
629	during fork.	784	during fork.
630		785
631	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
…		…
667	prepare and check phases.	822	prepare and check phases.
668		823
669	=item unsigned int ev_depth (loop)	824	=item unsigned int ev_depth (loop)
670		825
671	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
672	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.
673		828
674	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
675	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),
676	in which case it is higher.	831	in which case it is higher.
677		832
678	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread	833	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
679	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
680	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.
681		837
682	=item unsigned int ev_backend (loop)	838	=item unsigned int ev_backend (loop)
683		839
684	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
685	use.	841	use.
…		…
700		856
701	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
702	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
703	the current time is a good idea.	859	the current time is a good idea.
704		860
705	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.
706		862
707	=item ev_suspend (loop)	863	=item ev_suspend (loop)
708		864
709	=item ev_resume (loop)	865	=item ev_resume (loop)
710		866
…		…
728	without a previous call to C<ev_suspend>.	884	without a previous call to C<ev_suspend>.
729		885
730	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
731	event loop time (see C<ev_now_update>).	887	event loop time (see C<ev_now_update>).
732		888
733	=item ev_run (loop, int flags)	889	=item bool ev_run (loop, int flags)
734		890
735	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
736	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
737	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
738	the watcher callbacks, an then repeat the whole process indefinitely: This	894	the watcher callbacks, and then repeat the whole process indefinitely: This
739	is why event loops are called I<loops>.	895	is why event loops are called I<loops>.
740		896
741	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
742	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
743	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").
744		904
745	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
746	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
747	finished (especially in interactive programs), but having a program	907	finished (especially in interactive programs), but having a program
748	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
749	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
750	beauty.	910	beauty.
751		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
752	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
753	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
754	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
755	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
756	events while doing lengthy calculations, to keep the program responsive.	921	events while doing lengthy calculations, to keep the program responsive.
…		…
765	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
766	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
767	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
768	usually a better approach for this kind of thing.	933	usually a better approach for this kind of thing.
769		934
770	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):
771		938
772	- Increment loop depth.	939	- Increment loop depth.
773	- Reset the ev_break status.	940	- Reset the ev_break status.
774	- Before the first iteration, call any pending watchers.	941	- Before the first iteration, call any pending watchers.
775	LOOP:	942	LOOP:
…		…
808	anymore.	975	anymore.
809		976
810	... queue jobs here, make sure they register event watchers as long	977	... queue jobs here, make sure they register event watchers as long
811	... 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..)
812	ev_run (my_loop, 0);	979	ev_run (my_loop, 0);
813	... jobs done or somebody called unloop. yeah!	980	... jobs done or somebody called break. yeah!
814		981
815	=item ev_break (loop, how)	982	=item ev_break (loop, how)
816		983
817	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
818	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
819	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
820	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.
821		988
822	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>.
823		990
824	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.
825		993
826	=item ev_ref (loop)	994	=item ev_ref (loop)
827		995
828	=item ev_unref (loop)	996	=item ev_unref (loop)
829		997
…		…
850	running when nothing else is active.	1018	running when nothing else is active.
851		1019
852	ev_signal exitsig;	1020	ev_signal exitsig;
853	ev_signal_init (&exitsig, sig_cb, SIGINT);	1021	ev_signal_init (&exitsig, sig_cb, SIGINT);
854	ev_signal_start (loop, &exitsig);	1022	ev_signal_start (loop, &exitsig);
855	evf_unref (loop);	1023	ev_unref (loop);
856		1024
857	Example: For some weird reason, unregister the above signal handler again.	1025	Example: For some weird reason, unregister the above signal handler again.
858		1026
859	ev_ref (loop);	1027	ev_ref (loop);
860	ev_signal_stop (loop, &exitsig);	1028	ev_signal_stop (loop, &exitsig);
…		…
880	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.
881		1049
882	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
883	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,
884	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
885	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
886	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
887	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
888	once per this interval, on average.	1056	once per this interval, on average (as long as the host time resolution is
		1057	good enough).
889		1058
890	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
891	to spend more time collecting timeouts, at the expense of increased	1060	to spend more time collecting timeouts, at the expense of increased
892	latency/jitter/inexactness (the watcher callback will be called	1061	latency/jitter/inexactness (the watcher callback will be called
893	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
…		…
939	invoke the actual watchers inside another context (another thread etc.).	1108	invoke the actual watchers inside another context (another thread etc.).
940		1109
941	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
942	callback.	1111	callback.
943		1112
944	=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 ())
945		1114
946	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
947	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
948	each call to a libev function.	1117	each call to a libev function.
949		1118
950	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
951	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
952	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
953	I<release> and I<acquire> callbacks on the loop.	1122	I<release> and I<acquire> callbacks on the loop.
954		1123
955	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
956	suspended waiting for new events, and C<acquire> is called just	1125	suspended waiting for new events, and C<acquire> is called just
957	afterwards.	1126	afterwards.
…		…
972	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
973	document.	1142	document.
974		1143
975	=item ev_set_userdata (loop, void *data)	1144	=item ev_set_userdata (loop, void *data)
976		1145
977	=item ev_userdata (loop)	1146	=item void *ev_userdata (loop)
978		1147
979	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
980	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
981	C<0.>	1150	C<0>.
982		1151
983	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,
984	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
985	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
986	any other purpose as well.	1155	any other purpose as well.
…		…
1049	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher	1218	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
1050	*) >>), and you can stop watching for events at any time by calling the	1219	*) >>), and you can stop watching for events at any time by calling the
1051	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.	1220	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
1052		1221
1053	As long as your watcher is active (has been started but not stopped) you	1222	As long as your watcher is active (has been started but not stopped) you
1054	must not touch the values stored in it. Most specifically you must never	1223	must not touch the values stored in it except when explicitly documented
1055	reinitialise it or call its C<ev_TYPE_set> macro.	1224	otherwise. Most specifically you must never reinitialise it or call its
		1225	C<ev_TYPE_set> macro.
1056		1226
1057	Each and every callback receives the event loop pointer as first, the	1227	Each and every callback receives the event loop pointer as first, the
1058	registered watcher structure as second, and a bitset of received events as	1228	registered watcher structure as second, and a bitset of received events as
1059	third argument.	1229	third argument.
1060		1230
…		…
1097		1267
1098	=item C<EV_PREPARE>	1268	=item C<EV_PREPARE>
1099		1269
1100	=item C<EV_CHECK>	1270	=item C<EV_CHECK>
1101		1271
1102	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts	1272	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts to
1103	to gather new events, and all C<ev_check> watchers are invoked just after	1273	gather new events, and all C<ev_check> watchers are queued (not invoked)
1104	C<ev_run> has gathered them, but before it invokes any callbacks for any	1274	just after C<ev_run> has gathered them, but before it queues any callbacks
		1275	for any received events. That means C<ev_prepare> watchers are the last
		1276	watchers invoked before the event loop sleeps or polls for new events, and
		1277	C<ev_check> watchers will be invoked before any other watchers of the same
		1278	or lower priority within an event loop iteration.
		1279
1105	received events. Callbacks of both watcher types can start and stop as	1280	Callbacks of both watcher types can start and stop as many watchers as
1106	many watchers as they want, and all of them will be taken into account	1281	they want, and all of them will be taken into account (for example, a
1107	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1282	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
1108	C<ev_run> from blocking).	1283	blocking).
1109		1284
1110	=item C<EV_EMBED>	1285	=item C<EV_EMBED>
1111		1286
1112	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1287	The embedded event loop specified in the C<ev_embed> watcher needs attention.
1113		1288
1114	=item C<EV_FORK>	1289	=item C<EV_FORK>
1115		1290
1116	The event loop has been resumed in the child process after fork (see	1291	The event loop has been resumed in the child process after fork (see
1117	C<ev_fork>).	1292	C<ev_fork>).
		1293
		1294	=item C<EV_CLEANUP>
		1295
		1296	The event loop is about to be destroyed (see C<ev_cleanup>).
1118		1297
1119	=item C<EV_ASYNC>	1298	=item C<EV_ASYNC>
1120		1299
1121	The given async watcher has been asynchronously notified (see C<ev_async>).	1300	The given async watcher has been asynchronously notified (see C<ev_async>).
1122		1301
…		…
1144	programs, though, as the fd could already be closed and reused for another	1323	programs, though, as the fd could already be closed and reused for another
1145	thing, so beware.	1324	thing, so beware.
1146		1325
1147	=back	1326	=back
1148		1327
		1328	=head2 GENERIC WATCHER FUNCTIONS
		1329
		1330	=over 4
		1331
		1332	=item C<ev_init> (ev_TYPE *watcher, callback)
		1333
		1334	This macro initialises the generic portion of a watcher. The contents
		1335	of the watcher object can be arbitrary (so C<malloc> will do). Only
		1336	the generic parts of the watcher are initialised, you I<need> to call
		1337	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		1338	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		1339	which rolls both calls into one.
		1340
		1341	You can reinitialise a watcher at any time as long as it has been stopped
		1342	(or never started) and there are no pending events outstanding.
		1343
		1344	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
		1345	int revents)>.
		1346
		1347	Example: Initialise an C<ev_io> watcher in two steps.
		1348
		1349	ev_io w;
		1350	ev_init (&w, my_cb);
		1351	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1352
		1353	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
		1354
		1355	This macro initialises the type-specific parts of a watcher. You need to
		1356	call C<ev_init> at least once before you call this macro, but you can
		1357	call C<ev_TYPE_set> any number of times. You must not, however, call this
		1358	macro on a watcher that is active (it can be pending, however, which is a
		1359	difference to the C<ev_init> macro).
		1360
		1361	Although some watcher types do not have type-specific arguments
		1362	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		1363
		1364	See C<ev_init>, above, for an example.
		1365
		1366	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		1367
		1368	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		1369	calls into a single call. This is the most convenient method to initialise
		1370	a watcher. The same limitations apply, of course.
		1371
		1372	Example: Initialise and set an C<ev_io> watcher in one step.
		1373
		1374	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1375
		1376	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
		1377
		1378	Starts (activates) the given watcher. Only active watchers will receive
		1379	events. If the watcher is already active nothing will happen.
		1380
		1381	Example: Start the C<ev_io> watcher that is being abused as example in this
		1382	whole section.
		1383
		1384	ev_io_start (EV_DEFAULT_UC, &w);
		1385
		1386	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
		1387
		1388	Stops the given watcher if active, and clears the pending status (whether
		1389	the watcher was active or not).
		1390
		1391	It is possible that stopped watchers are pending - for example,
		1392	non-repeating timers are being stopped when they become pending - but
		1393	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
		1394	pending. If you want to free or reuse the memory used by the watcher it is
		1395	therefore a good idea to always call its C<ev_TYPE_stop> function.
		1396
		1397	=item bool ev_is_active (ev_TYPE *watcher)
		1398
		1399	Returns a true value iff the watcher is active (i.e. it has been started
		1400	and not yet been stopped). As long as a watcher is active you must not modify
		1401	it.
		1402
		1403	=item bool ev_is_pending (ev_TYPE *watcher)
		1404
		1405	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		1406	events but its callback has not yet been invoked). As long as a watcher
		1407	is pending (but not active) you must not call an init function on it (but
		1408	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		1409	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1410	it).
		1411
		1412	=item callback ev_cb (ev_TYPE *watcher)
		1413
		1414	Returns the callback currently set on the watcher.
		1415
		1416	=item ev_set_cb (ev_TYPE *watcher, callback)
		1417
		1418	Change the callback. You can change the callback at virtually any time
		1419	(modulo threads).
		1420
		1421	=item ev_set_priority (ev_TYPE *watcher, int priority)
		1422
		1423	=item int ev_priority (ev_TYPE *watcher)
		1424
		1425	Set and query the priority of the watcher. The priority is a small
		1426	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1427	(default: C<-2>). Pending watchers with higher priority will be invoked
		1428	before watchers with lower priority, but priority will not keep watchers
		1429	from being executed (except for C<ev_idle> watchers).
		1430
		1431	If you need to suppress invocation when higher priority events are pending
		1432	you need to look at C<ev_idle> watchers, which provide this functionality.
		1433
		1434	You I<must not> change the priority of a watcher as long as it is active or
		1435	pending.
		1436
		1437	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1438	fine, as long as you do not mind that the priority value you query might
		1439	or might not have been clamped to the valid range.
		1440
		1441	The default priority used by watchers when no priority has been set is
		1442	always C<0>, which is supposed to not be too high and not be too low :).
		1443
		1444	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1445	priorities.
		1446
		1447	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1448
		1449	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1450	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1451	can deal with that fact, as both are simply passed through to the
		1452	callback.
		1453
		1454	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1455
		1456	If the watcher is pending, this function clears its pending status and
		1457	returns its C<revents> bitset (as if its callback was invoked). If the
		1458	watcher isn't pending it does nothing and returns C<0>.
		1459
		1460	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1461	callback to be invoked, which can be accomplished with this function.
		1462
		1463	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1464
		1465	Feeds the given event set into the event loop, as if the specified event
		1466	had happened for the specified watcher (which must be a pointer to an
		1467	initialised but not necessarily started event watcher). Obviously you must
		1468	not free the watcher as long as it has pending events.
		1469
		1470	Stopping the watcher, letting libev invoke it, or calling
		1471	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1472	not started in the first place.
		1473
		1474	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1475	functions that do not need a watcher.
		1476
		1477	=back
		1478
		1479	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
		1480	OWN COMPOSITE WATCHERS> idioms.
		1481
1149	=head2 WATCHER STATES	1482	=head2 WATCHER STATES
1150		1483
1151	There are various watcher states mentioned throughout this manual -	1484	There are various watcher states mentioned throughout this manual -
1152	active, pending and so on. In this section these states and the rules to	1485	active, pending and so on. In this section these states and the rules to
1153	transition between them will be described in more detail - and while these	1486	transition between them will be described in more detail - and while these
1154	rules might look complicated, they usually do "the right thing".	1487	rules might look complicated, they usually do "the right thing".
1155		1488
1156	=over 4	1489	=over 4
1157		1490
1158	=item initialiased	1491	=item initialised
1159		1492
1160	Before a watcher can be registered with the event looop it has to be	1493	Before a watcher can be registered with the event loop it has to be
1161	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to	1494	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
1162	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.	1495	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1163		1496
1164	In this state it is simply some block of memory that is suitable for use	1497	In this state it is simply some block of memory that is suitable for
1165	in an event loop. It can be moved around, freed, reused etc. at will.	1498	use in an event loop. It can be moved around, freed, reused etc. at
		1499	will - as long as you either keep the memory contents intact, or call
		1500	C<ev_TYPE_init> again.
1166		1501
1167	=item started/running/active	1502	=item started/running/active
1168		1503
1169	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes	1504	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
1170	property of the event loop, and is actively waiting for events. While in	1505	property of the event loop, and is actively waiting for events. While in
…		…
1198	latter will clear any pending state the watcher might be in, regardless	1533	latter will clear any pending state the watcher might be in, regardless
1199	of whether it was active or not, so stopping a watcher explicitly before	1534	of whether it was active or not, so stopping a watcher explicitly before
1200	freeing it is often a good idea.	1535	freeing it is often a good idea.
1201		1536
1202	While stopped (and not pending) the watcher is essentially in the	1537	While stopped (and not pending) the watcher is essentially in the
1203	initialised state, that is it can be reused, moved, modified in any way	1538	initialised state, that is, it can be reused, moved, modified in any way
1204	you wish.	1539	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1540	it again).
1205		1541
1206	=back	1542	=back
1207
1208	=head2 GENERIC WATCHER FUNCTIONS
1209
1210	=over 4
1211
1212	=item C<ev_init> (ev_TYPE *watcher, callback)
1213
1214	This macro initialises the generic portion of a watcher. The contents
1215	of the watcher object can be arbitrary (so C<malloc> will do). Only
1216	the generic parts of the watcher are initialised, you I<need> to call
1217	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
1218	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
1219	which rolls both calls into one.
1220
1221	You can reinitialise a watcher at any time as long as it has been stopped
1222	(or never started) and there are no pending events outstanding.
1223
1224	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
1225	int revents)>.
1226
1227	Example: Initialise an C<ev_io> watcher in two steps.
1228
1229	ev_io w;
1230	ev_init (&w, my_cb);
1231	ev_io_set (&w, STDIN_FILENO, EV_READ);
1232
1233	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
1234
1235	This macro initialises the type-specific parts of a watcher. You need to
1236	call C<ev_init> at least once before you call this macro, but you can
1237	call C<ev_TYPE_set> any number of times. You must not, however, call this
1238	macro on a watcher that is active (it can be pending, however, which is a
1239	difference to the C<ev_init> macro).
1240
1241	Although some watcher types do not have type-specific arguments
1242	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
1243
1244	See C<ev_init>, above, for an example.
1245
1246	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
1247
1248	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
1249	calls into a single call. This is the most convenient method to initialise
1250	a watcher. The same limitations apply, of course.
1251
1252	Example: Initialise and set an C<ev_io> watcher in one step.
1253
1254	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1255
1256	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
1257
1258	Starts (activates) the given watcher. Only active watchers will receive
1259	events. If the watcher is already active nothing will happen.
1260
1261	Example: Start the C<ev_io> watcher that is being abused as example in this
1262	whole section.
1263
1264	ev_io_start (EV_DEFAULT_UC, &w);
1265
1266	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
1267
1268	Stops the given watcher if active, and clears the pending status (whether
1269	the watcher was active or not).
1270
1271	It is possible that stopped watchers are pending - for example,
1272	non-repeating timers are being stopped when they become pending - but
1273	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
1274	pending. If you want to free or reuse the memory used by the watcher it is
1275	therefore a good idea to always call its C<ev_TYPE_stop> function.
1276
1277	=item bool ev_is_active (ev_TYPE *watcher)
1278
1279	Returns a true value iff the watcher is active (i.e. it has been started
1280	and not yet been stopped). As long as a watcher is active you must not modify
1281	it.
1282
1283	=item bool ev_is_pending (ev_TYPE *watcher)
1284
1285	Returns a true value iff the watcher is pending, (i.e. it has outstanding
1286	events but its callback has not yet been invoked). As long as a watcher
1287	is pending (but not active) you must not call an init function on it (but
1288	C<ev_TYPE_set> is safe), you must not change its priority, and you must
1289	make sure the watcher is available to libev (e.g. you cannot C<free ()>
1290	it).
1291
1292	=item callback ev_cb (ev_TYPE *watcher)
1293
1294	Returns the callback currently set on the watcher.
1295
1296	=item ev_cb_set (ev_TYPE *watcher, callback)
1297
1298	Change the callback. You can change the callback at virtually any time
1299	(modulo threads).
1300
1301	=item ev_set_priority (ev_TYPE *watcher, int priority)
1302
1303	=item int ev_priority (ev_TYPE *watcher)
1304
1305	Set and query the priority of the watcher. The priority is a small
1306	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
1307	(default: C<-2>). Pending watchers with higher priority will be invoked
1308	before watchers with lower priority, but priority will not keep watchers
1309	from being executed (except for C<ev_idle> watchers).
1310
1311	If you need to suppress invocation when higher priority events are pending
1312	you need to look at C<ev_idle> watchers, which provide this functionality.
1313
1314	You I<must not> change the priority of a watcher as long as it is active or
1315	pending.
1316
1317	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
1318	fine, as long as you do not mind that the priority value you query might
1319	or might not have been clamped to the valid range.
1320
1321	The default priority used by watchers when no priority has been set is
1322	always C<0>, which is supposed to not be too high and not be too low :).
1323
1324	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1325	priorities.
1326
1327	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1328
1329	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
1330	C<loop> nor C<revents> need to be valid as long as the watcher callback
1331	can deal with that fact, as both are simply passed through to the
1332	callback.
1333
1334	=item int ev_clear_pending (loop, ev_TYPE *watcher)
1335
1336	If the watcher is pending, this function clears its pending status and
1337	returns its C<revents> bitset (as if its callback was invoked). If the
1338	watcher isn't pending it does nothing and returns C<0>.
1339
1340	Sometimes it can be useful to "poll" a watcher instead of waiting for its
1341	callback to be invoked, which can be accomplished with this function.
1342
1343	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
1344
1345	Feeds the given event set into the event loop, as if the specified event
1346	had happened for the specified watcher (which must be a pointer to an
1347	initialised but not necessarily started event watcher). Obviously you must
1348	not free the watcher as long as it has pending events.
1349
1350	Stopping the watcher, letting libev invoke it, or calling
1351	C<ev_clear_pending> will clear the pending event, even if the watcher was
1352	not started in the first place.
1353
1354	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1355	functions that do not need a watcher.
1356
1357	=back
1358
1359
1360	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
1361
1362	Each watcher has, by default, a member C<void *data> that you can change
1363	and read at any time: libev will completely ignore it. This can be used
1364	to associate arbitrary data with your watcher. If you need more data and
1365	don't want to allocate memory and store a pointer to it in that data
1366	member, you can also "subclass" the watcher type and provide your own
1367	data:
1368
1369	struct my_io
1370	{
1371	ev_io io;
1372	int otherfd;
1373	void *somedata;
1374	struct whatever *mostinteresting;
1375	};
1376
1377	...
1378	struct my_io w;
1379	ev_io_init (&w.io, my_cb, fd, EV_READ);
1380
1381	And since your callback will be called with a pointer to the watcher, you
1382	can cast it back to your own type:
1383
1384	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1385	{
1386	struct my_io *w = (struct my_io *)w_;
1387	...
1388	}
1389
1390	More interesting and less C-conformant ways of casting your callback type
1391	instead have been omitted.
1392
1393	Another common scenario is to use some data structure with multiple
1394	embedded watchers:
1395
1396	struct my_biggy
1397	{
1398	int some_data;
1399	ev_timer t1;
1400	ev_timer t2;
1401	}
1402
1403	In this case getting the pointer to C<my_biggy> is a bit more
1404	complicated: Either you store the address of your C<my_biggy> struct
1405	in the C<data> member of the watcher (for woozies), or you need to use
1406	some pointer arithmetic using C<offsetof> inside your watchers (for real
1407	programmers):
1408
1409	#include <stddef.h>
1410
1411	static void
1412	t1_cb (EV_P_ ev_timer *w, int revents)
1413	{
1414	struct my_biggy big = (struct my_biggy *)
1415	(((char *)w) - offsetof (struct my_biggy, t1));
1416	}
1417
1418	static void
1419	t2_cb (EV_P_ ev_timer *w, int revents)
1420	{
1421	struct my_biggy big = (struct my_biggy *)
1422	(((char *)w) - offsetof (struct my_biggy, t2));
1423	}
1424		1543
1425	=head2 WATCHER PRIORITY MODELS	1544	=head2 WATCHER PRIORITY MODELS
1426		1545
1427	Many event loops support I<watcher priorities>, which are usually small	1546	Many event loops support I<watcher priorities>, which are usually small
1428	integers that influence the ordering of event callback invocation	1547	integers that influence the ordering of event callback invocation
1429	between watchers in some way, all else being equal.	1548	between watchers in some way, all else being equal.
1430		1549
1431	In libev, Watcher priorities can be set using C<ev_set_priority>. See its	1550	In libev, watcher priorities can be set using C<ev_set_priority>. See its
1432	description for the more technical details such as the actual priority	1551	description for the more technical details such as the actual priority
1433	range.	1552	range.
1434		1553
1435	There are two common ways how these these priorities are being interpreted	1554	There are two common ways how these these priorities are being interpreted
1436	by event loops:	1555	by event loops:
…		…
1530		1649
1531	This section describes each watcher in detail, but will not repeat	1650	This section describes each watcher in detail, but will not repeat
1532	information given in the last section. Any initialisation/set macros,	1651	information given in the last section. Any initialisation/set macros,
1533	functions and members specific to the watcher type are explained.	1652	functions and members specific to the watcher type are explained.
1534		1653
1535	Members are additionally marked with either I<[read-only]>, meaning that,	1654	Most members are additionally marked with either I<[read-only]>, meaning
1536	while the watcher is active, you can look at the member and expect some	1655	that, while the watcher is active, you can look at the member and expect
1537	sensible content, but you must not modify it (you can modify it while the	1656	some sensible content, but you must not modify it (you can modify it while
1538	watcher is stopped to your hearts content), or I<[read-write]>, which	1657	the watcher is stopped to your hearts content), or I<[read-write]>, which
1539	means you can expect it to have some sensible content while the watcher	1658	means you can expect it to have some sensible content while the watcher
1540	is active, but you can also modify it. Modifying it may not do something	1659	is active, but you can also modify it. Modifying it may not do something
1541	sensible or take immediate effect (or do anything at all), but libev will	1660	sensible or take immediate effect (or do anything at all), but libev will
1542	not crash or malfunction in any way.	1661	not crash or malfunction in any way.
1543		1662
		1663	In any case, the documentation for each member will explain what the
		1664	effects are, and if there are any additional access restrictions.
1544		1665
1545	=head2 C<ev_io> - is this file descriptor readable or writable?	1666	=head2 C<ev_io> - is this file descriptor readable or writable?
1546		1667
1547	I/O watchers check whether a file descriptor is readable or writable	1668	I/O watchers check whether a file descriptor is readable or writable
1548	in each iteration of the event loop, or, more precisely, when reading	1669	in each iteration of the event loop, or, more precisely, when reading
…		…
1555	In general you can register as many read and/or write event watchers per	1676	In general you can register as many read and/or write event watchers per
1556	fd as you want (as long as you don't confuse yourself). Setting all file	1677	fd as you want (as long as you don't confuse yourself). Setting all file
1557	descriptors to non-blocking mode is also usually a good idea (but not	1678	descriptors to non-blocking mode is also usually a good idea (but not
1558	required if you know what you are doing).	1679	required if you know what you are doing).
1559		1680
1560	If you cannot use non-blocking mode, then force the use of a
1561	known-to-be-good backend (at the time of this writing, this includes only
1562	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
1563	descriptors for which non-blocking operation makes no sense (such as
1564	files) - libev doesn't guarantee any specific behaviour in that case.
1565
1566	Another thing you have to watch out for is that it is quite easy to	1681	Another thing you have to watch out for is that it is quite easy to
1567	receive "spurious" readiness notifications, that is your callback might	1682	receive "spurious" readiness notifications, that is, your callback might
1568	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1683	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1569	because there is no data. Not only are some backends known to create a	1684	because there is no data. It is very easy to get into this situation even
1570	lot of those (for example Solaris ports), it is very easy to get into	1685	with a relatively standard program structure. Thus it is best to always
1571	this situation even with a relatively standard program structure. Thus	1686	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1572	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1573	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1687	preferable to a program hanging until some data arrives.
1574		1688
1575	If you cannot run the fd in non-blocking mode (for example you should	1689	If you cannot run the fd in non-blocking mode (for example you should
1576	not play around with an Xlib connection), then you have to separately	1690	not play around with an Xlib connection), then you have to separately
1577	re-test whether a file descriptor is really ready with a known-to-be good	1691	re-test whether a file descriptor is really ready with a known-to-be good
1578	interface such as poll (fortunately in our Xlib example, Xlib already	1692	interface such as poll (fortunately in the case of Xlib, it already does
1579	does this on its own, so its quite safe to use). Some people additionally	1693	this on its own, so its quite safe to use). Some people additionally
1580	use C<SIGALRM> and an interval timer, just to be sure you won't block	1694	use C<SIGALRM> and an interval timer, just to be sure you won't block
1581	indefinitely.	1695	indefinitely.
1582		1696
1583	But really, best use non-blocking mode.	1697	But really, best use non-blocking mode.
1584		1698
1585	=head3 The special problem of disappearing file descriptors	1699	=head3 The special problem of disappearing file descriptors
1586		1700
1587	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1701	Some backends (e.g. kqueue, epoll, linuxaio) need to be told about closing
1588	descriptor (either due to calling C<close> explicitly or any other means,	1702	a file descriptor (either due to calling C<close> explicitly or any other
1589	such as C<dup2>). The reason is that you register interest in some file	1703	means, such as C<dup2>). The reason is that you register interest in some
1590	descriptor, but when it goes away, the operating system will silently drop	1704	file descriptor, but when it goes away, the operating system will silently
1591	this interest. If another file descriptor with the same number then is	1705	drop this interest. If another file descriptor with the same number then
1592	registered with libev, there is no efficient way to see that this is, in	1706	is registered with libev, there is no efficient way to see that this is,
1593	fact, a different file descriptor.	1707	in fact, a different file descriptor.
1594		1708
1595	To avoid having to explicitly tell libev about such cases, libev follows	1709	To avoid having to explicitly tell libev about such cases, libev follows
1596	the following policy: Each time C<ev_io_set> is being called, libev	1710	the following policy: Each time C<ev_io_set> is being called, libev
1597	will assume that this is potentially a new file descriptor, otherwise	1711	will assume that this is potentially a new file descriptor, otherwise
1598	it is assumed that the file descriptor stays the same. That means that	1712	it is assumed that the file descriptor stays the same. That means that
…		…
1612		1726
1613	There is no workaround possible except not registering events	1727	There is no workaround possible except not registering events
1614	for potentially C<dup ()>'ed file descriptors, or to resort to	1728	for potentially C<dup ()>'ed file descriptors, or to resort to
1615	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1729	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1616		1730
		1731	=head3 The special problem of files
		1732
		1733	Many people try to use C<select> (or libev) on file descriptors
		1734	representing files, and expect it to become ready when their program
		1735	doesn't block on disk accesses (which can take a long time on their own).
		1736
		1737	However, this cannot ever work in the "expected" way - you get a readiness
		1738	notification as soon as the kernel knows whether and how much data is
		1739	there, and in the case of open files, that's always the case, so you
		1740	always get a readiness notification instantly, and your read (or possibly
		1741	write) will still block on the disk I/O.
		1742
		1743	Another way to view it is that in the case of sockets, pipes, character
		1744	devices and so on, there is another party (the sender) that delivers data
		1745	on its own, but in the case of files, there is no such thing: the disk
		1746	will not send data on its own, simply because it doesn't know what you
		1747	wish to read - you would first have to request some data.
		1748
		1749	Since files are typically not-so-well supported by advanced notification
		1750	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1751	to files, even though you should not use it. The reason for this is
		1752	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1753	usually a tty, often a pipe, but also sometimes files or special devices
		1754	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1755	F</dev/urandom>), and even though the file might better be served with
		1756	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1757	it "just works" instead of freezing.
		1758
		1759	So avoid file descriptors pointing to files when you know it (e.g. use
		1760	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1761	when you rarely read from a file instead of from a socket, and want to
		1762	reuse the same code path.
		1763
1617	=head3 The special problem of fork	1764	=head3 The special problem of fork
1618		1765
1619	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1766	Some backends (epoll, kqueue, linuxaio, iouring) do not support C<fork ()>
1620	useless behaviour. Libev fully supports fork, but needs to be told about	1767	at all or exhibit useless behaviour. Libev fully supports fork, but needs
1621	it in the child.	1768	to be told about it in the child if you want to continue to use it in the
		1769	child.
1622		1770
1623	To support fork in your programs, you either have to call	1771	To support fork in your child processes, you have to call C<ev_loop_fork
1624	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1772	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1625	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1773	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1626	C<EVBACKEND_POLL>.
1627		1774
1628	=head3 The special problem of SIGPIPE	1775	=head3 The special problem of SIGPIPE
1629		1776
1630	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1777	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1631	when writing to a pipe whose other end has been closed, your program gets	1778	when writing to a pipe whose other end has been closed, your program gets
…		…
1682	=item ev_io_init (ev_io *, callback, int fd, int events)	1829	=item ev_io_init (ev_io *, callback, int fd, int events)
1683		1830
1684	=item ev_io_set (ev_io *, int fd, int events)	1831	=item ev_io_set (ev_io *, int fd, int events)
1685		1832
1686	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1833	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1687	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or	1834	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE>, both
1688	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.	1835	C<EV_READ | EV_WRITE> or C<0>, to express the desire to receive the given
		1836	events.
1689		1837
1690	=item int fd [read-only]	1838	Note that setting the C<events> to C<0> and starting the watcher is
		1839	supported, but not specially optimized - if your program sometimes happens
		1840	to generate this combination this is fine, but if it is easy to avoid
		1841	starting an io watcher watching for no events you should do so.
1691		1842
1692	The file descriptor being watched.	1843	=item ev_io_modify (ev_io *, int events)
1693		1844
		1845	Similar to C<ev_io_set>, but only changes the event mask. Using this might
		1846	be faster with some backends, as libev can assume that the C<fd> still
		1847	refers to the same underlying file description, something it cannot do
		1848	when using C<ev_io_set>.
		1849
		1850	=item int fd [no-modify]
		1851
		1852	The file descriptor being watched. While it can be read at any time, you
		1853	must not modify this member even when the watcher is stopped - always use
		1854	C<ev_io_set> for that.
		1855
1694	=item int events [read-only]	1856	=item int events [no-modify]
1695		1857
1696	The events being watched.	1858	The set of events the fd is being watched for, among other flags. Remember
		1859	that this is a bit set - to test for C<EV_READ>, use C<< w->events &
		1860	EV_READ >>, and similarly for C<EV_WRITE>.
		1861
		1862	As with C<fd>, you must not modify this member even when the watcher is
		1863	stopped, always use C<ev_io_set> or C<ev_io_modify> for that.
1697		1864
1698	=back	1865	=back
1699		1866
1700	=head3 Examples	1867	=head3 Examples
1701		1868
…		…
1729	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1896	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1730	monotonic clock option helps a lot here).	1897	monotonic clock option helps a lot here).
1731		1898
1732	The callback is guaranteed to be invoked only I<after> its timeout has	1899	The callback is guaranteed to be invoked only I<after> its timeout has
1733	passed (not I<at>, so on systems with very low-resolution clocks this	1900	passed (not I<at>, so on systems with very low-resolution clocks this
1734	might introduce a small delay). If multiple timers become ready during the	1901	might introduce a small delay, see "the special problem of being too
		1902	early", below). If multiple timers become ready during the same loop
1735	same loop iteration then the ones with earlier time-out values are invoked	1903	iteration then the ones with earlier time-out values are invoked before
1736	before ones of the same priority with later time-out values (but this is	1904	ones of the same priority with later time-out values (but this is no
1737	no longer true when a callback calls C<ev_run> recursively).	1905	longer true when a callback calls C<ev_run> recursively).
1738		1906
1739	=head3 Be smart about timeouts	1907	=head3 Be smart about timeouts
1740		1908
1741	Many real-world problems involve some kind of timeout, usually for error	1909	Many real-world problems involve some kind of timeout, usually for error
1742	recovery. A typical example is an HTTP request - if the other side hangs,	1910	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1817		1985
1818	In this case, it would be more efficient to leave the C<ev_timer> alone,	1986	In this case, it would be more efficient to leave the C<ev_timer> alone,
1819	but remember the time of last activity, and check for a real timeout only	1987	but remember the time of last activity, and check for a real timeout only
1820	within the callback:	1988	within the callback:
1821		1989
		1990	ev_tstamp timeout = 60.;
1822	ev_tstamp last_activity; // time of last activity	1991	ev_tstamp last_activity; // time of last activity
		1992	ev_timer timer;
1823		1993
1824	static void	1994	static void
1825	callback (EV_P_ ev_timer *w, int revents)	1995	callback (EV_P_ ev_timer *w, int revents)
1826	{	1996	{
1827	ev_tstamp now = ev_now (EV_A);	1997	// calculate when the timeout would happen
1828	ev_tstamp timeout = last_activity + 60.;	1998	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
1829		1999
1830	// if last_activity + 60. is older than now, we did time out	2000	// if negative, it means we the timeout already occurred
1831	if (timeout < now)	2001	if (after < 0.)
1832	{	2002	{
1833	// timeout occurred, take action	2003	// timeout occurred, take action
1834	}	2004	}
1835	else	2005	else
1836	{	2006	{
1837	// callback was invoked, but there was some activity, re-arm	2007	// callback was invoked, but there was some recent
1838	// the watcher to fire in last_activity + 60, which is	2008	// activity. simply restart the timer to time out
1839	// guaranteed to be in the future, so "again" is positive:	2009	// after "after" seconds, which is the earliest time
1840	w->repeat = timeout - now;	2010	// the timeout can occur.
		2011	ev_timer_set (w, after, 0.);
1841	ev_timer_again (EV_A_ w);	2012	ev_timer_start (EV_A_ w);
1842	}	2013	}
1843	}	2014	}
1844		2015
1845	To summarise the callback: first calculate the real timeout (defined	2016	To summarise the callback: first calculate in how many seconds the
1846	as "60 seconds after the last activity"), then check if that time has	2017	timeout will occur (by calculating the absolute time when it would occur,
1847	been reached, which means something I<did>, in fact, time out. Otherwise	2018	C<last_activity + timeout>, and subtracting the current time, C<ev_now
1848	the callback was invoked too early (C<timeout> is in the future), so	2019	(EV_A)> from that).
1849	re-schedule the timer to fire at that future time, to see if maybe we have
1850	a timeout then.
1851		2020
1852	Note how C<ev_timer_again> is used, taking advantage of the	2021	If this value is negative, then we are already past the timeout, i.e. we
1853	C<ev_timer_again> optimisation when the timer is already running.	2022	timed out, and need to do whatever is needed in this case.
		2023
		2024	Otherwise, we now the earliest time at which the timeout would trigger,
		2025	and simply start the timer with this timeout value.
		2026
		2027	In other words, each time the callback is invoked it will check whether
		2028	the timeout occurred. If not, it will simply reschedule itself to check
		2029	again at the earliest time it could time out. Rinse. Repeat.
1854		2030
1855	This scheme causes more callback invocations (about one every 60 seconds	2031	This scheme causes more callback invocations (about one every 60 seconds
1856	minus half the average time between activity), but virtually no calls to	2032	minus half the average time between activity), but virtually no calls to
1857	libev to change the timeout.	2033	libev to change the timeout.
1858		2034
1859	To start the timer, simply initialise the watcher and set C<last_activity>	2035	To start the machinery, simply initialise the watcher and set
1860	to the current time (meaning we just have some activity :), then call the	2036	C<last_activity> to the current time (meaning there was some activity just
1861	callback, which will "do the right thing" and start the timer:	2037	now), then call the callback, which will "do the right thing" and start
		2038	the timer:
1862		2039
		2040	last_activity = ev_now (EV_A);
1863	ev_init (timer, callback);	2041	ev_init (&timer, callback);
1864	last_activity = ev_now (loop);	2042	callback (EV_A_ &timer, 0);
1865	callback (loop, timer, EV_TIMER);
1866		2043
1867	And when there is some activity, simply store the current time in	2044	When there is some activity, simply store the current time in
1868	C<last_activity>, no libev calls at all:	2045	C<last_activity>, no libev calls at all:
1869		2046
		2047	if (activity detected)
1870	last_activity = ev_now (loop);	2048	last_activity = ev_now (EV_A);
		2049
		2050	When your timeout value changes, then the timeout can be changed by simply
		2051	providing a new value, stopping the timer and calling the callback, which
		2052	will again do the right thing (for example, time out immediately :).
		2053
		2054	timeout = new_value;
		2055	ev_timer_stop (EV_A_ &timer);
		2056	callback (EV_A_ &timer, 0);
1871		2057
1872	This technique is slightly more complex, but in most cases where the	2058	This technique is slightly more complex, but in most cases where the
1873	time-out is unlikely to be triggered, much more efficient.	2059	time-out is unlikely to be triggered, much more efficient.
1874
1875	Changing the timeout is trivial as well (if it isn't hard-coded in the
1876	callback :) - just change the timeout and invoke the callback, which will
1877	fix things for you.
1878		2060
1879	=item 4. Wee, just use a double-linked list for your timeouts.	2061	=item 4. Wee, just use a double-linked list for your timeouts.
1880		2062
1881	If there is not one request, but many thousands (millions...), all	2063	If there is not one request, but many thousands (millions...), all
1882	employing some kind of timeout with the same timeout value, then one can	2064	employing some kind of timeout with the same timeout value, then one can
…		…
1909	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is	2091	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
1910	rather complicated, but extremely efficient, something that really pays	2092	rather complicated, but extremely efficient, something that really pays
1911	off after the first million or so of active timers, i.e. it's usually	2093	off after the first million or so of active timers, i.e. it's usually
1912	overkill :)	2094	overkill :)
1913		2095
		2096	=head3 The special problem of being too early
		2097
		2098	If you ask a timer to call your callback after three seconds, then
		2099	you expect it to be invoked after three seconds - but of course, this
		2100	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		2101	guaranteed to any precision by libev - imagine somebody suspending the
		2102	process with a STOP signal for a few hours for example.
		2103
		2104	So, libev tries to invoke your callback as soon as possible I<after> the
		2105	delay has occurred, but cannot guarantee this.
		2106
		2107	A less obvious failure mode is calling your callback too early: many event
		2108	loops compare timestamps with a "elapsed delay >= requested delay", but
		2109	this can cause your callback to be invoked much earlier than you would
		2110	expect.
		2111
		2112	To see why, imagine a system with a clock that only offers full second
		2113	resolution (think windows if you can't come up with a broken enough OS
		2114	yourself). If you schedule a one-second timer at the time 500.9, then the
		2115	event loop will schedule your timeout to elapse at a system time of 500
		2116	(500.9 truncated to the resolution) + 1, or 501.
		2117
		2118	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2119	501" and invoke the callback 0.1s after it was started, even though a
		2120	one-second delay was requested - this is being "too early", despite best
		2121	intentions.
		2122
		2123	This is the reason why libev will never invoke the callback if the elapsed
		2124	delay equals the requested delay, but only when the elapsed delay is
		2125	larger than the requested delay. In the example above, libev would only invoke
		2126	the callback at system time 502, or 1.1s after the timer was started.
		2127
		2128	So, while libev cannot guarantee that your callback will be invoked
		2129	exactly when requested, it I<can> and I<does> guarantee that the requested
		2130	delay has actually elapsed, or in other words, it always errs on the "too
		2131	late" side of things.
		2132
1914	=head3 The special problem of time updates	2133	=head3 The special problem of time updates
1915		2134
1916	Establishing the current time is a costly operation (it usually takes at	2135	Establishing the current time is a costly operation (it usually takes
1917	least two system calls): EV therefore updates its idea of the current	2136	at least one system call): EV therefore updates its idea of the current
1918	time only before and after C<ev_run> collects new events, which causes a	2137	time only before and after C<ev_run> collects new events, which causes a
1919	growing difference between C<ev_now ()> and C<ev_time ()> when handling	2138	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1920	lots of events in one iteration.	2139	lots of events in one iteration.
1921		2140
1922	The relative timeouts are calculated relative to the C<ev_now ()>	2141	The relative timeouts are calculated relative to the C<ev_now ()>
1923	time. This is usually the right thing as this timestamp refers to the time	2142	time. This is usually the right thing as this timestamp refers to the time
1924	of the event triggering whatever timeout you are modifying/starting. If	2143	of the event triggering whatever timeout you are modifying/starting. If
1925	you suspect event processing to be delayed and you I<need> to base the	2144	you suspect event processing to be delayed and you I<need> to base the
1926	timeout on the current time, use something like this to adjust for this:	2145	timeout on the current time, use something like the following to adjust
		2146	for it:
1927		2147
1928	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2148	ev_timer_set (&timer, after + (ev_time () - ev_now ()), 0.);
1929		2149
1930	If the event loop is suspended for a long time, you can also force an	2150	If the event loop is suspended for a long time, you can also force an
1931	update of the time returned by C<ev_now ()> by calling C<ev_now_update	2151	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1932	()>.	2152	()>, although that will push the event time of all outstanding events
		2153	further into the future.
		2154
		2155	=head3 The special problem of unsynchronised clocks
		2156
		2157	Modern systems have a variety of clocks - libev itself uses the normal
		2158	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2159	jumps).
		2160
		2161	Neither of these clocks is synchronised with each other or any other clock
		2162	on the system, so C<ev_time ()> might return a considerably different time
		2163	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2164	a call to C<gettimeofday> might return a second count that is one higher
		2165	than a directly following call to C<time>.
		2166
		2167	The moral of this is to only compare libev-related timestamps with
		2168	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2169	a second or so.
		2170
		2171	One more problem arises due to this lack of synchronisation: if libev uses
		2172	the system monotonic clock and you compare timestamps from C<ev_time>
		2173	or C<ev_now> from when you started your timer and when your callback is
		2174	invoked, you will find that sometimes the callback is a bit "early".
		2175
		2176	This is because C<ev_timer>s work in real time, not wall clock time, so
		2177	libev makes sure your callback is not invoked before the delay happened,
		2178	I<measured according to the real time>, not the system clock.
		2179
		2180	If your timeouts are based on a physical timescale (e.g. "time out this
		2181	connection after 100 seconds") then this shouldn't bother you as it is
		2182	exactly the right behaviour.
		2183
		2184	If you want to compare wall clock/system timestamps to your timers, then
		2185	you need to use C<ev_periodic>s, as these are based on the wall clock
		2186	time, where your comparisons will always generate correct results.
1933		2187
1934	=head3 The special problems of suspended animation	2188	=head3 The special problems of suspended animation
1935		2189
1936	When you leave the server world it is quite customary to hit machines that	2190	When you leave the server world it is quite customary to hit machines that
1937	can suspend/hibernate - what happens to the clocks during such a suspend?	2191	can suspend/hibernate - what happens to the clocks during such a suspend?
…		…
1967		2221
1968	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2222	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1969		2223
1970	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2224	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1971		2225
1972	Configure the timer to trigger after C<after> seconds. If C<repeat>	2226	Configure the timer to trigger after C<after> seconds (fractional and
1973	is C<0.>, then it will automatically be stopped once the timeout is	2227	negative values are supported). If C<repeat> is C<0.>, then it will
1974	reached. If it is positive, then the timer will automatically be	2228	automatically be stopped once the timeout is reached. If it is positive,
1975	configured to trigger again C<repeat> seconds later, again, and again,	2229	then the timer will automatically be configured to trigger again C<repeat>
1976	until stopped manually.	2230	seconds later, again, and again, until stopped manually.
1977		2231
1978	The timer itself will do a best-effort at avoiding drift, that is, if	2232	The timer itself will do a best-effort at avoiding drift, that is, if
1979	you configure a timer to trigger every 10 seconds, then it will normally	2233	you configure a timer to trigger every 10 seconds, then it will normally
1980	trigger at exactly 10 second intervals. If, however, your program cannot	2234	trigger at exactly 10 second intervals. If, however, your program cannot
1981	keep up with the timer (because it takes longer than those 10 seconds to	2235	keep up with the timer (because it takes longer than those 10 seconds to
1982	do stuff) the timer will not fire more than once per event loop iteration.	2236	do stuff) the timer will not fire more than once per event loop iteration.
1983		2237
1984	=item ev_timer_again (loop, ev_timer *)	2238	=item ev_timer_again (loop, ev_timer *)
1985		2239
1986	This will act as if the timer timed out and restart it again if it is	2240	This will act as if the timer timed out, and restarts it again if it is
1987	repeating. The exact semantics are:	2241	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2242	timeout to the C<repeat> value and calling C<ev_timer_start>.
1988		2243
		2244	The exact semantics are as in the following rules, all of which will be
		2245	applied to the watcher:
		2246
		2247	=over 4
		2248
1989	If the timer is pending, its pending status is cleared.	2249	=item If the timer is pending, the pending status is always cleared.
1990		2250
1991	If the timer is started but non-repeating, stop it (as if it timed out).	2251	=item If the timer is started but non-repeating, stop it (as if it timed
		2252	out, without invoking it).
1992		2253
1993	If the timer is repeating, either start it if necessary (with the	2254	=item If the timer is repeating, make the C<repeat> value the new timeout
1994	C<repeat> value), or reset the running timer to the C<repeat> value.	2255	and start the timer, if necessary.
1995		2256
		2257	=back
		2258
1996	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a	2259	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
1997	usage example.	2260	usage example.
1998		2261
1999	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)	2262	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
2000		2263
2001	Returns the remaining time until a timer fires. If the timer is active,	2264	Returns the remaining time until a timer fires. If the timer is active,
…		…
2054	Periodic watchers are also timers of a kind, but they are very versatile	2317	Periodic watchers are also timers of a kind, but they are very versatile
2055	(and unfortunately a bit complex).	2318	(and unfortunately a bit complex).
2056		2319
2057	Unlike C<ev_timer>, periodic watchers are not based on real time (or	2320	Unlike C<ev_timer>, periodic watchers are not based on real time (or
2058	relative time, the physical time that passes) but on wall clock time	2321	relative time, the physical time that passes) but on wall clock time
2059	(absolute time, the thing you can read on your calender or clock). The	2322	(absolute time, the thing you can read on your calendar or clock). The
2060	difference is that wall clock time can run faster or slower than real	2323	difference is that wall clock time can run faster or slower than real
2061	time, and time jumps are not uncommon (e.g. when you adjust your	2324	time, and time jumps are not uncommon (e.g. when you adjust your
2062	wrist-watch).	2325	wrist-watch).
2063		2326
2064	You can tell a periodic watcher to trigger after some specific point	2327	You can tell a periodic watcher to trigger after some specific point
…		…
2069	C<ev_timer>, which would still trigger roughly 10 seconds after starting	2332	C<ev_timer>, which would still trigger roughly 10 seconds after starting
2070	it, as it uses a relative timeout).	2333	it, as it uses a relative timeout).
2071		2334
2072	C<ev_periodic> watchers can also be used to implement vastly more complex	2335	C<ev_periodic> watchers can also be used to implement vastly more complex
2073	timers, such as triggering an event on each "midnight, local time", or	2336	timers, such as triggering an event on each "midnight, local time", or
2074	other complicated rules. This cannot be done with C<ev_timer> watchers, as	2337	other complicated rules. This cannot easily be done with C<ev_timer>
2075	those cannot react to time jumps.	2338	watchers, as those cannot react to time jumps.
2076		2339
2077	As with timers, the callback is guaranteed to be invoked only when the	2340	As with timers, the callback is guaranteed to be invoked only when the
2078	point in time where it is supposed to trigger has passed. If multiple	2341	point in time where it is supposed to trigger has passed. If multiple
2079	timers become ready during the same loop iteration then the ones with	2342	timers become ready during the same loop iteration then the ones with
2080	earlier time-out values are invoked before ones with later time-out values	2343	earlier time-out values are invoked before ones with later time-out values
…		…
2121		2384
2122	Another way to think about it (for the mathematically inclined) is that	2385	Another way to think about it (for the mathematically inclined) is that
2123	C<ev_periodic> will try to run the callback in this mode at the next possible	2386	C<ev_periodic> will try to run the callback in this mode at the next possible
2124	time where C<time = offset (mod interval)>, regardless of any time jumps.	2387	time where C<time = offset (mod interval)>, regardless of any time jumps.
2125		2388
2126	For numerical stability it is preferable that the C<offset> value is near	2389	The C<interval> I<MUST> be positive, and for numerical stability, the
2127	C<ev_now ()> (the current time), but there is no range requirement for	2390	interval value should be higher than C<1/8192> (which is around 100
2128	this value, and in fact is often specified as zero.	2391	microseconds) and C<offset> should be higher than C<0> and should have
		2392	at most a similar magnitude as the current time (say, within a factor of
		2393	ten). Typical values for offset are, in fact, C<0> or something between
		2394	C<0> and C<interval>, which is also the recommended range.
2129		2395
2130	Note also that there is an upper limit to how often a timer can fire (CPU	2396	Note also that there is an upper limit to how often a timer can fire (CPU
2131	speed for example), so if C<interval> is very small then timing stability	2397	speed for example), so if C<interval> is very small then timing stability
2132	will of course deteriorate. Libev itself tries to be exact to be about one	2398	will of course deteriorate. Libev itself tries to be exact to be about one
2133	millisecond (if the OS supports it and the machine is fast enough).	2399	millisecond (if the OS supports it and the machine is fast enough).
…		…
2163		2429
2164	NOTE: I<< This callback must always return a time that is higher than or	2430	NOTE: I<< This callback must always return a time that is higher than or
2165	equal to the passed C<now> value >>.	2431	equal to the passed C<now> value >>.
2166		2432
2167	This can be used to create very complex timers, such as a timer that	2433	This can be used to create very complex timers, such as a timer that
2168	triggers on "next midnight, local time". To do this, you would calculate the	2434	triggers on "next midnight, local time". To do this, you would calculate
2169	next midnight after C<now> and return the timestamp value for this. How	2435	the next midnight after C<now> and return the timestamp value for
2170	you do this is, again, up to you (but it is not trivial, which is the main	2436	this. Here is a (completely untested, no error checking) example on how to
2171	reason I omitted it as an example).	2437	do this:
		2438
		2439	#include <time.h>
		2440
		2441	static ev_tstamp
		2442	my_rescheduler (ev_periodic *w, ev_tstamp now)
		2443	{
		2444	time_t tnow = (time_t)now;
		2445	struct tm tm;
		2446	localtime_r (&tnow, &tm);
		2447
		2448	tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
		2449	++tm.tm_mday; // midnight next day
		2450
		2451	return mktime (&tm);
		2452	}
		2453
		2454	Note: this code might run into trouble on days that have more then two
		2455	midnights (beginning and end).
2172		2456
2173	=back	2457	=back
2174		2458
2175	=item ev_periodic_again (loop, ev_periodic *)	2459	=item ev_periodic_again (loop, ev_periodic *)
2176		2460
…		…
2241		2525
2242	ev_periodic hourly_tick;	2526	ev_periodic hourly_tick;
2243	ev_periodic_init (&hourly_tick, clock_cb,	2527	ev_periodic_init (&hourly_tick, clock_cb,
2244	fmod (ev_now (loop), 3600.), 3600., 0);	2528	fmod (ev_now (loop), 3600.), 3600., 0);
2245	ev_periodic_start (loop, &hourly_tick);	2529	ev_periodic_start (loop, &hourly_tick);
2246		2530
2247		2531
2248	=head2 C<ev_signal> - signal me when a signal gets signalled!	2532	=head2 C<ev_signal> - signal me when a signal gets signalled!
2249		2533
2250	Signal watchers will trigger an event when the process receives a specific	2534	Signal watchers will trigger an event when the process receives a specific
2251	signal one or more times. Even though signals are very asynchronous, libev	2535	signal one or more times. Even though signals are very asynchronous, libev
2252	will try it's best to deliver signals synchronously, i.e. as part of the	2536	will try its best to deliver signals synchronously, i.e. as part of the
2253	normal event processing, like any other event.	2537	normal event processing, like any other event.
2254		2538
2255	If you want signals to be delivered truly asynchronously, just use	2539	If you want signals to be delivered truly asynchronously, just use
2256	C<sigaction> as you would do without libev and forget about sharing	2540	C<sigaction> as you would do without libev and forget about sharing
2257	the signal. You can even use C<ev_async> from a signal handler to	2541	the signal. You can even use C<ev_async> from a signal handler to
…		…
2261	only within the same loop, i.e. you can watch for C<SIGINT> in your	2545	only within the same loop, i.e. you can watch for C<SIGINT> in your
2262	default loop and for C<SIGIO> in another loop, but you cannot watch for	2546	default loop and for C<SIGIO> in another loop, but you cannot watch for
2263	C<SIGINT> in both the default loop and another loop at the same time. At	2547	C<SIGINT> in both the default loop and another loop at the same time. At
2264	the moment, C<SIGCHLD> is permanently tied to the default loop.	2548	the moment, C<SIGCHLD> is permanently tied to the default loop.
2265		2549
2266	When the first watcher gets started will libev actually register something	2550	Only after the first watcher for a signal is started will libev actually
2267	with the kernel (thus it coexists with your own signal handlers as long as	2551	register something with the kernel. It thus coexists with your own signal
2268	you don't register any with libev for the same signal).	2552	handlers as long as you don't register any with libev for the same signal.
2269		2553
2270	If possible and supported, libev will install its handlers with	2554	If possible and supported, libev will install its handlers with
2271	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should	2555	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
2272	not be unduly interrupted. If you have a problem with system calls getting	2556	not be unduly interrupted. If you have a problem with system calls getting
2273	interrupted by signals you can block all signals in an C<ev_check> watcher	2557	interrupted by signals you can block all signals in an C<ev_check> watcher
…		…
2276	=head3 The special problem of inheritance over fork/execve/pthread_create	2560	=head3 The special problem of inheritance over fork/execve/pthread_create
2277		2561
2278	Both the signal mask (C<sigprocmask>) and the signal disposition	2562	Both the signal mask (C<sigprocmask>) and the signal disposition
2279	(C<sigaction>) are unspecified after starting a signal watcher (and after	2563	(C<sigaction>) are unspecified after starting a signal watcher (and after
2280	stopping it again), that is, libev might or might not block the signal,	2564	stopping it again), that is, libev might or might not block the signal,
2281	and might or might not set or restore the installed signal handler.	2565	and might or might not set or restore the installed signal handler (but
		2566	see C<EVFLAG_NOSIGMASK>).
2282		2567
2283	While this does not matter for the signal disposition (libev never	2568	While this does not matter for the signal disposition (libev never
2284	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on	2569	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
2285	C<execve>), this matters for the signal mask: many programs do not expect	2570	C<execve>), this matters for the signal mask: many programs do not expect
2286	certain signals to be blocked.	2571	certain signals to be blocked.
…		…
2299	I<has> to modify the signal mask, at least temporarily.	2584	I<has> to modify the signal mask, at least temporarily.
2300		2585
2301	So I can't stress this enough: I<If you do not reset your signal mask when	2586	So I can't stress this enough: I<If you do not reset your signal mask when
2302	you expect it to be empty, you have a race condition in your code>. This	2587	you expect it to be empty, you have a race condition in your code>. This
2303	is not a libev-specific thing, this is true for most event libraries.	2588	is not a libev-specific thing, this is true for most event libraries.
		2589
		2590	=head3 The special problem of threads signal handling
		2591
		2592	POSIX threads has problematic signal handling semantics, specifically,
		2593	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2594	threads in a process block signals, which is hard to achieve.
		2595
		2596	When you want to use sigwait (or mix libev signal handling with your own
		2597	for the same signals), you can tackle this problem by globally blocking
		2598	all signals before creating any threads (or creating them with a fully set
		2599	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2600	loops. Then designate one thread as "signal receiver thread" which handles
		2601	these signals. You can pass on any signals that libev might be interested
		2602	in by calling C<ev_feed_signal>.
2304		2603
2305	=head3 Watcher-Specific Functions and Data Members	2604	=head3 Watcher-Specific Functions and Data Members
2306		2605
2307	=over 4	2606	=over 4
2308		2607
…		…
2443		2742
2444	=head2 C<ev_stat> - did the file attributes just change?	2743	=head2 C<ev_stat> - did the file attributes just change?
2445		2744
2446	This watches a file system path for attribute changes. That is, it calls	2745	This watches a file system path for attribute changes. That is, it calls
2447	C<stat> on that path in regular intervals (or when the OS says it changed)	2746	C<stat> on that path in regular intervals (or when the OS says it changed)
2448	and sees if it changed compared to the last time, invoking the callback if	2747	and sees if it changed compared to the last time, invoking the callback
2449	it did.	2748	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2749	happen after the watcher has been started will be reported.
2450		2750
2451	The path does not need to exist: changing from "path exists" to "path does	2751	The path does not need to exist: changing from "path exists" to "path does
2452	not exist" is a status change like any other. The condition "path does not	2752	not exist" is a status change like any other. The condition "path does not
2453	exist" (or more correctly "path cannot be stat'ed") is signified by the	2753	exist" (or more correctly "path cannot be stat'ed") is signified by the
2454	C<st_nlink> field being zero (which is otherwise always forced to be at	2754	C<st_nlink> field being zero (which is otherwise always forced to be at
…		…
2684	Apart from keeping your process non-blocking (which is a useful	2984	Apart from keeping your process non-blocking (which is a useful
2685	effect on its own sometimes), idle watchers are a good place to do	2985	effect on its own sometimes), idle watchers are a good place to do
2686	"pseudo-background processing", or delay processing stuff to after the	2986	"pseudo-background processing", or delay processing stuff to after the
2687	event loop has handled all outstanding events.	2987	event loop has handled all outstanding events.
2688		2988
		2989	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2990
		2991	As long as there is at least one active idle watcher, libev will never
		2992	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2993	For this to work, the idle watcher doesn't need to be invoked at all - the
		2994	lowest priority will do.
		2995
		2996	This mode of operation can be useful together with an C<ev_check> watcher,
		2997	to do something on each event loop iteration - for example to balance load
		2998	between different connections.
		2999
		3000	See L</Abusing an ev_check watcher for its side-effect> for a longer
		3001	example.
		3002
2689	=head3 Watcher-Specific Functions and Data Members	3003	=head3 Watcher-Specific Functions and Data Members
2690		3004
2691	=over 4	3005	=over 4
2692		3006
2693	=item ev_idle_init (ev_idle *, callback)	3007	=item ev_idle_init (ev_idle *, callback)
…		…
2704	callback, free it. Also, use no error checking, as usual.	3018	callback, free it. Also, use no error checking, as usual.
2705		3019
2706	static void	3020	static void
2707	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)	3021	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2708	{	3022	{
		3023	// stop the watcher
		3024	ev_idle_stop (loop, w);
		3025
		3026	// now we can free it
2709	free (w);	3027	free (w);
		3028
2710	// now do something you wanted to do when the program has	3029	// now do something you wanted to do when the program has
2711	// no longer anything immediate to do.	3030	// no longer anything immediate to do.
2712	}	3031	}
2713		3032
2714	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	3033	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
…		…
2716	ev_idle_start (loop, idle_watcher);	3035	ev_idle_start (loop, idle_watcher);
2717		3036
2718		3037
2719	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	3038	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2720		3039
2721	Prepare and check watchers are usually (but not always) used in pairs:	3040	Prepare and check watchers are often (but not always) used in pairs:
2722	prepare watchers get invoked before the process blocks and check watchers	3041	prepare watchers get invoked before the process blocks and check watchers
2723	afterwards.	3042	afterwards.
2724		3043
2725	You I<must not> call C<ev_run> or similar functions that enter	3044	You I<must not> call C<ev_run> (or similar functions that enter the
2726	the current event loop from either C<ev_prepare> or C<ev_check>	3045	current event loop) or C<ev_loop_fork> from either C<ev_prepare> or
2727	watchers. Other loops than the current one are fine, however. The	3046	C<ev_check> watchers. Other loops than the current one are fine,
2728	rationale behind this is that you do not need to check for recursion in	3047	however. The rationale behind this is that you do not need to check
2729	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	3048	for recursion in those watchers, i.e. the sequence will always be
2730	C<ev_check> so if you have one watcher of each kind they will always be	3049	C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
2731	called in pairs bracketing the blocking call.	3050	kind they will always be called in pairs bracketing the blocking call.
2732		3051
2733	Their main purpose is to integrate other event mechanisms into libev and	3052	Their main purpose is to integrate other event mechanisms into libev and
2734	their use is somewhat advanced. They could be used, for example, to track	3053	their use is somewhat advanced. They could be used, for example, to track
2735	variable changes, implement your own watchers, integrate net-snmp or a	3054	variable changes, implement your own watchers, integrate net-snmp or a
2736	coroutine library and lots more. They are also occasionally useful if	3055	coroutine library and lots more. They are also occasionally useful if
…		…
2754	with priority higher than or equal to the event loop and one coroutine	3073	with priority higher than or equal to the event loop and one coroutine
2755	of lower priority, but only once, using idle watchers to keep the event	3074	of lower priority, but only once, using idle watchers to keep the event
2756	loop from blocking if lower-priority coroutines are active, thus mapping	3075	loop from blocking if lower-priority coroutines are active, thus mapping
2757	low-priority coroutines to idle/background tasks).	3076	low-priority coroutines to idle/background tasks).
2758		3077
2759	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	3078	When used for this purpose, it is recommended to give C<ev_check> watchers
2760	priority, to ensure that they are being run before any other watchers	3079	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
2761	after the poll (this doesn't matter for C<ev_prepare> watchers).	3080	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		3081	watchers).
2762		3082
2763	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not	3083	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
2764	activate ("feed") events into libev. While libev fully supports this, they	3084	activate ("feed") events into libev. While libev fully supports this, they
2765	might get executed before other C<ev_check> watchers did their job. As	3085	might get executed before other C<ev_check> watchers did their job. As
2766	C<ev_check> watchers are often used to embed other (non-libev) event	3086	C<ev_check> watchers are often used to embed other (non-libev) event
2767	loops those other event loops might be in an unusable state until their	3087	loops those other event loops might be in an unusable state until their
2768	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	3088	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
2769	others).	3089	others).
		3090
		3091	=head3 Abusing an C<ev_check> watcher for its side-effect
		3092
		3093	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		3094	useful because they are called once per event loop iteration. For
		3095	example, if you want to handle a large number of connections fairly, you
		3096	normally only do a bit of work for each active connection, and if there
		3097	is more work to do, you wait for the next event loop iteration, so other
		3098	connections have a chance of making progress.
		3099
		3100	Using an C<ev_check> watcher is almost enough: it will be called on the
		3101	next event loop iteration. However, that isn't as soon as possible -
		3102	without external events, your C<ev_check> watcher will not be invoked.
		3103
		3104	This is where C<ev_idle> watchers come in handy - all you need is a
		3105	single global idle watcher that is active as long as you have one active
		3106	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		3107	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		3108	invoked. Neither watcher alone can do that.
2770		3109
2771	=head3 Watcher-Specific Functions and Data Members	3110	=head3 Watcher-Specific Functions and Data Members
2772		3111
2773	=over 4	3112	=over 4
2774		3113
…		…
2975		3314
2976	=over 4	3315	=over 4
2977		3316
2978	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3317	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
2979		3318
2980	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3319	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
2981		3320
2982	Configures the watcher to embed the given loop, which must be	3321	Configures the watcher to embed the given loop, which must be
2983	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3322	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
2984	invoked automatically, otherwise it is the responsibility of the callback	3323	invoked automatically, otherwise it is the responsibility of the callback
2985	to invoke it (it will continue to be called until the sweep has been done,	3324	to invoke it (it will continue to be called until the sweep has been done,
…		…
3006	used).	3345	used).
3007		3346
3008	struct ev_loop *loop_hi = ev_default_init (0);	3347	struct ev_loop *loop_hi = ev_default_init (0);
3009	struct ev_loop *loop_lo = 0;	3348	struct ev_loop *loop_lo = 0;
3010	ev_embed embed;	3349	ev_embed embed;
3011		3350
3012	// see if there is a chance of getting one that works	3351	// see if there is a chance of getting one that works
3013	// (remember that a flags value of 0 means autodetection)	3352	// (remember that a flags value of 0 means autodetection)
3014	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3353	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3015	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3354	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3016	: 0;	3355	: 0;
…		…
3030	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3369	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
3031		3370
3032	struct ev_loop *loop = ev_default_init (0);	3371	struct ev_loop *loop = ev_default_init (0);
3033	struct ev_loop *loop_socket = 0;	3372	struct ev_loop *loop_socket = 0;
3034	ev_embed embed;	3373	ev_embed embed;
3035		3374
3036	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3375	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3037	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3376	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3038	{	3377	{
3039	ev_embed_init (&embed, 0, loop_socket);	3378	ev_embed_init (&embed, 0, loop_socket);
3040	ev_embed_start (loop, &embed);	3379	ev_embed_start (loop, &embed);
…		…
3048		3387
3049	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3388	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
3050		3389
3051	Fork watchers are called when a C<fork ()> was detected (usually because	3390	Fork watchers are called when a C<fork ()> was detected (usually because
3052	whoever is a good citizen cared to tell libev about it by calling	3391	whoever is a good citizen cared to tell libev about it by calling
3053	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the	3392	C<ev_loop_fork>). The invocation is done before the event loop blocks next
3054	event loop blocks next and before C<ev_check> watchers are being called,	3393	and before C<ev_check> watchers are being called, and only in the child
3055	and only in the child after the fork. If whoever good citizen calling	3394	after the fork. If whoever good citizen calling C<ev_default_fork> cheats
3056	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3395	and calls it in the wrong process, the fork handlers will be invoked, too,
3057	handlers will be invoked, too, of course.	3396	of course.
3058		3397
3059	=head3 The special problem of life after fork - how is it possible?	3398	=head3 The special problem of life after fork - how is it possible?
3060		3399
3061	Most uses of C<fork()> consist of forking, then some simple calls to set	3400	Most uses of C<fork ()> consist of forking, then some simple calls to set
3062	up/change the process environment, followed by a call to C<exec()>. This	3401	up/change the process environment, followed by a call to C<exec()>. This
3063	sequence should be handled by libev without any problems.	3402	sequence should be handled by libev without any problems.
3064		3403
3065	This changes when the application actually wants to do event handling	3404	This changes when the application actually wants to do event handling
3066	in the child, or both parent in child, in effect "continuing" after the	3405	in the child, or both parent in child, in effect "continuing" after the
…		…
3092		3431
3093	=head3 Watcher-Specific Functions and Data Members	3432	=head3 Watcher-Specific Functions and Data Members
3094		3433
3095	=over 4	3434	=over 4
3096		3435
3097	=item ev_fork_init (ev_signal *, callback)	3436	=item ev_fork_init (ev_fork *, callback)
3098		3437
3099	Initialises and configures the fork watcher - it has no parameters of any	3438	Initialises and configures the fork watcher - it has no parameters of any
3100	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,	3439	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
3101	believe me.	3440	really.
3102		3441
3103	=back	3442	=back
3104		3443
3105		3444
		3445	=head2 C<ev_cleanup> - even the best things end
		3446
		3447	Cleanup watchers are called just before the event loop is being destroyed
		3448	by a call to C<ev_loop_destroy>.
		3449
		3450	While there is no guarantee that the event loop gets destroyed, cleanup
		3451	watchers provide a convenient method to install cleanup hooks for your
		3452	program, worker threads and so on - you just to make sure to destroy the
		3453	loop when you want them to be invoked.
		3454
		3455	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3456	all other watchers, they do not keep a reference to the event loop (which
		3457	makes a lot of sense if you think about it). Like all other watchers, you
		3458	can call libev functions in the callback, except C<ev_cleanup_start>.
		3459
		3460	=head3 Watcher-Specific Functions and Data Members
		3461
		3462	=over 4
		3463
		3464	=item ev_cleanup_init (ev_cleanup *, callback)
		3465
		3466	Initialises and configures the cleanup watcher - it has no parameters of
		3467	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3468	pointless, I assure you.
		3469
		3470	=back
		3471
		3472	Example: Register an atexit handler to destroy the default loop, so any
		3473	cleanup functions are called.
		3474
		3475	static void
		3476	program_exits (void)
		3477	{
		3478	ev_loop_destroy (EV_DEFAULT_UC);
		3479	}
		3480
		3481	...
		3482	atexit (program_exits);
		3483
		3484
3106	=head2 C<ev_async> - how to wake up an event loop	3485	=head2 C<ev_async> - how to wake up an event loop
3107		3486
3108	In general, you cannot use an C<ev_run> from multiple threads or other	3487	In general, you cannot use an C<ev_loop> from multiple threads or other
3109	asynchronous sources such as signal handlers (as opposed to multiple event	3488	asynchronous sources such as signal handlers (as opposed to multiple event
3110	loops - those are of course safe to use in different threads).	3489	loops - those are of course safe to use in different threads).
3111		3490
3112	Sometimes, however, you need to wake up an event loop you do not control,	3491	Sometimes, however, you need to wake up an event loop you do not control,
3113	for example because it belongs to another thread. This is what C<ev_async>	3492	for example because it belongs to another thread. This is what C<ev_async>
…		…
3115	it by calling C<ev_async_send>, which is thread- and signal safe.	3494	it by calling C<ev_async_send>, which is thread- and signal safe.
3116		3495
3117	This functionality is very similar to C<ev_signal> watchers, as signals,	3496	This functionality is very similar to C<ev_signal> watchers, as signals,
3118	too, are asynchronous in nature, and signals, too, will be compressed	3497	too, are asynchronous in nature, and signals, too, will be compressed
3119	(i.e. the number of callback invocations may be less than the number of	3498	(i.e. the number of callback invocations may be less than the number of
3120	C<ev_async_sent> calls).	3499	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
3121		3500	of "global async watchers" by using a watcher on an otherwise unused
3122	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not	3501	signal, and C<ev_feed_signal> to signal this watcher from another thread,
3123	just the default loop.	3502	even without knowing which loop owns the signal.
3124		3503
3125	=head3 Queueing	3504	=head3 Queueing
3126		3505
3127	C<ev_async> does not support queueing of data in any way. The reason	3506	C<ev_async> does not support queueing of data in any way. The reason
3128	is that the author does not know of a simple (or any) algorithm for a	3507	is that the author does not know of a simple (or any) algorithm for a
…		…
3220	trust me.	3599	trust me.
3221		3600
3222	=item ev_async_send (loop, ev_async *)	3601	=item ev_async_send (loop, ev_async *)
3223		3602
3224	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3603	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
3225	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3604	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3605	returns.
		3606
3226	C<ev_feed_event>, this call is safe to do from other threads, signal or	3607	Unlike C<ev_feed_event>, this call is safe to do from other threads,
3227	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3608	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3228	section below on what exactly this means).	3609	embedding section below on what exactly this means).
3229		3610
3230	Note that, as with other watchers in libev, multiple events might get	3611	Note that, as with other watchers in libev, multiple events might get
3231	compressed into a single callback invocation (another way to look at this	3612	compressed into a single callback invocation (another way to look at
3232	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,	3613	this is that C<ev_async> watchers are level-triggered: they are set on
3233	reset when the event loop detects that).	3614	C<ev_async_send>, reset when the event loop detects that).
3234		3615
3235	This call incurs the overhead of a system call only once per event loop	3616	This call incurs the overhead of at most one extra system call per event
3236	iteration, so while the overhead might be noticeable, it doesn't apply to	3617	loop iteration, if the event loop is blocked, and no syscall at all if
3237	repeated calls to C<ev_async_send> for the same event loop.	3618	the event loop (or your program) is processing events. That means that
		3619	repeated calls are basically free (there is no need to avoid calls for
		3620	performance reasons) and that the overhead becomes smaller (typically
		3621	zero) under load.
3238		3622
3239	=item bool = ev_async_pending (ev_async *)	3623	=item bool = ev_async_pending (ev_async *)
3240		3624
3241	Returns a non-zero value when C<ev_async_send> has been called on the	3625	Returns a non-zero value when C<ev_async_send> has been called on the
3242	watcher but the event has not yet been processed (or even noted) by the	3626	watcher but the event has not yet been processed (or even noted) by the
…		…
3259		3643
3260	There are some other functions of possible interest. Described. Here. Now.	3644	There are some other functions of possible interest. Described. Here. Now.
3261		3645
3262	=over 4	3646	=over 4
3263		3647
3264	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3648	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)
3265		3649
3266	This function combines a simple timer and an I/O watcher, calls your	3650	This function combines a simple timer and an I/O watcher, calls your
3267	callback on whichever event happens first and automatically stops both	3651	callback on whichever event happens first and automatically stops both
3268	watchers. This is useful if you want to wait for a single event on an fd	3652	watchers. This is useful if you want to wait for a single event on an fd
3269	or timeout without having to allocate/configure/start/stop/free one or	3653	or timeout without having to allocate/configure/start/stop/free one or
…		…
3297	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3681	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3298		3682
3299	=item ev_feed_fd_event (loop, int fd, int revents)	3683	=item ev_feed_fd_event (loop, int fd, int revents)
3300		3684
3301	Feed an event on the given fd, as if a file descriptor backend detected	3685	Feed an event on the given fd, as if a file descriptor backend detected
3302	the given events it.	3686	the given events.
3303		3687
3304	=item ev_feed_signal_event (loop, int signum)	3688	=item ev_feed_signal_event (loop, int signum)
3305		3689
3306	Feed an event as if the given signal occurred (C<loop> must be the default	3690	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3307	loop!).	3691	which is async-safe.
3308		3692
3309	=back	3693	=back
		3694
		3695
		3696	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3697
		3698	This section explains some common idioms that are not immediately
		3699	obvious. Note that examples are sprinkled over the whole manual, and this
		3700	section only contains stuff that wouldn't fit anywhere else.
		3701
		3702	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3703
		3704	Each watcher has, by default, a C<void *data> member that you can read
		3705	or modify at any time: libev will completely ignore it. This can be used
		3706	to associate arbitrary data with your watcher. If you need more data and
		3707	don't want to allocate memory separately and store a pointer to it in that
		3708	data member, you can also "subclass" the watcher type and provide your own
		3709	data:
		3710
		3711	struct my_io
		3712	{
		3713	ev_io io;
		3714	int otherfd;
		3715	void *somedata;
		3716	struct whatever *mostinteresting;
		3717	};
		3718
		3719	...
		3720	struct my_io w;
		3721	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3722
		3723	And since your callback will be called with a pointer to the watcher, you
		3724	can cast it back to your own type:
		3725
		3726	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3727	{
		3728	struct my_io *w = (struct my_io *)w_;
		3729	...
		3730	}
		3731
		3732	More interesting and less C-conformant ways of casting your callback
		3733	function type instead have been omitted.
		3734
		3735	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3736
		3737	Another common scenario is to use some data structure with multiple
		3738	embedded watchers, in effect creating your own watcher that combines
		3739	multiple libev event sources into one "super-watcher":
		3740
		3741	struct my_biggy
		3742	{
		3743	int some_data;
		3744	ev_timer t1;
		3745	ev_timer t2;
		3746	}
		3747
		3748	In this case getting the pointer to C<my_biggy> is a bit more
		3749	complicated: Either you store the address of your C<my_biggy> struct in
		3750	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3751	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3752	real programmers):
		3753
		3754	#include <stddef.h>
		3755
		3756	static void
		3757	t1_cb (EV_P_ ev_timer *w, int revents)
		3758	{
		3759	struct my_biggy big = (struct my_biggy *)
		3760	(((char *)w) - offsetof (struct my_biggy, t1));
		3761	}
		3762
		3763	static void
		3764	t2_cb (EV_P_ ev_timer *w, int revents)
		3765	{
		3766	struct my_biggy big = (struct my_biggy *)
		3767	(((char *)w) - offsetof (struct my_biggy, t2));
		3768	}
		3769
		3770	=head2 AVOIDING FINISHING BEFORE RETURNING
		3771
		3772	Often you have structures like this in event-based programs:
		3773
		3774	callback ()
		3775	{
		3776	free (request);
		3777	}
		3778
		3779	request = start_new_request (..., callback);
		3780
		3781	The intent is to start some "lengthy" operation. The C<request> could be
		3782	used to cancel the operation, or do other things with it.
		3783
		3784	It's not uncommon to have code paths in C<start_new_request> that
		3785	immediately invoke the callback, for example, to report errors. Or you add
		3786	some caching layer that finds that it can skip the lengthy aspects of the
		3787	operation and simply invoke the callback with the result.
		3788
		3789	The problem here is that this will happen I<before> C<start_new_request>
		3790	has returned, so C<request> is not set.
		3791
		3792	Even if you pass the request by some safer means to the callback, you
		3793	might want to do something to the request after starting it, such as
		3794	canceling it, which probably isn't working so well when the callback has
		3795	already been invoked.
		3796
		3797	A common way around all these issues is to make sure that
		3798	C<start_new_request> I<always> returns before the callback is invoked. If
		3799	C<start_new_request> immediately knows the result, it can artificially
		3800	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3801	example, or more sneakily, by reusing an existing (stopped) watcher and
		3802	pushing it into the pending queue:
		3803
		3804	ev_set_cb (watcher, callback);
		3805	ev_feed_event (EV_A_ watcher, 0);
		3806
		3807	This way, C<start_new_request> can safely return before the callback is
		3808	invoked, while not delaying callback invocation too much.
		3809
		3810	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3811
		3812	Often (especially in GUI toolkits) there are places where you have
		3813	I<modal> interaction, which is most easily implemented by recursively
		3814	invoking C<ev_run>.
		3815
		3816	This brings the problem of exiting - a callback might want to finish the
		3817	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3818	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3819	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3820	other combination: In these cases, a simple C<ev_break> will not work.
		3821
		3822	The solution is to maintain "break this loop" variable for each C<ev_run>
		3823	invocation, and use a loop around C<ev_run> until the condition is
		3824	triggered, using C<EVRUN_ONCE>:
		3825
		3826	// main loop
		3827	int exit_main_loop = 0;
		3828
		3829	while (!exit_main_loop)
		3830	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3831
		3832	// in a modal watcher
		3833	int exit_nested_loop = 0;
		3834
		3835	while (!exit_nested_loop)
		3836	ev_run (EV_A_ EVRUN_ONCE);
		3837
		3838	To exit from any of these loops, just set the corresponding exit variable:
		3839
		3840	// exit modal loop
		3841	exit_nested_loop = 1;
		3842
		3843	// exit main program, after modal loop is finished
		3844	exit_main_loop = 1;
		3845
		3846	// exit both
		3847	exit_main_loop = exit_nested_loop = 1;
		3848
		3849	=head2 THREAD LOCKING EXAMPLE
		3850
		3851	Here is a fictitious example of how to run an event loop in a different
		3852	thread from where callbacks are being invoked and watchers are
		3853	created/added/removed.
		3854
		3855	For a real-world example, see the C<EV::Loop::Async> perl module,
		3856	which uses exactly this technique (which is suited for many high-level
		3857	languages).
		3858
		3859	The example uses a pthread mutex to protect the loop data, a condition
		3860	variable to wait for callback invocations, an async watcher to notify the
		3861	event loop thread and an unspecified mechanism to wake up the main thread.
		3862
		3863	First, you need to associate some data with the event loop:
		3864
		3865	typedef struct {
		3866	mutex_t lock; /* global loop lock */
		3867	ev_async async_w;
		3868	thread_t tid;
		3869	cond_t invoke_cv;
		3870	} userdata;
		3871
		3872	void prepare_loop (EV_P)
		3873	{
		3874	// for simplicity, we use a static userdata struct.
		3875	static userdata u;
		3876
		3877	ev_async_init (&u->async_w, async_cb);
		3878	ev_async_start (EV_A_ &u->async_w);
		3879
		3880	pthread_mutex_init (&u->lock, 0);
		3881	pthread_cond_init (&u->invoke_cv, 0);
		3882
		3883	// now associate this with the loop
		3884	ev_set_userdata (EV_A_ u);
		3885	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3886	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3887
		3888	// then create the thread running ev_run
		3889	pthread_create (&u->tid, 0, l_run, EV_A);
		3890	}
		3891
		3892	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3893	solely to wake up the event loop so it takes notice of any new watchers
		3894	that might have been added:
		3895
		3896	static void
		3897	async_cb (EV_P_ ev_async *w, int revents)
		3898	{
		3899	// just used for the side effects
		3900	}
		3901
		3902	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3903	protecting the loop data, respectively.
		3904
		3905	static void
		3906	l_release (EV_P)
		3907	{
		3908	userdata *u = ev_userdata (EV_A);
		3909	pthread_mutex_unlock (&u->lock);
		3910	}
		3911
		3912	static void
		3913	l_acquire (EV_P)
		3914	{
		3915	userdata *u = ev_userdata (EV_A);
		3916	pthread_mutex_lock (&u->lock);
		3917	}
		3918
		3919	The event loop thread first acquires the mutex, and then jumps straight
		3920	into C<ev_run>:
		3921
		3922	void *
		3923	l_run (void *thr_arg)
		3924	{
		3925	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3926
		3927	l_acquire (EV_A);
		3928	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3929	ev_run (EV_A_ 0);
		3930	l_release (EV_A);
		3931
		3932	return 0;
		3933	}
		3934
		3935	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3936	signal the main thread via some unspecified mechanism (signals? pipe
		3937	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3938	have been called (in a while loop because a) spurious wakeups are possible
		3939	and b) skipping inter-thread-communication when there are no pending
		3940	watchers is very beneficial):
		3941
		3942	static void
		3943	l_invoke (EV_P)
		3944	{
		3945	userdata *u = ev_userdata (EV_A);
		3946
		3947	while (ev_pending_count (EV_A))
		3948	{
		3949	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3950	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3951	}
		3952	}
		3953
		3954	Now, whenever the main thread gets told to invoke pending watchers, it
		3955	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3956	thread to continue:
		3957
		3958	static void
		3959	real_invoke_pending (EV_P)
		3960	{
		3961	userdata *u = ev_userdata (EV_A);
		3962
		3963	pthread_mutex_lock (&u->lock);
		3964	ev_invoke_pending (EV_A);
		3965	pthread_cond_signal (&u->invoke_cv);
		3966	pthread_mutex_unlock (&u->lock);
		3967	}
		3968
		3969	Whenever you want to start/stop a watcher or do other modifications to an
		3970	event loop, you will now have to lock:
		3971
		3972	ev_timer timeout_watcher;
		3973	userdata *u = ev_userdata (EV_A);
		3974
		3975	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3976
		3977	pthread_mutex_lock (&u->lock);
		3978	ev_timer_start (EV_A_ &timeout_watcher);
		3979	ev_async_send (EV_A_ &u->async_w);
		3980	pthread_mutex_unlock (&u->lock);
		3981
		3982	Note that sending the C<ev_async> watcher is required because otherwise
		3983	an event loop currently blocking in the kernel will have no knowledge
		3984	about the newly added timer. By waking up the loop it will pick up any new
		3985	watchers in the next event loop iteration.
		3986
		3987	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3988
		3989	While the overhead of a callback that e.g. schedules a thread is small, it
		3990	is still an overhead. If you embed libev, and your main usage is with some
		3991	kind of threads or coroutines, you might want to customise libev so that
		3992	doesn't need callbacks anymore.
		3993
		3994	Imagine you have coroutines that you can switch to using a function
		3995	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3996	and that due to some magic, the currently active coroutine is stored in a
		3997	global called C<current_coro>. Then you can build your own "wait for libev
		3998	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3999	the differing C<;> conventions):
		4000
		4001	#define EV_CB_DECLARE(type) struct my_coro *cb;
		4002	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		4003
		4004	That means instead of having a C callback function, you store the
		4005	coroutine to switch to in each watcher, and instead of having libev call
		4006	your callback, you instead have it switch to that coroutine.
		4007
		4008	A coroutine might now wait for an event with a function called
		4009	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		4010	matter when, or whether the watcher is active or not when this function is
		4011	called):
		4012
		4013	void
		4014	wait_for_event (ev_watcher *w)
		4015	{
		4016	ev_set_cb (w, current_coro);
		4017	switch_to (libev_coro);
		4018	}
		4019
		4020	That basically suspends the coroutine inside C<wait_for_event> and
		4021	continues the libev coroutine, which, when appropriate, switches back to
		4022	this or any other coroutine.
		4023
		4024	You can do similar tricks if you have, say, threads with an event queue -
		4025	instead of storing a coroutine, you store the queue object and instead of
		4026	switching to a coroutine, you push the watcher onto the queue and notify
		4027	any waiters.
		4028
		4029	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		4030	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		4031
		4032	// my_ev.h
		4033	#define EV_CB_DECLARE(type) struct my_coro *cb;
		4034	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		4035	#include "../libev/ev.h"
		4036
		4037	// my_ev.c
		4038	#define EV_H "my_ev.h"
		4039	#include "../libev/ev.c"
		4040
		4041	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		4042	F<my_ev.c> into your project. When properly specifying include paths, you
		4043	can even use F<ev.h> as header file name directly.
3310		4044
3311		4045
3312	=head1 LIBEVENT EMULATION	4046	=head1 LIBEVENT EMULATION
3313		4047
3314	Libev offers a compatibility emulation layer for libevent. It cannot	4048	Libev offers a compatibility emulation layer for libevent. It cannot
3315	emulate the internals of libevent, so here are some usage hints:	4049	emulate the internals of libevent, so here are some usage hints:
3316		4050
3317	=over 4	4051	=over 4
		4052
		4053	=item * Only the libevent-1.4.1-beta API is being emulated.
		4054
		4055	This was the newest libevent version available when libev was implemented,
		4056	and is still mostly unchanged in 2010.
3318		4057
3319	=item * Use it by including <event.h>, as usual.	4058	=item * Use it by including <event.h>, as usual.
3320		4059
3321	=item * The following members are fully supported: ev_base, ev_callback,	4060	=item * The following members are fully supported: ev_base, ev_callback,
3322	ev_arg, ev_fd, ev_res, ev_events.	4061	ev_arg, ev_fd, ev_res, ev_events.
…		…
3328	=item * Priorities are not currently supported. Initialising priorities	4067	=item * Priorities are not currently supported. Initialising priorities
3329	will fail and all watchers will have the same priority, even though there	4068	will fail and all watchers will have the same priority, even though there
3330	is an ev_pri field.	4069	is an ev_pri field.
3331		4070
3332	=item * In libevent, the last base created gets the signals, in libev, the	4071	=item * In libevent, the last base created gets the signals, in libev, the
3333	first base created (== the default loop) gets the signals.	4072	base that registered the signal gets the signals.
3334		4073
3335	=item * Other members are not supported.	4074	=item * Other members are not supported.
3336		4075
3337	=item * The libev emulation is I<not> ABI compatible to libevent, you need	4076	=item * The libev emulation is I<not> ABI compatible to libevent, you need
3338	to use the libev header file and library.	4077	to use the libev header file and library.
3339		4078
3340	=back	4079	=back
3341		4080
3342	=head1 C++ SUPPORT	4081	=head1 C++ SUPPORT
		4082
		4083	=head2 C API
		4084
		4085	The normal C API should work fine when used from C++: both ev.h and the
		4086	libev sources can be compiled as C++. Therefore, code that uses the C API
		4087	will work fine.
		4088
		4089	Proper exception specifications might have to be added to callbacks passed
		4090	to libev: exceptions may be thrown only from watcher callbacks, all other
		4091	callbacks (allocator, syserr, loop acquire/release and periodic reschedule
		4092	callbacks) must not throw exceptions, and might need a C<noexcept>
		4093	specification. If you have code that needs to be compiled as both C and
		4094	C++ you can use the C<EV_NOEXCEPT> macro for this:
		4095
		4096	static void
		4097	fatal_error (const char *msg) EV_NOEXCEPT
		4098	{
		4099	perror (msg);
		4100	abort ();
		4101	}
		4102
		4103	...
		4104	ev_set_syserr_cb (fatal_error);
		4105
		4106	The only API functions that can currently throw exceptions are C<ev_run>,
		4107	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		4108	because it runs cleanup watchers).
		4109
		4110	Throwing exceptions in watcher callbacks is only supported if libev itself
		4111	is compiled with a C++ compiler or your C and C++ environments allow
		4112	throwing exceptions through C libraries (most do).
		4113
		4114	=head2 C++ API
3343		4115
3344	Libev comes with some simplistic wrapper classes for C++ that mainly allow	4116	Libev comes with some simplistic wrapper classes for C++ that mainly allow
3345	you to use some convenience methods to start/stop watchers and also change	4117	you to use some convenience methods to start/stop watchers and also change
3346	the callback model to a model using method callbacks on objects.	4118	the callback model to a model using method callbacks on objects.
3347		4119
3348	To use it,	4120	To use it,
3349		4121
3350	#include <ev++.h>	4122	#include <ev++.h>
3351		4123
3352	This automatically includes F<ev.h> and puts all of its definitions (many	4124	This automatically includes F<ev.h> and puts all of its definitions (many
3353	of them macros) into the global namespace. All C++ specific things are	4125	of them macros) into the global namespace. All C++ specific things are
3354	put into the C<ev> namespace. It should support all the same embedding	4126	put into the C<ev> namespace. It should support all the same embedding
…		…
3357	Care has been taken to keep the overhead low. The only data member the C++	4129	Care has been taken to keep the overhead low. The only data member the C++
3358	classes add (compared to plain C-style watchers) is the event loop pointer	4130	classes add (compared to plain C-style watchers) is the event loop pointer
3359	that the watcher is associated with (or no additional members at all if	4131	that the watcher is associated with (or no additional members at all if
3360	you disable C<EV_MULTIPLICITY> when embedding libev).	4132	you disable C<EV_MULTIPLICITY> when embedding libev).
3361		4133
3362	Currently, functions, and static and non-static member functions can be	4134	Currently, functions, static and non-static member functions and classes
3363	used as callbacks. Other types should be easy to add as long as they only	4135	with C<operator ()> can be used as callbacks. Other types should be easy
3364	need one additional pointer for context. If you need support for other	4136	to add as long as they only need one additional pointer for context. If
3365	types of functors please contact the author (preferably after implementing	4137	you need support for other types of functors please contact the author
3366	it).	4138	(preferably after implementing it).
		4139
		4140	For all this to work, your C++ compiler either has to use the same calling
		4141	conventions as your C compiler (for static member functions), or you have
		4142	to embed libev and compile libev itself as C++.
3367		4143
3368	Here is a list of things available in the C<ev> namespace:	4144	Here is a list of things available in the C<ev> namespace:
3369		4145
3370	=over 4	4146	=over 4
3371		4147
…		…
3381	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4157	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
3382		4158
3383	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4159	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
3384	the same name in the C<ev> namespace, with the exception of C<ev_signal>	4160	the same name in the C<ev> namespace, with the exception of C<ev_signal>
3385	which is called C<ev::sig> to avoid clashes with the C<signal> macro	4161	which is called C<ev::sig> to avoid clashes with the C<signal> macro
3386	defines by many implementations.	4162	defined by many implementations.
3387		4163
3388	All of those classes have these methods:	4164	All of those classes have these methods:
3389		4165
3390	=over 4	4166	=over 4
3391		4167
…		…
3453	void operator() (ev::io &w, int revents)	4229	void operator() (ev::io &w, int revents)
3454	{	4230	{
3455	...	4231	...
3456	}	4232	}
3457	}	4233	}
3458		4234
3459	myfunctor f;	4235	myfunctor f;
3460		4236
3461	ev::io w;	4237	ev::io w;
3462	w.set (&f);	4238	w.set (&f);
3463		4239
…		…
3481	Associates a different C<struct ev_loop> with this watcher. You can only	4257	Associates a different C<struct ev_loop> with this watcher. You can only
3482	do this when the watcher is inactive (and not pending either).	4258	do this when the watcher is inactive (and not pending either).
3483		4259
3484	=item w->set ([arguments])	4260	=item w->set ([arguments])
3485		4261
3486	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this	4262	Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
3487	method or a suitable start method must be called at least once. Unlike the	4263	with the same arguments. Either this method or a suitable start method
3488	C counterpart, an active watcher gets automatically stopped and restarted	4264	must be called at least once. Unlike the C counterpart, an active watcher
3489	when reconfiguring it with this method.	4265	gets automatically stopped and restarted when reconfiguring it with this
		4266	method.
		4267
		4268	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4269	clashing with the C<set (loop)> method.
		4270
		4271	For C<ev::io> watchers there is an additional C<set> method that acepts a
		4272	new event mask only, and internally calls C<ev_io_modfify>.
3490		4273
3491	=item w->start ()	4274	=item w->start ()
3492		4275
3493	Starts the watcher. Note that there is no C<loop> argument, as the	4276	Starts the watcher. Note that there is no C<loop> argument, as the
3494	constructor already stores the event loop.	4277	constructor already stores the event loop.
…		…
3524	watchers in the constructor.	4307	watchers in the constructor.
3525		4308
3526	class myclass	4309	class myclass
3527	{	4310	{
3528	ev::io io ; void io_cb (ev::io &w, int revents);	4311	ev::io io ; void io_cb (ev::io &w, int revents);
3529	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);	4312	ev::io io2 ; void io2_cb (ev::io &w, int revents);
3530	ev::idle idle; void idle_cb (ev::idle &w, int revents);	4313	ev::idle idle; void idle_cb (ev::idle &w, int revents);
3531		4314
3532	myclass (int fd)	4315	myclass (int fd)
3533	{	4316	{
3534	io .set <myclass, &myclass::io_cb > (this);	4317	io .set <myclass, &myclass::io_cb > (this);
…		…
3585	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.	4368	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3586		4369
3587	=item D	4370	=item D
3588		4371
3589	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4372	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
3590	be found at L<http://proj.llucax.com.ar/wiki/evd>.	4373	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
3591		4374
3592	=item Ocaml	4375	=item Ocaml
3593		4376
3594	Erkki Seppala has written Ocaml bindings for libev, to be found at	4377	Erkki Seppala has written Ocaml bindings for libev, to be found at
3595	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	4378	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
…		…
3598		4381
3599	Brian Maher has written a partial interface to libev for lua (at the	4382	Brian Maher has written a partial interface to libev for lua (at the
3600	time of this writing, only C<ev_io> and C<ev_timer>), to be found at	4383	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
3601	L<http://github.com/brimworks/lua-ev>.	4384	L<http://github.com/brimworks/lua-ev>.
3602		4385
		4386	=item Javascript
		4387
		4388	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4389
		4390	=item Others
		4391
		4392	There are others, and I stopped counting.
		4393
3603	=back	4394	=back
3604		4395
3605		4396
3606	=head1 MACRO MAGIC	4397	=head1 MACRO MAGIC
3607		4398
…		…
3643	suitable for use with C<EV_A>.	4434	suitable for use with C<EV_A>.
3644		4435
3645	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4436	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
3646		4437
3647	Similar to the other two macros, this gives you the value of the default	4438	Similar to the other two macros, this gives you the value of the default
3648	loop, if multiple loops are supported ("ev loop default").	4439	loop, if multiple loops are supported ("ev loop default"). The default loop
		4440	will be initialised if it isn't already initialised.
		4441
		4442	For non-multiplicity builds, these macros do nothing, so you always have
		4443	to initialise the loop somewhere.
3649		4444
3650	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4445	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
3651		4446
3652	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4447	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
3653	default loop has been initialised (C<UC> == unchecked). Their behaviour	4448	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
3720	ev_vars.h	4515	ev_vars.h
3721	ev_wrap.h	4516	ev_wrap.h
3722		4517
3723	ev_win32.c required on win32 platforms only	4518	ev_win32.c required on win32 platforms only
3724		4519
3725	ev_select.c only when select backend is enabled (which is enabled by default)	4520	ev_select.c only when select backend is enabled
3726	ev_poll.c only when poll backend is enabled (disabled by default)	4521	ev_poll.c only when poll backend is enabled
3727	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4522	ev_epoll.c only when the epoll backend is enabled
		4523	ev_linuxaio.c only when the linux aio backend is enabled
		4524	ev_iouring.c only when the linux io_uring backend is enabled
3728	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4525	ev_kqueue.c only when the kqueue backend is enabled
3729	ev_port.c only when the solaris port backend is enabled (disabled by default)	4526	ev_port.c only when the solaris port backend is enabled
3730		4527
3731	F<ev.c> includes the backend files directly when enabled, so you only need	4528	F<ev.c> includes the backend files directly when enabled, so you only need
3732	to compile this single file.	4529	to compile this single file.
3733		4530
3734	=head3 LIBEVENT COMPATIBILITY API	4531	=head3 LIBEVENT COMPATIBILITY API
…		…
3798	supported). It will also not define any of the structs usually found in	4595	supported). It will also not define any of the structs usually found in
3799	F<event.h> that are not directly supported by the libev core alone.	4596	F<event.h> that are not directly supported by the libev core alone.
3800		4597
3801	In standalone mode, libev will still try to automatically deduce the	4598	In standalone mode, libev will still try to automatically deduce the
3802	configuration, but has to be more conservative.	4599	configuration, but has to be more conservative.
		4600
		4601	=item EV_USE_FLOOR
		4602
		4603	If defined to be C<1>, libev will use the C<floor ()> function for its
		4604	periodic reschedule calculations, otherwise libev will fall back on a
		4605	portable (slower) implementation. If you enable this, you usually have to
		4606	link against libm or something equivalent. Enabling this when the C<floor>
		4607	function is not available will fail, so the safe default is to not enable
		4608	this.
3803		4609
3804	=item EV_USE_MONOTONIC	4610	=item EV_USE_MONOTONIC
3805		4611
3806	If defined to be C<1>, libev will try to detect the availability of the	4612	If defined to be C<1>, libev will try to detect the availability of the
3807	monotonic clock option at both compile time and runtime. Otherwise no	4613	monotonic clock option at both compile time and runtime. Otherwise no
…		…
3844	available and will probe for kernel support at runtime. This will improve	4650	available and will probe for kernel support at runtime. This will improve
3845	C<ev_signal> and C<ev_async> performance and reduce resource consumption.	4651	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
3846	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc	4652	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
3847	2.7 or newer, otherwise disabled.	4653	2.7 or newer, otherwise disabled.
3848		4654
		4655	=item EV_USE_SIGNALFD
		4656
		4657	If defined to be C<1>, then libev will assume that C<signalfd ()> is
		4658	available and will probe for kernel support at runtime. This enables
		4659	the use of EVFLAG_SIGNALFD for faster and simpler signal handling. If
		4660	undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4661	2.7 or newer, otherwise disabled.
		4662
		4663	=item EV_USE_TIMERFD
		4664
		4665	If defined to be C<1>, then libev will assume that C<timerfd ()> is
		4666	available and will probe for kernel support at runtime. This allows
		4667	libev to detect time jumps accurately. If undefined, it will be enabled
		4668	if the headers indicate GNU/Linux + Glibc 2.8 or newer and define
		4669	C<TFD_TIMER_CANCEL_ON_SET>, otherwise disabled.
		4670
		4671	=item EV_USE_EVENTFD
		4672
		4673	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		4674	available and will probe for kernel support at runtime. This will improve
		4675	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		4676	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4677	2.7 or newer, otherwise disabled.
		4678
3849	=item EV_USE_SELECT	4679	=item EV_USE_SELECT
3850		4680
3851	If undefined or defined to be C<1>, libev will compile in support for the	4681	If undefined or defined to be C<1>, libev will compile in support for the
3852	C<select>(2) backend. No attempt at auto-detection will be done: if no	4682	C<select>(2) backend. No attempt at auto-detection will be done: if no
3853	other method takes over, select will be it. Otherwise the select backend	4683	other method takes over, select will be it. Otherwise the select backend
…		…
3893	If programs implement their own fd to handle mapping on win32, then this	4723	If programs implement their own fd to handle mapping on win32, then this
3894	macro can be used to override the C<close> function, useful to unregister	4724	macro can be used to override the C<close> function, useful to unregister
3895	file descriptors again. Note that the replacement function has to close	4725	file descriptors again. Note that the replacement function has to close
3896	the underlying OS handle.	4726	the underlying OS handle.
3897		4727
		4728	=item EV_USE_WSASOCKET
		4729
		4730	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4731	communication socket, which works better in some environments. Otherwise,
		4732	the normal C<socket> function will be used, which works better in other
		4733	environments.
		4734
3898	=item EV_USE_POLL	4735	=item EV_USE_POLL
3899		4736
3900	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4737	If defined to be C<1>, libev will compile in support for the C<poll>(2)
3901	backend. Otherwise it will be enabled on non-win32 platforms. It	4738	backend. Otherwise it will be enabled on non-win32 platforms. It
3902	takes precedence over select.	4739	takes precedence over select.
…		…
3906	If defined to be C<1>, libev will compile in support for the Linux	4743	If defined to be C<1>, libev will compile in support for the Linux
3907	C<epoll>(7) backend. Its availability will be detected at runtime,	4744	C<epoll>(7) backend. Its availability will be detected at runtime,
3908	otherwise another method will be used as fallback. This is the preferred	4745	otherwise another method will be used as fallback. This is the preferred
3909	backend for GNU/Linux systems. If undefined, it will be enabled if the	4746	backend for GNU/Linux systems. If undefined, it will be enabled if the
3910	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4747	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4748
		4749	=item EV_USE_LINUXAIO
		4750
		4751	If defined to be C<1>, libev will compile in support for the Linux aio
		4752	backend (C<EV_USE_EPOLL> must also be enabled). If undefined, it will be
		4753	enabled on linux, otherwise disabled.
		4754
		4755	=item EV_USE_IOURING
		4756
		4757	If defined to be C<1>, libev will compile in support for the Linux
		4758	io_uring backend (C<EV_USE_EPOLL> must also be enabled). Due to it's
		4759	current limitations it has to be requested explicitly. If undefined, it
		4760	will be enabled on linux, otherwise disabled.
3911		4761
3912	=item EV_USE_KQUEUE	4762	=item EV_USE_KQUEUE
3913		4763
3914	If defined to be C<1>, libev will compile in support for the BSD style	4764	If defined to be C<1>, libev will compile in support for the BSD style
3915	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	4765	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
3937	If defined to be C<1>, libev will compile in support for the Linux inotify	4787	If defined to be C<1>, libev will compile in support for the Linux inotify
3938	interface to speed up C<ev_stat> watchers. Its actual availability will	4788	interface to speed up C<ev_stat> watchers. Its actual availability will
3939	be detected at runtime. If undefined, it will be enabled if the headers	4789	be detected at runtime. If undefined, it will be enabled if the headers
3940	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4790	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
3941		4791
		4792	=item EV_NO_SMP
		4793
		4794	If defined to be C<1>, libev will assume that memory is always coherent
		4795	between threads, that is, threads can be used, but threads never run on
		4796	different cpus (or different cpu cores). This reduces dependencies
		4797	and makes libev faster.
		4798
		4799	=item EV_NO_THREADS
		4800
		4801	If defined to be C<1>, libev will assume that it will never be called from
		4802	different threads (that includes signal handlers), which is a stronger
		4803	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4804	libev faster.
		4805
3942	=item EV_ATOMIC_T	4806	=item EV_ATOMIC_T
3943		4807
3944	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4808	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
3945	access is atomic with respect to other threads or signal contexts. No such	4809	access is atomic with respect to other threads or signal contexts. No
3946	type is easily found in the C language, so you can provide your own type	4810	such type is easily found in the C language, so you can provide your own
3947	that you know is safe for your purposes. It is used both for signal handler "locking"	4811	type that you know is safe for your purposes. It is used both for signal
3948	as well as for signal and thread safety in C<ev_async> watchers.	4812	handler "locking" as well as for signal and thread safety in C<ev_async>
		4813	watchers.
3949		4814
3950	In the absence of this define, libev will use C<sig_atomic_t volatile>	4815	In the absence of this define, libev will use C<sig_atomic_t volatile>
3951	(from F<signal.h>), which is usually good enough on most platforms.	4816	(from F<signal.h>), which is usually good enough on most platforms.
3952		4817
3953	=item EV_H (h)	4818	=item EV_H (h)
…		…
3980	will have the C<struct ev_loop *> as first argument, and you can create	4845	will have the C<struct ev_loop *> as first argument, and you can create
3981	additional independent event loops. Otherwise there will be no support	4846	additional independent event loops. Otherwise there will be no support
3982	for multiple event loops and there is no first event loop pointer	4847	for multiple event loops and there is no first event loop pointer
3983	argument. Instead, all functions act on the single default loop.	4848	argument. Instead, all functions act on the single default loop.
3984		4849
		4850	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4851	default loop when multiplicity is switched off - you always have to
		4852	initialise the loop manually in this case.
		4853
3985	=item EV_MINPRI	4854	=item EV_MINPRI
3986		4855
3987	=item EV_MAXPRI	4856	=item EV_MAXPRI
3988		4857
3989	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4858	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
4025	#define EV_USE_POLL 1	4894	#define EV_USE_POLL 1
4026	#define EV_CHILD_ENABLE 1	4895	#define EV_CHILD_ENABLE 1
4027	#define EV_ASYNC_ENABLE 1	4896	#define EV_ASYNC_ENABLE 1
4028		4897
4029	The actual value is a bitset, it can be a combination of the following	4898	The actual value is a bitset, it can be a combination of the following
4030	values:	4899	values (by default, all of these are enabled):
4031		4900
4032	=over 4	4901	=over 4
4033		4902
4034	=item C<1> - faster/larger code	4903	=item C<1> - faster/larger code
4035		4904
…		…
4039	code size by roughly 30% on amd64).	4908	code size by roughly 30% on amd64).
4040		4909
4041	When optimising for size, use of compiler flags such as C<-Os> with	4910	When optimising for size, use of compiler flags such as C<-Os> with
4042	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of	4911	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
4043	assertions.	4912	assertions.
		4913
		4914	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4915	(e.g. gcc with C<-Os>).
4044		4916
4045	=item C<2> - faster/larger data structures	4917	=item C<2> - faster/larger data structures
4046		4918
4047	Replaces the small 2-heap for timer management by a faster 4-heap, larger	4919	Replaces the small 2-heap for timer management by a faster 4-heap, larger
4048	hash table sizes and so on. This will usually further increase code size	4920	hash table sizes and so on. This will usually further increase code size
4049	and can additionally have an effect on the size of data structures at	4921	and can additionally have an effect on the size of data structures at
4050	runtime.	4922	runtime.
4051		4923
		4924	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4925	(e.g. gcc with C<-Os>).
		4926
4052	=item C<4> - full API configuration	4927	=item C<4> - full API configuration
4053		4928
4054	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and	4929	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
4055	enables multiplicity (C<EV_MULTIPLICITY>=1).	4930	enables multiplicity (C<EV_MULTIPLICITY>=1).
4056		4931
…		…
4086		4961
4087	With an intelligent-enough linker (gcc+binutils are intelligent enough	4962	With an intelligent-enough linker (gcc+binutils are intelligent enough
4088	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by	4963	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
4089	your program might be left out as well - a binary starting a timer and an	4964	your program might be left out as well - a binary starting a timer and an
4090	I/O watcher then might come out at only 5Kb.	4965	I/O watcher then might come out at only 5Kb.
		4966
		4967	=item EV_API_STATIC
		4968
		4969	If this symbol is defined (by default it is not), then all identifiers
		4970	will have static linkage. This means that libev will not export any
		4971	identifiers, and you cannot link against libev anymore. This can be useful
		4972	when you embed libev, only want to use libev functions in a single file,
		4973	and do not want its identifiers to be visible.
		4974
		4975	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4976	wants to use libev.
		4977
		4978	This option only works when libev is compiled with a C compiler, as C++
		4979	doesn't support the required declaration syntax.
4091		4980
4092	=item EV_AVOID_STDIO	4981	=item EV_AVOID_STDIO
4093		4982
4094	If this is set to C<1> at compiletime, then libev will avoid using stdio	4983	If this is set to C<1> at compiletime, then libev will avoid using stdio
4095	functions (printf, scanf, perror etc.). This will increase the code size	4984	functions (printf, scanf, perror etc.). This will increase the code size
…		…
4153	in. If set to C<1>, then verification code will be compiled in, but not	5042	in. If set to C<1>, then verification code will be compiled in, but not
4154	called. If set to C<2>, then the internal verification code will be	5043	called. If set to C<2>, then the internal verification code will be
4155	called once per loop, which can slow down libev. If set to C<3>, then the	5044	called once per loop, which can slow down libev. If set to C<3>, then the
4156	verification code will be called very frequently, which will slow down	5045	verification code will be called very frequently, which will slow down
4157	libev considerably.	5046	libev considerably.
		5047
		5048	Verification errors are reported via C's C<assert> mechanism, so if you
		5049	disable that (e.g. by defining C<NDEBUG>) then no errors will be reported.
4158		5050
4159	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it	5051	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
4160	will be C<0>.	5052	will be C<0>.
4161		5053
4162	=item EV_COMMON	5054	=item EV_COMMON
…		…
4239	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	5131	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4240		5132
4241	#include "ev_cpp.h"	5133	#include "ev_cpp.h"
4242	#include "ev.c"	5134	#include "ev.c"
4243		5135
4244	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	5136	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4245		5137
4246	=head2 THREADS AND COROUTINES	5138	=head2 THREADS AND COROUTINES
4247		5139
4248	=head3 THREADS	5140	=head3 THREADS
4249		5141
…		…
4300	default loop and triggering an C<ev_async> watcher from the default loop	5192	default loop and triggering an C<ev_async> watcher from the default loop
4301	watcher callback into the event loop interested in the signal.	5193	watcher callback into the event loop interested in the signal.
4302		5194
4303	=back	5195	=back
4304		5196
4305	=head4 THREAD LOCKING EXAMPLE	5197	See also L</THREAD LOCKING EXAMPLE>.
4306
4307	Here is a fictitious example of how to run an event loop in a different
4308	thread than where callbacks are being invoked and watchers are
4309	created/added/removed.
4310
4311	For a real-world example, see the C<EV::Loop::Async> perl module,
4312	which uses exactly this technique (which is suited for many high-level
4313	languages).
4314
4315	The example uses a pthread mutex to protect the loop data, a condition
4316	variable to wait for callback invocations, an async watcher to notify the
4317	event loop thread and an unspecified mechanism to wake up the main thread.
4318
4319	First, you need to associate some data with the event loop:
4320
4321	typedef struct {
4322	mutex_t lock; /* global loop lock */
4323	ev_async async_w;
4324	thread_t tid;
4325	cond_t invoke_cv;
4326	} userdata;
4327
4328	void prepare_loop (EV_P)
4329	{
4330	// for simplicity, we use a static userdata struct.
4331	static userdata u;
4332
4333	ev_async_init (&u->async_w, async_cb);
4334	ev_async_start (EV_A_ &u->async_w);
4335
4336	pthread_mutex_init (&u->lock, 0);
4337	pthread_cond_init (&u->invoke_cv, 0);
4338
4339	// now associate this with the loop
4340	ev_set_userdata (EV_A_ u);
4341	ev_set_invoke_pending_cb (EV_A_ l_invoke);
4342	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4343
4344	// then create the thread running ev_loop
4345	pthread_create (&u->tid, 0, l_run, EV_A);
4346	}
4347
4348	The callback for the C<ev_async> watcher does nothing: the watcher is used
4349	solely to wake up the event loop so it takes notice of any new watchers
4350	that might have been added:
4351
4352	static void
4353	async_cb (EV_P_ ev_async *w, int revents)
4354	{
4355	// just used for the side effects
4356	}
4357
4358	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
4359	protecting the loop data, respectively.
4360
4361	static void
4362	l_release (EV_P)
4363	{
4364	userdata *u = ev_userdata (EV_A);
4365	pthread_mutex_unlock (&u->lock);
4366	}
4367
4368	static void
4369	l_acquire (EV_P)
4370	{
4371	userdata *u = ev_userdata (EV_A);
4372	pthread_mutex_lock (&u->lock);
4373	}
4374
4375	The event loop thread first acquires the mutex, and then jumps straight
4376	into C<ev_run>:
4377
4378	void *
4379	l_run (void *thr_arg)
4380	{
4381	struct ev_loop *loop = (struct ev_loop *)thr_arg;
4382
4383	l_acquire (EV_A);
4384	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4385	ev_run (EV_A_ 0);
4386	l_release (EV_A);
4387
4388	return 0;
4389	}
4390
4391	Instead of invoking all pending watchers, the C<l_invoke> callback will
4392	signal the main thread via some unspecified mechanism (signals? pipe
4393	writes? C<Async::Interrupt>?) and then waits until all pending watchers
4394	have been called (in a while loop because a) spurious wakeups are possible
4395	and b) skipping inter-thread-communication when there are no pending
4396	watchers is very beneficial):
4397
4398	static void
4399	l_invoke (EV_P)
4400	{
4401	userdata *u = ev_userdata (EV_A);
4402
4403	while (ev_pending_count (EV_A))
4404	{
4405	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4406	pthread_cond_wait (&u->invoke_cv, &u->lock);
4407	}
4408	}
4409
4410	Now, whenever the main thread gets told to invoke pending watchers, it
4411	will grab the lock, call C<ev_invoke_pending> and then signal the loop
4412	thread to continue:
4413
4414	static void
4415	real_invoke_pending (EV_P)
4416	{
4417	userdata *u = ev_userdata (EV_A);
4418
4419	pthread_mutex_lock (&u->lock);
4420	ev_invoke_pending (EV_A);
4421	pthread_cond_signal (&u->invoke_cv);
4422	pthread_mutex_unlock (&u->lock);
4423	}
4424
4425	Whenever you want to start/stop a watcher or do other modifications to an
4426	event loop, you will now have to lock:
4427
4428	ev_timer timeout_watcher;
4429	userdata *u = ev_userdata (EV_A);
4430
4431	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4432
4433	pthread_mutex_lock (&u->lock);
4434	ev_timer_start (EV_A_ &timeout_watcher);
4435	ev_async_send (EV_A_ &u->async_w);
4436	pthread_mutex_unlock (&u->lock);
4437
4438	Note that sending the C<ev_async> watcher is required because otherwise
4439	an event loop currently blocking in the kernel will have no knowledge
4440	about the newly added timer. By waking up the loop it will pick up any new
4441	watchers in the next event loop iteration.
4442		5198
4443	=head3 COROUTINES	5199	=head3 COROUTINES
4444		5200
4445	Libev is very accommodating to coroutines ("cooperative threads"):	5201	Libev is very accommodating to coroutines ("cooperative threads"):
4446	libev fully supports nesting calls to its functions from different	5202	libev fully supports nesting calls to its functions from different
…		…
4611	requires, and its I/O model is fundamentally incompatible with the POSIX	5367	requires, and its I/O model is fundamentally incompatible with the POSIX
4612	model. Libev still offers limited functionality on this platform in	5368	model. Libev still offers limited functionality on this platform in
4613	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5369	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
4614	descriptors. This only applies when using Win32 natively, not when using	5370	descriptors. This only applies when using Win32 natively, not when using
4615	e.g. cygwin. Actually, it only applies to the microsofts own compilers,	5371	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4616	as every compielr comes with a slightly differently broken/incompatible	5372	as every compiler comes with a slightly differently broken/incompatible
4617	environment.	5373	environment.
4618		5374
4619	Lifting these limitations would basically require the full	5375	Lifting these limitations would basically require the full
4620	re-implementation of the I/O system. If you are into this kind of thing,	5376	re-implementation of the I/O system. If you are into this kind of thing,
4621	then note that glib does exactly that for you in a very portable way (note	5377	then note that glib does exactly that for you in a very portable way (note
…		…
4715	structure (guaranteed by POSIX but not by ISO C for example), but it also	5471	structure (guaranteed by POSIX but not by ISO C for example), but it also
4716	assumes that the same (machine) code can be used to call any watcher	5472	assumes that the same (machine) code can be used to call any watcher
4717	callback: The watcher callbacks have different type signatures, but libev	5473	callback: The watcher callbacks have different type signatures, but libev
4718	calls them using an C<ev_watcher *> internally.	5474	calls them using an C<ev_watcher *> internally.
4719		5475
		5476	=item null pointers and integer zero are represented by 0 bytes
		5477
		5478	Libev uses C<memset> to initialise structs and arrays to C<0> bytes, and
		5479	relies on this setting pointers and integers to null.
		5480
		5481	=item pointer accesses must be thread-atomic
		5482
		5483	Accessing a pointer value must be atomic, it must both be readable and
		5484	writable in one piece - this is the case on all current architectures.
		5485
4720	=item C<sig_atomic_t volatile> must be thread-atomic as well	5486	=item C<sig_atomic_t volatile> must be thread-atomic as well
4721		5487
4722	The type C<sig_atomic_t volatile> (or whatever is defined as	5488	The type C<sig_atomic_t volatile> (or whatever is defined as
4723	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different	5489	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
4724	threads. This is not part of the specification for C<sig_atomic_t>, but is	5490	threads. This is not part of the specification for C<sig_atomic_t>, but is
…		…
4732	thread" or will block signals process-wide, both behaviours would	5498	thread" or will block signals process-wide, both behaviours would
4733	be compatible with libev. Interaction between C<sigprocmask> and	5499	be compatible with libev. Interaction between C<sigprocmask> and
4734	C<pthread_sigmask> could complicate things, however.	5500	C<pthread_sigmask> could complicate things, however.
4735		5501
4736	The most portable way to handle signals is to block signals in all threads	5502	The most portable way to handle signals is to block signals in all threads
4737	except the initial one, and run the default loop in the initial thread as	5503	except the initial one, and run the signal handling loop in the initial
4738	well.	5504	thread as well.
4739		5505
4740	=item C<long> must be large enough for common memory allocation sizes	5506	=item C<long> must be large enough for common memory allocation sizes
4741		5507
4742	To improve portability and simplify its API, libev uses C<long> internally	5508	To improve portability and simplify its API, libev uses C<long> internally
4743	instead of C<size_t> when allocating its data structures. On non-POSIX	5509	instead of C<size_t> when allocating its data structures. On non-POSIX
…		…
4749		5515
4750	The type C<double> is used to represent timestamps. It is required to	5516	The type C<double> is used to represent timestamps. It is required to
4751	have at least 51 bits of mantissa (and 9 bits of exponent), which is	5517	have at least 51 bits of mantissa (and 9 bits of exponent), which is
4752	good enough for at least into the year 4000 with millisecond accuracy	5518	good enough for at least into the year 4000 with millisecond accuracy
4753	(the design goal for libev). This requirement is overfulfilled by	5519	(the design goal for libev). This requirement is overfulfilled by
4754	implementations using IEEE 754, which is basically all existing ones. With	5520	implementations using IEEE 754, which is basically all existing ones.
		5521
4755	IEEE 754 doubles, you get microsecond accuracy until at least 2200.	5522	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5523	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5524	is either obsolete or somebody patched it to use C<long double> or
		5525	something like that, just kidding).
4756		5526
4757	=back	5527	=back
4758		5528
4759	If you know of other additional requirements drop me a note.	5529	If you know of other additional requirements drop me a note.
4760		5530
…		…
4822	=item Processing ev_async_send: O(number_of_async_watchers)	5592	=item Processing ev_async_send: O(number_of_async_watchers)
4823		5593
4824	=item Processing signals: O(max_signal_number)	5594	=item Processing signals: O(max_signal_number)
4825		5595
4826	Sending involves a system call I<iff> there were no other C<ev_async_send>	5596	Sending involves a system call I<iff> there were no other C<ev_async_send>
4827	calls in the current loop iteration. Checking for async and signal events	5597	calls in the current loop iteration and the loop is currently
		5598	blocked. Checking for async and signal events involves iterating over all
4828	involves iterating over all running async watchers or all signal numbers.	5599	running async watchers or all signal numbers.
4829		5600
4830	=back	5601	=back
4831		5602
4832		5603
4833	=head1 PORTING FROM LIBEV 3.X TO 4.X	5604	=head1 PORTING FROM LIBEV 3.X TO 4.X
4834		5605
4835	The major version 4 introduced some minor incompatible changes to the API.	5606	The major version 4 introduced some incompatible changes to the API.
4836		5607
4837	At the moment, the C<ev.h> header file tries to implement superficial	5608	At the moment, the C<ev.h> header file provides compatibility definitions
4838	compatibility, so most programs should still compile. Those might be	5609	for all changes, so most programs should still compile. The compatibility
4839	removed in later versions of libev, so better update early than late.	5610	layer might be removed in later versions of libev, so better update to the
		5611	new API early than late.
4840		5612
4841	=over 4	5613	=over 4
4842		5614
		5615	=item C<EV_COMPAT3> backwards compatibility mechanism
		5616
		5617	The backward compatibility mechanism can be controlled by
		5618	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
		5619	section.
		5620
4843	=item C<ev_default_destroy> and C<ev_default_fork> have been removed	5621	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
4844		5622
4845	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:	5623	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
4846		5624
4847	ev_loop_destroy (EV_DEFAULT);	5625	ev_loop_destroy (EV_DEFAULT_UC);
4848	ev_loop_fork (EV_DEFAULT);	5626	ev_loop_fork (EV_DEFAULT);
4849		5627
4850	=item function/symbol renames	5628	=item function/symbol renames
4851		5629
4852	A number of functions and symbols have been renamed:	5630	A number of functions and symbols have been renamed:
…		…
4872	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme	5650	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
4873	as all other watcher types. Note that C<ev_loop_fork> is still called	5651	as all other watcher types. Note that C<ev_loop_fork> is still called
4874	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>	5652	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
4875	typedef.	5653	typedef.
4876		5654
4877	=item C<EV_COMPAT3> backwards compatibility mechanism
4878
4879	The backward compatibility mechanism can be controlled by
4880	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
4881	section.
4882
4883	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>	5655	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
4884		5656
4885	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different	5657	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
4886	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile	5658	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
4887	and work, but the library code will of course be larger.	5659	and work, but the library code will of course be larger.
…		…
4894	=over 4	5666	=over 4
4895		5667
4896	=item active	5668	=item active
4897		5669
4898	A watcher is active as long as it has been started and not yet stopped.	5670	A watcher is active as long as it has been started and not yet stopped.
4899	See L<WATCHER STATES> for details.	5671	See L</WATCHER STATES> for details.
4900		5672
4901	=item application	5673	=item application
4902		5674
4903	In this document, an application is whatever is using libev.	5675	In this document, an application is whatever is using libev.
4904		5676
…		…
4940	watchers and events.	5712	watchers and events.
4941		5713
4942	=item pending	5714	=item pending
4943		5715
4944	A watcher is pending as soon as the corresponding event has been	5716	A watcher is pending as soon as the corresponding event has been
4945	detected. See L<WATCHER STATES> for details.	5717	detected. See L</WATCHER STATES> for details.
4946		5718
4947	=item real time	5719	=item real time
4948		5720
4949	The physical time that is observed. It is apparently strictly monotonic :)	5721	The physical time that is observed. It is apparently strictly monotonic :)
4950		5722
4951	=item wall-clock time	5723	=item wall-clock time
4952		5724
4953	The time and date as shown on clocks. Unlike real time, it can actually	5725	The time and date as shown on clocks. Unlike real time, it can actually
4954	be wrong and jump forwards and backwards, e.g. when the you adjust your	5726	be wrong and jump forwards and backwards, e.g. when you adjust your
4955	clock.	5727	clock.
4956		5728
4957	=item watcher	5729	=item watcher
4958		5730
4959	A data structure that describes interest in certain events. Watchers need	5731	A data structure that describes interest in certain events. Watchers need
…		…
4961		5733
4962	=back	5734	=back
4963		5735
4964	=head1 AUTHOR	5736	=head1 AUTHOR
4965		5737
4966	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.	5738	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5739	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
4967		5740

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