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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
…		…
82		84
83	=head1 WHAT TO READ WHEN IN A HURRY	85	=head1 WHAT TO READ WHEN IN A HURRY
84		86
85	This manual tries to be very detailed, but unfortunately, this also makes	87	This manual tries to be very detailed, but unfortunately, this also makes
86	it very long. If you just want to know the basics of libev, I suggest	88	it very long. If you just want to know the basics of libev, I suggest
87	reading L<ANATOMY OF A WATCHER>, then the L<EXAMPLE PROGRAM> above and	89	reading L</ANATOMY OF A WATCHER>, then the L</EXAMPLE PROGRAM> above and
88	look up the missing functions in L<GLOBAL FUNCTIONS> and the C<ev_io> and	90	look up the missing functions in L</GLOBAL FUNCTIONS> and the C<ev_io> and
89	C<ev_timer> sections in L<WATCHER TYPES>.	91	C<ev_timer> sections in L</WATCHER TYPES>.
90		92
91	=head1 ABOUT LIBEV	93	=head1 ABOUT LIBEV
92		94
93	Libev is an event loop: you register interest in certain events (such as a	95	Libev is an event loop: you register interest in certain events (such as a
94	file descriptor being readable or a timeout occurring), and it will manage	96	file descriptor being readable or a timeout occurring), and it will manage
…		…
103	details of the event, and then hand it over to libev by I<starting> the	105	details of the event, and then hand it over to libev by I<starting> the
104	watcher.	106	watcher.
105		107
106	=head2 FEATURES	108	=head2 FEATURES
107		109
108	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	110	Libev supports C<select>, C<poll>, the Linux-specific aio and C<epoll>
109	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	111	interfaces, the BSD-specific C<kqueue> and the Solaris-specific event port
110	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	112	mechanisms for file descriptor events (C<ev_io>), the Linux C<inotify>
111	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner	113	interface (for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
112	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative	114	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
113	timers (C<ev_timer>), absolute timers with customised rescheduling	115	timers (C<ev_timer>), absolute timers with customised rescheduling
114	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status	116	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
115	change events (C<ev_child>), and event watchers dealing with the event	117	change events (C<ev_child>), and event watchers dealing with the event
116	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and	118	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
…		…
157	When libev detects a usage error such as a negative timer interval, then	159	When libev detects a usage error such as a negative timer interval, then
158	it will print a diagnostic message and abort (via the C<assert> mechanism,	160	it will print a diagnostic message and abort (via the C<assert> mechanism,
159	so C<NDEBUG> will disable this checking): these are programming errors in	161	so C<NDEBUG> will disable this checking): these are programming errors in
160	the libev caller and need to be fixed there.	162	the libev caller and need to be fixed there.
161		163
		164	Via the C<EV_FREQUENT> macro you can compile in and/or enable extensive
		165	consistency checking code inside libev that can be used to check for
		166	internal inconsistencies, suually caused by application bugs.
		167
162	Libev also has a few internal error-checking C<assert>ions, and also has	168	Libev also has a few internal error-checking C<assert>ions. These do not
163	extensive consistency checking code. These do not trigger under normal
164	circumstances, as they indicate either a bug in libev or worse.	169	trigger under normal circumstances, as they indicate either a bug in libev
		170	or worse.
165		171
166		172
167	=head1 GLOBAL FUNCTIONS	173	=head1 GLOBAL FUNCTIONS
168		174
169	These functions can be called anytime, even before initialising the	175	These functions can be called anytime, even before initialising the
…		…
174	=item ev_tstamp ev_time ()	180	=item ev_tstamp ev_time ()
175		181
176	Returns the current time as libev would use it. Please note that the	182	Returns the current time as libev would use it. Please note that the
177	C<ev_now> function is usually faster and also often returns the timestamp	183	C<ev_now> function is usually faster and also often returns the timestamp
178	you actually want to know. Also interesting is the combination of	184	you actually want to know. Also interesting is the combination of
179	C<ev_update_now> and C<ev_now>.	185	C<ev_now_update> and C<ev_now>.
180		186
181	=item ev_sleep (ev_tstamp interval)	187	=item ev_sleep (ev_tstamp interval)
182		188
183	Sleep for the given interval: The current thread will be blocked until	189	Sleep for the given interval: The current thread will be blocked
184	either it is interrupted or the given time interval has passed. Basically	190	until either it is interrupted or the given time interval has
		191	passed (approximately - it might return a bit earlier even if not
		192	interrupted). Returns immediately if C<< interval <= 0 >>.
		193
185	this is a sub-second-resolution C<sleep ()>.	194	Basically this is a sub-second-resolution C<sleep ()>.
		195
		196	The range of the C<interval> is limited - libev only guarantees to work
		197	with sleep times of up to one day (C<< interval <= 86400 >>).
186		198
187	=item int ev_version_major ()	199	=item int ev_version_major ()
188		200
189	=item int ev_version_minor ()	201	=item int ev_version_minor ()
190		202
…		…
241	the current system, you would need to look at C<ev_embeddable_backends ()	253	the current system, you would need to look at C<ev_embeddable_backends ()
242	& ev_supported_backends ()>, likewise for recommended ones.	254	& ev_supported_backends ()>, likewise for recommended ones.
243		255
244	See the description of C<ev_embed> watchers for more info.	256	See the description of C<ev_embed> watchers for more info.
245		257
246	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]	258	=item ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())
247		259
248	Sets the allocation function to use (the prototype is similar - the	260	Sets the allocation function to use (the prototype is similar - the
249	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is	261	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
250	used to allocate and free memory (no surprises here). If it returns zero	262	used to allocate and free memory (no surprises here). If it returns zero
251	when memory needs to be allocated (C<size != 0>), the library might abort	263	when memory needs to be allocated (C<size != 0>), the library might abort
…		…
257		269
258	You could override this function in high-availability programs to, say,	270	You could override this function in high-availability programs to, say,
259	free some memory if it cannot allocate memory, to use a special allocator,	271	free some memory if it cannot allocate memory, to use a special allocator,
260	or even to sleep a while and retry until some memory is available.	272	or even to sleep a while and retry until some memory is available.
261		273
		274	Example: The following is the C<realloc> function that libev itself uses
		275	which should work with C<realloc> and C<free> functions of all kinds and
		276	is probably a good basis for your own implementation.
		277
		278	static void *
		279	ev_realloc_emul (void *ptr, long size) EV_NOEXCEPT
		280	{
		281	if (size)
		282	return realloc (ptr, size);
		283
		284	free (ptr);
		285	return 0;
		286	}
		287
262	Example: Replace the libev allocator with one that waits a bit and then	288	Example: Replace the libev allocator with one that waits a bit and then
263	retries (example requires a standards-compliant C<realloc>).	289	retries.
264		290
265	static void *	291	static void *
266	persistent_realloc (void *ptr, size_t size)	292	persistent_realloc (void *ptr, size_t size)
267	{	293	{
		294	if (!size)
		295	{
		296	free (ptr);
		297	return 0;
		298	}
		299
268	for (;;)	300	for (;;)
269	{	301	{
270	void *newptr = realloc (ptr, size);	302	void *newptr = realloc (ptr, size);
271		303
272	if (newptr)	304	if (newptr)
…		…
277	}	309	}
278		310
279	...	311	...
280	ev_set_allocator (persistent_realloc);	312	ev_set_allocator (persistent_realloc);
281		313
282	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]	314	=item ev_set_syserr_cb (void (*cb)(const char *msg) throw ())
283		315
284	Set the callback function to call on a retryable system call error (such	316	Set the callback function to call on a retryable system call error (such
285	as failed select, poll, epoll_wait). The message is a printable string	317	as failed select, poll, epoll_wait). The message is a printable string
286	indicating the system call or subsystem causing the problem. If this	318	indicating the system call or subsystem causing the problem. If this
287	callback is set, then libev will expect it to remedy the situation, no	319	callback is set, then libev will expect it to remedy the situation, no
…		…
299	}	331	}
300		332
301	...	333	...
302	ev_set_syserr_cb (fatal_error);	334	ev_set_syserr_cb (fatal_error);
303		335
		336	=item ev_feed_signal (int signum)
		337
		338	This function can be used to "simulate" a signal receive. It is completely
		339	safe to call this function at any time, from any context, including signal
		340	handlers or random threads.
		341
		342	Its main use is to customise signal handling in your process, especially
		343	in the presence of threads. For example, you could block signals
		344	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		345	creating any loops), and in one thread, use C<sigwait> or any other
		346	mechanism to wait for signals, then "deliver" them to libev by calling
		347	C<ev_feed_signal>.
		348
304	=back	349	=back
305		350
306	=head1 FUNCTIONS CONTROLLING EVENT LOOPS	351	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
307		352
308	An event loop is described by a C<struct ev_loop *> (the C<struct> is	353	An event loop is described by a C<struct ev_loop *> (the C<struct> is
…		…
355	=item struct ev_loop *ev_loop_new (unsigned int flags)	400	=item struct ev_loop *ev_loop_new (unsigned int flags)
356		401
357	This will create and initialise a new event loop object. If the loop	402	This will create and initialise a new event loop object. If the loop
358	could not be initialised, returns false.	403	could not be initialised, returns false.
359		404
360	Note that this function I<is> thread-safe, and one common way to use	405	This function is thread-safe, and one common way to use libev with
361	libev with threads is indeed to create one loop per thread, and using the	406	threads is indeed to create one loop per thread, and using the default
362	default loop in the "main" or "initial" thread.	407	loop in the "main" or "initial" thread.
363		408
364	The flags argument can be used to specify special behaviour or specific	409	The flags argument can be used to specify special behaviour or specific
365	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	410	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
366		411
367	The following flags are supported:	412	The following flags are supported:
…		…
377		422
378	If this flag bit is or'ed into the flag value (or the program runs setuid	423	If this flag bit is or'ed into the flag value (or the program runs setuid
379	or setgid) then libev will I<not> look at the environment variable	424	or setgid) then libev will I<not> look at the environment variable
380	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	425	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
381	override the flags completely if it is found in the environment. This is	426	override the flags completely if it is found in the environment. This is
382	useful to try out specific backends to test their performance, or to work	427	useful to try out specific backends to test their performance, to work
383	around bugs.	428	around bugs, or to make libev threadsafe (accessing environment variables
		429	cannot be done in a threadsafe way, but usually it works if no other
		430	thread modifies them).
384		431
385	=item C<EVFLAG_FORKCHECK>	432	=item C<EVFLAG_FORKCHECK>
386		433
387	Instead of calling C<ev_loop_fork> manually after a fork, you can also	434	Instead of calling C<ev_loop_fork> manually after a fork, you can also
388	make libev check for a fork in each iteration by enabling this flag.	435	make libev check for a fork in each iteration by enabling this flag.
389		436
390	This works by calling C<getpid ()> on every iteration of the loop,	437	This works by calling C<getpid ()> on every iteration of the loop,
391	and thus this might slow down your event loop if you do a lot of loop	438	and thus this might slow down your event loop if you do a lot of loop
392	iterations and little real work, but is usually not noticeable (on my	439	iterations and little real work, but is usually not noticeable (on my
393	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence	440	GNU/Linux system for example, C<getpid> is actually a simple 5-insn
394	without a system call and thus I<very> fast, but my GNU/Linux system also has	441	sequence without a system call and thus I<very> fast, but my GNU/Linux
395	C<pthread_atfork> which is even faster).	442	system also has C<pthread_atfork> which is even faster). (Update: glibc
		443	versions 2.25 apparently removed the C<getpid> optimisation again).
396		444
397	The big advantage of this flag is that you can forget about fork (and	445	The big advantage of this flag is that you can forget about fork (and
398	forget about forgetting to tell libev about forking) when you use this	446	forget about forgetting to tell libev about forking, although you still
399	flag.	447	have to ignore C<SIGPIPE>) when you use this flag.
400		448
401	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>	449	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
402	environment variable.	450	environment variable.
403		451
404	=item C<EVFLAG_NOINOTIFY>	452	=item C<EVFLAG_NOINOTIFY>
405		453
406	When this flag is specified, then libev will not attempt to use the	454	When this flag is specified, then libev will not attempt to use the
407	I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and	455	I<inotify> API for its C<ev_stat> watchers. Apart from debugging and
408	testing, this flag can be useful to conserve inotify file descriptors, as	456	testing, this flag can be useful to conserve inotify file descriptors, as
409	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.	457	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
410		458
411	=item C<EVFLAG_SIGNALFD>	459	=item C<EVFLAG_SIGNALFD>
412		460
413	When this flag is specified, then libev will attempt to use the	461	When this flag is specified, then libev will attempt to use the
414	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This API	462	I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API
415	delivers signals synchronously, which makes it both faster and might make	463	delivers signals synchronously, which makes it both faster and might make
416	it possible to get the queued signal data. It can also simplify signal	464	it possible to get the queued signal data. It can also simplify signal
417	handling with threads, as long as you properly block signals in your	465	handling with threads, as long as you properly block signals in your
418	threads that are not interested in handling them.	466	threads that are not interested in handling them.
419		467
420	Signalfd will not be used by default as this changes your signal mask, and	468	Signalfd will not be used by default as this changes your signal mask, and
421	there are a lot of shoddy libraries and programs (glib's threadpool for	469	there are a lot of shoddy libraries and programs (glib's threadpool for
422	example) that can't properly initialise their signal masks.	470	example) that can't properly initialise their signal masks.
		471
		472	=item C<EVFLAG_NOSIGMASK>
		473
		474	When this flag is specified, then libev will avoid to modify the signal
		475	mask. Specifically, this means you have to make sure signals are unblocked
		476	when you want to receive them.
		477
		478	This behaviour is useful when you want to do your own signal handling, or
		479	want to handle signals only in specific threads and want to avoid libev
		480	unblocking the signals.
		481
		482	It's also required by POSIX in a threaded program, as libev calls
		483	C<sigprocmask>, whose behaviour is officially unspecified.
		484
		485	=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.
423		495
424	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	496	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
425		497
426	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
427	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,
…		…
452	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
453	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.	525	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
454		526
455	=item C<EVBACKEND_EPOLL> (value 4, Linux)	527	=item C<EVBACKEND_EPOLL> (value 4, Linux)
456		528
457	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
458	kernels).	530	kernels).
459		531
460	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
461	but it scales phenomenally better. While poll and select usually scale	533	it scales phenomenally better. While poll and select usually scale like
462	like O(total_fds) where n is the total number of fds (or the highest fd),	534	O(total_fds) where total_fds is the total number of fds (or the highest
463	epoll scales either O(1) or O(active_fds).	535	fd), epoll scales either O(1) or O(active_fds).
464		536
465	The epoll mechanism deserves honorable mention as the most misdesigned	537	The epoll mechanism deserves honorable mention as the most misdesigned
466	of the more advanced event mechanisms: mere annoyances include silently	538	of the more advanced event mechanisms: mere annoyances include silently
467	dropping file descriptors, requiring a system call per change per file	539	dropping file descriptors, requiring a system call per change per file
468	descriptor (and unnecessary guessing of parameters), problems with dup,	540	descriptor (and unnecessary guessing of parameters), problems with dup,
469	returning before the timeout value requiring additional iterations and so	541	returning before the timeout value, resulting in additional iterations
		542	(and only giving 5ms accuracy while select on the same platform gives
470	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
471	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
472	take considerable time (one syscall per file descriptor) and is of course	545	set, which can take considerable time (one syscall per file descriptor)
473	hard to detect.	546	and is of course hard to detect.
474		547
475	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but	548	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
476	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
477	I<different> file descriptors (even already closed ones, so one cannot	550	totally I<different> file descriptors (even already closed ones, so
478	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
479	on SMP systems). Libev tries to counter these spurious notifications by	552	(especially on SMP systems). Libev tries to counter these spurious
480	employing an additional generation counter and comparing that against the	553	notifications by employing an additional generation counter and comparing
481	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
482	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
483	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...
484		564
485	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
486	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
487	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
488	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
…		…
500	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
501	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
502	the usage. So sad.	582	the usage. So sad.
503		583
504	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
505	all kernel versions tested so far.	585	a lot of kernel revisions, but probably(!) works in current versions.
506		586
507	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
508	C<EVBACKEND_POLL>.	588	C<EVBACKEND_POLL>.
509		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
510	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	634	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
511		635
512	Kqueue deserves special mention, as at the time of this writing, it	636	Kqueue deserves special mention, as at the time this backend was
513	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
514	with anything but sockets and pipes, except on Darwin, where of course	638	work reliably with anything but sockets and pipes, except on Darwin,
515	it's completely useless). Unlike epoll, however, whose brokenness	639	where of course it's completely useless). Unlike epoll, however, whose
516	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)
517	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
518	"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
519	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
520	system like NetBSD.	644	known-to-be-good (-enough) system like NetBSD.
521		645
522	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
523	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
524	the target platform). See C<ev_embed> watchers for more info.	648	the target platform). See C<ev_embed> watchers for more info.
525		649
526	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
527	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
528	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
529	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
530	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
531	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
532	cases	656	drops fds silently in similarly hard-to-detect cases.
533		657
534	This backend usually performs well under most conditions.	658	This backend usually performs well under most conditions.
535		659
536	While nominally embeddable in other event loops, this doesn't work	660	While nominally embeddable in other event loops, this doesn't work
537	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
…		…
554	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	678	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
555		679
556	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,
557	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)).
558		682
559	Please note that Solaris event ports can deliver a lot of spurious
560	notifications, so you need to use non-blocking I/O or other means to avoid
561	blocking when no data (or space) is available.
562
563	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
564	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
565	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	685	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
566	might perform better.	686	might perform better.
567		687
568	On the positive side, with the exception of the spurious readiness	688	On the positive side, this backend actually performed fully to
569	notifications, this backend actually performed fully to specification
570	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
571	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.
572		702
573	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
574	C<EVBACKEND_POLL>.	704	C<EVBACKEND_POLL>.
575		705
576	=item C<EVBACKEND_ALL>	706	=item C<EVBACKEND_ALL>
577		707
578	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
579	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
580	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	710	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
581		711
582	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).
583		721
584	=back	722	=back
585		723
586	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,
587	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
…		…
596		734
597	Example: Use whatever libev has to offer, but make sure that kqueue is	735	Example: Use whatever libev has to offer, but make sure that kqueue is
598	used if available.	736	used if available.
599		737
600	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);	738	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		739
		740	Example: Similarly, on linux, you mgiht want to take advantage of the
		741	linux aio backend if possible, but fall back to something else if that
		742	isn't available.
		743
		744	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_LINUXAIO);
601		745
602	=item ev_loop_destroy (loop)	746	=item ev_loop_destroy (loop)
603		747
604	Destroys an event loop object (frees all memory and kernel state	748	Destroys an event loop object (frees all memory and kernel state
605	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
…		…
616	This function is normally used on loop objects allocated by	760	This function is normally used on loop objects allocated by
617	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
618	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.
619		763
620	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
621	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.
622	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>
623	and C<ev_loop_destroy>.	767	and C<ev_loop_destroy>.
624		768
625	=item ev_loop_fork (loop)	769	=item ev_loop_fork (loop)
626		770
627	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
628	reinitialise the kernel state for backends that have one. Despite the	772	to reinitialise the kernel state for backends that have one. Despite
629	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
630	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
631	child before resuming or calling C<ev_run>.	776	C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.
632		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
633	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
634	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
635	because some kernel interfaces *cough* I<kqueue> *cough* do funny things	783	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
636	during fork.	784	during fork.
637		785
638	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
…		…
674	prepare and check phases.	822	prepare and check phases.
675		823
676	=item unsigned int ev_depth (loop)	824	=item unsigned int ev_depth (loop)
677		825
678	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
679	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.
680		828
681	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
682	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),
683	in which case it is higher.	831	in which case it is higher.
684		832
685	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread	833	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
686	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
687	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.
688		837
689	=item unsigned int ev_backend (loop)	838	=item unsigned int ev_backend (loop)
690		839
691	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
692	use.	841	use.
…		…
707		856
708	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
709	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
710	the current time is a good idea.	859	the current time is a good idea.
711		860
712	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.
713		862
714	=item ev_suspend (loop)	863	=item ev_suspend (loop)
715		864
716	=item ev_resume (loop)	865	=item ev_resume (loop)
717		866
…		…
735	without a previous call to C<ev_suspend>.	884	without a previous call to C<ev_suspend>.
736		885
737	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
738	event loop time (see C<ev_now_update>).	887	event loop time (see C<ev_now_update>).
739		888
740	=item ev_run (loop, int flags)	889	=item bool ev_run (loop, int flags)
741		890
742	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
743	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
744	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
745	the watcher callbacks, an then repeat the whole process indefinitely: This	894	the watcher callbacks, and then repeat the whole process indefinitely: This
746	is why event loops are called I<loops>.	895	is why event loops are called I<loops>.
747		896
748	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
749	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
750	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").
751		904
752	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
753	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
754	finished (especially in interactive programs), but having a program	907	finished (especially in interactive programs), but having a program
755	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
756	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
757	beauty.	910	beauty.
758		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
759	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
760	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
761	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
762	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
763	events while doing lengthy calculations, to keep the program responsive.	921	events while doing lengthy calculations, to keep the program responsive.
…		…
772	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
773	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
774	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
775	usually a better approach for this kind of thing.	933	usually a better approach for this kind of thing.
776		934
777	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):
778		938
779	- Increment loop depth.	939	- Increment loop depth.
780	- Reset the ev_break status.	940	- Reset the ev_break status.
781	- Before the first iteration, call any pending watchers.	941	- Before the first iteration, call any pending watchers.
782	LOOP:	942	LOOP:
…		…
815	anymore.	975	anymore.
816		976
817	... queue jobs here, make sure they register event watchers as long	977	... queue jobs here, make sure they register event watchers as long
818	... 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..)
819	ev_run (my_loop, 0);	979	ev_run (my_loop, 0);
820	... jobs done or somebody called unloop. yeah!	980	... jobs done or somebody called break. yeah!
821		981
822	=item ev_break (loop, how)	982	=item ev_break (loop, how)
823		983
824	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
825	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
826	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
827	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.
828		988
829	This "break 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>.
830		990
831	It is safe to call C<ev_break> from outside any C<ev_run> calls, too.	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.
832		993
833	=item ev_ref (loop)	994	=item ev_ref (loop)
834		995
835	=item ev_unref (loop)	996	=item ev_unref (loop)
836		997
…		…
857	running when nothing else is active.	1018	running when nothing else is active.
858		1019
859	ev_signal exitsig;	1020	ev_signal exitsig;
860	ev_signal_init (&exitsig, sig_cb, SIGINT);	1021	ev_signal_init (&exitsig, sig_cb, SIGINT);
861	ev_signal_start (loop, &exitsig);	1022	ev_signal_start (loop, &exitsig);
862	evf_unref (loop);	1023	ev_unref (loop);
863		1024
864	Example: For some weird reason, unregister the above signal handler again.	1025	Example: For some weird reason, unregister the above signal handler again.
865		1026
866	ev_ref (loop);	1027	ev_ref (loop);
867	ev_signal_stop (loop, &exitsig);	1028	ev_signal_stop (loop, &exitsig);
…		…
887	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.
888		1049
889	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
890	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,
891	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
892	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
893	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
894	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
895	once per this interval, on average.	1056	once per this interval, on average (as long as the host time resolution is
		1057	good enough).
896		1058
897	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
898	to spend more time collecting timeouts, at the expense of increased	1060	to spend more time collecting timeouts, at the expense of increased
899	latency/jitter/inexactness (the watcher callback will be called	1061	latency/jitter/inexactness (the watcher callback will be called
900	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
…		…
946	invoke the actual watchers inside another context (another thread etc.).	1108	invoke the actual watchers inside another context (another thread etc.).
947		1109
948	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
949	callback.	1111	callback.
950		1112
951	=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 ())
952		1114
953	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
954	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
955	each call to a libev function.	1117	each call to a libev function.
956		1118
957	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
958	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
959	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
960	I<release> and I<acquire> callbacks on the loop.	1122	I<release> and I<acquire> callbacks on the loop.
961		1123
962	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
963	suspended waiting for new events, and C<acquire> is called just	1125	suspended waiting for new events, and C<acquire> is called just
964	afterwards.	1126	afterwards.
…		…
979	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
980	document.	1142	document.
981		1143
982	=item ev_set_userdata (loop, void *data)	1144	=item ev_set_userdata (loop, void *data)
983		1145
984	=item ev_userdata (loop)	1146	=item void *ev_userdata (loop)
985		1147
986	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
987	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
988	C<0.>	1150	C<0>.
989		1151
990	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,
991	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
992	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
993	any other purpose as well.	1155	any other purpose as well.
…		…
1104		1266
1105	=item C<EV_PREPARE>	1267	=item C<EV_PREPARE>
1106		1268
1107	=item C<EV_CHECK>	1269	=item C<EV_CHECK>
1108		1270
1109	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts	1271	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts to
1110	to gather new events, and all C<ev_check> watchers are invoked just after	1272	gather new events, and all C<ev_check> watchers are queued (not invoked)
1111	C<ev_run> has gathered them, but before it invokes any callbacks for any	1273	just after C<ev_run> has gathered them, but before it queues any callbacks
		1274	for any received events. That means C<ev_prepare> watchers are the last
		1275	watchers invoked before the event loop sleeps or polls for new events, and
		1276	C<ev_check> watchers will be invoked before any other watchers of the same
		1277	or lower priority within an event loop iteration.
		1278
1112	received events. Callbacks of both watcher types can start and stop as	1279	Callbacks of both watcher types can start and stop as many watchers as
1113	many watchers as they want, and all of them will be taken into account	1280	they want, and all of them will be taken into account (for example, a
1114	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1281	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
1115	C<ev_run> from blocking).	1282	blocking).
1116		1283
1117	=item C<EV_EMBED>	1284	=item C<EV_EMBED>
1118		1285
1119	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1286	The embedded event loop specified in the C<ev_embed> watcher needs attention.
1120		1287
…		…
1243		1410
1244	=item callback ev_cb (ev_TYPE *watcher)	1411	=item callback ev_cb (ev_TYPE *watcher)
1245		1412
1246	Returns the callback currently set on the watcher.	1413	Returns the callback currently set on the watcher.
1247		1414
1248	=item ev_cb_set (ev_TYPE *watcher, callback)	1415	=item ev_set_cb (ev_TYPE *watcher, callback)
1249		1416
1250	Change the callback. You can change the callback at virtually any time	1417	Change the callback. You can change the callback at virtually any time
1251	(modulo threads).	1418	(modulo threads).
1252		1419
1253	=item ev_set_priority (ev_TYPE *watcher, int priority)	1420	=item ev_set_priority (ev_TYPE *watcher, int priority)
…		…
1271	or might not have been clamped to the valid range.	1438	or might not have been clamped to the valid range.
1272		1439
1273	The default priority used by watchers when no priority has been set is	1440	The default priority used by watchers when no priority has been set is
1274	always C<0>, which is supposed to not be too high and not be too low :).	1441	always C<0>, which is supposed to not be too high and not be too low :).
1275		1442
1276	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of	1443	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1277	priorities.	1444	priorities.
1278		1445
1279	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1446	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1280		1447
1281	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1448	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
…		…
1306	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related	1473	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1307	functions that do not need a watcher.	1474	functions that do not need a watcher.
1308		1475
1309	=back	1476	=back
1310		1477
1311	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1478	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
1312		1479	OWN COMPOSITE WATCHERS> idioms.
1313	Each watcher has, by default, a member C<void *data> that you can change
1314	and read at any time: libev will completely ignore it. This can be used
1315	to associate arbitrary data with your watcher. If you need more data and
1316	don't want to allocate memory and store a pointer to it in that data
1317	member, you can also "subclass" the watcher type and provide your own
1318	data:
1319
1320	struct my_io
1321	{
1322	ev_io io;
1323	int otherfd;
1324	void *somedata;
1325	struct whatever *mostinteresting;
1326	};
1327
1328	...
1329	struct my_io w;
1330	ev_io_init (&w.io, my_cb, fd, EV_READ);
1331
1332	And since your callback will be called with a pointer to the watcher, you
1333	can cast it back to your own type:
1334
1335	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1336	{
1337	struct my_io *w = (struct my_io *)w_;
1338	...
1339	}
1340
1341	More interesting and less C-conformant ways of casting your callback type
1342	instead have been omitted.
1343
1344	Another common scenario is to use some data structure with multiple
1345	embedded watchers:
1346
1347	struct my_biggy
1348	{
1349	int some_data;
1350	ev_timer t1;
1351	ev_timer t2;
1352	}
1353
1354	In this case getting the pointer to C<my_biggy> is a bit more
1355	complicated: Either you store the address of your C<my_biggy> struct
1356	in the C<data> member of the watcher (for woozies), or you need to use
1357	some pointer arithmetic using C<offsetof> inside your watchers (for real
1358	programmers):
1359
1360	#include <stddef.h>
1361
1362	static void
1363	t1_cb (EV_P_ ev_timer *w, int revents)
1364	{
1365	struct my_biggy big = (struct my_biggy *)
1366	(((char *)w) - offsetof (struct my_biggy, t1));
1367	}
1368
1369	static void
1370	t2_cb (EV_P_ ev_timer *w, int revents)
1371	{
1372	struct my_biggy big = (struct my_biggy *)
1373	(((char *)w) - offsetof (struct my_biggy, t2));
1374	}
1375		1480
1376	=head2 WATCHER STATES	1481	=head2 WATCHER STATES
1377		1482
1378	There are various watcher states mentioned throughout this manual -	1483	There are various watcher states mentioned throughout this manual -
1379	active, pending and so on. In this section these states and the rules to	1484	active, pending and so on. In this section these states and the rules to
1380	transition between them will be described in more detail - and while these	1485	transition between them will be described in more detail - and while these
1381	rules might look complicated, they usually do "the right thing".	1486	rules might look complicated, they usually do "the right thing".
1382		1487
1383	=over 4	1488	=over 4
1384		1489
1385	=item initialiased	1490	=item initialised
1386		1491
1387	Before a watcher can be registered with the event looop it has to be	1492	Before a watcher can be registered with the event loop it has to be
1388	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to	1493	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
1389	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.	1494	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1390		1495
1391	In this state it is simply some block of memory that is suitable for use	1496	In this state it is simply some block of memory that is suitable for
1392	in an event loop. It can be moved around, freed, reused etc. at will.	1497	use in an event loop. It can be moved around, freed, reused etc. at
		1498	will - as long as you either keep the memory contents intact, or call
		1499	C<ev_TYPE_init> again.
1393		1500
1394	=item started/running/active	1501	=item started/running/active
1395		1502
1396	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes	1503	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
1397	property of the event loop, and is actively waiting for events. While in	1504	property of the event loop, and is actively waiting for events. While in
…		…
1425	latter will clear any pending state the watcher might be in, regardless	1532	latter will clear any pending state the watcher might be in, regardless
1426	of whether it was active or not, so stopping a watcher explicitly before	1533	of whether it was active or not, so stopping a watcher explicitly before
1427	freeing it is often a good idea.	1534	freeing it is often a good idea.
1428		1535
1429	While stopped (and not pending) the watcher is essentially in the	1536	While stopped (and not pending) the watcher is essentially in the
1430	initialised state, that is it can be reused, moved, modified in any way	1537	initialised state, that is, it can be reused, moved, modified in any way
1431	you wish.	1538	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1539	it again).
1432		1540
1433	=back	1541	=back
1434		1542
1435	=head2 WATCHER PRIORITY MODELS	1543	=head2 WATCHER PRIORITY MODELS
1436		1544
1437	Many event loops support I<watcher priorities>, which are usually small	1545	Many event loops support I<watcher priorities>, which are usually small
1438	integers that influence the ordering of event callback invocation	1546	integers that influence the ordering of event callback invocation
1439	between watchers in some way, all else being equal.	1547	between watchers in some way, all else being equal.
1440		1548
1441	In libev, Watcher priorities can be set using C<ev_set_priority>. See its	1549	In libev, watcher priorities can be set using C<ev_set_priority>. See its
1442	description for the more technical details such as the actual priority	1550	description for the more technical details such as the actual priority
1443	range.	1551	range.
1444		1552
1445	There are two common ways how these these priorities are being interpreted	1553	There are two common ways how these these priorities are being interpreted
1446	by event loops:	1554	by event loops:
…		…
1565	In general you can register as many read and/or write event watchers per	1673	In general you can register as many read and/or write event watchers per
1566	fd as you want (as long as you don't confuse yourself). Setting all file	1674	fd as you want (as long as you don't confuse yourself). Setting all file
1567	descriptors to non-blocking mode is also usually a good idea (but not	1675	descriptors to non-blocking mode is also usually a good idea (but not
1568	required if you know what you are doing).	1676	required if you know what you are doing).
1569		1677
1570	If you cannot use non-blocking mode, then force the use of a
1571	known-to-be-good backend (at the time of this writing, this includes only
1572	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
1573	descriptors for which non-blocking operation makes no sense (such as
1574	files) - libev doesn't guarantee any specific behaviour in that case.
1575
1576	Another thing you have to watch out for is that it is quite easy to	1678	Another thing you have to watch out for is that it is quite easy to
1577	receive "spurious" readiness notifications, that is your callback might	1679	receive "spurious" readiness notifications, that is, your callback might
1578	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1680	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1579	because there is no data. Not only are some backends known to create a	1681	because there is no data. It is very easy to get into this situation even
1580	lot of those (for example Solaris ports), it is very easy to get into	1682	with a relatively standard program structure. Thus it is best to always
1581	this situation even with a relatively standard program structure. Thus	1683	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1582	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1583	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1684	preferable to a program hanging until some data arrives.
1584		1685
1585	If you cannot run the fd in non-blocking mode (for example you should	1686	If you cannot run the fd in non-blocking mode (for example you should
1586	not play around with an Xlib connection), then you have to separately	1687	not play around with an Xlib connection), then you have to separately
1587	re-test whether a file descriptor is really ready with a known-to-be good	1688	re-test whether a file descriptor is really ready with a known-to-be good
1588	interface such as poll (fortunately in our Xlib example, Xlib already	1689	interface such as poll (fortunately in the case of Xlib, it already does
1589	does this on its own, so its quite safe to use). Some people additionally	1690	this on its own, so its quite safe to use). Some people additionally
1590	use C<SIGALRM> and an interval timer, just to be sure you won't block	1691	use C<SIGALRM> and an interval timer, just to be sure you won't block
1591	indefinitely.	1692	indefinitely.
1592		1693
1593	But really, best use non-blocking mode.	1694	But really, best use non-blocking mode.
1594		1695
1595	=head3 The special problem of disappearing file descriptors	1696	=head3 The special problem of disappearing file descriptors
1596		1697
1597	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1698	Some backends (e.g. kqueue, epoll, linuxaio) need to be told about closing
1598	descriptor (either due to calling C<close> explicitly or any other means,	1699	a file descriptor (either due to calling C<close> explicitly or any other
1599	such as C<dup2>). The reason is that you register interest in some file	1700	means, such as C<dup2>). The reason is that you register interest in some
1600	descriptor, but when it goes away, the operating system will silently drop	1701	file descriptor, but when it goes away, the operating system will silently
1601	this interest. If another file descriptor with the same number then is	1702	drop this interest. If another file descriptor with the same number then
1602	registered with libev, there is no efficient way to see that this is, in	1703	is registered with libev, there is no efficient way to see that this is,
1603	fact, a different file descriptor.	1704	in fact, a different file descriptor.
1604		1705
1605	To avoid having to explicitly tell libev about such cases, libev follows	1706	To avoid having to explicitly tell libev about such cases, libev follows
1606	the following policy: Each time C<ev_io_set> is being called, libev	1707	the following policy: Each time C<ev_io_set> is being called, libev
1607	will assume that this is potentially a new file descriptor, otherwise	1708	will assume that this is potentially a new file descriptor, otherwise
1608	it is assumed that the file descriptor stays the same. That means that	1709	it is assumed that the file descriptor stays the same. That means that
…		…
1622		1723
1623	There is no workaround possible except not registering events	1724	There is no workaround possible except not registering events
1624	for potentially C<dup ()>'ed file descriptors, or to resort to	1725	for potentially C<dup ()>'ed file descriptors, or to resort to
1625	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1726	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1626		1727
		1728	=head3 The special problem of files
		1729
		1730	Many people try to use C<select> (or libev) on file descriptors
		1731	representing files, and expect it to become ready when their program
		1732	doesn't block on disk accesses (which can take a long time on their own).
		1733
		1734	However, this cannot ever work in the "expected" way - you get a readiness
		1735	notification as soon as the kernel knows whether and how much data is
		1736	there, and in the case of open files, that's always the case, so you
		1737	always get a readiness notification instantly, and your read (or possibly
		1738	write) will still block on the disk I/O.
		1739
		1740	Another way to view it is that in the case of sockets, pipes, character
		1741	devices and so on, there is another party (the sender) that delivers data
		1742	on its own, but in the case of files, there is no such thing: the disk
		1743	will not send data on its own, simply because it doesn't know what you
		1744	wish to read - you would first have to request some data.
		1745
		1746	Since files are typically not-so-well supported by advanced notification
		1747	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1748	to files, even though you should not use it. The reason for this is
		1749	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1750	usually a tty, often a pipe, but also sometimes files or special devices
		1751	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1752	F</dev/urandom>), and even though the file might better be served with
		1753	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1754	it "just works" instead of freezing.
		1755
		1756	So avoid file descriptors pointing to files when you know it (e.g. use
		1757	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1758	when you rarely read from a file instead of from a socket, and want to
		1759	reuse the same code path.
		1760
1627	=head3 The special problem of fork	1761	=head3 The special problem of fork
1628		1762
1629	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1763	Some backends (epoll, kqueue, linuxaio, iouring) do not support C<fork ()>
1630	useless behaviour. Libev fully supports fork, but needs to be told about	1764	at all or exhibit useless behaviour. Libev fully supports fork, but needs
1631	it in the child.	1765	to be told about it in the child if you want to continue to use it in the
		1766	child.
1632		1767
1633	To support fork in your programs, you either have to call	1768	To support fork in your child processes, you have to call C<ev_loop_fork
1634	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1769	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1635	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1770	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1636	C<EVBACKEND_POLL>.
1637		1771
1638	=head3 The special problem of SIGPIPE	1772	=head3 The special problem of SIGPIPE
1639		1773
1640	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1774	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1641	when writing to a pipe whose other end has been closed, your program gets	1775	when writing to a pipe whose other end has been closed, your program gets
…		…
1739	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1873	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1740	monotonic clock option helps a lot here).	1874	monotonic clock option helps a lot here).
1741		1875
1742	The callback is guaranteed to be invoked only I<after> its timeout has	1876	The callback is guaranteed to be invoked only I<after> its timeout has
1743	passed (not I<at>, so on systems with very low-resolution clocks this	1877	passed (not I<at>, so on systems with very low-resolution clocks this
1744	might introduce a small delay). If multiple timers become ready during the	1878	might introduce a small delay, see "the special problem of being too
		1879	early", below). If multiple timers become ready during the same loop
1745	same loop iteration then the ones with earlier time-out values are invoked	1880	iteration then the ones with earlier time-out values are invoked before
1746	before ones of the same priority with later time-out values (but this is	1881	ones of the same priority with later time-out values (but this is no
1747	no longer true when a callback calls C<ev_run> recursively).	1882	longer true when a callback calls C<ev_run> recursively).
1748		1883
1749	=head3 Be smart about timeouts	1884	=head3 Be smart about timeouts
1750		1885
1751	Many real-world problems involve some kind of timeout, usually for error	1886	Many real-world problems involve some kind of timeout, usually for error
1752	recovery. A typical example is an HTTP request - if the other side hangs,	1887	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1827		1962
1828	In this case, it would be more efficient to leave the C<ev_timer> alone,	1963	In this case, it would be more efficient to leave the C<ev_timer> alone,
1829	but remember the time of last activity, and check for a real timeout only	1964	but remember the time of last activity, and check for a real timeout only
1830	within the callback:	1965	within the callback:
1831		1966
		1967	ev_tstamp timeout = 60.;
1832	ev_tstamp last_activity; // time of last activity	1968	ev_tstamp last_activity; // time of last activity
		1969	ev_timer timer;
1833		1970
1834	static void	1971	static void
1835	callback (EV_P_ ev_timer *w, int revents)	1972	callback (EV_P_ ev_timer *w, int revents)
1836	{	1973	{
1837	ev_tstamp now = ev_now (EV_A);	1974	// calculate when the timeout would happen
1838	ev_tstamp timeout = last_activity + 60.;	1975	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
1839		1976
1840	// if last_activity + 60. is older than now, we did time out	1977	// if negative, it means we the timeout already occurred
1841	if (timeout < now)	1978	if (after < 0.)
1842	{	1979	{
1843	// timeout occurred, take action	1980	// timeout occurred, take action
1844	}	1981	}
1845	else	1982	else
1846	{	1983	{
1847	// callback was invoked, but there was some activity, re-arm	1984	// callback was invoked, but there was some recent
1848	// the watcher to fire in last_activity + 60, which is	1985	// activity. simply restart the timer to time out
1849	// guaranteed to be in the future, so "again" is positive:	1986	// after "after" seconds, which is the earliest time
1850	w->repeat = timeout - now;	1987	// the timeout can occur.
		1988	ev_timer_set (w, after, 0.);
1851	ev_timer_again (EV_A_ w);	1989	ev_timer_start (EV_A_ w);
1852	}	1990	}
1853	}	1991	}
1854		1992
1855	To summarise the callback: first calculate the real timeout (defined	1993	To summarise the callback: first calculate in how many seconds the
1856	as "60 seconds after the last activity"), then check if that time has	1994	timeout will occur (by calculating the absolute time when it would occur,
1857	been reached, which means something I<did>, in fact, time out. Otherwise	1995	C<last_activity + timeout>, and subtracting the current time, C<ev_now
1858	the callback was invoked too early (C<timeout> is in the future), so	1996	(EV_A)> from that).
1859	re-schedule the timer to fire at that future time, to see if maybe we have
1860	a timeout then.
1861		1997
1862	Note how C<ev_timer_again> is used, taking advantage of the	1998	If this value is negative, then we are already past the timeout, i.e. we
1863	C<ev_timer_again> optimisation when the timer is already running.	1999	timed out, and need to do whatever is needed in this case.
		2000
		2001	Otherwise, we now the earliest time at which the timeout would trigger,
		2002	and simply start the timer with this timeout value.
		2003
		2004	In other words, each time the callback is invoked it will check whether
		2005	the timeout occurred. If not, it will simply reschedule itself to check
		2006	again at the earliest time it could time out. Rinse. Repeat.
1864		2007
1865	This scheme causes more callback invocations (about one every 60 seconds	2008	This scheme causes more callback invocations (about one every 60 seconds
1866	minus half the average time between activity), but virtually no calls to	2009	minus half the average time between activity), but virtually no calls to
1867	libev to change the timeout.	2010	libev to change the timeout.
1868		2011
1869	To start the timer, simply initialise the watcher and set C<last_activity>	2012	To start the machinery, simply initialise the watcher and set
1870	to the current time (meaning we just have some activity :), then call the	2013	C<last_activity> to the current time (meaning there was some activity just
1871	callback, which will "do the right thing" and start the timer:	2014	now), then call the callback, which will "do the right thing" and start
		2015	the timer:
1872		2016
		2017	last_activity = ev_now (EV_A);
1873	ev_init (timer, callback);	2018	ev_init (&timer, callback);
1874	last_activity = ev_now (loop);	2019	callback (EV_A_ &timer, 0);
1875	callback (loop, timer, EV_TIMER);
1876		2020
1877	And when there is some activity, simply store the current time in	2021	When there is some activity, simply store the current time in
1878	C<last_activity>, no libev calls at all:	2022	C<last_activity>, no libev calls at all:
1879		2023
		2024	if (activity detected)
1880	last_activity = ev_now (loop);	2025	last_activity = ev_now (EV_A);
		2026
		2027	When your timeout value changes, then the timeout can be changed by simply
		2028	providing a new value, stopping the timer and calling the callback, which
		2029	will again do the right thing (for example, time out immediately :).
		2030
		2031	timeout = new_value;
		2032	ev_timer_stop (EV_A_ &timer);
		2033	callback (EV_A_ &timer, 0);
1881		2034
1882	This technique is slightly more complex, but in most cases where the	2035	This technique is slightly more complex, but in most cases where the
1883	time-out is unlikely to be triggered, much more efficient.	2036	time-out is unlikely to be triggered, much more efficient.
1884
1885	Changing the timeout is trivial as well (if it isn't hard-coded in the
1886	callback :) - just change the timeout and invoke the callback, which will
1887	fix things for you.
1888		2037
1889	=item 4. Wee, just use a double-linked list for your timeouts.	2038	=item 4. Wee, just use a double-linked list for your timeouts.
1890		2039
1891	If there is not one request, but many thousands (millions...), all	2040	If there is not one request, but many thousands (millions...), all
1892	employing some kind of timeout with the same timeout value, then one can	2041	employing some kind of timeout with the same timeout value, then one can
…		…
1919	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is	2068	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
1920	rather complicated, but extremely efficient, something that really pays	2069	rather complicated, but extremely efficient, something that really pays
1921	off after the first million or so of active timers, i.e. it's usually	2070	off after the first million or so of active timers, i.e. it's usually
1922	overkill :)	2071	overkill :)
1923		2072
		2073	=head3 The special problem of being too early
		2074
		2075	If you ask a timer to call your callback after three seconds, then
		2076	you expect it to be invoked after three seconds - but of course, this
		2077	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		2078	guaranteed to any precision by libev - imagine somebody suspending the
		2079	process with a STOP signal for a few hours for example.
		2080
		2081	So, libev tries to invoke your callback as soon as possible I<after> the
		2082	delay has occurred, but cannot guarantee this.
		2083
		2084	A less obvious failure mode is calling your callback too early: many event
		2085	loops compare timestamps with a "elapsed delay >= requested delay", but
		2086	this can cause your callback to be invoked much earlier than you would
		2087	expect.
		2088
		2089	To see why, imagine a system with a clock that only offers full second
		2090	resolution (think windows if you can't come up with a broken enough OS
		2091	yourself). If you schedule a one-second timer at the time 500.9, then the
		2092	event loop will schedule your timeout to elapse at a system time of 500
		2093	(500.9 truncated to the resolution) + 1, or 501.
		2094
		2095	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2096	501" and invoke the callback 0.1s after it was started, even though a
		2097	one-second delay was requested - this is being "too early", despite best
		2098	intentions.
		2099
		2100	This is the reason why libev will never invoke the callback if the elapsed
		2101	delay equals the requested delay, but only when the elapsed delay is
		2102	larger than the requested delay. In the example above, libev would only invoke
		2103	the callback at system time 502, or 1.1s after the timer was started.
		2104
		2105	So, while libev cannot guarantee that your callback will be invoked
		2106	exactly when requested, it I<can> and I<does> guarantee that the requested
		2107	delay has actually elapsed, or in other words, it always errs on the "too
		2108	late" side of things.
		2109
1924	=head3 The special problem of time updates	2110	=head3 The special problem of time updates
1925		2111
1926	Establishing the current time is a costly operation (it usually takes at	2112	Establishing the current time is a costly operation (it usually takes
1927	least two system calls): EV therefore updates its idea of the current	2113	at least one system call): EV therefore updates its idea of the current
1928	time only before and after C<ev_run> collects new events, which causes a	2114	time only before and after C<ev_run> collects new events, which causes a
1929	growing difference between C<ev_now ()> and C<ev_time ()> when handling	2115	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1930	lots of events in one iteration.	2116	lots of events in one iteration.
1931		2117
1932	The relative timeouts are calculated relative to the C<ev_now ()>	2118	The relative timeouts are calculated relative to the C<ev_now ()>
1933	time. This is usually the right thing as this timestamp refers to the time	2119	time. This is usually the right thing as this timestamp refers to the time
1934	of the event triggering whatever timeout you are modifying/starting. If	2120	of the event triggering whatever timeout you are modifying/starting. If
1935	you suspect event processing to be delayed and you I<need> to base the	2121	you suspect event processing to be delayed and you I<need> to base the
1936	timeout on the current time, use something like this to adjust for this:	2122	timeout on the current time, use something like the following to adjust
		2123	for it:
1937		2124
1938	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2125	ev_timer_set (&timer, after + (ev_time () - ev_now ()), 0.);
1939		2126
1940	If the event loop is suspended for a long time, you can also force an	2127	If the event loop is suspended for a long time, you can also force an
1941	update of the time returned by C<ev_now ()> by calling C<ev_now_update	2128	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1942	()>.	2129	()>, although that will push the event time of all outstanding events
		2130	further into the future.
		2131
		2132	=head3 The special problem of unsynchronised clocks
		2133
		2134	Modern systems have a variety of clocks - libev itself uses the normal
		2135	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2136	jumps).
		2137
		2138	Neither of these clocks is synchronised with each other or any other clock
		2139	on the system, so C<ev_time ()> might return a considerably different time
		2140	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2141	a call to C<gettimeofday> might return a second count that is one higher
		2142	than a directly following call to C<time>.
		2143
		2144	The moral of this is to only compare libev-related timestamps with
		2145	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2146	a second or so.
		2147
		2148	One more problem arises due to this lack of synchronisation: if libev uses
		2149	the system monotonic clock and you compare timestamps from C<ev_time>
		2150	or C<ev_now> from when you started your timer and when your callback is
		2151	invoked, you will find that sometimes the callback is a bit "early".
		2152
		2153	This is because C<ev_timer>s work in real time, not wall clock time, so
		2154	libev makes sure your callback is not invoked before the delay happened,
		2155	I<measured according to the real time>, not the system clock.
		2156
		2157	If your timeouts are based on a physical timescale (e.g. "time out this
		2158	connection after 100 seconds") then this shouldn't bother you as it is
		2159	exactly the right behaviour.
		2160
		2161	If you want to compare wall clock/system timestamps to your timers, then
		2162	you need to use C<ev_periodic>s, as these are based on the wall clock
		2163	time, where your comparisons will always generate correct results.
1943		2164
1944	=head3 The special problems of suspended animation	2165	=head3 The special problems of suspended animation
1945		2166
1946	When you leave the server world it is quite customary to hit machines that	2167	When you leave the server world it is quite customary to hit machines that
1947	can suspend/hibernate - what happens to the clocks during such a suspend?	2168	can suspend/hibernate - what happens to the clocks during such a suspend?
…		…
1977		2198
1978	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2199	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1979		2200
1980	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2201	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1981		2202
1982	Configure the timer to trigger after C<after> seconds. If C<repeat>	2203	Configure the timer to trigger after C<after> seconds (fractional and
1983	is C<0.>, then it will automatically be stopped once the timeout is	2204	negative values are supported). If C<repeat> is C<0.>, then it will
1984	reached. If it is positive, then the timer will automatically be	2205	automatically be stopped once the timeout is reached. If it is positive,
1985	configured to trigger again C<repeat> seconds later, again, and again,	2206	then the timer will automatically be configured to trigger again C<repeat>
1986	until stopped manually.	2207	seconds later, again, and again, until stopped manually.
1987		2208
1988	The timer itself will do a best-effort at avoiding drift, that is, if	2209	The timer itself will do a best-effort at avoiding drift, that is, if
1989	you configure a timer to trigger every 10 seconds, then it will normally	2210	you configure a timer to trigger every 10 seconds, then it will normally
1990	trigger at exactly 10 second intervals. If, however, your program cannot	2211	trigger at exactly 10 second intervals. If, however, your program cannot
1991	keep up with the timer (because it takes longer than those 10 seconds to	2212	keep up with the timer (because it takes longer than those 10 seconds to
1992	do stuff) the timer will not fire more than once per event loop iteration.	2213	do stuff) the timer will not fire more than once per event loop iteration.
1993		2214
1994	=item ev_timer_again (loop, ev_timer *)	2215	=item ev_timer_again (loop, ev_timer *)
1995		2216
1996	This will act as if the timer timed out and restart it again if it is	2217	This will act as if the timer timed out, and restarts it again if it is
1997	repeating. The exact semantics are:	2218	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2219	timeout to the C<repeat> value and calling C<ev_timer_start>.
1998		2220
		2221	The exact semantics are as in the following rules, all of which will be
		2222	applied to the watcher:
		2223
		2224	=over 4
		2225
1999	If the timer is pending, its pending status is cleared.	2226	=item If the timer is pending, the pending status is always cleared.
2000		2227
2001	If the timer is started but non-repeating, stop it (as if it timed out).	2228	=item If the timer is started but non-repeating, stop it (as if it timed
		2229	out, without invoking it).
2002		2230
2003	If the timer is repeating, either start it if necessary (with the	2231	=item If the timer is repeating, make the C<repeat> value the new timeout
2004	C<repeat> value), or reset the running timer to the C<repeat> value.	2232	and start the timer, if necessary.
2005		2233
		2234	=back
		2235
2006	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a	2236	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
2007	usage example.	2237	usage example.
2008		2238
2009	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)	2239	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
2010		2240
2011	Returns the remaining time until a timer fires. If the timer is active,	2241	Returns the remaining time until a timer fires. If the timer is active,
…		…
2064	Periodic watchers are also timers of a kind, but they are very versatile	2294	Periodic watchers are also timers of a kind, but they are very versatile
2065	(and unfortunately a bit complex).	2295	(and unfortunately a bit complex).
2066		2296
2067	Unlike C<ev_timer>, periodic watchers are not based on real time (or	2297	Unlike C<ev_timer>, periodic watchers are not based on real time (or
2068	relative time, the physical time that passes) but on wall clock time	2298	relative time, the physical time that passes) but on wall clock time
2069	(absolute time, the thing you can read on your calender or clock). The	2299	(absolute time, the thing you can read on your calendar or clock). The
2070	difference is that wall clock time can run faster or slower than real	2300	difference is that wall clock time can run faster or slower than real
2071	time, and time jumps are not uncommon (e.g. when you adjust your	2301	time, and time jumps are not uncommon (e.g. when you adjust your
2072	wrist-watch).	2302	wrist-watch).
2073		2303
2074	You can tell a periodic watcher to trigger after some specific point	2304	You can tell a periodic watcher to trigger after some specific point
…		…
2079	C<ev_timer>, which would still trigger roughly 10 seconds after starting	2309	C<ev_timer>, which would still trigger roughly 10 seconds after starting
2080	it, as it uses a relative timeout).	2310	it, as it uses a relative timeout).
2081		2311
2082	C<ev_periodic> watchers can also be used to implement vastly more complex	2312	C<ev_periodic> watchers can also be used to implement vastly more complex
2083	timers, such as triggering an event on each "midnight, local time", or	2313	timers, such as triggering an event on each "midnight, local time", or
2084	other complicated rules. This cannot be done with C<ev_timer> watchers, as	2314	other complicated rules. This cannot easily be done with C<ev_timer>
2085	those cannot react to time jumps.	2315	watchers, as those cannot react to time jumps.
2086		2316
2087	As with timers, the callback is guaranteed to be invoked only when the	2317	As with timers, the callback is guaranteed to be invoked only when the
2088	point in time where it is supposed to trigger has passed. If multiple	2318	point in time where it is supposed to trigger has passed. If multiple
2089	timers become ready during the same loop iteration then the ones with	2319	timers become ready during the same loop iteration then the ones with
2090	earlier time-out values are invoked before ones with later time-out values	2320	earlier time-out values are invoked before ones with later time-out values
…		…
2131		2361
2132	Another way to think about it (for the mathematically inclined) is that	2362	Another way to think about it (for the mathematically inclined) is that
2133	C<ev_periodic> will try to run the callback in this mode at the next possible	2363	C<ev_periodic> will try to run the callback in this mode at the next possible
2134	time where C<time = offset (mod interval)>, regardless of any time jumps.	2364	time where C<time = offset (mod interval)>, regardless of any time jumps.
2135		2365
2136	For numerical stability it is preferable that the C<offset> value is near	2366	The C<interval> I<MUST> be positive, and for numerical stability, the
2137	C<ev_now ()> (the current time), but there is no range requirement for	2367	interval value should be higher than C<1/8192> (which is around 100
2138	this value, and in fact is often specified as zero.	2368	microseconds) and C<offset> should be higher than C<0> and should have
		2369	at most a similar magnitude as the current time (say, within a factor of
		2370	ten). Typical values for offset are, in fact, C<0> or something between
		2371	C<0> and C<interval>, which is also the recommended range.
2139		2372
2140	Note also that there is an upper limit to how often a timer can fire (CPU	2373	Note also that there is an upper limit to how often a timer can fire (CPU
2141	speed for example), so if C<interval> is very small then timing stability	2374	speed for example), so if C<interval> is very small then timing stability
2142	will of course deteriorate. Libev itself tries to be exact to be about one	2375	will of course deteriorate. Libev itself tries to be exact to be about one
2143	millisecond (if the OS supports it and the machine is fast enough).	2376	millisecond (if the OS supports it and the machine is fast enough).
…		…
2173		2406
2174	NOTE: I<< This callback must always return a time that is higher than or	2407	NOTE: I<< This callback must always return a time that is higher than or
2175	equal to the passed C<now> value >>.	2408	equal to the passed C<now> value >>.
2176		2409
2177	This can be used to create very complex timers, such as a timer that	2410	This can be used to create very complex timers, such as a timer that
2178	triggers on "next midnight, local time". To do this, you would calculate the	2411	triggers on "next midnight, local time". To do this, you would calculate
2179	next midnight after C<now> and return the timestamp value for this. How	2412	the next midnight after C<now> and return the timestamp value for
2180	you do this is, again, up to you (but it is not trivial, which is the main	2413	this. Here is a (completely untested, no error checking) example on how to
2181	reason I omitted it as an example).	2414	do this:
		2415
		2416	#include <time.h>
		2417
		2418	static ev_tstamp
		2419	my_rescheduler (ev_periodic *w, ev_tstamp now)
		2420	{
		2421	time_t tnow = (time_t)now;
		2422	struct tm tm;
		2423	localtime_r (&tnow, &tm);
		2424
		2425	tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
		2426	++tm.tm_mday; // midnight next day
		2427
		2428	return mktime (&tm);
		2429	}
		2430
		2431	Note: this code might run into trouble on days that have more then two
		2432	midnights (beginning and end).
2182		2433
2183	=back	2434	=back
2184		2435
2185	=item ev_periodic_again (loop, ev_periodic *)	2436	=item ev_periodic_again (loop, ev_periodic *)
2186		2437
…		…
2251		2502
2252	ev_periodic hourly_tick;	2503	ev_periodic hourly_tick;
2253	ev_periodic_init (&hourly_tick, clock_cb,	2504	ev_periodic_init (&hourly_tick, clock_cb,
2254	fmod (ev_now (loop), 3600.), 3600., 0);	2505	fmod (ev_now (loop), 3600.), 3600., 0);
2255	ev_periodic_start (loop, &hourly_tick);	2506	ev_periodic_start (loop, &hourly_tick);
2256		2507
2257		2508
2258	=head2 C<ev_signal> - signal me when a signal gets signalled!	2509	=head2 C<ev_signal> - signal me when a signal gets signalled!
2259		2510
2260	Signal watchers will trigger an event when the process receives a specific	2511	Signal watchers will trigger an event when the process receives a specific
2261	signal one or more times. Even though signals are very asynchronous, libev	2512	signal one or more times. Even though signals are very asynchronous, libev
2262	will try it's best to deliver signals synchronously, i.e. as part of the	2513	will try its best to deliver signals synchronously, i.e. as part of the
2263	normal event processing, like any other event.	2514	normal event processing, like any other event.
2264		2515
2265	If you want signals to be delivered truly asynchronously, just use	2516	If you want signals to be delivered truly asynchronously, just use
2266	C<sigaction> as you would do without libev and forget about sharing	2517	C<sigaction> as you would do without libev and forget about sharing
2267	the signal. You can even use C<ev_async> from a signal handler to	2518	the signal. You can even use C<ev_async> from a signal handler to
…		…
2271	only within the same loop, i.e. you can watch for C<SIGINT> in your	2522	only within the same loop, i.e. you can watch for C<SIGINT> in your
2272	default loop and for C<SIGIO> in another loop, but you cannot watch for	2523	default loop and for C<SIGIO> in another loop, but you cannot watch for
2273	C<SIGINT> in both the default loop and another loop at the same time. At	2524	C<SIGINT> in both the default loop and another loop at the same time. At
2274	the moment, C<SIGCHLD> is permanently tied to the default loop.	2525	the moment, C<SIGCHLD> is permanently tied to the default loop.
2275		2526
2276	When the first watcher gets started will libev actually register something	2527	Only after the first watcher for a signal is started will libev actually
2277	with the kernel (thus it coexists with your own signal handlers as long as	2528	register something with the kernel. It thus coexists with your own signal
2278	you don't register any with libev for the same signal).	2529	handlers as long as you don't register any with libev for the same signal.
2279		2530
2280	If possible and supported, libev will install its handlers with	2531	If possible and supported, libev will install its handlers with
2281	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should	2532	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
2282	not be unduly interrupted. If you have a problem with system calls getting	2533	not be unduly interrupted. If you have a problem with system calls getting
2283	interrupted by signals you can block all signals in an C<ev_check> watcher	2534	interrupted by signals you can block all signals in an C<ev_check> watcher
…		…
2286	=head3 The special problem of inheritance over fork/execve/pthread_create	2537	=head3 The special problem of inheritance over fork/execve/pthread_create
2287		2538
2288	Both the signal mask (C<sigprocmask>) and the signal disposition	2539	Both the signal mask (C<sigprocmask>) and the signal disposition
2289	(C<sigaction>) are unspecified after starting a signal watcher (and after	2540	(C<sigaction>) are unspecified after starting a signal watcher (and after
2290	stopping it again), that is, libev might or might not block the signal,	2541	stopping it again), that is, libev might or might not block the signal,
2291	and might or might not set or restore the installed signal handler.	2542	and might or might not set or restore the installed signal handler (but
		2543	see C<EVFLAG_NOSIGMASK>).
2292		2544
2293	While this does not matter for the signal disposition (libev never	2545	While this does not matter for the signal disposition (libev never
2294	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on	2546	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
2295	C<execve>), this matters for the signal mask: many programs do not expect	2547	C<execve>), this matters for the signal mask: many programs do not expect
2296	certain signals to be blocked.	2548	certain signals to be blocked.
…		…
2309	I<has> to modify the signal mask, at least temporarily.	2561	I<has> to modify the signal mask, at least temporarily.
2310		2562
2311	So I can't stress this enough: I<If you do not reset your signal mask when	2563	So I can't stress this enough: I<If you do not reset your signal mask when
2312	you expect it to be empty, you have a race condition in your code>. This	2564	you expect it to be empty, you have a race condition in your code>. This
2313	is not a libev-specific thing, this is true for most event libraries.	2565	is not a libev-specific thing, this is true for most event libraries.
		2566
		2567	=head3 The special problem of threads signal handling
		2568
		2569	POSIX threads has problematic signal handling semantics, specifically,
		2570	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2571	threads in a process block signals, which is hard to achieve.
		2572
		2573	When you want to use sigwait (or mix libev signal handling with your own
		2574	for the same signals), you can tackle this problem by globally blocking
		2575	all signals before creating any threads (or creating them with a fully set
		2576	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2577	loops. Then designate one thread as "signal receiver thread" which handles
		2578	these signals. You can pass on any signals that libev might be interested
		2579	in by calling C<ev_feed_signal>.
2314		2580
2315	=head3 Watcher-Specific Functions and Data Members	2581	=head3 Watcher-Specific Functions and Data Members
2316		2582
2317	=over 4	2583	=over 4
2318		2584
…		…
2453		2719
2454	=head2 C<ev_stat> - did the file attributes just change?	2720	=head2 C<ev_stat> - did the file attributes just change?
2455		2721
2456	This watches a file system path for attribute changes. That is, it calls	2722	This watches a file system path for attribute changes. That is, it calls
2457	C<stat> on that path in regular intervals (or when the OS says it changed)	2723	C<stat> on that path in regular intervals (or when the OS says it changed)
2458	and sees if it changed compared to the last time, invoking the callback if	2724	and sees if it changed compared to the last time, invoking the callback
2459	it did.	2725	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2726	happen after the watcher has been started will be reported.
2460		2727
2461	The path does not need to exist: changing from "path exists" to "path does	2728	The path does not need to exist: changing from "path exists" to "path does
2462	not exist" is a status change like any other. The condition "path does not	2729	not exist" is a status change like any other. The condition "path does not
2463	exist" (or more correctly "path cannot be stat'ed") is signified by the	2730	exist" (or more correctly "path cannot be stat'ed") is signified by the
2464	C<st_nlink> field being zero (which is otherwise always forced to be at	2731	C<st_nlink> field being zero (which is otherwise always forced to be at
…		…
2694	Apart from keeping your process non-blocking (which is a useful	2961	Apart from keeping your process non-blocking (which is a useful
2695	effect on its own sometimes), idle watchers are a good place to do	2962	effect on its own sometimes), idle watchers are a good place to do
2696	"pseudo-background processing", or delay processing stuff to after the	2963	"pseudo-background processing", or delay processing stuff to after the
2697	event loop has handled all outstanding events.	2964	event loop has handled all outstanding events.
2698		2965
		2966	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2967
		2968	As long as there is at least one active idle watcher, libev will never
		2969	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2970	For this to work, the idle watcher doesn't need to be invoked at all - the
		2971	lowest priority will do.
		2972
		2973	This mode of operation can be useful together with an C<ev_check> watcher,
		2974	to do something on each event loop iteration - for example to balance load
		2975	between different connections.
		2976
		2977	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2978	example.
		2979
2699	=head3 Watcher-Specific Functions and Data Members	2980	=head3 Watcher-Specific Functions and Data Members
2700		2981
2701	=over 4	2982	=over 4
2702		2983
2703	=item ev_idle_init (ev_idle *, callback)	2984	=item ev_idle_init (ev_idle *, callback)
…		…
2714	callback, free it. Also, use no error checking, as usual.	2995	callback, free it. Also, use no error checking, as usual.
2715		2996
2716	static void	2997	static void
2717	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)	2998	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2718	{	2999	{
		3000	// stop the watcher
		3001	ev_idle_stop (loop, w);
		3002
		3003	// now we can free it
2719	free (w);	3004	free (w);
		3005
2720	// now do something you wanted to do when the program has	3006	// now do something you wanted to do when the program has
2721	// no longer anything immediate to do.	3007	// no longer anything immediate to do.
2722	}	3008	}
2723		3009
2724	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	3010	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
…		…
2726	ev_idle_start (loop, idle_watcher);	3012	ev_idle_start (loop, idle_watcher);
2727		3013
2728		3014
2729	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	3015	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2730		3016
2731	Prepare and check watchers are usually (but not always) used in pairs:	3017	Prepare and check watchers are often (but not always) used in pairs:
2732	prepare watchers get invoked before the process blocks and check watchers	3018	prepare watchers get invoked before the process blocks and check watchers
2733	afterwards.	3019	afterwards.
2734		3020
2735	You I<must not> call C<ev_run> or similar functions that enter	3021	You I<must not> call C<ev_run> (or similar functions that enter the
2736	the current event loop from either C<ev_prepare> or C<ev_check>	3022	current event loop) or C<ev_loop_fork> from either C<ev_prepare> or
2737	watchers. Other loops than the current one are fine, however. The	3023	C<ev_check> watchers. Other loops than the current one are fine,
2738	rationale behind this is that you do not need to check for recursion in	3024	however. The rationale behind this is that you do not need to check
2739	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	3025	for recursion in those watchers, i.e. the sequence will always be
2740	C<ev_check> so if you have one watcher of each kind they will always be	3026	C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
2741	called in pairs bracketing the blocking call.	3027	kind they will always be called in pairs bracketing the blocking call.
2742		3028
2743	Their main purpose is to integrate other event mechanisms into libev and	3029	Their main purpose is to integrate other event mechanisms into libev and
2744	their use is somewhat advanced. They could be used, for example, to track	3030	their use is somewhat advanced. They could be used, for example, to track
2745	variable changes, implement your own watchers, integrate net-snmp or a	3031	variable changes, implement your own watchers, integrate net-snmp or a
2746	coroutine library and lots more. They are also occasionally useful if	3032	coroutine library and lots more. They are also occasionally useful if
…		…
2764	with priority higher than or equal to the event loop and one coroutine	3050	with priority higher than or equal to the event loop and one coroutine
2765	of lower priority, but only once, using idle watchers to keep the event	3051	of lower priority, but only once, using idle watchers to keep the event
2766	loop from blocking if lower-priority coroutines are active, thus mapping	3052	loop from blocking if lower-priority coroutines are active, thus mapping
2767	low-priority coroutines to idle/background tasks).	3053	low-priority coroutines to idle/background tasks).
2768		3054
2769	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	3055	When used for this purpose, it is recommended to give C<ev_check> watchers
2770	priority, to ensure that they are being run before any other watchers	3056	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
2771	after the poll (this doesn't matter for C<ev_prepare> watchers).	3057	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		3058	watchers).
2772		3059
2773	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not	3060	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
2774	activate ("feed") events into libev. While libev fully supports this, they	3061	activate ("feed") events into libev. While libev fully supports this, they
2775	might get executed before other C<ev_check> watchers did their job. As	3062	might get executed before other C<ev_check> watchers did their job. As
2776	C<ev_check> watchers are often used to embed other (non-libev) event	3063	C<ev_check> watchers are often used to embed other (non-libev) event
2777	loops those other event loops might be in an unusable state until their	3064	loops those other event loops might be in an unusable state until their
2778	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	3065	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
2779	others).	3066	others).
		3067
		3068	=head3 Abusing an C<ev_check> watcher for its side-effect
		3069
		3070	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		3071	useful because they are called once per event loop iteration. For
		3072	example, if you want to handle a large number of connections fairly, you
		3073	normally only do a bit of work for each active connection, and if there
		3074	is more work to do, you wait for the next event loop iteration, so other
		3075	connections have a chance of making progress.
		3076
		3077	Using an C<ev_check> watcher is almost enough: it will be called on the
		3078	next event loop iteration. However, that isn't as soon as possible -
		3079	without external events, your C<ev_check> watcher will not be invoked.
		3080
		3081	This is where C<ev_idle> watchers come in handy - all you need is a
		3082	single global idle watcher that is active as long as you have one active
		3083	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		3084	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		3085	invoked. Neither watcher alone can do that.
2780		3086
2781	=head3 Watcher-Specific Functions and Data Members	3087	=head3 Watcher-Specific Functions and Data Members
2782		3088
2783	=over 4	3089	=over 4
2784		3090
…		…
2985		3291
2986	=over 4	3292	=over 4
2987		3293
2988	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3294	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
2989		3295
2990	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3296	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
2991		3297
2992	Configures the watcher to embed the given loop, which must be	3298	Configures the watcher to embed the given loop, which must be
2993	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3299	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
2994	invoked automatically, otherwise it is the responsibility of the callback	3300	invoked automatically, otherwise it is the responsibility of the callback
2995	to invoke it (it will continue to be called until the sweep has been done,	3301	to invoke it (it will continue to be called until the sweep has been done,
…		…
3016	used).	3322	used).
3017		3323
3018	struct ev_loop *loop_hi = ev_default_init (0);	3324	struct ev_loop *loop_hi = ev_default_init (0);
3019	struct ev_loop *loop_lo = 0;	3325	struct ev_loop *loop_lo = 0;
3020	ev_embed embed;	3326	ev_embed embed;
3021		3327
3022	// see if there is a chance of getting one that works	3328	// see if there is a chance of getting one that works
3023	// (remember that a flags value of 0 means autodetection)	3329	// (remember that a flags value of 0 means autodetection)
3024	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3330	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3025	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3331	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3026	: 0;	3332	: 0;
…		…
3040	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3346	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
3041		3347
3042	struct ev_loop *loop = ev_default_init (0);	3348	struct ev_loop *loop = ev_default_init (0);
3043	struct ev_loop *loop_socket = 0;	3349	struct ev_loop *loop_socket = 0;
3044	ev_embed embed;	3350	ev_embed embed;
3045		3351
3046	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3352	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3047	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3353	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3048	{	3354	{
3049	ev_embed_init (&embed, 0, loop_socket);	3355	ev_embed_init (&embed, 0, loop_socket);
3050	ev_embed_start (loop, &embed);	3356	ev_embed_start (loop, &embed);
…		…
3058		3364
3059	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3365	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
3060		3366
3061	Fork watchers are called when a C<fork ()> was detected (usually because	3367	Fork watchers are called when a C<fork ()> was detected (usually because
3062	whoever is a good citizen cared to tell libev about it by calling	3368	whoever is a good citizen cared to tell libev about it by calling
3063	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the	3369	C<ev_loop_fork>). The invocation is done before the event loop blocks next
3064	event loop blocks next and before C<ev_check> watchers are being called,	3370	and before C<ev_check> watchers are being called, and only in the child
3065	and only in the child after the fork. If whoever good citizen calling	3371	after the fork. If whoever good citizen calling C<ev_default_fork> cheats
3066	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3372	and calls it in the wrong process, the fork handlers will be invoked, too,
3067	handlers will be invoked, too, of course.	3373	of course.
3068		3374
3069	=head3 The special problem of life after fork - how is it possible?	3375	=head3 The special problem of life after fork - how is it possible?
3070		3376
3071	Most uses of C<fork()> consist of forking, then some simple calls to set	3377	Most uses of C<fork ()> consist of forking, then some simple calls to set
3072	up/change the process environment, followed by a call to C<exec()>. This	3378	up/change the process environment, followed by a call to C<exec()>. This
3073	sequence should be handled by libev without any problems.	3379	sequence should be handled by libev without any problems.
3074		3380
3075	This changes when the application actually wants to do event handling	3381	This changes when the application actually wants to do event handling
3076	in the child, or both parent in child, in effect "continuing" after the	3382	in the child, or both parent in child, in effect "continuing" after the
…		…
3153	atexit (program_exits);	3459	atexit (program_exits);
3154		3460
3155		3461
3156	=head2 C<ev_async> - how to wake up an event loop	3462	=head2 C<ev_async> - how to wake up an event loop
3157		3463
3158	In general, you cannot use an C<ev_run> from multiple threads or other	3464	In general, you cannot use an C<ev_loop> from multiple threads or other
3159	asynchronous sources such as signal handlers (as opposed to multiple event	3465	asynchronous sources such as signal handlers (as opposed to multiple event
3160	loops - those are of course safe to use in different threads).	3466	loops - those are of course safe to use in different threads).
3161		3467
3162	Sometimes, however, you need to wake up an event loop you do not control,	3468	Sometimes, however, you need to wake up an event loop you do not control,
3163	for example because it belongs to another thread. This is what C<ev_async>	3469	for example because it belongs to another thread. This is what C<ev_async>
…		…
3165	it by calling C<ev_async_send>, which is thread- and signal safe.	3471	it by calling C<ev_async_send>, which is thread- and signal safe.
3166		3472
3167	This functionality is very similar to C<ev_signal> watchers, as signals,	3473	This functionality is very similar to C<ev_signal> watchers, as signals,
3168	too, are asynchronous in nature, and signals, too, will be compressed	3474	too, are asynchronous in nature, and signals, too, will be compressed
3169	(i.e. the number of callback invocations may be less than the number of	3475	(i.e. the number of callback invocations may be less than the number of
3170	C<ev_async_sent> calls).	3476	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
3171		3477	of "global async watchers" by using a watcher on an otherwise unused
3172	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not	3478	signal, and C<ev_feed_signal> to signal this watcher from another thread,
3173	just the default loop.	3479	even without knowing which loop owns the signal.
3174		3480
3175	=head3 Queueing	3481	=head3 Queueing
3176		3482
3177	C<ev_async> does not support queueing of data in any way. The reason	3483	C<ev_async> does not support queueing of data in any way. The reason
3178	is that the author does not know of a simple (or any) algorithm for a	3484	is that the author does not know of a simple (or any) algorithm for a
…		…
3270	trust me.	3576	trust me.
3271		3577
3272	=item ev_async_send (loop, ev_async *)	3578	=item ev_async_send (loop, ev_async *)
3273		3579
3274	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3580	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
3275	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3581	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3582	returns.
		3583
3276	C<ev_feed_event>, this call is safe to do from other threads, signal or	3584	Unlike C<ev_feed_event>, this call is safe to do from other threads,
3277	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3585	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3278	section below on what exactly this means).	3586	embedding section below on what exactly this means).
3279		3587
3280	Note that, as with other watchers in libev, multiple events might get	3588	Note that, as with other watchers in libev, multiple events might get
3281	compressed into a single callback invocation (another way to look at this	3589	compressed into a single callback invocation (another way to look at
3282	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,	3590	this is that C<ev_async> watchers are level-triggered: they are set on
3283	reset when the event loop detects that).	3591	C<ev_async_send>, reset when the event loop detects that).
3284		3592
3285	This call incurs the overhead of a system call only once per event loop	3593	This call incurs the overhead of at most one extra system call per event
3286	iteration, so while the overhead might be noticeable, it doesn't apply to	3594	loop iteration, if the event loop is blocked, and no syscall at all if
3287	repeated calls to C<ev_async_send> for the same event loop.	3595	the event loop (or your program) is processing events. That means that
		3596	repeated calls are basically free (there is no need to avoid calls for
		3597	performance reasons) and that the overhead becomes smaller (typically
		3598	zero) under load.
3288		3599
3289	=item bool = ev_async_pending (ev_async *)	3600	=item bool = ev_async_pending (ev_async *)
3290		3601
3291	Returns a non-zero value when C<ev_async_send> has been called on the	3602	Returns a non-zero value when C<ev_async_send> has been called on the
3292	watcher but the event has not yet been processed (or even noted) by the	3603	watcher but the event has not yet been processed (or even noted) by the
…		…
3309		3620
3310	There are some other functions of possible interest. Described. Here. Now.	3621	There are some other functions of possible interest. Described. Here. Now.
3311		3622
3312	=over 4	3623	=over 4
3313		3624
3314	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3625	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)
3315		3626
3316	This function combines a simple timer and an I/O watcher, calls your	3627	This function combines a simple timer and an I/O watcher, calls your
3317	callback on whichever event happens first and automatically stops both	3628	callback on whichever event happens first and automatically stops both
3318	watchers. This is useful if you want to wait for a single event on an fd	3629	watchers. This is useful if you want to wait for a single event on an fd
3319	or timeout without having to allocate/configure/start/stop/free one or	3630	or timeout without having to allocate/configure/start/stop/free one or
…		…
3347	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3658	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3348		3659
3349	=item ev_feed_fd_event (loop, int fd, int revents)	3660	=item ev_feed_fd_event (loop, int fd, int revents)
3350		3661
3351	Feed an event on the given fd, as if a file descriptor backend detected	3662	Feed an event on the given fd, as if a file descriptor backend detected
3352	the given events it.	3663	the given events.
3353		3664
3354	=item ev_feed_signal_event (loop, int signum)	3665	=item ev_feed_signal_event (loop, int signum)
3355		3666
3356	Feed an event as if the given signal occurred (C<loop> must be the default	3667	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3357	loop!).	3668	which is async-safe.
3358		3669
3359	=back	3670	=back
		3671
		3672
		3673	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3674
		3675	This section explains some common idioms that are not immediately
		3676	obvious. Note that examples are sprinkled over the whole manual, and this
		3677	section only contains stuff that wouldn't fit anywhere else.
		3678
		3679	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3680
		3681	Each watcher has, by default, a C<void *data> member that you can read
		3682	or modify at any time: libev will completely ignore it. This can be used
		3683	to associate arbitrary data with your watcher. If you need more data and
		3684	don't want to allocate memory separately and store a pointer to it in that
		3685	data member, you can also "subclass" the watcher type and provide your own
		3686	data:
		3687
		3688	struct my_io
		3689	{
		3690	ev_io io;
		3691	int otherfd;
		3692	void *somedata;
		3693	struct whatever *mostinteresting;
		3694	};
		3695
		3696	...
		3697	struct my_io w;
		3698	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3699
		3700	And since your callback will be called with a pointer to the watcher, you
		3701	can cast it back to your own type:
		3702
		3703	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3704	{
		3705	struct my_io *w = (struct my_io *)w_;
		3706	...
		3707	}
		3708
		3709	More interesting and less C-conformant ways of casting your callback
		3710	function type instead have been omitted.
		3711
		3712	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3713
		3714	Another common scenario is to use some data structure with multiple
		3715	embedded watchers, in effect creating your own watcher that combines
		3716	multiple libev event sources into one "super-watcher":
		3717
		3718	struct my_biggy
		3719	{
		3720	int some_data;
		3721	ev_timer t1;
		3722	ev_timer t2;
		3723	}
		3724
		3725	In this case getting the pointer to C<my_biggy> is a bit more
		3726	complicated: Either you store the address of your C<my_biggy> struct in
		3727	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3728	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3729	real programmers):
		3730
		3731	#include <stddef.h>
		3732
		3733	static void
		3734	t1_cb (EV_P_ ev_timer *w, int revents)
		3735	{
		3736	struct my_biggy big = (struct my_biggy *)
		3737	(((char *)w) - offsetof (struct my_biggy, t1));
		3738	}
		3739
		3740	static void
		3741	t2_cb (EV_P_ ev_timer *w, int revents)
		3742	{
		3743	struct my_biggy big = (struct my_biggy *)
		3744	(((char *)w) - offsetof (struct my_biggy, t2));
		3745	}
		3746
		3747	=head2 AVOIDING FINISHING BEFORE RETURNING
		3748
		3749	Often you have structures like this in event-based programs:
		3750
		3751	callback ()
		3752	{
		3753	free (request);
		3754	}
		3755
		3756	request = start_new_request (..., callback);
		3757
		3758	The intent is to start some "lengthy" operation. The C<request> could be
		3759	used to cancel the operation, or do other things with it.
		3760
		3761	It's not uncommon to have code paths in C<start_new_request> that
		3762	immediately invoke the callback, for example, to report errors. Or you add
		3763	some caching layer that finds that it can skip the lengthy aspects of the
		3764	operation and simply invoke the callback with the result.
		3765
		3766	The problem here is that this will happen I<before> C<start_new_request>
		3767	has returned, so C<request> is not set.
		3768
		3769	Even if you pass the request by some safer means to the callback, you
		3770	might want to do something to the request after starting it, such as
		3771	canceling it, which probably isn't working so well when the callback has
		3772	already been invoked.
		3773
		3774	A common way around all these issues is to make sure that
		3775	C<start_new_request> I<always> returns before the callback is invoked. If
		3776	C<start_new_request> immediately knows the result, it can artificially
		3777	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3778	example, or more sneakily, by reusing an existing (stopped) watcher and
		3779	pushing it into the pending queue:
		3780
		3781	ev_set_cb (watcher, callback);
		3782	ev_feed_event (EV_A_ watcher, 0);
		3783
		3784	This way, C<start_new_request> can safely return before the callback is
		3785	invoked, while not delaying callback invocation too much.
		3786
		3787	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3788
		3789	Often (especially in GUI toolkits) there are places where you have
		3790	I<modal> interaction, which is most easily implemented by recursively
		3791	invoking C<ev_run>.
		3792
		3793	This brings the problem of exiting - a callback might want to finish the
		3794	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3795	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3796	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3797	other combination: In these cases, a simple C<ev_break> will not work.
		3798
		3799	The solution is to maintain "break this loop" variable for each C<ev_run>
		3800	invocation, and use a loop around C<ev_run> until the condition is
		3801	triggered, using C<EVRUN_ONCE>:
		3802
		3803	// main loop
		3804	int exit_main_loop = 0;
		3805
		3806	while (!exit_main_loop)
		3807	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3808
		3809	// in a modal watcher
		3810	int exit_nested_loop = 0;
		3811
		3812	while (!exit_nested_loop)
		3813	ev_run (EV_A_ EVRUN_ONCE);
		3814
		3815	To exit from any of these loops, just set the corresponding exit variable:
		3816
		3817	// exit modal loop
		3818	exit_nested_loop = 1;
		3819
		3820	// exit main program, after modal loop is finished
		3821	exit_main_loop = 1;
		3822
		3823	// exit both
		3824	exit_main_loop = exit_nested_loop = 1;
		3825
		3826	=head2 THREAD LOCKING EXAMPLE
		3827
		3828	Here is a fictitious example of how to run an event loop in a different
		3829	thread from where callbacks are being invoked and watchers are
		3830	created/added/removed.
		3831
		3832	For a real-world example, see the C<EV::Loop::Async> perl module,
		3833	which uses exactly this technique (which is suited for many high-level
		3834	languages).
		3835
		3836	The example uses a pthread mutex to protect the loop data, a condition
		3837	variable to wait for callback invocations, an async watcher to notify the
		3838	event loop thread and an unspecified mechanism to wake up the main thread.
		3839
		3840	First, you need to associate some data with the event loop:
		3841
		3842	typedef struct {
		3843	mutex_t lock; /* global loop lock */
		3844	ev_async async_w;
		3845	thread_t tid;
		3846	cond_t invoke_cv;
		3847	} userdata;
		3848
		3849	void prepare_loop (EV_P)
		3850	{
		3851	// for simplicity, we use a static userdata struct.
		3852	static userdata u;
		3853
		3854	ev_async_init (&u->async_w, async_cb);
		3855	ev_async_start (EV_A_ &u->async_w);
		3856
		3857	pthread_mutex_init (&u->lock, 0);
		3858	pthread_cond_init (&u->invoke_cv, 0);
		3859
		3860	// now associate this with the loop
		3861	ev_set_userdata (EV_A_ u);
		3862	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3863	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3864
		3865	// then create the thread running ev_run
		3866	pthread_create (&u->tid, 0, l_run, EV_A);
		3867	}
		3868
		3869	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3870	solely to wake up the event loop so it takes notice of any new watchers
		3871	that might have been added:
		3872
		3873	static void
		3874	async_cb (EV_P_ ev_async *w, int revents)
		3875	{
		3876	// just used for the side effects
		3877	}
		3878
		3879	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3880	protecting the loop data, respectively.
		3881
		3882	static void
		3883	l_release (EV_P)
		3884	{
		3885	userdata *u = ev_userdata (EV_A);
		3886	pthread_mutex_unlock (&u->lock);
		3887	}
		3888
		3889	static void
		3890	l_acquire (EV_P)
		3891	{
		3892	userdata *u = ev_userdata (EV_A);
		3893	pthread_mutex_lock (&u->lock);
		3894	}
		3895
		3896	The event loop thread first acquires the mutex, and then jumps straight
		3897	into C<ev_run>:
		3898
		3899	void *
		3900	l_run (void *thr_arg)
		3901	{
		3902	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3903
		3904	l_acquire (EV_A);
		3905	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3906	ev_run (EV_A_ 0);
		3907	l_release (EV_A);
		3908
		3909	return 0;
		3910	}
		3911
		3912	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3913	signal the main thread via some unspecified mechanism (signals? pipe
		3914	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3915	have been called (in a while loop because a) spurious wakeups are possible
		3916	and b) skipping inter-thread-communication when there are no pending
		3917	watchers is very beneficial):
		3918
		3919	static void
		3920	l_invoke (EV_P)
		3921	{
		3922	userdata *u = ev_userdata (EV_A);
		3923
		3924	while (ev_pending_count (EV_A))
		3925	{
		3926	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3927	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3928	}
		3929	}
		3930
		3931	Now, whenever the main thread gets told to invoke pending watchers, it
		3932	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3933	thread to continue:
		3934
		3935	static void
		3936	real_invoke_pending (EV_P)
		3937	{
		3938	userdata *u = ev_userdata (EV_A);
		3939
		3940	pthread_mutex_lock (&u->lock);
		3941	ev_invoke_pending (EV_A);
		3942	pthread_cond_signal (&u->invoke_cv);
		3943	pthread_mutex_unlock (&u->lock);
		3944	}
		3945
		3946	Whenever you want to start/stop a watcher or do other modifications to an
		3947	event loop, you will now have to lock:
		3948
		3949	ev_timer timeout_watcher;
		3950	userdata *u = ev_userdata (EV_A);
		3951
		3952	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3953
		3954	pthread_mutex_lock (&u->lock);
		3955	ev_timer_start (EV_A_ &timeout_watcher);
		3956	ev_async_send (EV_A_ &u->async_w);
		3957	pthread_mutex_unlock (&u->lock);
		3958
		3959	Note that sending the C<ev_async> watcher is required because otherwise
		3960	an event loop currently blocking in the kernel will have no knowledge
		3961	about the newly added timer. By waking up the loop it will pick up any new
		3962	watchers in the next event loop iteration.
		3963
		3964	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3965
		3966	While the overhead of a callback that e.g. schedules a thread is small, it
		3967	is still an overhead. If you embed libev, and your main usage is with some
		3968	kind of threads or coroutines, you might want to customise libev so that
		3969	doesn't need callbacks anymore.
		3970
		3971	Imagine you have coroutines that you can switch to using a function
		3972	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3973	and that due to some magic, the currently active coroutine is stored in a
		3974	global called C<current_coro>. Then you can build your own "wait for libev
		3975	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3976	the differing C<;> conventions):
		3977
		3978	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3979	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3980
		3981	That means instead of having a C callback function, you store the
		3982	coroutine to switch to in each watcher, and instead of having libev call
		3983	your callback, you instead have it switch to that coroutine.
		3984
		3985	A coroutine might now wait for an event with a function called
		3986	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3987	matter when, or whether the watcher is active or not when this function is
		3988	called):
		3989
		3990	void
		3991	wait_for_event (ev_watcher *w)
		3992	{
		3993	ev_set_cb (w, current_coro);
		3994	switch_to (libev_coro);
		3995	}
		3996
		3997	That basically suspends the coroutine inside C<wait_for_event> and
		3998	continues the libev coroutine, which, when appropriate, switches back to
		3999	this or any other coroutine.
		4000
		4001	You can do similar tricks if you have, say, threads with an event queue -
		4002	instead of storing a coroutine, you store the queue object and instead of
		4003	switching to a coroutine, you push the watcher onto the queue and notify
		4004	any waiters.
		4005
		4006	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		4007	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		4008
		4009	// my_ev.h
		4010	#define EV_CB_DECLARE(type) struct my_coro *cb;
		4011	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		4012	#include "../libev/ev.h"
		4013
		4014	// my_ev.c
		4015	#define EV_H "my_ev.h"
		4016	#include "../libev/ev.c"
		4017
		4018	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		4019	F<my_ev.c> into your project. When properly specifying include paths, you
		4020	can even use F<ev.h> as header file name directly.
3360		4021
3361		4022
3362	=head1 LIBEVENT EMULATION	4023	=head1 LIBEVENT EMULATION
3363		4024
3364	Libev offers a compatibility emulation layer for libevent. It cannot	4025	Libev offers a compatibility emulation layer for libevent. It cannot
3365	emulate the internals of libevent, so here are some usage hints:	4026	emulate the internals of libevent, so here are some usage hints:
3366		4027
3367	=over 4	4028	=over 4
		4029
		4030	=item * Only the libevent-1.4.1-beta API is being emulated.
		4031
		4032	This was the newest libevent version available when libev was implemented,
		4033	and is still mostly unchanged in 2010.
3368		4034
3369	=item * Use it by including <event.h>, as usual.	4035	=item * Use it by including <event.h>, as usual.
3370		4036
3371	=item * The following members are fully supported: ev_base, ev_callback,	4037	=item * The following members are fully supported: ev_base, ev_callback,
3372	ev_arg, ev_fd, ev_res, ev_events.	4038	ev_arg, ev_fd, ev_res, ev_events.
…		…
3378	=item * Priorities are not currently supported. Initialising priorities	4044	=item * Priorities are not currently supported. Initialising priorities
3379	will fail and all watchers will have the same priority, even though there	4045	will fail and all watchers will have the same priority, even though there
3380	is an ev_pri field.	4046	is an ev_pri field.
3381		4047
3382	=item * In libevent, the last base created gets the signals, in libev, the	4048	=item * In libevent, the last base created gets the signals, in libev, the
3383	first base created (== the default loop) gets the signals.	4049	base that registered the signal gets the signals.
3384		4050
3385	=item * Other members are not supported.	4051	=item * Other members are not supported.
3386		4052
3387	=item * The libev emulation is I<not> ABI compatible to libevent, you need	4053	=item * The libev emulation is I<not> ABI compatible to libevent, you need
3388	to use the libev header file and library.	4054	to use the libev header file and library.
3389		4055
3390	=back	4056	=back
3391		4057
3392	=head1 C++ SUPPORT	4058	=head1 C++ SUPPORT
		4059
		4060	=head2 C API
		4061
		4062	The normal C API should work fine when used from C++: both ev.h and the
		4063	libev sources can be compiled as C++. Therefore, code that uses the C API
		4064	will work fine.
		4065
		4066	Proper exception specifications might have to be added to callbacks passed
		4067	to libev: exceptions may be thrown only from watcher callbacks, all other
		4068	callbacks (allocator, syserr, loop acquire/release and periodic reschedule
		4069	callbacks) must not throw exceptions, and might need a C<noexcept>
		4070	specification. If you have code that needs to be compiled as both C and
		4071	C++ you can use the C<EV_NOEXCEPT> macro for this:
		4072
		4073	static void
		4074	fatal_error (const char *msg) EV_NOEXCEPT
		4075	{
		4076	perror (msg);
		4077	abort ();
		4078	}
		4079
		4080	...
		4081	ev_set_syserr_cb (fatal_error);
		4082
		4083	The only API functions that can currently throw exceptions are C<ev_run>,
		4084	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		4085	because it runs cleanup watchers).
		4086
		4087	Throwing exceptions in watcher callbacks is only supported if libev itself
		4088	is compiled with a C++ compiler or your C and C++ environments allow
		4089	throwing exceptions through C libraries (most do).
		4090
		4091	=head2 C++ API
3393		4092
3394	Libev comes with some simplistic wrapper classes for C++ that mainly allow	4093	Libev comes with some simplistic wrapper classes for C++ that mainly allow
3395	you to use some convenience methods to start/stop watchers and also change	4094	you to use some convenience methods to start/stop watchers and also change
3396	the callback model to a model using method callbacks on objects.	4095	the callback model to a model using method callbacks on objects.
3397		4096
3398	To use it,	4097	To use it,
3399		4098
3400	#include <ev++.h>	4099	#include <ev++.h>
3401		4100
3402	This automatically includes F<ev.h> and puts all of its definitions (many	4101	This automatically includes F<ev.h> and puts all of its definitions (many
3403	of them macros) into the global namespace. All C++ specific things are	4102	of them macros) into the global namespace. All C++ specific things are
3404	put into the C<ev> namespace. It should support all the same embedding	4103	put into the C<ev> namespace. It should support all the same embedding
…		…
3407	Care has been taken to keep the overhead low. The only data member the C++	4106	Care has been taken to keep the overhead low. The only data member the C++
3408	classes add (compared to plain C-style watchers) is the event loop pointer	4107	classes add (compared to plain C-style watchers) is the event loop pointer
3409	that the watcher is associated with (or no additional members at all if	4108	that the watcher is associated with (or no additional members at all if
3410	you disable C<EV_MULTIPLICITY> when embedding libev).	4109	you disable C<EV_MULTIPLICITY> when embedding libev).
3411		4110
3412	Currently, functions, and static and non-static member functions can be	4111	Currently, functions, static and non-static member functions and classes
3413	used as callbacks. Other types should be easy to add as long as they only	4112	with C<operator ()> can be used as callbacks. Other types should be easy
3414	need one additional pointer for context. If you need support for other	4113	to add as long as they only need one additional pointer for context. If
3415	types of functors please contact the author (preferably after implementing	4114	you need support for other types of functors please contact the author
3416	it).	4115	(preferably after implementing it).
		4116
		4117	For all this to work, your C++ compiler either has to use the same calling
		4118	conventions as your C compiler (for static member functions), or you have
		4119	to embed libev and compile libev itself as C++.
3417		4120
3418	Here is a list of things available in the C<ev> namespace:	4121	Here is a list of things available in the C<ev> namespace:
3419		4122
3420	=over 4	4123	=over 4
3421		4124
…		…
3431	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4134	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
3432		4135
3433	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4136	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
3434	the same name in the C<ev> namespace, with the exception of C<ev_signal>	4137	the same name in the C<ev> namespace, with the exception of C<ev_signal>
3435	which is called C<ev::sig> to avoid clashes with the C<signal> macro	4138	which is called C<ev::sig> to avoid clashes with the C<signal> macro
3436	defines by many implementations.	4139	defined by many implementations.
3437		4140
3438	All of those classes have these methods:	4141	All of those classes have these methods:
3439		4142
3440	=over 4	4143	=over 4
3441		4144
…		…
3503	void operator() (ev::io &w, int revents)	4206	void operator() (ev::io &w, int revents)
3504	{	4207	{
3505	...	4208	...
3506	}	4209	}
3507	}	4210	}
3508		4211
3509	myfunctor f;	4212	myfunctor f;
3510		4213
3511	ev::io w;	4214	ev::io w;
3512	w.set (&f);	4215	w.set (&f);
3513		4216
…		…
3531	Associates a different C<struct ev_loop> with this watcher. You can only	4234	Associates a different C<struct ev_loop> with this watcher. You can only
3532	do this when the watcher is inactive (and not pending either).	4235	do this when the watcher is inactive (and not pending either).
3533		4236
3534	=item w->set ([arguments])	4237	=item w->set ([arguments])
3535		4238
3536	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this	4239	Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
3537	method or a suitable start method must be called at least once. Unlike the	4240	with the same arguments. Either this method or a suitable start method
3538	C counterpart, an active watcher gets automatically stopped and restarted	4241	must be called at least once. Unlike the C counterpart, an active watcher
3539	when reconfiguring it with this method.	4242	gets automatically stopped and restarted when reconfiguring it with this
		4243	method.
		4244
		4245	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4246	clashing with the C<set (loop)> method.
3540		4247
3541	=item w->start ()	4248	=item w->start ()
3542		4249
3543	Starts the watcher. Note that there is no C<loop> argument, as the	4250	Starts the watcher. Note that there is no C<loop> argument, as the
3544	constructor already stores the event loop.	4251	constructor already stores the event loop.
…		…
3574	watchers in the constructor.	4281	watchers in the constructor.
3575		4282
3576	class myclass	4283	class myclass
3577	{	4284	{
3578	ev::io io ; void io_cb (ev::io &w, int revents);	4285	ev::io io ; void io_cb (ev::io &w, int revents);
3579	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);	4286	ev::io io2 ; void io2_cb (ev::io &w, int revents);
3580	ev::idle idle; void idle_cb (ev::idle &w, int revents);	4287	ev::idle idle; void idle_cb (ev::idle &w, int revents);
3581		4288
3582	myclass (int fd)	4289	myclass (int fd)
3583	{	4290	{
3584	io .set <myclass, &myclass::io_cb > (this);	4291	io .set <myclass, &myclass::io_cb > (this);
…		…
3635	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.	4342	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3636		4343
3637	=item D	4344	=item D
3638		4345
3639	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4346	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
3640	be found at L<http://proj.llucax.com.ar/wiki/evd>.	4347	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
3641		4348
3642	=item Ocaml	4349	=item Ocaml
3643		4350
3644	Erkki Seppala has written Ocaml bindings for libev, to be found at	4351	Erkki Seppala has written Ocaml bindings for libev, to be found at
3645	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	4352	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
…		…
3648		4355
3649	Brian Maher has written a partial interface to libev for lua (at the	4356	Brian Maher has written a partial interface to libev for lua (at the
3650	time of this writing, only C<ev_io> and C<ev_timer>), to be found at	4357	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
3651	L<http://github.com/brimworks/lua-ev>.	4358	L<http://github.com/brimworks/lua-ev>.
3652		4359
		4360	=item Javascript
		4361
		4362	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4363
		4364	=item Others
		4365
		4366	There are others, and I stopped counting.
		4367
3653	=back	4368	=back
3654		4369
3655		4370
3656	=head1 MACRO MAGIC	4371	=head1 MACRO MAGIC
3657		4372
…		…
3693	suitable for use with C<EV_A>.	4408	suitable for use with C<EV_A>.
3694		4409
3695	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4410	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
3696		4411
3697	Similar to the other two macros, this gives you the value of the default	4412	Similar to the other two macros, this gives you the value of the default
3698	loop, if multiple loops are supported ("ev loop default").	4413	loop, if multiple loops are supported ("ev loop default"). The default loop
		4414	will be initialised if it isn't already initialised.
		4415
		4416	For non-multiplicity builds, these macros do nothing, so you always have
		4417	to initialise the loop somewhere.
3699		4418
3700	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4419	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
3701		4420
3702	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4421	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
3703	default loop has been initialised (C<UC> == unchecked). Their behaviour	4422	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
3770	ev_vars.h	4489	ev_vars.h
3771	ev_wrap.h	4490	ev_wrap.h
3772		4491
3773	ev_win32.c required on win32 platforms only	4492	ev_win32.c required on win32 platforms only
3774		4493
3775	ev_select.c only when select backend is enabled (which is enabled by default)	4494	ev_select.c only when select backend is enabled
3776	ev_poll.c only when poll backend is enabled (disabled by default)	4495	ev_poll.c only when poll backend is enabled
3777	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4496	ev_epoll.c only when the epoll backend is enabled
		4497	ev_linuxaio.c only when the linux aio backend is enabled
		4498	ev_iouring.c only when the linux io_uring backend is enabled
3778	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4499	ev_kqueue.c only when the kqueue backend is enabled
3779	ev_port.c only when the solaris port backend is enabled (disabled by default)	4500	ev_port.c only when the solaris port backend is enabled
3780		4501
3781	F<ev.c> includes the backend files directly when enabled, so you only need	4502	F<ev.c> includes the backend files directly when enabled, so you only need
3782	to compile this single file.	4503	to compile this single file.
3783		4504
3784	=head3 LIBEVENT COMPATIBILITY API	4505	=head3 LIBEVENT COMPATIBILITY API
…		…
3848	supported). It will also not define any of the structs usually found in	4569	supported). It will also not define any of the structs usually found in
3849	F<event.h> that are not directly supported by the libev core alone.	4570	F<event.h> that are not directly supported by the libev core alone.
3850		4571
3851	In standalone mode, libev will still try to automatically deduce the	4572	In standalone mode, libev will still try to automatically deduce the
3852	configuration, but has to be more conservative.	4573	configuration, but has to be more conservative.
		4574
		4575	=item EV_USE_FLOOR
		4576
		4577	If defined to be C<1>, libev will use the C<floor ()> function for its
		4578	periodic reschedule calculations, otherwise libev will fall back on a
		4579	portable (slower) implementation. If you enable this, you usually have to
		4580	link against libm or something equivalent. Enabling this when the C<floor>
		4581	function is not available will fail, so the safe default is to not enable
		4582	this.
3853		4583
3854	=item EV_USE_MONOTONIC	4584	=item EV_USE_MONOTONIC
3855		4585
3856	If defined to be C<1>, libev will try to detect the availability of the	4586	If defined to be C<1>, libev will try to detect the availability of the
3857	monotonic clock option at both compile time and runtime. Otherwise no	4587	monotonic clock option at both compile time and runtime. Otherwise no
…		…
3894	available and will probe for kernel support at runtime. This will improve	4624	available and will probe for kernel support at runtime. This will improve
3895	C<ev_signal> and C<ev_async> performance and reduce resource consumption.	4625	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
3896	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc	4626	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
3897	2.7 or newer, otherwise disabled.	4627	2.7 or newer, otherwise disabled.
3898		4628
		4629	=item EV_USE_SIGNALFD
		4630
		4631	If defined to be C<1>, then libev will assume that C<signalfd ()> is
		4632	available and will probe for kernel support at runtime. This enables
		4633	the use of EVFLAG_SIGNALFD for faster and simpler signal handling. If
		4634	undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4635	2.7 or newer, otherwise disabled.
		4636
		4637	=item EV_USE_TIMERFD
		4638
		4639	If defined to be C<1>, then libev will assume that C<timerfd ()> is
		4640	available and will probe for kernel support at runtime. This allows
		4641	libev to detect time jumps accurately. If undefined, it will be enabled
		4642	if the headers indicate GNU/Linux + Glibc 2.8 or newer and define
		4643	C<TFD_TIMER_CANCEL_ON_SET>, otherwise disabled.
		4644
		4645	=item EV_USE_EVENTFD
		4646
		4647	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		4648	available and will probe for kernel support at runtime. This will improve
		4649	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		4650	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4651	2.7 or newer, otherwise disabled.
		4652
3899	=item EV_USE_SELECT	4653	=item EV_USE_SELECT
3900		4654
3901	If undefined or defined to be C<1>, libev will compile in support for the	4655	If undefined or defined to be C<1>, libev will compile in support for the
3902	C<select>(2) backend. No attempt at auto-detection will be done: if no	4656	C<select>(2) backend. No attempt at auto-detection will be done: if no
3903	other method takes over, select will be it. Otherwise the select backend	4657	other method takes over, select will be it. Otherwise the select backend
…		…
3943	If programs implement their own fd to handle mapping on win32, then this	4697	If programs implement their own fd to handle mapping on win32, then this
3944	macro can be used to override the C<close> function, useful to unregister	4698	macro can be used to override the C<close> function, useful to unregister
3945	file descriptors again. Note that the replacement function has to close	4699	file descriptors again. Note that the replacement function has to close
3946	the underlying OS handle.	4700	the underlying OS handle.
3947		4701
		4702	=item EV_USE_WSASOCKET
		4703
		4704	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4705	communication socket, which works better in some environments. Otherwise,
		4706	the normal C<socket> function will be used, which works better in other
		4707	environments.
		4708
3948	=item EV_USE_POLL	4709	=item EV_USE_POLL
3949		4710
3950	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4711	If defined to be C<1>, libev will compile in support for the C<poll>(2)
3951	backend. Otherwise it will be enabled on non-win32 platforms. It	4712	backend. Otherwise it will be enabled on non-win32 platforms. It
3952	takes precedence over select.	4713	takes precedence over select.
…		…
3956	If defined to be C<1>, libev will compile in support for the Linux	4717	If defined to be C<1>, libev will compile in support for the Linux
3957	C<epoll>(7) backend. Its availability will be detected at runtime,	4718	C<epoll>(7) backend. Its availability will be detected at runtime,
3958	otherwise another method will be used as fallback. This is the preferred	4719	otherwise another method will be used as fallback. This is the preferred
3959	backend for GNU/Linux systems. If undefined, it will be enabled if the	4720	backend for GNU/Linux systems. If undefined, it will be enabled if the
3960	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4721	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4722
		4723	=item EV_USE_LINUXAIO
		4724
		4725	If defined to be C<1>, libev will compile in support for the Linux aio
		4726	backend (C<EV_USE_EPOLL> must also be enabled). If undefined, it will be
		4727	enabled on linux, otherwise disabled.
		4728
		4729	=item EV_USE_IOURING
		4730
		4731	If defined to be C<1>, libev will compile in support for the Linux
		4732	io_uring backend (C<EV_USE_EPOLL> must also be enabled). Due to it's
		4733	current limitations it has to be requested explicitly. If undefined, it
		4734	will be enabled on linux, otherwise disabled.
3961		4735
3962	=item EV_USE_KQUEUE	4736	=item EV_USE_KQUEUE
3963		4737
3964	If defined to be C<1>, libev will compile in support for the BSD style	4738	If defined to be C<1>, libev will compile in support for the BSD style
3965	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	4739	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
3987	If defined to be C<1>, libev will compile in support for the Linux inotify	4761	If defined to be C<1>, libev will compile in support for the Linux inotify
3988	interface to speed up C<ev_stat> watchers. Its actual availability will	4762	interface to speed up C<ev_stat> watchers. Its actual availability will
3989	be detected at runtime. If undefined, it will be enabled if the headers	4763	be detected at runtime. If undefined, it will be enabled if the headers
3990	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4764	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
3991		4765
		4766	=item EV_NO_SMP
		4767
		4768	If defined to be C<1>, libev will assume that memory is always coherent
		4769	between threads, that is, threads can be used, but threads never run on
		4770	different cpus (or different cpu cores). This reduces dependencies
		4771	and makes libev faster.
		4772
		4773	=item EV_NO_THREADS
		4774
		4775	If defined to be C<1>, libev will assume that it will never be called from
		4776	different threads (that includes signal handlers), which is a stronger
		4777	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4778	libev faster.
		4779
3992	=item EV_ATOMIC_T	4780	=item EV_ATOMIC_T
3993		4781
3994	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4782	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
3995	access is atomic with respect to other threads or signal contexts. No such	4783	access is atomic with respect to other threads or signal contexts. No
3996	type is easily found in the C language, so you can provide your own type	4784	such type is easily found in the C language, so you can provide your own
3997	that you know is safe for your purposes. It is used both for signal handler "locking"	4785	type that you know is safe for your purposes. It is used both for signal
3998	as well as for signal and thread safety in C<ev_async> watchers.	4786	handler "locking" as well as for signal and thread safety in C<ev_async>
		4787	watchers.
3999		4788
4000	In the absence of this define, libev will use C<sig_atomic_t volatile>	4789	In the absence of this define, libev will use C<sig_atomic_t volatile>
4001	(from F<signal.h>), which is usually good enough on most platforms.	4790	(from F<signal.h>), which is usually good enough on most platforms.
4002		4791
4003	=item EV_H (h)	4792	=item EV_H (h)
…		…
4030	will have the C<struct ev_loop *> as first argument, and you can create	4819	will have the C<struct ev_loop *> as first argument, and you can create
4031	additional independent event loops. Otherwise there will be no support	4820	additional independent event loops. Otherwise there will be no support
4032	for multiple event loops and there is no first event loop pointer	4821	for multiple event loops and there is no first event loop pointer
4033	argument. Instead, all functions act on the single default loop.	4822	argument. Instead, all functions act on the single default loop.
4034		4823
		4824	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4825	default loop when multiplicity is switched off - you always have to
		4826	initialise the loop manually in this case.
		4827
4035	=item EV_MINPRI	4828	=item EV_MINPRI
4036		4829
4037	=item EV_MAXPRI	4830	=item EV_MAXPRI
4038		4831
4039	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4832	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
4075	#define EV_USE_POLL 1	4868	#define EV_USE_POLL 1
4076	#define EV_CHILD_ENABLE 1	4869	#define EV_CHILD_ENABLE 1
4077	#define EV_ASYNC_ENABLE 1	4870	#define EV_ASYNC_ENABLE 1
4078		4871
4079	The actual value is a bitset, it can be a combination of the following	4872	The actual value is a bitset, it can be a combination of the following
4080	values:	4873	values (by default, all of these are enabled):
4081		4874
4082	=over 4	4875	=over 4
4083		4876
4084	=item C<1> - faster/larger code	4877	=item C<1> - faster/larger code
4085		4878
…		…
4089	code size by roughly 30% on amd64).	4882	code size by roughly 30% on amd64).
4090		4883
4091	When optimising for size, use of compiler flags such as C<-Os> with	4884	When optimising for size, use of compiler flags such as C<-Os> with
4092	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of	4885	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
4093	assertions.	4886	assertions.
		4887
		4888	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4889	(e.g. gcc with C<-Os>).
4094		4890
4095	=item C<2> - faster/larger data structures	4891	=item C<2> - faster/larger data structures
4096		4892
4097	Replaces the small 2-heap for timer management by a faster 4-heap, larger	4893	Replaces the small 2-heap for timer management by a faster 4-heap, larger
4098	hash table sizes and so on. This will usually further increase code size	4894	hash table sizes and so on. This will usually further increase code size
4099	and can additionally have an effect on the size of data structures at	4895	and can additionally have an effect on the size of data structures at
4100	runtime.	4896	runtime.
4101		4897
		4898	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4899	(e.g. gcc with C<-Os>).
		4900
4102	=item C<4> - full API configuration	4901	=item C<4> - full API configuration
4103		4902
4104	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and	4903	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
4105	enables multiplicity (C<EV_MULTIPLICITY>=1).	4904	enables multiplicity (C<EV_MULTIPLICITY>=1).
4106		4905
…		…
4136		4935
4137	With an intelligent-enough linker (gcc+binutils are intelligent enough	4936	With an intelligent-enough linker (gcc+binutils are intelligent enough
4138	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by	4937	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
4139	your program might be left out as well - a binary starting a timer and an	4938	your program might be left out as well - a binary starting a timer and an
4140	I/O watcher then might come out at only 5Kb.	4939	I/O watcher then might come out at only 5Kb.
		4940
		4941	=item EV_API_STATIC
		4942
		4943	If this symbol is defined (by default it is not), then all identifiers
		4944	will have static linkage. This means that libev will not export any
		4945	identifiers, and you cannot link against libev anymore. This can be useful
		4946	when you embed libev, only want to use libev functions in a single file,
		4947	and do not want its identifiers to be visible.
		4948
		4949	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4950	wants to use libev.
		4951
		4952	This option only works when libev is compiled with a C compiler, as C++
		4953	doesn't support the required declaration syntax.
4141		4954
4142	=item EV_AVOID_STDIO	4955	=item EV_AVOID_STDIO
4143		4956
4144	If this is set to C<1> at compiletime, then libev will avoid using stdio	4957	If this is set to C<1> at compiletime, then libev will avoid using stdio
4145	functions (printf, scanf, perror etc.). This will increase the code size	4958	functions (printf, scanf, perror etc.). This will increase the code size
…		…
4203	in. If set to C<1>, then verification code will be compiled in, but not	5016	in. If set to C<1>, then verification code will be compiled in, but not
4204	called. If set to C<2>, then the internal verification code will be	5017	called. If set to C<2>, then the internal verification code will be
4205	called once per loop, which can slow down libev. If set to C<3>, then the	5018	called once per loop, which can slow down libev. If set to C<3>, then the
4206	verification code will be called very frequently, which will slow down	5019	verification code will be called very frequently, which will slow down
4207	libev considerably.	5020	libev considerably.
		5021
		5022	Verification errors are reported via C's C<assert> mechanism, so if you
		5023	disable that (e.g. by defining C<NDEBUG>) then no errors will be reported.
4208		5024
4209	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it	5025	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
4210	will be C<0>.	5026	will be C<0>.
4211		5027
4212	=item EV_COMMON	5028	=item EV_COMMON
…		…
4289	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	5105	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4290		5106
4291	#include "ev_cpp.h"	5107	#include "ev_cpp.h"
4292	#include "ev.c"	5108	#include "ev.c"
4293		5109
4294	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	5110	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4295		5111
4296	=head2 THREADS AND COROUTINES	5112	=head2 THREADS AND COROUTINES
4297		5113
4298	=head3 THREADS	5114	=head3 THREADS
4299		5115
…		…
4350	default loop and triggering an C<ev_async> watcher from the default loop	5166	default loop and triggering an C<ev_async> watcher from the default loop
4351	watcher callback into the event loop interested in the signal.	5167	watcher callback into the event loop interested in the signal.
4352		5168
4353	=back	5169	=back
4354		5170
4355	=head4 THREAD LOCKING EXAMPLE	5171	See also L</THREAD LOCKING EXAMPLE>.
4356
4357	Here is a fictitious example of how to run an event loop in a different
4358	thread than where callbacks are being invoked and watchers are
4359	created/added/removed.
4360
4361	For a real-world example, see the C<EV::Loop::Async> perl module,
4362	which uses exactly this technique (which is suited for many high-level
4363	languages).
4364
4365	The example uses a pthread mutex to protect the loop data, a condition
4366	variable to wait for callback invocations, an async watcher to notify the
4367	event loop thread and an unspecified mechanism to wake up the main thread.
4368
4369	First, you need to associate some data with the event loop:
4370
4371	typedef struct {
4372	mutex_t lock; /* global loop lock */
4373	ev_async async_w;
4374	thread_t tid;
4375	cond_t invoke_cv;
4376	} userdata;
4377
4378	void prepare_loop (EV_P)
4379	{
4380	// for simplicity, we use a static userdata struct.
4381	static userdata u;
4382
4383	ev_async_init (&u->async_w, async_cb);
4384	ev_async_start (EV_A_ &u->async_w);
4385
4386	pthread_mutex_init (&u->lock, 0);
4387	pthread_cond_init (&u->invoke_cv, 0);
4388
4389	// now associate this with the loop
4390	ev_set_userdata (EV_A_ u);
4391	ev_set_invoke_pending_cb (EV_A_ l_invoke);
4392	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4393
4394	// then create the thread running ev_loop
4395	pthread_create (&u->tid, 0, l_run, EV_A);
4396	}
4397
4398	The callback for the C<ev_async> watcher does nothing: the watcher is used
4399	solely to wake up the event loop so it takes notice of any new watchers
4400	that might have been added:
4401
4402	static void
4403	async_cb (EV_P_ ev_async *w, int revents)
4404	{
4405	// just used for the side effects
4406	}
4407
4408	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
4409	protecting the loop data, respectively.
4410
4411	static void
4412	l_release (EV_P)
4413	{
4414	userdata *u = ev_userdata (EV_A);
4415	pthread_mutex_unlock (&u->lock);
4416	}
4417
4418	static void
4419	l_acquire (EV_P)
4420	{
4421	userdata *u = ev_userdata (EV_A);
4422	pthread_mutex_lock (&u->lock);
4423	}
4424
4425	The event loop thread first acquires the mutex, and then jumps straight
4426	into C<ev_run>:
4427
4428	void *
4429	l_run (void *thr_arg)
4430	{
4431	struct ev_loop *loop = (struct ev_loop *)thr_arg;
4432
4433	l_acquire (EV_A);
4434	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4435	ev_run (EV_A_ 0);
4436	l_release (EV_A);
4437
4438	return 0;
4439	}
4440
4441	Instead of invoking all pending watchers, the C<l_invoke> callback will
4442	signal the main thread via some unspecified mechanism (signals? pipe
4443	writes? C<Async::Interrupt>?) and then waits until all pending watchers
4444	have been called (in a while loop because a) spurious wakeups are possible
4445	and b) skipping inter-thread-communication when there are no pending
4446	watchers is very beneficial):
4447
4448	static void
4449	l_invoke (EV_P)
4450	{
4451	userdata *u = ev_userdata (EV_A);
4452
4453	while (ev_pending_count (EV_A))
4454	{
4455	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4456	pthread_cond_wait (&u->invoke_cv, &u->lock);
4457	}
4458	}
4459
4460	Now, whenever the main thread gets told to invoke pending watchers, it
4461	will grab the lock, call C<ev_invoke_pending> and then signal the loop
4462	thread to continue:
4463
4464	static void
4465	real_invoke_pending (EV_P)
4466	{
4467	userdata *u = ev_userdata (EV_A);
4468
4469	pthread_mutex_lock (&u->lock);
4470	ev_invoke_pending (EV_A);
4471	pthread_cond_signal (&u->invoke_cv);
4472	pthread_mutex_unlock (&u->lock);
4473	}
4474
4475	Whenever you want to start/stop a watcher or do other modifications to an
4476	event loop, you will now have to lock:
4477
4478	ev_timer timeout_watcher;
4479	userdata *u = ev_userdata (EV_A);
4480
4481	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4482
4483	pthread_mutex_lock (&u->lock);
4484	ev_timer_start (EV_A_ &timeout_watcher);
4485	ev_async_send (EV_A_ &u->async_w);
4486	pthread_mutex_unlock (&u->lock);
4487
4488	Note that sending the C<ev_async> watcher is required because otherwise
4489	an event loop currently blocking in the kernel will have no knowledge
4490	about the newly added timer. By waking up the loop it will pick up any new
4491	watchers in the next event loop iteration.
4492		5172
4493	=head3 COROUTINES	5173	=head3 COROUTINES
4494		5174
4495	Libev is very accommodating to coroutines ("cooperative threads"):	5175	Libev is very accommodating to coroutines ("cooperative threads"):
4496	libev fully supports nesting calls to its functions from different	5176	libev fully supports nesting calls to its functions from different
…		…
4661	requires, and its I/O model is fundamentally incompatible with the POSIX	5341	requires, and its I/O model is fundamentally incompatible with the POSIX
4662	model. Libev still offers limited functionality on this platform in	5342	model. Libev still offers limited functionality on this platform in
4663	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5343	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
4664	descriptors. This only applies when using Win32 natively, not when using	5344	descriptors. This only applies when using Win32 natively, not when using
4665	e.g. cygwin. Actually, it only applies to the microsofts own compilers,	5345	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4666	as every compielr comes with a slightly differently broken/incompatible	5346	as every compiler comes with a slightly differently broken/incompatible
4667	environment.	5347	environment.
4668		5348
4669	Lifting these limitations would basically require the full	5349	Lifting these limitations would basically require the full
4670	re-implementation of the I/O system. If you are into this kind of thing,	5350	re-implementation of the I/O system. If you are into this kind of thing,
4671	then note that glib does exactly that for you in a very portable way (note	5351	then note that glib does exactly that for you in a very portable way (note
…		…
4765	structure (guaranteed by POSIX but not by ISO C for example), but it also	5445	structure (guaranteed by POSIX but not by ISO C for example), but it also
4766	assumes that the same (machine) code can be used to call any watcher	5446	assumes that the same (machine) code can be used to call any watcher
4767	callback: The watcher callbacks have different type signatures, but libev	5447	callback: The watcher callbacks have different type signatures, but libev
4768	calls them using an C<ev_watcher *> internally.	5448	calls them using an C<ev_watcher *> internally.
4769		5449
		5450	=item null pointers and integer zero are represented by 0 bytes
		5451
		5452	Libev uses C<memset> to initialise structs and arrays to C<0> bytes, and
		5453	relies on this setting pointers and integers to null.
		5454
4770	=item pointer accesses must be thread-atomic	5455	=item pointer accesses must be thread-atomic
4771		5456
4772	Accessing a pointer value must be atomic, it must both be readable and	5457	Accessing a pointer value must be atomic, it must both be readable and
4773	writable in one piece - this is the case on all current architectures.	5458	writable in one piece - this is the case on all current architectures.
4774		5459
…		…
4787	thread" or will block signals process-wide, both behaviours would	5472	thread" or will block signals process-wide, both behaviours would
4788	be compatible with libev. Interaction between C<sigprocmask> and	5473	be compatible with libev. Interaction between C<sigprocmask> and
4789	C<pthread_sigmask> could complicate things, however.	5474	C<pthread_sigmask> could complicate things, however.
4790		5475
4791	The most portable way to handle signals is to block signals in all threads	5476	The most portable way to handle signals is to block signals in all threads
4792	except the initial one, and run the default loop in the initial thread as	5477	except the initial one, and run the signal handling loop in the initial
4793	well.	5478	thread as well.
4794		5479
4795	=item C<long> must be large enough for common memory allocation sizes	5480	=item C<long> must be large enough for common memory allocation sizes
4796		5481
4797	To improve portability and simplify its API, libev uses C<long> internally	5482	To improve portability and simplify its API, libev uses C<long> internally
4798	instead of C<size_t> when allocating its data structures. On non-POSIX	5483	instead of C<size_t> when allocating its data structures. On non-POSIX
…		…
4804		5489
4805	The type C<double> is used to represent timestamps. It is required to	5490	The type C<double> is used to represent timestamps. It is required to
4806	have at least 51 bits of mantissa (and 9 bits of exponent), which is	5491	have at least 51 bits of mantissa (and 9 bits of exponent), which is
4807	good enough for at least into the year 4000 with millisecond accuracy	5492	good enough for at least into the year 4000 with millisecond accuracy
4808	(the design goal for libev). This requirement is overfulfilled by	5493	(the design goal for libev). This requirement is overfulfilled by
4809	implementations using IEEE 754, which is basically all existing ones. With	5494	implementations using IEEE 754, which is basically all existing ones.
		5495
4810	IEEE 754 doubles, you get microsecond accuracy until at least 2200.	5496	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5497	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5498	is either obsolete or somebody patched it to use C<long double> or
		5499	something like that, just kidding).
4811		5500
4812	=back	5501	=back
4813		5502
4814	If you know of other additional requirements drop me a note.	5503	If you know of other additional requirements drop me a note.
4815		5504
…		…
4877	=item Processing ev_async_send: O(number_of_async_watchers)	5566	=item Processing ev_async_send: O(number_of_async_watchers)
4878		5567
4879	=item Processing signals: O(max_signal_number)	5568	=item Processing signals: O(max_signal_number)
4880		5569
4881	Sending involves a system call I<iff> there were no other C<ev_async_send>	5570	Sending involves a system call I<iff> there were no other C<ev_async_send>
4882	calls in the current loop iteration. Checking for async and signal events	5571	calls in the current loop iteration and the loop is currently
		5572	blocked. Checking for async and signal events involves iterating over all
4883	involves iterating over all running async watchers or all signal numbers.	5573	running async watchers or all signal numbers.
4884		5574
4885	=back	5575	=back
4886		5576
4887		5577
4888	=head1 PORTING FROM LIBEV 3.X TO 4.X	5578	=head1 PORTING FROM LIBEV 3.X TO 4.X
…		…
4897	=over 4	5587	=over 4
4898		5588
4899	=item C<EV_COMPAT3> backwards compatibility mechanism	5589	=item C<EV_COMPAT3> backwards compatibility mechanism
4900		5590
4901	The backward compatibility mechanism can be controlled by	5591	The backward compatibility mechanism can be controlled by
4902	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>	5592	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
4903	section.	5593	section.
4904		5594
4905	=item C<ev_default_destroy> and C<ev_default_fork> have been removed	5595	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
4906		5596
4907	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:	5597	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
…		…
4950	=over 4	5640	=over 4
4951		5641
4952	=item active	5642	=item active
4953		5643
4954	A watcher is active as long as it has been started and not yet stopped.	5644	A watcher is active as long as it has been started and not yet stopped.
4955	See L<WATCHER STATES> for details.	5645	See L</WATCHER STATES> for details.
4956		5646
4957	=item application	5647	=item application
4958		5648
4959	In this document, an application is whatever is using libev.	5649	In this document, an application is whatever is using libev.
4960		5650
…		…
4996	watchers and events.	5686	watchers and events.
4997		5687
4998	=item pending	5688	=item pending
4999		5689
5000	A watcher is pending as soon as the corresponding event has been	5690	A watcher is pending as soon as the corresponding event has been
5001	detected. See L<WATCHER STATES> for details.	5691	detected. See L</WATCHER STATES> for details.
5002		5692
5003	=item real time	5693	=item real time
5004		5694
5005	The physical time that is observed. It is apparently strictly monotonic :)	5695	The physical time that is observed. It is apparently strictly monotonic :)
5006		5696
5007	=item wall-clock time	5697	=item wall-clock time
5008		5698
5009	The time and date as shown on clocks. Unlike real time, it can actually	5699	The time and date as shown on clocks. Unlike real time, it can actually
5010	be wrong and jump forwards and backwards, e.g. when the you adjust your	5700	be wrong and jump forwards and backwards, e.g. when you adjust your
5011	clock.	5701	clock.
5012		5702
5013	=item watcher	5703	=item watcher
5014		5704
5015	A data structure that describes interest in certain events. Watchers need	5705	A data structure that describes interest in certain events. Watchers need
…		…
5018	=back	5708	=back
5019		5709
5020	=head1 AUTHOR	5710	=head1 AUTHOR
5021		5711
5022	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael	5712	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5023	Magnusson and Emanuele Giaquinta.	5713	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
5024		5714

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