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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
…		…
174	=item ev_tstamp ev_time ()	176	=item ev_tstamp ev_time ()
175		177
176	Returns the current time as libev would use it. Please note that the	178	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	179	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	180	you actually want to know. Also interesting is the combination of
179	C<ev_update_now> and C<ev_now>.	181	C<ev_now_update> and C<ev_now>.
180		182
181	=item ev_sleep (ev_tstamp interval)	183	=item ev_sleep (ev_tstamp interval)
182		184
183	Sleep for the given interval: The current thread will be blocked until	185	Sleep for the given interval: The current thread will be blocked
184	either it is interrupted or the given time interval has passed. Basically	186	until either it is interrupted or the given time interval has
		187	passed (approximately - it might return a bit earlier even if not
		188	interrupted). Returns immediately if C<< interval <= 0 >>.
		189
185	this is a sub-second-resolution C<sleep ()>.	190	Basically this is a sub-second-resolution C<sleep ()>.
		191
		192	The range of the C<interval> is limited - libev only guarantees to work
		193	with sleep times of up to one day (C<< interval <= 86400 >>).
186		194
187	=item int ev_version_major ()	195	=item int ev_version_major ()
188		196
189	=item int ev_version_minor ()	197	=item int ev_version_minor ()
190		198
…		…
241	the current system, you would need to look at C<ev_embeddable_backends ()	249	the current system, you would need to look at C<ev_embeddable_backends ()
242	& ev_supported_backends ()>, likewise for recommended ones.	250	& ev_supported_backends ()>, likewise for recommended ones.
243		251
244	See the description of C<ev_embed> watchers for more info.	252	See the description of C<ev_embed> watchers for more info.
245		253
246	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]	254	=item ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())
247		255
248	Sets the allocation function to use (the prototype is similar - the	256	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	257	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	258	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	259	when memory needs to be allocated (C<size != 0>), the library might abort
…		…
257		265
258	You could override this function in high-availability programs to, say,	266	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,	267	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.	268	or even to sleep a while and retry until some memory is available.
261		269
		270	Example: The following is the C<realloc> function that libev itself uses
		271	which should work with C<realloc> and C<free> functions of all kinds and
		272	is probably a good basis for your own implementation.
		273
		274	static void *
		275	ev_realloc_emul (void *ptr, long size) EV_NOEXCEPT
		276	{
		277	if (size)
		278	return realloc (ptr, size);
		279
		280	free (ptr);
		281	return 0;
		282	}
		283
262	Example: Replace the libev allocator with one that waits a bit and then	284	Example: Replace the libev allocator with one that waits a bit and then
263	retries (example requires a standards-compliant C<realloc>).	285	retries.
264		286
265	static void *	287	static void *
266	persistent_realloc (void *ptr, size_t size)	288	persistent_realloc (void *ptr, size_t size)
267	{	289	{
		290	if (!size)
		291	{
		292	free (ptr);
		293	return 0;
		294	}
		295
268	for (;;)	296	for (;;)
269	{	297	{
270	void *newptr = realloc (ptr, size);	298	void *newptr = realloc (ptr, size);
271		299
272	if (newptr)	300	if (newptr)
…		…
277	}	305	}
278		306
279	...	307	...
280	ev_set_allocator (persistent_realloc);	308	ev_set_allocator (persistent_realloc);
281		309
282	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]	310	=item ev_set_syserr_cb (void (*cb)(const char *msg) throw ())
283		311
284	Set the callback function to call on a retryable system call error (such	312	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	313	as failed select, poll, epoll_wait). The message is a printable string
286	indicating the system call or subsystem causing the problem. If this	314	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	315	callback is set, then libev will expect it to remedy the situation, no
…		…
299	}	327	}
300		328
301	...	329	...
302	ev_set_syserr_cb (fatal_error);	330	ev_set_syserr_cb (fatal_error);
303		331
		332	=item ev_feed_signal (int signum)
		333
		334	This function can be used to "simulate" a signal receive. It is completely
		335	safe to call this function at any time, from any context, including signal
		336	handlers or random threads.
		337
		338	Its main use is to customise signal handling in your process, especially
		339	in the presence of threads. For example, you could block signals
		340	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		341	creating any loops), and in one thread, use C<sigwait> or any other
		342	mechanism to wait for signals, then "deliver" them to libev by calling
		343	C<ev_feed_signal>.
		344
304	=back	345	=back
305		346
306	=head1 FUNCTIONS CONTROLLING EVENT LOOPS	347	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
307		348
308	An event loop is described by a C<struct ev_loop *> (the C<struct> is	349	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)	396	=item struct ev_loop *ev_loop_new (unsigned int flags)
356		397
357	This will create and initialise a new event loop object. If the loop	398	This will create and initialise a new event loop object. If the loop
358	could not be initialised, returns false.	399	could not be initialised, returns false.
359		400
360	Note that this function I<is> thread-safe, and one common way to use	401	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	402	threads is indeed to create one loop per thread, and using the default
362	default loop in the "main" or "initial" thread.	403	loop in the "main" or "initial" thread.
363		404
364	The flags argument can be used to specify special behaviour or specific	405	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>).	406	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
366		407
367	The following flags are supported:	408	The following flags are supported:
…		…
377		418
378	If this flag bit is or'ed into the flag value (or the program runs setuid	419	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	420	or setgid) then libev will I<not> look at the environment variable
380	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	421	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
381	override the flags completely if it is found in the environment. This is	422	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	423	useful to try out specific backends to test their performance, to work
383	around bugs.	424	around bugs, or to make libev threadsafe (accessing environment variables
		425	cannot be done in a threadsafe way, but usually it works if no other
		426	thread modifies them).
384		427
385	=item C<EVFLAG_FORKCHECK>	428	=item C<EVFLAG_FORKCHECK>
386		429
387	Instead of calling C<ev_loop_fork> manually after a fork, you can also	430	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.	431	make libev check for a fork in each iteration by enabling this flag.
389		432
390	This works by calling C<getpid ()> on every iteration of the loop,	433	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	434	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	435	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	436	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	437	sequence without a system call and thus I<very> fast, but my GNU/Linux
395	C<pthread_atfork> which is even faster).	438	system also has C<pthread_atfork> which is even faster). (Update: glibc
		439	versions 2.25 apparently removed the C<getpid> optimisation again).
396		440
397	The big advantage of this flag is that you can forget about fork (and	441	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	442	forget about forgetting to tell libev about forking, although you still
399	flag.	443	have to ignore C<SIGPIPE>) when you use this flag.
400		444
401	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>	445	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
402	environment variable.	446	environment variable.
403		447
404	=item C<EVFLAG_NOINOTIFY>	448	=item C<EVFLAG_NOINOTIFY>
405		449
406	When this flag is specified, then libev will not attempt to use the	450	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	451	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	452	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.	453	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
410		454
411	=item C<EVFLAG_SIGNALFD>	455	=item C<EVFLAG_SIGNALFD>
412		456
413	When this flag is specified, then libev will attempt to use the	457	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	458	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	459	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	460	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	461	handling with threads, as long as you properly block signals in your
418	threads that are not interested in handling them.	462	threads that are not interested in handling them.
419		463
420	Signalfd will not be used by default as this changes your signal mask, and	464	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	465	there are a lot of shoddy libraries and programs (glib's threadpool for
422	example) that can't properly initialise their signal masks.	466	example) that can't properly initialise their signal masks.
		467
		468	=item C<EVFLAG_NOSIGMASK>
		469
		470	When this flag is specified, then libev will avoid to modify the signal
		471	mask. Specifically, this means you have to make sure signals are unblocked
		472	when you want to receive them.
		473
		474	This behaviour is useful when you want to do your own signal handling, or
		475	want to handle signals only in specific threads and want to avoid libev
		476	unblocking the signals.
		477
		478	It's also required by POSIX in a threaded program, as libev calls
		479	C<sigprocmask>, whose behaviour is officially unspecified.
		480
		481	This flag's behaviour will become the default in future versions of libev.
423		482
424	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	483	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
425		484
426	This is your standard select(2) backend. Not I<completely> standard, as	485	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,	486	libev tries to roll its own fd_set with no limits on the number of fds,
…		…
455	=item C<EVBACKEND_EPOLL> (value 4, Linux)	514	=item C<EVBACKEND_EPOLL> (value 4, Linux)
456		515
457	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9	516	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
458	kernels).	517	kernels).
459		518
460	For few fds, this backend is a bit little slower than poll and select,	519	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	520	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),	521	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).	522	fd), epoll scales either O(1) or O(active_fds).
464		523
465	The epoll mechanism deserves honorable mention as the most misdesigned	524	The epoll mechanism deserves honorable mention as the most misdesigned
466	of the more advanced event mechanisms: mere annoyances include silently	525	of the more advanced event mechanisms: mere annoyances include silently
467	dropping file descriptors, requiring a system call per change per file	526	dropping file descriptors, requiring a system call per change per file
468	descriptor (and unnecessary guessing of parameters), problems with dup and	527	descriptor (and unnecessary guessing of parameters), problems with dup,
		528	returning before the timeout value, resulting in additional iterations
		529	(and only giving 5ms accuracy while select on the same platform gives
469	so on. The biggest issue is fork races, however - if a program forks then	530	0.1ms) and so on. The biggest issue is fork races, however - if a program
470	I<both> parent and child process have to recreate the epoll set, which can	531	forks then I<both> parent and child process have to recreate the epoll
471	take considerable time (one syscall per file descriptor) and is of course	532	set, which can take considerable time (one syscall per file descriptor)
472	hard to detect.	533	and is of course hard to detect.
473		534
474	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but	535	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
475	of course I<doesn't>, and epoll just loves to report events for totally	536	but of course I<doesn't>, and epoll just loves to report events for
476	I<different> file descriptors (even already closed ones, so one cannot	537	totally I<different> file descriptors (even already closed ones, so
477	even remove them from the set) than registered in the set (especially	538	one cannot even remove them from the set) than registered in the set
478	on SMP systems). Libev tries to counter these spurious notifications by	539	(especially on SMP systems). Libev tries to counter these spurious
479	employing an additional generation counter and comparing that against the	540	notifications by employing an additional generation counter and comparing
480	events to filter out spurious ones, recreating the set when required. Last	541	that against the events to filter out spurious ones, recreating the set
		542	when required. Epoll also erroneously rounds down timeouts, but gives you
		543	no way to know when and by how much, so sometimes you have to busy-wait
		544	because epoll returns immediately despite a nonzero timeout. And last
481	not least, it also refuses to work with some file descriptors which work	545	not least, it also refuses to work with some file descriptors which work
482	perfectly fine with C<select> (files, many character devices...).	546	perfectly fine with C<select> (files, many character devices...).
		547
		548	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		549	cobbled together in a hurry, no thought to design or interaction with
		550	others. Oh, the pain, will it ever stop...
483		551
484	While stopping, setting and starting an I/O watcher in the same iteration	552	While stopping, setting and starting an I/O watcher in the same iteration
485	will result in some caching, there is still a system call per such	553	will result in some caching, there is still a system call per such
486	incident (because the same I<file descriptor> could point to a different	554	incident (because the same I<file descriptor> could point to a different
487	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed	555	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
…		…
499	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or	567	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
500	faster than epoll for maybe up to a hundred file descriptors, depending on	568	faster than epoll for maybe up to a hundred file descriptors, depending on
501	the usage. So sad.	569	the usage. So sad.
502		570
503	While nominally embeddable in other event loops, this feature is broken in	571	While nominally embeddable in other event loops, this feature is broken in
504	all kernel versions tested so far.	572	a lot of kernel revisions, but probably(!) works in current versions.
		573
		574	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		575	C<EVBACKEND_POLL>.
		576
		577	=item C<EVBACKEND_LINUXAIO> (value 64, Linux)
		578
		579	Use the linux-specific linux aio (I<not> C<< aio(7) >> but C<<
		580	io_submit(2) >>) event interface available in post-4.18 kernels.
		581
		582	If this backend works for you (as of this writing, it was very
		583	experimental), it is the best event interface available on linux and might
		584	be well worth enabling it - if it isn't available in your kernel this will
		585	be detected and this backend will be skipped.
		586
		587	This backend can batch oneshot requests and supports a user-space ring
		588	buffer to receive events. It also doesn't suffer from most of the design
		589	problems of epoll (such as not being able to remove event sources from the
		590	epoll set), and generally sounds too good to be true. Because, this being
		591	the linux kernel, of course it suffers from a whole new set of limitations.
		592
		593	For one, it is not easily embeddable (but probably could be done using
		594	an event fd at some extra overhead). It also is subject to a system wide
		595	limit that can be configured in F</proc/sys/fs/aio-max-nr> - each loop
		596	currently requires C<61> of this number. If no aio requests are left, this
		597	backend will be skipped during initialisation.
		598
		599	Most problematic in practise, however, is that not all file descriptors
		600	work with it. For example, in linux 5.1, tcp sockets, pipes, event fds,
		601	files, F</dev/null> and a few others are supported, but ttys do not work
		602	properly (a known bug that the kernel developers don't care about, see
		603	L<https://lore.kernel.org/patchwork/patch/1047453/>), so this is not
		604	(yet?) a generic event polling interface.
		605
		606	Overall, it seems the linux developers just don't want it to have a
		607	generic event handling mechanism other than C<select> or C<poll>.
		608
		609	To work around the fd type problem, the current version of libev uses
		610	epoll as a fallback for file deescriptor types that do not work. Epoll
		611	is used in, kind of, slow mode that hopefully avoids most of its design
		612	problems and requires 1-3 extra syscalls per active fd every iteration.
505		613
506	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	614	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
507	C<EVBACKEND_POLL>.	615	C<EVBACKEND_POLL>.
508		616
509	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	617	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
…		…
524		632
525	It scales in the same way as the epoll backend, but the interface to the	633	It scales in the same way as the epoll backend, but the interface to the
526	kernel is more efficient (which says nothing about its actual speed, of	634	kernel is more efficient (which says nothing about its actual speed, of
527	course). While stopping, setting and starting an I/O watcher does never	635	course). While stopping, setting and starting an I/O watcher does never
528	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to	636	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
529	two event changes per incident. Support for C<fork ()> is very bad (but	637	two event changes per incident. Support for C<fork ()> is very bad (you
530	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect	638	might have to leak fd's on fork, but it's more sane than epoll) and it
531	cases	639	drops fds silently in similarly hard-to-detect cases.
532		640
533	This backend usually performs well under most conditions.	641	This backend usually performs well under most conditions.
534		642
535	While nominally embeddable in other event loops, this doesn't work	643	While nominally embeddable in other event loops, this doesn't work
536	everywhere, so you might need to test for this. And since it is broken	644	everywhere, so you might need to test for this. And since it is broken
…		…
553	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	661	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
554		662
555	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	663	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
556	it's really slow, but it still scales very well (O(active_fds)).	664	it's really slow, but it still scales very well (O(active_fds)).
557		665
558	Please note that Solaris event ports can deliver a lot of spurious
559	notifications, so you need to use non-blocking I/O or other means to avoid
560	blocking when no data (or space) is available.
561
562	While this backend scales well, it requires one system call per active	666	While this backend scales well, it requires one system call per active
563	file descriptor per loop iteration. For small and medium numbers of file	667	file descriptor per loop iteration. For small and medium numbers of file
564	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	668	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
565	might perform better.	669	might perform better.
566		670
567	On the positive side, with the exception of the spurious readiness	671	On the positive side, this backend actually performed fully to
568	notifications, this backend actually performed fully to specification
569	in all tests and is fully embeddable, which is a rare feat among the	672	specification in all tests and is fully embeddable, which is a rare feat
570	OS-specific backends (I vastly prefer correctness over speed hacks).	673	among the OS-specific backends (I vastly prefer correctness over speed
		674	hacks).
		675
		676	On the negative side, the interface is I<bizarre> - so bizarre that
		677	even sun itself gets it wrong in their code examples: The event polling
		678	function sometimes returns events to the caller even though an error
		679	occurred, but with no indication whether it has done so or not (yes, it's
		680	even documented that way) - deadly for edge-triggered interfaces where you
		681	absolutely have to know whether an event occurred or not because you have
		682	to re-arm the watcher.
		683
		684	Fortunately libev seems to be able to work around these idiocies.
571		685
572	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	686	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
573	C<EVBACKEND_POLL>.	687	C<EVBACKEND_POLL>.
574		688
575	=item C<EVBACKEND_ALL>	689	=item C<EVBACKEND_ALL>
576		690
577	Try all backends (even potentially broken ones that wouldn't be tried	691	Try all backends (even potentially broken ones that wouldn't be tried
578	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	692	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
579	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	693	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
580		694
581	It is definitely not recommended to use this flag.	695	It is definitely not recommended to use this flag, use whatever
		696	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		697	at all.
		698
		699	=item C<EVBACKEND_MASK>
		700
		701	Not a backend at all, but a mask to select all backend bits from a
		702	C<flags> value, in case you want to mask out any backends from a flags
		703	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
582		704
583	=back	705	=back
584		706
585	If one or more of the backend flags are or'ed into the flags value,	707	If one or more of the backend flags are or'ed into the flags value,
586	then only these backends will be tried (in the reverse order as listed	708	then only these backends will be tried (in the reverse order as listed
…		…
595		717
596	Example: Use whatever libev has to offer, but make sure that kqueue is	718	Example: Use whatever libev has to offer, but make sure that kqueue is
597	used if available.	719	used if available.
598		720
599	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);	721	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		722
		723	Example: Similarly, on linux, you mgiht want to take advantage of the
		724	linux aio backend if possible, but fall back to something else if that
		725	isn't available.
		726
		727	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_LINUXAIO);
600		728
601	=item ev_loop_destroy (loop)	729	=item ev_loop_destroy (loop)
602		730
603	Destroys an event loop object (frees all memory and kernel state	731	Destroys an event loop object (frees all memory and kernel state
604	etc.). None of the active event watchers will be stopped in the normal	732	etc.). None of the active event watchers will be stopped in the normal
…		…
615	This function is normally used on loop objects allocated by	743	This function is normally used on loop objects allocated by
616	C<ev_loop_new>, but it can also be used on the default loop returned by	744	C<ev_loop_new>, but it can also be used on the default loop returned by
617	C<ev_default_loop>, in which case it is not thread-safe.	745	C<ev_default_loop>, in which case it is not thread-safe.
618		746
619	Note that it is not advisable to call this function on the default loop	747	Note that it is not advisable to call this function on the default loop
620	except in the rare occasion where you really need to free it's resources.	748	except in the rare occasion where you really need to free its resources.
621	If you need dynamically allocated loops it is better to use C<ev_loop_new>	749	If you need dynamically allocated loops it is better to use C<ev_loop_new>
622	and C<ev_loop_destroy>.	750	and C<ev_loop_destroy>.
623		751
624	=item ev_loop_fork (loop)	752	=item ev_loop_fork (loop)
625		753
626	This function sets a flag that causes subsequent C<ev_run> iterations to	754	This function sets a flag that causes subsequent C<ev_run> iterations
627	reinitialise the kernel state for backends that have one. Despite the	755	to reinitialise the kernel state for backends that have one. Despite
628	name, you can call it anytime, but it makes most sense after forking, in	756	the name, you can call it anytime you are allowed to start or stop
629	the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the	757	watchers (except inside an C<ev_prepare> callback), but it makes most
		758	sense after forking, in the child process. You I<must> call it (or use
630	child before resuming or calling C<ev_run>.	759	C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.
631		760
		761	In addition, if you want to reuse a loop (via this function or
		762	C<EVFLAG_FORKCHECK>), you I<also> have to ignore C<SIGPIPE>.
		763
632	Again, you I<have> to call it on I<any> loop that you want to re-use after	764	Again, you I<have> to call it on I<any> loop that you want to re-use after
633	a fork, I<even if you do not plan to use the loop in the parent>. This is	765	a fork, I<even if you do not plan to use the loop in the parent>. This is
634	because some kernel interfaces *cough* I<kqueue> *cough* do funny things	766	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
635	during fork.	767	during fork.
636		768
637	On the other hand, you only need to call this function in the child	769	On the other hand, you only need to call this function in the child
…		…
673	prepare and check phases.	805	prepare and check phases.
674		806
675	=item unsigned int ev_depth (loop)	807	=item unsigned int ev_depth (loop)
676		808
677	Returns the number of times C<ev_run> was entered minus the number of	809	Returns the number of times C<ev_run> was entered minus the number of
678	times C<ev_run> was exited, in other words, the recursion depth.	810	times C<ev_run> was exited normally, in other words, the recursion depth.
679		811
680	Outside C<ev_run>, this number is zero. In a callback, this number is	812	Outside C<ev_run>, this number is zero. In a callback, this number is
681	C<1>, unless C<ev_run> was invoked recursively (or from another thread),	813	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
682	in which case it is higher.	814	in which case it is higher.
683		815
684	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread	816	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
685	etc.), doesn't count as "exit" - consider this as a hint to avoid such	817	throwing an exception etc.), doesn't count as "exit" - consider this
686	ungentleman-like behaviour unless it's really convenient.	818	as a hint to avoid such ungentleman-like behaviour unless it's really
		819	convenient, in which case it is fully supported.
687		820
688	=item unsigned int ev_backend (loop)	821	=item unsigned int ev_backend (loop)
689		822
690	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	823	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
691	use.	824	use.
…		…
706		839
707	This function is rarely useful, but when some event callback runs for a	840	This function is rarely useful, but when some event callback runs for a
708	very long time without entering the event loop, updating libev's idea of	841	very long time without entering the event loop, updating libev's idea of
709	the current time is a good idea.	842	the current time is a good idea.
710		843
711	See also L<The special problem of time updates> in the C<ev_timer> section.	844	See also L</The special problem of time updates> in the C<ev_timer> section.
712		845
713	=item ev_suspend (loop)	846	=item ev_suspend (loop)
714		847
715	=item ev_resume (loop)	848	=item ev_resume (loop)
716		849
…		…
734	without a previous call to C<ev_suspend>.	867	without a previous call to C<ev_suspend>.
735		868
736	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the	869	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
737	event loop time (see C<ev_now_update>).	870	event loop time (see C<ev_now_update>).
738		871
739	=item ev_run (loop, int flags)	872	=item bool ev_run (loop, int flags)
740		873
741	Finally, this is it, the event handler. This function usually is called	874	Finally, this is it, the event handler. This function usually is called
742	after you have initialised all your watchers and you want to start	875	after you have initialised all your watchers and you want to start
743	handling events. It will ask the operating system for any new events, call	876	handling events. It will ask the operating system for any new events, call
744	the watcher callbacks, an then repeat the whole process indefinitely: This	877	the watcher callbacks, and then repeat the whole process indefinitely: This
745	is why event loops are called I<loops>.	878	is why event loops are called I<loops>.
746		879
747	If the flags argument is specified as C<0>, it will keep handling events	880	If the flags argument is specified as C<0>, it will keep handling events
748	until either no event watchers are active anymore or C<ev_break> was	881	until either no event watchers are active anymore or C<ev_break> was
749	called.	882	called.
		883
		884	The return value is false if there are no more active watchers (which
		885	usually means "all jobs done" or "deadlock"), and true in all other cases
		886	(which usually means " you should call C<ev_run> again").
750		887
751	Please note that an explicit C<ev_break> is usually better than	888	Please note that an explicit C<ev_break> is usually better than
752	relying on all watchers to be stopped when deciding when a program has	889	relying on all watchers to be stopped when deciding when a program has
753	finished (especially in interactive programs), but having a program	890	finished (especially in interactive programs), but having a program
754	that automatically loops as long as it has to and no longer by virtue	891	that automatically loops as long as it has to and no longer by virtue
755	of relying on its watchers stopping correctly, that is truly a thing of	892	of relying on its watchers stopping correctly, that is truly a thing of
756	beauty.	893	beauty.
757		894
		895	This function is I<mostly> exception-safe - you can break out of a
		896	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		897	exception and so on. This does not decrement the C<ev_depth> value, nor
		898	will it clear any outstanding C<EVBREAK_ONE> breaks.
		899
758	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle	900	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
759	those events and any already outstanding ones, but will not wait and	901	those events and any already outstanding ones, but will not wait and
760	block your process in case there are no events and will return after one	902	block your process in case there are no events and will return after one
761	iteration of the loop. This is sometimes useful to poll and handle new	903	iteration of the loop. This is sometimes useful to poll and handle new
762	events while doing lengthy calculations, to keep the program responsive.	904	events while doing lengthy calculations, to keep the program responsive.
…		…
771	This is useful if you are waiting for some external event in conjunction	913	This is useful if you are waiting for some external event in conjunction
772	with something not expressible using other libev watchers (i.e. "roll your	914	with something not expressible using other libev watchers (i.e. "roll your
773	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is	915	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
774	usually a better approach for this kind of thing.	916	usually a better approach for this kind of thing.
775		917
776	Here are the gory details of what C<ev_run> does:	918	Here are the gory details of what C<ev_run> does (this is for your
		919	understanding, not a guarantee that things will work exactly like this in
		920	future versions):
777		921
778	- Increment loop depth.	922	- Increment loop depth.
779	- Reset the ev_break status.	923	- Reset the ev_break status.
780	- Before the first iteration, call any pending watchers.	924	- Before the first iteration, call any pending watchers.
781	LOOP:	925	LOOP:
…		…
814	anymore.	958	anymore.
815		959
816	... queue jobs here, make sure they register event watchers as long	960	... queue jobs here, make sure they register event watchers as long
817	... as they still have work to do (even an idle watcher will do..)	961	... as they still have work to do (even an idle watcher will do..)
818	ev_run (my_loop, 0);	962	ev_run (my_loop, 0);
819	... jobs done or somebody called unloop. yeah!	963	... jobs done or somebody called break. yeah!
820		964
821	=item ev_break (loop, how)	965	=item ev_break (loop, how)
822		966
823	Can be used to make a call to C<ev_run> return early (but only after it	967	Can be used to make a call to C<ev_run> return early (but only after it
824	has processed all outstanding events). The C<how> argument must be either	968	has processed all outstanding events). The C<how> argument must be either
825	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or	969	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
826	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.	970	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
827		971
828	This "unloop state" will be cleared when entering C<ev_run> again.	972	This "break state" will be cleared on the next call to C<ev_run>.
829		973
830	It is safe to call C<ev_break> from outside any C<ev_run> calls. ##TODO##	974	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		975	which case it will have no effect.
831		976
832	=item ev_ref (loop)	977	=item ev_ref (loop)
833		978
834	=item ev_unref (loop)	979	=item ev_unref (loop)
835		980
…		…
856	running when nothing else is active.	1001	running when nothing else is active.
857		1002
858	ev_signal exitsig;	1003	ev_signal exitsig;
859	ev_signal_init (&exitsig, sig_cb, SIGINT);	1004	ev_signal_init (&exitsig, sig_cb, SIGINT);
860	ev_signal_start (loop, &exitsig);	1005	ev_signal_start (loop, &exitsig);
861	evf_unref (loop);	1006	ev_unref (loop);
862		1007
863	Example: For some weird reason, unregister the above signal handler again.	1008	Example: For some weird reason, unregister the above signal handler again.
864		1009
865	ev_ref (loop);	1010	ev_ref (loop);
866	ev_signal_stop (loop, &exitsig);	1011	ev_signal_stop (loop, &exitsig);
…		…
886	overhead for the actual polling but can deliver many events at once.	1031	overhead for the actual polling but can deliver many events at once.
887		1032
888	By setting a higher I<io collect interval> you allow libev to spend more	1033	By setting a higher I<io collect interval> you allow libev to spend more
889	time collecting I/O events, so you can handle more events per iteration,	1034	time collecting I/O events, so you can handle more events per iteration,
890	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	1035	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
891	C<ev_timer>) will be not affected. Setting this to a non-null value will	1036	C<ev_timer>) will not be affected. Setting this to a non-null value will
892	introduce an additional C<ev_sleep ()> call into most loop iterations. The	1037	introduce an additional C<ev_sleep ()> call into most loop iterations. The
893	sleep time ensures that libev will not poll for I/O events more often then	1038	sleep time ensures that libev will not poll for I/O events more often then
894	once per this interval, on average.	1039	once per this interval, on average (as long as the host time resolution is
		1040	good enough).
895		1041
896	Likewise, by setting a higher I<timeout collect interval> you allow libev	1042	Likewise, by setting a higher I<timeout collect interval> you allow libev
897	to spend more time collecting timeouts, at the expense of increased	1043	to spend more time collecting timeouts, at the expense of increased
898	latency/jitter/inexactness (the watcher callback will be called	1044	latency/jitter/inexactness (the watcher callback will be called
899	later). C<ev_io> watchers will not be affected. Setting this to a non-null	1045	later). C<ev_io> watchers will not be affected. Setting this to a non-null
…		…
945	invoke the actual watchers inside another context (another thread etc.).	1091	invoke the actual watchers inside another context (another thread etc.).
946		1092
947	If you want to reset the callback, use C<ev_invoke_pending> as new	1093	If you want to reset the callback, use C<ev_invoke_pending> as new
948	callback.	1094	callback.
949		1095
950	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))	1096	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
951		1097
952	Sometimes you want to share the same loop between multiple threads. This	1098	Sometimes you want to share the same loop between multiple threads. This
953	can be done relatively simply by putting mutex_lock/unlock calls around	1099	can be done relatively simply by putting mutex_lock/unlock calls around
954	each call to a libev function.	1100	each call to a libev function.
955		1101
956	However, C<ev_run> can run an indefinite time, so it is not feasible	1102	However, C<ev_run> can run an indefinite time, so it is not feasible
957	to wait for it to return. One way around this is to wake up the event	1103	to wait for it to return. One way around this is to wake up the event
958	loop via C<ev_break> and C<av_async_send>, another way is to set these	1104	loop via C<ev_break> and C<ev_async_send>, another way is to set these
959	I<release> and I<acquire> callbacks on the loop.	1105	I<release> and I<acquire> callbacks on the loop.
960		1106
961	When set, then C<release> will be called just before the thread is	1107	When set, then C<release> will be called just before the thread is
962	suspended waiting for new events, and C<acquire> is called just	1108	suspended waiting for new events, and C<acquire> is called just
963	afterwards.	1109	afterwards.
…		…
978	See also the locking example in the C<THREADS> section later in this	1124	See also the locking example in the C<THREADS> section later in this
979	document.	1125	document.
980		1126
981	=item ev_set_userdata (loop, void *data)	1127	=item ev_set_userdata (loop, void *data)
982		1128
983	=item ev_userdata (loop)	1129	=item void *ev_userdata (loop)
984		1130
985	Set and retrieve a single C<void *> associated with a loop. When	1131	Set and retrieve a single C<void *> associated with a loop. When
986	C<ev_set_userdata> has never been called, then C<ev_userdata> returns	1132	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
987	C<0.>	1133	C<0>.
988		1134
989	These two functions can be used to associate arbitrary data with a loop,	1135	These two functions can be used to associate arbitrary data with a loop,
990	and are intended solely for the C<invoke_pending_cb>, C<release> and	1136	and are intended solely for the C<invoke_pending_cb>, C<release> and
991	C<acquire> callbacks described above, but of course can be (ab-)used for	1137	C<acquire> callbacks described above, but of course can be (ab-)used for
992	any other purpose as well.	1138	any other purpose as well.
…		…
1103		1249
1104	=item C<EV_PREPARE>	1250	=item C<EV_PREPARE>
1105		1251
1106	=item C<EV_CHECK>	1252	=item C<EV_CHECK>
1107		1253
1108	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts	1254	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts to
1109	to gather new events, and all C<ev_check> watchers are invoked just after	1255	gather new events, and all C<ev_check> watchers are queued (not invoked)
1110	C<ev_run> has gathered them, but before it invokes any callbacks for any	1256	just after C<ev_run> has gathered them, but before it queues any callbacks
		1257	for any received events. That means C<ev_prepare> watchers are the last
		1258	watchers invoked before the event loop sleeps or polls for new events, and
		1259	C<ev_check> watchers will be invoked before any other watchers of the same
		1260	or lower priority within an event loop iteration.
		1261
1111	received events. Callbacks of both watcher types can start and stop as	1262	Callbacks of both watcher types can start and stop as many watchers as
1112	many watchers as they want, and all of them will be taken into account	1263	they want, and all of them will be taken into account (for example, a
1113	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1264	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
1114	C<ev_run> from blocking).	1265	blocking).
1115		1266
1116	=item C<EV_EMBED>	1267	=item C<EV_EMBED>
1117		1268
1118	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1269	The embedded event loop specified in the C<ev_embed> watcher needs attention.
1119		1270
…		…
1154	programs, though, as the fd could already be closed and reused for another	1305	programs, though, as the fd could already be closed and reused for another
1155	thing, so beware.	1306	thing, so beware.
1156		1307
1157	=back	1308	=back
1158		1309
		1310	=head2 GENERIC WATCHER FUNCTIONS
		1311
		1312	=over 4
		1313
		1314	=item C<ev_init> (ev_TYPE *watcher, callback)
		1315
		1316	This macro initialises the generic portion of a watcher. The contents
		1317	of the watcher object can be arbitrary (so C<malloc> will do). Only
		1318	the generic parts of the watcher are initialised, you I<need> to call
		1319	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		1320	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		1321	which rolls both calls into one.
		1322
		1323	You can reinitialise a watcher at any time as long as it has been stopped
		1324	(or never started) and there are no pending events outstanding.
		1325
		1326	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
		1327	int revents)>.
		1328
		1329	Example: Initialise an C<ev_io> watcher in two steps.
		1330
		1331	ev_io w;
		1332	ev_init (&w, my_cb);
		1333	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1334
		1335	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
		1336
		1337	This macro initialises the type-specific parts of a watcher. You need to
		1338	call C<ev_init> at least once before you call this macro, but you can
		1339	call C<ev_TYPE_set> any number of times. You must not, however, call this
		1340	macro on a watcher that is active (it can be pending, however, which is a
		1341	difference to the C<ev_init> macro).
		1342
		1343	Although some watcher types do not have type-specific arguments
		1344	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		1345
		1346	See C<ev_init>, above, for an example.
		1347
		1348	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		1349
		1350	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		1351	calls into a single call. This is the most convenient method to initialise
		1352	a watcher. The same limitations apply, of course.
		1353
		1354	Example: Initialise and set an C<ev_io> watcher in one step.
		1355
		1356	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1357
		1358	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
		1359
		1360	Starts (activates) the given watcher. Only active watchers will receive
		1361	events. If the watcher is already active nothing will happen.
		1362
		1363	Example: Start the C<ev_io> watcher that is being abused as example in this
		1364	whole section.
		1365
		1366	ev_io_start (EV_DEFAULT_UC, &w);
		1367
		1368	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
		1369
		1370	Stops the given watcher if active, and clears the pending status (whether
		1371	the watcher was active or not).
		1372
		1373	It is possible that stopped watchers are pending - for example,
		1374	non-repeating timers are being stopped when they become pending - but
		1375	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
		1376	pending. If you want to free or reuse the memory used by the watcher it is
		1377	therefore a good idea to always call its C<ev_TYPE_stop> function.
		1378
		1379	=item bool ev_is_active (ev_TYPE *watcher)
		1380
		1381	Returns a true value iff the watcher is active (i.e. it has been started
		1382	and not yet been stopped). As long as a watcher is active you must not modify
		1383	it.
		1384
		1385	=item bool ev_is_pending (ev_TYPE *watcher)
		1386
		1387	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		1388	events but its callback has not yet been invoked). As long as a watcher
		1389	is pending (but not active) you must not call an init function on it (but
		1390	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		1391	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1392	it).
		1393
		1394	=item callback ev_cb (ev_TYPE *watcher)
		1395
		1396	Returns the callback currently set on the watcher.
		1397
		1398	=item ev_set_cb (ev_TYPE *watcher, callback)
		1399
		1400	Change the callback. You can change the callback at virtually any time
		1401	(modulo threads).
		1402
		1403	=item ev_set_priority (ev_TYPE *watcher, int priority)
		1404
		1405	=item int ev_priority (ev_TYPE *watcher)
		1406
		1407	Set and query the priority of the watcher. The priority is a small
		1408	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1409	(default: C<-2>). Pending watchers with higher priority will be invoked
		1410	before watchers with lower priority, but priority will not keep watchers
		1411	from being executed (except for C<ev_idle> watchers).
		1412
		1413	If you need to suppress invocation when higher priority events are pending
		1414	you need to look at C<ev_idle> watchers, which provide this functionality.
		1415
		1416	You I<must not> change the priority of a watcher as long as it is active or
		1417	pending.
		1418
		1419	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1420	fine, as long as you do not mind that the priority value you query might
		1421	or might not have been clamped to the valid range.
		1422
		1423	The default priority used by watchers when no priority has been set is
		1424	always C<0>, which is supposed to not be too high and not be too low :).
		1425
		1426	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1427	priorities.
		1428
		1429	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1430
		1431	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1432	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1433	can deal with that fact, as both are simply passed through to the
		1434	callback.
		1435
		1436	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1437
		1438	If the watcher is pending, this function clears its pending status and
		1439	returns its C<revents> bitset (as if its callback was invoked). If the
		1440	watcher isn't pending it does nothing and returns C<0>.
		1441
		1442	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1443	callback to be invoked, which can be accomplished with this function.
		1444
		1445	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1446
		1447	Feeds the given event set into the event loop, as if the specified event
		1448	had happened for the specified watcher (which must be a pointer to an
		1449	initialised but not necessarily started event watcher). Obviously you must
		1450	not free the watcher as long as it has pending events.
		1451
		1452	Stopping the watcher, letting libev invoke it, or calling
		1453	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1454	not started in the first place.
		1455
		1456	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1457	functions that do not need a watcher.
		1458
		1459	=back
		1460
		1461	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
		1462	OWN COMPOSITE WATCHERS> idioms.
		1463
1159	=head2 WATCHER STATES	1464	=head2 WATCHER STATES
1160		1465
1161	There are various watcher states mentioned throughout this manual -	1466	There are various watcher states mentioned throughout this manual -
1162	active, pending and so on. In this section these states and the rules to	1467	active, pending and so on. In this section these states and the rules to
1163	transition between them will be described in more detail - and while these	1468	transition between them will be described in more detail - and while these
1164	rules might look complicated, they usually do "the right thing".	1469	rules might look complicated, they usually do "the right thing".
1165		1470
1166	=over 4	1471	=over 4
1167		1472
1168	=item initialiased	1473	=item initialised
1169		1474
1170	Before a watcher can be registered with the event looop it has to be	1475	Before a watcher can be registered with the event loop it has to be
1171	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to	1476	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
1172	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.	1477	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1173		1478
1174	In this state it is simply some block of memory that is suitable for use	1479	In this state it is simply some block of memory that is suitable for
1175	in an event loop. It can be moved around, freed, reused etc. at will.	1480	use in an event loop. It can be moved around, freed, reused etc. at
		1481	will - as long as you either keep the memory contents intact, or call
		1482	C<ev_TYPE_init> again.
1176		1483
1177	=item started/running/active	1484	=item started/running/active
1178		1485
1179	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes	1486	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
1180	property of the event loop, and is actively waiting for events. While in	1487	property of the event loop, and is actively waiting for events. While in
…		…
1208	latter will clear any pending state the watcher might be in, regardless	1515	latter will clear any pending state the watcher might be in, regardless
1209	of whether it was active or not, so stopping a watcher explicitly before	1516	of whether it was active or not, so stopping a watcher explicitly before
1210	freeing it is often a good idea.	1517	freeing it is often a good idea.
1211		1518
1212	While stopped (and not pending) the watcher is essentially in the	1519	While stopped (and not pending) the watcher is essentially in the
1213	initialised state, that is it can be reused, moved, modified in any way	1520	initialised state, that is, it can be reused, moved, modified in any way
1214	you wish.	1521	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1522	it again).
1215		1523
1216	=back	1524	=back
1217
1218	=head2 GENERIC WATCHER FUNCTIONS
1219
1220	=over 4
1221
1222	=item C<ev_init> (ev_TYPE *watcher, callback)
1223
1224	This macro initialises the generic portion of a watcher. The contents
1225	of the watcher object can be arbitrary (so C<malloc> will do). Only
1226	the generic parts of the watcher are initialised, you I<need> to call
1227	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
1228	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
1229	which rolls both calls into one.
1230
1231	You can reinitialise a watcher at any time as long as it has been stopped
1232	(or never started) and there are no pending events outstanding.
1233
1234	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
1235	int revents)>.
1236
1237	Example: Initialise an C<ev_io> watcher in two steps.
1238
1239	ev_io w;
1240	ev_init (&w, my_cb);
1241	ev_io_set (&w, STDIN_FILENO, EV_READ);
1242
1243	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
1244
1245	This macro initialises the type-specific parts of a watcher. You need to
1246	call C<ev_init> at least once before you call this macro, but you can
1247	call C<ev_TYPE_set> any number of times. You must not, however, call this
1248	macro on a watcher that is active (it can be pending, however, which is a
1249	difference to the C<ev_init> macro).
1250
1251	Although some watcher types do not have type-specific arguments
1252	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
1253
1254	See C<ev_init>, above, for an example.
1255
1256	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
1257
1258	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
1259	calls into a single call. This is the most convenient method to initialise
1260	a watcher. The same limitations apply, of course.
1261
1262	Example: Initialise and set an C<ev_io> watcher in one step.
1263
1264	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1265
1266	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
1267
1268	Starts (activates) the given watcher. Only active watchers will receive
1269	events. If the watcher is already active nothing will happen.
1270
1271	Example: Start the C<ev_io> watcher that is being abused as example in this
1272	whole section.
1273
1274	ev_io_start (EV_DEFAULT_UC, &w);
1275
1276	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
1277
1278	Stops the given watcher if active, and clears the pending status (whether
1279	the watcher was active or not).
1280
1281	It is possible that stopped watchers are pending - for example,
1282	non-repeating timers are being stopped when they become pending - but
1283	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
1284	pending. If you want to free or reuse the memory used by the watcher it is
1285	therefore a good idea to always call its C<ev_TYPE_stop> function.
1286
1287	=item bool ev_is_active (ev_TYPE *watcher)
1288
1289	Returns a true value iff the watcher is active (i.e. it has been started
1290	and not yet been stopped). As long as a watcher is active you must not modify
1291	it.
1292
1293	=item bool ev_is_pending (ev_TYPE *watcher)
1294
1295	Returns a true value iff the watcher is pending, (i.e. it has outstanding
1296	events but its callback has not yet been invoked). As long as a watcher
1297	is pending (but not active) you must not call an init function on it (but
1298	C<ev_TYPE_set> is safe), you must not change its priority, and you must
1299	make sure the watcher is available to libev (e.g. you cannot C<free ()>
1300	it).
1301
1302	=item callback ev_cb (ev_TYPE *watcher)
1303
1304	Returns the callback currently set on the watcher.
1305
1306	=item ev_cb_set (ev_TYPE *watcher, callback)
1307
1308	Change the callback. You can change the callback at virtually any time
1309	(modulo threads).
1310
1311	=item ev_set_priority (ev_TYPE *watcher, int priority)
1312
1313	=item int ev_priority (ev_TYPE *watcher)
1314
1315	Set and query the priority of the watcher. The priority is a small
1316	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
1317	(default: C<-2>). Pending watchers with higher priority will be invoked
1318	before watchers with lower priority, but priority will not keep watchers
1319	from being executed (except for C<ev_idle> watchers).
1320
1321	If you need to suppress invocation when higher priority events are pending
1322	you need to look at C<ev_idle> watchers, which provide this functionality.
1323
1324	You I<must not> change the priority of a watcher as long as it is active or
1325	pending.
1326
1327	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
1328	fine, as long as you do not mind that the priority value you query might
1329	or might not have been clamped to the valid range.
1330
1331	The default priority used by watchers when no priority has been set is
1332	always C<0>, which is supposed to not be too high and not be too low :).
1333
1334	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1335	priorities.
1336
1337	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1338
1339	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
1340	C<loop> nor C<revents> need to be valid as long as the watcher callback
1341	can deal with that fact, as both are simply passed through to the
1342	callback.
1343
1344	=item int ev_clear_pending (loop, ev_TYPE *watcher)
1345
1346	If the watcher is pending, this function clears its pending status and
1347	returns its C<revents> bitset (as if its callback was invoked). If the
1348	watcher isn't pending it does nothing and returns C<0>.
1349
1350	Sometimes it can be useful to "poll" a watcher instead of waiting for its
1351	callback to be invoked, which can be accomplished with this function.
1352
1353	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
1354
1355	Feeds the given event set into the event loop, as if the specified event
1356	had happened for the specified watcher (which must be a pointer to an
1357	initialised but not necessarily started event watcher). Obviously you must
1358	not free the watcher as long as it has pending events.
1359
1360	Stopping the watcher, letting libev invoke it, or calling
1361	C<ev_clear_pending> will clear the pending event, even if the watcher was
1362	not started in the first place.
1363
1364	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1365	functions that do not need a watcher.
1366
1367	=back
1368
1369
1370	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
1371
1372	Each watcher has, by default, a member C<void *data> that you can change
1373	and read at any time: libev will completely ignore it. This can be used
1374	to associate arbitrary data with your watcher. If you need more data and
1375	don't want to allocate memory and store a pointer to it in that data
1376	member, you can also "subclass" the watcher type and provide your own
1377	data:
1378
1379	struct my_io
1380	{
1381	ev_io io;
1382	int otherfd;
1383	void *somedata;
1384	struct whatever *mostinteresting;
1385	};
1386
1387	...
1388	struct my_io w;
1389	ev_io_init (&w.io, my_cb, fd, EV_READ);
1390
1391	And since your callback will be called with a pointer to the watcher, you
1392	can cast it back to your own type:
1393
1394	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1395	{
1396	struct my_io *w = (struct my_io *)w_;
1397	...
1398	}
1399
1400	More interesting and less C-conformant ways of casting your callback type
1401	instead have been omitted.
1402
1403	Another common scenario is to use some data structure with multiple
1404	embedded watchers:
1405
1406	struct my_biggy
1407	{
1408	int some_data;
1409	ev_timer t1;
1410	ev_timer t2;
1411	}
1412
1413	In this case getting the pointer to C<my_biggy> is a bit more
1414	complicated: Either you store the address of your C<my_biggy> struct
1415	in the C<data> member of the watcher (for woozies), or you need to use
1416	some pointer arithmetic using C<offsetof> inside your watchers (for real
1417	programmers):
1418
1419	#include <stddef.h>
1420
1421	static void
1422	t1_cb (EV_P_ ev_timer *w, int revents)
1423	{
1424	struct my_biggy big = (struct my_biggy *)
1425	(((char *)w) - offsetof (struct my_biggy, t1));
1426	}
1427
1428	static void
1429	t2_cb (EV_P_ ev_timer *w, int revents)
1430	{
1431	struct my_biggy big = (struct my_biggy *)
1432	(((char *)w) - offsetof (struct my_biggy, t2));
1433	}
1434		1525
1435	=head2 WATCHER PRIORITY MODELS	1526	=head2 WATCHER PRIORITY MODELS
1436		1527
1437	Many event loops support I<watcher priorities>, which are usually small	1528	Many event loops support I<watcher priorities>, which are usually small
1438	integers that influence the ordering of event callback invocation	1529	integers that influence the ordering of event callback invocation
…		…
1565	In general you can register as many read and/or write event watchers per	1656	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	1657	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	1658	descriptors to non-blocking mode is also usually a good idea (but not
1568	required if you know what you are doing).	1659	required if you know what you are doing).
1569		1660
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	1661	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	1662	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	1663	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	1664	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	1665	with a relatively standard program structure. Thus it is best to always
1581	this situation even with a relatively standard program structure. Thus	1666	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.	1667	preferable to a program hanging until some data arrives.
1584		1668
1585	If you cannot run the fd in non-blocking mode (for example you should	1669	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	1670	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	1671	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	1672	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	1673	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	1674	use C<SIGALRM> and an interval timer, just to be sure you won't block
1591	indefinitely.	1675	indefinitely.
1592		1676
1593	But really, best use non-blocking mode.	1677	But really, best use non-blocking mode.
1594		1678
1595	=head3 The special problem of disappearing file descriptors	1679	=head3 The special problem of disappearing file descriptors
1596		1680
1597	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1681	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,	1682	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	1683	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	1684	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	1685	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	1686	is registered with libev, there is no efficient way to see that this is,
1603	fact, a different file descriptor.	1687	in fact, a different file descriptor.
1604		1688
1605	To avoid having to explicitly tell libev about such cases, libev follows	1689	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	1690	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	1691	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	1692	it is assumed that the file descriptor stays the same. That means that
…		…
1622		1706
1623	There is no workaround possible except not registering events	1707	There is no workaround possible except not registering events
1624	for potentially C<dup ()>'ed file descriptors, or to resort to	1708	for potentially C<dup ()>'ed file descriptors, or to resort to
1625	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1709	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1626		1710
		1711	=head3 The special problem of files
		1712
		1713	Many people try to use C<select> (or libev) on file descriptors
		1714	representing files, and expect it to become ready when their program
		1715	doesn't block on disk accesses (which can take a long time on their own).
		1716
		1717	However, this cannot ever work in the "expected" way - you get a readiness
		1718	notification as soon as the kernel knows whether and how much data is
		1719	there, and in the case of open files, that's always the case, so you
		1720	always get a readiness notification instantly, and your read (or possibly
		1721	write) will still block on the disk I/O.
		1722
		1723	Another way to view it is that in the case of sockets, pipes, character
		1724	devices and so on, there is another party (the sender) that delivers data
		1725	on its own, but in the case of files, there is no such thing: the disk
		1726	will not send data on its own, simply because it doesn't know what you
		1727	wish to read - you would first have to request some data.
		1728
		1729	Since files are typically not-so-well supported by advanced notification
		1730	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1731	to files, even though you should not use it. The reason for this is
		1732	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1733	usually a tty, often a pipe, but also sometimes files or special devices
		1734	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1735	F</dev/urandom>), and even though the file might better be served with
		1736	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1737	it "just works" instead of freezing.
		1738
		1739	So avoid file descriptors pointing to files when you know it (e.g. use
		1740	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1741	when you rarely read from a file instead of from a socket, and want to
		1742	reuse the same code path.
		1743
1627	=head3 The special problem of fork	1744	=head3 The special problem of fork
1628		1745
1629	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1746	Some backends (epoll, kqueue, probably linuxaio) do not support C<fork ()>
1630	useless behaviour. Libev fully supports fork, but needs to be told about	1747	at all or exhibit useless behaviour. Libev fully supports fork, but needs
1631	it in the child.	1748	to be told about it in the child if you want to continue to use it in the
		1749	child.
1632		1750
1633	To support fork in your programs, you either have to call	1751	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,	1752	()> 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	1753	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1636	C<EVBACKEND_POLL>.
1637		1754
1638	=head3 The special problem of SIGPIPE	1755	=head3 The special problem of SIGPIPE
1639		1756
1640	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1757	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	1758	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	1856	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1740	monotonic clock option helps a lot here).	1857	monotonic clock option helps a lot here).
1741		1858
1742	The callback is guaranteed to be invoked only I<after> its timeout has	1859	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	1860	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	1861	might introduce a small delay, see "the special problem of being too
		1862	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	1863	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	1864	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).	1865	longer true when a callback calls C<ev_run> recursively).
1748		1866
1749	=head3 Be smart about timeouts	1867	=head3 Be smart about timeouts
1750		1868
1751	Many real-world problems involve some kind of timeout, usually for error	1869	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,	1870	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1827		1945
1828	In this case, it would be more efficient to leave the C<ev_timer> alone,	1946	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	1947	but remember the time of last activity, and check for a real timeout only
1830	within the callback:	1948	within the callback:
1831		1949
		1950	ev_tstamp timeout = 60.;
1832	ev_tstamp last_activity; // time of last activity	1951	ev_tstamp last_activity; // time of last activity
		1952	ev_timer timer;
1833		1953
1834	static void	1954	static void
1835	callback (EV_P_ ev_timer *w, int revents)	1955	callback (EV_P_ ev_timer *w, int revents)
1836	{	1956	{
1837	ev_tstamp now = ev_now (EV_A);	1957	// calculate when the timeout would happen
1838	ev_tstamp timeout = last_activity + 60.;	1958	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
1839		1959
1840	// if last_activity + 60. is older than now, we did time out	1960	// if negative, it means we the timeout already occurred
1841	if (timeout < now)	1961	if (after < 0.)
1842	{	1962	{
1843	// timeout occurred, take action	1963	// timeout occurred, take action
1844	}	1964	}
1845	else	1965	else
1846	{	1966	{
1847	// callback was invoked, but there was some activity, re-arm	1967	// callback was invoked, but there was some recent
1848	// the watcher to fire in last_activity + 60, which is	1968	// activity. simply restart the timer to time out
1849	// guaranteed to be in the future, so "again" is positive:	1969	// after "after" seconds, which is the earliest time
1850	w->repeat = timeout - now;	1970	// the timeout can occur.
		1971	ev_timer_set (w, after, 0.);
1851	ev_timer_again (EV_A_ w);	1972	ev_timer_start (EV_A_ w);
1852	}	1973	}
1853	}	1974	}
1854		1975
1855	To summarise the callback: first calculate the real timeout (defined	1976	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	1977	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	1978	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	1979	(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		1980
1862	Note how C<ev_timer_again> is used, taking advantage of the	1981	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.	1982	timed out, and need to do whatever is needed in this case.
		1983
		1984	Otherwise, we now the earliest time at which the timeout would trigger,
		1985	and simply start the timer with this timeout value.
		1986
		1987	In other words, each time the callback is invoked it will check whether
		1988	the timeout occurred. If not, it will simply reschedule itself to check
		1989	again at the earliest time it could time out. Rinse. Repeat.
1864		1990
1865	This scheme causes more callback invocations (about one every 60 seconds	1991	This scheme causes more callback invocations (about one every 60 seconds
1866	minus half the average time between activity), but virtually no calls to	1992	minus half the average time between activity), but virtually no calls to
1867	libev to change the timeout.	1993	libev to change the timeout.
1868		1994
1869	To start the timer, simply initialise the watcher and set C<last_activity>	1995	To start the machinery, simply initialise the watcher and set
1870	to the current time (meaning we just have some activity :), then call the	1996	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:	1997	now), then call the callback, which will "do the right thing" and start
		1998	the timer:
1872		1999
		2000	last_activity = ev_now (EV_A);
1873	ev_init (timer, callback);	2001	ev_init (&timer, callback);
1874	last_activity = ev_now (loop);	2002	callback (EV_A_ &timer, 0);
1875	callback (loop, timer, EV_TIMER);
1876		2003
1877	And when there is some activity, simply store the current time in	2004	When there is some activity, simply store the current time in
1878	C<last_activity>, no libev calls at all:	2005	C<last_activity>, no libev calls at all:
1879		2006
		2007	if (activity detected)
1880	last_activity = ev_now (loop);	2008	last_activity = ev_now (EV_A);
		2009
		2010	When your timeout value changes, then the timeout can be changed by simply
		2011	providing a new value, stopping the timer and calling the callback, which
		2012	will again do the right thing (for example, time out immediately :).
		2013
		2014	timeout = new_value;
		2015	ev_timer_stop (EV_A_ &timer);
		2016	callback (EV_A_ &timer, 0);
1881		2017
1882	This technique is slightly more complex, but in most cases where the	2018	This technique is slightly more complex, but in most cases where the
1883	time-out is unlikely to be triggered, much more efficient.	2019	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		2020
1889	=item 4. Wee, just use a double-linked list for your timeouts.	2021	=item 4. Wee, just use a double-linked list for your timeouts.
1890		2022
1891	If there is not one request, but many thousands (millions...), all	2023	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	2024	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	2051	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	2052	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	2053	off after the first million or so of active timers, i.e. it's usually
1922	overkill :)	2054	overkill :)
1923		2055
		2056	=head3 The special problem of being too early
		2057
		2058	If you ask a timer to call your callback after three seconds, then
		2059	you expect it to be invoked after three seconds - but of course, this
		2060	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		2061	guaranteed to any precision by libev - imagine somebody suspending the
		2062	process with a STOP signal for a few hours for example.
		2063
		2064	So, libev tries to invoke your callback as soon as possible I<after> the
		2065	delay has occurred, but cannot guarantee this.
		2066
		2067	A less obvious failure mode is calling your callback too early: many event
		2068	loops compare timestamps with a "elapsed delay >= requested delay", but
		2069	this can cause your callback to be invoked much earlier than you would
		2070	expect.
		2071
		2072	To see why, imagine a system with a clock that only offers full second
		2073	resolution (think windows if you can't come up with a broken enough OS
		2074	yourself). If you schedule a one-second timer at the time 500.9, then the
		2075	event loop will schedule your timeout to elapse at a system time of 500
		2076	(500.9 truncated to the resolution) + 1, or 501.
		2077
		2078	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2079	501" and invoke the callback 0.1s after it was started, even though a
		2080	one-second delay was requested - this is being "too early", despite best
		2081	intentions.
		2082
		2083	This is the reason why libev will never invoke the callback if the elapsed
		2084	delay equals the requested delay, but only when the elapsed delay is
		2085	larger than the requested delay. In the example above, libev would only invoke
		2086	the callback at system time 502, or 1.1s after the timer was started.
		2087
		2088	So, while libev cannot guarantee that your callback will be invoked
		2089	exactly when requested, it I<can> and I<does> guarantee that the requested
		2090	delay has actually elapsed, or in other words, it always errs on the "too
		2091	late" side of things.
		2092
1924	=head3 The special problem of time updates	2093	=head3 The special problem of time updates
1925		2094
1926	Establishing the current time is a costly operation (it usually takes at	2095	Establishing the current time is a costly operation (it usually takes
1927	least two system calls): EV therefore updates its idea of the current	2096	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	2097	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	2098	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1930	lots of events in one iteration.	2099	lots of events in one iteration.
1931		2100
1932	The relative timeouts are calculated relative to the C<ev_now ()>	2101	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	2102	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	2103	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	2104	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:	2105	timeout on the current time, use something like the following to adjust
		2106	for it:
1937		2107
1938	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2108	ev_timer_set (&timer, after + (ev_time () - ev_now ()), 0.);
1939		2109
1940	If the event loop is suspended for a long time, you can also force an	2110	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	2111	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1942	()>.	2112	()>, although that will push the event time of all outstanding events
		2113	further into the future.
		2114
		2115	=head3 The special problem of unsynchronised clocks
		2116
		2117	Modern systems have a variety of clocks - libev itself uses the normal
		2118	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2119	jumps).
		2120
		2121	Neither of these clocks is synchronised with each other or any other clock
		2122	on the system, so C<ev_time ()> might return a considerably different time
		2123	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2124	a call to C<gettimeofday> might return a second count that is one higher
		2125	than a directly following call to C<time>.
		2126
		2127	The moral of this is to only compare libev-related timestamps with
		2128	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2129	a second or so.
		2130
		2131	One more problem arises due to this lack of synchronisation: if libev uses
		2132	the system monotonic clock and you compare timestamps from C<ev_time>
		2133	or C<ev_now> from when you started your timer and when your callback is
		2134	invoked, you will find that sometimes the callback is a bit "early".
		2135
		2136	This is because C<ev_timer>s work in real time, not wall clock time, so
		2137	libev makes sure your callback is not invoked before the delay happened,
		2138	I<measured according to the real time>, not the system clock.
		2139
		2140	If your timeouts are based on a physical timescale (e.g. "time out this
		2141	connection after 100 seconds") then this shouldn't bother you as it is
		2142	exactly the right behaviour.
		2143
		2144	If you want to compare wall clock/system timestamps to your timers, then
		2145	you need to use C<ev_periodic>s, as these are based on the wall clock
		2146	time, where your comparisons will always generate correct results.
1943		2147
1944	=head3 The special problems of suspended animation	2148	=head3 The special problems of suspended animation
1945		2149
1946	When you leave the server world it is quite customary to hit machines that	2150	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?	2151	can suspend/hibernate - what happens to the clocks during such a suspend?
…		…
1977		2181
1978	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2182	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1979		2183
1980	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2184	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1981		2185
1982	Configure the timer to trigger after C<after> seconds. If C<repeat>	2186	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	2187	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	2188	automatically be stopped once the timeout is reached. If it is positive,
1985	configured to trigger again C<repeat> seconds later, again, and again,	2189	then the timer will automatically be configured to trigger again C<repeat>
1986	until stopped manually.	2190	seconds later, again, and again, until stopped manually.
1987		2191
1988	The timer itself will do a best-effort at avoiding drift, that is, if	2192	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	2193	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	2194	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	2195	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.	2196	do stuff) the timer will not fire more than once per event loop iteration.
1993		2197
1994	=item ev_timer_again (loop, ev_timer *)	2198	=item ev_timer_again (loop, ev_timer *)
1995		2199
1996	This will act as if the timer timed out and restart it again if it is	2200	This will act as if the timer timed out, and restarts it again if it is
1997	repeating. The exact semantics are:	2201	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2202	timeout to the C<repeat> value and calling C<ev_timer_start>.
1998		2203
		2204	The exact semantics are as in the following rules, all of which will be
		2205	applied to the watcher:
		2206
		2207	=over 4
		2208
1999	If the timer is pending, its pending status is cleared.	2209	=item If the timer is pending, the pending status is always cleared.
2000		2210
2001	If the timer is started but non-repeating, stop it (as if it timed out).	2211	=item If the timer is started but non-repeating, stop it (as if it timed
		2212	out, without invoking it).
2002		2213
2003	If the timer is repeating, either start it if necessary (with the	2214	=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.	2215	and start the timer, if necessary.
2005		2216
		2217	=back
		2218
2006	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a	2219	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
2007	usage example.	2220	usage example.
2008		2221
2009	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)	2222	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
2010		2223
2011	Returns the remaining time until a timer fires. If the timer is active,	2224	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	2277	Periodic watchers are also timers of a kind, but they are very versatile
2065	(and unfortunately a bit complex).	2278	(and unfortunately a bit complex).
2066		2279
2067	Unlike C<ev_timer>, periodic watchers are not based on real time (or	2280	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	2281	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	2282	(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	2283	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	2284	time, and time jumps are not uncommon (e.g. when you adjust your
2072	wrist-watch).	2285	wrist-watch).
2073		2286
2074	You can tell a periodic watcher to trigger after some specific point	2287	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	2292	C<ev_timer>, which would still trigger roughly 10 seconds after starting
2080	it, as it uses a relative timeout).	2293	it, as it uses a relative timeout).
2081		2294
2082	C<ev_periodic> watchers can also be used to implement vastly more complex	2295	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	2296	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	2297	other complicated rules. This cannot easily be done with C<ev_timer>
2085	those cannot react to time jumps.	2298	watchers, as those cannot react to time jumps.
2086		2299
2087	As with timers, the callback is guaranteed to be invoked only when the	2300	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	2301	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	2302	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	2303	earlier time-out values are invoked before ones with later time-out values
…		…
2131		2344
2132	Another way to think about it (for the mathematically inclined) is that	2345	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	2346	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.	2347	time where C<time = offset (mod interval)>, regardless of any time jumps.
2135		2348
2136	For numerical stability it is preferable that the C<offset> value is near	2349	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	2350	interval value should be higher than C<1/8192> (which is around 100
2138	this value, and in fact is often specified as zero.	2351	microseconds) and C<offset> should be higher than C<0> and should have
		2352	at most a similar magnitude as the current time (say, within a factor of
		2353	ten). Typical values for offset are, in fact, C<0> or something between
		2354	C<0> and C<interval>, which is also the recommended range.
2139		2355
2140	Note also that there is an upper limit to how often a timer can fire (CPU	2356	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	2357	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	2358	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).	2359	millisecond (if the OS supports it and the machine is fast enough).
…		…
2173		2389
2174	NOTE: I<< This callback must always return a time that is higher than or	2390	NOTE: I<< This callback must always return a time that is higher than or
2175	equal to the passed C<now> value >>.	2391	equal to the passed C<now> value >>.
2176		2392
2177	This can be used to create very complex timers, such as a timer that	2393	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	2394	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	2395	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	2396	this. Here is a (completely untested, no error checking) example on how to
2181	reason I omitted it as an example).	2397	do this:
		2398
		2399	#include <time.h>
		2400
		2401	static ev_tstamp
		2402	my_rescheduler (ev_periodic *w, ev_tstamp now)
		2403	{
		2404	time_t tnow = (time_t)now;
		2405	struct tm tm;
		2406	localtime_r (&tnow, &tm);
		2407
		2408	tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
		2409	++tm.tm_mday; // midnight next day
		2410
		2411	return mktime (&tm);
		2412	}
		2413
		2414	Note: this code might run into trouble on days that have more then two
		2415	midnights (beginning and end).
2182		2416
2183	=back	2417	=back
2184		2418
2185	=item ev_periodic_again (loop, ev_periodic *)	2419	=item ev_periodic_again (loop, ev_periodic *)
2186		2420
…		…
2251		2485
2252	ev_periodic hourly_tick;	2486	ev_periodic hourly_tick;
2253	ev_periodic_init (&hourly_tick, clock_cb,	2487	ev_periodic_init (&hourly_tick, clock_cb,
2254	fmod (ev_now (loop), 3600.), 3600., 0);	2488	fmod (ev_now (loop), 3600.), 3600., 0);
2255	ev_periodic_start (loop, &hourly_tick);	2489	ev_periodic_start (loop, &hourly_tick);
2256		2490
2257		2491
2258	=head2 C<ev_signal> - signal me when a signal gets signalled!	2492	=head2 C<ev_signal> - signal me when a signal gets signalled!
2259		2493
2260	Signal watchers will trigger an event when the process receives a specific	2494	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	2495	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	2496	will try its best to deliver signals synchronously, i.e. as part of the
2263	normal event processing, like any other event.	2497	normal event processing, like any other event.
2264		2498
2265	If you want signals to be delivered truly asynchronously, just use	2499	If you want signals to be delivered truly asynchronously, just use
2266	C<sigaction> as you would do without libev and forget about sharing	2500	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	2501	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	2505	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	2506	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	2507	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.	2508	the moment, C<SIGCHLD> is permanently tied to the default loop.
2275		2509
2276	When the first watcher gets started will libev actually register something	2510	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	2511	register something with the kernel. It thus coexists with your own signal
2278	you don't register any with libev for the same signal).	2512	handlers as long as you don't register any with libev for the same signal.
2279		2513
2280	If possible and supported, libev will install its handlers with	2514	If possible and supported, libev will install its handlers with
2281	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should	2515	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	2516	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	2517	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	2520	=head3 The special problem of inheritance over fork/execve/pthread_create
2287		2521
2288	Both the signal mask (C<sigprocmask>) and the signal disposition	2522	Both the signal mask (C<sigprocmask>) and the signal disposition
2289	(C<sigaction>) are unspecified after starting a signal watcher (and after	2523	(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,	2524	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.	2525	and might or might not set or restore the installed signal handler (but
		2526	see C<EVFLAG_NOSIGMASK>).
2292		2527
2293	While this does not matter for the signal disposition (libev never	2528	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	2529	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	2530	C<execve>), this matters for the signal mask: many programs do not expect
2296	certain signals to be blocked.	2531	certain signals to be blocked.
…		…
2309	I<has> to modify the signal mask, at least temporarily.	2544	I<has> to modify the signal mask, at least temporarily.
2310		2545
2311	So I can't stress this enough: I<If you do not reset your signal mask when	2546	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	2547	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.	2548	is not a libev-specific thing, this is true for most event libraries.
		2549
		2550	=head3 The special problem of threads signal handling
		2551
		2552	POSIX threads has problematic signal handling semantics, specifically,
		2553	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2554	threads in a process block signals, which is hard to achieve.
		2555
		2556	When you want to use sigwait (or mix libev signal handling with your own
		2557	for the same signals), you can tackle this problem by globally blocking
		2558	all signals before creating any threads (or creating them with a fully set
		2559	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2560	loops. Then designate one thread as "signal receiver thread" which handles
		2561	these signals. You can pass on any signals that libev might be interested
		2562	in by calling C<ev_feed_signal>.
2314		2563
2315	=head3 Watcher-Specific Functions and Data Members	2564	=head3 Watcher-Specific Functions and Data Members
2316		2565
2317	=over 4	2566	=over 4
2318		2567
…		…
2453		2702
2454	=head2 C<ev_stat> - did the file attributes just change?	2703	=head2 C<ev_stat> - did the file attributes just change?
2455		2704
2456	This watches a file system path for attribute changes. That is, it calls	2705	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)	2706	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	2707	and sees if it changed compared to the last time, invoking the callback
2459	it did.	2708	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2709	happen after the watcher has been started will be reported.
2460		2710
2461	The path does not need to exist: changing from "path exists" to "path does	2711	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	2712	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	2713	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	2714	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	2944	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	2945	effect on its own sometimes), idle watchers are a good place to do
2696	"pseudo-background processing", or delay processing stuff to after the	2946	"pseudo-background processing", or delay processing stuff to after the
2697	event loop has handled all outstanding events.	2947	event loop has handled all outstanding events.
2698		2948
		2949	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2950
		2951	As long as there is at least one active idle watcher, libev will never
		2952	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2953	For this to work, the idle watcher doesn't need to be invoked at all - the
		2954	lowest priority will do.
		2955
		2956	This mode of operation can be useful together with an C<ev_check> watcher,
		2957	to do something on each event loop iteration - for example to balance load
		2958	between different connections.
		2959
		2960	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2961	example.
		2962
2699	=head3 Watcher-Specific Functions and Data Members	2963	=head3 Watcher-Specific Functions and Data Members
2700		2964
2701	=over 4	2965	=over 4
2702		2966
2703	=item ev_idle_init (ev_idle *, callback)	2967	=item ev_idle_init (ev_idle *, callback)
…		…
2714	callback, free it. Also, use no error checking, as usual.	2978	callback, free it. Also, use no error checking, as usual.
2715		2979
2716	static void	2980	static void
2717	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)	2981	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2718	{	2982	{
		2983	// stop the watcher
		2984	ev_idle_stop (loop, w);
		2985
		2986	// now we can free it
2719	free (w);	2987	free (w);
		2988
2720	// now do something you wanted to do when the program has	2989	// now do something you wanted to do when the program has
2721	// no longer anything immediate to do.	2990	// no longer anything immediate to do.
2722	}	2991	}
2723		2992
2724	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	2993	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
…		…
2726	ev_idle_start (loop, idle_watcher);	2995	ev_idle_start (loop, idle_watcher);
2727		2996
2728		2997
2729	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2998	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2730		2999
2731	Prepare and check watchers are usually (but not always) used in pairs:	3000	Prepare and check watchers are often (but not always) used in pairs:
2732	prepare watchers get invoked before the process blocks and check watchers	3001	prepare watchers get invoked before the process blocks and check watchers
2733	afterwards.	3002	afterwards.
2734		3003
2735	You I<must not> call C<ev_run> or similar functions that enter	3004	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>	3005	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	3006	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	3007	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,	3008	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	3009	C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
2741	called in pairs bracketing the blocking call.	3010	kind they will always be called in pairs bracketing the blocking call.
2742		3011
2743	Their main purpose is to integrate other event mechanisms into libev and	3012	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	3013	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	3014	variable changes, implement your own watchers, integrate net-snmp or a
2746	coroutine library and lots more. They are also occasionally useful if	3015	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	3033	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	3034	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	3035	loop from blocking if lower-priority coroutines are active, thus mapping
2767	low-priority coroutines to idle/background tasks).	3036	low-priority coroutines to idle/background tasks).
2768		3037
2769	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	3038	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	3039	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).	3040	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		3041	watchers).
2772		3042
2773	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not	3043	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	3044	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	3045	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	3046	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	3047	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	3048	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
2779	others).	3049	others).
		3050
		3051	=head3 Abusing an C<ev_check> watcher for its side-effect
		3052
		3053	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		3054	useful because they are called once per event loop iteration. For
		3055	example, if you want to handle a large number of connections fairly, you
		3056	normally only do a bit of work for each active connection, and if there
		3057	is more work to do, you wait for the next event loop iteration, so other
		3058	connections have a chance of making progress.
		3059
		3060	Using an C<ev_check> watcher is almost enough: it will be called on the
		3061	next event loop iteration. However, that isn't as soon as possible -
		3062	without external events, your C<ev_check> watcher will not be invoked.
		3063
		3064	This is where C<ev_idle> watchers come in handy - all you need is a
		3065	single global idle watcher that is active as long as you have one active
		3066	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		3067	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		3068	invoked. Neither watcher alone can do that.
2780		3069
2781	=head3 Watcher-Specific Functions and Data Members	3070	=head3 Watcher-Specific Functions and Data Members
2782		3071
2783	=over 4	3072	=over 4
2784		3073
…		…
2985		3274
2986	=over 4	3275	=over 4
2987		3276
2988	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3277	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
2989		3278
2990	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3279	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
2991		3280
2992	Configures the watcher to embed the given loop, which must be	3281	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	3282	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	3283	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,	3284	to invoke it (it will continue to be called until the sweep has been done,
…		…
3016	used).	3305	used).
3017		3306
3018	struct ev_loop *loop_hi = ev_default_init (0);	3307	struct ev_loop *loop_hi = ev_default_init (0);
3019	struct ev_loop *loop_lo = 0;	3308	struct ev_loop *loop_lo = 0;
3020	ev_embed embed;	3309	ev_embed embed;
3021		3310
3022	// see if there is a chance of getting one that works	3311	// see if there is a chance of getting one that works
3023	// (remember that a flags value of 0 means autodetection)	3312	// (remember that a flags value of 0 means autodetection)
3024	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3313	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3025	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3314	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3026	: 0;	3315	: 0;
…		…
3040	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3329	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
3041		3330
3042	struct ev_loop *loop = ev_default_init (0);	3331	struct ev_loop *loop = ev_default_init (0);
3043	struct ev_loop *loop_socket = 0;	3332	struct ev_loop *loop_socket = 0;
3044	ev_embed embed;	3333	ev_embed embed;
3045		3334
3046	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3335	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3047	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3336	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3048	{	3337	{
3049	ev_embed_init (&embed, 0, loop_socket);	3338	ev_embed_init (&embed, 0, loop_socket);
3050	ev_embed_start (loop, &embed);	3339	ev_embed_start (loop, &embed);
…		…
3058		3347
3059	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3348	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
3060		3349
3061	Fork watchers are called when a C<fork ()> was detected (usually because	3350	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	3351	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	3352	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,	3353	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	3354	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	3355	and calls it in the wrong process, the fork handlers will be invoked, too,
3067	handlers will be invoked, too, of course.	3356	of course.
3068		3357
3069	=head3 The special problem of life after fork - how is it possible?	3358	=head3 The special problem of life after fork - how is it possible?
3070		3359
3071	Most uses of C<fork()> consist of forking, then some simple calls to set	3360	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	3361	up/change the process environment, followed by a call to C<exec()>. This
3073	sequence should be handled by libev without any problems.	3362	sequence should be handled by libev without any problems.
3074		3363
3075	This changes when the application actually wants to do event handling	3364	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	3365	in the child, or both parent in child, in effect "continuing" after the
…		…
3153	atexit (program_exits);	3442	atexit (program_exits);
3154		3443
3155		3444
3156	=head2 C<ev_async> - how to wake up an event loop	3445	=head2 C<ev_async> - how to wake up an event loop
3157		3446
3158	In general, you cannot use an C<ev_run> from multiple threads or other	3447	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	3448	asynchronous sources such as signal handlers (as opposed to multiple event
3160	loops - those are of course safe to use in different threads).	3449	loops - those are of course safe to use in different threads).
3161		3450
3162	Sometimes, however, you need to wake up an event loop you do not control,	3451	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>	3452	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.	3454	it by calling C<ev_async_send>, which is thread- and signal safe.
3166		3455
3167	This functionality is very similar to C<ev_signal> watchers, as signals,	3456	This functionality is very similar to C<ev_signal> watchers, as signals,
3168	too, are asynchronous in nature, and signals, too, will be compressed	3457	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	3458	(i.e. the number of callback invocations may be less than the number of
3170	C<ev_async_sent> calls).	3459	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
3171		3460	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	3461	signal, and C<ev_feed_signal> to signal this watcher from another thread,
3173	just the default loop.	3462	even without knowing which loop owns the signal.
3174		3463
3175	=head3 Queueing	3464	=head3 Queueing
3176		3465
3177	C<ev_async> does not support queueing of data in any way. The reason	3466	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	3467	is that the author does not know of a simple (or any) algorithm for a
…		…
3270	trust me.	3559	trust me.
3271		3560
3272	=item ev_async_send (loop, ev_async *)	3561	=item ev_async_send (loop, ev_async *)
3273		3562
3274	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3563	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	3564	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3565	returns.
		3566
3276	C<ev_feed_event>, this call is safe to do from other threads, signal or	3567	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	3568	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3278	section below on what exactly this means).	3569	embedding section below on what exactly this means).
3279		3570
3280	Note that, as with other watchers in libev, multiple events might get	3571	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	3572	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>,	3573	this is that C<ev_async> watchers are level-triggered: they are set on
3283	reset when the event loop detects that).	3574	C<ev_async_send>, reset when the event loop detects that).
3284		3575
3285	This call incurs the overhead of a system call only once per event loop	3576	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	3577	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.	3578	the event loop (or your program) is processing events. That means that
		3579	repeated calls are basically free (there is no need to avoid calls for
		3580	performance reasons) and that the overhead becomes smaller (typically
		3581	zero) under load.
3288		3582
3289	=item bool = ev_async_pending (ev_async *)	3583	=item bool = ev_async_pending (ev_async *)
3290		3584
3291	Returns a non-zero value when C<ev_async_send> has been called on the	3585	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	3586	watcher but the event has not yet been processed (or even noted) by the
…		…
3309		3603
3310	There are some other functions of possible interest. Described. Here. Now.	3604	There are some other functions of possible interest. Described. Here. Now.
3311		3605
3312	=over 4	3606	=over 4
3313		3607
3314	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3608	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)
3315		3609
3316	This function combines a simple timer and an I/O watcher, calls your	3610	This function combines a simple timer and an I/O watcher, calls your
3317	callback on whichever event happens first and automatically stops both	3611	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	3612	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	3613	or timeout without having to allocate/configure/start/stop/free one or
…		…
3347	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3641	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3348		3642
3349	=item ev_feed_fd_event (loop, int fd, int revents)	3643	=item ev_feed_fd_event (loop, int fd, int revents)
3350		3644
3351	Feed an event on the given fd, as if a file descriptor backend detected	3645	Feed an event on the given fd, as if a file descriptor backend detected
3352	the given events it.	3646	the given events.
3353		3647
3354	=item ev_feed_signal_event (loop, int signum)	3648	=item ev_feed_signal_event (loop, int signum)
3355		3649
3356	Feed an event as if the given signal occurred (C<loop> must be the default	3650	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3357	loop!).	3651	which is async-safe.
3358		3652
3359	=back	3653	=back
		3654
		3655
		3656	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3657
		3658	This section explains some common idioms that are not immediately
		3659	obvious. Note that examples are sprinkled over the whole manual, and this
		3660	section only contains stuff that wouldn't fit anywhere else.
		3661
		3662	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3663
		3664	Each watcher has, by default, a C<void *data> member that you can read
		3665	or modify at any time: libev will completely ignore it. This can be used
		3666	to associate arbitrary data with your watcher. If you need more data and
		3667	don't want to allocate memory separately and store a pointer to it in that
		3668	data member, you can also "subclass" the watcher type and provide your own
		3669	data:
		3670
		3671	struct my_io
		3672	{
		3673	ev_io io;
		3674	int otherfd;
		3675	void *somedata;
		3676	struct whatever *mostinteresting;
		3677	};
		3678
		3679	...
		3680	struct my_io w;
		3681	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3682
		3683	And since your callback will be called with a pointer to the watcher, you
		3684	can cast it back to your own type:
		3685
		3686	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3687	{
		3688	struct my_io *w = (struct my_io *)w_;
		3689	...
		3690	}
		3691
		3692	More interesting and less C-conformant ways of casting your callback
		3693	function type instead have been omitted.
		3694
		3695	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3696
		3697	Another common scenario is to use some data structure with multiple
		3698	embedded watchers, in effect creating your own watcher that combines
		3699	multiple libev event sources into one "super-watcher":
		3700
		3701	struct my_biggy
		3702	{
		3703	int some_data;
		3704	ev_timer t1;
		3705	ev_timer t2;
		3706	}
		3707
		3708	In this case getting the pointer to C<my_biggy> is a bit more
		3709	complicated: Either you store the address of your C<my_biggy> struct in
		3710	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3711	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3712	real programmers):
		3713
		3714	#include <stddef.h>
		3715
		3716	static void
		3717	t1_cb (EV_P_ ev_timer *w, int revents)
		3718	{
		3719	struct my_biggy big = (struct my_biggy *)
		3720	(((char *)w) - offsetof (struct my_biggy, t1));
		3721	}
		3722
		3723	static void
		3724	t2_cb (EV_P_ ev_timer *w, int revents)
		3725	{
		3726	struct my_biggy big = (struct my_biggy *)
		3727	(((char *)w) - offsetof (struct my_biggy, t2));
		3728	}
		3729
		3730	=head2 AVOIDING FINISHING BEFORE RETURNING
		3731
		3732	Often you have structures like this in event-based programs:
		3733
		3734	callback ()
		3735	{
		3736	free (request);
		3737	}
		3738
		3739	request = start_new_request (..., callback);
		3740
		3741	The intent is to start some "lengthy" operation. The C<request> could be
		3742	used to cancel the operation, or do other things with it.
		3743
		3744	It's not uncommon to have code paths in C<start_new_request> that
		3745	immediately invoke the callback, for example, to report errors. Or you add
		3746	some caching layer that finds that it can skip the lengthy aspects of the
		3747	operation and simply invoke the callback with the result.
		3748
		3749	The problem here is that this will happen I<before> C<start_new_request>
		3750	has returned, so C<request> is not set.
		3751
		3752	Even if you pass the request by some safer means to the callback, you
		3753	might want to do something to the request after starting it, such as
		3754	canceling it, which probably isn't working so well when the callback has
		3755	already been invoked.
		3756
		3757	A common way around all these issues is to make sure that
		3758	C<start_new_request> I<always> returns before the callback is invoked. If
		3759	C<start_new_request> immediately knows the result, it can artificially
		3760	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3761	example, or more sneakily, by reusing an existing (stopped) watcher and
		3762	pushing it into the pending queue:
		3763
		3764	ev_set_cb (watcher, callback);
		3765	ev_feed_event (EV_A_ watcher, 0);
		3766
		3767	This way, C<start_new_request> can safely return before the callback is
		3768	invoked, while not delaying callback invocation too much.
		3769
		3770	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3771
		3772	Often (especially in GUI toolkits) there are places where you have
		3773	I<modal> interaction, which is most easily implemented by recursively
		3774	invoking C<ev_run>.
		3775
		3776	This brings the problem of exiting - a callback might want to finish the
		3777	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3778	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3779	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3780	other combination: In these cases, a simple C<ev_break> will not work.
		3781
		3782	The solution is to maintain "break this loop" variable for each C<ev_run>
		3783	invocation, and use a loop around C<ev_run> until the condition is
		3784	triggered, using C<EVRUN_ONCE>:
		3785
		3786	// main loop
		3787	int exit_main_loop = 0;
		3788
		3789	while (!exit_main_loop)
		3790	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3791
		3792	// in a modal watcher
		3793	int exit_nested_loop = 0;
		3794
		3795	while (!exit_nested_loop)
		3796	ev_run (EV_A_ EVRUN_ONCE);
		3797
		3798	To exit from any of these loops, just set the corresponding exit variable:
		3799
		3800	// exit modal loop
		3801	exit_nested_loop = 1;
		3802
		3803	// exit main program, after modal loop is finished
		3804	exit_main_loop = 1;
		3805
		3806	// exit both
		3807	exit_main_loop = exit_nested_loop = 1;
		3808
		3809	=head2 THREAD LOCKING EXAMPLE
		3810
		3811	Here is a fictitious example of how to run an event loop in a different
		3812	thread from where callbacks are being invoked and watchers are
		3813	created/added/removed.
		3814
		3815	For a real-world example, see the C<EV::Loop::Async> perl module,
		3816	which uses exactly this technique (which is suited for many high-level
		3817	languages).
		3818
		3819	The example uses a pthread mutex to protect the loop data, a condition
		3820	variable to wait for callback invocations, an async watcher to notify the
		3821	event loop thread and an unspecified mechanism to wake up the main thread.
		3822
		3823	First, you need to associate some data with the event loop:
		3824
		3825	typedef struct {
		3826	mutex_t lock; /* global loop lock */
		3827	ev_async async_w;
		3828	thread_t tid;
		3829	cond_t invoke_cv;
		3830	} userdata;
		3831
		3832	void prepare_loop (EV_P)
		3833	{
		3834	// for simplicity, we use a static userdata struct.
		3835	static userdata u;
		3836
		3837	ev_async_init (&u->async_w, async_cb);
		3838	ev_async_start (EV_A_ &u->async_w);
		3839
		3840	pthread_mutex_init (&u->lock, 0);
		3841	pthread_cond_init (&u->invoke_cv, 0);
		3842
		3843	// now associate this with the loop
		3844	ev_set_userdata (EV_A_ u);
		3845	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3846	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3847
		3848	// then create the thread running ev_run
		3849	pthread_create (&u->tid, 0, l_run, EV_A);
		3850	}
		3851
		3852	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3853	solely to wake up the event loop so it takes notice of any new watchers
		3854	that might have been added:
		3855
		3856	static void
		3857	async_cb (EV_P_ ev_async *w, int revents)
		3858	{
		3859	// just used for the side effects
		3860	}
		3861
		3862	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3863	protecting the loop data, respectively.
		3864
		3865	static void
		3866	l_release (EV_P)
		3867	{
		3868	userdata *u = ev_userdata (EV_A);
		3869	pthread_mutex_unlock (&u->lock);
		3870	}
		3871
		3872	static void
		3873	l_acquire (EV_P)
		3874	{
		3875	userdata *u = ev_userdata (EV_A);
		3876	pthread_mutex_lock (&u->lock);
		3877	}
		3878
		3879	The event loop thread first acquires the mutex, and then jumps straight
		3880	into C<ev_run>:
		3881
		3882	void *
		3883	l_run (void *thr_arg)
		3884	{
		3885	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3886
		3887	l_acquire (EV_A);
		3888	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3889	ev_run (EV_A_ 0);
		3890	l_release (EV_A);
		3891
		3892	return 0;
		3893	}
		3894
		3895	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3896	signal the main thread via some unspecified mechanism (signals? pipe
		3897	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3898	have been called (in a while loop because a) spurious wakeups are possible
		3899	and b) skipping inter-thread-communication when there are no pending
		3900	watchers is very beneficial):
		3901
		3902	static void
		3903	l_invoke (EV_P)
		3904	{
		3905	userdata *u = ev_userdata (EV_A);
		3906
		3907	while (ev_pending_count (EV_A))
		3908	{
		3909	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3910	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3911	}
		3912	}
		3913
		3914	Now, whenever the main thread gets told to invoke pending watchers, it
		3915	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3916	thread to continue:
		3917
		3918	static void
		3919	real_invoke_pending (EV_P)
		3920	{
		3921	userdata *u = ev_userdata (EV_A);
		3922
		3923	pthread_mutex_lock (&u->lock);
		3924	ev_invoke_pending (EV_A);
		3925	pthread_cond_signal (&u->invoke_cv);
		3926	pthread_mutex_unlock (&u->lock);
		3927	}
		3928
		3929	Whenever you want to start/stop a watcher or do other modifications to an
		3930	event loop, you will now have to lock:
		3931
		3932	ev_timer timeout_watcher;
		3933	userdata *u = ev_userdata (EV_A);
		3934
		3935	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3936
		3937	pthread_mutex_lock (&u->lock);
		3938	ev_timer_start (EV_A_ &timeout_watcher);
		3939	ev_async_send (EV_A_ &u->async_w);
		3940	pthread_mutex_unlock (&u->lock);
		3941
		3942	Note that sending the C<ev_async> watcher is required because otherwise
		3943	an event loop currently blocking in the kernel will have no knowledge
		3944	about the newly added timer. By waking up the loop it will pick up any new
		3945	watchers in the next event loop iteration.
		3946
		3947	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3948
		3949	While the overhead of a callback that e.g. schedules a thread is small, it
		3950	is still an overhead. If you embed libev, and your main usage is with some
		3951	kind of threads or coroutines, you might want to customise libev so that
		3952	doesn't need callbacks anymore.
		3953
		3954	Imagine you have coroutines that you can switch to using a function
		3955	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3956	and that due to some magic, the currently active coroutine is stored in a
		3957	global called C<current_coro>. Then you can build your own "wait for libev
		3958	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3959	the differing C<;> conventions):
		3960
		3961	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3962	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3963
		3964	That means instead of having a C callback function, you store the
		3965	coroutine to switch to in each watcher, and instead of having libev call
		3966	your callback, you instead have it switch to that coroutine.
		3967
		3968	A coroutine might now wait for an event with a function called
		3969	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3970	matter when, or whether the watcher is active or not when this function is
		3971	called):
		3972
		3973	void
		3974	wait_for_event (ev_watcher *w)
		3975	{
		3976	ev_set_cb (w, current_coro);
		3977	switch_to (libev_coro);
		3978	}
		3979
		3980	That basically suspends the coroutine inside C<wait_for_event> and
		3981	continues the libev coroutine, which, when appropriate, switches back to
		3982	this or any other coroutine.
		3983
		3984	You can do similar tricks if you have, say, threads with an event queue -
		3985	instead of storing a coroutine, you store the queue object and instead of
		3986	switching to a coroutine, you push the watcher onto the queue and notify
		3987	any waiters.
		3988
		3989	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		3990	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3991
		3992	// my_ev.h
		3993	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3994	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3995	#include "../libev/ev.h"
		3996
		3997	// my_ev.c
		3998	#define EV_H "my_ev.h"
		3999	#include "../libev/ev.c"
		4000
		4001	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		4002	F<my_ev.c> into your project. When properly specifying include paths, you
		4003	can even use F<ev.h> as header file name directly.
3360		4004
3361		4005
3362	=head1 LIBEVENT EMULATION	4006	=head1 LIBEVENT EMULATION
3363		4007
3364	Libev offers a compatibility emulation layer for libevent. It cannot	4008	Libev offers a compatibility emulation layer for libevent. It cannot
3365	emulate the internals of libevent, so here are some usage hints:	4009	emulate the internals of libevent, so here are some usage hints:
3366		4010
3367	=over 4	4011	=over 4
		4012
		4013	=item * Only the libevent-1.4.1-beta API is being emulated.
		4014
		4015	This was the newest libevent version available when libev was implemented,
		4016	and is still mostly unchanged in 2010.
3368		4017
3369	=item * Use it by including <event.h>, as usual.	4018	=item * Use it by including <event.h>, as usual.
3370		4019
3371	=item * The following members are fully supported: ev_base, ev_callback,	4020	=item * The following members are fully supported: ev_base, ev_callback,
3372	ev_arg, ev_fd, ev_res, ev_events.	4021	ev_arg, ev_fd, ev_res, ev_events.
…		…
3378	=item * Priorities are not currently supported. Initialising priorities	4027	=item * Priorities are not currently supported. Initialising priorities
3379	will fail and all watchers will have the same priority, even though there	4028	will fail and all watchers will have the same priority, even though there
3380	is an ev_pri field.	4029	is an ev_pri field.
3381		4030
3382	=item * In libevent, the last base created gets the signals, in libev, the	4031	=item * In libevent, the last base created gets the signals, in libev, the
3383	first base created (== the default loop) gets the signals.	4032	base that registered the signal gets the signals.
3384		4033
3385	=item * Other members are not supported.	4034	=item * Other members are not supported.
3386		4035
3387	=item * The libev emulation is I<not> ABI compatible to libevent, you need	4036	=item * The libev emulation is I<not> ABI compatible to libevent, you need
3388	to use the libev header file and library.	4037	to use the libev header file and library.
3389		4038
3390	=back	4039	=back
3391		4040
3392	=head1 C++ SUPPORT	4041	=head1 C++ SUPPORT
		4042
		4043	=head2 C API
		4044
		4045	The normal C API should work fine when used from C++: both ev.h and the
		4046	libev sources can be compiled as C++. Therefore, code that uses the C API
		4047	will work fine.
		4048
		4049	Proper exception specifications might have to be added to callbacks passed
		4050	to libev: exceptions may be thrown only from watcher callbacks, all other
		4051	callbacks (allocator, syserr, loop acquire/release and periodic reschedule
		4052	callbacks) must not throw exceptions, and might need a C<noexcept>
		4053	specification. If you have code that needs to be compiled as both C and
		4054	C++ you can use the C<EV_NOEXCEPT> macro for this:
		4055
		4056	static void
		4057	fatal_error (const char *msg) EV_NOEXCEPT
		4058	{
		4059	perror (msg);
		4060	abort ();
		4061	}
		4062
		4063	...
		4064	ev_set_syserr_cb (fatal_error);
		4065
		4066	The only API functions that can currently throw exceptions are C<ev_run>,
		4067	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		4068	because it runs cleanup watchers).
		4069
		4070	Throwing exceptions in watcher callbacks is only supported if libev itself
		4071	is compiled with a C++ compiler or your C and C++ environments allow
		4072	throwing exceptions through C libraries (most do).
		4073
		4074	=head2 C++ API
3393		4075
3394	Libev comes with some simplistic wrapper classes for C++ that mainly allow	4076	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	4077	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.	4078	the callback model to a model using method callbacks on objects.
3397		4079
3398	To use it,	4080	To use it,
3399		4081
3400	#include <ev++.h>	4082	#include <ev++.h>
3401		4083
3402	This automatically includes F<ev.h> and puts all of its definitions (many	4084	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	4085	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	4086	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++	4089	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	4090	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	4091	that the watcher is associated with (or no additional members at all if
3410	you disable C<EV_MULTIPLICITY> when embedding libev).	4092	you disable C<EV_MULTIPLICITY> when embedding libev).
3411		4093
3412	Currently, functions, and static and non-static member functions can be	4094	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	4095	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	4096	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	4097	you need support for other types of functors please contact the author
3416	it).	4098	(preferably after implementing it).
		4099
		4100	For all this to work, your C++ compiler either has to use the same calling
		4101	conventions as your C compiler (for static member functions), or you have
		4102	to embed libev and compile libev itself as C++.
3417		4103
3418	Here is a list of things available in the C<ev> namespace:	4104	Here is a list of things available in the C<ev> namespace:
3419		4105
3420	=over 4	4106	=over 4
3421		4107
…		…
3431	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4117	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
3432		4118
3433	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4119	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>	4120	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	4121	which is called C<ev::sig> to avoid clashes with the C<signal> macro
3436	defines by many implementations.	4122	defined by many implementations.
3437		4123
3438	All of those classes have these methods:	4124	All of those classes have these methods:
3439		4125
3440	=over 4	4126	=over 4
3441		4127
…		…
3503	void operator() (ev::io &w, int revents)	4189	void operator() (ev::io &w, int revents)
3504	{	4190	{
3505	...	4191	...
3506	}	4192	}
3507	}	4193	}
3508		4194
3509	myfunctor f;	4195	myfunctor f;
3510		4196
3511	ev::io w;	4197	ev::io w;
3512	w.set (&f);	4198	w.set (&f);
3513		4199
…		…
3531	Associates a different C<struct ev_loop> with this watcher. You can only	4217	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).	4218	do this when the watcher is inactive (and not pending either).
3533		4219
3534	=item w->set ([arguments])	4220	=item w->set ([arguments])
3535		4221
3536	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this	4222	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	4223	with the same arguments. Either this method or a suitable start method
3538	C counterpart, an active watcher gets automatically stopped and restarted	4224	must be called at least once. Unlike the C counterpart, an active watcher
3539	when reconfiguring it with this method.	4225	gets automatically stopped and restarted when reconfiguring it with this
		4226	method.
		4227
		4228	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4229	clashing with the C<set (loop)> method.
3540		4230
3541	=item w->start ()	4231	=item w->start ()
3542		4232
3543	Starts the watcher. Note that there is no C<loop> argument, as the	4233	Starts the watcher. Note that there is no C<loop> argument, as the
3544	constructor already stores the event loop.	4234	constructor already stores the event loop.
…		…
3574	watchers in the constructor.	4264	watchers in the constructor.
3575		4265
3576	class myclass	4266	class myclass
3577	{	4267	{
3578	ev::io io ; void io_cb (ev::io &w, int revents);	4268	ev::io io ; void io_cb (ev::io &w, int revents);
3579	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);	4269	ev::io io2 ; void io2_cb (ev::io &w, int revents);
3580	ev::idle idle; void idle_cb (ev::idle &w, int revents);	4270	ev::idle idle; void idle_cb (ev::idle &w, int revents);
3581		4271
3582	myclass (int fd)	4272	myclass (int fd)
3583	{	4273	{
3584	io .set <myclass, &myclass::io_cb > (this);	4274	io .set <myclass, &myclass::io_cb > (this);
…		…
3635	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.	4325	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3636		4326
3637	=item D	4327	=item D
3638		4328
3639	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4329	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>.	4330	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
3641		4331
3642	=item Ocaml	4332	=item Ocaml
3643		4333
3644	Erkki Seppala has written Ocaml bindings for libev, to be found at	4334	Erkki Seppala has written Ocaml bindings for libev, to be found at
3645	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	4335	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
…		…
3648		4338
3649	Brian Maher has written a partial interface to libev for lua (at the	4339	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	4340	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
3651	L<http://github.com/brimworks/lua-ev>.	4341	L<http://github.com/brimworks/lua-ev>.
3652		4342
		4343	=item Javascript
		4344
		4345	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4346
		4347	=item Others
		4348
		4349	There are others, and I stopped counting.
		4350
3653	=back	4351	=back
3654		4352
3655		4353
3656	=head1 MACRO MAGIC	4354	=head1 MACRO MAGIC
3657		4355
…		…
3693	suitable for use with C<EV_A>.	4391	suitable for use with C<EV_A>.
3694		4392
3695	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4393	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
3696		4394
3697	Similar to the other two macros, this gives you the value of the default	4395	Similar to the other two macros, this gives you the value of the default
3698	loop, if multiple loops are supported ("ev loop default").	4396	loop, if multiple loops are supported ("ev loop default"). The default loop
		4397	will be initialised if it isn't already initialised.
		4398
		4399	For non-multiplicity builds, these macros do nothing, so you always have
		4400	to initialise the loop somewhere.
3699		4401
3700	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4402	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
3701		4403
3702	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4404	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	4405	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
3770	ev_vars.h	4472	ev_vars.h
3771	ev_wrap.h	4473	ev_wrap.h
3772		4474
3773	ev_win32.c required on win32 platforms only	4475	ev_win32.c required on win32 platforms only
3774		4476
3775	ev_select.c only when select backend is enabled (which is enabled by default)	4477	ev_select.c only when select backend is enabled
3776	ev_poll.c only when poll backend is enabled (disabled by default)	4478	ev_poll.c only when poll backend is enabled
3777	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4479	ev_epoll.c only when the epoll backend is enabled
		4480	ev_linuxaio.c only when the linux aio backend is enabled
3778	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4481	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)	4482	ev_port.c only when the solaris port backend is enabled
3780		4483
3781	F<ev.c> includes the backend files directly when enabled, so you only need	4484	F<ev.c> includes the backend files directly when enabled, so you only need
3782	to compile this single file.	4485	to compile this single file.
3783		4486
3784	=head3 LIBEVENT COMPATIBILITY API	4487	=head3 LIBEVENT COMPATIBILITY API
…		…
3848	supported). It will also not define any of the structs usually found in	4551	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.	4552	F<event.h> that are not directly supported by the libev core alone.
3850		4553
3851	In standalone mode, libev will still try to automatically deduce the	4554	In standalone mode, libev will still try to automatically deduce the
3852	configuration, but has to be more conservative.	4555	configuration, but has to be more conservative.
		4556
		4557	=item EV_USE_FLOOR
		4558
		4559	If defined to be C<1>, libev will use the C<floor ()> function for its
		4560	periodic reschedule calculations, otherwise libev will fall back on a
		4561	portable (slower) implementation. If you enable this, you usually have to
		4562	link against libm or something equivalent. Enabling this when the C<floor>
		4563	function is not available will fail, so the safe default is to not enable
		4564	this.
3853		4565
3854	=item EV_USE_MONOTONIC	4566	=item EV_USE_MONOTONIC
3855		4567
3856	If defined to be C<1>, libev will try to detect the availability of the	4568	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	4569	monotonic clock option at both compile time and runtime. Otherwise no
…		…
3943	If programs implement their own fd to handle mapping on win32, then this	4655	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	4656	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	4657	file descriptors again. Note that the replacement function has to close
3946	the underlying OS handle.	4658	the underlying OS handle.
3947		4659
		4660	=item EV_USE_WSASOCKET
		4661
		4662	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4663	communication socket, which works better in some environments. Otherwise,
		4664	the normal C<socket> function will be used, which works better in other
		4665	environments.
		4666
3948	=item EV_USE_POLL	4667	=item EV_USE_POLL
3949		4668
3950	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4669	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	4670	backend. Otherwise it will be enabled on non-win32 platforms. It
3952	takes precedence over select.	4671	takes precedence over select.
…		…
3956	If defined to be C<1>, libev will compile in support for the Linux	4675	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,	4676	C<epoll>(7) backend. Its availability will be detected at runtime,
3958	otherwise another method will be used as fallback. This is the preferred	4677	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	4678	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.	4679	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4680
		4681	=item EV_USE_LINUXAIO
		4682
		4683	If defined to be C<1>, libev will compile in support for the Linux
		4684	aio backend. Due to it's currenbt limitations it has to be requested
		4685	explicitly. If undefined, it will be enabled on linux, otherwise
		4686	disabled.
3961		4687
3962	=item EV_USE_KQUEUE	4688	=item EV_USE_KQUEUE
3963		4689
3964	If defined to be C<1>, libev will compile in support for the BSD style	4690	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,	4691	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	4713	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	4714	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	4715	be detected at runtime. If undefined, it will be enabled if the headers
3990	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4716	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
3991		4717
		4718	=item EV_NO_SMP
		4719
		4720	If defined to be C<1>, libev will assume that memory is always coherent
		4721	between threads, that is, threads can be used, but threads never run on
		4722	different cpus (or different cpu cores). This reduces dependencies
		4723	and makes libev faster.
		4724
		4725	=item EV_NO_THREADS
		4726
		4727	If defined to be C<1>, libev will assume that it will never be called from
		4728	different threads (that includes signal handlers), which is a stronger
		4729	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4730	libev faster.
		4731
3992	=item EV_ATOMIC_T	4732	=item EV_ATOMIC_T
3993		4733
3994	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4734	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	4735	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	4736	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"	4737	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.	4738	handler "locking" as well as for signal and thread safety in C<ev_async>
		4739	watchers.
3999		4740
4000	In the absence of this define, libev will use C<sig_atomic_t volatile>	4741	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.	4742	(from F<signal.h>), which is usually good enough on most platforms.
4002		4743
4003	=item EV_H (h)	4744	=item EV_H (h)
…		…
4030	will have the C<struct ev_loop *> as first argument, and you can create	4771	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	4772	additional independent event loops. Otherwise there will be no support
4032	for multiple event loops and there is no first event loop pointer	4773	for multiple event loops and there is no first event loop pointer
4033	argument. Instead, all functions act on the single default loop.	4774	argument. Instead, all functions act on the single default loop.
4034		4775
		4776	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4777	default loop when multiplicity is switched off - you always have to
		4778	initialise the loop manually in this case.
		4779
4035	=item EV_MINPRI	4780	=item EV_MINPRI
4036		4781
4037	=item EV_MAXPRI	4782	=item EV_MAXPRI
4038		4783
4039	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4784	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
4075	#define EV_USE_POLL 1	4820	#define EV_USE_POLL 1
4076	#define EV_CHILD_ENABLE 1	4821	#define EV_CHILD_ENABLE 1
4077	#define EV_ASYNC_ENABLE 1	4822	#define EV_ASYNC_ENABLE 1
4078		4823
4079	The actual value is a bitset, it can be a combination of the following	4824	The actual value is a bitset, it can be a combination of the following
4080	values:	4825	values (by default, all of these are enabled):
4081		4826
4082	=over 4	4827	=over 4
4083		4828
4084	=item C<1> - faster/larger code	4829	=item C<1> - faster/larger code
4085		4830
…		…
4089	code size by roughly 30% on amd64).	4834	code size by roughly 30% on amd64).
4090		4835
4091	When optimising for size, use of compiler flags such as C<-Os> with	4836	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	4837	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
4093	assertions.	4838	assertions.
		4839
		4840	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4841	(e.g. gcc with C<-Os>).
4094		4842
4095	=item C<2> - faster/larger data structures	4843	=item C<2> - faster/larger data structures
4096		4844
4097	Replaces the small 2-heap for timer management by a faster 4-heap, larger	4845	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	4846	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	4847	and can additionally have an effect on the size of data structures at
4100	runtime.	4848	runtime.
4101		4849
		4850	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4851	(e.g. gcc with C<-Os>).
		4852
4102	=item C<4> - full API configuration	4853	=item C<4> - full API configuration
4103		4854
4104	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and	4855	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
4105	enables multiplicity (C<EV_MULTIPLICITY>=1).	4856	enables multiplicity (C<EV_MULTIPLICITY>=1).
4106		4857
…		…
4136		4887
4137	With an intelligent-enough linker (gcc+binutils are intelligent enough	4888	With an intelligent-enough linker (gcc+binutils are intelligent enough
4138	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by	4889	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	4890	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.	4891	I/O watcher then might come out at only 5Kb.
		4892
		4893	=item EV_API_STATIC
		4894
		4895	If this symbol is defined (by default it is not), then all identifiers
		4896	will have static linkage. This means that libev will not export any
		4897	identifiers, and you cannot link against libev anymore. This can be useful
		4898	when you embed libev, only want to use libev functions in a single file,
		4899	and do not want its identifiers to be visible.
		4900
		4901	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4902	wants to use libev.
		4903
		4904	This option only works when libev is compiled with a C compiler, as C++
		4905	doesn't support the required declaration syntax.
4141		4906
4142	=item EV_AVOID_STDIO	4907	=item EV_AVOID_STDIO
4143		4908
4144	If this is set to C<1> at compiletime, then libev will avoid using stdio	4909	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	4910	functions (printf, scanf, perror etc.). This will increase the code size
…		…
4289	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	5054	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4290		5055
4291	#include "ev_cpp.h"	5056	#include "ev_cpp.h"
4292	#include "ev.c"	5057	#include "ev.c"
4293		5058
4294	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	5059	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4295		5060
4296	=head2 THREADS AND COROUTINES	5061	=head2 THREADS AND COROUTINES
4297		5062
4298	=head3 THREADS	5063	=head3 THREADS
4299		5064
…		…
4350	default loop and triggering an C<ev_async> watcher from the default loop	5115	default loop and triggering an C<ev_async> watcher from the default loop
4351	watcher callback into the event loop interested in the signal.	5116	watcher callback into the event loop interested in the signal.
4352		5117
4353	=back	5118	=back
4354		5119
4355	=head4 THREAD LOCKING EXAMPLE	5120	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		5121
4493	=head3 COROUTINES	5122	=head3 COROUTINES
4494		5123
4495	Libev is very accommodating to coroutines ("cooperative threads"):	5124	Libev is very accommodating to coroutines ("cooperative threads"):
4496	libev fully supports nesting calls to its functions from different	5125	libev fully supports nesting calls to its functions from different
…		…
4661	requires, and its I/O model is fundamentally incompatible with the POSIX	5290	requires, and its I/O model is fundamentally incompatible with the POSIX
4662	model. Libev still offers limited functionality on this platform in	5291	model. Libev still offers limited functionality on this platform in
4663	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5292	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
4664	descriptors. This only applies when using Win32 natively, not when using	5293	descriptors. This only applies when using Win32 natively, not when using
4665	e.g. cygwin. Actually, it only applies to the microsofts own compilers,	5294	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4666	as every compielr comes with a slightly differently broken/incompatible	5295	as every compiler comes with a slightly differently broken/incompatible
4667	environment.	5296	environment.
4668		5297
4669	Lifting these limitations would basically require the full	5298	Lifting these limitations would basically require the full
4670	re-implementation of the I/O system. If you are into this kind of thing,	5299	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	5300	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	5394	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	5395	assumes that the same (machine) code can be used to call any watcher
4767	callback: The watcher callbacks have different type signatures, but libev	5396	callback: The watcher callbacks have different type signatures, but libev
4768	calls them using an C<ev_watcher *> internally.	5397	calls them using an C<ev_watcher *> internally.
4769		5398
		5399	=item null pointers and integer zero are represented by 0 bytes
		5400
		5401	Libev uses C<memset> to initialise structs and arrays to C<0> bytes, and
		5402	relies on this setting pointers and integers to null.
		5403
4770	=item pointer accesses must be thread-atomic	5404	=item pointer accesses must be thread-atomic
4771		5405
4772	Accessing a pointer value must be atomic, it must both be readable and	5406	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.	5407	writable in one piece - this is the case on all current architectures.
4774		5408
…		…
4787	thread" or will block signals process-wide, both behaviours would	5421	thread" or will block signals process-wide, both behaviours would
4788	be compatible with libev. Interaction between C<sigprocmask> and	5422	be compatible with libev. Interaction between C<sigprocmask> and
4789	C<pthread_sigmask> could complicate things, however.	5423	C<pthread_sigmask> could complicate things, however.
4790		5424
4791	The most portable way to handle signals is to block signals in all threads	5425	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	5426	except the initial one, and run the signal handling loop in the initial
4793	well.	5427	thread as well.
4794		5428
4795	=item C<long> must be large enough for common memory allocation sizes	5429	=item C<long> must be large enough for common memory allocation sizes
4796		5430
4797	To improve portability and simplify its API, libev uses C<long> internally	5431	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	5432	instead of C<size_t> when allocating its data structures. On non-POSIX
…		…
4804		5438
4805	The type C<double> is used to represent timestamps. It is required to	5439	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	5440	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	5441	good enough for at least into the year 4000 with millisecond accuracy
4808	(the design goal for libev). This requirement is overfulfilled by	5442	(the design goal for libev). This requirement is overfulfilled by
4809	implementations using IEEE 754, which is basically all existing ones. With	5443	implementations using IEEE 754, which is basically all existing ones.
		5444
4810	IEEE 754 doubles, you get microsecond accuracy until at least 2200.	5445	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5446	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5447	is either obsolete or somebody patched it to use C<long double> or
		5448	something like that, just kidding).
4811		5449
4812	=back	5450	=back
4813		5451
4814	If you know of other additional requirements drop me a note.	5452	If you know of other additional requirements drop me a note.
4815		5453
…		…
4877	=item Processing ev_async_send: O(number_of_async_watchers)	5515	=item Processing ev_async_send: O(number_of_async_watchers)
4878		5516
4879	=item Processing signals: O(max_signal_number)	5517	=item Processing signals: O(max_signal_number)
4880		5518
4881	Sending involves a system call I<iff> there were no other C<ev_async_send>	5519	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	5520	calls in the current loop iteration and the loop is currently
		5521	blocked. Checking for async and signal events involves iterating over all
4883	involves iterating over all running async watchers or all signal numbers.	5522	running async watchers or all signal numbers.
4884		5523
4885	=back	5524	=back
4886		5525
4887		5526
4888	=head1 PORTING FROM LIBEV 3.X TO 4.X	5527	=head1 PORTING FROM LIBEV 3.X TO 4.X
…		…
4897	=over 4	5536	=over 4
4898		5537
4899	=item C<EV_COMPAT3> backwards compatibility mechanism	5538	=item C<EV_COMPAT3> backwards compatibility mechanism
4900		5539
4901	The backward compatibility mechanism can be controlled by	5540	The backward compatibility mechanism can be controlled by
4902	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>	5541	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
4903	section.	5542	section.
4904		5543
4905	=item C<ev_default_destroy> and C<ev_default_fork> have been removed	5544	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
4906		5545
4907	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:	5546	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
…		…
4950	=over 4	5589	=over 4
4951		5590
4952	=item active	5591	=item active
4953		5592
4954	A watcher is active as long as it has been started and not yet stopped.	5593	A watcher is active as long as it has been started and not yet stopped.
4955	See L<WATCHER STATES> for details.	5594	See L</WATCHER STATES> for details.
4956		5595
4957	=item application	5596	=item application
4958		5597
4959	In this document, an application is whatever is using libev.	5598	In this document, an application is whatever is using libev.
4960		5599
…		…
4996	watchers and events.	5635	watchers and events.
4997		5636
4998	=item pending	5637	=item pending
4999		5638
5000	A watcher is pending as soon as the corresponding event has been	5639	A watcher is pending as soon as the corresponding event has been
5001	detected. See L<WATCHER STATES> for details.	5640	detected. See L</WATCHER STATES> for details.
5002		5641
5003	=item real time	5642	=item real time
5004		5643
5005	The physical time that is observed. It is apparently strictly monotonic :)	5644	The physical time that is observed. It is apparently strictly monotonic :)
5006		5645
5007	=item wall-clock time	5646	=item wall-clock time
5008		5647
5009	The time and date as shown on clocks. Unlike real time, it can actually	5648	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	5649	be wrong and jump forwards and backwards, e.g. when you adjust your
5011	clock.	5650	clock.
5012		5651
5013	=item watcher	5652	=item watcher
5014		5653
5015	A data structure that describes interest in certain events. Watchers need	5654	A data structure that describes interest in certain events. Watchers need
…		…
5018	=back	5657	=back
5019		5658
5020	=head1 AUTHOR	5659	=head1 AUTHOR
5021		5660
5022	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael	5661	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5023	Magnusson and Emanuele Giaquinta.	5662	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
5024		5663

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