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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
		590	the epoll set), and generally sounds too good to be true. Because, this
		591	being the linux kernel, of course it suffers from a whole new set of
		592	limitations.
		593
		594	For one, it is not easily embeddable (but probably could be done using
		595	an event fd at some extra overhead). It also is subject to a system wide
		596	limit that can be configured in F</proc/sys/fs/aio-max-nr> - each loop
		597	currently requires C<61> of this number. If no aio requests are left, this
		598	backend will be skipped during initialisation.
		599
		600	Most problematic in practise, however, is that not all file descriptors
		601	work with it. For example, in linux 5.1, tcp sockets, pipes, event fds,
		602	files, F</dev/null> and a few others are supported, but ttys do not work
		603	properly (a known bug that the kernel developers don't care about, see
		604	L<https://lore.kernel.org/patchwork/patch/1047453/>), so this is not
		605	(yet?) a generic event polling interface.
		606
		607	To work around this latter problem, the current version of libev uses
		608	epoll as a fallback for file deescriptor types that do not work. Epoll
		609	is used in, kind of, slow mode that hopefully avoids most of its design
		610	problems and requires 1-3 extra syscalls per active fd every iteration.
505		611
506	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	612	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
507	C<EVBACKEND_POLL>.	613	C<EVBACKEND_POLL>.
508		614
509	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	615	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
…		…
524		630
525	It scales in the same way as the epoll backend, but the interface to the	631	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	632	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	633	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	634	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	635	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	636	might have to leak fd's on fork, but it's more sane than epoll) and it
531	cases	637	drops fds silently in similarly hard-to-detect cases.
532		638
533	This backend usually performs well under most conditions.	639	This backend usually performs well under most conditions.
534		640
535	While nominally embeddable in other event loops, this doesn't work	641	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	642	everywhere, so you might need to test for this. And since it is broken
…		…
553	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	659	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
554		660
555	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	661	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)).	662	it's really slow, but it still scales very well (O(active_fds)).
557		663
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	664	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	665	file descriptor per loop iteration. For small and medium numbers of file
564	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	666	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
565	might perform better.	667	might perform better.
566		668
567	On the positive side, with the exception of the spurious readiness	669	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	670	specification in all tests and is fully embeddable, which is a rare feat
570	OS-specific backends (I vastly prefer correctness over speed hacks).	671	among the OS-specific backends (I vastly prefer correctness over speed
		672	hacks).
		673
		674	On the negative side, the interface is I<bizarre> - so bizarre that
		675	even sun itself gets it wrong in their code examples: The event polling
		676	function sometimes returns events to the caller even though an error
		677	occurred, but with no indication whether it has done so or not (yes, it's
		678	even documented that way) - deadly for edge-triggered interfaces where you
		679	absolutely have to know whether an event occurred or not because you have
		680	to re-arm the watcher.
		681
		682	Fortunately libev seems to be able to work around these idiocies.
571		683
572	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	684	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
573	C<EVBACKEND_POLL>.	685	C<EVBACKEND_POLL>.
574		686
575	=item C<EVBACKEND_ALL>	687	=item C<EVBACKEND_ALL>
576		688
577	Try all backends (even potentially broken ones that wouldn't be tried	689	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	690	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
579	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	691	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
580		692
581	It is definitely not recommended to use this flag.	693	It is definitely not recommended to use this flag, use whatever
		694	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		695	at all.
		696
		697	=item C<EVBACKEND_MASK>
		698
		699	Not a backend at all, but a mask to select all backend bits from a
		700	C<flags> value, in case you want to mask out any backends from a flags
		701	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
582		702
583	=back	703	=back
584		704
585	If one or more of the backend flags are or'ed into the flags value,	705	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	706	then only these backends will be tried (in the reverse order as listed
…		…
595		715
596	Example: Use whatever libev has to offer, but make sure that kqueue is	716	Example: Use whatever libev has to offer, but make sure that kqueue is
597	used if available.	717	used if available.
598		718
599	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);	719	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		720
		721	Example: Similarly, on linux, you mgiht want to take advantage of the
		722	linux aio backend if possible, but fall back to something else if that
		723	isn't available.
		724
		725	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_LINUXAIO);
600		726
601	=item ev_loop_destroy (loop)	727	=item ev_loop_destroy (loop)
602		728
603	Destroys an event loop object (frees all memory and kernel state	729	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	730	etc.). None of the active event watchers will be stopped in the normal
…		…
615	This function is normally used on loop objects allocated by	741	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	742	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.	743	C<ev_default_loop>, in which case it is not thread-safe.
618		744
619	Note that it is not advisable to call this function on the default loop	745	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.	746	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>	747	If you need dynamically allocated loops it is better to use C<ev_loop_new>
622	and C<ev_loop_destroy>.	748	and C<ev_loop_destroy>.
623		749
624	=item ev_loop_fork (loop)	750	=item ev_loop_fork (loop)
625		751
626	This function sets a flag that causes subsequent C<ev_run> iterations to	752	This function sets a flag that causes subsequent C<ev_run> iterations
627	reinitialise the kernel state for backends that have one. Despite the	753	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	754	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	755	watchers (except inside an C<ev_prepare> callback), but it makes most
		756	sense after forking, in the child process. You I<must> call it (or use
630	child before resuming or calling C<ev_run>.	757	C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.
631		758
		759	In addition, if you want to reuse a loop (via this function or
		760	C<EVFLAG_FORKCHECK>), you I<also> have to ignore C<SIGPIPE>.
		761
632	Again, you I<have> to call it on I<any> loop that you want to re-use after	762	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	763	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	764	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
635	during fork.	765	during fork.
636		766
637	On the other hand, you only need to call this function in the child	767	On the other hand, you only need to call this function in the child
…		…
673	prepare and check phases.	803	prepare and check phases.
674		804
675	=item unsigned int ev_depth (loop)	805	=item unsigned int ev_depth (loop)
676		806
677	Returns the number of times C<ev_run> was entered minus the number of	807	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.	808	times C<ev_run> was exited normally, in other words, the recursion depth.
679		809
680	Outside C<ev_run>, this number is zero. In a callback, this number is	810	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),	811	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
682	in which case it is higher.	812	in which case it is higher.
683		813
684	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread	814	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	815	throwing an exception etc.), doesn't count as "exit" - consider this
686	ungentleman-like behaviour unless it's really convenient.	816	as a hint to avoid such ungentleman-like behaviour unless it's really
		817	convenient, in which case it is fully supported.
687		818
688	=item unsigned int ev_backend (loop)	819	=item unsigned int ev_backend (loop)
689		820
690	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	821	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
691	use.	822	use.
…		…
706		837
707	This function is rarely useful, but when some event callback runs for a	838	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	839	very long time without entering the event loop, updating libev's idea of
709	the current time is a good idea.	840	the current time is a good idea.
710		841
711	See also L<The special problem of time updates> in the C<ev_timer> section.	842	See also L</The special problem of time updates> in the C<ev_timer> section.
712		843
713	=item ev_suspend (loop)	844	=item ev_suspend (loop)
714		845
715	=item ev_resume (loop)	846	=item ev_resume (loop)
716		847
…		…
734	without a previous call to C<ev_suspend>.	865	without a previous call to C<ev_suspend>.
735		866
736	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the	867	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
737	event loop time (see C<ev_now_update>).	868	event loop time (see C<ev_now_update>).
738		869
739	=item ev_run (loop, int flags)	870	=item bool ev_run (loop, int flags)
740		871
741	Finally, this is it, the event handler. This function usually is called	872	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	873	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	874	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	875	the watcher callbacks, and then repeat the whole process indefinitely: This
745	is why event loops are called I<loops>.	876	is why event loops are called I<loops>.
746		877
747	If the flags argument is specified as C<0>, it will keep handling events	878	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	879	until either no event watchers are active anymore or C<ev_break> was
749	called.	880	called.
		881
		882	The return value is false if there are no more active watchers (which
		883	usually means "all jobs done" or "deadlock"), and true in all other cases
		884	(which usually means " you should call C<ev_run> again").
750		885
751	Please note that an explicit C<ev_break> is usually better than	886	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	887	relying on all watchers to be stopped when deciding when a program has
753	finished (especially in interactive programs), but having a program	888	finished (especially in interactive programs), but having a program
754	that automatically loops as long as it has to and no longer by virtue	889	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	890	of relying on its watchers stopping correctly, that is truly a thing of
756	beauty.	891	beauty.
757		892
		893	This function is I<mostly> exception-safe - you can break out of a
		894	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		895	exception and so on. This does not decrement the C<ev_depth> value, nor
		896	will it clear any outstanding C<EVBREAK_ONE> breaks.
		897
758	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle	898	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	899	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	900	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	901	iteration of the loop. This is sometimes useful to poll and handle new
762	events while doing lengthy calculations, to keep the program responsive.	902	events while doing lengthy calculations, to keep the program responsive.
…		…
771	This is useful if you are waiting for some external event in conjunction	911	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	912	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	913	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.	914	usually a better approach for this kind of thing.
775		915
776	Here are the gory details of what C<ev_run> does:	916	Here are the gory details of what C<ev_run> does (this is for your
		917	understanding, not a guarantee that things will work exactly like this in
		918	future versions):
777		919
778	- Increment loop depth.	920	- Increment loop depth.
779	- Reset the ev_break status.	921	- Reset the ev_break status.
780	- Before the first iteration, call any pending watchers.	922	- Before the first iteration, call any pending watchers.
781	LOOP:	923	LOOP:
…		…
814	anymore.	956	anymore.
815		957
816	... queue jobs here, make sure they register event watchers as long	958	... 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..)	959	... as they still have work to do (even an idle watcher will do..)
818	ev_run (my_loop, 0);	960	ev_run (my_loop, 0);
819	... jobs done or somebody called unloop. yeah!	961	... jobs done or somebody called break. yeah!
820		962
821	=item ev_break (loop, how)	963	=item ev_break (loop, how)
822		964
823	Can be used to make a call to C<ev_run> return early (but only after it	965	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	966	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	967	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.	968	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
827		969
828	This "unloop state" will be cleared when entering C<ev_run> again.	970	This "break state" will be cleared on the next call to C<ev_run>.
829		971
830	It is safe to call C<ev_break> from outside any C<ev_run> calls. ##TODO##	972	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		973	which case it will have no effect.
831		974
832	=item ev_ref (loop)	975	=item ev_ref (loop)
833		976
834	=item ev_unref (loop)	977	=item ev_unref (loop)
835		978
…		…
856	running when nothing else is active.	999	running when nothing else is active.
857		1000
858	ev_signal exitsig;	1001	ev_signal exitsig;
859	ev_signal_init (&exitsig, sig_cb, SIGINT);	1002	ev_signal_init (&exitsig, sig_cb, SIGINT);
860	ev_signal_start (loop, &exitsig);	1003	ev_signal_start (loop, &exitsig);
861	evf_unref (loop);	1004	ev_unref (loop);
862		1005
863	Example: For some weird reason, unregister the above signal handler again.	1006	Example: For some weird reason, unregister the above signal handler again.
864		1007
865	ev_ref (loop);	1008	ev_ref (loop);
866	ev_signal_stop (loop, &exitsig);	1009	ev_signal_stop (loop, &exitsig);
…		…
886	overhead for the actual polling but can deliver many events at once.	1029	overhead for the actual polling but can deliver many events at once.
887		1030
888	By setting a higher I<io collect interval> you allow libev to spend more	1031	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,	1032	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	1033	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	1034	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	1035	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	1036	sleep time ensures that libev will not poll for I/O events more often then
894	once per this interval, on average.	1037	once per this interval, on average (as long as the host time resolution is
		1038	good enough).
895		1039
896	Likewise, by setting a higher I<timeout collect interval> you allow libev	1040	Likewise, by setting a higher I<timeout collect interval> you allow libev
897	to spend more time collecting timeouts, at the expense of increased	1041	to spend more time collecting timeouts, at the expense of increased
898	latency/jitter/inexactness (the watcher callback will be called	1042	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	1043	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.).	1089	invoke the actual watchers inside another context (another thread etc.).
946		1090
947	If you want to reset the callback, use C<ev_invoke_pending> as new	1091	If you want to reset the callback, use C<ev_invoke_pending> as new
948	callback.	1092	callback.
949		1093
950	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))	1094	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
951		1095
952	Sometimes you want to share the same loop between multiple threads. This	1096	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	1097	can be done relatively simply by putting mutex_lock/unlock calls around
954	each call to a libev function.	1098	each call to a libev function.
955		1099
956	However, C<ev_run> can run an indefinite time, so it is not feasible	1100	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	1101	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	1102	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.	1103	I<release> and I<acquire> callbacks on the loop.
960		1104
961	When set, then C<release> will be called just before the thread is	1105	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	1106	suspended waiting for new events, and C<acquire> is called just
963	afterwards.	1107	afterwards.
…		…
978	See also the locking example in the C<THREADS> section later in this	1122	See also the locking example in the C<THREADS> section later in this
979	document.	1123	document.
980		1124
981	=item ev_set_userdata (loop, void *data)	1125	=item ev_set_userdata (loop, void *data)
982		1126
983	=item ev_userdata (loop)	1127	=item void *ev_userdata (loop)
984		1128
985	Set and retrieve a single C<void *> associated with a loop. When	1129	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	1130	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
987	C<0.>	1131	C<0>.
988		1132
989	These two functions can be used to associate arbitrary data with a loop,	1133	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	1134	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	1135	C<acquire> callbacks described above, but of course can be (ab-)used for
992	any other purpose as well.	1136	any other purpose as well.
…		…
1103		1247
1104	=item C<EV_PREPARE>	1248	=item C<EV_PREPARE>
1105		1249
1106	=item C<EV_CHECK>	1250	=item C<EV_CHECK>
1107		1251
1108	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts	1252	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	1253	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	1254	just after C<ev_run> has gathered them, but before it queues any callbacks
		1255	for any received events. That means C<ev_prepare> watchers are the last
		1256	watchers invoked before the event loop sleeps or polls for new events, and
		1257	C<ev_check> watchers will be invoked before any other watchers of the same
		1258	or lower priority within an event loop iteration.
		1259
1111	received events. Callbacks of both watcher types can start and stop as	1260	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	1261	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	1262	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
1114	C<ev_run> from blocking).	1263	blocking).
1115		1264
1116	=item C<EV_EMBED>	1265	=item C<EV_EMBED>
1117		1266
1118	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1267	The embedded event loop specified in the C<ev_embed> watcher needs attention.
1119		1268
…		…
1154	programs, though, as the fd could already be closed and reused for another	1303	programs, though, as the fd could already be closed and reused for another
1155	thing, so beware.	1304	thing, so beware.
1156		1305
1157	=back	1306	=back
1158		1307
		1308	=head2 GENERIC WATCHER FUNCTIONS
		1309
		1310	=over 4
		1311
		1312	=item C<ev_init> (ev_TYPE *watcher, callback)
		1313
		1314	This macro initialises the generic portion of a watcher. The contents
		1315	of the watcher object can be arbitrary (so C<malloc> will do). Only
		1316	the generic parts of the watcher are initialised, you I<need> to call
		1317	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		1318	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		1319	which rolls both calls into one.
		1320
		1321	You can reinitialise a watcher at any time as long as it has been stopped
		1322	(or never started) and there are no pending events outstanding.
		1323
		1324	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
		1325	int revents)>.
		1326
		1327	Example: Initialise an C<ev_io> watcher in two steps.
		1328
		1329	ev_io w;
		1330	ev_init (&w, my_cb);
		1331	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1332
		1333	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
		1334
		1335	This macro initialises the type-specific parts of a watcher. You need to
		1336	call C<ev_init> at least once before you call this macro, but you can
		1337	call C<ev_TYPE_set> any number of times. You must not, however, call this
		1338	macro on a watcher that is active (it can be pending, however, which is a
		1339	difference to the C<ev_init> macro).
		1340
		1341	Although some watcher types do not have type-specific arguments
		1342	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		1343
		1344	See C<ev_init>, above, for an example.
		1345
		1346	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		1347
		1348	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		1349	calls into a single call. This is the most convenient method to initialise
		1350	a watcher. The same limitations apply, of course.
		1351
		1352	Example: Initialise and set an C<ev_io> watcher in one step.
		1353
		1354	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1355
		1356	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
		1357
		1358	Starts (activates) the given watcher. Only active watchers will receive
		1359	events. If the watcher is already active nothing will happen.
		1360
		1361	Example: Start the C<ev_io> watcher that is being abused as example in this
		1362	whole section.
		1363
		1364	ev_io_start (EV_DEFAULT_UC, &w);
		1365
		1366	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
		1367
		1368	Stops the given watcher if active, and clears the pending status (whether
		1369	the watcher was active or not).
		1370
		1371	It is possible that stopped watchers are pending - for example,
		1372	non-repeating timers are being stopped when they become pending - but
		1373	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
		1374	pending. If you want to free or reuse the memory used by the watcher it is
		1375	therefore a good idea to always call its C<ev_TYPE_stop> function.
		1376
		1377	=item bool ev_is_active (ev_TYPE *watcher)
		1378
		1379	Returns a true value iff the watcher is active (i.e. it has been started
		1380	and not yet been stopped). As long as a watcher is active you must not modify
		1381	it.
		1382
		1383	=item bool ev_is_pending (ev_TYPE *watcher)
		1384
		1385	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		1386	events but its callback has not yet been invoked). As long as a watcher
		1387	is pending (but not active) you must not call an init function on it (but
		1388	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		1389	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1390	it).
		1391
		1392	=item callback ev_cb (ev_TYPE *watcher)
		1393
		1394	Returns the callback currently set on the watcher.
		1395
		1396	=item ev_set_cb (ev_TYPE *watcher, callback)
		1397
		1398	Change the callback. You can change the callback at virtually any time
		1399	(modulo threads).
		1400
		1401	=item ev_set_priority (ev_TYPE *watcher, int priority)
		1402
		1403	=item int ev_priority (ev_TYPE *watcher)
		1404
		1405	Set and query the priority of the watcher. The priority is a small
		1406	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1407	(default: C<-2>). Pending watchers with higher priority will be invoked
		1408	before watchers with lower priority, but priority will not keep watchers
		1409	from being executed (except for C<ev_idle> watchers).
		1410
		1411	If you need to suppress invocation when higher priority events are pending
		1412	you need to look at C<ev_idle> watchers, which provide this functionality.
		1413
		1414	You I<must not> change the priority of a watcher as long as it is active or
		1415	pending.
		1416
		1417	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1418	fine, as long as you do not mind that the priority value you query might
		1419	or might not have been clamped to the valid range.
		1420
		1421	The default priority used by watchers when no priority has been set is
		1422	always C<0>, which is supposed to not be too high and not be too low :).
		1423
		1424	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1425	priorities.
		1426
		1427	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1428
		1429	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1430	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1431	can deal with that fact, as both are simply passed through to the
		1432	callback.
		1433
		1434	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1435
		1436	If the watcher is pending, this function clears its pending status and
		1437	returns its C<revents> bitset (as if its callback was invoked). If the
		1438	watcher isn't pending it does nothing and returns C<0>.
		1439
		1440	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1441	callback to be invoked, which can be accomplished with this function.
		1442
		1443	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1444
		1445	Feeds the given event set into the event loop, as if the specified event
		1446	had happened for the specified watcher (which must be a pointer to an
		1447	initialised but not necessarily started event watcher). Obviously you must
		1448	not free the watcher as long as it has pending events.
		1449
		1450	Stopping the watcher, letting libev invoke it, or calling
		1451	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1452	not started in the first place.
		1453
		1454	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1455	functions that do not need a watcher.
		1456
		1457	=back
		1458
		1459	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
		1460	OWN COMPOSITE WATCHERS> idioms.
		1461
1159	=head2 WATCHER STATES	1462	=head2 WATCHER STATES
1160		1463
1161	There are various watcher states mentioned throughout this manual -	1464	There are various watcher states mentioned throughout this manual -
1162	active, pending and so on. In this section these states and the rules to	1465	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	1466	transition between them will be described in more detail - and while these
1164	rules might look complicated, they usually do "the right thing".	1467	rules might look complicated, they usually do "the right thing".
1165		1468
1166	=over 4	1469	=over 4
1167		1470
1168	=item initialiased	1471	=item initialised
1169		1472
1170	Before a watcher can be registered with the event looop it has to be	1473	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	1474	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.	1475	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1173		1476
1174	In this state it is simply some block of memory that is suitable for use	1477	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.	1478	use in an event loop. It can be moved around, freed, reused etc. at
		1479	will - as long as you either keep the memory contents intact, or call
		1480	C<ev_TYPE_init> again.
1176		1481
1177	=item started/running/active	1482	=item started/running/active
1178		1483
1179	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes	1484	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	1485	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	1513	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	1514	of whether it was active or not, so stopping a watcher explicitly before
1210	freeing it is often a good idea.	1515	freeing it is often a good idea.
1211		1516
1212	While stopped (and not pending) the watcher is essentially in the	1517	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	1518	initialised state, that is, it can be reused, moved, modified in any way
1214	you wish.	1519	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1520	it again).
1215		1521
1216	=back	1522	=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		1523
1435	=head2 WATCHER PRIORITY MODELS	1524	=head2 WATCHER PRIORITY MODELS
1436		1525
1437	Many event loops support I<watcher priorities>, which are usually small	1526	Many event loops support I<watcher priorities>, which are usually small
1438	integers that influence the ordering of event callback invocation	1527	integers that influence the ordering of event callback invocation
…		…
1565	In general you can register as many read and/or write event watchers per	1654	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	1655	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	1656	descriptors to non-blocking mode is also usually a good idea (but not
1568	required if you know what you are doing).	1657	required if you know what you are doing).
1569		1658
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	1659	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	1660	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	1661	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	1662	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	1663	with a relatively standard program structure. Thus it is best to always
1581	this situation even with a relatively standard program structure. Thus	1664	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.	1665	preferable to a program hanging until some data arrives.
1584		1666
1585	If you cannot run the fd in non-blocking mode (for example you should	1667	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	1668	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	1669	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	1670	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	1671	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	1672	use C<SIGALRM> and an interval timer, just to be sure you won't block
1591	indefinitely.	1673	indefinitely.
1592		1674
1593	But really, best use non-blocking mode.	1675	But really, best use non-blocking mode.
1594		1676
1595	=head3 The special problem of disappearing file descriptors	1677	=head3 The special problem of disappearing file descriptors
1596		1678
1597	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1679	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,	1680	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	1681	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	1682	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	1683	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	1684	is registered with libev, there is no efficient way to see that this is,
1603	fact, a different file descriptor.	1685	in fact, a different file descriptor.
1604		1686
1605	To avoid having to explicitly tell libev about such cases, libev follows	1687	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	1688	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	1689	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	1690	it is assumed that the file descriptor stays the same. That means that
…		…
1622		1704
1623	There is no workaround possible except not registering events	1705	There is no workaround possible except not registering events
1624	for potentially C<dup ()>'ed file descriptors, or to resort to	1706	for potentially C<dup ()>'ed file descriptors, or to resort to
1625	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1707	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1626		1708
		1709	=head3 The special problem of files
		1710
		1711	Many people try to use C<select> (or libev) on file descriptors
		1712	representing files, and expect it to become ready when their program
		1713	doesn't block on disk accesses (which can take a long time on their own).
		1714
		1715	However, this cannot ever work in the "expected" way - you get a readiness
		1716	notification as soon as the kernel knows whether and how much data is
		1717	there, and in the case of open files, that's always the case, so you
		1718	always get a readiness notification instantly, and your read (or possibly
		1719	write) will still block on the disk I/O.
		1720
		1721	Another way to view it is that in the case of sockets, pipes, character
		1722	devices and so on, there is another party (the sender) that delivers data
		1723	on its own, but in the case of files, there is no such thing: the disk
		1724	will not send data on its own, simply because it doesn't know what you
		1725	wish to read - you would first have to request some data.
		1726
		1727	Since files are typically not-so-well supported by advanced notification
		1728	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1729	to files, even though you should not use it. The reason for this is
		1730	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1731	usually a tty, often a pipe, but also sometimes files or special devices
		1732	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1733	F</dev/urandom>), and even though the file might better be served with
		1734	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1735	it "just works" instead of freezing.
		1736
		1737	So avoid file descriptors pointing to files when you know it (e.g. use
		1738	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1739	when you rarely read from a file instead of from a socket, and want to
		1740	reuse the same code path.
		1741
1627	=head3 The special problem of fork	1742	=head3 The special problem of fork
1628		1743
1629	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1744	Some backends (epoll, kqueue, probably linuxaio) do not support C<fork ()>
1630	useless behaviour. Libev fully supports fork, but needs to be told about	1745	at all or exhibit useless behaviour. Libev fully supports fork, but needs
1631	it in the child.	1746	to be told about it in the child if you want to continue to use it in the
		1747	child.
1632		1748
1633	To support fork in your programs, you either have to call	1749	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,	1750	()> 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	1751	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1636	C<EVBACKEND_POLL>.
1637		1752
1638	=head3 The special problem of SIGPIPE	1753	=head3 The special problem of SIGPIPE
1639		1754
1640	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1755	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	1756	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	1854	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1740	monotonic clock option helps a lot here).	1855	monotonic clock option helps a lot here).
1741		1856
1742	The callback is guaranteed to be invoked only I<after> its timeout has	1857	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	1858	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	1859	might introduce a small delay, see "the special problem of being too
		1860	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	1861	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	1862	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).	1863	longer true when a callback calls C<ev_run> recursively).
1748		1864
1749	=head3 Be smart about timeouts	1865	=head3 Be smart about timeouts
1750		1866
1751	Many real-world problems involve some kind of timeout, usually for error	1867	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,	1868	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1827		1943
1828	In this case, it would be more efficient to leave the C<ev_timer> alone,	1944	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	1945	but remember the time of last activity, and check for a real timeout only
1830	within the callback:	1946	within the callback:
1831		1947
		1948	ev_tstamp timeout = 60.;
1832	ev_tstamp last_activity; // time of last activity	1949	ev_tstamp last_activity; // time of last activity
		1950	ev_timer timer;
1833		1951
1834	static void	1952	static void
1835	callback (EV_P_ ev_timer *w, int revents)	1953	callback (EV_P_ ev_timer *w, int revents)
1836	{	1954	{
1837	ev_tstamp now = ev_now (EV_A);	1955	// calculate when the timeout would happen
1838	ev_tstamp timeout = last_activity + 60.;	1956	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
1839		1957
1840	// if last_activity + 60. is older than now, we did time out	1958	// if negative, it means we the timeout already occurred
1841	if (timeout < now)	1959	if (after < 0.)
1842	{	1960	{
1843	// timeout occurred, take action	1961	// timeout occurred, take action
1844	}	1962	}
1845	else	1963	else
1846	{	1964	{
1847	// callback was invoked, but there was some activity, re-arm	1965	// callback was invoked, but there was some recent
1848	// the watcher to fire in last_activity + 60, which is	1966	// activity. simply restart the timer to time out
1849	// guaranteed to be in the future, so "again" is positive:	1967	// after "after" seconds, which is the earliest time
1850	w->repeat = timeout - now;	1968	// the timeout can occur.
		1969	ev_timer_set (w, after, 0.);
1851	ev_timer_again (EV_A_ w);	1970	ev_timer_start (EV_A_ w);
1852	}	1971	}
1853	}	1972	}
1854		1973
1855	To summarise the callback: first calculate the real timeout (defined	1974	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	1975	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	1976	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	1977	(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		1978
1862	Note how C<ev_timer_again> is used, taking advantage of the	1979	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.	1980	timed out, and need to do whatever is needed in this case.
		1981
		1982	Otherwise, we now the earliest time at which the timeout would trigger,
		1983	and simply start the timer with this timeout value.
		1984
		1985	In other words, each time the callback is invoked it will check whether
		1986	the timeout occurred. If not, it will simply reschedule itself to check
		1987	again at the earliest time it could time out. Rinse. Repeat.
1864		1988
1865	This scheme causes more callback invocations (about one every 60 seconds	1989	This scheme causes more callback invocations (about one every 60 seconds
1866	minus half the average time between activity), but virtually no calls to	1990	minus half the average time between activity), but virtually no calls to
1867	libev to change the timeout.	1991	libev to change the timeout.
1868		1992
1869	To start the timer, simply initialise the watcher and set C<last_activity>	1993	To start the machinery, simply initialise the watcher and set
1870	to the current time (meaning we just have some activity :), then call the	1994	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:	1995	now), then call the callback, which will "do the right thing" and start
		1996	the timer:
1872		1997
		1998	last_activity = ev_now (EV_A);
1873	ev_init (timer, callback);	1999	ev_init (&timer, callback);
1874	last_activity = ev_now (loop);	2000	callback (EV_A_ &timer, 0);
1875	callback (loop, timer, EV_TIMER);
1876		2001
1877	And when there is some activity, simply store the current time in	2002	When there is some activity, simply store the current time in
1878	C<last_activity>, no libev calls at all:	2003	C<last_activity>, no libev calls at all:
1879		2004
		2005	if (activity detected)
1880	last_activity = ev_now (loop);	2006	last_activity = ev_now (EV_A);
		2007
		2008	When your timeout value changes, then the timeout can be changed by simply
		2009	providing a new value, stopping the timer and calling the callback, which
		2010	will again do the right thing (for example, time out immediately :).
		2011
		2012	timeout = new_value;
		2013	ev_timer_stop (EV_A_ &timer);
		2014	callback (EV_A_ &timer, 0);
1881		2015
1882	This technique is slightly more complex, but in most cases where the	2016	This technique is slightly more complex, but in most cases where the
1883	time-out is unlikely to be triggered, much more efficient.	2017	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		2018
1889	=item 4. Wee, just use a double-linked list for your timeouts.	2019	=item 4. Wee, just use a double-linked list for your timeouts.
1890		2020
1891	If there is not one request, but many thousands (millions...), all	2021	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	2022	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	2049	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	2050	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	2051	off after the first million or so of active timers, i.e. it's usually
1922	overkill :)	2052	overkill :)
1923		2053
		2054	=head3 The special problem of being too early
		2055
		2056	If you ask a timer to call your callback after three seconds, then
		2057	you expect it to be invoked after three seconds - but of course, this
		2058	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		2059	guaranteed to any precision by libev - imagine somebody suspending the
		2060	process with a STOP signal for a few hours for example.
		2061
		2062	So, libev tries to invoke your callback as soon as possible I<after> the
		2063	delay has occurred, but cannot guarantee this.
		2064
		2065	A less obvious failure mode is calling your callback too early: many event
		2066	loops compare timestamps with a "elapsed delay >= requested delay", but
		2067	this can cause your callback to be invoked much earlier than you would
		2068	expect.
		2069
		2070	To see why, imagine a system with a clock that only offers full second
		2071	resolution (think windows if you can't come up with a broken enough OS
		2072	yourself). If you schedule a one-second timer at the time 500.9, then the
		2073	event loop will schedule your timeout to elapse at a system time of 500
		2074	(500.9 truncated to the resolution) + 1, or 501.
		2075
		2076	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2077	501" and invoke the callback 0.1s after it was started, even though a
		2078	one-second delay was requested - this is being "too early", despite best
		2079	intentions.
		2080
		2081	This is the reason why libev will never invoke the callback if the elapsed
		2082	delay equals the requested delay, but only when the elapsed delay is
		2083	larger than the requested delay. In the example above, libev would only invoke
		2084	the callback at system time 502, or 1.1s after the timer was started.
		2085
		2086	So, while libev cannot guarantee that your callback will be invoked
		2087	exactly when requested, it I<can> and I<does> guarantee that the requested
		2088	delay has actually elapsed, or in other words, it always errs on the "too
		2089	late" side of things.
		2090
1924	=head3 The special problem of time updates	2091	=head3 The special problem of time updates
1925		2092
1926	Establishing the current time is a costly operation (it usually takes at	2093	Establishing the current time is a costly operation (it usually takes
1927	least two system calls): EV therefore updates its idea of the current	2094	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	2095	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	2096	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1930	lots of events in one iteration.	2097	lots of events in one iteration.
1931		2098
1932	The relative timeouts are calculated relative to the C<ev_now ()>	2099	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	2100	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	2101	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	2102	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:	2103	timeout on the current time, use something like the following to adjust
		2104	for it:
1937		2105
1938	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2106	ev_timer_set (&timer, after + (ev_time () - ev_now ()), 0.);
1939		2107
1940	If the event loop is suspended for a long time, you can also force an	2108	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	2109	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1942	()>.	2110	()>, although that will push the event time of all outstanding events
		2111	further into the future.
		2112
		2113	=head3 The special problem of unsynchronised clocks
		2114
		2115	Modern systems have a variety of clocks - libev itself uses the normal
		2116	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2117	jumps).
		2118
		2119	Neither of these clocks is synchronised with each other or any other clock
		2120	on the system, so C<ev_time ()> might return a considerably different time
		2121	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2122	a call to C<gettimeofday> might return a second count that is one higher
		2123	than a directly following call to C<time>.
		2124
		2125	The moral of this is to only compare libev-related timestamps with
		2126	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2127	a second or so.
		2128
		2129	One more problem arises due to this lack of synchronisation: if libev uses
		2130	the system monotonic clock and you compare timestamps from C<ev_time>
		2131	or C<ev_now> from when you started your timer and when your callback is
		2132	invoked, you will find that sometimes the callback is a bit "early".
		2133
		2134	This is because C<ev_timer>s work in real time, not wall clock time, so
		2135	libev makes sure your callback is not invoked before the delay happened,
		2136	I<measured according to the real time>, not the system clock.
		2137
		2138	If your timeouts are based on a physical timescale (e.g. "time out this
		2139	connection after 100 seconds") then this shouldn't bother you as it is
		2140	exactly the right behaviour.
		2141
		2142	If you want to compare wall clock/system timestamps to your timers, then
		2143	you need to use C<ev_periodic>s, as these are based on the wall clock
		2144	time, where your comparisons will always generate correct results.
1943		2145
1944	=head3 The special problems of suspended animation	2146	=head3 The special problems of suspended animation
1945		2147
1946	When you leave the server world it is quite customary to hit machines that	2148	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?	2149	can suspend/hibernate - what happens to the clocks during such a suspend?
…		…
1977		2179
1978	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2180	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1979		2181
1980	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2182	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1981		2183
1982	Configure the timer to trigger after C<after> seconds. If C<repeat>	2184	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	2185	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	2186	automatically be stopped once the timeout is reached. If it is positive,
1985	configured to trigger again C<repeat> seconds later, again, and again,	2187	then the timer will automatically be configured to trigger again C<repeat>
1986	until stopped manually.	2188	seconds later, again, and again, until stopped manually.
1987		2189
1988	The timer itself will do a best-effort at avoiding drift, that is, if	2190	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	2191	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	2192	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	2193	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.	2194	do stuff) the timer will not fire more than once per event loop iteration.
1993		2195
1994	=item ev_timer_again (loop, ev_timer *)	2196	=item ev_timer_again (loop, ev_timer *)
1995		2197
1996	This will act as if the timer timed out and restart it again if it is	2198	This will act as if the timer timed out, and restarts it again if it is
1997	repeating. The exact semantics are:	2199	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2200	timeout to the C<repeat> value and calling C<ev_timer_start>.
1998		2201
		2202	The exact semantics are as in the following rules, all of which will be
		2203	applied to the watcher:
		2204
		2205	=over 4
		2206
1999	If the timer is pending, its pending status is cleared.	2207	=item If the timer is pending, the pending status is always cleared.
2000		2208
2001	If the timer is started but non-repeating, stop it (as if it timed out).	2209	=item If the timer is started but non-repeating, stop it (as if it timed
		2210	out, without invoking it).
2002		2211
2003	If the timer is repeating, either start it if necessary (with the	2212	=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.	2213	and start the timer, if necessary.
2005		2214
		2215	=back
		2216
2006	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a	2217	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
2007	usage example.	2218	usage example.
2008		2219
2009	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)	2220	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
2010		2221
2011	Returns the remaining time until a timer fires. If the timer is active,	2222	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	2275	Periodic watchers are also timers of a kind, but they are very versatile
2065	(and unfortunately a bit complex).	2276	(and unfortunately a bit complex).
2066		2277
2067	Unlike C<ev_timer>, periodic watchers are not based on real time (or	2278	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	2279	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	2280	(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	2281	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	2282	time, and time jumps are not uncommon (e.g. when you adjust your
2072	wrist-watch).	2283	wrist-watch).
2073		2284
2074	You can tell a periodic watcher to trigger after some specific point	2285	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	2290	C<ev_timer>, which would still trigger roughly 10 seconds after starting
2080	it, as it uses a relative timeout).	2291	it, as it uses a relative timeout).
2081		2292
2082	C<ev_periodic> watchers can also be used to implement vastly more complex	2293	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	2294	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	2295	other complicated rules. This cannot easily be done with C<ev_timer>
2085	those cannot react to time jumps.	2296	watchers, as those cannot react to time jumps.
2086		2297
2087	As with timers, the callback is guaranteed to be invoked only when the	2298	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	2299	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	2300	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	2301	earlier time-out values are invoked before ones with later time-out values
…		…
2131		2342
2132	Another way to think about it (for the mathematically inclined) is that	2343	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	2344	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.	2345	time where C<time = offset (mod interval)>, regardless of any time jumps.
2135		2346
2136	For numerical stability it is preferable that the C<offset> value is near	2347	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	2348	interval value should be higher than C<1/8192> (which is around 100
2138	this value, and in fact is often specified as zero.	2349	microseconds) and C<offset> should be higher than C<0> and should have
		2350	at most a similar magnitude as the current time (say, within a factor of
		2351	ten). Typical values for offset are, in fact, C<0> or something between
		2352	C<0> and C<interval>, which is also the recommended range.
2139		2353
2140	Note also that there is an upper limit to how often a timer can fire (CPU	2354	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	2355	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	2356	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).	2357	millisecond (if the OS supports it and the machine is fast enough).
…		…
2173		2387
2174	NOTE: I<< This callback must always return a time that is higher than or	2388	NOTE: I<< This callback must always return a time that is higher than or
2175	equal to the passed C<now> value >>.	2389	equal to the passed C<now> value >>.
2176		2390
2177	This can be used to create very complex timers, such as a timer that	2391	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	2392	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	2393	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	2394	this. Here is a (completely untested, no error checking) example on how to
2181	reason I omitted it as an example).	2395	do this:
		2396
		2397	#include <time.h>
		2398
		2399	static ev_tstamp
		2400	my_rescheduler (ev_periodic *w, ev_tstamp now)
		2401	{
		2402	time_t tnow = (time_t)now;
		2403	struct tm tm;
		2404	localtime_r (&tnow, &tm);
		2405
		2406	tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
		2407	++tm.tm_mday; // midnight next day
		2408
		2409	return mktime (&tm);
		2410	}
		2411
		2412	Note: this code might run into trouble on days that have more then two
		2413	midnights (beginning and end).
2182		2414
2183	=back	2415	=back
2184		2416
2185	=item ev_periodic_again (loop, ev_periodic *)	2417	=item ev_periodic_again (loop, ev_periodic *)
2186		2418
…		…
2251		2483
2252	ev_periodic hourly_tick;	2484	ev_periodic hourly_tick;
2253	ev_periodic_init (&hourly_tick, clock_cb,	2485	ev_periodic_init (&hourly_tick, clock_cb,
2254	fmod (ev_now (loop), 3600.), 3600., 0);	2486	fmod (ev_now (loop), 3600.), 3600., 0);
2255	ev_periodic_start (loop, &hourly_tick);	2487	ev_periodic_start (loop, &hourly_tick);
2256		2488
2257		2489
2258	=head2 C<ev_signal> - signal me when a signal gets signalled!	2490	=head2 C<ev_signal> - signal me when a signal gets signalled!
2259		2491
2260	Signal watchers will trigger an event when the process receives a specific	2492	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	2493	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	2494	will try its best to deliver signals synchronously, i.e. as part of the
2263	normal event processing, like any other event.	2495	normal event processing, like any other event.
2264		2496
2265	If you want signals to be delivered truly asynchronously, just use	2497	If you want signals to be delivered truly asynchronously, just use
2266	C<sigaction> as you would do without libev and forget about sharing	2498	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	2499	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	2503	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	2504	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	2505	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.	2506	the moment, C<SIGCHLD> is permanently tied to the default loop.
2275		2507
2276	When the first watcher gets started will libev actually register something	2508	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	2509	register something with the kernel. It thus coexists with your own signal
2278	you don't register any with libev for the same signal).	2510	handlers as long as you don't register any with libev for the same signal.
2279		2511
2280	If possible and supported, libev will install its handlers with	2512	If possible and supported, libev will install its handlers with
2281	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should	2513	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	2514	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	2515	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	2518	=head3 The special problem of inheritance over fork/execve/pthread_create
2287		2519
2288	Both the signal mask (C<sigprocmask>) and the signal disposition	2520	Both the signal mask (C<sigprocmask>) and the signal disposition
2289	(C<sigaction>) are unspecified after starting a signal watcher (and after	2521	(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,	2522	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.	2523	and might or might not set or restore the installed signal handler (but
		2524	see C<EVFLAG_NOSIGMASK>).
2292		2525
2293	While this does not matter for the signal disposition (libev never	2526	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	2527	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	2528	C<execve>), this matters for the signal mask: many programs do not expect
2296	certain signals to be blocked.	2529	certain signals to be blocked.
…		…
2309	I<has> to modify the signal mask, at least temporarily.	2542	I<has> to modify the signal mask, at least temporarily.
2310		2543
2311	So I can't stress this enough: I<If you do not reset your signal mask when	2544	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	2545	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.	2546	is not a libev-specific thing, this is true for most event libraries.
		2547
		2548	=head3 The special problem of threads signal handling
		2549
		2550	POSIX threads has problematic signal handling semantics, specifically,
		2551	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2552	threads in a process block signals, which is hard to achieve.
		2553
		2554	When you want to use sigwait (or mix libev signal handling with your own
		2555	for the same signals), you can tackle this problem by globally blocking
		2556	all signals before creating any threads (or creating them with a fully set
		2557	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2558	loops. Then designate one thread as "signal receiver thread" which handles
		2559	these signals. You can pass on any signals that libev might be interested
		2560	in by calling C<ev_feed_signal>.
2314		2561
2315	=head3 Watcher-Specific Functions and Data Members	2562	=head3 Watcher-Specific Functions and Data Members
2316		2563
2317	=over 4	2564	=over 4
2318		2565
…		…
2453		2700
2454	=head2 C<ev_stat> - did the file attributes just change?	2701	=head2 C<ev_stat> - did the file attributes just change?
2455		2702
2456	This watches a file system path for attribute changes. That is, it calls	2703	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)	2704	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	2705	and sees if it changed compared to the last time, invoking the callback
2459	it did.	2706	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2707	happen after the watcher has been started will be reported.
2460		2708
2461	The path does not need to exist: changing from "path exists" to "path does	2709	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	2710	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	2711	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	2712	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	2942	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	2943	effect on its own sometimes), idle watchers are a good place to do
2696	"pseudo-background processing", or delay processing stuff to after the	2944	"pseudo-background processing", or delay processing stuff to after the
2697	event loop has handled all outstanding events.	2945	event loop has handled all outstanding events.
2698		2946
		2947	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2948
		2949	As long as there is at least one active idle watcher, libev will never
		2950	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2951	For this to work, the idle watcher doesn't need to be invoked at all - the
		2952	lowest priority will do.
		2953
		2954	This mode of operation can be useful together with an C<ev_check> watcher,
		2955	to do something on each event loop iteration - for example to balance load
		2956	between different connections.
		2957
		2958	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2959	example.
		2960
2699	=head3 Watcher-Specific Functions and Data Members	2961	=head3 Watcher-Specific Functions and Data Members
2700		2962
2701	=over 4	2963	=over 4
2702		2964
2703	=item ev_idle_init (ev_idle *, callback)	2965	=item ev_idle_init (ev_idle *, callback)
…		…
2714	callback, free it. Also, use no error checking, as usual.	2976	callback, free it. Also, use no error checking, as usual.
2715		2977
2716	static void	2978	static void
2717	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)	2979	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2718	{	2980	{
		2981	// stop the watcher
		2982	ev_idle_stop (loop, w);
		2983
		2984	// now we can free it
2719	free (w);	2985	free (w);
		2986
2720	// now do something you wanted to do when the program has	2987	// now do something you wanted to do when the program has
2721	// no longer anything immediate to do.	2988	// no longer anything immediate to do.
2722	}	2989	}
2723		2990
2724	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	2991	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
…		…
2726	ev_idle_start (loop, idle_watcher);	2993	ev_idle_start (loop, idle_watcher);
2727		2994
2728		2995
2729	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2996	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2730		2997
2731	Prepare and check watchers are usually (but not always) used in pairs:	2998	Prepare and check watchers are often (but not always) used in pairs:
2732	prepare watchers get invoked before the process blocks and check watchers	2999	prepare watchers get invoked before the process blocks and check watchers
2733	afterwards.	3000	afterwards.
2734		3001
2735	You I<must not> call C<ev_run> or similar functions that enter	3002	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>	3003	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	3004	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	3005	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,	3006	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	3007	C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
2741	called in pairs bracketing the blocking call.	3008	kind they will always be called in pairs bracketing the blocking call.
2742		3009
2743	Their main purpose is to integrate other event mechanisms into libev and	3010	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	3011	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	3012	variable changes, implement your own watchers, integrate net-snmp or a
2746	coroutine library and lots more. They are also occasionally useful if	3013	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	3031	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	3032	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	3033	loop from blocking if lower-priority coroutines are active, thus mapping
2767	low-priority coroutines to idle/background tasks).	3034	low-priority coroutines to idle/background tasks).
2768		3035
2769	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	3036	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	3037	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).	3038	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		3039	watchers).
2772		3040
2773	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not	3041	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	3042	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	3043	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	3044	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	3045	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	3046	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
2779	others).	3047	others).
		3048
		3049	=head3 Abusing an C<ev_check> watcher for its side-effect
		3050
		3051	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		3052	useful because they are called once per event loop iteration. For
		3053	example, if you want to handle a large number of connections fairly, you
		3054	normally only do a bit of work for each active connection, and if there
		3055	is more work to do, you wait for the next event loop iteration, so other
		3056	connections have a chance of making progress.
		3057
		3058	Using an C<ev_check> watcher is almost enough: it will be called on the
		3059	next event loop iteration. However, that isn't as soon as possible -
		3060	without external events, your C<ev_check> watcher will not be invoked.
		3061
		3062	This is where C<ev_idle> watchers come in handy - all you need is a
		3063	single global idle watcher that is active as long as you have one active
		3064	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		3065	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		3066	invoked. Neither watcher alone can do that.
2780		3067
2781	=head3 Watcher-Specific Functions and Data Members	3068	=head3 Watcher-Specific Functions and Data Members
2782		3069
2783	=over 4	3070	=over 4
2784		3071
…		…
2985		3272
2986	=over 4	3273	=over 4
2987		3274
2988	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3275	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
2989		3276
2990	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3277	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
2991		3278
2992	Configures the watcher to embed the given loop, which must be	3279	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	3280	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	3281	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,	3282	to invoke it (it will continue to be called until the sweep has been done,
…		…
3016	used).	3303	used).
3017		3304
3018	struct ev_loop *loop_hi = ev_default_init (0);	3305	struct ev_loop *loop_hi = ev_default_init (0);
3019	struct ev_loop *loop_lo = 0;	3306	struct ev_loop *loop_lo = 0;
3020	ev_embed embed;	3307	ev_embed embed;
3021		3308
3022	// see if there is a chance of getting one that works	3309	// see if there is a chance of getting one that works
3023	// (remember that a flags value of 0 means autodetection)	3310	// (remember that a flags value of 0 means autodetection)
3024	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3311	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3025	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3312	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3026	: 0;	3313	: 0;
…		…
3040	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3327	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
3041		3328
3042	struct ev_loop *loop = ev_default_init (0);	3329	struct ev_loop *loop = ev_default_init (0);
3043	struct ev_loop *loop_socket = 0;	3330	struct ev_loop *loop_socket = 0;
3044	ev_embed embed;	3331	ev_embed embed;
3045		3332
3046	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3333	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3047	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3334	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3048	{	3335	{
3049	ev_embed_init (&embed, 0, loop_socket);	3336	ev_embed_init (&embed, 0, loop_socket);
3050	ev_embed_start (loop, &embed);	3337	ev_embed_start (loop, &embed);
…		…
3058		3345
3059	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3346	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
3060		3347
3061	Fork watchers are called when a C<fork ()> was detected (usually because	3348	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	3349	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	3350	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,	3351	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	3352	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	3353	and calls it in the wrong process, the fork handlers will be invoked, too,
3067	handlers will be invoked, too, of course.	3354	of course.
3068		3355
3069	=head3 The special problem of life after fork - how is it possible?	3356	=head3 The special problem of life after fork - how is it possible?
3070		3357
3071	Most uses of C<fork()> consist of forking, then some simple calls to set	3358	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	3359	up/change the process environment, followed by a call to C<exec()>. This
3073	sequence should be handled by libev without any problems.	3360	sequence should be handled by libev without any problems.
3074		3361
3075	This changes when the application actually wants to do event handling	3362	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	3363	in the child, or both parent in child, in effect "continuing" after the
…		…
3153	atexit (program_exits);	3440	atexit (program_exits);
3154		3441
3155		3442
3156	=head2 C<ev_async> - how to wake up an event loop	3443	=head2 C<ev_async> - how to wake up an event loop
3157		3444
3158	In general, you cannot use an C<ev_run> from multiple threads or other	3445	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	3446	asynchronous sources such as signal handlers (as opposed to multiple event
3160	loops - those are of course safe to use in different threads).	3447	loops - those are of course safe to use in different threads).
3161		3448
3162	Sometimes, however, you need to wake up an event loop you do not control,	3449	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>	3450	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.	3452	it by calling C<ev_async_send>, which is thread- and signal safe.
3166		3453
3167	This functionality is very similar to C<ev_signal> watchers, as signals,	3454	This functionality is very similar to C<ev_signal> watchers, as signals,
3168	too, are asynchronous in nature, and signals, too, will be compressed	3455	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	3456	(i.e. the number of callback invocations may be less than the number of
3170	C<ev_async_sent> calls).	3457	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
3171		3458	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	3459	signal, and C<ev_feed_signal> to signal this watcher from another thread,
3173	just the default loop.	3460	even without knowing which loop owns the signal.
3174		3461
3175	=head3 Queueing	3462	=head3 Queueing
3176		3463
3177	C<ev_async> does not support queueing of data in any way. The reason	3464	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	3465	is that the author does not know of a simple (or any) algorithm for a
…		…
3270	trust me.	3557	trust me.
3271		3558
3272	=item ev_async_send (loop, ev_async *)	3559	=item ev_async_send (loop, ev_async *)
3273		3560
3274	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3561	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	3562	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3563	returns.
		3564
3276	C<ev_feed_event>, this call is safe to do from other threads, signal or	3565	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	3566	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3278	section below on what exactly this means).	3567	embedding section below on what exactly this means).
3279		3568
3280	Note that, as with other watchers in libev, multiple events might get	3569	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	3570	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>,	3571	this is that C<ev_async> watchers are level-triggered: they are set on
3283	reset when the event loop detects that).	3572	C<ev_async_send>, reset when the event loop detects that).
3284		3573
3285	This call incurs the overhead of a system call only once per event loop	3574	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	3575	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.	3576	the event loop (or your program) is processing events. That means that
		3577	repeated calls are basically free (there is no need to avoid calls for
		3578	performance reasons) and that the overhead becomes smaller (typically
		3579	zero) under load.
3288		3580
3289	=item bool = ev_async_pending (ev_async *)	3581	=item bool = ev_async_pending (ev_async *)
3290		3582
3291	Returns a non-zero value when C<ev_async_send> has been called on the	3583	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	3584	watcher but the event has not yet been processed (or even noted) by the
…		…
3309		3601
3310	There are some other functions of possible interest. Described. Here. Now.	3602	There are some other functions of possible interest. Described. Here. Now.
3311		3603
3312	=over 4	3604	=over 4
3313		3605
3314	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3606	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)
3315		3607
3316	This function combines a simple timer and an I/O watcher, calls your	3608	This function combines a simple timer and an I/O watcher, calls your
3317	callback on whichever event happens first and automatically stops both	3609	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	3610	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	3611	or timeout without having to allocate/configure/start/stop/free one or
…		…
3347	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3639	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3348		3640
3349	=item ev_feed_fd_event (loop, int fd, int revents)	3641	=item ev_feed_fd_event (loop, int fd, int revents)
3350		3642
3351	Feed an event on the given fd, as if a file descriptor backend detected	3643	Feed an event on the given fd, as if a file descriptor backend detected
3352	the given events it.	3644	the given events.
3353		3645
3354	=item ev_feed_signal_event (loop, int signum)	3646	=item ev_feed_signal_event (loop, int signum)
3355		3647
3356	Feed an event as if the given signal occurred (C<loop> must be the default	3648	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3357	loop!).	3649	which is async-safe.
3358		3650
3359	=back	3651	=back
		3652
		3653
		3654	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3655
		3656	This section explains some common idioms that are not immediately
		3657	obvious. Note that examples are sprinkled over the whole manual, and this
		3658	section only contains stuff that wouldn't fit anywhere else.
		3659
		3660	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3661
		3662	Each watcher has, by default, a C<void *data> member that you can read
		3663	or modify at any time: libev will completely ignore it. This can be used
		3664	to associate arbitrary data with your watcher. If you need more data and
		3665	don't want to allocate memory separately and store a pointer to it in that
		3666	data member, you can also "subclass" the watcher type and provide your own
		3667	data:
		3668
		3669	struct my_io
		3670	{
		3671	ev_io io;
		3672	int otherfd;
		3673	void *somedata;
		3674	struct whatever *mostinteresting;
		3675	};
		3676
		3677	...
		3678	struct my_io w;
		3679	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3680
		3681	And since your callback will be called with a pointer to the watcher, you
		3682	can cast it back to your own type:
		3683
		3684	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3685	{
		3686	struct my_io *w = (struct my_io *)w_;
		3687	...
		3688	}
		3689
		3690	More interesting and less C-conformant ways of casting your callback
		3691	function type instead have been omitted.
		3692
		3693	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3694
		3695	Another common scenario is to use some data structure with multiple
		3696	embedded watchers, in effect creating your own watcher that combines
		3697	multiple libev event sources into one "super-watcher":
		3698
		3699	struct my_biggy
		3700	{
		3701	int some_data;
		3702	ev_timer t1;
		3703	ev_timer t2;
		3704	}
		3705
		3706	In this case getting the pointer to C<my_biggy> is a bit more
		3707	complicated: Either you store the address of your C<my_biggy> struct in
		3708	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3709	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3710	real programmers):
		3711
		3712	#include <stddef.h>
		3713
		3714	static void
		3715	t1_cb (EV_P_ ev_timer *w, int revents)
		3716	{
		3717	struct my_biggy big = (struct my_biggy *)
		3718	(((char *)w) - offsetof (struct my_biggy, t1));
		3719	}
		3720
		3721	static void
		3722	t2_cb (EV_P_ ev_timer *w, int revents)
		3723	{
		3724	struct my_biggy big = (struct my_biggy *)
		3725	(((char *)w) - offsetof (struct my_biggy, t2));
		3726	}
		3727
		3728	=head2 AVOIDING FINISHING BEFORE RETURNING
		3729
		3730	Often you have structures like this in event-based programs:
		3731
		3732	callback ()
		3733	{
		3734	free (request);
		3735	}
		3736
		3737	request = start_new_request (..., callback);
		3738
		3739	The intent is to start some "lengthy" operation. The C<request> could be
		3740	used to cancel the operation, or do other things with it.
		3741
		3742	It's not uncommon to have code paths in C<start_new_request> that
		3743	immediately invoke the callback, for example, to report errors. Or you add
		3744	some caching layer that finds that it can skip the lengthy aspects of the
		3745	operation and simply invoke the callback with the result.
		3746
		3747	The problem here is that this will happen I<before> C<start_new_request>
		3748	has returned, so C<request> is not set.
		3749
		3750	Even if you pass the request by some safer means to the callback, you
		3751	might want to do something to the request after starting it, such as
		3752	canceling it, which probably isn't working so well when the callback has
		3753	already been invoked.
		3754
		3755	A common way around all these issues is to make sure that
		3756	C<start_new_request> I<always> returns before the callback is invoked. If
		3757	C<start_new_request> immediately knows the result, it can artificially
		3758	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3759	example, or more sneakily, by reusing an existing (stopped) watcher and
		3760	pushing it into the pending queue:
		3761
		3762	ev_set_cb (watcher, callback);
		3763	ev_feed_event (EV_A_ watcher, 0);
		3764
		3765	This way, C<start_new_request> can safely return before the callback is
		3766	invoked, while not delaying callback invocation too much.
		3767
		3768	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3769
		3770	Often (especially in GUI toolkits) there are places where you have
		3771	I<modal> interaction, which is most easily implemented by recursively
		3772	invoking C<ev_run>.
		3773
		3774	This brings the problem of exiting - a callback might want to finish the
		3775	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3776	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3777	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3778	other combination: In these cases, a simple C<ev_break> will not work.
		3779
		3780	The solution is to maintain "break this loop" variable for each C<ev_run>
		3781	invocation, and use a loop around C<ev_run> until the condition is
		3782	triggered, using C<EVRUN_ONCE>:
		3783
		3784	// main loop
		3785	int exit_main_loop = 0;
		3786
		3787	while (!exit_main_loop)
		3788	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3789
		3790	// in a modal watcher
		3791	int exit_nested_loop = 0;
		3792
		3793	while (!exit_nested_loop)
		3794	ev_run (EV_A_ EVRUN_ONCE);
		3795
		3796	To exit from any of these loops, just set the corresponding exit variable:
		3797
		3798	// exit modal loop
		3799	exit_nested_loop = 1;
		3800
		3801	// exit main program, after modal loop is finished
		3802	exit_main_loop = 1;
		3803
		3804	// exit both
		3805	exit_main_loop = exit_nested_loop = 1;
		3806
		3807	=head2 THREAD LOCKING EXAMPLE
		3808
		3809	Here is a fictitious example of how to run an event loop in a different
		3810	thread from where callbacks are being invoked and watchers are
		3811	created/added/removed.
		3812
		3813	For a real-world example, see the C<EV::Loop::Async> perl module,
		3814	which uses exactly this technique (which is suited for many high-level
		3815	languages).
		3816
		3817	The example uses a pthread mutex to protect the loop data, a condition
		3818	variable to wait for callback invocations, an async watcher to notify the
		3819	event loop thread and an unspecified mechanism to wake up the main thread.
		3820
		3821	First, you need to associate some data with the event loop:
		3822
		3823	typedef struct {
		3824	mutex_t lock; /* global loop lock */
		3825	ev_async async_w;
		3826	thread_t tid;
		3827	cond_t invoke_cv;
		3828	} userdata;
		3829
		3830	void prepare_loop (EV_P)
		3831	{
		3832	// for simplicity, we use a static userdata struct.
		3833	static userdata u;
		3834
		3835	ev_async_init (&u->async_w, async_cb);
		3836	ev_async_start (EV_A_ &u->async_w);
		3837
		3838	pthread_mutex_init (&u->lock, 0);
		3839	pthread_cond_init (&u->invoke_cv, 0);
		3840
		3841	// now associate this with the loop
		3842	ev_set_userdata (EV_A_ u);
		3843	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3844	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3845
		3846	// then create the thread running ev_run
		3847	pthread_create (&u->tid, 0, l_run, EV_A);
		3848	}
		3849
		3850	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3851	solely to wake up the event loop so it takes notice of any new watchers
		3852	that might have been added:
		3853
		3854	static void
		3855	async_cb (EV_P_ ev_async *w, int revents)
		3856	{
		3857	// just used for the side effects
		3858	}
		3859
		3860	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3861	protecting the loop data, respectively.
		3862
		3863	static void
		3864	l_release (EV_P)
		3865	{
		3866	userdata *u = ev_userdata (EV_A);
		3867	pthread_mutex_unlock (&u->lock);
		3868	}
		3869
		3870	static void
		3871	l_acquire (EV_P)
		3872	{
		3873	userdata *u = ev_userdata (EV_A);
		3874	pthread_mutex_lock (&u->lock);
		3875	}
		3876
		3877	The event loop thread first acquires the mutex, and then jumps straight
		3878	into C<ev_run>:
		3879
		3880	void *
		3881	l_run (void *thr_arg)
		3882	{
		3883	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3884
		3885	l_acquire (EV_A);
		3886	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3887	ev_run (EV_A_ 0);
		3888	l_release (EV_A);
		3889
		3890	return 0;
		3891	}
		3892
		3893	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3894	signal the main thread via some unspecified mechanism (signals? pipe
		3895	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3896	have been called (in a while loop because a) spurious wakeups are possible
		3897	and b) skipping inter-thread-communication when there are no pending
		3898	watchers is very beneficial):
		3899
		3900	static void
		3901	l_invoke (EV_P)
		3902	{
		3903	userdata *u = ev_userdata (EV_A);
		3904
		3905	while (ev_pending_count (EV_A))
		3906	{
		3907	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3908	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3909	}
		3910	}
		3911
		3912	Now, whenever the main thread gets told to invoke pending watchers, it
		3913	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3914	thread to continue:
		3915
		3916	static void
		3917	real_invoke_pending (EV_P)
		3918	{
		3919	userdata *u = ev_userdata (EV_A);
		3920
		3921	pthread_mutex_lock (&u->lock);
		3922	ev_invoke_pending (EV_A);
		3923	pthread_cond_signal (&u->invoke_cv);
		3924	pthread_mutex_unlock (&u->lock);
		3925	}
		3926
		3927	Whenever you want to start/stop a watcher or do other modifications to an
		3928	event loop, you will now have to lock:
		3929
		3930	ev_timer timeout_watcher;
		3931	userdata *u = ev_userdata (EV_A);
		3932
		3933	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3934
		3935	pthread_mutex_lock (&u->lock);
		3936	ev_timer_start (EV_A_ &timeout_watcher);
		3937	ev_async_send (EV_A_ &u->async_w);
		3938	pthread_mutex_unlock (&u->lock);
		3939
		3940	Note that sending the C<ev_async> watcher is required because otherwise
		3941	an event loop currently blocking in the kernel will have no knowledge
		3942	about the newly added timer. By waking up the loop it will pick up any new
		3943	watchers in the next event loop iteration.
		3944
		3945	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3946
		3947	While the overhead of a callback that e.g. schedules a thread is small, it
		3948	is still an overhead. If you embed libev, and your main usage is with some
		3949	kind of threads or coroutines, you might want to customise libev so that
		3950	doesn't need callbacks anymore.
		3951
		3952	Imagine you have coroutines that you can switch to using a function
		3953	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3954	and that due to some magic, the currently active coroutine is stored in a
		3955	global called C<current_coro>. Then you can build your own "wait for libev
		3956	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3957	the differing C<;> conventions):
		3958
		3959	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3960	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3961
		3962	That means instead of having a C callback function, you store the
		3963	coroutine to switch to in each watcher, and instead of having libev call
		3964	your callback, you instead have it switch to that coroutine.
		3965
		3966	A coroutine might now wait for an event with a function called
		3967	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3968	matter when, or whether the watcher is active or not when this function is
		3969	called):
		3970
		3971	void
		3972	wait_for_event (ev_watcher *w)
		3973	{
		3974	ev_set_cb (w, current_coro);
		3975	switch_to (libev_coro);
		3976	}
		3977
		3978	That basically suspends the coroutine inside C<wait_for_event> and
		3979	continues the libev coroutine, which, when appropriate, switches back to
		3980	this or any other coroutine.
		3981
		3982	You can do similar tricks if you have, say, threads with an event queue -
		3983	instead of storing a coroutine, you store the queue object and instead of
		3984	switching to a coroutine, you push the watcher onto the queue and notify
		3985	any waiters.
		3986
		3987	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		3988	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3989
		3990	// my_ev.h
		3991	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3992	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3993	#include "../libev/ev.h"
		3994
		3995	// my_ev.c
		3996	#define EV_H "my_ev.h"
		3997	#include "../libev/ev.c"
		3998
		3999	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		4000	F<my_ev.c> into your project. When properly specifying include paths, you
		4001	can even use F<ev.h> as header file name directly.
3360		4002
3361		4003
3362	=head1 LIBEVENT EMULATION	4004	=head1 LIBEVENT EMULATION
3363		4005
3364	Libev offers a compatibility emulation layer for libevent. It cannot	4006	Libev offers a compatibility emulation layer for libevent. It cannot
3365	emulate the internals of libevent, so here are some usage hints:	4007	emulate the internals of libevent, so here are some usage hints:
3366		4008
3367	=over 4	4009	=over 4
		4010
		4011	=item * Only the libevent-1.4.1-beta API is being emulated.
		4012
		4013	This was the newest libevent version available when libev was implemented,
		4014	and is still mostly unchanged in 2010.
3368		4015
3369	=item * Use it by including <event.h>, as usual.	4016	=item * Use it by including <event.h>, as usual.
3370		4017
3371	=item * The following members are fully supported: ev_base, ev_callback,	4018	=item * The following members are fully supported: ev_base, ev_callback,
3372	ev_arg, ev_fd, ev_res, ev_events.	4019	ev_arg, ev_fd, ev_res, ev_events.
…		…
3378	=item * Priorities are not currently supported. Initialising priorities	4025	=item * Priorities are not currently supported. Initialising priorities
3379	will fail and all watchers will have the same priority, even though there	4026	will fail and all watchers will have the same priority, even though there
3380	is an ev_pri field.	4027	is an ev_pri field.
3381		4028
3382	=item * In libevent, the last base created gets the signals, in libev, the	4029	=item * In libevent, the last base created gets the signals, in libev, the
3383	first base created (== the default loop) gets the signals.	4030	base that registered the signal gets the signals.
3384		4031
3385	=item * Other members are not supported.	4032	=item * Other members are not supported.
3386		4033
3387	=item * The libev emulation is I<not> ABI compatible to libevent, you need	4034	=item * The libev emulation is I<not> ABI compatible to libevent, you need
3388	to use the libev header file and library.	4035	to use the libev header file and library.
3389		4036
3390	=back	4037	=back
3391		4038
3392	=head1 C++ SUPPORT	4039	=head1 C++ SUPPORT
		4040
		4041	=head2 C API
		4042
		4043	The normal C API should work fine when used from C++: both ev.h and the
		4044	libev sources can be compiled as C++. Therefore, code that uses the C API
		4045	will work fine.
		4046
		4047	Proper exception specifications might have to be added to callbacks passed
		4048	to libev: exceptions may be thrown only from watcher callbacks, all other
		4049	callbacks (allocator, syserr, loop acquire/release and periodic reschedule
		4050	callbacks) must not throw exceptions, and might need a C<noexcept>
		4051	specification. If you have code that needs to be compiled as both C and
		4052	C++ you can use the C<EV_NOEXCEPT> macro for this:
		4053
		4054	static void
		4055	fatal_error (const char *msg) EV_NOEXCEPT
		4056	{
		4057	perror (msg);
		4058	abort ();
		4059	}
		4060
		4061	...
		4062	ev_set_syserr_cb (fatal_error);
		4063
		4064	The only API functions that can currently throw exceptions are C<ev_run>,
		4065	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		4066	because it runs cleanup watchers).
		4067
		4068	Throwing exceptions in watcher callbacks is only supported if libev itself
		4069	is compiled with a C++ compiler or your C and C++ environments allow
		4070	throwing exceptions through C libraries (most do).
		4071
		4072	=head2 C++ API
3393		4073
3394	Libev comes with some simplistic wrapper classes for C++ that mainly allow	4074	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	4075	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.	4076	the callback model to a model using method callbacks on objects.
3397		4077
3398	To use it,	4078	To use it,
3399		4079
3400	#include <ev++.h>	4080	#include <ev++.h>
3401		4081
3402	This automatically includes F<ev.h> and puts all of its definitions (many	4082	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	4083	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	4084	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++	4087	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	4088	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	4089	that the watcher is associated with (or no additional members at all if
3410	you disable C<EV_MULTIPLICITY> when embedding libev).	4090	you disable C<EV_MULTIPLICITY> when embedding libev).
3411		4091
3412	Currently, functions, and static and non-static member functions can be	4092	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	4093	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	4094	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	4095	you need support for other types of functors please contact the author
3416	it).	4096	(preferably after implementing it).
		4097
		4098	For all this to work, your C++ compiler either has to use the same calling
		4099	conventions as your C compiler (for static member functions), or you have
		4100	to embed libev and compile libev itself as C++.
3417		4101
3418	Here is a list of things available in the C<ev> namespace:	4102	Here is a list of things available in the C<ev> namespace:
3419		4103
3420	=over 4	4104	=over 4
3421		4105
…		…
3431	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4115	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
3432		4116
3433	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4117	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>	4118	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	4119	which is called C<ev::sig> to avoid clashes with the C<signal> macro
3436	defines by many implementations.	4120	defined by many implementations.
3437		4121
3438	All of those classes have these methods:	4122	All of those classes have these methods:
3439		4123
3440	=over 4	4124	=over 4
3441		4125
…		…
3503	void operator() (ev::io &w, int revents)	4187	void operator() (ev::io &w, int revents)
3504	{	4188	{
3505	...	4189	...
3506	}	4190	}
3507	}	4191	}
3508		4192
3509	myfunctor f;	4193	myfunctor f;
3510		4194
3511	ev::io w;	4195	ev::io w;
3512	w.set (&f);	4196	w.set (&f);
3513		4197
…		…
3531	Associates a different C<struct ev_loop> with this watcher. You can only	4215	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).	4216	do this when the watcher is inactive (and not pending either).
3533		4217
3534	=item w->set ([arguments])	4218	=item w->set ([arguments])
3535		4219
3536	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this	4220	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	4221	with the same arguments. Either this method or a suitable start method
3538	C counterpart, an active watcher gets automatically stopped and restarted	4222	must be called at least once. Unlike the C counterpart, an active watcher
3539	when reconfiguring it with this method.	4223	gets automatically stopped and restarted when reconfiguring it with this
		4224	method.
		4225
		4226	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4227	clashing with the C<set (loop)> method.
3540		4228
3541	=item w->start ()	4229	=item w->start ()
3542		4230
3543	Starts the watcher. Note that there is no C<loop> argument, as the	4231	Starts the watcher. Note that there is no C<loop> argument, as the
3544	constructor already stores the event loop.	4232	constructor already stores the event loop.
…		…
3574	watchers in the constructor.	4262	watchers in the constructor.
3575		4263
3576	class myclass	4264	class myclass
3577	{	4265	{
3578	ev::io io ; void io_cb (ev::io &w, int revents);	4266	ev::io io ; void io_cb (ev::io &w, int revents);
3579	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);	4267	ev::io io2 ; void io2_cb (ev::io &w, int revents);
3580	ev::idle idle; void idle_cb (ev::idle &w, int revents);	4268	ev::idle idle; void idle_cb (ev::idle &w, int revents);
3581		4269
3582	myclass (int fd)	4270	myclass (int fd)
3583	{	4271	{
3584	io .set <myclass, &myclass::io_cb > (this);	4272	io .set <myclass, &myclass::io_cb > (this);
…		…
3635	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.	4323	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3636		4324
3637	=item D	4325	=item D
3638		4326
3639	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4327	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>.	4328	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
3641		4329
3642	=item Ocaml	4330	=item Ocaml
3643		4331
3644	Erkki Seppala has written Ocaml bindings for libev, to be found at	4332	Erkki Seppala has written Ocaml bindings for libev, to be found at
3645	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	4333	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
…		…
3648		4336
3649	Brian Maher has written a partial interface to libev for lua (at the	4337	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	4338	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
3651	L<http://github.com/brimworks/lua-ev>.	4339	L<http://github.com/brimworks/lua-ev>.
3652		4340
		4341	=item Javascript
		4342
		4343	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4344
		4345	=item Others
		4346
		4347	There are others, and I stopped counting.
		4348
3653	=back	4349	=back
3654		4350
3655		4351
3656	=head1 MACRO MAGIC	4352	=head1 MACRO MAGIC
3657		4353
…		…
3693	suitable for use with C<EV_A>.	4389	suitable for use with C<EV_A>.
3694		4390
3695	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4391	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
3696		4392
3697	Similar to the other two macros, this gives you the value of the default	4393	Similar to the other two macros, this gives you the value of the default
3698	loop, if multiple loops are supported ("ev loop default").	4394	loop, if multiple loops are supported ("ev loop default"). The default loop
		4395	will be initialised if it isn't already initialised.
		4396
		4397	For non-multiplicity builds, these macros do nothing, so you always have
		4398	to initialise the loop somewhere.
3699		4399
3700	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4400	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
3701		4401
3702	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4402	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	4403	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
3770	ev_vars.h	4470	ev_vars.h
3771	ev_wrap.h	4471	ev_wrap.h
3772		4472
3773	ev_win32.c required on win32 platforms only	4473	ev_win32.c required on win32 platforms only
3774		4474
3775	ev_select.c only when select backend is enabled (which is enabled by default)	4475	ev_select.c only when select backend is enabled
3776	ev_poll.c only when poll backend is enabled (disabled by default)	4476	ev_poll.c only when poll backend is enabled
3777	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4477	ev_epoll.c only when the epoll backend is enabled
		4478	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)	4479	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)	4480	ev_port.c only when the solaris port backend is enabled
3780		4481
3781	F<ev.c> includes the backend files directly when enabled, so you only need	4482	F<ev.c> includes the backend files directly when enabled, so you only need
3782	to compile this single file.	4483	to compile this single file.
3783		4484
3784	=head3 LIBEVENT COMPATIBILITY API	4485	=head3 LIBEVENT COMPATIBILITY API
…		…
3848	supported). It will also not define any of the structs usually found in	4549	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.	4550	F<event.h> that are not directly supported by the libev core alone.
3850		4551
3851	In standalone mode, libev will still try to automatically deduce the	4552	In standalone mode, libev will still try to automatically deduce the
3852	configuration, but has to be more conservative.	4553	configuration, but has to be more conservative.
		4554
		4555	=item EV_USE_FLOOR
		4556
		4557	If defined to be C<1>, libev will use the C<floor ()> function for its
		4558	periodic reschedule calculations, otherwise libev will fall back on a
		4559	portable (slower) implementation. If you enable this, you usually have to
		4560	link against libm or something equivalent. Enabling this when the C<floor>
		4561	function is not available will fail, so the safe default is to not enable
		4562	this.
3853		4563
3854	=item EV_USE_MONOTONIC	4564	=item EV_USE_MONOTONIC
3855		4565
3856	If defined to be C<1>, libev will try to detect the availability of the	4566	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	4567	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	4653	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	4654	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	4655	file descriptors again. Note that the replacement function has to close
3946	the underlying OS handle.	4656	the underlying OS handle.
3947		4657
		4658	=item EV_USE_WSASOCKET
		4659
		4660	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4661	communication socket, which works better in some environments. Otherwise,
		4662	the normal C<socket> function will be used, which works better in other
		4663	environments.
		4664
3948	=item EV_USE_POLL	4665	=item EV_USE_POLL
3949		4666
3950	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4667	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	4668	backend. Otherwise it will be enabled on non-win32 platforms. It
3952	takes precedence over select.	4669	takes precedence over select.
…		…
3956	If defined to be C<1>, libev will compile in support for the Linux	4673	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,	4674	C<epoll>(7) backend. Its availability will be detected at runtime,
3958	otherwise another method will be used as fallback. This is the preferred	4675	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	4676	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.	4677	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4678
		4679	=item EV_USE_LINUXAIO
		4680
		4681	If defined to be C<1>, libev will compile in support for the Linux
		4682	aio backend. Due to it's currenbt limitations it has to be requested
		4683	explicitly. If undefined, it will be enabled on linux, otherwise
		4684	disabled.
3961		4685
3962	=item EV_USE_KQUEUE	4686	=item EV_USE_KQUEUE
3963		4687
3964	If defined to be C<1>, libev will compile in support for the BSD style	4688	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,	4689	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	4711	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	4712	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	4713	be detected at runtime. If undefined, it will be enabled if the headers
3990	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4714	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
3991		4715
		4716	=item EV_NO_SMP
		4717
		4718	If defined to be C<1>, libev will assume that memory is always coherent
		4719	between threads, that is, threads can be used, but threads never run on
		4720	different cpus (or different cpu cores). This reduces dependencies
		4721	and makes libev faster.
		4722
		4723	=item EV_NO_THREADS
		4724
		4725	If defined to be C<1>, libev will assume that it will never be called from
		4726	different threads (that includes signal handlers), which is a stronger
		4727	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4728	libev faster.
		4729
3992	=item EV_ATOMIC_T	4730	=item EV_ATOMIC_T
3993		4731
3994	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4732	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	4733	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	4734	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"	4735	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.	4736	handler "locking" as well as for signal and thread safety in C<ev_async>
		4737	watchers.
3999		4738
4000	In the absence of this define, libev will use C<sig_atomic_t volatile>	4739	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.	4740	(from F<signal.h>), which is usually good enough on most platforms.
4002		4741
4003	=item EV_H (h)	4742	=item EV_H (h)
…		…
4030	will have the C<struct ev_loop *> as first argument, and you can create	4769	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	4770	additional independent event loops. Otherwise there will be no support
4032	for multiple event loops and there is no first event loop pointer	4771	for multiple event loops and there is no first event loop pointer
4033	argument. Instead, all functions act on the single default loop.	4772	argument. Instead, all functions act on the single default loop.
4034		4773
		4774	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4775	default loop when multiplicity is switched off - you always have to
		4776	initialise the loop manually in this case.
		4777
4035	=item EV_MINPRI	4778	=item EV_MINPRI
4036		4779
4037	=item EV_MAXPRI	4780	=item EV_MAXPRI
4038		4781
4039	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4782	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
4075	#define EV_USE_POLL 1	4818	#define EV_USE_POLL 1
4076	#define EV_CHILD_ENABLE 1	4819	#define EV_CHILD_ENABLE 1
4077	#define EV_ASYNC_ENABLE 1	4820	#define EV_ASYNC_ENABLE 1
4078		4821
4079	The actual value is a bitset, it can be a combination of the following	4822	The actual value is a bitset, it can be a combination of the following
4080	values:	4823	values (by default, all of these are enabled):
4081		4824
4082	=over 4	4825	=over 4
4083		4826
4084	=item C<1> - faster/larger code	4827	=item C<1> - faster/larger code
4085		4828
…		…
4089	code size by roughly 30% on amd64).	4832	code size by roughly 30% on amd64).
4090		4833
4091	When optimising for size, use of compiler flags such as C<-Os> with	4834	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	4835	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
4093	assertions.	4836	assertions.
		4837
		4838	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4839	(e.g. gcc with C<-Os>).
4094		4840
4095	=item C<2> - faster/larger data structures	4841	=item C<2> - faster/larger data structures
4096		4842
4097	Replaces the small 2-heap for timer management by a faster 4-heap, larger	4843	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	4844	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	4845	and can additionally have an effect on the size of data structures at
4100	runtime.	4846	runtime.
4101		4847
		4848	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4849	(e.g. gcc with C<-Os>).
		4850
4102	=item C<4> - full API configuration	4851	=item C<4> - full API configuration
4103		4852
4104	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and	4853	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
4105	enables multiplicity (C<EV_MULTIPLICITY>=1).	4854	enables multiplicity (C<EV_MULTIPLICITY>=1).
4106		4855
…		…
4136		4885
4137	With an intelligent-enough linker (gcc+binutils are intelligent enough	4886	With an intelligent-enough linker (gcc+binutils are intelligent enough
4138	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by	4887	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	4888	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.	4889	I/O watcher then might come out at only 5Kb.
		4890
		4891	=item EV_API_STATIC
		4892
		4893	If this symbol is defined (by default it is not), then all identifiers
		4894	will have static linkage. This means that libev will not export any
		4895	identifiers, and you cannot link against libev anymore. This can be useful
		4896	when you embed libev, only want to use libev functions in a single file,
		4897	and do not want its identifiers to be visible.
		4898
		4899	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4900	wants to use libev.
		4901
		4902	This option only works when libev is compiled with a C compiler, as C++
		4903	doesn't support the required declaration syntax.
4141		4904
4142	=item EV_AVOID_STDIO	4905	=item EV_AVOID_STDIO
4143		4906
4144	If this is set to C<1> at compiletime, then libev will avoid using stdio	4907	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	4908	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:	5052	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4290		5053
4291	#include "ev_cpp.h"	5054	#include "ev_cpp.h"
4292	#include "ev.c"	5055	#include "ev.c"
4293		5056
4294	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	5057	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4295		5058
4296	=head2 THREADS AND COROUTINES	5059	=head2 THREADS AND COROUTINES
4297		5060
4298	=head3 THREADS	5061	=head3 THREADS
4299		5062
…		…
4350	default loop and triggering an C<ev_async> watcher from the default loop	5113	default loop and triggering an C<ev_async> watcher from the default loop
4351	watcher callback into the event loop interested in the signal.	5114	watcher callback into the event loop interested in the signal.
4352		5115
4353	=back	5116	=back
4354		5117
4355	=head4 THREAD LOCKING EXAMPLE	5118	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		5119
4493	=head3 COROUTINES	5120	=head3 COROUTINES
4494		5121
4495	Libev is very accommodating to coroutines ("cooperative threads"):	5122	Libev is very accommodating to coroutines ("cooperative threads"):
4496	libev fully supports nesting calls to its functions from different	5123	libev fully supports nesting calls to its functions from different
…		…
4661	requires, and its I/O model is fundamentally incompatible with the POSIX	5288	requires, and its I/O model is fundamentally incompatible with the POSIX
4662	model. Libev still offers limited functionality on this platform in	5289	model. Libev still offers limited functionality on this platform in
4663	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5290	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
4664	descriptors. This only applies when using Win32 natively, not when using	5291	descriptors. This only applies when using Win32 natively, not when using
4665	e.g. cygwin. Actually, it only applies to the microsofts own compilers,	5292	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4666	as every compielr comes with a slightly differently broken/incompatible	5293	as every compiler comes with a slightly differently broken/incompatible
4667	environment.	5294	environment.
4668		5295
4669	Lifting these limitations would basically require the full	5296	Lifting these limitations would basically require the full
4670	re-implementation of the I/O system. If you are into this kind of thing,	5297	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	5298	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	5392	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	5393	assumes that the same (machine) code can be used to call any watcher
4767	callback: The watcher callbacks have different type signatures, but libev	5394	callback: The watcher callbacks have different type signatures, but libev
4768	calls them using an C<ev_watcher *> internally.	5395	calls them using an C<ev_watcher *> internally.
4769		5396
		5397	=item null pointers and integer zero are represented by 0 bytes
		5398
		5399	Libev uses C<memset> to initialise structs and arrays to C<0> bytes, and
		5400	relies on this setting pointers and integers to null.
		5401
4770	=item pointer accesses must be thread-atomic	5402	=item pointer accesses must be thread-atomic
4771		5403
4772	Accessing a pointer value must be atomic, it must both be readable and	5404	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.	5405	writable in one piece - this is the case on all current architectures.
4774		5406
…		…
4787	thread" or will block signals process-wide, both behaviours would	5419	thread" or will block signals process-wide, both behaviours would
4788	be compatible with libev. Interaction between C<sigprocmask> and	5420	be compatible with libev. Interaction between C<sigprocmask> and
4789	C<pthread_sigmask> could complicate things, however.	5421	C<pthread_sigmask> could complicate things, however.
4790		5422
4791	The most portable way to handle signals is to block signals in all threads	5423	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	5424	except the initial one, and run the signal handling loop in the initial
4793	well.	5425	thread as well.
4794		5426
4795	=item C<long> must be large enough for common memory allocation sizes	5427	=item C<long> must be large enough for common memory allocation sizes
4796		5428
4797	To improve portability and simplify its API, libev uses C<long> internally	5429	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	5430	instead of C<size_t> when allocating its data structures. On non-POSIX
…		…
4804		5436
4805	The type C<double> is used to represent timestamps. It is required to	5437	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	5438	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	5439	good enough for at least into the year 4000 with millisecond accuracy
4808	(the design goal for libev). This requirement is overfulfilled by	5440	(the design goal for libev). This requirement is overfulfilled by
4809	implementations using IEEE 754, which is basically all existing ones. With	5441	implementations using IEEE 754, which is basically all existing ones.
		5442
4810	IEEE 754 doubles, you get microsecond accuracy until at least 2200.	5443	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5444	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5445	is either obsolete or somebody patched it to use C<long double> or
		5446	something like that, just kidding).
4811		5447
4812	=back	5448	=back
4813		5449
4814	If you know of other additional requirements drop me a note.	5450	If you know of other additional requirements drop me a note.
4815		5451
…		…
4877	=item Processing ev_async_send: O(number_of_async_watchers)	5513	=item Processing ev_async_send: O(number_of_async_watchers)
4878		5514
4879	=item Processing signals: O(max_signal_number)	5515	=item Processing signals: O(max_signal_number)
4880		5516
4881	Sending involves a system call I<iff> there were no other C<ev_async_send>	5517	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	5518	calls in the current loop iteration and the loop is currently
		5519	blocked. Checking for async and signal events involves iterating over all
4883	involves iterating over all running async watchers or all signal numbers.	5520	running async watchers or all signal numbers.
4884		5521
4885	=back	5522	=back
4886		5523
4887		5524
4888	=head1 PORTING FROM LIBEV 3.X TO 4.X	5525	=head1 PORTING FROM LIBEV 3.X TO 4.X
…		…
4897	=over 4	5534	=over 4
4898		5535
4899	=item C<EV_COMPAT3> backwards compatibility mechanism	5536	=item C<EV_COMPAT3> backwards compatibility mechanism
4900		5537
4901	The backward compatibility mechanism can be controlled by	5538	The backward compatibility mechanism can be controlled by
4902	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>	5539	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
4903	section.	5540	section.
4904		5541
4905	=item C<ev_default_destroy> and C<ev_default_fork> have been removed	5542	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
4906		5543
4907	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:	5544	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
…		…
4950	=over 4	5587	=over 4
4951		5588
4952	=item active	5589	=item active
4953		5590
4954	A watcher is active as long as it has been started and not yet stopped.	5591	A watcher is active as long as it has been started and not yet stopped.
4955	See L<WATCHER STATES> for details.	5592	See L</WATCHER STATES> for details.
4956		5593
4957	=item application	5594	=item application
4958		5595
4959	In this document, an application is whatever is using libev.	5596	In this document, an application is whatever is using libev.
4960		5597
…		…
4996	watchers and events.	5633	watchers and events.
4997		5634
4998	=item pending	5635	=item pending
4999		5636
5000	A watcher is pending as soon as the corresponding event has been	5637	A watcher is pending as soon as the corresponding event has been
5001	detected. See L<WATCHER STATES> for details.	5638	detected. See L</WATCHER STATES> for details.
5002		5639
5003	=item real time	5640	=item real time
5004		5641
5005	The physical time that is observed. It is apparently strictly monotonic :)	5642	The physical time that is observed. It is apparently strictly monotonic :)
5006		5643
5007	=item wall-clock time	5644	=item wall-clock time
5008		5645
5009	The time and date as shown on clocks. Unlike real time, it can actually	5646	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	5647	be wrong and jump forwards and backwards, e.g. when you adjust your
5011	clock.	5648	clock.
5012		5649
5013	=item watcher	5650	=item watcher
5014		5651
5015	A data structure that describes interest in certain events. Watchers need	5652	A data structure that describes interest in certain events. Watchers need
…		…
5018	=back	5655	=back
5019		5656
5020	=head1 AUTHOR	5657	=head1 AUTHOR
5021		5658
5022	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael	5659	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5023	Magnusson and Emanuele Giaquinta.	5660	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
5024		5661

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