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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
…		…
43		45
44	int	46	int
45	main (void)	47	main (void)
46	{	48	{
47	// use the default event loop unless you have special needs	49	// use the default event loop unless you have special needs
48	struct ev_loop *loop = ev_default_loop (0);	50	struct ev_loop *loop = EV_DEFAULT;
49		51
50	// initialise an io watcher, then start it	52	// initialise an io watcher, then start it
51	// this one will watch for stdin to become readable	53	// this one will watch for stdin to become readable
52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	54	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
53	ev_io_start (loop, &stdin_watcher);	55	ev_io_start (loop, &stdin_watcher);
…		…
58	ev_timer_start (loop, &timeout_watcher);	60	ev_timer_start (loop, &timeout_watcher);
59		61
60	// now wait for events to arrive	62	// now wait for events to arrive
61	ev_run (loop, 0);	63	ev_run (loop, 0);
62		64
63	// unloop was called, so exit	65	// break was called, so exit
64	return 0;	66	return 0;
65	}	67	}
66		68
67	=head1 ABOUT THIS DOCUMENT	69	=head1 ABOUT THIS DOCUMENT
68		70
…		…
78	with libev.	80	with libev.
79		81
80	Familiarity with event based programming techniques in general is assumed	82	Familiarity with event based programming techniques in general is assumed
81	throughout this document.	83	throughout this document.
82		84
		85	=head1 WHAT TO READ WHEN IN A HURRY
		86
		87	This manual tries to be very detailed, but unfortunately, this also makes
		88	it very long. If you just want to know the basics of libev, I suggest
		89	reading L</ANATOMY OF A WATCHER>, then the L</EXAMPLE PROGRAM> above and
		90	look up the missing functions in L</GLOBAL FUNCTIONS> and the C<ev_io> and
		91	C<ev_timer> sections in L</WATCHER TYPES>.
		92
83	=head1 ABOUT LIBEV	93	=head1 ABOUT LIBEV
84		94
85	Libev is an event loop: you register interest in certain events (such as a	95	Libev is an event loop: you register interest in certain events (such as a
86	file descriptor being readable or a timeout occurring), and it will manage	96	file descriptor being readable or a timeout occurring), and it will manage
87	these event sources and provide your program with events.	97	these event sources and provide your program with events.
…		…
95	details of the event, and then hand it over to libev by I<starting> the	105	details of the event, and then hand it over to libev by I<starting> the
96	watcher.	106	watcher.
97		107
98	=head2 FEATURES	108	=head2 FEATURES
99		109
100	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	110	Libev supports C<select>, C<poll>, the Linux-specific aio and C<epoll>
101	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	111	interfaces, the BSD-specific C<kqueue> and the Solaris-specific event port
102	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	112	mechanisms for file descriptor events (C<ev_io>), the Linux C<inotify>
103	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner	113	interface (for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
104	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative	114	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
105	timers (C<ev_timer>), absolute timers with customised rescheduling	115	timers (C<ev_timer>), absolute timers with customised rescheduling
106	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status	116	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
107	change events (C<ev_child>), and event watchers dealing with the event	117	change events (C<ev_child>), and event watchers dealing with the event
108	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and	118	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
…		…
165		175
166	=item ev_tstamp ev_time ()	176	=item ev_tstamp ev_time ()
167		177
168	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
169	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
170	you actually want to know. Also interetsing is the combination of	180	you actually want to know. Also interesting is the combination of
171	C<ev_update_now> and C<ev_now>.	181	C<ev_now_update> and C<ev_now>.
172		182
173	=item ev_sleep (ev_tstamp interval)	183	=item ev_sleep (ev_tstamp interval)
174		184
175	Sleep for the given interval: The current thread will be blocked until	185	Sleep for the given interval: The current thread will be blocked
176	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
177	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 >>).
178		194
179	=item int ev_version_major ()	195	=item int ev_version_major ()
180		196
181	=item int ev_version_minor ()	197	=item int ev_version_minor ()
182		198
…		…
233	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 ()
234	& ev_supported_backends ()>, likewise for recommended ones.	250	& ev_supported_backends ()>, likewise for recommended ones.
235		251
236	See the description of C<ev_embed> watchers for more info.	252	See the description of C<ev_embed> watchers for more info.
237		253
238	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]	254	=item ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())
239		255
240	Sets the allocation function to use (the prototype is similar - the	256	Sets the allocation function to use (the prototype is similar - the
241	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is	257	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
242	used to allocate and free memory (no surprises here). If it returns zero	258	used to allocate and free memory (no surprises here). If it returns zero
243	when memory needs to be allocated (C<size != 0>), the library might abort	259	when memory needs to be allocated (C<size != 0>), the library might abort
…		…
249		265
250	You could override this function in high-availability programs to, say,	266	You could override this function in high-availability programs to, say,
251	free some memory if it cannot allocate memory, to use a special allocator,	267	free some memory if it cannot allocate memory, to use a special allocator,
252	or even to sleep a while and retry until some memory is available.	268	or even to sleep a while and retry until some memory is available.
253		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
254	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
255	retries (example requires a standards-compliant C<realloc>).	285	retries.
256		286
257	static void *	287	static void *
258	persistent_realloc (void *ptr, size_t size)	288	persistent_realloc (void *ptr, size_t size)
259	{	289	{
		290	if (!size)
		291	{
		292	free (ptr);
		293	return 0;
		294	}
		295
260	for (;;)	296	for (;;)
261	{	297	{
262	void *newptr = realloc (ptr, size);	298	void *newptr = realloc (ptr, size);
263		299
264	if (newptr)	300	if (newptr)
…		…
269	}	305	}
270		306
271	...	307	...
272	ev_set_allocator (persistent_realloc);	308	ev_set_allocator (persistent_realloc);
273		309
274	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]	310	=item ev_set_syserr_cb (void (*cb)(const char *msg) throw ())
275		311
276	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
277	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
278	indicating the system call or subsystem causing the problem. If this	314	indicating the system call or subsystem causing the problem. If this
279	callback is set, then libev will expect it to remedy the situation, no	315	callback is set, then libev will expect it to remedy the situation, no
…		…
291	}	327	}
292		328
293	...	329	...
294	ev_set_syserr_cb (fatal_error);	330	ev_set_syserr_cb (fatal_error);
295		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
296	=back	345	=back
297		346
298	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	347	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
299		348
300	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
301	I<not> optional in this case unless libev 3 compatibility is disabled, as	350	I<not> optional in this case unless libev 3 compatibility is disabled, as
302	libev 3 had an C<ev_loop> function colliding with the struct name).	351	libev 3 had an C<ev_loop> function colliding with the struct name).
303		352
304	The library knows two types of such loops, the I<default> loop, which	353	The library knows two types of such loops, the I<default> loop, which
305	supports signals and child events, and dynamically created event loops	354	supports child process events, and dynamically created event loops which
306	which do not.	355	do not.
307		356
308	=over 4	357	=over 4
309		358
310	=item struct ev_loop *ev_default_loop (unsigned int flags)	359	=item struct ev_loop *ev_default_loop (unsigned int flags)
311		360
312	This will initialise the default event loop if it hasn't been initialised	361	This returns the "default" event loop object, which is what you should
313	yet and return it. If the default loop could not be initialised, returns	362	normally use when you just need "the event loop". Event loop objects and
314	false. If it already was initialised it simply returns it (and ignores the	363	the C<flags> parameter are described in more detail in the entry for
315	flags. If that is troubling you, check C<ev_backend ()> afterwards).	364	C<ev_loop_new>.
		365
		366	If the default loop is already initialised then this function simply
		367	returns it (and ignores the flags. If that is troubling you, check
		368	C<ev_backend ()> afterwards). Otherwise it will create it with the given
		369	flags, which should almost always be C<0>, unless the caller is also the
		370	one calling C<ev_run> or otherwise qualifies as "the main program".
316		371
317	If you don't know what event loop to use, use the one returned from this	372	If you don't know what event loop to use, use the one returned from this
318	function.	373	function (or via the C<EV_DEFAULT> macro).
319		374
320	Note that this function is I<not> thread-safe, so if you want to use it	375	Note that this function is I<not> thread-safe, so if you want to use it
321	from multiple threads, you have to lock (note also that this is unlikely,	376	from multiple threads, you have to employ some kind of mutex (note also
322	as loops cannot be shared easily between threads anyway).	377	that this case is unlikely, as loops cannot be shared easily between
		378	threads anyway).
323		379
324	The default loop is the only loop that can handle C<ev_signal> and	380	The default loop is the only loop that can handle C<ev_child> watchers,
325	C<ev_child> watchers, and to do this, it always registers a handler	381	and to do this, it always registers a handler for C<SIGCHLD>. If this is
326	for C<SIGCHLD>. If this is a problem for your application you can either	382	a problem for your application you can either create a dynamic loop with
327	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you	383	C<ev_loop_new> which doesn't do that, or you can simply overwrite the
328	can simply overwrite the C<SIGCHLD> signal handler I<after> calling	384	C<SIGCHLD> signal handler I<after> calling C<ev_default_init>.
329	C<ev_default_init>.	385
		386	Example: This is the most typical usage.
		387
		388	if (!ev_default_loop (0))
		389	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		390
		391	Example: Restrict libev to the select and poll backends, and do not allow
		392	environment settings to be taken into account:
		393
		394	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		395
		396	=item struct ev_loop *ev_loop_new (unsigned int flags)
		397
		398	This will create and initialise a new event loop object. If the loop
		399	could not be initialised, returns false.
		400
		401	This function is thread-safe, and one common way to use libev with
		402	threads is indeed to create one loop per thread, and using the default
		403	loop in the "main" or "initial" thread.
330		404
331	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
332	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>).
333		407
334	The following flags are supported:	408	The following flags are supported:
…		…
344		418
345	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
346	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
347	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	421	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
348	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
349	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
350	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).
351		427
352	=item C<EVFLAG_FORKCHECK>	428	=item C<EVFLAG_FORKCHECK>
353		429
354	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
355	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.
356		432
357	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,
358	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
359	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
360	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
361	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
362	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).
363		440
364	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
365	forget about forgetting to tell libev about forking) when you use this	442	forget about forgetting to tell libev about forking, although you still
366	flag.	443	have to ignore C<SIGPIPE>) when you use this flag.
367		444
368	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>
369	environment variable.	446	environment variable.
370		447
371	=item C<EVFLAG_NOINOTIFY>	448	=item C<EVFLAG_NOINOTIFY>
372		449
373	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
374	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
375	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
376	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.
377		454
378	=item C<EVFLAG_SIGNALFD>	455	=item C<EVFLAG_SIGNALFD>
379		456
380	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
381	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
382	delivers signals synchronously, which makes it both faster and might make	459	delivers signals synchronously, which makes it both faster and might make
383	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
384	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
385	threads that are not interested in handling them.	462	threads that are not interested in handling them.
386		463
387	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
388	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
389	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.
390		482
391	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	483	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
392		484
393	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
394	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,
…		…
422	=item C<EVBACKEND_EPOLL> (value 4, Linux)	514	=item C<EVBACKEND_EPOLL> (value 4, Linux)
423		515
424	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
425	kernels).	517	kernels).
426		518
427	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
428	but it scales phenomenally better. While poll and select usually scale	520	it scales phenomenally better. While poll and select usually scale like
429	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
430	epoll scales either O(1) or O(active_fds).	522	fd), epoll scales either O(1) or O(active_fds).
431		523
432	The epoll mechanism deserves honorable mention as the most misdesigned	524	The epoll mechanism deserves honorable mention as the most misdesigned
433	of the more advanced event mechanisms: mere annoyances include silently	525	of the more advanced event mechanisms: mere annoyances include silently
434	dropping file descriptors, requiring a system call per change per file	526	dropping file descriptors, requiring a system call per change per file
435	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
436	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
437	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
438	take considerable time (one syscall per file descriptor) and is of course	532	set, which can take considerable time (one syscall per file descriptor)
439	hard to detect.	533	and is of course hard to detect.
440		534
441	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but	535	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
442	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
443	I<different> file descriptors (even already closed ones, so one cannot	537	totally I<different> file descriptors (even already closed ones, so
444	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
445	on SMP systems). Libev tries to counter these spurious notifications by	539	(especially on SMP systems). Libev tries to counter these spurious
446	employing an additional generation counter and comparing that against the	540	notifications by employing an additional generation counter and comparing
447	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
448	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
449	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...
450		551
451	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
452	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
453	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
454	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
…		…
466	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
467	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
468	the usage. So sad.	569	the usage. So sad.
469		570
470	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
471	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) >>) event interface
		580	available in post-4.18 kernels.
		581
		582	If this backend works for you (as of this writing, it was very
		583	experimental and only supports a subset of file types), it is the best
		584	event interface available on linux and might be well worth it enabling it
		585	- if it isn't available in your kernel this will be detected and another
		586	backend will be chosen.
		587
		588	This backend can batch oneshot requests and uses a user-space ring buffer
		589	to receive events. It also doesn't suffer from most of the design problems
		590	of epoll (such as not being able to remove event sources from the epoll
		591	set), and generally sounds too good to be true. Because, this being the
		592	linux kernel, of course it suffers from a whole new set of 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 various
		596	arbitrary limits that can be configured in F</proc/sys/fs/aio-max-nr>
		597	and F</proc/sys/fs/aio-nr>), which could lead to it being skipped during
		598	initialisation.
		599
		600	Most problematic in practise, however, is that, like kqueue, it requires
		601	special support from drivers, and, not surprisingly, not all drivers
		602	implement it. For example, in linux 4.19, tcp sockets, pipes, event fds,
		603	files, F</dev/null> and a few others are supported, but ttys are not, so
		604	this is not (yet?) a generic event polling interface but is probably still
		605	be very useful in a web server or similar program.
472		606
473	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	607	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
474	C<EVBACKEND_POLL>.	608	C<EVBACKEND_POLL>.
475		609
476	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	610	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
…		…
491		625
492	It scales in the same way as the epoll backend, but the interface to the	626	It scales in the same way as the epoll backend, but the interface to the
493	kernel is more efficient (which says nothing about its actual speed, of	627	kernel is more efficient (which says nothing about its actual speed, of
494	course). While stopping, setting and starting an I/O watcher does never	628	course). While stopping, setting and starting an I/O watcher does never
495	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to	629	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
496	two event changes per incident. Support for C<fork ()> is very bad (but	630	two event changes per incident. Support for C<fork ()> is very bad (you
497	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect	631	might have to leak fd's on fork, but it's more sane than epoll) and it
498	cases	632	drops fds silently in similarly hard-to-detect cases.
499		633
500	This backend usually performs well under most conditions.	634	This backend usually performs well under most conditions.
501		635
502	While nominally embeddable in other event loops, this doesn't work	636	While nominally embeddable in other event loops, this doesn't work
503	everywhere, so you might need to test for this. And since it is broken	637	everywhere, so you might need to test for this. And since it is broken
…		…
520	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	654	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
521		655
522	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	656	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
523	it's really slow, but it still scales very well (O(active_fds)).	657	it's really slow, but it still scales very well (O(active_fds)).
524		658
525	Please note that Solaris event ports can deliver a lot of spurious
526	notifications, so you need to use non-blocking I/O or other means to avoid
527	blocking when no data (or space) is available.
528
529	While this backend scales well, it requires one system call per active	659	While this backend scales well, it requires one system call per active
530	file descriptor per loop iteration. For small and medium numbers of file	660	file descriptor per loop iteration. For small and medium numbers of file
531	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	661	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
532	might perform better.	662	might perform better.
533		663
534	On the positive side, with the exception of the spurious readiness	664	On the positive side, this backend actually performed fully to
535	notifications, this backend actually performed fully to specification
536	in all tests and is fully embeddable, which is a rare feat among the	665	specification in all tests and is fully embeddable, which is a rare feat
537	OS-specific backends (I vastly prefer correctness over speed hacks).	666	among the OS-specific backends (I vastly prefer correctness over speed
		667	hacks).
		668
		669	On the negative side, the interface is I<bizarre> - so bizarre that
		670	even sun itself gets it wrong in their code examples: The event polling
		671	function sometimes returns events to the caller even though an error
		672	occurred, but with no indication whether it has done so or not (yes, it's
		673	even documented that way) - deadly for edge-triggered interfaces where you
		674	absolutely have to know whether an event occurred or not because you have
		675	to re-arm the watcher.
		676
		677	Fortunately libev seems to be able to work around these idiocies.
538		678
539	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	679	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
540	C<EVBACKEND_POLL>.	680	C<EVBACKEND_POLL>.
541		681
542	=item C<EVBACKEND_ALL>	682	=item C<EVBACKEND_ALL>
543		683
544	Try all backends (even potentially broken ones that wouldn't be tried	684	Try all backends (even potentially broken ones that wouldn't be tried
545	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	685	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
546	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	686	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
547		687
548	It is definitely not recommended to use this flag.	688	It is definitely not recommended to use this flag, use whatever
		689	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		690	at all.
		691
		692	=item C<EVBACKEND_MASK>
		693
		694	Not a backend at all, but a mask to select all backend bits from a
		695	C<flags> value, in case you want to mask out any backends from a flags
		696	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
549		697
550	=back	698	=back
551		699
552	If one or more of the backend flags are or'ed into the flags value,	700	If one or more of the backend flags are or'ed into the flags value,
553	then only these backends will be tried (in the reverse order as listed	701	then only these backends will be tried (in the reverse order as listed
554	here). If none are specified, all backends in C<ev_recommended_backends	702	here). If none are specified, all backends in C<ev_recommended_backends
555	()> will be tried.	703	()> will be tried.
556		704
557	Example: This is the most typical usage.
558
559	if (!ev_default_loop (0))
560	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
561
562	Example: Restrict libev to the select and poll backends, and do not allow
563	environment settings to be taken into account:
564
565	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
566
567	Example: Use whatever libev has to offer, but make sure that kqueue is
568	used if available (warning, breaks stuff, best use only with your own
569	private event loop and only if you know the OS supports your types of
570	fds):
571
572	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
573
574	=item struct ev_loop *ev_loop_new (unsigned int flags)
575
576	Similar to C<ev_default_loop>, but always creates a new event loop that is
577	always distinct from the default loop.
578
579	Note that this function I<is> thread-safe, and one common way to use
580	libev with threads is indeed to create one loop per thread, and using the
581	default loop in the "main" or "initial" thread.
582
583	Example: Try to create a event loop that uses epoll and nothing else.	705	Example: Try to create a event loop that uses epoll and nothing else.
584		706
585	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	707	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
586	if (!epoller)	708	if (!epoller)
587	fatal ("no epoll found here, maybe it hides under your chair");	709	fatal ("no epoll found here, maybe it hides under your chair");
588		710
		711	Example: Use whatever libev has to offer, but make sure that kqueue is
		712	used if available.
		713
		714	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		715
		716	Example: Similarly, on linux, you mgiht want to take advantage of the
		717	linux aio backend if possible, but fall back to something else if that
		718	isn't available.
		719
		720	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_LINUXAIO);
		721
589	=item ev_default_destroy ()	722	=item ev_loop_destroy (loop)
590		723
591	Destroys the default loop (frees all memory and kernel state etc.). None	724	Destroys an event loop object (frees all memory and kernel state
592	of the active event watchers will be stopped in the normal sense, so	725	etc.). None of the active event watchers will be stopped in the normal
593	e.g. C<ev_is_active> might still return true. It is your responsibility to	726	sense, so e.g. C<ev_is_active> might still return true. It is your
594	either stop all watchers cleanly yourself I<before> calling this function,	727	responsibility to either stop all watchers cleanly yourself I<before>
595	or cope with the fact afterwards (which is usually the easiest thing, you	728	calling this function, or cope with the fact afterwards (which is usually
596	can just ignore the watchers and/or C<free ()> them for example).	729	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		730	for example).
597		731
598	Note that certain global state, such as signal state (and installed signal	732	Note that certain global state, such as signal state (and installed signal
599	handlers), will not be freed by this function, and related watchers (such	733	handlers), will not be freed by this function, and related watchers (such
600	as signal and child watchers) would need to be stopped manually.	734	as signal and child watchers) would need to be stopped manually.
601		735
602	In general it is not advisable to call this function except in the	736	This function is normally used on loop objects allocated by
603	rare occasion where you really need to free e.g. the signal handling	737	C<ev_loop_new>, but it can also be used on the default loop returned by
		738	C<ev_default_loop>, in which case it is not thread-safe.
		739
		740	Note that it is not advisable to call this function on the default loop
		741	except in the rare occasion where you really need to free its resources.
604	pipe fds. If you need dynamically allocated loops it is better to use	742	If you need dynamically allocated loops it is better to use C<ev_loop_new>
605	C<ev_loop_new> and C<ev_loop_destroy>.	743	and C<ev_loop_destroy>.
606		744
607	=item ev_loop_destroy (loop)	745	=item ev_loop_fork (loop)
608
609	Like C<ev_default_destroy>, but destroys an event loop created by an
610	earlier call to C<ev_loop_new>.
611
612	=item ev_default_fork ()
613		746
614	This function sets a flag that causes subsequent C<ev_run> iterations	747	This function sets a flag that causes subsequent C<ev_run> iterations
615	to reinitialise the kernel state for backends that have one. Despite the	748	to reinitialise the kernel state for backends that have one. Despite
616	name, you can call it anytime, but it makes most sense after forking, in	749	the name, you can call it anytime you are allowed to start or stop
617	the child process (or both child and parent, but that again makes little	750	watchers (except inside an C<ev_prepare> callback), but it makes most
618	sense). You I<must> call it in the child before using any of the libev	751	sense after forking, in the child process. You I<must> call it (or use
619	functions, and it will only take effect at the next C<ev_run> iteration.	752	C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.
620		753
		754	In addition, if you want to reuse a loop (via this function or
		755	C<EVFLAG_FORKCHECK>), you I<also> have to ignore C<SIGPIPE>.
		756
621	Again, you I<have> to call it on I<any> loop that you want to re-use after	757	Again, you I<have> to call it on I<any> loop that you want to re-use after
622	a fork, I<even if you do not plan to use the loop in the parent>. This is	758	a fork, I<even if you do not plan to use the loop in the parent>. This is
623	because some kernel interfaces *cough* I<kqueue> *cough* do funny things	759	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
624	during fork.	760	during fork.
625		761
626	On the other hand, you only need to call this function in the child	762	On the other hand, you only need to call this function in the child
…		…
629	call it at all (in fact, C<epoll> is so badly broken that it makes a	765	call it at all (in fact, C<epoll> is so badly broken that it makes a
630	difference, but libev will usually detect this case on its own and do a	766	difference, but libev will usually detect this case on its own and do a
631	costly reset of the backend).	767	costly reset of the backend).
632		768
633	The function itself is quite fast and it's usually not a problem to call	769	The function itself is quite fast and it's usually not a problem to call
634	it just in case after a fork. To make this easy, the function will fit in	770	it just in case after a fork.
635	quite nicely into a call to C<pthread_atfork>:
636		771
		772	Example: Automate calling C<ev_loop_fork> on the default loop when
		773	using pthreads.
		774
		775	static void
		776	post_fork_child (void)
		777	{
		778	ev_loop_fork (EV_DEFAULT);
		779	}
		780
		781	...
637	pthread_atfork (0, 0, ev_default_fork);	782	pthread_atfork (0, 0, post_fork_child);
638
639	=item ev_loop_fork (loop)
640
641	Like C<ev_default_fork>, but acts on an event loop created by
642	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
643	after fork that you want to re-use in the child, and how you keep track of
644	them is entirely your own problem.
645		783
646	=item int ev_is_default_loop (loop)	784	=item int ev_is_default_loop (loop)
647		785
648	Returns true when the given loop is, in fact, the default loop, and false	786	Returns true when the given loop is, in fact, the default loop, and false
649	otherwise.	787	otherwise.
…		…
660	prepare and check phases.	798	prepare and check phases.
661		799
662	=item unsigned int ev_depth (loop)	800	=item unsigned int ev_depth (loop)
663		801
664	Returns the number of times C<ev_run> was entered minus the number of	802	Returns the number of times C<ev_run> was entered minus the number of
665	times C<ev_run> was exited, in other words, the recursion depth.	803	times C<ev_run> was exited normally, in other words, the recursion depth.
666		804
667	Outside C<ev_run>, this number is zero. In a callback, this number is	805	Outside C<ev_run>, this number is zero. In a callback, this number is
668	C<1>, unless C<ev_run> was invoked recursively (or from another thread),	806	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
669	in which case it is higher.	807	in which case it is higher.
670		808
671	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread	809	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
672	etc.), doesn't count as "exit" - consider this as a hint to avoid such	810	throwing an exception etc.), doesn't count as "exit" - consider this
673	ungentleman-like behaviour unless it's really convenient.	811	as a hint to avoid such ungentleman-like behaviour unless it's really
		812	convenient, in which case it is fully supported.
674		813
675	=item unsigned int ev_backend (loop)	814	=item unsigned int ev_backend (loop)
676		815
677	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	816	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
678	use.	817	use.
…		…
693		832
694	This function is rarely useful, but when some event callback runs for a	833	This function is rarely useful, but when some event callback runs for a
695	very long time without entering the event loop, updating libev's idea of	834	very long time without entering the event loop, updating libev's idea of
696	the current time is a good idea.	835	the current time is a good idea.
697		836
698	See also L<The special problem of time updates> in the C<ev_timer> section.	837	See also L</The special problem of time updates> in the C<ev_timer> section.
699		838
700	=item ev_suspend (loop)	839	=item ev_suspend (loop)
701		840
702	=item ev_resume (loop)	841	=item ev_resume (loop)
703		842
…		…
721	without a previous call to C<ev_suspend>.	860	without a previous call to C<ev_suspend>.
722		861
723	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the	862	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
724	event loop time (see C<ev_now_update>).	863	event loop time (see C<ev_now_update>).
725		864
726	=item ev_run (loop, int flags)	865	=item bool ev_run (loop, int flags)
727		866
728	Finally, this is it, the event handler. This function usually is called	867	Finally, this is it, the event handler. This function usually is called
729	after you have initialised all your watchers and you want to start	868	after you have initialised all your watchers and you want to start
730	handling events. It will ask the operating system for any new events, call	869	handling events. It will ask the operating system for any new events, call
731	the watcher callbacks, an then repeat the whole process indefinitely: This	870	the watcher callbacks, and then repeat the whole process indefinitely: This
732	is why event loops are called I<loops>.	871	is why event loops are called I<loops>.
733		872
734	If the flags argument is specified as C<0>, it will keep handling events	873	If the flags argument is specified as C<0>, it will keep handling events
735	until either no event watchers are active anymore or C<ev_break> was	874	until either no event watchers are active anymore or C<ev_break> was
736	called.	875	called.
		876
		877	The return value is false if there are no more active watchers (which
		878	usually means "all jobs done" or "deadlock"), and true in all other cases
		879	(which usually means " you should call C<ev_run> again").
737		880
738	Please note that an explicit C<ev_break> is usually better than	881	Please note that an explicit C<ev_break> is usually better than
739	relying on all watchers to be stopped when deciding when a program has	882	relying on all watchers to be stopped when deciding when a program has
740	finished (especially in interactive programs), but having a program	883	finished (especially in interactive programs), but having a program
741	that automatically loops as long as it has to and no longer by virtue	884	that automatically loops as long as it has to and no longer by virtue
742	of relying on its watchers stopping correctly, that is truly a thing of	885	of relying on its watchers stopping correctly, that is truly a thing of
743	beauty.	886	beauty.
744		887
		888	This function is I<mostly> exception-safe - you can break out of a
		889	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		890	exception and so on. This does not decrement the C<ev_depth> value, nor
		891	will it clear any outstanding C<EVBREAK_ONE> breaks.
		892
745	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle	893	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
746	those events and any already outstanding ones, but will not wait and	894	those events and any already outstanding ones, but will not wait and
747	block your process in case there are no events and will return after one	895	block your process in case there are no events and will return after one
748	iteration of the loop. This is sometimes useful to poll and handle new	896	iteration of the loop. This is sometimes useful to poll and handle new
749	events while doing lengthy calculations, to keep the program responsive.	897	events while doing lengthy calculations, to keep the program responsive.
…		…
758	This is useful if you are waiting for some external event in conjunction	906	This is useful if you are waiting for some external event in conjunction
759	with something not expressible using other libev watchers (i.e. "roll your	907	with something not expressible using other libev watchers (i.e. "roll your
760	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is	908	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
761	usually a better approach for this kind of thing.	909	usually a better approach for this kind of thing.
762		910
763	Here are the gory details of what C<ev_run> does:	911	Here are the gory details of what C<ev_run> does (this is for your
		912	understanding, not a guarantee that things will work exactly like this in
		913	future versions):
764		914
765	- Increment loop depth.	915	- Increment loop depth.
766	- Reset the ev_break status.	916	- Reset the ev_break status.
767	- Before the first iteration, call any pending watchers.	917	- Before the first iteration, call any pending watchers.
768	LOOP:	918	LOOP:
…		…
801	anymore.	951	anymore.
802		952
803	... queue jobs here, make sure they register event watchers as long	953	... queue jobs here, make sure they register event watchers as long
804	... as they still have work to do (even an idle watcher will do..)	954	... as they still have work to do (even an idle watcher will do..)
805	ev_run (my_loop, 0);	955	ev_run (my_loop, 0);
806	... jobs done or somebody called unloop. yeah!	956	... jobs done or somebody called break. yeah!
807		957
808	=item ev_break (loop, how)	958	=item ev_break (loop, how)
809		959
810	Can be used to make a call to C<ev_run> return early (but only after it	960	Can be used to make a call to C<ev_run> return early (but only after it
811	has processed all outstanding events). The C<how> argument must be either	961	has processed all outstanding events). The C<how> argument must be either
812	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or	962	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
813	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.	963	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
814		964
815	This "unloop state" will be cleared when entering C<ev_run> again.	965	This "break state" will be cleared on the next call to C<ev_run>.
816		966
817	It is safe to call C<ev_break> from outside any C<ev_run> calls. ##TODO##	967	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		968	which case it will have no effect.
818		969
819	=item ev_ref (loop)	970	=item ev_ref (loop)
820		971
821	=item ev_unref (loop)	972	=item ev_unref (loop)
822		973
…		…
843	running when nothing else is active.	994	running when nothing else is active.
844		995
845	ev_signal exitsig;	996	ev_signal exitsig;
846	ev_signal_init (&exitsig, sig_cb, SIGINT);	997	ev_signal_init (&exitsig, sig_cb, SIGINT);
847	ev_signal_start (loop, &exitsig);	998	ev_signal_start (loop, &exitsig);
848	evf_unref (loop);	999	ev_unref (loop);
849		1000
850	Example: For some weird reason, unregister the above signal handler again.	1001	Example: For some weird reason, unregister the above signal handler again.
851		1002
852	ev_ref (loop);	1003	ev_ref (loop);
853	ev_signal_stop (loop, &exitsig);	1004	ev_signal_stop (loop, &exitsig);
…		…
873	overhead for the actual polling but can deliver many events at once.	1024	overhead for the actual polling but can deliver many events at once.
874		1025
875	By setting a higher I<io collect interval> you allow libev to spend more	1026	By setting a higher I<io collect interval> you allow libev to spend more
876	time collecting I/O events, so you can handle more events per iteration,	1027	time collecting I/O events, so you can handle more events per iteration,
877	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	1028	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
878	C<ev_timer>) will be not affected. Setting this to a non-null value will	1029	C<ev_timer>) will not be affected. Setting this to a non-null value will
879	introduce an additional C<ev_sleep ()> call into most loop iterations. The	1030	introduce an additional C<ev_sleep ()> call into most loop iterations. The
880	sleep time ensures that libev will not poll for I/O events more often then	1031	sleep time ensures that libev will not poll for I/O events more often then
881	once per this interval, on average.	1032	once per this interval, on average (as long as the host time resolution is
		1033	good enough).
882		1034
883	Likewise, by setting a higher I<timeout collect interval> you allow libev	1035	Likewise, by setting a higher I<timeout collect interval> you allow libev
884	to spend more time collecting timeouts, at the expense of increased	1036	to spend more time collecting timeouts, at the expense of increased
885	latency/jitter/inexactness (the watcher callback will be called	1037	latency/jitter/inexactness (the watcher callback will be called
886	later). C<ev_io> watchers will not be affected. Setting this to a non-null	1038	later). C<ev_io> watchers will not be affected. Setting this to a non-null
…		…
932	invoke the actual watchers inside another context (another thread etc.).	1084	invoke the actual watchers inside another context (another thread etc.).
933		1085
934	If you want to reset the callback, use C<ev_invoke_pending> as new	1086	If you want to reset the callback, use C<ev_invoke_pending> as new
935	callback.	1087	callback.
936		1088
937	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))	1089	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
938		1090
939	Sometimes you want to share the same loop between multiple threads. This	1091	Sometimes you want to share the same loop between multiple threads. This
940	can be done relatively simply by putting mutex_lock/unlock calls around	1092	can be done relatively simply by putting mutex_lock/unlock calls around
941	each call to a libev function.	1093	each call to a libev function.
942		1094
943	However, C<ev_run> can run an indefinite time, so it is not feasible	1095	However, C<ev_run> can run an indefinite time, so it is not feasible
944	to wait for it to return. One way around this is to wake up the event	1096	to wait for it to return. One way around this is to wake up the event
945	loop via C<ev_break> and C<av_async_send>, another way is to set these	1097	loop via C<ev_break> and C<ev_async_send>, another way is to set these
946	I<release> and I<acquire> callbacks on the loop.	1098	I<release> and I<acquire> callbacks on the loop.
947		1099
948	When set, then C<release> will be called just before the thread is	1100	When set, then C<release> will be called just before the thread is
949	suspended waiting for new events, and C<acquire> is called just	1101	suspended waiting for new events, and C<acquire> is called just
950	afterwards.	1102	afterwards.
…		…
965	See also the locking example in the C<THREADS> section later in this	1117	See also the locking example in the C<THREADS> section later in this
966	document.	1118	document.
967		1119
968	=item ev_set_userdata (loop, void *data)	1120	=item ev_set_userdata (loop, void *data)
969		1121
970	=item ev_userdata (loop)	1122	=item void *ev_userdata (loop)
971		1123
972	Set and retrieve a single C<void *> associated with a loop. When	1124	Set and retrieve a single C<void *> associated with a loop. When
973	C<ev_set_userdata> has never been called, then C<ev_userdata> returns	1125	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
974	C<0.>	1126	C<0>.
975		1127
976	These two functions can be used to associate arbitrary data with a loop,	1128	These two functions can be used to associate arbitrary data with a loop,
977	and are intended solely for the C<invoke_pending_cb>, C<release> and	1129	and are intended solely for the C<invoke_pending_cb>, C<release> and
978	C<acquire> callbacks described above, but of course can be (ab-)used for	1130	C<acquire> callbacks described above, but of course can be (ab-)used for
979	any other purpose as well.	1131	any other purpose as well.
…		…
1090		1242
1091	=item C<EV_PREPARE>	1243	=item C<EV_PREPARE>
1092		1244
1093	=item C<EV_CHECK>	1245	=item C<EV_CHECK>
1094		1246
1095	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts	1247	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts to
1096	to gather new events, and all C<ev_check> watchers are invoked just after	1248	gather new events, and all C<ev_check> watchers are queued (not invoked)
1097	C<ev_run> has gathered them, but before it invokes any callbacks for any	1249	just after C<ev_run> has gathered them, but before it queues any callbacks
		1250	for any received events. That means C<ev_prepare> watchers are the last
		1251	watchers invoked before the event loop sleeps or polls for new events, and
		1252	C<ev_check> watchers will be invoked before any other watchers of the same
		1253	or lower priority within an event loop iteration.
		1254
1098	received events. Callbacks of both watcher types can start and stop as	1255	Callbacks of both watcher types can start and stop as many watchers as
1099	many watchers as they want, and all of them will be taken into account	1256	they want, and all of them will be taken into account (for example, a
1100	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1257	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
1101	C<ev_run> from blocking).	1258	blocking).
1102		1259
1103	=item C<EV_EMBED>	1260	=item C<EV_EMBED>
1104		1261
1105	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1262	The embedded event loop specified in the C<ev_embed> watcher needs attention.
1106		1263
1107	=item C<EV_FORK>	1264	=item C<EV_FORK>
1108		1265
1109	The event loop has been resumed in the child process after fork (see	1266	The event loop has been resumed in the child process after fork (see
1110	C<ev_fork>).	1267	C<ev_fork>).
		1268
		1269	=item C<EV_CLEANUP>
		1270
		1271	The event loop is about to be destroyed (see C<ev_cleanup>).
1111		1272
1112	=item C<EV_ASYNC>	1273	=item C<EV_ASYNC>
1113		1274
1114	The given async watcher has been asynchronously notified (see C<ev_async>).	1275	The given async watcher has been asynchronously notified (see C<ev_async>).
1115		1276
…		…
1137	programs, though, as the fd could already be closed and reused for another	1298	programs, though, as the fd could already be closed and reused for another
1138	thing, so beware.	1299	thing, so beware.
1139		1300
1140	=back	1301	=back
1141		1302
		1303	=head2 GENERIC WATCHER FUNCTIONS
		1304
		1305	=over 4
		1306
		1307	=item C<ev_init> (ev_TYPE *watcher, callback)
		1308
		1309	This macro initialises the generic portion of a watcher. The contents
		1310	of the watcher object can be arbitrary (so C<malloc> will do). Only
		1311	the generic parts of the watcher are initialised, you I<need> to call
		1312	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		1313	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		1314	which rolls both calls into one.
		1315
		1316	You can reinitialise a watcher at any time as long as it has been stopped
		1317	(or never started) and there are no pending events outstanding.
		1318
		1319	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
		1320	int revents)>.
		1321
		1322	Example: Initialise an C<ev_io> watcher in two steps.
		1323
		1324	ev_io w;
		1325	ev_init (&w, my_cb);
		1326	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1327
		1328	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
		1329
		1330	This macro initialises the type-specific parts of a watcher. You need to
		1331	call C<ev_init> at least once before you call this macro, but you can
		1332	call C<ev_TYPE_set> any number of times. You must not, however, call this
		1333	macro on a watcher that is active (it can be pending, however, which is a
		1334	difference to the C<ev_init> macro).
		1335
		1336	Although some watcher types do not have type-specific arguments
		1337	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		1338
		1339	See C<ev_init>, above, for an example.
		1340
		1341	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		1342
		1343	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		1344	calls into a single call. This is the most convenient method to initialise
		1345	a watcher. The same limitations apply, of course.
		1346
		1347	Example: Initialise and set an C<ev_io> watcher in one step.
		1348
		1349	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1350
		1351	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
		1352
		1353	Starts (activates) the given watcher. Only active watchers will receive
		1354	events. If the watcher is already active nothing will happen.
		1355
		1356	Example: Start the C<ev_io> watcher that is being abused as example in this
		1357	whole section.
		1358
		1359	ev_io_start (EV_DEFAULT_UC, &w);
		1360
		1361	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
		1362
		1363	Stops the given watcher if active, and clears the pending status (whether
		1364	the watcher was active or not).
		1365
		1366	It is possible that stopped watchers are pending - for example,
		1367	non-repeating timers are being stopped when they become pending - but
		1368	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
		1369	pending. If you want to free or reuse the memory used by the watcher it is
		1370	therefore a good idea to always call its C<ev_TYPE_stop> function.
		1371
		1372	=item bool ev_is_active (ev_TYPE *watcher)
		1373
		1374	Returns a true value iff the watcher is active (i.e. it has been started
		1375	and not yet been stopped). As long as a watcher is active you must not modify
		1376	it.
		1377
		1378	=item bool ev_is_pending (ev_TYPE *watcher)
		1379
		1380	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		1381	events but its callback has not yet been invoked). As long as a watcher
		1382	is pending (but not active) you must not call an init function on it (but
		1383	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		1384	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1385	it).
		1386
		1387	=item callback ev_cb (ev_TYPE *watcher)
		1388
		1389	Returns the callback currently set on the watcher.
		1390
		1391	=item ev_set_cb (ev_TYPE *watcher, callback)
		1392
		1393	Change the callback. You can change the callback at virtually any time
		1394	(modulo threads).
		1395
		1396	=item ev_set_priority (ev_TYPE *watcher, int priority)
		1397
		1398	=item int ev_priority (ev_TYPE *watcher)
		1399
		1400	Set and query the priority of the watcher. The priority is a small
		1401	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1402	(default: C<-2>). Pending watchers with higher priority will be invoked
		1403	before watchers with lower priority, but priority will not keep watchers
		1404	from being executed (except for C<ev_idle> watchers).
		1405
		1406	If you need to suppress invocation when higher priority events are pending
		1407	you need to look at C<ev_idle> watchers, which provide this functionality.
		1408
		1409	You I<must not> change the priority of a watcher as long as it is active or
		1410	pending.
		1411
		1412	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1413	fine, as long as you do not mind that the priority value you query might
		1414	or might not have been clamped to the valid range.
		1415
		1416	The default priority used by watchers when no priority has been set is
		1417	always C<0>, which is supposed to not be too high and not be too low :).
		1418
		1419	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1420	priorities.
		1421
		1422	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1423
		1424	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1425	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1426	can deal with that fact, as both are simply passed through to the
		1427	callback.
		1428
		1429	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1430
		1431	If the watcher is pending, this function clears its pending status and
		1432	returns its C<revents> bitset (as if its callback was invoked). If the
		1433	watcher isn't pending it does nothing and returns C<0>.
		1434
		1435	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1436	callback to be invoked, which can be accomplished with this function.
		1437
		1438	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1439
		1440	Feeds the given event set into the event loop, as if the specified event
		1441	had happened for the specified watcher (which must be a pointer to an
		1442	initialised but not necessarily started event watcher). Obviously you must
		1443	not free the watcher as long as it has pending events.
		1444
		1445	Stopping the watcher, letting libev invoke it, or calling
		1446	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1447	not started in the first place.
		1448
		1449	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1450	functions that do not need a watcher.
		1451
		1452	=back
		1453
		1454	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
		1455	OWN COMPOSITE WATCHERS> idioms.
		1456
1142	=head2 WATCHER STATES	1457	=head2 WATCHER STATES
1143		1458
1144	There are various watcher states mentioned throughout this manual -	1459	There are various watcher states mentioned throughout this manual -
1145	active, pending and so on. In this section these states and the rules to	1460	active, pending and so on. In this section these states and the rules to
1146	transition between them will be described in more detail - and while these	1461	transition between them will be described in more detail - and while these
1147	rules might look complicated, they usually do "the right thing".	1462	rules might look complicated, they usually do "the right thing".
1148		1463
1149	=over 4	1464	=over 4
1150		1465
1151	=item initialiased	1466	=item initialised
1152		1467
1153	Before a watcher can be registered with the event looop it has to be	1468	Before a watcher can be registered with the event loop it has to be
1154	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to	1469	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
1155	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.	1470	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1156		1471
1157	In this state it is simply some block of memory that is suitable for use	1472	In this state it is simply some block of memory that is suitable for
1158	in an event loop. It can be moved around, freed, reused etc. at will.	1473	use in an event loop. It can be moved around, freed, reused etc. at
		1474	will - as long as you either keep the memory contents intact, or call
		1475	C<ev_TYPE_init> again.
1159		1476
1160	=item started/running/active	1477	=item started/running/active
1161		1478
1162	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes	1479	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
1163	property of the event loop, and is actively waiting for events. While in	1480	property of the event loop, and is actively waiting for events. While in
…		…
1191	latter will clear any pending state the watcher might be in, regardless	1508	latter will clear any pending state the watcher might be in, regardless
1192	of whether it was active or not, so stopping a watcher explicitly before	1509	of whether it was active or not, so stopping a watcher explicitly before
1193	freeing it is often a good idea.	1510	freeing it is often a good idea.
1194		1511
1195	While stopped (and not pending) the watcher is essentially in the	1512	While stopped (and not pending) the watcher is essentially in the
1196	initialised state, that is it can be reused, moved, modified in any way	1513	initialised state, that is, it can be reused, moved, modified in any way
1197	you wish.	1514	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1515	it again).
1198		1516
1199	=back	1517	=back
1200
1201	=head2 GENERIC WATCHER FUNCTIONS
1202
1203	=over 4
1204
1205	=item C<ev_init> (ev_TYPE *watcher, callback)
1206
1207	This macro initialises the generic portion of a watcher. The contents
1208	of the watcher object can be arbitrary (so C<malloc> will do). Only
1209	the generic parts of the watcher are initialised, you I<need> to call
1210	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
1211	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
1212	which rolls both calls into one.
1213
1214	You can reinitialise a watcher at any time as long as it has been stopped
1215	(or never started) and there are no pending events outstanding.
1216
1217	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
1218	int revents)>.
1219
1220	Example: Initialise an C<ev_io> watcher in two steps.
1221
1222	ev_io w;
1223	ev_init (&w, my_cb);
1224	ev_io_set (&w, STDIN_FILENO, EV_READ);
1225
1226	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
1227
1228	This macro initialises the type-specific parts of a watcher. You need to
1229	call C<ev_init> at least once before you call this macro, but you can
1230	call C<ev_TYPE_set> any number of times. You must not, however, call this
1231	macro on a watcher that is active (it can be pending, however, which is a
1232	difference to the C<ev_init> macro).
1233
1234	Although some watcher types do not have type-specific arguments
1235	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
1236
1237	See C<ev_init>, above, for an example.
1238
1239	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
1240
1241	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
1242	calls into a single call. This is the most convenient method to initialise
1243	a watcher. The same limitations apply, of course.
1244
1245	Example: Initialise and set an C<ev_io> watcher in one step.
1246
1247	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1248
1249	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
1250
1251	Starts (activates) the given watcher. Only active watchers will receive
1252	events. If the watcher is already active nothing will happen.
1253
1254	Example: Start the C<ev_io> watcher that is being abused as example in this
1255	whole section.
1256
1257	ev_io_start (EV_DEFAULT_UC, &w);
1258
1259	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
1260
1261	Stops the given watcher if active, and clears the pending status (whether
1262	the watcher was active or not).
1263
1264	It is possible that stopped watchers are pending - for example,
1265	non-repeating timers are being stopped when they become pending - but
1266	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
1267	pending. If you want to free or reuse the memory used by the watcher it is
1268	therefore a good idea to always call its C<ev_TYPE_stop> function.
1269
1270	=item bool ev_is_active (ev_TYPE *watcher)
1271
1272	Returns a true value iff the watcher is active (i.e. it has been started
1273	and not yet been stopped). As long as a watcher is active you must not modify
1274	it.
1275
1276	=item bool ev_is_pending (ev_TYPE *watcher)
1277
1278	Returns a true value iff the watcher is pending, (i.e. it has outstanding
1279	events but its callback has not yet been invoked). As long as a watcher
1280	is pending (but not active) you must not call an init function on it (but
1281	C<ev_TYPE_set> is safe), you must not change its priority, and you must
1282	make sure the watcher is available to libev (e.g. you cannot C<free ()>
1283	it).
1284
1285	=item callback ev_cb (ev_TYPE *watcher)
1286
1287	Returns the callback currently set on the watcher.
1288
1289	=item ev_cb_set (ev_TYPE *watcher, callback)
1290
1291	Change the callback. You can change the callback at virtually any time
1292	(modulo threads).
1293
1294	=item ev_set_priority (ev_TYPE *watcher, int priority)
1295
1296	=item int ev_priority (ev_TYPE *watcher)
1297
1298	Set and query the priority of the watcher. The priority is a small
1299	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
1300	(default: C<-2>). Pending watchers with higher priority will be invoked
1301	before watchers with lower priority, but priority will not keep watchers
1302	from being executed (except for C<ev_idle> watchers).
1303
1304	If you need to suppress invocation when higher priority events are pending
1305	you need to look at C<ev_idle> watchers, which provide this functionality.
1306
1307	You I<must not> change the priority of a watcher as long as it is active or
1308	pending.
1309
1310	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
1311	fine, as long as you do not mind that the priority value you query might
1312	or might not have been clamped to the valid range.
1313
1314	The default priority used by watchers when no priority has been set is
1315	always C<0>, which is supposed to not be too high and not be too low :).
1316
1317	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1318	priorities.
1319
1320	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1321
1322	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
1323	C<loop> nor C<revents> need to be valid as long as the watcher callback
1324	can deal with that fact, as both are simply passed through to the
1325	callback.
1326
1327	=item int ev_clear_pending (loop, ev_TYPE *watcher)
1328
1329	If the watcher is pending, this function clears its pending status and
1330	returns its C<revents> bitset (as if its callback was invoked). If the
1331	watcher isn't pending it does nothing and returns C<0>.
1332
1333	Sometimes it can be useful to "poll" a watcher instead of waiting for its
1334	callback to be invoked, which can be accomplished with this function.
1335
1336	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
1337
1338	Feeds the given event set into the event loop, as if the specified event
1339	had happened for the specified watcher (which must be a pointer to an
1340	initialised but not necessarily started event watcher). Obviously you must
1341	not free the watcher as long as it has pending events.
1342
1343	Stopping the watcher, letting libev invoke it, or calling
1344	C<ev_clear_pending> will clear the pending event, even if the watcher was
1345	not started in the first place.
1346
1347	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1348	functions that do not need a watcher.
1349
1350	=back
1351
1352
1353	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
1354
1355	Each watcher has, by default, a member C<void *data> that you can change
1356	and read at any time: libev will completely ignore it. This can be used
1357	to associate arbitrary data with your watcher. If you need more data and
1358	don't want to allocate memory and store a pointer to it in that data
1359	member, you can also "subclass" the watcher type and provide your own
1360	data:
1361
1362	struct my_io
1363	{
1364	ev_io io;
1365	int otherfd;
1366	void *somedata;
1367	struct whatever *mostinteresting;
1368	};
1369
1370	...
1371	struct my_io w;
1372	ev_io_init (&w.io, my_cb, fd, EV_READ);
1373
1374	And since your callback will be called with a pointer to the watcher, you
1375	can cast it back to your own type:
1376
1377	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1378	{
1379	struct my_io *w = (struct my_io *)w_;
1380	...
1381	}
1382
1383	More interesting and less C-conformant ways of casting your callback type
1384	instead have been omitted.
1385
1386	Another common scenario is to use some data structure with multiple
1387	embedded watchers:
1388
1389	struct my_biggy
1390	{
1391	int some_data;
1392	ev_timer t1;
1393	ev_timer t2;
1394	}
1395
1396	In this case getting the pointer to C<my_biggy> is a bit more
1397	complicated: Either you store the address of your C<my_biggy> struct
1398	in the C<data> member of the watcher (for woozies), or you need to use
1399	some pointer arithmetic using C<offsetof> inside your watchers (for real
1400	programmers):
1401
1402	#include <stddef.h>
1403
1404	static void
1405	t1_cb (EV_P_ ev_timer *w, int revents)
1406	{
1407	struct my_biggy big = (struct my_biggy *)
1408	(((char *)w) - offsetof (struct my_biggy, t1));
1409	}
1410
1411	static void
1412	t2_cb (EV_P_ ev_timer *w, int revents)
1413	{
1414	struct my_biggy big = (struct my_biggy *)
1415	(((char *)w) - offsetof (struct my_biggy, t2));
1416	}
1417		1518
1418	=head2 WATCHER PRIORITY MODELS	1519	=head2 WATCHER PRIORITY MODELS
1419		1520
1420	Many event loops support I<watcher priorities>, which are usually small	1521	Many event loops support I<watcher priorities>, which are usually small
1421	integers that influence the ordering of event callback invocation	1522	integers that influence the ordering of event callback invocation
…		…
1548	In general you can register as many read and/or write event watchers per	1649	In general you can register as many read and/or write event watchers per
1549	fd as you want (as long as you don't confuse yourself). Setting all file	1650	fd as you want (as long as you don't confuse yourself). Setting all file
1550	descriptors to non-blocking mode is also usually a good idea (but not	1651	descriptors to non-blocking mode is also usually a good idea (but not
1551	required if you know what you are doing).	1652	required if you know what you are doing).
1552		1653
1553	If you cannot use non-blocking mode, then force the use of a
1554	known-to-be-good backend (at the time of this writing, this includes only
1555	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
1556	descriptors for which non-blocking operation makes no sense (such as
1557	files) - libev doesn't guarantee any specific behaviour in that case.
1558
1559	Another thing you have to watch out for is that it is quite easy to	1654	Another thing you have to watch out for is that it is quite easy to
1560	receive "spurious" readiness notifications, that is your callback might	1655	receive "spurious" readiness notifications, that is, your callback might
1561	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1656	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1562	because there is no data. Not only are some backends known to create a	1657	because there is no data. It is very easy to get into this situation even
1563	lot of those (for example Solaris ports), it is very easy to get into	1658	with a relatively standard program structure. Thus it is best to always
1564	this situation even with a relatively standard program structure. Thus	1659	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1565	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1566	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1660	preferable to a program hanging until some data arrives.
1567		1661
1568	If you cannot run the fd in non-blocking mode (for example you should	1662	If you cannot run the fd in non-blocking mode (for example you should
1569	not play around with an Xlib connection), then you have to separately	1663	not play around with an Xlib connection), then you have to separately
1570	re-test whether a file descriptor is really ready with a known-to-be good	1664	re-test whether a file descriptor is really ready with a known-to-be good
1571	interface such as poll (fortunately in our Xlib example, Xlib already	1665	interface such as poll (fortunately in the case of Xlib, it already does
1572	does this on its own, so its quite safe to use). Some people additionally	1666	this on its own, so its quite safe to use). Some people additionally
1573	use C<SIGALRM> and an interval timer, just to be sure you won't block	1667	use C<SIGALRM> and an interval timer, just to be sure you won't block
1574	indefinitely.	1668	indefinitely.
1575		1669
1576	But really, best use non-blocking mode.	1670	But really, best use non-blocking mode.
1577		1671
1578	=head3 The special problem of disappearing file descriptors	1672	=head3 The special problem of disappearing file descriptors
1579		1673
1580	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1674	Some backends (e.g. kqueue, epoll, linuxaio) need to be told about closing
1581	descriptor (either due to calling C<close> explicitly or any other means,	1675	a file descriptor (either due to calling C<close> explicitly or any other
1582	such as C<dup2>). The reason is that you register interest in some file	1676	means, such as C<dup2>). The reason is that you register interest in some
1583	descriptor, but when it goes away, the operating system will silently drop	1677	file descriptor, but when it goes away, the operating system will silently
1584	this interest. If another file descriptor with the same number then is	1678	drop this interest. If another file descriptor with the same number then
1585	registered with libev, there is no efficient way to see that this is, in	1679	is registered with libev, there is no efficient way to see that this is,
1586	fact, a different file descriptor.	1680	in fact, a different file descriptor.
1587		1681
1588	To avoid having to explicitly tell libev about such cases, libev follows	1682	To avoid having to explicitly tell libev about such cases, libev follows
1589	the following policy: Each time C<ev_io_set> is being called, libev	1683	the following policy: Each time C<ev_io_set> is being called, libev
1590	will assume that this is potentially a new file descriptor, otherwise	1684	will assume that this is potentially a new file descriptor, otherwise
1591	it is assumed that the file descriptor stays the same. That means that	1685	it is assumed that the file descriptor stays the same. That means that
…		…
1605		1699
1606	There is no workaround possible except not registering events	1700	There is no workaround possible except not registering events
1607	for potentially C<dup ()>'ed file descriptors, or to resort to	1701	for potentially C<dup ()>'ed file descriptors, or to resort to
1608	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1702	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1609		1703
		1704	=head3 The special problem of files
		1705
		1706	Many people try to use C<select> (or libev) on file descriptors
		1707	representing files, and expect it to become ready when their program
		1708	doesn't block on disk accesses (which can take a long time on their own).
		1709
		1710	However, this cannot ever work in the "expected" way - you get a readiness
		1711	notification as soon as the kernel knows whether and how much data is
		1712	there, and in the case of open files, that's always the case, so you
		1713	always get a readiness notification instantly, and your read (or possibly
		1714	write) will still block on the disk I/O.
		1715
		1716	Another way to view it is that in the case of sockets, pipes, character
		1717	devices and so on, there is another party (the sender) that delivers data
		1718	on its own, but in the case of files, there is no such thing: the disk
		1719	will not send data on its own, simply because it doesn't know what you
		1720	wish to read - you would first have to request some data.
		1721
		1722	Since files are typically not-so-well supported by advanced notification
		1723	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1724	to files, even though you should not use it. The reason for this is
		1725	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1726	usually a tty, often a pipe, but also sometimes files or special devices
		1727	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1728	F</dev/urandom>), and even though the file might better be served with
		1729	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1730	it "just works" instead of freezing.
		1731
		1732	So avoid file descriptors pointing to files when you know it (e.g. use
		1733	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1734	when you rarely read from a file instead of from a socket, and want to
		1735	reuse the same code path.
		1736
1610	=head3 The special problem of fork	1737	=head3 The special problem of fork
1611		1738
1612	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1739	Some backends (epoll, kqueue, probably linuxaio) do not support C<fork ()>
1613	useless behaviour. Libev fully supports fork, but needs to be told about	1740	at all or exhibit useless behaviour. Libev fully supports fork, but needs
1614	it in the child.	1741	to be told about it in the child if you want to continue to use it in the
		1742	child.
1615		1743
1616	To support fork in your programs, you either have to call	1744	To support fork in your child processes, you have to call C<ev_loop_fork
1617	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1745	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1618	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1746	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1619	C<EVBACKEND_POLL>.
1620		1747
1621	=head3 The special problem of SIGPIPE	1748	=head3 The special problem of SIGPIPE
1622		1749
1623	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1750	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1624	when writing to a pipe whose other end has been closed, your program gets	1751	when writing to a pipe whose other end has been closed, your program gets
…		…
1722	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1849	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1723	monotonic clock option helps a lot here).	1850	monotonic clock option helps a lot here).
1724		1851
1725	The callback is guaranteed to be invoked only I<after> its timeout has	1852	The callback is guaranteed to be invoked only I<after> its timeout has
1726	passed (not I<at>, so on systems with very low-resolution clocks this	1853	passed (not I<at>, so on systems with very low-resolution clocks this
1727	might introduce a small delay). If multiple timers become ready during the	1854	might introduce a small delay, see "the special problem of being too
		1855	early", below). If multiple timers become ready during the same loop
1728	same loop iteration then the ones with earlier time-out values are invoked	1856	iteration then the ones with earlier time-out values are invoked before
1729	before ones of the same priority with later time-out values (but this is	1857	ones of the same priority with later time-out values (but this is no
1730	no longer true when a callback calls C<ev_run> recursively).	1858	longer true when a callback calls C<ev_run> recursively).
1731		1859
1732	=head3 Be smart about timeouts	1860	=head3 Be smart about timeouts
1733		1861
1734	Many real-world problems involve some kind of timeout, usually for error	1862	Many real-world problems involve some kind of timeout, usually for error
1735	recovery. A typical example is an HTTP request - if the other side hangs,	1863	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1810		1938
1811	In this case, it would be more efficient to leave the C<ev_timer> alone,	1939	In this case, it would be more efficient to leave the C<ev_timer> alone,
1812	but remember the time of last activity, and check for a real timeout only	1940	but remember the time of last activity, and check for a real timeout only
1813	within the callback:	1941	within the callback:
1814		1942
		1943	ev_tstamp timeout = 60.;
1815	ev_tstamp last_activity; // time of last activity	1944	ev_tstamp last_activity; // time of last activity
		1945	ev_timer timer;
1816		1946
1817	static void	1947	static void
1818	callback (EV_P_ ev_timer *w, int revents)	1948	callback (EV_P_ ev_timer *w, int revents)
1819	{	1949	{
1820	ev_tstamp now = ev_now (EV_A);	1950	// calculate when the timeout would happen
1821	ev_tstamp timeout = last_activity + 60.;	1951	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
1822		1952
1823	// if last_activity + 60. is older than now, we did time out	1953	// if negative, it means we the timeout already occurred
1824	if (timeout < now)	1954	if (after < 0.)
1825	{	1955	{
1826	// timeout occurred, take action	1956	// timeout occurred, take action
1827	}	1957	}
1828	else	1958	else
1829	{	1959	{
1830	// callback was invoked, but there was some activity, re-arm	1960	// callback was invoked, but there was some recent
1831	// the watcher to fire in last_activity + 60, which is	1961	// activity. simply restart the timer to time out
1832	// guaranteed to be in the future, so "again" is positive:	1962	// after "after" seconds, which is the earliest time
1833	w->repeat = timeout - now;	1963	// the timeout can occur.
		1964	ev_timer_set (w, after, 0.);
1834	ev_timer_again (EV_A_ w);	1965	ev_timer_start (EV_A_ w);
1835	}	1966	}
1836	}	1967	}
1837		1968
1838	To summarise the callback: first calculate the real timeout (defined	1969	To summarise the callback: first calculate in how many seconds the
1839	as "60 seconds after the last activity"), then check if that time has	1970	timeout will occur (by calculating the absolute time when it would occur,
1840	been reached, which means something I<did>, in fact, time out. Otherwise	1971	C<last_activity + timeout>, and subtracting the current time, C<ev_now
1841	the callback was invoked too early (C<timeout> is in the future), so	1972	(EV_A)> from that).
1842	re-schedule the timer to fire at that future time, to see if maybe we have
1843	a timeout then.
1844		1973
1845	Note how C<ev_timer_again> is used, taking advantage of the	1974	If this value is negative, then we are already past the timeout, i.e. we
1846	C<ev_timer_again> optimisation when the timer is already running.	1975	timed out, and need to do whatever is needed in this case.
		1976
		1977	Otherwise, we now the earliest time at which the timeout would trigger,
		1978	and simply start the timer with this timeout value.
		1979
		1980	In other words, each time the callback is invoked it will check whether
		1981	the timeout occurred. If not, it will simply reschedule itself to check
		1982	again at the earliest time it could time out. Rinse. Repeat.
1847		1983
1848	This scheme causes more callback invocations (about one every 60 seconds	1984	This scheme causes more callback invocations (about one every 60 seconds
1849	minus half the average time between activity), but virtually no calls to	1985	minus half the average time between activity), but virtually no calls to
1850	libev to change the timeout.	1986	libev to change the timeout.
1851		1987
1852	To start the timer, simply initialise the watcher and set C<last_activity>	1988	To start the machinery, simply initialise the watcher and set
1853	to the current time (meaning we just have some activity :), then call the	1989	C<last_activity> to the current time (meaning there was some activity just
1854	callback, which will "do the right thing" and start the timer:	1990	now), then call the callback, which will "do the right thing" and start
		1991	the timer:
1855		1992
		1993	last_activity = ev_now (EV_A);
1856	ev_init (timer, callback);	1994	ev_init (&timer, callback);
1857	last_activity = ev_now (loop);	1995	callback (EV_A_ &timer, 0);
1858	callback (loop, timer, EV_TIMER);
1859		1996
1860	And when there is some activity, simply store the current time in	1997	When there is some activity, simply store the current time in
1861	C<last_activity>, no libev calls at all:	1998	C<last_activity>, no libev calls at all:
1862		1999
		2000	if (activity detected)
1863	last_activity = ev_now (loop);	2001	last_activity = ev_now (EV_A);
		2002
		2003	When your timeout value changes, then the timeout can be changed by simply
		2004	providing a new value, stopping the timer and calling the callback, which
		2005	will again do the right thing (for example, time out immediately :).
		2006
		2007	timeout = new_value;
		2008	ev_timer_stop (EV_A_ &timer);
		2009	callback (EV_A_ &timer, 0);
1864		2010
1865	This technique is slightly more complex, but in most cases where the	2011	This technique is slightly more complex, but in most cases where the
1866	time-out is unlikely to be triggered, much more efficient.	2012	time-out is unlikely to be triggered, much more efficient.
1867
1868	Changing the timeout is trivial as well (if it isn't hard-coded in the
1869	callback :) - just change the timeout and invoke the callback, which will
1870	fix things for you.
1871		2013
1872	=item 4. Wee, just use a double-linked list for your timeouts.	2014	=item 4. Wee, just use a double-linked list for your timeouts.
1873		2015
1874	If there is not one request, but many thousands (millions...), all	2016	If there is not one request, but many thousands (millions...), all
1875	employing some kind of timeout with the same timeout value, then one can	2017	employing some kind of timeout with the same timeout value, then one can
…		…
1902	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is	2044	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
1903	rather complicated, but extremely efficient, something that really pays	2045	rather complicated, but extremely efficient, something that really pays
1904	off after the first million or so of active timers, i.e. it's usually	2046	off after the first million or so of active timers, i.e. it's usually
1905	overkill :)	2047	overkill :)
1906		2048
		2049	=head3 The special problem of being too early
		2050
		2051	If you ask a timer to call your callback after three seconds, then
		2052	you expect it to be invoked after three seconds - but of course, this
		2053	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		2054	guaranteed to any precision by libev - imagine somebody suspending the
		2055	process with a STOP signal for a few hours for example.
		2056
		2057	So, libev tries to invoke your callback as soon as possible I<after> the
		2058	delay has occurred, but cannot guarantee this.
		2059
		2060	A less obvious failure mode is calling your callback too early: many event
		2061	loops compare timestamps with a "elapsed delay >= requested delay", but
		2062	this can cause your callback to be invoked much earlier than you would
		2063	expect.
		2064
		2065	To see why, imagine a system with a clock that only offers full second
		2066	resolution (think windows if you can't come up with a broken enough OS
		2067	yourself). If you schedule a one-second timer at the time 500.9, then the
		2068	event loop will schedule your timeout to elapse at a system time of 500
		2069	(500.9 truncated to the resolution) + 1, or 501.
		2070
		2071	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2072	501" and invoke the callback 0.1s after it was started, even though a
		2073	one-second delay was requested - this is being "too early", despite best
		2074	intentions.
		2075
		2076	This is the reason why libev will never invoke the callback if the elapsed
		2077	delay equals the requested delay, but only when the elapsed delay is
		2078	larger than the requested delay. In the example above, libev would only invoke
		2079	the callback at system time 502, or 1.1s after the timer was started.
		2080
		2081	So, while libev cannot guarantee that your callback will be invoked
		2082	exactly when requested, it I<can> and I<does> guarantee that the requested
		2083	delay has actually elapsed, or in other words, it always errs on the "too
		2084	late" side of things.
		2085
1907	=head3 The special problem of time updates	2086	=head3 The special problem of time updates
1908		2087
1909	Establishing the current time is a costly operation (it usually takes at	2088	Establishing the current time is a costly operation (it usually takes
1910	least two system calls): EV therefore updates its idea of the current	2089	at least one system call): EV therefore updates its idea of the current
1911	time only before and after C<ev_run> collects new events, which causes a	2090	time only before and after C<ev_run> collects new events, which causes a
1912	growing difference between C<ev_now ()> and C<ev_time ()> when handling	2091	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1913	lots of events in one iteration.	2092	lots of events in one iteration.
1914		2093
1915	The relative timeouts are calculated relative to the C<ev_now ()>	2094	The relative timeouts are calculated relative to the C<ev_now ()>
1916	time. This is usually the right thing as this timestamp refers to the time	2095	time. This is usually the right thing as this timestamp refers to the time
1917	of the event triggering whatever timeout you are modifying/starting. If	2096	of the event triggering whatever timeout you are modifying/starting. If
1918	you suspect event processing to be delayed and you I<need> to base the	2097	you suspect event processing to be delayed and you I<need> to base the
1919	timeout on the current time, use something like this to adjust for this:	2098	timeout on the current time, use something like the following to adjust
		2099	for it:
1920		2100
1921	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2101	ev_timer_set (&timer, after + (ev_time () - ev_now ()), 0.);
1922		2102
1923	If the event loop is suspended for a long time, you can also force an	2103	If the event loop is suspended for a long time, you can also force an
1924	update of the time returned by C<ev_now ()> by calling C<ev_now_update	2104	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1925	()>.	2105	()>, although that will push the event time of all outstanding events
		2106	further into the future.
		2107
		2108	=head3 The special problem of unsynchronised clocks
		2109
		2110	Modern systems have a variety of clocks - libev itself uses the normal
		2111	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2112	jumps).
		2113
		2114	Neither of these clocks is synchronised with each other or any other clock
		2115	on the system, so C<ev_time ()> might return a considerably different time
		2116	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2117	a call to C<gettimeofday> might return a second count that is one higher
		2118	than a directly following call to C<time>.
		2119
		2120	The moral of this is to only compare libev-related timestamps with
		2121	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2122	a second or so.
		2123
		2124	One more problem arises due to this lack of synchronisation: if libev uses
		2125	the system monotonic clock and you compare timestamps from C<ev_time>
		2126	or C<ev_now> from when you started your timer and when your callback is
		2127	invoked, you will find that sometimes the callback is a bit "early".
		2128
		2129	This is because C<ev_timer>s work in real time, not wall clock time, so
		2130	libev makes sure your callback is not invoked before the delay happened,
		2131	I<measured according to the real time>, not the system clock.
		2132
		2133	If your timeouts are based on a physical timescale (e.g. "time out this
		2134	connection after 100 seconds") then this shouldn't bother you as it is
		2135	exactly the right behaviour.
		2136
		2137	If you want to compare wall clock/system timestamps to your timers, then
		2138	you need to use C<ev_periodic>s, as these are based on the wall clock
		2139	time, where your comparisons will always generate correct results.
1926		2140
1927	=head3 The special problems of suspended animation	2141	=head3 The special problems of suspended animation
1928		2142
1929	When you leave the server world it is quite customary to hit machines that	2143	When you leave the server world it is quite customary to hit machines that
1930	can suspend/hibernate - what happens to the clocks during such a suspend?	2144	can suspend/hibernate - what happens to the clocks during such a suspend?
…		…
1960		2174
1961	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2175	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1962		2176
1963	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2177	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1964		2178
1965	Configure the timer to trigger after C<after> seconds. If C<repeat>	2179	Configure the timer to trigger after C<after> seconds (fractional and
1966	is C<0.>, then it will automatically be stopped once the timeout is	2180	negative values are supported). If C<repeat> is C<0.>, then it will
1967	reached. If it is positive, then the timer will automatically be	2181	automatically be stopped once the timeout is reached. If it is positive,
1968	configured to trigger again C<repeat> seconds later, again, and again,	2182	then the timer will automatically be configured to trigger again C<repeat>
1969	until stopped manually.	2183	seconds later, again, and again, until stopped manually.
1970		2184
1971	The timer itself will do a best-effort at avoiding drift, that is, if	2185	The timer itself will do a best-effort at avoiding drift, that is, if
1972	you configure a timer to trigger every 10 seconds, then it will normally	2186	you configure a timer to trigger every 10 seconds, then it will normally
1973	trigger at exactly 10 second intervals. If, however, your program cannot	2187	trigger at exactly 10 second intervals. If, however, your program cannot
1974	keep up with the timer (because it takes longer than those 10 seconds to	2188	keep up with the timer (because it takes longer than those 10 seconds to
1975	do stuff) the timer will not fire more than once per event loop iteration.	2189	do stuff) the timer will not fire more than once per event loop iteration.
1976		2190
1977	=item ev_timer_again (loop, ev_timer *)	2191	=item ev_timer_again (loop, ev_timer *)
1978		2192
1979	This will act as if the timer timed out and restart it again if it is	2193	This will act as if the timer timed out, and restarts it again if it is
1980	repeating. The exact semantics are:	2194	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2195	timeout to the C<repeat> value and calling C<ev_timer_start>.
1981		2196
		2197	The exact semantics are as in the following rules, all of which will be
		2198	applied to the watcher:
		2199
		2200	=over 4
		2201
1982	If the timer is pending, its pending status is cleared.	2202	=item If the timer is pending, the pending status is always cleared.
1983		2203
1984	If the timer is started but non-repeating, stop it (as if it timed out).	2204	=item If the timer is started but non-repeating, stop it (as if it timed
		2205	out, without invoking it).
1985		2206
1986	If the timer is repeating, either start it if necessary (with the	2207	=item If the timer is repeating, make the C<repeat> value the new timeout
1987	C<repeat> value), or reset the running timer to the C<repeat> value.	2208	and start the timer, if necessary.
1988		2209
		2210	=back
		2211
1989	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a	2212	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
1990	usage example.	2213	usage example.
1991		2214
1992	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)	2215	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1993		2216
1994	Returns the remaining time until a timer fires. If the timer is active,	2217	Returns the remaining time until a timer fires. If the timer is active,
…		…
2047	Periodic watchers are also timers of a kind, but they are very versatile	2270	Periodic watchers are also timers of a kind, but they are very versatile
2048	(and unfortunately a bit complex).	2271	(and unfortunately a bit complex).
2049		2272
2050	Unlike C<ev_timer>, periodic watchers are not based on real time (or	2273	Unlike C<ev_timer>, periodic watchers are not based on real time (or
2051	relative time, the physical time that passes) but on wall clock time	2274	relative time, the physical time that passes) but on wall clock time
2052	(absolute time, the thing you can read on your calender or clock). The	2275	(absolute time, the thing you can read on your calendar or clock). The
2053	difference is that wall clock time can run faster or slower than real	2276	difference is that wall clock time can run faster or slower than real
2054	time, and time jumps are not uncommon (e.g. when you adjust your	2277	time, and time jumps are not uncommon (e.g. when you adjust your
2055	wrist-watch).	2278	wrist-watch).
2056		2279
2057	You can tell a periodic watcher to trigger after some specific point	2280	You can tell a periodic watcher to trigger after some specific point
…		…
2062	C<ev_timer>, which would still trigger roughly 10 seconds after starting	2285	C<ev_timer>, which would still trigger roughly 10 seconds after starting
2063	it, as it uses a relative timeout).	2286	it, as it uses a relative timeout).
2064		2287
2065	C<ev_periodic> watchers can also be used to implement vastly more complex	2288	C<ev_periodic> watchers can also be used to implement vastly more complex
2066	timers, such as triggering an event on each "midnight, local time", or	2289	timers, such as triggering an event on each "midnight, local time", or
2067	other complicated rules. This cannot be done with C<ev_timer> watchers, as	2290	other complicated rules. This cannot easily be done with C<ev_timer>
2068	those cannot react to time jumps.	2291	watchers, as those cannot react to time jumps.
2069		2292
2070	As with timers, the callback is guaranteed to be invoked only when the	2293	As with timers, the callback is guaranteed to be invoked only when the
2071	point in time where it is supposed to trigger has passed. If multiple	2294	point in time where it is supposed to trigger has passed. If multiple
2072	timers become ready during the same loop iteration then the ones with	2295	timers become ready during the same loop iteration then the ones with
2073	earlier time-out values are invoked before ones with later time-out values	2296	earlier time-out values are invoked before ones with later time-out values
…		…
2114		2337
2115	Another way to think about it (for the mathematically inclined) is that	2338	Another way to think about it (for the mathematically inclined) is that
2116	C<ev_periodic> will try to run the callback in this mode at the next possible	2339	C<ev_periodic> will try to run the callback in this mode at the next possible
2117	time where C<time = offset (mod interval)>, regardless of any time jumps.	2340	time where C<time = offset (mod interval)>, regardless of any time jumps.
2118		2341
2119	For numerical stability it is preferable that the C<offset> value is near	2342	The C<interval> I<MUST> be positive, and for numerical stability, the
2120	C<ev_now ()> (the current time), but there is no range requirement for	2343	interval value should be higher than C<1/8192> (which is around 100
2121	this value, and in fact is often specified as zero.	2344	microseconds) and C<offset> should be higher than C<0> and should have
		2345	at most a similar magnitude as the current time (say, within a factor of
		2346	ten). Typical values for offset are, in fact, C<0> or something between
		2347	C<0> and C<interval>, which is also the recommended range.
2122		2348
2123	Note also that there is an upper limit to how often a timer can fire (CPU	2349	Note also that there is an upper limit to how often a timer can fire (CPU
2124	speed for example), so if C<interval> is very small then timing stability	2350	speed for example), so if C<interval> is very small then timing stability
2125	will of course deteriorate. Libev itself tries to be exact to be about one	2351	will of course deteriorate. Libev itself tries to be exact to be about one
2126	millisecond (if the OS supports it and the machine is fast enough).	2352	millisecond (if the OS supports it and the machine is fast enough).
…		…
2156		2382
2157	NOTE: I<< This callback must always return a time that is higher than or	2383	NOTE: I<< This callback must always return a time that is higher than or
2158	equal to the passed C<now> value >>.	2384	equal to the passed C<now> value >>.
2159		2385
2160	This can be used to create very complex timers, such as a timer that	2386	This can be used to create very complex timers, such as a timer that
2161	triggers on "next midnight, local time". To do this, you would calculate the	2387	triggers on "next midnight, local time". To do this, you would calculate
2162	next midnight after C<now> and return the timestamp value for this. How	2388	the next midnight after C<now> and return the timestamp value for
2163	you do this is, again, up to you (but it is not trivial, which is the main	2389	this. Here is a (completely untested, no error checking) example on how to
2164	reason I omitted it as an example).	2390	do this:
		2391
		2392	#include <time.h>
		2393
		2394	static ev_tstamp
		2395	my_rescheduler (ev_periodic *w, ev_tstamp now)
		2396	{
		2397	time_t tnow = (time_t)now;
		2398	struct tm tm;
		2399	localtime_r (&tnow, &tm);
		2400
		2401	tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
		2402	++tm.tm_mday; // midnight next day
		2403
		2404	return mktime (&tm);
		2405	}
		2406
		2407	Note: this code might run into trouble on days that have more then two
		2408	midnights (beginning and end).
2165		2409
2166	=back	2410	=back
2167		2411
2168	=item ev_periodic_again (loop, ev_periodic *)	2412	=item ev_periodic_again (loop, ev_periodic *)
2169		2413
…		…
2234		2478
2235	ev_periodic hourly_tick;	2479	ev_periodic hourly_tick;
2236	ev_periodic_init (&hourly_tick, clock_cb,	2480	ev_periodic_init (&hourly_tick, clock_cb,
2237	fmod (ev_now (loop), 3600.), 3600., 0);	2481	fmod (ev_now (loop), 3600.), 3600., 0);
2238	ev_periodic_start (loop, &hourly_tick);	2482	ev_periodic_start (loop, &hourly_tick);
2239		2483
2240		2484
2241	=head2 C<ev_signal> - signal me when a signal gets signalled!	2485	=head2 C<ev_signal> - signal me when a signal gets signalled!
2242		2486
2243	Signal watchers will trigger an event when the process receives a specific	2487	Signal watchers will trigger an event when the process receives a specific
2244	signal one or more times. Even though signals are very asynchronous, libev	2488	signal one or more times. Even though signals are very asynchronous, libev
2245	will try it's best to deliver signals synchronously, i.e. as part of the	2489	will try its best to deliver signals synchronously, i.e. as part of the
2246	normal event processing, like any other event.	2490	normal event processing, like any other event.
2247		2491
2248	If you want signals to be delivered truly asynchronously, just use	2492	If you want signals to be delivered truly asynchronously, just use
2249	C<sigaction> as you would do without libev and forget about sharing	2493	C<sigaction> as you would do without libev and forget about sharing
2250	the signal. You can even use C<ev_async> from a signal handler to	2494	the signal. You can even use C<ev_async> from a signal handler to
…		…
2254	only within the same loop, i.e. you can watch for C<SIGINT> in your	2498	only within the same loop, i.e. you can watch for C<SIGINT> in your
2255	default loop and for C<SIGIO> in another loop, but you cannot watch for	2499	default loop and for C<SIGIO> in another loop, but you cannot watch for
2256	C<SIGINT> in both the default loop and another loop at the same time. At	2500	C<SIGINT> in both the default loop and another loop at the same time. At
2257	the moment, C<SIGCHLD> is permanently tied to the default loop.	2501	the moment, C<SIGCHLD> is permanently tied to the default loop.
2258		2502
2259	When the first watcher gets started will libev actually register something	2503	Only after the first watcher for a signal is started will libev actually
2260	with the kernel (thus it coexists with your own signal handlers as long as	2504	register something with the kernel. It thus coexists with your own signal
2261	you don't register any with libev for the same signal).	2505	handlers as long as you don't register any with libev for the same signal.
2262		2506
2263	If possible and supported, libev will install its handlers with	2507	If possible and supported, libev will install its handlers with
2264	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should	2508	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
2265	not be unduly interrupted. If you have a problem with system calls getting	2509	not be unduly interrupted. If you have a problem with system calls getting
2266	interrupted by signals you can block all signals in an C<ev_check> watcher	2510	interrupted by signals you can block all signals in an C<ev_check> watcher
…		…
2269	=head3 The special problem of inheritance over fork/execve/pthread_create	2513	=head3 The special problem of inheritance over fork/execve/pthread_create
2270		2514
2271	Both the signal mask (C<sigprocmask>) and the signal disposition	2515	Both the signal mask (C<sigprocmask>) and the signal disposition
2272	(C<sigaction>) are unspecified after starting a signal watcher (and after	2516	(C<sigaction>) are unspecified after starting a signal watcher (and after
2273	stopping it again), that is, libev might or might not block the signal,	2517	stopping it again), that is, libev might or might not block the signal,
2274	and might or might not set or restore the installed signal handler.	2518	and might or might not set or restore the installed signal handler (but
		2519	see C<EVFLAG_NOSIGMASK>).
2275		2520
2276	While this does not matter for the signal disposition (libev never	2521	While this does not matter for the signal disposition (libev never
2277	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on	2522	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
2278	C<execve>), this matters for the signal mask: many programs do not expect	2523	C<execve>), this matters for the signal mask: many programs do not expect
2279	certain signals to be blocked.	2524	certain signals to be blocked.
…		…
2292	I<has> to modify the signal mask, at least temporarily.	2537	I<has> to modify the signal mask, at least temporarily.
2293		2538
2294	So I can't stress this enough: I<If you do not reset your signal mask when	2539	So I can't stress this enough: I<If you do not reset your signal mask when
2295	you expect it to be empty, you have a race condition in your code>. This	2540	you expect it to be empty, you have a race condition in your code>. This
2296	is not a libev-specific thing, this is true for most event libraries.	2541	is not a libev-specific thing, this is true for most event libraries.
		2542
		2543	=head3 The special problem of threads signal handling
		2544
		2545	POSIX threads has problematic signal handling semantics, specifically,
		2546	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2547	threads in a process block signals, which is hard to achieve.
		2548
		2549	When you want to use sigwait (or mix libev signal handling with your own
		2550	for the same signals), you can tackle this problem by globally blocking
		2551	all signals before creating any threads (or creating them with a fully set
		2552	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2553	loops. Then designate one thread as "signal receiver thread" which handles
		2554	these signals. You can pass on any signals that libev might be interested
		2555	in by calling C<ev_feed_signal>.
2297		2556
2298	=head3 Watcher-Specific Functions and Data Members	2557	=head3 Watcher-Specific Functions and Data Members
2299		2558
2300	=over 4	2559	=over 4
2301		2560
…		…
2436		2695
2437	=head2 C<ev_stat> - did the file attributes just change?	2696	=head2 C<ev_stat> - did the file attributes just change?
2438		2697
2439	This watches a file system path for attribute changes. That is, it calls	2698	This watches a file system path for attribute changes. That is, it calls
2440	C<stat> on that path in regular intervals (or when the OS says it changed)	2699	C<stat> on that path in regular intervals (or when the OS says it changed)
2441	and sees if it changed compared to the last time, invoking the callback if	2700	and sees if it changed compared to the last time, invoking the callback
2442	it did.	2701	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2702	happen after the watcher has been started will be reported.
2443		2703
2444	The path does not need to exist: changing from "path exists" to "path does	2704	The path does not need to exist: changing from "path exists" to "path does
2445	not exist" is a status change like any other. The condition "path does not	2705	not exist" is a status change like any other. The condition "path does not
2446	exist" (or more correctly "path cannot be stat'ed") is signified by the	2706	exist" (or more correctly "path cannot be stat'ed") is signified by the
2447	C<st_nlink> field being zero (which is otherwise always forced to be at	2707	C<st_nlink> field being zero (which is otherwise always forced to be at
…		…
2677	Apart from keeping your process non-blocking (which is a useful	2937	Apart from keeping your process non-blocking (which is a useful
2678	effect on its own sometimes), idle watchers are a good place to do	2938	effect on its own sometimes), idle watchers are a good place to do
2679	"pseudo-background processing", or delay processing stuff to after the	2939	"pseudo-background processing", or delay processing stuff to after the
2680	event loop has handled all outstanding events.	2940	event loop has handled all outstanding events.
2681		2941
		2942	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2943
		2944	As long as there is at least one active idle watcher, libev will never
		2945	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2946	For this to work, the idle watcher doesn't need to be invoked at all - the
		2947	lowest priority will do.
		2948
		2949	This mode of operation can be useful together with an C<ev_check> watcher,
		2950	to do something on each event loop iteration - for example to balance load
		2951	between different connections.
		2952
		2953	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2954	example.
		2955
2682	=head3 Watcher-Specific Functions and Data Members	2956	=head3 Watcher-Specific Functions and Data Members
2683		2957
2684	=over 4	2958	=over 4
2685		2959
2686	=item ev_idle_init (ev_idle *, callback)	2960	=item ev_idle_init (ev_idle *, callback)
…		…
2697	callback, free it. Also, use no error checking, as usual.	2971	callback, free it. Also, use no error checking, as usual.
2698		2972
2699	static void	2973	static void
2700	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)	2974	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2701	{	2975	{
		2976	// stop the watcher
		2977	ev_idle_stop (loop, w);
		2978
		2979	// now we can free it
2702	free (w);	2980	free (w);
		2981
2703	// now do something you wanted to do when the program has	2982	// now do something you wanted to do when the program has
2704	// no longer anything immediate to do.	2983	// no longer anything immediate to do.
2705	}	2984	}
2706		2985
2707	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	2986	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
…		…
2709	ev_idle_start (loop, idle_watcher);	2988	ev_idle_start (loop, idle_watcher);
2710		2989
2711		2990
2712	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2991	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2713		2992
2714	Prepare and check watchers are usually (but not always) used in pairs:	2993	Prepare and check watchers are often (but not always) used in pairs:
2715	prepare watchers get invoked before the process blocks and check watchers	2994	prepare watchers get invoked before the process blocks and check watchers
2716	afterwards.	2995	afterwards.
2717		2996
2718	You I<must not> call C<ev_run> or similar functions that enter	2997	You I<must not> call C<ev_run> (or similar functions that enter the
2719	the current event loop from either C<ev_prepare> or C<ev_check>	2998	current event loop) or C<ev_loop_fork> from either C<ev_prepare> or
2720	watchers. Other loops than the current one are fine, however. The	2999	C<ev_check> watchers. Other loops than the current one are fine,
2721	rationale behind this is that you do not need to check for recursion in	3000	however. The rationale behind this is that you do not need to check
2722	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	3001	for recursion in those watchers, i.e. the sequence will always be
2723	C<ev_check> so if you have one watcher of each kind they will always be	3002	C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
2724	called in pairs bracketing the blocking call.	3003	kind they will always be called in pairs bracketing the blocking call.
2725		3004
2726	Their main purpose is to integrate other event mechanisms into libev and	3005	Their main purpose is to integrate other event mechanisms into libev and
2727	their use is somewhat advanced. They could be used, for example, to track	3006	their use is somewhat advanced. They could be used, for example, to track
2728	variable changes, implement your own watchers, integrate net-snmp or a	3007	variable changes, implement your own watchers, integrate net-snmp or a
2729	coroutine library and lots more. They are also occasionally useful if	3008	coroutine library and lots more. They are also occasionally useful if
…		…
2747	with priority higher than or equal to the event loop and one coroutine	3026	with priority higher than or equal to the event loop and one coroutine
2748	of lower priority, but only once, using idle watchers to keep the event	3027	of lower priority, but only once, using idle watchers to keep the event
2749	loop from blocking if lower-priority coroutines are active, thus mapping	3028	loop from blocking if lower-priority coroutines are active, thus mapping
2750	low-priority coroutines to idle/background tasks).	3029	low-priority coroutines to idle/background tasks).
2751		3030
2752	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	3031	When used for this purpose, it is recommended to give C<ev_check> watchers
2753	priority, to ensure that they are being run before any other watchers	3032	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
2754	after the poll (this doesn't matter for C<ev_prepare> watchers).	3033	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		3034	watchers).
2755		3035
2756	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not	3036	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
2757	activate ("feed") events into libev. While libev fully supports this, they	3037	activate ("feed") events into libev. While libev fully supports this, they
2758	might get executed before other C<ev_check> watchers did their job. As	3038	might get executed before other C<ev_check> watchers did their job. As
2759	C<ev_check> watchers are often used to embed other (non-libev) event	3039	C<ev_check> watchers are often used to embed other (non-libev) event
2760	loops those other event loops might be in an unusable state until their	3040	loops those other event loops might be in an unusable state until their
2761	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	3041	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
2762	others).	3042	others).
		3043
		3044	=head3 Abusing an C<ev_check> watcher for its side-effect
		3045
		3046	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		3047	useful because they are called once per event loop iteration. For
		3048	example, if you want to handle a large number of connections fairly, you
		3049	normally only do a bit of work for each active connection, and if there
		3050	is more work to do, you wait for the next event loop iteration, so other
		3051	connections have a chance of making progress.
		3052
		3053	Using an C<ev_check> watcher is almost enough: it will be called on the
		3054	next event loop iteration. However, that isn't as soon as possible -
		3055	without external events, your C<ev_check> watcher will not be invoked.
		3056
		3057	This is where C<ev_idle> watchers come in handy - all you need is a
		3058	single global idle watcher that is active as long as you have one active
		3059	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		3060	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		3061	invoked. Neither watcher alone can do that.
2763		3062
2764	=head3 Watcher-Specific Functions and Data Members	3063	=head3 Watcher-Specific Functions and Data Members
2765		3064
2766	=over 4	3065	=over 4
2767		3066
…		…
2968		3267
2969	=over 4	3268	=over 4
2970		3269
2971	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3270	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
2972		3271
2973	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3272	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
2974		3273
2975	Configures the watcher to embed the given loop, which must be	3274	Configures the watcher to embed the given loop, which must be
2976	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3275	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
2977	invoked automatically, otherwise it is the responsibility of the callback	3276	invoked automatically, otherwise it is the responsibility of the callback
2978	to invoke it (it will continue to be called until the sweep has been done,	3277	to invoke it (it will continue to be called until the sweep has been done,
…		…
2999	used).	3298	used).
3000		3299
3001	struct ev_loop *loop_hi = ev_default_init (0);	3300	struct ev_loop *loop_hi = ev_default_init (0);
3002	struct ev_loop *loop_lo = 0;	3301	struct ev_loop *loop_lo = 0;
3003	ev_embed embed;	3302	ev_embed embed;
3004		3303
3005	// see if there is a chance of getting one that works	3304	// see if there is a chance of getting one that works
3006	// (remember that a flags value of 0 means autodetection)	3305	// (remember that a flags value of 0 means autodetection)
3007	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3306	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3008	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3307	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3009	: 0;	3308	: 0;
…		…
3023	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3322	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
3024		3323
3025	struct ev_loop *loop = ev_default_init (0);	3324	struct ev_loop *loop = ev_default_init (0);
3026	struct ev_loop *loop_socket = 0;	3325	struct ev_loop *loop_socket = 0;
3027	ev_embed embed;	3326	ev_embed embed;
3028		3327
3029	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3328	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3030	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3329	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3031	{	3330	{
3032	ev_embed_init (&embed, 0, loop_socket);	3331	ev_embed_init (&embed, 0, loop_socket);
3033	ev_embed_start (loop, &embed);	3332	ev_embed_start (loop, &embed);
…		…
3041		3340
3042	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3341	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
3043		3342
3044	Fork watchers are called when a C<fork ()> was detected (usually because	3343	Fork watchers are called when a C<fork ()> was detected (usually because
3045	whoever is a good citizen cared to tell libev about it by calling	3344	whoever is a good citizen cared to tell libev about it by calling
3046	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the	3345	C<ev_loop_fork>). The invocation is done before the event loop blocks next
3047	event loop blocks next and before C<ev_check> watchers are being called,	3346	and before C<ev_check> watchers are being called, and only in the child
3048	and only in the child after the fork. If whoever good citizen calling	3347	after the fork. If whoever good citizen calling C<ev_default_fork> cheats
3049	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3348	and calls it in the wrong process, the fork handlers will be invoked, too,
3050	handlers will be invoked, too, of course.	3349	of course.
3051		3350
3052	=head3 The special problem of life after fork - how is it possible?	3351	=head3 The special problem of life after fork - how is it possible?
3053		3352
3054	Most uses of C<fork()> consist of forking, then some simple calls to set	3353	Most uses of C<fork ()> consist of forking, then some simple calls to set
3055	up/change the process environment, followed by a call to C<exec()>. This	3354	up/change the process environment, followed by a call to C<exec()>. This
3056	sequence should be handled by libev without any problems.	3355	sequence should be handled by libev without any problems.
3057		3356
3058	This changes when the application actually wants to do event handling	3357	This changes when the application actually wants to do event handling
3059	in the child, or both parent in child, in effect "continuing" after the	3358	in the child, or both parent in child, in effect "continuing" after the
…		…
3075	disadvantage of having to use multiple event loops (which do not support	3374	disadvantage of having to use multiple event loops (which do not support
3076	signal watchers).	3375	signal watchers).
3077		3376
3078	When this is not possible, or you want to use the default loop for	3377	When this is not possible, or you want to use the default loop for
3079	other reasons, then in the process that wants to start "fresh", call	3378	other reasons, then in the process that wants to start "fresh", call
3080	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying	3379	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
3081	the default loop will "orphan" (not stop) all registered watchers, so you	3380	Destroying the default loop will "orphan" (not stop) all registered
3082	have to be careful not to execute code that modifies those watchers. Note	3381	watchers, so you have to be careful not to execute code that modifies
3083	also that in that case, you have to re-register any signal watchers.	3382	those watchers. Note also that in that case, you have to re-register any
		3383	signal watchers.
3084		3384
3085	=head3 Watcher-Specific Functions and Data Members	3385	=head3 Watcher-Specific Functions and Data Members
3086		3386
3087	=over 4	3387	=over 4
3088		3388
3089	=item ev_fork_init (ev_signal *, callback)	3389	=item ev_fork_init (ev_fork *, callback)
3090		3390
3091	Initialises and configures the fork watcher - it has no parameters of any	3391	Initialises and configures the fork watcher - it has no parameters of any
3092	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,	3392	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
3093	believe me.	3393	really.
3094		3394
3095	=back	3395	=back
3096		3396
3097		3397
		3398	=head2 C<ev_cleanup> - even the best things end
		3399
		3400	Cleanup watchers are called just before the event loop is being destroyed
		3401	by a call to C<ev_loop_destroy>.
		3402
		3403	While there is no guarantee that the event loop gets destroyed, cleanup
		3404	watchers provide a convenient method to install cleanup hooks for your
		3405	program, worker threads and so on - you just to make sure to destroy the
		3406	loop when you want them to be invoked.
		3407
		3408	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3409	all other watchers, they do not keep a reference to the event loop (which
		3410	makes a lot of sense if you think about it). Like all other watchers, you
		3411	can call libev functions in the callback, except C<ev_cleanup_start>.
		3412
		3413	=head3 Watcher-Specific Functions and Data Members
		3414
		3415	=over 4
		3416
		3417	=item ev_cleanup_init (ev_cleanup *, callback)
		3418
		3419	Initialises and configures the cleanup watcher - it has no parameters of
		3420	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3421	pointless, I assure you.
		3422
		3423	=back
		3424
		3425	Example: Register an atexit handler to destroy the default loop, so any
		3426	cleanup functions are called.
		3427
		3428	static void
		3429	program_exits (void)
		3430	{
		3431	ev_loop_destroy (EV_DEFAULT_UC);
		3432	}
		3433
		3434	...
		3435	atexit (program_exits);
		3436
		3437
3098	=head2 C<ev_async> - how to wake up an event loop	3438	=head2 C<ev_async> - how to wake up an event loop
3099		3439
3100	In general, you cannot use an C<ev_run> from multiple threads or other	3440	In general, you cannot use an C<ev_loop> from multiple threads or other
3101	asynchronous sources such as signal handlers (as opposed to multiple event	3441	asynchronous sources such as signal handlers (as opposed to multiple event
3102	loops - those are of course safe to use in different threads).	3442	loops - those are of course safe to use in different threads).
3103		3443
3104	Sometimes, however, you need to wake up an event loop you do not control,	3444	Sometimes, however, you need to wake up an event loop you do not control,
3105	for example because it belongs to another thread. This is what C<ev_async>	3445	for example because it belongs to another thread. This is what C<ev_async>
…		…
3107	it by calling C<ev_async_send>, which is thread- and signal safe.	3447	it by calling C<ev_async_send>, which is thread- and signal safe.
3108		3448
3109	This functionality is very similar to C<ev_signal> watchers, as signals,	3449	This functionality is very similar to C<ev_signal> watchers, as signals,
3110	too, are asynchronous in nature, and signals, too, will be compressed	3450	too, are asynchronous in nature, and signals, too, will be compressed
3111	(i.e. the number of callback invocations may be less than the number of	3451	(i.e. the number of callback invocations may be less than the number of
3112	C<ev_async_sent> calls).	3452	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
3113		3453	of "global async watchers" by using a watcher on an otherwise unused
3114	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not	3454	signal, and C<ev_feed_signal> to signal this watcher from another thread,
3115	just the default loop.	3455	even without knowing which loop owns the signal.
3116		3456
3117	=head3 Queueing	3457	=head3 Queueing
3118		3458
3119	C<ev_async> does not support queueing of data in any way. The reason	3459	C<ev_async> does not support queueing of data in any way. The reason
3120	is that the author does not know of a simple (or any) algorithm for a	3460	is that the author does not know of a simple (or any) algorithm for a
…		…
3212	trust me.	3552	trust me.
3213		3553
3214	=item ev_async_send (loop, ev_async *)	3554	=item ev_async_send (loop, ev_async *)
3215		3555
3216	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3556	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
3217	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3557	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3558	returns.
		3559
3218	C<ev_feed_event>, this call is safe to do from other threads, signal or	3560	Unlike C<ev_feed_event>, this call is safe to do from other threads,
3219	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3561	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3220	section below on what exactly this means).	3562	embedding section below on what exactly this means).
3221		3563
3222	Note that, as with other watchers in libev, multiple events might get	3564	Note that, as with other watchers in libev, multiple events might get
3223	compressed into a single callback invocation (another way to look at this	3565	compressed into a single callback invocation (another way to look at
3224	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,	3566	this is that C<ev_async> watchers are level-triggered: they are set on
3225	reset when the event loop detects that).	3567	C<ev_async_send>, reset when the event loop detects that).
3226		3568
3227	This call incurs the overhead of a system call only once per event loop	3569	This call incurs the overhead of at most one extra system call per event
3228	iteration, so while the overhead might be noticeable, it doesn't apply to	3570	loop iteration, if the event loop is blocked, and no syscall at all if
3229	repeated calls to C<ev_async_send> for the same event loop.	3571	the event loop (or your program) is processing events. That means that
		3572	repeated calls are basically free (there is no need to avoid calls for
		3573	performance reasons) and that the overhead becomes smaller (typically
		3574	zero) under load.
3230		3575
3231	=item bool = ev_async_pending (ev_async *)	3576	=item bool = ev_async_pending (ev_async *)
3232		3577
3233	Returns a non-zero value when C<ev_async_send> has been called on the	3578	Returns a non-zero value when C<ev_async_send> has been called on the
3234	watcher but the event has not yet been processed (or even noted) by the	3579	watcher but the event has not yet been processed (or even noted) by the
…		…
3251		3596
3252	There are some other functions of possible interest. Described. Here. Now.	3597	There are some other functions of possible interest. Described. Here. Now.
3253		3598
3254	=over 4	3599	=over 4
3255		3600
3256	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3601	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)
3257		3602
3258	This function combines a simple timer and an I/O watcher, calls your	3603	This function combines a simple timer and an I/O watcher, calls your
3259	callback on whichever event happens first and automatically stops both	3604	callback on whichever event happens first and automatically stops both
3260	watchers. This is useful if you want to wait for a single event on an fd	3605	watchers. This is useful if you want to wait for a single event on an fd
3261	or timeout without having to allocate/configure/start/stop/free one or	3606	or timeout without having to allocate/configure/start/stop/free one or
…		…
3289	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3634	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3290		3635
3291	=item ev_feed_fd_event (loop, int fd, int revents)	3636	=item ev_feed_fd_event (loop, int fd, int revents)
3292		3637
3293	Feed an event on the given fd, as if a file descriptor backend detected	3638	Feed an event on the given fd, as if a file descriptor backend detected
3294	the given events it.	3639	the given events.
3295		3640
3296	=item ev_feed_signal_event (loop, int signum)	3641	=item ev_feed_signal_event (loop, int signum)
3297		3642
3298	Feed an event as if the given signal occurred (C<loop> must be the default	3643	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3299	loop!).	3644	which is async-safe.
3300		3645
3301	=back	3646	=back
		3647
		3648
		3649	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3650
		3651	This section explains some common idioms that are not immediately
		3652	obvious. Note that examples are sprinkled over the whole manual, and this
		3653	section only contains stuff that wouldn't fit anywhere else.
		3654
		3655	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3656
		3657	Each watcher has, by default, a C<void *data> member that you can read
		3658	or modify at any time: libev will completely ignore it. This can be used
		3659	to associate arbitrary data with your watcher. If you need more data and
		3660	don't want to allocate memory separately and store a pointer to it in that
		3661	data member, you can also "subclass" the watcher type and provide your own
		3662	data:
		3663
		3664	struct my_io
		3665	{
		3666	ev_io io;
		3667	int otherfd;
		3668	void *somedata;
		3669	struct whatever *mostinteresting;
		3670	};
		3671
		3672	...
		3673	struct my_io w;
		3674	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3675
		3676	And since your callback will be called with a pointer to the watcher, you
		3677	can cast it back to your own type:
		3678
		3679	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3680	{
		3681	struct my_io *w = (struct my_io *)w_;
		3682	...
		3683	}
		3684
		3685	More interesting and less C-conformant ways of casting your callback
		3686	function type instead have been omitted.
		3687
		3688	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3689
		3690	Another common scenario is to use some data structure with multiple
		3691	embedded watchers, in effect creating your own watcher that combines
		3692	multiple libev event sources into one "super-watcher":
		3693
		3694	struct my_biggy
		3695	{
		3696	int some_data;
		3697	ev_timer t1;
		3698	ev_timer t2;
		3699	}
		3700
		3701	In this case getting the pointer to C<my_biggy> is a bit more
		3702	complicated: Either you store the address of your C<my_biggy> struct in
		3703	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3704	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3705	real programmers):
		3706
		3707	#include <stddef.h>
		3708
		3709	static void
		3710	t1_cb (EV_P_ ev_timer *w, int revents)
		3711	{
		3712	struct my_biggy big = (struct my_biggy *)
		3713	(((char *)w) - offsetof (struct my_biggy, t1));
		3714	}
		3715
		3716	static void
		3717	t2_cb (EV_P_ ev_timer *w, int revents)
		3718	{
		3719	struct my_biggy big = (struct my_biggy *)
		3720	(((char *)w) - offsetof (struct my_biggy, t2));
		3721	}
		3722
		3723	=head2 AVOIDING FINISHING BEFORE RETURNING
		3724
		3725	Often you have structures like this in event-based programs:
		3726
		3727	callback ()
		3728	{
		3729	free (request);
		3730	}
		3731
		3732	request = start_new_request (..., callback);
		3733
		3734	The intent is to start some "lengthy" operation. The C<request> could be
		3735	used to cancel the operation, or do other things with it.
		3736
		3737	It's not uncommon to have code paths in C<start_new_request> that
		3738	immediately invoke the callback, for example, to report errors. Or you add
		3739	some caching layer that finds that it can skip the lengthy aspects of the
		3740	operation and simply invoke the callback with the result.
		3741
		3742	The problem here is that this will happen I<before> C<start_new_request>
		3743	has returned, so C<request> is not set.
		3744
		3745	Even if you pass the request by some safer means to the callback, you
		3746	might want to do something to the request after starting it, such as
		3747	canceling it, which probably isn't working so well when the callback has
		3748	already been invoked.
		3749
		3750	A common way around all these issues is to make sure that
		3751	C<start_new_request> I<always> returns before the callback is invoked. If
		3752	C<start_new_request> immediately knows the result, it can artificially
		3753	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3754	example, or more sneakily, by reusing an existing (stopped) watcher and
		3755	pushing it into the pending queue:
		3756
		3757	ev_set_cb (watcher, callback);
		3758	ev_feed_event (EV_A_ watcher, 0);
		3759
		3760	This way, C<start_new_request> can safely return before the callback is
		3761	invoked, while not delaying callback invocation too much.
		3762
		3763	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3764
		3765	Often (especially in GUI toolkits) there are places where you have
		3766	I<modal> interaction, which is most easily implemented by recursively
		3767	invoking C<ev_run>.
		3768
		3769	This brings the problem of exiting - a callback might want to finish the
		3770	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3771	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3772	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3773	other combination: In these cases, a simple C<ev_break> will not work.
		3774
		3775	The solution is to maintain "break this loop" variable for each C<ev_run>
		3776	invocation, and use a loop around C<ev_run> until the condition is
		3777	triggered, using C<EVRUN_ONCE>:
		3778
		3779	// main loop
		3780	int exit_main_loop = 0;
		3781
		3782	while (!exit_main_loop)
		3783	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3784
		3785	// in a modal watcher
		3786	int exit_nested_loop = 0;
		3787
		3788	while (!exit_nested_loop)
		3789	ev_run (EV_A_ EVRUN_ONCE);
		3790
		3791	To exit from any of these loops, just set the corresponding exit variable:
		3792
		3793	// exit modal loop
		3794	exit_nested_loop = 1;
		3795
		3796	// exit main program, after modal loop is finished
		3797	exit_main_loop = 1;
		3798
		3799	// exit both
		3800	exit_main_loop = exit_nested_loop = 1;
		3801
		3802	=head2 THREAD LOCKING EXAMPLE
		3803
		3804	Here is a fictitious example of how to run an event loop in a different
		3805	thread from where callbacks are being invoked and watchers are
		3806	created/added/removed.
		3807
		3808	For a real-world example, see the C<EV::Loop::Async> perl module,
		3809	which uses exactly this technique (which is suited for many high-level
		3810	languages).
		3811
		3812	The example uses a pthread mutex to protect the loop data, a condition
		3813	variable to wait for callback invocations, an async watcher to notify the
		3814	event loop thread and an unspecified mechanism to wake up the main thread.
		3815
		3816	First, you need to associate some data with the event loop:
		3817
		3818	typedef struct {
		3819	mutex_t lock; /* global loop lock */
		3820	ev_async async_w;
		3821	thread_t tid;
		3822	cond_t invoke_cv;
		3823	} userdata;
		3824
		3825	void prepare_loop (EV_P)
		3826	{
		3827	// for simplicity, we use a static userdata struct.
		3828	static userdata u;
		3829
		3830	ev_async_init (&u->async_w, async_cb);
		3831	ev_async_start (EV_A_ &u->async_w);
		3832
		3833	pthread_mutex_init (&u->lock, 0);
		3834	pthread_cond_init (&u->invoke_cv, 0);
		3835
		3836	// now associate this with the loop
		3837	ev_set_userdata (EV_A_ u);
		3838	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3839	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3840
		3841	// then create the thread running ev_run
		3842	pthread_create (&u->tid, 0, l_run, EV_A);
		3843	}
		3844
		3845	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3846	solely to wake up the event loop so it takes notice of any new watchers
		3847	that might have been added:
		3848
		3849	static void
		3850	async_cb (EV_P_ ev_async *w, int revents)
		3851	{
		3852	// just used for the side effects
		3853	}
		3854
		3855	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3856	protecting the loop data, respectively.
		3857
		3858	static void
		3859	l_release (EV_P)
		3860	{
		3861	userdata *u = ev_userdata (EV_A);
		3862	pthread_mutex_unlock (&u->lock);
		3863	}
		3864
		3865	static void
		3866	l_acquire (EV_P)
		3867	{
		3868	userdata *u = ev_userdata (EV_A);
		3869	pthread_mutex_lock (&u->lock);
		3870	}
		3871
		3872	The event loop thread first acquires the mutex, and then jumps straight
		3873	into C<ev_run>:
		3874
		3875	void *
		3876	l_run (void *thr_arg)
		3877	{
		3878	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3879
		3880	l_acquire (EV_A);
		3881	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3882	ev_run (EV_A_ 0);
		3883	l_release (EV_A);
		3884
		3885	return 0;
		3886	}
		3887
		3888	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3889	signal the main thread via some unspecified mechanism (signals? pipe
		3890	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3891	have been called (in a while loop because a) spurious wakeups are possible
		3892	and b) skipping inter-thread-communication when there are no pending
		3893	watchers is very beneficial):
		3894
		3895	static void
		3896	l_invoke (EV_P)
		3897	{
		3898	userdata *u = ev_userdata (EV_A);
		3899
		3900	while (ev_pending_count (EV_A))
		3901	{
		3902	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3903	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3904	}
		3905	}
		3906
		3907	Now, whenever the main thread gets told to invoke pending watchers, it
		3908	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3909	thread to continue:
		3910
		3911	static void
		3912	real_invoke_pending (EV_P)
		3913	{
		3914	userdata *u = ev_userdata (EV_A);
		3915
		3916	pthread_mutex_lock (&u->lock);
		3917	ev_invoke_pending (EV_A);
		3918	pthread_cond_signal (&u->invoke_cv);
		3919	pthread_mutex_unlock (&u->lock);
		3920	}
		3921
		3922	Whenever you want to start/stop a watcher or do other modifications to an
		3923	event loop, you will now have to lock:
		3924
		3925	ev_timer timeout_watcher;
		3926	userdata *u = ev_userdata (EV_A);
		3927
		3928	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3929
		3930	pthread_mutex_lock (&u->lock);
		3931	ev_timer_start (EV_A_ &timeout_watcher);
		3932	ev_async_send (EV_A_ &u->async_w);
		3933	pthread_mutex_unlock (&u->lock);
		3934
		3935	Note that sending the C<ev_async> watcher is required because otherwise
		3936	an event loop currently blocking in the kernel will have no knowledge
		3937	about the newly added timer. By waking up the loop it will pick up any new
		3938	watchers in the next event loop iteration.
		3939
		3940	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3941
		3942	While the overhead of a callback that e.g. schedules a thread is small, it
		3943	is still an overhead. If you embed libev, and your main usage is with some
		3944	kind of threads or coroutines, you might want to customise libev so that
		3945	doesn't need callbacks anymore.
		3946
		3947	Imagine you have coroutines that you can switch to using a function
		3948	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3949	and that due to some magic, the currently active coroutine is stored in a
		3950	global called C<current_coro>. Then you can build your own "wait for libev
		3951	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3952	the differing C<;> conventions):
		3953
		3954	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3955	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3956
		3957	That means instead of having a C callback function, you store the
		3958	coroutine to switch to in each watcher, and instead of having libev call
		3959	your callback, you instead have it switch to that coroutine.
		3960
		3961	A coroutine might now wait for an event with a function called
		3962	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3963	matter when, or whether the watcher is active or not when this function is
		3964	called):
		3965
		3966	void
		3967	wait_for_event (ev_watcher *w)
		3968	{
		3969	ev_set_cb (w, current_coro);
		3970	switch_to (libev_coro);
		3971	}
		3972
		3973	That basically suspends the coroutine inside C<wait_for_event> and
		3974	continues the libev coroutine, which, when appropriate, switches back to
		3975	this or any other coroutine.
		3976
		3977	You can do similar tricks if you have, say, threads with an event queue -
		3978	instead of storing a coroutine, you store the queue object and instead of
		3979	switching to a coroutine, you push the watcher onto the queue and notify
		3980	any waiters.
		3981
		3982	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		3983	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3984
		3985	// my_ev.h
		3986	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3987	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3988	#include "../libev/ev.h"
		3989
		3990	// my_ev.c
		3991	#define EV_H "my_ev.h"
		3992	#include "../libev/ev.c"
		3993
		3994	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3995	F<my_ev.c> into your project. When properly specifying include paths, you
		3996	can even use F<ev.h> as header file name directly.
3302		3997
3303		3998
3304	=head1 LIBEVENT EMULATION	3999	=head1 LIBEVENT EMULATION
3305		4000
3306	Libev offers a compatibility emulation layer for libevent. It cannot	4001	Libev offers a compatibility emulation layer for libevent. It cannot
3307	emulate the internals of libevent, so here are some usage hints:	4002	emulate the internals of libevent, so here are some usage hints:
3308		4003
3309	=over 4	4004	=over 4
		4005
		4006	=item * Only the libevent-1.4.1-beta API is being emulated.
		4007
		4008	This was the newest libevent version available when libev was implemented,
		4009	and is still mostly unchanged in 2010.
3310		4010
3311	=item * Use it by including <event.h>, as usual.	4011	=item * Use it by including <event.h>, as usual.
3312		4012
3313	=item * The following members are fully supported: ev_base, ev_callback,	4013	=item * The following members are fully supported: ev_base, ev_callback,
3314	ev_arg, ev_fd, ev_res, ev_events.	4014	ev_arg, ev_fd, ev_res, ev_events.
…		…
3320	=item * Priorities are not currently supported. Initialising priorities	4020	=item * Priorities are not currently supported. Initialising priorities
3321	will fail and all watchers will have the same priority, even though there	4021	will fail and all watchers will have the same priority, even though there
3322	is an ev_pri field.	4022	is an ev_pri field.
3323		4023
3324	=item * In libevent, the last base created gets the signals, in libev, the	4024	=item * In libevent, the last base created gets the signals, in libev, the
3325	first base created (== the default loop) gets the signals.	4025	base that registered the signal gets the signals.
3326		4026
3327	=item * Other members are not supported.	4027	=item * Other members are not supported.
3328		4028
3329	=item * The libev emulation is I<not> ABI compatible to libevent, you need	4029	=item * The libev emulation is I<not> ABI compatible to libevent, you need
3330	to use the libev header file and library.	4030	to use the libev header file and library.
3331		4031
3332	=back	4032	=back
3333		4033
3334	=head1 C++ SUPPORT	4034	=head1 C++ SUPPORT
		4035
		4036	=head2 C API
		4037
		4038	The normal C API should work fine when used from C++: both ev.h and the
		4039	libev sources can be compiled as C++. Therefore, code that uses the C API
		4040	will work fine.
		4041
		4042	Proper exception specifications might have to be added to callbacks passed
		4043	to libev: exceptions may be thrown only from watcher callbacks, all other
		4044	callbacks (allocator, syserr, loop acquire/release and periodic reschedule
		4045	callbacks) must not throw exceptions, and might need a C<noexcept>
		4046	specification. If you have code that needs to be compiled as both C and
		4047	C++ you can use the C<EV_NOEXCEPT> macro for this:
		4048
		4049	static void
		4050	fatal_error (const char *msg) EV_NOEXCEPT
		4051	{
		4052	perror (msg);
		4053	abort ();
		4054	}
		4055
		4056	...
		4057	ev_set_syserr_cb (fatal_error);
		4058
		4059	The only API functions that can currently throw exceptions are C<ev_run>,
		4060	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		4061	because it runs cleanup watchers).
		4062
		4063	Throwing exceptions in watcher callbacks is only supported if libev itself
		4064	is compiled with a C++ compiler or your C and C++ environments allow
		4065	throwing exceptions through C libraries (most do).
		4066
		4067	=head2 C++ API
3335		4068
3336	Libev comes with some simplistic wrapper classes for C++ that mainly allow	4069	Libev comes with some simplistic wrapper classes for C++ that mainly allow
3337	you to use some convenience methods to start/stop watchers and also change	4070	you to use some convenience methods to start/stop watchers and also change
3338	the callback model to a model using method callbacks on objects.	4071	the callback model to a model using method callbacks on objects.
3339		4072
3340	To use it,	4073	To use it,
3341		4074
3342	#include <ev++.h>	4075	#include <ev++.h>
3343		4076
3344	This automatically includes F<ev.h> and puts all of its definitions (many	4077	This automatically includes F<ev.h> and puts all of its definitions (many
3345	of them macros) into the global namespace. All C++ specific things are	4078	of them macros) into the global namespace. All C++ specific things are
3346	put into the C<ev> namespace. It should support all the same embedding	4079	put into the C<ev> namespace. It should support all the same embedding
…		…
3349	Care has been taken to keep the overhead low. The only data member the C++	4082	Care has been taken to keep the overhead low. The only data member the C++
3350	classes add (compared to plain C-style watchers) is the event loop pointer	4083	classes add (compared to plain C-style watchers) is the event loop pointer
3351	that the watcher is associated with (or no additional members at all if	4084	that the watcher is associated with (or no additional members at all if
3352	you disable C<EV_MULTIPLICITY> when embedding libev).	4085	you disable C<EV_MULTIPLICITY> when embedding libev).
3353		4086
3354	Currently, functions, and static and non-static member functions can be	4087	Currently, functions, static and non-static member functions and classes
3355	used as callbacks. Other types should be easy to add as long as they only	4088	with C<operator ()> can be used as callbacks. Other types should be easy
3356	need one additional pointer for context. If you need support for other	4089	to add as long as they only need one additional pointer for context. If
3357	types of functors please contact the author (preferably after implementing	4090	you need support for other types of functors please contact the author
3358	it).	4091	(preferably after implementing it).
		4092
		4093	For all this to work, your C++ compiler either has to use the same calling
		4094	conventions as your C compiler (for static member functions), or you have
		4095	to embed libev and compile libev itself as C++.
3359		4096
3360	Here is a list of things available in the C<ev> namespace:	4097	Here is a list of things available in the C<ev> namespace:
3361		4098
3362	=over 4	4099	=over 4
3363		4100
…		…
3373	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4110	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
3374		4111
3375	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4112	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
3376	the same name in the C<ev> namespace, with the exception of C<ev_signal>	4113	the same name in the C<ev> namespace, with the exception of C<ev_signal>
3377	which is called C<ev::sig> to avoid clashes with the C<signal> macro	4114	which is called C<ev::sig> to avoid clashes with the C<signal> macro
3378	defines by many implementations.	4115	defined by many implementations.
3379		4116
3380	All of those classes have these methods:	4117	All of those classes have these methods:
3381		4118
3382	=over 4	4119	=over 4
3383		4120
…		…
3445	void operator() (ev::io &w, int revents)	4182	void operator() (ev::io &w, int revents)
3446	{	4183	{
3447	...	4184	...
3448	}	4185	}
3449	}	4186	}
3450		4187
3451	myfunctor f;	4188	myfunctor f;
3452		4189
3453	ev::io w;	4190	ev::io w;
3454	w.set (&f);	4191	w.set (&f);
3455		4192
…		…
3473	Associates a different C<struct ev_loop> with this watcher. You can only	4210	Associates a different C<struct ev_loop> with this watcher. You can only
3474	do this when the watcher is inactive (and not pending either).	4211	do this when the watcher is inactive (and not pending either).
3475		4212
3476	=item w->set ([arguments])	4213	=item w->set ([arguments])
3477		4214
3478	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this	4215	Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
3479	method or a suitable start method must be called at least once. Unlike the	4216	with the same arguments. Either this method or a suitable start method
3480	C counterpart, an active watcher gets automatically stopped and restarted	4217	must be called at least once. Unlike the C counterpart, an active watcher
3481	when reconfiguring it with this method.	4218	gets automatically stopped and restarted when reconfiguring it with this
		4219	method.
		4220
		4221	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4222	clashing with the C<set (loop)> method.
3482		4223
3483	=item w->start ()	4224	=item w->start ()
3484		4225
3485	Starts the watcher. Note that there is no C<loop> argument, as the	4226	Starts the watcher. Note that there is no C<loop> argument, as the
3486	constructor already stores the event loop.	4227	constructor already stores the event loop.
…		…
3516	watchers in the constructor.	4257	watchers in the constructor.
3517		4258
3518	class myclass	4259	class myclass
3519	{	4260	{
3520	ev::io io ; void io_cb (ev::io &w, int revents);	4261	ev::io io ; void io_cb (ev::io &w, int revents);
3521	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);	4262	ev::io io2 ; void io2_cb (ev::io &w, int revents);
3522	ev::idle idle; void idle_cb (ev::idle &w, int revents);	4263	ev::idle idle; void idle_cb (ev::idle &w, int revents);
3523		4264
3524	myclass (int fd)	4265	myclass (int fd)
3525	{	4266	{
3526	io .set <myclass, &myclass::io_cb > (this);	4267	io .set <myclass, &myclass::io_cb > (this);
…		…
3577	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.	4318	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3578		4319
3579	=item D	4320	=item D
3580		4321
3581	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4322	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
3582	be found at L<http://proj.llucax.com.ar/wiki/evd>.	4323	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
3583		4324
3584	=item Ocaml	4325	=item Ocaml
3585		4326
3586	Erkki Seppala has written Ocaml bindings for libev, to be found at	4327	Erkki Seppala has written Ocaml bindings for libev, to be found at
3587	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	4328	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
…		…
3590		4331
3591	Brian Maher has written a partial interface to libev for lua (at the	4332	Brian Maher has written a partial interface to libev for lua (at the
3592	time of this writing, only C<ev_io> and C<ev_timer>), to be found at	4333	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
3593	L<http://github.com/brimworks/lua-ev>.	4334	L<http://github.com/brimworks/lua-ev>.
3594		4335
		4336	=item Javascript
		4337
		4338	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4339
		4340	=item Others
		4341
		4342	There are others, and I stopped counting.
		4343
3595	=back	4344	=back
3596		4345
3597		4346
3598	=head1 MACRO MAGIC	4347	=head1 MACRO MAGIC
3599		4348
…		…
3635	suitable for use with C<EV_A>.	4384	suitable for use with C<EV_A>.
3636		4385
3637	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4386	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
3638		4387
3639	Similar to the other two macros, this gives you the value of the default	4388	Similar to the other two macros, this gives you the value of the default
3640	loop, if multiple loops are supported ("ev loop default").	4389	loop, if multiple loops are supported ("ev loop default"). The default loop
		4390	will be initialised if it isn't already initialised.
		4391
		4392	For non-multiplicity builds, these macros do nothing, so you always have
		4393	to initialise the loop somewhere.
3641		4394
3642	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4395	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
3643		4396
3644	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4397	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
3645	default loop has been initialised (C<UC> == unchecked). Their behaviour	4398	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
3712	ev_vars.h	4465	ev_vars.h
3713	ev_wrap.h	4466	ev_wrap.h
3714		4467
3715	ev_win32.c required on win32 platforms only	4468	ev_win32.c required on win32 platforms only
3716		4469
3717	ev_select.c only when select backend is enabled (which is enabled by default)	4470	ev_select.c only when select backend is enabled
3718	ev_poll.c only when poll backend is enabled (disabled by default)	4471	ev_poll.c only when poll backend is enabled
3719	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4472	ev_epoll.c only when the epoll backend is enabled
		4473	ev_linuxaio.c only when the linux aio backend is enabled
3720	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4474	ev_kqueue.c only when the kqueue backend is enabled
3721	ev_port.c only when the solaris port backend is enabled (disabled by default)	4475	ev_port.c only when the solaris port backend is enabled
3722		4476
3723	F<ev.c> includes the backend files directly when enabled, so you only need	4477	F<ev.c> includes the backend files directly when enabled, so you only need
3724	to compile this single file.	4478	to compile this single file.
3725		4479
3726	=head3 LIBEVENT COMPATIBILITY API	4480	=head3 LIBEVENT COMPATIBILITY API
…		…
3790	supported). It will also not define any of the structs usually found in	4544	supported). It will also not define any of the structs usually found in
3791	F<event.h> that are not directly supported by the libev core alone.	4545	F<event.h> that are not directly supported by the libev core alone.
3792		4546
3793	In standalone mode, libev will still try to automatically deduce the	4547	In standalone mode, libev will still try to automatically deduce the
3794	configuration, but has to be more conservative.	4548	configuration, but has to be more conservative.
		4549
		4550	=item EV_USE_FLOOR
		4551
		4552	If defined to be C<1>, libev will use the C<floor ()> function for its
		4553	periodic reschedule calculations, otherwise libev will fall back on a
		4554	portable (slower) implementation. If you enable this, you usually have to
		4555	link against libm or something equivalent. Enabling this when the C<floor>
		4556	function is not available will fail, so the safe default is to not enable
		4557	this.
3795		4558
3796	=item EV_USE_MONOTONIC	4559	=item EV_USE_MONOTONIC
3797		4560
3798	If defined to be C<1>, libev will try to detect the availability of the	4561	If defined to be C<1>, libev will try to detect the availability of the
3799	monotonic clock option at both compile time and runtime. Otherwise no	4562	monotonic clock option at both compile time and runtime. Otherwise no
…		…
3885	If programs implement their own fd to handle mapping on win32, then this	4648	If programs implement their own fd to handle mapping on win32, then this
3886	macro can be used to override the C<close> function, useful to unregister	4649	macro can be used to override the C<close> function, useful to unregister
3887	file descriptors again. Note that the replacement function has to close	4650	file descriptors again. Note that the replacement function has to close
3888	the underlying OS handle.	4651	the underlying OS handle.
3889		4652
		4653	=item EV_USE_WSASOCKET
		4654
		4655	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4656	communication socket, which works better in some environments. Otherwise,
		4657	the normal C<socket> function will be used, which works better in other
		4658	environments.
		4659
3890	=item EV_USE_POLL	4660	=item EV_USE_POLL
3891		4661
3892	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4662	If defined to be C<1>, libev will compile in support for the C<poll>(2)
3893	backend. Otherwise it will be enabled on non-win32 platforms. It	4663	backend. Otherwise it will be enabled on non-win32 platforms. It
3894	takes precedence over select.	4664	takes precedence over select.
…		…
3898	If defined to be C<1>, libev will compile in support for the Linux	4668	If defined to be C<1>, libev will compile in support for the Linux
3899	C<epoll>(7) backend. Its availability will be detected at runtime,	4669	C<epoll>(7) backend. Its availability will be detected at runtime,
3900	otherwise another method will be used as fallback. This is the preferred	4670	otherwise another method will be used as fallback. This is the preferred
3901	backend for GNU/Linux systems. If undefined, it will be enabled if the	4671	backend for GNU/Linux systems. If undefined, it will be enabled if the
3902	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4672	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4673
		4674	=item EV_USE_LINUXAIO
		4675
		4676	If defined to be C<1>, libev will compile in support for the Linux
		4677	aio backend. Due to it's currenbt limitations it has to be requested
		4678	explicitly. If undefined, it will be enabled on linux, otherwise
		4679	disabled.
3903		4680
3904	=item EV_USE_KQUEUE	4681	=item EV_USE_KQUEUE
3905		4682
3906	If defined to be C<1>, libev will compile in support for the BSD style	4683	If defined to be C<1>, libev will compile in support for the BSD style
3907	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	4684	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
3929	If defined to be C<1>, libev will compile in support for the Linux inotify	4706	If defined to be C<1>, libev will compile in support for the Linux inotify
3930	interface to speed up C<ev_stat> watchers. Its actual availability will	4707	interface to speed up C<ev_stat> watchers. Its actual availability will
3931	be detected at runtime. If undefined, it will be enabled if the headers	4708	be detected at runtime. If undefined, it will be enabled if the headers
3932	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4709	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
3933		4710
		4711	=item EV_NO_SMP
		4712
		4713	If defined to be C<1>, libev will assume that memory is always coherent
		4714	between threads, that is, threads can be used, but threads never run on
		4715	different cpus (or different cpu cores). This reduces dependencies
		4716	and makes libev faster.
		4717
		4718	=item EV_NO_THREADS
		4719
		4720	If defined to be C<1>, libev will assume that it will never be called from
		4721	different threads (that includes signal handlers), which is a stronger
		4722	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4723	libev faster.
		4724
3934	=item EV_ATOMIC_T	4725	=item EV_ATOMIC_T
3935		4726
3936	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4727	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
3937	access is atomic with respect to other threads or signal contexts. No such	4728	access is atomic with respect to other threads or signal contexts. No
3938	type is easily found in the C language, so you can provide your own type	4729	such type is easily found in the C language, so you can provide your own
3939	that you know is safe for your purposes. It is used both for signal handler "locking"	4730	type that you know is safe for your purposes. It is used both for signal
3940	as well as for signal and thread safety in C<ev_async> watchers.	4731	handler "locking" as well as for signal and thread safety in C<ev_async>
		4732	watchers.
3941		4733
3942	In the absence of this define, libev will use C<sig_atomic_t volatile>	4734	In the absence of this define, libev will use C<sig_atomic_t volatile>
3943	(from F<signal.h>), which is usually good enough on most platforms.	4735	(from F<signal.h>), which is usually good enough on most platforms.
3944		4736
3945	=item EV_H (h)	4737	=item EV_H (h)
…		…
3972	will have the C<struct ev_loop *> as first argument, and you can create	4764	will have the C<struct ev_loop *> as first argument, and you can create
3973	additional independent event loops. Otherwise there will be no support	4765	additional independent event loops. Otherwise there will be no support
3974	for multiple event loops and there is no first event loop pointer	4766	for multiple event loops and there is no first event loop pointer
3975	argument. Instead, all functions act on the single default loop.	4767	argument. Instead, all functions act on the single default loop.
3976		4768
		4769	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4770	default loop when multiplicity is switched off - you always have to
		4771	initialise the loop manually in this case.
		4772
3977	=item EV_MINPRI	4773	=item EV_MINPRI
3978		4774
3979	=item EV_MAXPRI	4775	=item EV_MAXPRI
3980		4776
3981	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4777	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
4017	#define EV_USE_POLL 1	4813	#define EV_USE_POLL 1
4018	#define EV_CHILD_ENABLE 1	4814	#define EV_CHILD_ENABLE 1
4019	#define EV_ASYNC_ENABLE 1	4815	#define EV_ASYNC_ENABLE 1
4020		4816
4021	The actual value is a bitset, it can be a combination of the following	4817	The actual value is a bitset, it can be a combination of the following
4022	values:	4818	values (by default, all of these are enabled):
4023		4819
4024	=over 4	4820	=over 4
4025		4821
4026	=item C<1> - faster/larger code	4822	=item C<1> - faster/larger code
4027		4823
…		…
4031	code size by roughly 30% on amd64).	4827	code size by roughly 30% on amd64).
4032		4828
4033	When optimising for size, use of compiler flags such as C<-Os> with	4829	When optimising for size, use of compiler flags such as C<-Os> with
4034	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of	4830	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
4035	assertions.	4831	assertions.
		4832
		4833	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4834	(e.g. gcc with C<-Os>).
4036		4835
4037	=item C<2> - faster/larger data structures	4836	=item C<2> - faster/larger data structures
4038		4837
4039	Replaces the small 2-heap for timer management by a faster 4-heap, larger	4838	Replaces the small 2-heap for timer management by a faster 4-heap, larger
4040	hash table sizes and so on. This will usually further increase code size	4839	hash table sizes and so on. This will usually further increase code size
4041	and can additionally have an effect on the size of data structures at	4840	and can additionally have an effect on the size of data structures at
4042	runtime.	4841	runtime.
4043		4842
		4843	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4844	(e.g. gcc with C<-Os>).
		4845
4044	=item C<4> - full API configuration	4846	=item C<4> - full API configuration
4045		4847
4046	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and	4848	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
4047	enables multiplicity (C<EV_MULTIPLICITY>=1).	4849	enables multiplicity (C<EV_MULTIPLICITY>=1).
4048		4850
…		…
4078		4880
4079	With an intelligent-enough linker (gcc+binutils are intelligent enough	4881	With an intelligent-enough linker (gcc+binutils are intelligent enough
4080	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by	4882	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
4081	your program might be left out as well - a binary starting a timer and an	4883	your program might be left out as well - a binary starting a timer and an
4082	I/O watcher then might come out at only 5Kb.	4884	I/O watcher then might come out at only 5Kb.
		4885
		4886	=item EV_API_STATIC
		4887
		4888	If this symbol is defined (by default it is not), then all identifiers
		4889	will have static linkage. This means that libev will not export any
		4890	identifiers, and you cannot link against libev anymore. This can be useful
		4891	when you embed libev, only want to use libev functions in a single file,
		4892	and do not want its identifiers to be visible.
		4893
		4894	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4895	wants to use libev.
		4896
		4897	This option only works when libev is compiled with a C compiler, as C++
		4898	doesn't support the required declaration syntax.
4083		4899
4084	=item EV_AVOID_STDIO	4900	=item EV_AVOID_STDIO
4085		4901
4086	If this is set to C<1> at compiletime, then libev will avoid using stdio	4902	If this is set to C<1> at compiletime, then libev will avoid using stdio
4087	functions (printf, scanf, perror etc.). This will increase the code size	4903	functions (printf, scanf, perror etc.). This will increase the code size
…		…
4231	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	5047	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4232		5048
4233	#include "ev_cpp.h"	5049	#include "ev_cpp.h"
4234	#include "ev.c"	5050	#include "ev.c"
4235		5051
4236	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	5052	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4237		5053
4238	=head2 THREADS AND COROUTINES	5054	=head2 THREADS AND COROUTINES
4239		5055
4240	=head3 THREADS	5056	=head3 THREADS
4241		5057
…		…
4292	default loop and triggering an C<ev_async> watcher from the default loop	5108	default loop and triggering an C<ev_async> watcher from the default loop
4293	watcher callback into the event loop interested in the signal.	5109	watcher callback into the event loop interested in the signal.
4294		5110
4295	=back	5111	=back
4296		5112
4297	=head4 THREAD LOCKING EXAMPLE	5113	See also L</THREAD LOCKING EXAMPLE>.
4298
4299	Here is a fictitious example of how to run an event loop in a different
4300	thread than where callbacks are being invoked and watchers are
4301	created/added/removed.
4302
4303	For a real-world example, see the C<EV::Loop::Async> perl module,
4304	which uses exactly this technique (which is suited for many high-level
4305	languages).
4306
4307	The example uses a pthread mutex to protect the loop data, a condition
4308	variable to wait for callback invocations, an async watcher to notify the
4309	event loop thread and an unspecified mechanism to wake up the main thread.
4310
4311	First, you need to associate some data with the event loop:
4312
4313	typedef struct {
4314	mutex_t lock; /* global loop lock */
4315	ev_async async_w;
4316	thread_t tid;
4317	cond_t invoke_cv;
4318	} userdata;
4319
4320	void prepare_loop (EV_P)
4321	{
4322	// for simplicity, we use a static userdata struct.
4323	static userdata u;
4324
4325	ev_async_init (&u->async_w, async_cb);
4326	ev_async_start (EV_A_ &u->async_w);
4327
4328	pthread_mutex_init (&u->lock, 0);
4329	pthread_cond_init (&u->invoke_cv, 0);
4330
4331	// now associate this with the loop
4332	ev_set_userdata (EV_A_ u);
4333	ev_set_invoke_pending_cb (EV_A_ l_invoke);
4334	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4335
4336	// then create the thread running ev_loop
4337	pthread_create (&u->tid, 0, l_run, EV_A);
4338	}
4339
4340	The callback for the C<ev_async> watcher does nothing: the watcher is used
4341	solely to wake up the event loop so it takes notice of any new watchers
4342	that might have been added:
4343
4344	static void
4345	async_cb (EV_P_ ev_async *w, int revents)
4346	{
4347	// just used for the side effects
4348	}
4349
4350	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
4351	protecting the loop data, respectively.
4352
4353	static void
4354	l_release (EV_P)
4355	{
4356	userdata *u = ev_userdata (EV_A);
4357	pthread_mutex_unlock (&u->lock);
4358	}
4359
4360	static void
4361	l_acquire (EV_P)
4362	{
4363	userdata *u = ev_userdata (EV_A);
4364	pthread_mutex_lock (&u->lock);
4365	}
4366
4367	The event loop thread first acquires the mutex, and then jumps straight
4368	into C<ev_run>:
4369
4370	void *
4371	l_run (void *thr_arg)
4372	{
4373	struct ev_loop *loop = (struct ev_loop *)thr_arg;
4374
4375	l_acquire (EV_A);
4376	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4377	ev_run (EV_A_ 0);
4378	l_release (EV_A);
4379
4380	return 0;
4381	}
4382
4383	Instead of invoking all pending watchers, the C<l_invoke> callback will
4384	signal the main thread via some unspecified mechanism (signals? pipe
4385	writes? C<Async::Interrupt>?) and then waits until all pending watchers
4386	have been called (in a while loop because a) spurious wakeups are possible
4387	and b) skipping inter-thread-communication when there are no pending
4388	watchers is very beneficial):
4389
4390	static void
4391	l_invoke (EV_P)
4392	{
4393	userdata *u = ev_userdata (EV_A);
4394
4395	while (ev_pending_count (EV_A))
4396	{
4397	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4398	pthread_cond_wait (&u->invoke_cv, &u->lock);
4399	}
4400	}
4401
4402	Now, whenever the main thread gets told to invoke pending watchers, it
4403	will grab the lock, call C<ev_invoke_pending> and then signal the loop
4404	thread to continue:
4405
4406	static void
4407	real_invoke_pending (EV_P)
4408	{
4409	userdata *u = ev_userdata (EV_A);
4410
4411	pthread_mutex_lock (&u->lock);
4412	ev_invoke_pending (EV_A);
4413	pthread_cond_signal (&u->invoke_cv);
4414	pthread_mutex_unlock (&u->lock);
4415	}
4416
4417	Whenever you want to start/stop a watcher or do other modifications to an
4418	event loop, you will now have to lock:
4419
4420	ev_timer timeout_watcher;
4421	userdata *u = ev_userdata (EV_A);
4422
4423	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4424
4425	pthread_mutex_lock (&u->lock);
4426	ev_timer_start (EV_A_ &timeout_watcher);
4427	ev_async_send (EV_A_ &u->async_w);
4428	pthread_mutex_unlock (&u->lock);
4429
4430	Note that sending the C<ev_async> watcher is required because otherwise
4431	an event loop currently blocking in the kernel will have no knowledge
4432	about the newly added timer. By waking up the loop it will pick up any new
4433	watchers in the next event loop iteration.
4434		5114
4435	=head3 COROUTINES	5115	=head3 COROUTINES
4436		5116
4437	Libev is very accommodating to coroutines ("cooperative threads"):	5117	Libev is very accommodating to coroutines ("cooperative threads"):
4438	libev fully supports nesting calls to its functions from different	5118	libev fully supports nesting calls to its functions from different
…		…
4603	requires, and its I/O model is fundamentally incompatible with the POSIX	5283	requires, and its I/O model is fundamentally incompatible with the POSIX
4604	model. Libev still offers limited functionality on this platform in	5284	model. Libev still offers limited functionality on this platform in
4605	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5285	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
4606	descriptors. This only applies when using Win32 natively, not when using	5286	descriptors. This only applies when using Win32 natively, not when using
4607	e.g. cygwin. Actually, it only applies to the microsofts own compilers,	5287	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4608	as every compielr comes with a slightly differently broken/incompatible	5288	as every compiler comes with a slightly differently broken/incompatible
4609	environment.	5289	environment.
4610		5290
4611	Lifting these limitations would basically require the full	5291	Lifting these limitations would basically require the full
4612	re-implementation of the I/O system. If you are into this kind of thing,	5292	re-implementation of the I/O system. If you are into this kind of thing,
4613	then note that glib does exactly that for you in a very portable way (note	5293	then note that glib does exactly that for you in a very portable way (note
…		…
4707	structure (guaranteed by POSIX but not by ISO C for example), but it also	5387	structure (guaranteed by POSIX but not by ISO C for example), but it also
4708	assumes that the same (machine) code can be used to call any watcher	5388	assumes that the same (machine) code can be used to call any watcher
4709	callback: The watcher callbacks have different type signatures, but libev	5389	callback: The watcher callbacks have different type signatures, but libev
4710	calls them using an C<ev_watcher *> internally.	5390	calls them using an C<ev_watcher *> internally.
4711		5391
		5392	=item null pointers and integer zero are represented by 0 bytes
		5393
		5394	Libev uses C<memset> to initialise structs and arrays to C<0> bytes, and
		5395	relies on this setting pointers and integers to null.
		5396
		5397	=item pointer accesses must be thread-atomic
		5398
		5399	Accessing a pointer value must be atomic, it must both be readable and
		5400	writable in one piece - this is the case on all current architectures.
		5401
4712	=item C<sig_atomic_t volatile> must be thread-atomic as well	5402	=item C<sig_atomic_t volatile> must be thread-atomic as well
4713		5403
4714	The type C<sig_atomic_t volatile> (or whatever is defined as	5404	The type C<sig_atomic_t volatile> (or whatever is defined as
4715	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different	5405	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
4716	threads. This is not part of the specification for C<sig_atomic_t>, but is	5406	threads. This is not part of the specification for C<sig_atomic_t>, but is
…		…
4724	thread" or will block signals process-wide, both behaviours would	5414	thread" or will block signals process-wide, both behaviours would
4725	be compatible with libev. Interaction between C<sigprocmask> and	5415	be compatible with libev. Interaction between C<sigprocmask> and
4726	C<pthread_sigmask> could complicate things, however.	5416	C<pthread_sigmask> could complicate things, however.
4727		5417
4728	The most portable way to handle signals is to block signals in all threads	5418	The most portable way to handle signals is to block signals in all threads
4729	except the initial one, and run the default loop in the initial thread as	5419	except the initial one, and run the signal handling loop in the initial
4730	well.	5420	thread as well.
4731		5421
4732	=item C<long> must be large enough for common memory allocation sizes	5422	=item C<long> must be large enough for common memory allocation sizes
4733		5423
4734	To improve portability and simplify its API, libev uses C<long> internally	5424	To improve portability and simplify its API, libev uses C<long> internally
4735	instead of C<size_t> when allocating its data structures. On non-POSIX	5425	instead of C<size_t> when allocating its data structures. On non-POSIX
…		…
4741		5431
4742	The type C<double> is used to represent timestamps. It is required to	5432	The type C<double> is used to represent timestamps. It is required to
4743	have at least 51 bits of mantissa (and 9 bits of exponent), which is	5433	have at least 51 bits of mantissa (and 9 bits of exponent), which is
4744	good enough for at least into the year 4000 with millisecond accuracy	5434	good enough for at least into the year 4000 with millisecond accuracy
4745	(the design goal for libev). This requirement is overfulfilled by	5435	(the design goal for libev). This requirement is overfulfilled by
4746	implementations using IEEE 754, which is basically all existing ones. With	5436	implementations using IEEE 754, which is basically all existing ones.
		5437
4747	IEEE 754 doubles, you get microsecond accuracy until at least 2200.	5438	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5439	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5440	is either obsolete or somebody patched it to use C<long double> or
		5441	something like that, just kidding).
4748		5442
4749	=back	5443	=back
4750		5444
4751	If you know of other additional requirements drop me a note.	5445	If you know of other additional requirements drop me a note.
4752		5446
…		…
4814	=item Processing ev_async_send: O(number_of_async_watchers)	5508	=item Processing ev_async_send: O(number_of_async_watchers)
4815		5509
4816	=item Processing signals: O(max_signal_number)	5510	=item Processing signals: O(max_signal_number)
4817		5511
4818	Sending involves a system call I<iff> there were no other C<ev_async_send>	5512	Sending involves a system call I<iff> there were no other C<ev_async_send>
4819	calls in the current loop iteration. Checking for async and signal events	5513	calls in the current loop iteration and the loop is currently
		5514	blocked. Checking for async and signal events involves iterating over all
4820	involves iterating over all running async watchers or all signal numbers.	5515	running async watchers or all signal numbers.
4821		5516
4822	=back	5517	=back
4823		5518
4824		5519
4825	=head1 PORTING FROM LIBEV 3.X TO 4.X	5520	=head1 PORTING FROM LIBEV 3.X TO 4.X
4826		5521
4827	The major version 4 introduced some minor incompatible changes to the API.	5522	The major version 4 introduced some incompatible changes to the API.
4828		5523
4829	At the moment, the C<ev.h> header file tries to implement superficial	5524	At the moment, the C<ev.h> header file provides compatibility definitions
4830	compatibility, so most programs should still compile. Those might be	5525	for all changes, so most programs should still compile. The compatibility
4831	removed in later versions of libev, so better update early than late.	5526	layer might be removed in later versions of libev, so better update to the
		5527	new API early than late.
4832		5528
4833	=over 4	5529	=over 4
		5530
		5531	=item C<EV_COMPAT3> backwards compatibility mechanism
		5532
		5533	The backward compatibility mechanism can be controlled by
		5534	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
		5535	section.
		5536
		5537	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5538
		5539	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5540
		5541	ev_loop_destroy (EV_DEFAULT_UC);
		5542	ev_loop_fork (EV_DEFAULT);
4834		5543
4835	=item function/symbol renames	5544	=item function/symbol renames
4836		5545
4837	A number of functions and symbols have been renamed:	5546	A number of functions and symbols have been renamed:
4838		5547
…		…
4857	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme	5566	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
4858	as all other watcher types. Note that C<ev_loop_fork> is still called	5567	as all other watcher types. Note that C<ev_loop_fork> is still called
4859	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>	5568	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
4860	typedef.	5569	typedef.
4861		5570
4862	=item C<EV_COMPAT3> backwards compatibility mechanism
4863
4864	The backward compatibility mechanism can be controlled by
4865	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
4866	section.
4867
4868	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>	5571	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
4869		5572
4870	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different	5573	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
4871	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile	5574	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
4872	and work, but the library code will of course be larger.	5575	and work, but the library code will of course be larger.
…		…
4879	=over 4	5582	=over 4
4880		5583
4881	=item active	5584	=item active
4882		5585
4883	A watcher is active as long as it has been started and not yet stopped.	5586	A watcher is active as long as it has been started and not yet stopped.
4884	See L<WATCHER STATES> for details.	5587	See L</WATCHER STATES> for details.
4885		5588
4886	=item application	5589	=item application
4887		5590
4888	In this document, an application is whatever is using libev.	5591	In this document, an application is whatever is using libev.
4889		5592
…		…
4925	watchers and events.	5628	watchers and events.
4926		5629
4927	=item pending	5630	=item pending
4928		5631
4929	A watcher is pending as soon as the corresponding event has been	5632	A watcher is pending as soon as the corresponding event has been
4930	detected. See L<WATCHER STATES> for details.	5633	detected. See L</WATCHER STATES> for details.
4931		5634
4932	=item real time	5635	=item real time
4933		5636
4934	The physical time that is observed. It is apparently strictly monotonic :)	5637	The physical time that is observed. It is apparently strictly monotonic :)
4935		5638
4936	=item wall-clock time	5639	=item wall-clock time
4937		5640
4938	The time and date as shown on clocks. Unlike real time, it can actually	5641	The time and date as shown on clocks. Unlike real time, it can actually
4939	be wrong and jump forwards and backwards, e.g. when the you adjust your	5642	be wrong and jump forwards and backwards, e.g. when you adjust your
4940	clock.	5643	clock.
4941		5644
4942	=item watcher	5645	=item watcher
4943		5646
4944	A data structure that describes interest in certain events. Watchers need	5647	A data structure that describes interest in certain events. Watchers need
…		…
4946		5649
4947	=back	5650	=back
4948		5651
4949	=head1 AUTHOR	5652	=head1 AUTHOR
4950		5653
4951	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.	5654	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5655	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
4952		5656

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