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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
…		…
193	as this indicates an incompatible change. Minor versions are usually	209	as this indicates an incompatible change. Minor versions are usually
194	compatible to older versions, so a larger minor version alone is usually	210	compatible to older versions, so a larger minor version alone is usually
195	not a problem.	211	not a problem.
196		212
197	Example: Make sure we haven't accidentally been linked against the wrong	213	Example: Make sure we haven't accidentally been linked against the wrong
198	version (note, however, that this will not detect ABI mismatches :).	214	version (note, however, that this will not detect other ABI mismatches,
		215	such as LFS or reentrancy).
199		216
200	assert (("libev version mismatch",	217	assert (("libev version mismatch",
201	ev_version_major () == EV_VERSION_MAJOR	218	ev_version_major () == EV_VERSION_MAJOR
202	&& ev_version_minor () >= EV_VERSION_MINOR));	219	&& ev_version_minor () >= EV_VERSION_MINOR));
203		220
…		…
232	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 ()
233	& ev_supported_backends ()>, likewise for recommended ones.	250	& ev_supported_backends ()>, likewise for recommended ones.
234		251
235	See the description of C<ev_embed> watchers for more info.	252	See the description of C<ev_embed> watchers for more info.
236		253
237	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]	254	=item ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())
238		255
239	Sets the allocation function to use (the prototype is similar - the	256	Sets the allocation function to use (the prototype is similar - the
240	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
241	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
242	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
…		…
248		265
249	You could override this function in high-availability programs to, say,	266	You could override this function in high-availability programs to, say,
250	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,
251	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.
252		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
253	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
254	retries (example requires a standards-compliant C<realloc>).	285	retries.
255		286
256	static void *	287	static void *
257	persistent_realloc (void *ptr, size_t size)	288	persistent_realloc (void *ptr, size_t size)
258	{	289	{
		290	if (!size)
		291	{
		292	free (ptr);
		293	return 0;
		294	}
		295
259	for (;;)	296	for (;;)
260	{	297	{
261	void *newptr = realloc (ptr, size);	298	void *newptr = realloc (ptr, size);
262		299
263	if (newptr)	300	if (newptr)
…		…
268	}	305	}
269		306
270	...	307	...
271	ev_set_allocator (persistent_realloc);	308	ev_set_allocator (persistent_realloc);
272		309
273	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]	310	=item ev_set_syserr_cb (void (*cb)(const char *msg) throw ())
274		311
275	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
276	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
277	indicating the system call or subsystem causing the problem. If this	314	indicating the system call or subsystem causing the problem. If this
278	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
…		…
290	}	327	}
291		328
292	...	329	...
293	ev_set_syserr_cb (fatal_error);	330	ev_set_syserr_cb (fatal_error);
294		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
295	=back	345	=back
296		346
297	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	347	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
298		348
299	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
300	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
301	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).
302		352
303	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
304	supports signals and child events, and dynamically created event loops	354	supports child process events, and dynamically created event loops which
305	which do not.	355	do not.
306		356
307	=over 4	357	=over 4
308		358
309	=item struct ev_loop *ev_default_loop (unsigned int flags)	359	=item struct ev_loop *ev_default_loop (unsigned int flags)
310		360
311	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
312	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
313	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
314	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".
315		371
316	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
317	function.	373	function (or via the C<EV_DEFAULT> macro).
318		374
319	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
320	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
321	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).
322		379
323	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,
324	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
325	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
326	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
327	can simply overwrite the C<SIGCHLD> signal handler I<after> calling	384	C<SIGCHLD> signal handler I<after> calling C<ev_default_init>.
328	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.
329		404
330	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
331	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>).
332		407
333	The following flags are supported:	408	The following flags are supported:
…		…
343		418
344	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
345	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
346	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	421	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
347	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
348	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
349	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).
350		427
351	=item C<EVFLAG_FORKCHECK>	428	=item C<EVFLAG_FORKCHECK>
352		429
353	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
354	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.
355		432
356	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,
357	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
358	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
359	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
360	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
361	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).
362		440
363	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
364	forget about forgetting to tell libev about forking) when you use this	442	forget about forgetting to tell libev about forking, although you still
365	flag.	443	have to ignore C<SIGPIPE>) when you use this flag.
366		444
367	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>
368	environment variable.	446	environment variable.
369		447
370	=item C<EVFLAG_NOINOTIFY>	448	=item C<EVFLAG_NOINOTIFY>
371		449
372	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
373	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
374	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
375	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.
376		454
377	=item C<EVFLAG_SIGNALFD>	455	=item C<EVFLAG_SIGNALFD>
378		456
379	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
380	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
381	delivers signals synchronously, which makes it both faster and might make	459	delivers signals synchronously, which makes it both faster and might make
382	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
383	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
384	threads that are not interested in handling them.	462	threads that are not interested in handling them.
385		463
386	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
387	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
388	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.
389		482
390	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	483	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
391		484
392	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
393	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,
…		…
421	=item C<EVBACKEND_EPOLL> (value 4, Linux)	514	=item C<EVBACKEND_EPOLL> (value 4, Linux)
422		515
423	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
424	kernels).	517	kernels).
425		518
426	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
427	but it scales phenomenally better. While poll and select usually scale	520	it scales phenomenally better. While poll and select usually scale like
428	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
429	epoll scales either O(1) or O(active_fds).	522	fd), epoll scales either O(1) or O(active_fds).
430		523
431	The epoll mechanism deserves honorable mention as the most misdesigned	524	The epoll mechanism deserves honorable mention as the most misdesigned
432	of the more advanced event mechanisms: mere annoyances include silently	525	of the more advanced event mechanisms: mere annoyances include silently
433	dropping file descriptors, requiring a system call per change per file	526	dropping file descriptors, requiring a system call per change per file
434	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
435	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
436	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
437	take considerable time (one syscall per file descriptor) and is of course	532	set, which can take considerable time (one syscall per file descriptor)
438	hard to detect.	533	and is of course hard to detect.
439		534
440	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but	535	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
441	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
442	I<different> file descriptors (even already closed ones, so one cannot	537	totally I<different> file descriptors (even already closed ones, so
443	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
444	on SMP systems). Libev tries to counter these spurious notifications by	539	(especially on SMP systems). Libev tries to counter these spurious
445	employing an additional generation counter and comparing that against the	540	notifications by employing an additional generation counter and comparing
446	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
447	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
448	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...
449		551
450	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
451	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
452	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
453	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
…		…
465	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
466	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
467	the usage. So sad.	569	the usage. So sad.
468		570
469	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
470	all kernel versions tested so far.	572	a lot of kernel revisions, but probably(!) works in current versions.
471		573
472	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	574	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
473	C<EVBACKEND_POLL>.	575	C<EVBACKEND_POLL>.
474		576
		577	=item C<EVBACKEND_LINUXAIO> (value 64, Linux)
		578
		579	Use the linux-specific linux aio (I<not> C<< aio(7) >> but C<<
		580	io_submit(2) >>) event interface available in post-4.18 kernels (but libev
		581	only tries to use it in 4.19+).
		582
		583	This is another linux trainwreck of an event interface.
		584
		585	If this backend works for you (as of this writing, it was very
		586	experimental), it is the best event interface available on linux and might
		587	be well worth enabling it - if it isn't available in your kernel this will
		588	be detected and this backend will be skipped.
		589
		590	This backend can batch oneshot requests and supports a user-space ring
		591	buffer to receive events. It also doesn't suffer from most of the design
		592	problems of epoll (such as not being able to remove event sources from
		593	the epoll set), and generally sounds too good to be true. Because, this
		594	being the linux kernel, of course it suffers from a whole new set of
		595	limitations, forcing you to fall back to epoll, inheriting all its design
		596	issues.
		597
		598	For one, it is not easily embeddable (but probably could be done using
		599	an event fd at some extra overhead). It also is subject to a system wide
		600	limit that can be configured in F</proc/sys/fs/aio-max-nr>. If no aio
		601	requests are left, this backend will be skipped during initialisation, and
		602	will switch to epoll when the loop is active.
		603
		604	Most problematic in practice, however, is that not all file descriptors
		605	work with it. For example, in linux 5.1, tcp sockets, pipes, event fds,
		606	files, F</dev/null> and a few others are supported, but ttys do not work
		607	properly (a known bug that the kernel developers don't care about, see
		608	L<https://lore.kernel.org/patchwork/patch/1047453/>), so this is not
		609	(yet?) a generic event polling interface.
		610
		611	Overall, it seems the linux developers just don't want it to have a
		612	generic event handling mechanism other than C<select> or C<poll>.
		613
		614	To work around all these problem, the current version of libev uses its
		615	epoll backend as a fallback for file descriptor types that do not work. Or
		616	falls back completely to epoll if the kernel acts up.
		617
		618	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		619	C<EVBACKEND_POLL>.
		620
475	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	621	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
476		622
477	Kqueue deserves special mention, as at the time of this writing, it	623	Kqueue deserves special mention, as at the time this backend was
478	was broken on all BSDs except NetBSD (usually it doesn't work reliably	624	implemented, it was broken on all BSDs except NetBSD (usually it doesn't
479	with anything but sockets and pipes, except on Darwin, where of course	625	work reliably with anything but sockets and pipes, except on Darwin,
480	it's completely useless). Unlike epoll, however, whose brokenness	626	where of course it's completely useless). Unlike epoll, however, whose
481	is by design, these kqueue bugs can (and eventually will) be fixed	627	brokenness is by design, these kqueue bugs can be (and mostly have been)
482	without API changes to existing programs. For this reason it's not being	628	fixed without API changes to existing programs. For this reason it's not
483	"auto-detected" unless you explicitly specify it in the flags (i.e. using	629	being "auto-detected" on all platforms unless you explicitly specify it
484	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)	630	in the flags (i.e. using C<EVBACKEND_KQUEUE>) or libev was compiled on a
485	system like NetBSD.	631	known-to-be-good (-enough) system like NetBSD.
486		632
487	You still can embed kqueue into a normal poll or select backend and use it	633	You still can embed kqueue into a normal poll or select backend and use it
488	only for sockets (after having made sure that sockets work with kqueue on	634	only for sockets (after having made sure that sockets work with kqueue on
489	the target platform). See C<ev_embed> watchers for more info.	635	the target platform). See C<ev_embed> watchers for more info.
490		636
491	It scales in the same way as the epoll backend, but the interface to the	637	It scales in the same way as the epoll backend, but the interface to the
492	kernel is more efficient (which says nothing about its actual speed, of	638	kernel is more efficient (which says nothing about its actual speed, of
493	course). While stopping, setting and starting an I/O watcher does never	639	course). While stopping, setting and starting an I/O watcher does never
494	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to	640	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
495	two event changes per incident. Support for C<fork ()> is very bad (but	641	two event changes per incident. Support for C<fork ()> is very bad (you
496	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect	642	might have to leak fd's on fork, but it's more sane than epoll) and it
497	cases	643	drops fds silently in similarly hard-to-detect cases.
498		644
499	This backend usually performs well under most conditions.	645	This backend usually performs well under most conditions.
500		646
501	While nominally embeddable in other event loops, this doesn't work	647	While nominally embeddable in other event loops, this doesn't work
502	everywhere, so you might need to test for this. And since it is broken	648	everywhere, so you might need to test for this. And since it is broken
…		…
519	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	665	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
520		666
521	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	667	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
522	it's really slow, but it still scales very well (O(active_fds)).	668	it's really slow, but it still scales very well (O(active_fds)).
523		669
524	Please note that Solaris event ports can deliver a lot of spurious
525	notifications, so you need to use non-blocking I/O or other means to avoid
526	blocking when no data (or space) is available.
527
528	While this backend scales well, it requires one system call per active	670	While this backend scales well, it requires one system call per active
529	file descriptor per loop iteration. For small and medium numbers of file	671	file descriptor per loop iteration. For small and medium numbers of file
530	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	672	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
531	might perform better.	673	might perform better.
532		674
533	On the positive side, with the exception of the spurious readiness	675	On the positive side, this backend actually performed fully to
534	notifications, this backend actually performed fully to specification
535	in all tests and is fully embeddable, which is a rare feat among the	676	specification in all tests and is fully embeddable, which is a rare feat
536	OS-specific backends (I vastly prefer correctness over speed hacks).	677	among the OS-specific backends (I vastly prefer correctness over speed
		678	hacks).
		679
		680	On the negative side, the interface is I<bizarre> - so bizarre that
		681	even sun itself gets it wrong in their code examples: The event polling
		682	function sometimes returns events to the caller even though an error
		683	occurred, but with no indication whether it has done so or not (yes, it's
		684	even documented that way) - deadly for edge-triggered interfaces where you
		685	absolutely have to know whether an event occurred or not because you have
		686	to re-arm the watcher.
		687
		688	Fortunately libev seems to be able to work around these idiocies.
537		689
538	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	690	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
539	C<EVBACKEND_POLL>.	691	C<EVBACKEND_POLL>.
540		692
541	=item C<EVBACKEND_ALL>	693	=item C<EVBACKEND_ALL>
542		694
543	Try all backends (even potentially broken ones that wouldn't be tried	695	Try all backends (even potentially broken ones that wouldn't be tried
544	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	696	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
545	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	697	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
546		698
547	It is definitely not recommended to use this flag.	699	It is definitely not recommended to use this flag, use whatever
		700	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		701	at all.
		702
		703	=item C<EVBACKEND_MASK>
		704
		705	Not a backend at all, but a mask to select all backend bits from a
		706	C<flags> value, in case you want to mask out any backends from a flags
		707	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
548		708
549	=back	709	=back
550		710
551	If one or more of the backend flags are or'ed into the flags value,	711	If one or more of the backend flags are or'ed into the flags value,
552	then only these backends will be tried (in the reverse order as listed	712	then only these backends will be tried (in the reverse order as listed
553	here). If none are specified, all backends in C<ev_recommended_backends	713	here). If none are specified, all backends in C<ev_recommended_backends
554	()> will be tried.	714	()> will be tried.
555		715
556	Example: This is the most typical usage.
557
558	if (!ev_default_loop (0))
559	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
560
561	Example: Restrict libev to the select and poll backends, and do not allow
562	environment settings to be taken into account:
563
564	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
565
566	Example: Use whatever libev has to offer, but make sure that kqueue is
567	used if available (warning, breaks stuff, best use only with your own
568	private event loop and only if you know the OS supports your types of
569	fds):
570
571	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
572
573	=item struct ev_loop *ev_loop_new (unsigned int flags)
574
575	Similar to C<ev_default_loop>, but always creates a new event loop that is
576	always distinct from the default loop.
577
578	Note that this function I<is> thread-safe, and one common way to use
579	libev with threads is indeed to create one loop per thread, and using the
580	default loop in the "main" or "initial" thread.
581
582	Example: Try to create a event loop that uses epoll and nothing else.	716	Example: Try to create a event loop that uses epoll and nothing else.
583		717
584	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	718	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
585	if (!epoller)	719	if (!epoller)
586	fatal ("no epoll found here, maybe it hides under your chair");	720	fatal ("no epoll found here, maybe it hides under your chair");
587		721
		722	Example: Use whatever libev has to offer, but make sure that kqueue is
		723	used if available.
		724
		725	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		726
		727	Example: Similarly, on linux, you mgiht want to take advantage of the
		728	linux aio backend if possible, but fall back to something else if that
		729	isn't available.
		730
		731	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_LINUXAIO);
		732
588	=item ev_default_destroy ()	733	=item ev_loop_destroy (loop)
589		734
590	Destroys the default loop (frees all memory and kernel state etc.). None	735	Destroys an event loop object (frees all memory and kernel state
591	of the active event watchers will be stopped in the normal sense, so	736	etc.). None of the active event watchers will be stopped in the normal
592	e.g. C<ev_is_active> might still return true. It is your responsibility to	737	sense, so e.g. C<ev_is_active> might still return true. It is your
593	either stop all watchers cleanly yourself I<before> calling this function,	738	responsibility to either stop all watchers cleanly yourself I<before>
594	or cope with the fact afterwards (which is usually the easiest thing, you	739	calling this function, or cope with the fact afterwards (which is usually
595	can just ignore the watchers and/or C<free ()> them for example).	740	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		741	for example).
596		742
597	Note that certain global state, such as signal state (and installed signal	743	Note that certain global state, such as signal state (and installed signal
598	handlers), will not be freed by this function, and related watchers (such	744	handlers), will not be freed by this function, and related watchers (such
599	as signal and child watchers) would need to be stopped manually.	745	as signal and child watchers) would need to be stopped manually.
600		746
601	In general it is not advisable to call this function except in the	747	This function is normally used on loop objects allocated by
602	rare occasion where you really need to free e.g. the signal handling	748	C<ev_loop_new>, but it can also be used on the default loop returned by
		749	C<ev_default_loop>, in which case it is not thread-safe.
		750
		751	Note that it is not advisable to call this function on the default loop
		752	except in the rare occasion where you really need to free its resources.
603	pipe fds. If you need dynamically allocated loops it is better to use	753	If you need dynamically allocated loops it is better to use C<ev_loop_new>
604	C<ev_loop_new> and C<ev_loop_destroy>.	754	and C<ev_loop_destroy>.
605		755
606	=item ev_loop_destroy (loop)	756	=item ev_loop_fork (loop)
607
608	Like C<ev_default_destroy>, but destroys an event loop created by an
609	earlier call to C<ev_loop_new>.
610
611	=item ev_default_fork ()
612		757
613	This function sets a flag that causes subsequent C<ev_run> iterations	758	This function sets a flag that causes subsequent C<ev_run> iterations
614	to reinitialise the kernel state for backends that have one. Despite the	759	to reinitialise the kernel state for backends that have one. Despite
615	name, you can call it anytime, but it makes most sense after forking, in	760	the name, you can call it anytime you are allowed to start or stop
616	the child process (or both child and parent, but that again makes little	761	watchers (except inside an C<ev_prepare> callback), but it makes most
617	sense). You I<must> call it in the child before using any of the libev	762	sense after forking, in the child process. You I<must> call it (or use
618	functions, and it will only take effect at the next C<ev_run> iteration.	763	C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.
619		764
		765	In addition, if you want to reuse a loop (via this function or
		766	C<EVFLAG_FORKCHECK>), you I<also> have to ignore C<SIGPIPE>.
		767
620	Again, you I<have> to call it on I<any> loop that you want to re-use after	768	Again, you I<have> to call it on I<any> loop that you want to re-use after
621	a fork, I<even if you do not plan to use the loop in the parent>. This is	769	a fork, I<even if you do not plan to use the loop in the parent>. This is
622	because some kernel interfaces *cough* I<kqueue> *cough* do funny things	770	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
623	during fork.	771	during fork.
624		772
625	On the other hand, you only need to call this function in the child	773	On the other hand, you only need to call this function in the child
…		…
628	call it at all (in fact, C<epoll> is so badly broken that it makes a	776	call it at all (in fact, C<epoll> is so badly broken that it makes a
629	difference, but libev will usually detect this case on its own and do a	777	difference, but libev will usually detect this case on its own and do a
630	costly reset of the backend).	778	costly reset of the backend).
631		779
632	The function itself is quite fast and it's usually not a problem to call	780	The function itself is quite fast and it's usually not a problem to call
633	it just in case after a fork. To make this easy, the function will fit in	781	it just in case after a fork.
634	quite nicely into a call to C<pthread_atfork>:
635		782
		783	Example: Automate calling C<ev_loop_fork> on the default loop when
		784	using pthreads.
		785
		786	static void
		787	post_fork_child (void)
		788	{
		789	ev_loop_fork (EV_DEFAULT);
		790	}
		791
		792	...
636	pthread_atfork (0, 0, ev_default_fork);	793	pthread_atfork (0, 0, post_fork_child);
637
638	=item ev_loop_fork (loop)
639
640	Like C<ev_default_fork>, but acts on an event loop created by
641	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
642	after fork that you want to re-use in the child, and how you keep track of
643	them is entirely your own problem.
644		794
645	=item int ev_is_default_loop (loop)	795	=item int ev_is_default_loop (loop)
646		796
647	Returns true when the given loop is, in fact, the default loop, and false	797	Returns true when the given loop is, in fact, the default loop, and false
648	otherwise.	798	otherwise.
…		…
659	prepare and check phases.	809	prepare and check phases.
660		810
661	=item unsigned int ev_depth (loop)	811	=item unsigned int ev_depth (loop)
662		812
663	Returns the number of times C<ev_run> was entered minus the number of	813	Returns the number of times C<ev_run> was entered minus the number of
664	times C<ev_run> was exited, in other words, the recursion depth.	814	times C<ev_run> was exited normally, in other words, the recursion depth.
665		815
666	Outside C<ev_run>, this number is zero. In a callback, this number is	816	Outside C<ev_run>, this number is zero. In a callback, this number is
667	C<1>, unless C<ev_run> was invoked recursively (or from another thread),	817	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
668	in which case it is higher.	818	in which case it is higher.
669		819
670	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread	820	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
671	etc.), doesn't count as "exit" - consider this as a hint to avoid such	821	throwing an exception etc.), doesn't count as "exit" - consider this
672	ungentleman-like behaviour unless it's really convenient.	822	as a hint to avoid such ungentleman-like behaviour unless it's really
		823	convenient, in which case it is fully supported.
673		824
674	=item unsigned int ev_backend (loop)	825	=item unsigned int ev_backend (loop)
675		826
676	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	827	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
677	use.	828	use.
…		…
692		843
693	This function is rarely useful, but when some event callback runs for a	844	This function is rarely useful, but when some event callback runs for a
694	very long time without entering the event loop, updating libev's idea of	845	very long time without entering the event loop, updating libev's idea of
695	the current time is a good idea.	846	the current time is a good idea.
696		847
697	See also L<The special problem of time updates> in the C<ev_timer> section.	848	See also L</The special problem of time updates> in the C<ev_timer> section.
698		849
699	=item ev_suspend (loop)	850	=item ev_suspend (loop)
700		851
701	=item ev_resume (loop)	852	=item ev_resume (loop)
702		853
…		…
720	without a previous call to C<ev_suspend>.	871	without a previous call to C<ev_suspend>.
721		872
722	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the	873	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
723	event loop time (see C<ev_now_update>).	874	event loop time (see C<ev_now_update>).
724		875
725	=item ev_run (loop, int flags)	876	=item bool ev_run (loop, int flags)
726		877
727	Finally, this is it, the event handler. This function usually is called	878	Finally, this is it, the event handler. This function usually is called
728	after you have initialised all your watchers and you want to start	879	after you have initialised all your watchers and you want to start
729	handling events. It will ask the operating system for any new events, call	880	handling events. It will ask the operating system for any new events, call
730	the watcher callbacks, an then repeat the whole process indefinitely: This	881	the watcher callbacks, and then repeat the whole process indefinitely: This
731	is why event loops are called I<loops>.	882	is why event loops are called I<loops>.
732		883
733	If the flags argument is specified as C<0>, it will keep handling events	884	If the flags argument is specified as C<0>, it will keep handling events
734	until either no event watchers are active anymore or C<ev_break> was	885	until either no event watchers are active anymore or C<ev_break> was
735	called.	886	called.
		887
		888	The return value is false if there are no more active watchers (which
		889	usually means "all jobs done" or "deadlock"), and true in all other cases
		890	(which usually means " you should call C<ev_run> again").
736		891
737	Please note that an explicit C<ev_break> is usually better than	892	Please note that an explicit C<ev_break> is usually better than
738	relying on all watchers to be stopped when deciding when a program has	893	relying on all watchers to be stopped when deciding when a program has
739	finished (especially in interactive programs), but having a program	894	finished (especially in interactive programs), but having a program
740	that automatically loops as long as it has to and no longer by virtue	895	that automatically loops as long as it has to and no longer by virtue
741	of relying on its watchers stopping correctly, that is truly a thing of	896	of relying on its watchers stopping correctly, that is truly a thing of
742	beauty.	897	beauty.
743		898
		899	This function is I<mostly> exception-safe - you can break out of a
		900	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		901	exception and so on. This does not decrement the C<ev_depth> value, nor
		902	will it clear any outstanding C<EVBREAK_ONE> breaks.
		903
744	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle	904	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
745	those events and any already outstanding ones, but will not wait and	905	those events and any already outstanding ones, but will not wait and
746	block your process in case there are no events and will return after one	906	block your process in case there are no events and will return after one
747	iteration of the loop. This is sometimes useful to poll and handle new	907	iteration of the loop. This is sometimes useful to poll and handle new
748	events while doing lengthy calculations, to keep the program responsive.	908	events while doing lengthy calculations, to keep the program responsive.
…		…
757	This is useful if you are waiting for some external event in conjunction	917	This is useful if you are waiting for some external event in conjunction
758	with something not expressible using other libev watchers (i.e. "roll your	918	with something not expressible using other libev watchers (i.e. "roll your
759	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is	919	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
760	usually a better approach for this kind of thing.	920	usually a better approach for this kind of thing.
761		921
762	Here are the gory details of what C<ev_run> does:	922	Here are the gory details of what C<ev_run> does (this is for your
		923	understanding, not a guarantee that things will work exactly like this in
		924	future versions):
763		925
764	- Increment loop depth.	926	- Increment loop depth.
765	- Reset the ev_break status.	927	- Reset the ev_break status.
766	- Before the first iteration, call any pending watchers.	928	- Before the first iteration, call any pending watchers.
767	LOOP:	929	LOOP:
…		…
800	anymore.	962	anymore.
801		963
802	... queue jobs here, make sure they register event watchers as long	964	... queue jobs here, make sure they register event watchers as long
803	... as they still have work to do (even an idle watcher will do..)	965	... as they still have work to do (even an idle watcher will do..)
804	ev_run (my_loop, 0);	966	ev_run (my_loop, 0);
805	... jobs done or somebody called unloop. yeah!	967	... jobs done or somebody called break. yeah!
806		968
807	=item ev_break (loop, how)	969	=item ev_break (loop, how)
808		970
809	Can be used to make a call to C<ev_run> return early (but only after it	971	Can be used to make a call to C<ev_run> return early (but only after it
810	has processed all outstanding events). The C<how> argument must be either	972	has processed all outstanding events). The C<how> argument must be either
811	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or	973	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
812	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.	974	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
813		975
814	This "unloop state" will be cleared when entering C<ev_run> again.	976	This "break state" will be cleared on the next call to C<ev_run>.
815		977
816	It is safe to call C<ev_break> from outside any C<ev_run> calls. ##TODO##	978	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		979	which case it will have no effect.
817		980
818	=item ev_ref (loop)	981	=item ev_ref (loop)
819		982
820	=item ev_unref (loop)	983	=item ev_unref (loop)
821		984
…		…
842	running when nothing else is active.	1005	running when nothing else is active.
843		1006
844	ev_signal exitsig;	1007	ev_signal exitsig;
845	ev_signal_init (&exitsig, sig_cb, SIGINT);	1008	ev_signal_init (&exitsig, sig_cb, SIGINT);
846	ev_signal_start (loop, &exitsig);	1009	ev_signal_start (loop, &exitsig);
847	evf_unref (loop);	1010	ev_unref (loop);
848		1011
849	Example: For some weird reason, unregister the above signal handler again.	1012	Example: For some weird reason, unregister the above signal handler again.
850		1013
851	ev_ref (loop);	1014	ev_ref (loop);
852	ev_signal_stop (loop, &exitsig);	1015	ev_signal_stop (loop, &exitsig);
…		…
872	overhead for the actual polling but can deliver many events at once.	1035	overhead for the actual polling but can deliver many events at once.
873		1036
874	By setting a higher I<io collect interval> you allow libev to spend more	1037	By setting a higher I<io collect interval> you allow libev to spend more
875	time collecting I/O events, so you can handle more events per iteration,	1038	time collecting I/O events, so you can handle more events per iteration,
876	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	1039	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
877	C<ev_timer>) will be not affected. Setting this to a non-null value will	1040	C<ev_timer>) will not be affected. Setting this to a non-null value will
878	introduce an additional C<ev_sleep ()> call into most loop iterations. The	1041	introduce an additional C<ev_sleep ()> call into most loop iterations. The
879	sleep time ensures that libev will not poll for I/O events more often then	1042	sleep time ensures that libev will not poll for I/O events more often then
880	once per this interval, on average.	1043	once per this interval, on average (as long as the host time resolution is
		1044	good enough).
881		1045
882	Likewise, by setting a higher I<timeout collect interval> you allow libev	1046	Likewise, by setting a higher I<timeout collect interval> you allow libev
883	to spend more time collecting timeouts, at the expense of increased	1047	to spend more time collecting timeouts, at the expense of increased
884	latency/jitter/inexactness (the watcher callback will be called	1048	latency/jitter/inexactness (the watcher callback will be called
885	later). C<ev_io> watchers will not be affected. Setting this to a non-null	1049	later). C<ev_io> watchers will not be affected. Setting this to a non-null
…		…
931	invoke the actual watchers inside another context (another thread etc.).	1095	invoke the actual watchers inside another context (another thread etc.).
932		1096
933	If you want to reset the callback, use C<ev_invoke_pending> as new	1097	If you want to reset the callback, use C<ev_invoke_pending> as new
934	callback.	1098	callback.
935		1099
936	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))	1100	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
937		1101
938	Sometimes you want to share the same loop between multiple threads. This	1102	Sometimes you want to share the same loop between multiple threads. This
939	can be done relatively simply by putting mutex_lock/unlock calls around	1103	can be done relatively simply by putting mutex_lock/unlock calls around
940	each call to a libev function.	1104	each call to a libev function.
941		1105
942	However, C<ev_run> can run an indefinite time, so it is not feasible	1106	However, C<ev_run> can run an indefinite time, so it is not feasible
943	to wait for it to return. One way around this is to wake up the event	1107	to wait for it to return. One way around this is to wake up the event
944	loop via C<ev_break> and C<av_async_send>, another way is to set these	1108	loop via C<ev_break> and C<ev_async_send>, another way is to set these
945	I<release> and I<acquire> callbacks on the loop.	1109	I<release> and I<acquire> callbacks on the loop.
946		1110
947	When set, then C<release> will be called just before the thread is	1111	When set, then C<release> will be called just before the thread is
948	suspended waiting for new events, and C<acquire> is called just	1112	suspended waiting for new events, and C<acquire> is called just
949	afterwards.	1113	afterwards.
…		…
964	See also the locking example in the C<THREADS> section later in this	1128	See also the locking example in the C<THREADS> section later in this
965	document.	1129	document.
966		1130
967	=item ev_set_userdata (loop, void *data)	1131	=item ev_set_userdata (loop, void *data)
968		1132
969	=item ev_userdata (loop)	1133	=item void *ev_userdata (loop)
970		1134
971	Set and retrieve a single C<void *> associated with a loop. When	1135	Set and retrieve a single C<void *> associated with a loop. When
972	C<ev_set_userdata> has never been called, then C<ev_userdata> returns	1136	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
973	C<0.>	1137	C<0>.
974		1138
975	These two functions can be used to associate arbitrary data with a loop,	1139	These two functions can be used to associate arbitrary data with a loop,
976	and are intended solely for the C<invoke_pending_cb>, C<release> and	1140	and are intended solely for the C<invoke_pending_cb>, C<release> and
977	C<acquire> callbacks described above, but of course can be (ab-)used for	1141	C<acquire> callbacks described above, but of course can be (ab-)used for
978	any other purpose as well.	1142	any other purpose as well.
…		…
1089		1253
1090	=item C<EV_PREPARE>	1254	=item C<EV_PREPARE>
1091		1255
1092	=item C<EV_CHECK>	1256	=item C<EV_CHECK>
1093		1257
1094	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts	1258	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts to
1095	to gather new events, and all C<ev_check> watchers are invoked just after	1259	gather new events, and all C<ev_check> watchers are queued (not invoked)
1096	C<ev_run> has gathered them, but before it invokes any callbacks for any	1260	just after C<ev_run> has gathered them, but before it queues any callbacks
		1261	for any received events. That means C<ev_prepare> watchers are the last
		1262	watchers invoked before the event loop sleeps or polls for new events, and
		1263	C<ev_check> watchers will be invoked before any other watchers of the same
		1264	or lower priority within an event loop iteration.
		1265
1097	received events. Callbacks of both watcher types can start and stop as	1266	Callbacks of both watcher types can start and stop as many watchers as
1098	many watchers as they want, and all of them will be taken into account	1267	they want, and all of them will be taken into account (for example, a
1099	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1268	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
1100	C<ev_run> from blocking).	1269	blocking).
1101		1270
1102	=item C<EV_EMBED>	1271	=item C<EV_EMBED>
1103		1272
1104	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1273	The embedded event loop specified in the C<ev_embed> watcher needs attention.
1105		1274
1106	=item C<EV_FORK>	1275	=item C<EV_FORK>
1107		1276
1108	The event loop has been resumed in the child process after fork (see	1277	The event loop has been resumed in the child process after fork (see
1109	C<ev_fork>).	1278	C<ev_fork>).
		1279
		1280	=item C<EV_CLEANUP>
		1281
		1282	The event loop is about to be destroyed (see C<ev_cleanup>).
1110		1283
1111	=item C<EV_ASYNC>	1284	=item C<EV_ASYNC>
1112		1285
1113	The given async watcher has been asynchronously notified (see C<ev_async>).	1286	The given async watcher has been asynchronously notified (see C<ev_async>).
1114		1287
…		…
1136	programs, though, as the fd could already be closed and reused for another	1309	programs, though, as the fd could already be closed and reused for another
1137	thing, so beware.	1310	thing, so beware.
1138		1311
1139	=back	1312	=back
1140		1313
		1314	=head2 GENERIC WATCHER FUNCTIONS
		1315
		1316	=over 4
		1317
		1318	=item C<ev_init> (ev_TYPE *watcher, callback)
		1319
		1320	This macro initialises the generic portion of a watcher. The contents
		1321	of the watcher object can be arbitrary (so C<malloc> will do). Only
		1322	the generic parts of the watcher are initialised, you I<need> to call
		1323	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		1324	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		1325	which rolls both calls into one.
		1326
		1327	You can reinitialise a watcher at any time as long as it has been stopped
		1328	(or never started) and there are no pending events outstanding.
		1329
		1330	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
		1331	int revents)>.
		1332
		1333	Example: Initialise an C<ev_io> watcher in two steps.
		1334
		1335	ev_io w;
		1336	ev_init (&w, my_cb);
		1337	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1338
		1339	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
		1340
		1341	This macro initialises the type-specific parts of a watcher. You need to
		1342	call C<ev_init> at least once before you call this macro, but you can
		1343	call C<ev_TYPE_set> any number of times. You must not, however, call this
		1344	macro on a watcher that is active (it can be pending, however, which is a
		1345	difference to the C<ev_init> macro).
		1346
		1347	Although some watcher types do not have type-specific arguments
		1348	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		1349
		1350	See C<ev_init>, above, for an example.
		1351
		1352	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		1353
		1354	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		1355	calls into a single call. This is the most convenient method to initialise
		1356	a watcher. The same limitations apply, of course.
		1357
		1358	Example: Initialise and set an C<ev_io> watcher in one step.
		1359
		1360	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1361
		1362	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
		1363
		1364	Starts (activates) the given watcher. Only active watchers will receive
		1365	events. If the watcher is already active nothing will happen.
		1366
		1367	Example: Start the C<ev_io> watcher that is being abused as example in this
		1368	whole section.
		1369
		1370	ev_io_start (EV_DEFAULT_UC, &w);
		1371
		1372	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
		1373
		1374	Stops the given watcher if active, and clears the pending status (whether
		1375	the watcher was active or not).
		1376
		1377	It is possible that stopped watchers are pending - for example,
		1378	non-repeating timers are being stopped when they become pending - but
		1379	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
		1380	pending. If you want to free or reuse the memory used by the watcher it is
		1381	therefore a good idea to always call its C<ev_TYPE_stop> function.
		1382
		1383	=item bool ev_is_active (ev_TYPE *watcher)
		1384
		1385	Returns a true value iff the watcher is active (i.e. it has been started
		1386	and not yet been stopped). As long as a watcher is active you must not modify
		1387	it.
		1388
		1389	=item bool ev_is_pending (ev_TYPE *watcher)
		1390
		1391	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		1392	events but its callback has not yet been invoked). As long as a watcher
		1393	is pending (but not active) you must not call an init function on it (but
		1394	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		1395	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1396	it).
		1397
		1398	=item callback ev_cb (ev_TYPE *watcher)
		1399
		1400	Returns the callback currently set on the watcher.
		1401
		1402	=item ev_set_cb (ev_TYPE *watcher, callback)
		1403
		1404	Change the callback. You can change the callback at virtually any time
		1405	(modulo threads).
		1406
		1407	=item ev_set_priority (ev_TYPE *watcher, int priority)
		1408
		1409	=item int ev_priority (ev_TYPE *watcher)
		1410
		1411	Set and query the priority of the watcher. The priority is a small
		1412	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1413	(default: C<-2>). Pending watchers with higher priority will be invoked
		1414	before watchers with lower priority, but priority will not keep watchers
		1415	from being executed (except for C<ev_idle> watchers).
		1416
		1417	If you need to suppress invocation when higher priority events are pending
		1418	you need to look at C<ev_idle> watchers, which provide this functionality.
		1419
		1420	You I<must not> change the priority of a watcher as long as it is active or
		1421	pending.
		1422
		1423	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1424	fine, as long as you do not mind that the priority value you query might
		1425	or might not have been clamped to the valid range.
		1426
		1427	The default priority used by watchers when no priority has been set is
		1428	always C<0>, which is supposed to not be too high and not be too low :).
		1429
		1430	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1431	priorities.
		1432
		1433	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1434
		1435	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1436	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1437	can deal with that fact, as both are simply passed through to the
		1438	callback.
		1439
		1440	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1441
		1442	If the watcher is pending, this function clears its pending status and
		1443	returns its C<revents> bitset (as if its callback was invoked). If the
		1444	watcher isn't pending it does nothing and returns C<0>.
		1445
		1446	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1447	callback to be invoked, which can be accomplished with this function.
		1448
		1449	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1450
		1451	Feeds the given event set into the event loop, as if the specified event
		1452	had happened for the specified watcher (which must be a pointer to an
		1453	initialised but not necessarily started event watcher). Obviously you must
		1454	not free the watcher as long as it has pending events.
		1455
		1456	Stopping the watcher, letting libev invoke it, or calling
		1457	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1458	not started in the first place.
		1459
		1460	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1461	functions that do not need a watcher.
		1462
		1463	=back
		1464
		1465	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
		1466	OWN COMPOSITE WATCHERS> idioms.
		1467
1141	=head2 WATCHER STATES	1468	=head2 WATCHER STATES
1142		1469
1143	There are various watcher states mentioned throughout this manual -	1470	There are various watcher states mentioned throughout this manual -
1144	active, pending and so on. In this section these states and the rules to	1471	active, pending and so on. In this section these states and the rules to
1145	transition between them will be described in more detail - and while these	1472	transition between them will be described in more detail - and while these
1146	rules might look complicated, they usually do "the right thing".	1473	rules might look complicated, they usually do "the right thing".
1147		1474
1148	=over 4	1475	=over 4
1149		1476
1150	=item initialiased	1477	=item initialised
1151		1478
1152	Before a watcher can be registered with the event looop it has to be	1479	Before a watcher can be registered with the event loop it has to be
1153	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to	1480	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
1154	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.	1481	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1155		1482
1156	In this state it is simply some block of memory that is suitable for use	1483	In this state it is simply some block of memory that is suitable for
1157	in an event loop. It can be moved around, freed, reused etc. at will.	1484	use in an event loop. It can be moved around, freed, reused etc. at
		1485	will - as long as you either keep the memory contents intact, or call
		1486	C<ev_TYPE_init> again.
1158		1487
1159	=item started/running/active	1488	=item started/running/active
1160		1489
1161	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes	1490	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
1162	property of the event loop, and is actively waiting for events. While in	1491	property of the event loop, and is actively waiting for events. While in
…		…
1190	latter will clear any pending state the watcher might be in, regardless	1519	latter will clear any pending state the watcher might be in, regardless
1191	of whether it was active or not, so stopping a watcher explicitly before	1520	of whether it was active or not, so stopping a watcher explicitly before
1192	freeing it is often a good idea.	1521	freeing it is often a good idea.
1193		1522
1194	While stopped (and not pending) the watcher is essentially in the	1523	While stopped (and not pending) the watcher is essentially in the
1195	initialised state, that is it can be reused, moved, modified in any way	1524	initialised state, that is, it can be reused, moved, modified in any way
1196	you wish.	1525	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1526	it again).
1197		1527
1198	=back	1528	=back
1199
1200	=head2 GENERIC WATCHER FUNCTIONS
1201
1202	=over 4
1203
1204	=item C<ev_init> (ev_TYPE *watcher, callback)
1205
1206	This macro initialises the generic portion of a watcher. The contents
1207	of the watcher object can be arbitrary (so C<malloc> will do). Only
1208	the generic parts of the watcher are initialised, you I<need> to call
1209	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
1210	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
1211	which rolls both calls into one.
1212
1213	You can reinitialise a watcher at any time as long as it has been stopped
1214	(or never started) and there are no pending events outstanding.
1215
1216	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
1217	int revents)>.
1218
1219	Example: Initialise an C<ev_io> watcher in two steps.
1220
1221	ev_io w;
1222	ev_init (&w, my_cb);
1223	ev_io_set (&w, STDIN_FILENO, EV_READ);
1224
1225	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
1226
1227	This macro initialises the type-specific parts of a watcher. You need to
1228	call C<ev_init> at least once before you call this macro, but you can
1229	call C<ev_TYPE_set> any number of times. You must not, however, call this
1230	macro on a watcher that is active (it can be pending, however, which is a
1231	difference to the C<ev_init> macro).
1232
1233	Although some watcher types do not have type-specific arguments
1234	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
1235
1236	See C<ev_init>, above, for an example.
1237
1238	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
1239
1240	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
1241	calls into a single call. This is the most convenient method to initialise
1242	a watcher. The same limitations apply, of course.
1243
1244	Example: Initialise and set an C<ev_io> watcher in one step.
1245
1246	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1247
1248	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
1249
1250	Starts (activates) the given watcher. Only active watchers will receive
1251	events. If the watcher is already active nothing will happen.
1252
1253	Example: Start the C<ev_io> watcher that is being abused as example in this
1254	whole section.
1255
1256	ev_io_start (EV_DEFAULT_UC, &w);
1257
1258	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
1259
1260	Stops the given watcher if active, and clears the pending status (whether
1261	the watcher was active or not).
1262
1263	It is possible that stopped watchers are pending - for example,
1264	non-repeating timers are being stopped when they become pending - but
1265	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
1266	pending. If you want to free or reuse the memory used by the watcher it is
1267	therefore a good idea to always call its C<ev_TYPE_stop> function.
1268
1269	=item bool ev_is_active (ev_TYPE *watcher)
1270
1271	Returns a true value iff the watcher is active (i.e. it has been started
1272	and not yet been stopped). As long as a watcher is active you must not modify
1273	it.
1274
1275	=item bool ev_is_pending (ev_TYPE *watcher)
1276
1277	Returns a true value iff the watcher is pending, (i.e. it has outstanding
1278	events but its callback has not yet been invoked). As long as a watcher
1279	is pending (but not active) you must not call an init function on it (but
1280	C<ev_TYPE_set> is safe), you must not change its priority, and you must
1281	make sure the watcher is available to libev (e.g. you cannot C<free ()>
1282	it).
1283
1284	=item callback ev_cb (ev_TYPE *watcher)
1285
1286	Returns the callback currently set on the watcher.
1287
1288	=item ev_cb_set (ev_TYPE *watcher, callback)
1289
1290	Change the callback. You can change the callback at virtually any time
1291	(modulo threads).
1292
1293	=item ev_set_priority (ev_TYPE *watcher, int priority)
1294
1295	=item int ev_priority (ev_TYPE *watcher)
1296
1297	Set and query the priority of the watcher. The priority is a small
1298	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
1299	(default: C<-2>). Pending watchers with higher priority will be invoked
1300	before watchers with lower priority, but priority will not keep watchers
1301	from being executed (except for C<ev_idle> watchers).
1302
1303	If you need to suppress invocation when higher priority events are pending
1304	you need to look at C<ev_idle> watchers, which provide this functionality.
1305
1306	You I<must not> change the priority of a watcher as long as it is active or
1307	pending.
1308
1309	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
1310	fine, as long as you do not mind that the priority value you query might
1311	or might not have been clamped to the valid range.
1312
1313	The default priority used by watchers when no priority has been set is
1314	always C<0>, which is supposed to not be too high and not be too low :).
1315
1316	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1317	priorities.
1318
1319	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1320
1321	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
1322	C<loop> nor C<revents> need to be valid as long as the watcher callback
1323	can deal with that fact, as both are simply passed through to the
1324	callback.
1325
1326	=item int ev_clear_pending (loop, ev_TYPE *watcher)
1327
1328	If the watcher is pending, this function clears its pending status and
1329	returns its C<revents> bitset (as if its callback was invoked). If the
1330	watcher isn't pending it does nothing and returns C<0>.
1331
1332	Sometimes it can be useful to "poll" a watcher instead of waiting for its
1333	callback to be invoked, which can be accomplished with this function.
1334
1335	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
1336
1337	Feeds the given event set into the event loop, as if the specified event
1338	had happened for the specified watcher (which must be a pointer to an
1339	initialised but not necessarily started event watcher). Obviously you must
1340	not free the watcher as long as it has pending events.
1341
1342	Stopping the watcher, letting libev invoke it, or calling
1343	C<ev_clear_pending> will clear the pending event, even if the watcher was
1344	not started in the first place.
1345
1346	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1347	functions that do not need a watcher.
1348
1349	=back
1350
1351
1352	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
1353
1354	Each watcher has, by default, a member C<void *data> that you can change
1355	and read at any time: libev will completely ignore it. This can be used
1356	to associate arbitrary data with your watcher. If you need more data and
1357	don't want to allocate memory and store a pointer to it in that data
1358	member, you can also "subclass" the watcher type and provide your own
1359	data:
1360
1361	struct my_io
1362	{
1363	ev_io io;
1364	int otherfd;
1365	void *somedata;
1366	struct whatever *mostinteresting;
1367	};
1368
1369	...
1370	struct my_io w;
1371	ev_io_init (&w.io, my_cb, fd, EV_READ);
1372
1373	And since your callback will be called with a pointer to the watcher, you
1374	can cast it back to your own type:
1375
1376	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1377	{
1378	struct my_io *w = (struct my_io *)w_;
1379	...
1380	}
1381
1382	More interesting and less C-conformant ways of casting your callback type
1383	instead have been omitted.
1384
1385	Another common scenario is to use some data structure with multiple
1386	embedded watchers:
1387
1388	struct my_biggy
1389	{
1390	int some_data;
1391	ev_timer t1;
1392	ev_timer t2;
1393	}
1394
1395	In this case getting the pointer to C<my_biggy> is a bit more
1396	complicated: Either you store the address of your C<my_biggy> struct
1397	in the C<data> member of the watcher (for woozies), or you need to use
1398	some pointer arithmetic using C<offsetof> inside your watchers (for real
1399	programmers):
1400
1401	#include <stddef.h>
1402
1403	static void
1404	t1_cb (EV_P_ ev_timer *w, int revents)
1405	{
1406	struct my_biggy big = (struct my_biggy *)
1407	(((char *)w) - offsetof (struct my_biggy, t1));
1408	}
1409
1410	static void
1411	t2_cb (EV_P_ ev_timer *w, int revents)
1412	{
1413	struct my_biggy big = (struct my_biggy *)
1414	(((char *)w) - offsetof (struct my_biggy, t2));
1415	}
1416		1529
1417	=head2 WATCHER PRIORITY MODELS	1530	=head2 WATCHER PRIORITY MODELS
1418		1531
1419	Many event loops support I<watcher priorities>, which are usually small	1532	Many event loops support I<watcher priorities>, which are usually small
1420	integers that influence the ordering of event callback invocation	1533	integers that influence the ordering of event callback invocation
…		…
1547	In general you can register as many read and/or write event watchers per	1660	In general you can register as many read and/or write event watchers per
1548	fd as you want (as long as you don't confuse yourself). Setting all file	1661	fd as you want (as long as you don't confuse yourself). Setting all file
1549	descriptors to non-blocking mode is also usually a good idea (but not	1662	descriptors to non-blocking mode is also usually a good idea (but not
1550	required if you know what you are doing).	1663	required if you know what you are doing).
1551		1664
1552	If you cannot use non-blocking mode, then force the use of a
1553	known-to-be-good backend (at the time of this writing, this includes only
1554	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
1555	descriptors for which non-blocking operation makes no sense (such as
1556	files) - libev doesn't guarantee any specific behaviour in that case.
1557
1558	Another thing you have to watch out for is that it is quite easy to	1665	Another thing you have to watch out for is that it is quite easy to
1559	receive "spurious" readiness notifications, that is your callback might	1666	receive "spurious" readiness notifications, that is, your callback might
1560	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1667	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1561	because there is no data. Not only are some backends known to create a	1668	because there is no data. It is very easy to get into this situation even
1562	lot of those (for example Solaris ports), it is very easy to get into	1669	with a relatively standard program structure. Thus it is best to always
1563	this situation even with a relatively standard program structure. Thus	1670	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1564	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1565	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1671	preferable to a program hanging until some data arrives.
1566		1672
1567	If you cannot run the fd in non-blocking mode (for example you should	1673	If you cannot run the fd in non-blocking mode (for example you should
1568	not play around with an Xlib connection), then you have to separately	1674	not play around with an Xlib connection), then you have to separately
1569	re-test whether a file descriptor is really ready with a known-to-be good	1675	re-test whether a file descriptor is really ready with a known-to-be good
1570	interface such as poll (fortunately in our Xlib example, Xlib already	1676	interface such as poll (fortunately in the case of Xlib, it already does
1571	does this on its own, so its quite safe to use). Some people additionally	1677	this on its own, so its quite safe to use). Some people additionally
1572	use C<SIGALRM> and an interval timer, just to be sure you won't block	1678	use C<SIGALRM> and an interval timer, just to be sure you won't block
1573	indefinitely.	1679	indefinitely.
1574		1680
1575	But really, best use non-blocking mode.	1681	But really, best use non-blocking mode.
1576		1682
1577	=head3 The special problem of disappearing file descriptors	1683	=head3 The special problem of disappearing file descriptors
1578		1684
1579	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1685	Some backends (e.g. kqueue, epoll, linuxaio) need to be told about closing
1580	descriptor (either due to calling C<close> explicitly or any other means,	1686	a file descriptor (either due to calling C<close> explicitly or any other
1581	such as C<dup2>). The reason is that you register interest in some file	1687	means, such as C<dup2>). The reason is that you register interest in some
1582	descriptor, but when it goes away, the operating system will silently drop	1688	file descriptor, but when it goes away, the operating system will silently
1583	this interest. If another file descriptor with the same number then is	1689	drop this interest. If another file descriptor with the same number then
1584	registered with libev, there is no efficient way to see that this is, in	1690	is registered with libev, there is no efficient way to see that this is,
1585	fact, a different file descriptor.	1691	in fact, a different file descriptor.
1586		1692
1587	To avoid having to explicitly tell libev about such cases, libev follows	1693	To avoid having to explicitly tell libev about such cases, libev follows
1588	the following policy: Each time C<ev_io_set> is being called, libev	1694	the following policy: Each time C<ev_io_set> is being called, libev
1589	will assume that this is potentially a new file descriptor, otherwise	1695	will assume that this is potentially a new file descriptor, otherwise
1590	it is assumed that the file descriptor stays the same. That means that	1696	it is assumed that the file descriptor stays the same. That means that
…		…
1604		1710
1605	There is no workaround possible except not registering events	1711	There is no workaround possible except not registering events
1606	for potentially C<dup ()>'ed file descriptors, or to resort to	1712	for potentially C<dup ()>'ed file descriptors, or to resort to
1607	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1713	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1608		1714
		1715	=head3 The special problem of files
		1716
		1717	Many people try to use C<select> (or libev) on file descriptors
		1718	representing files, and expect it to become ready when their program
		1719	doesn't block on disk accesses (which can take a long time on their own).
		1720
		1721	However, this cannot ever work in the "expected" way - you get a readiness
		1722	notification as soon as the kernel knows whether and how much data is
		1723	there, and in the case of open files, that's always the case, so you
		1724	always get a readiness notification instantly, and your read (or possibly
		1725	write) will still block on the disk I/O.
		1726
		1727	Another way to view it is that in the case of sockets, pipes, character
		1728	devices and so on, there is another party (the sender) that delivers data
		1729	on its own, but in the case of files, there is no such thing: the disk
		1730	will not send data on its own, simply because it doesn't know what you
		1731	wish to read - you would first have to request some data.
		1732
		1733	Since files are typically not-so-well supported by advanced notification
		1734	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1735	to files, even though you should not use it. The reason for this is
		1736	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1737	usually a tty, often a pipe, but also sometimes files or special devices
		1738	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1739	F</dev/urandom>), and even though the file might better be served with
		1740	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1741	it "just works" instead of freezing.
		1742
		1743	So avoid file descriptors pointing to files when you know it (e.g. use
		1744	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1745	when you rarely read from a file instead of from a socket, and want to
		1746	reuse the same code path.
		1747
1609	=head3 The special problem of fork	1748	=head3 The special problem of fork
1610		1749
1611	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1750	Some backends (epoll, kqueue, probably linuxaio) do not support C<fork ()>
1612	useless behaviour. Libev fully supports fork, but needs to be told about	1751	at all or exhibit useless behaviour. Libev fully supports fork, but needs
1613	it in the child.	1752	to be told about it in the child if you want to continue to use it in the
		1753	child.
1614		1754
1615	To support fork in your programs, you either have to call	1755	To support fork in your child processes, you have to call C<ev_loop_fork
1616	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1756	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1617	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1757	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1618	C<EVBACKEND_POLL>.
1619		1758
1620	=head3 The special problem of SIGPIPE	1759	=head3 The special problem of SIGPIPE
1621		1760
1622	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1761	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1623	when writing to a pipe whose other end has been closed, your program gets	1762	when writing to a pipe whose other end has been closed, your program gets
…		…
1721	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1860	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1722	monotonic clock option helps a lot here).	1861	monotonic clock option helps a lot here).
1723		1862
1724	The callback is guaranteed to be invoked only I<after> its timeout has	1863	The callback is guaranteed to be invoked only I<after> its timeout has
1725	passed (not I<at>, so on systems with very low-resolution clocks this	1864	passed (not I<at>, so on systems with very low-resolution clocks this
1726	might introduce a small delay). If multiple timers become ready during the	1865	might introduce a small delay, see "the special problem of being too
		1866	early", below). If multiple timers become ready during the same loop
1727	same loop iteration then the ones with earlier time-out values are invoked	1867	iteration then the ones with earlier time-out values are invoked before
1728	before ones of the same priority with later time-out values (but this is	1868	ones of the same priority with later time-out values (but this is no
1729	no longer true when a callback calls C<ev_run> recursively).	1869	longer true when a callback calls C<ev_run> recursively).
1730		1870
1731	=head3 Be smart about timeouts	1871	=head3 Be smart about timeouts
1732		1872
1733	Many real-world problems involve some kind of timeout, usually for error	1873	Many real-world problems involve some kind of timeout, usually for error
1734	recovery. A typical example is an HTTP request - if the other side hangs,	1874	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1809		1949
1810	In this case, it would be more efficient to leave the C<ev_timer> alone,	1950	In this case, it would be more efficient to leave the C<ev_timer> alone,
1811	but remember the time of last activity, and check for a real timeout only	1951	but remember the time of last activity, and check for a real timeout only
1812	within the callback:	1952	within the callback:
1813		1953
		1954	ev_tstamp timeout = 60.;
1814	ev_tstamp last_activity; // time of last activity	1955	ev_tstamp last_activity; // time of last activity
		1956	ev_timer timer;
1815		1957
1816	static void	1958	static void
1817	callback (EV_P_ ev_timer *w, int revents)	1959	callback (EV_P_ ev_timer *w, int revents)
1818	{	1960	{
1819	ev_tstamp now = ev_now (EV_A);	1961	// calculate when the timeout would happen
1820	ev_tstamp timeout = last_activity + 60.;	1962	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
1821		1963
1822	// if last_activity + 60. is older than now, we did time out	1964	// if negative, it means we the timeout already occurred
1823	if (timeout < now)	1965	if (after < 0.)
1824	{	1966	{
1825	// timeout occurred, take action	1967	// timeout occurred, take action
1826	}	1968	}
1827	else	1969	else
1828	{	1970	{
1829	// callback was invoked, but there was some activity, re-arm	1971	// callback was invoked, but there was some recent
1830	// the watcher to fire in last_activity + 60, which is	1972	// activity. simply restart the timer to time out
1831	// guaranteed to be in the future, so "again" is positive:	1973	// after "after" seconds, which is the earliest time
1832	w->repeat = timeout - now;	1974	// the timeout can occur.
		1975	ev_timer_set (w, after, 0.);
1833	ev_timer_again (EV_A_ w);	1976	ev_timer_start (EV_A_ w);
1834	}	1977	}
1835	}	1978	}
1836		1979
1837	To summarise the callback: first calculate the real timeout (defined	1980	To summarise the callback: first calculate in how many seconds the
1838	as "60 seconds after the last activity"), then check if that time has	1981	timeout will occur (by calculating the absolute time when it would occur,
1839	been reached, which means something I<did>, in fact, time out. Otherwise	1982	C<last_activity + timeout>, and subtracting the current time, C<ev_now
1840	the callback was invoked too early (C<timeout> is in the future), so	1983	(EV_A)> from that).
1841	re-schedule the timer to fire at that future time, to see if maybe we have
1842	a timeout then.
1843		1984
1844	Note how C<ev_timer_again> is used, taking advantage of the	1985	If this value is negative, then we are already past the timeout, i.e. we
1845	C<ev_timer_again> optimisation when the timer is already running.	1986	timed out, and need to do whatever is needed in this case.
		1987
		1988	Otherwise, we now the earliest time at which the timeout would trigger,
		1989	and simply start the timer with this timeout value.
		1990
		1991	In other words, each time the callback is invoked it will check whether
		1992	the timeout occurred. If not, it will simply reschedule itself to check
		1993	again at the earliest time it could time out. Rinse. Repeat.
1846		1994
1847	This scheme causes more callback invocations (about one every 60 seconds	1995	This scheme causes more callback invocations (about one every 60 seconds
1848	minus half the average time between activity), but virtually no calls to	1996	minus half the average time between activity), but virtually no calls to
1849	libev to change the timeout.	1997	libev to change the timeout.
1850		1998
1851	To start the timer, simply initialise the watcher and set C<last_activity>	1999	To start the machinery, simply initialise the watcher and set
1852	to the current time (meaning we just have some activity :), then call the	2000	C<last_activity> to the current time (meaning there was some activity just
1853	callback, which will "do the right thing" and start the timer:	2001	now), then call the callback, which will "do the right thing" and start
		2002	the timer:
1854		2003
		2004	last_activity = ev_now (EV_A);
1855	ev_init (timer, callback);	2005	ev_init (&timer, callback);
1856	last_activity = ev_now (loop);	2006	callback (EV_A_ &timer, 0);
1857	callback (loop, timer, EV_TIMER);
1858		2007
1859	And when there is some activity, simply store the current time in	2008	When there is some activity, simply store the current time in
1860	C<last_activity>, no libev calls at all:	2009	C<last_activity>, no libev calls at all:
1861		2010
		2011	if (activity detected)
1862	last_activity = ev_now (loop);	2012	last_activity = ev_now (EV_A);
		2013
		2014	When your timeout value changes, then the timeout can be changed by simply
		2015	providing a new value, stopping the timer and calling the callback, which
		2016	will again do the right thing (for example, time out immediately :).
		2017
		2018	timeout = new_value;
		2019	ev_timer_stop (EV_A_ &timer);
		2020	callback (EV_A_ &timer, 0);
1863		2021
1864	This technique is slightly more complex, but in most cases where the	2022	This technique is slightly more complex, but in most cases where the
1865	time-out is unlikely to be triggered, much more efficient.	2023	time-out is unlikely to be triggered, much more efficient.
1866
1867	Changing the timeout is trivial as well (if it isn't hard-coded in the
1868	callback :) - just change the timeout and invoke the callback, which will
1869	fix things for you.
1870		2024
1871	=item 4. Wee, just use a double-linked list for your timeouts.	2025	=item 4. Wee, just use a double-linked list for your timeouts.
1872		2026
1873	If there is not one request, but many thousands (millions...), all	2027	If there is not one request, but many thousands (millions...), all
1874	employing some kind of timeout with the same timeout value, then one can	2028	employing some kind of timeout with the same timeout value, then one can
…		…
1901	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is	2055	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
1902	rather complicated, but extremely efficient, something that really pays	2056	rather complicated, but extremely efficient, something that really pays
1903	off after the first million or so of active timers, i.e. it's usually	2057	off after the first million or so of active timers, i.e. it's usually
1904	overkill :)	2058	overkill :)
1905		2059
		2060	=head3 The special problem of being too early
		2061
		2062	If you ask a timer to call your callback after three seconds, then
		2063	you expect it to be invoked after three seconds - but of course, this
		2064	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		2065	guaranteed to any precision by libev - imagine somebody suspending the
		2066	process with a STOP signal for a few hours for example.
		2067
		2068	So, libev tries to invoke your callback as soon as possible I<after> the
		2069	delay has occurred, but cannot guarantee this.
		2070
		2071	A less obvious failure mode is calling your callback too early: many event
		2072	loops compare timestamps with a "elapsed delay >= requested delay", but
		2073	this can cause your callback to be invoked much earlier than you would
		2074	expect.
		2075
		2076	To see why, imagine a system with a clock that only offers full second
		2077	resolution (think windows if you can't come up with a broken enough OS
		2078	yourself). If you schedule a one-second timer at the time 500.9, then the
		2079	event loop will schedule your timeout to elapse at a system time of 500
		2080	(500.9 truncated to the resolution) + 1, or 501.
		2081
		2082	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2083	501" and invoke the callback 0.1s after it was started, even though a
		2084	one-second delay was requested - this is being "too early", despite best
		2085	intentions.
		2086
		2087	This is the reason why libev will never invoke the callback if the elapsed
		2088	delay equals the requested delay, but only when the elapsed delay is
		2089	larger than the requested delay. In the example above, libev would only invoke
		2090	the callback at system time 502, or 1.1s after the timer was started.
		2091
		2092	So, while libev cannot guarantee that your callback will be invoked
		2093	exactly when requested, it I<can> and I<does> guarantee that the requested
		2094	delay has actually elapsed, or in other words, it always errs on the "too
		2095	late" side of things.
		2096
1906	=head3 The special problem of time updates	2097	=head3 The special problem of time updates
1907		2098
1908	Establishing the current time is a costly operation (it usually takes at	2099	Establishing the current time is a costly operation (it usually takes
1909	least two system calls): EV therefore updates its idea of the current	2100	at least one system call): EV therefore updates its idea of the current
1910	time only before and after C<ev_run> collects new events, which causes a	2101	time only before and after C<ev_run> collects new events, which causes a
1911	growing difference between C<ev_now ()> and C<ev_time ()> when handling	2102	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1912	lots of events in one iteration.	2103	lots of events in one iteration.
1913		2104
1914	The relative timeouts are calculated relative to the C<ev_now ()>	2105	The relative timeouts are calculated relative to the C<ev_now ()>
1915	time. This is usually the right thing as this timestamp refers to the time	2106	time. This is usually the right thing as this timestamp refers to the time
1916	of the event triggering whatever timeout you are modifying/starting. If	2107	of the event triggering whatever timeout you are modifying/starting. If
1917	you suspect event processing to be delayed and you I<need> to base the	2108	you suspect event processing to be delayed and you I<need> to base the
1918	timeout on the current time, use something like this to adjust for this:	2109	timeout on the current time, use something like the following to adjust
		2110	for it:
1919		2111
1920	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2112	ev_timer_set (&timer, after + (ev_time () - ev_now ()), 0.);
1921		2113
1922	If the event loop is suspended for a long time, you can also force an	2114	If the event loop is suspended for a long time, you can also force an
1923	update of the time returned by C<ev_now ()> by calling C<ev_now_update	2115	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1924	()>.	2116	()>, although that will push the event time of all outstanding events
		2117	further into the future.
		2118
		2119	=head3 The special problem of unsynchronised clocks
		2120
		2121	Modern systems have a variety of clocks - libev itself uses the normal
		2122	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2123	jumps).
		2124
		2125	Neither of these clocks is synchronised with each other or any other clock
		2126	on the system, so C<ev_time ()> might return a considerably different time
		2127	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2128	a call to C<gettimeofday> might return a second count that is one higher
		2129	than a directly following call to C<time>.
		2130
		2131	The moral of this is to only compare libev-related timestamps with
		2132	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2133	a second or so.
		2134
		2135	One more problem arises due to this lack of synchronisation: if libev uses
		2136	the system monotonic clock and you compare timestamps from C<ev_time>
		2137	or C<ev_now> from when you started your timer and when your callback is
		2138	invoked, you will find that sometimes the callback is a bit "early".
		2139
		2140	This is because C<ev_timer>s work in real time, not wall clock time, so
		2141	libev makes sure your callback is not invoked before the delay happened,
		2142	I<measured according to the real time>, not the system clock.
		2143
		2144	If your timeouts are based on a physical timescale (e.g. "time out this
		2145	connection after 100 seconds") then this shouldn't bother you as it is
		2146	exactly the right behaviour.
		2147
		2148	If you want to compare wall clock/system timestamps to your timers, then
		2149	you need to use C<ev_periodic>s, as these are based on the wall clock
		2150	time, where your comparisons will always generate correct results.
1925		2151
1926	=head3 The special problems of suspended animation	2152	=head3 The special problems of suspended animation
1927		2153
1928	When you leave the server world it is quite customary to hit machines that	2154	When you leave the server world it is quite customary to hit machines that
1929	can suspend/hibernate - what happens to the clocks during such a suspend?	2155	can suspend/hibernate - what happens to the clocks during such a suspend?
…		…
1959		2185
1960	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2186	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1961		2187
1962	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2188	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1963		2189
1964	Configure the timer to trigger after C<after> seconds. If C<repeat>	2190	Configure the timer to trigger after C<after> seconds (fractional and
1965	is C<0.>, then it will automatically be stopped once the timeout is	2191	negative values are supported). If C<repeat> is C<0.>, then it will
1966	reached. If it is positive, then the timer will automatically be	2192	automatically be stopped once the timeout is reached. If it is positive,
1967	configured to trigger again C<repeat> seconds later, again, and again,	2193	then the timer will automatically be configured to trigger again C<repeat>
1968	until stopped manually.	2194	seconds later, again, and again, until stopped manually.
1969		2195
1970	The timer itself will do a best-effort at avoiding drift, that is, if	2196	The timer itself will do a best-effort at avoiding drift, that is, if
1971	you configure a timer to trigger every 10 seconds, then it will normally	2197	you configure a timer to trigger every 10 seconds, then it will normally
1972	trigger at exactly 10 second intervals. If, however, your program cannot	2198	trigger at exactly 10 second intervals. If, however, your program cannot
1973	keep up with the timer (because it takes longer than those 10 seconds to	2199	keep up with the timer (because it takes longer than those 10 seconds to
1974	do stuff) the timer will not fire more than once per event loop iteration.	2200	do stuff) the timer will not fire more than once per event loop iteration.
1975		2201
1976	=item ev_timer_again (loop, ev_timer *)	2202	=item ev_timer_again (loop, ev_timer *)
1977		2203
1978	This will act as if the timer timed out and restart it again if it is	2204	This will act as if the timer timed out, and restarts it again if it is
1979	repeating. The exact semantics are:	2205	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2206	timeout to the C<repeat> value and calling C<ev_timer_start>.
1980		2207
		2208	The exact semantics are as in the following rules, all of which will be
		2209	applied to the watcher:
		2210
		2211	=over 4
		2212
1981	If the timer is pending, its pending status is cleared.	2213	=item If the timer is pending, the pending status is always cleared.
1982		2214
1983	If the timer is started but non-repeating, stop it (as if it timed out).	2215	=item If the timer is started but non-repeating, stop it (as if it timed
		2216	out, without invoking it).
1984		2217
1985	If the timer is repeating, either start it if necessary (with the	2218	=item If the timer is repeating, make the C<repeat> value the new timeout
1986	C<repeat> value), or reset the running timer to the C<repeat> value.	2219	and start the timer, if necessary.
1987		2220
		2221	=back
		2222
1988	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a	2223	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
1989	usage example.	2224	usage example.
1990		2225
1991	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)	2226	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1992		2227
1993	Returns the remaining time until a timer fires. If the timer is active,	2228	Returns the remaining time until a timer fires. If the timer is active,
…		…
2046	Periodic watchers are also timers of a kind, but they are very versatile	2281	Periodic watchers are also timers of a kind, but they are very versatile
2047	(and unfortunately a bit complex).	2282	(and unfortunately a bit complex).
2048		2283
2049	Unlike C<ev_timer>, periodic watchers are not based on real time (or	2284	Unlike C<ev_timer>, periodic watchers are not based on real time (or
2050	relative time, the physical time that passes) but on wall clock time	2285	relative time, the physical time that passes) but on wall clock time
2051	(absolute time, the thing you can read on your calender or clock). The	2286	(absolute time, the thing you can read on your calendar or clock). The
2052	difference is that wall clock time can run faster or slower than real	2287	difference is that wall clock time can run faster or slower than real
2053	time, and time jumps are not uncommon (e.g. when you adjust your	2288	time, and time jumps are not uncommon (e.g. when you adjust your
2054	wrist-watch).	2289	wrist-watch).
2055		2290
2056	You can tell a periodic watcher to trigger after some specific point	2291	You can tell a periodic watcher to trigger after some specific point
…		…
2061	C<ev_timer>, which would still trigger roughly 10 seconds after starting	2296	C<ev_timer>, which would still trigger roughly 10 seconds after starting
2062	it, as it uses a relative timeout).	2297	it, as it uses a relative timeout).
2063		2298
2064	C<ev_periodic> watchers can also be used to implement vastly more complex	2299	C<ev_periodic> watchers can also be used to implement vastly more complex
2065	timers, such as triggering an event on each "midnight, local time", or	2300	timers, such as triggering an event on each "midnight, local time", or
2066	other complicated rules. This cannot be done with C<ev_timer> watchers, as	2301	other complicated rules. This cannot easily be done with C<ev_timer>
2067	those cannot react to time jumps.	2302	watchers, as those cannot react to time jumps.
2068		2303
2069	As with timers, the callback is guaranteed to be invoked only when the	2304	As with timers, the callback is guaranteed to be invoked only when the
2070	point in time where it is supposed to trigger has passed. If multiple	2305	point in time where it is supposed to trigger has passed. If multiple
2071	timers become ready during the same loop iteration then the ones with	2306	timers become ready during the same loop iteration then the ones with
2072	earlier time-out values are invoked before ones with later time-out values	2307	earlier time-out values are invoked before ones with later time-out values
…		…
2113		2348
2114	Another way to think about it (for the mathematically inclined) is that	2349	Another way to think about it (for the mathematically inclined) is that
2115	C<ev_periodic> will try to run the callback in this mode at the next possible	2350	C<ev_periodic> will try to run the callback in this mode at the next possible
2116	time where C<time = offset (mod interval)>, regardless of any time jumps.	2351	time where C<time = offset (mod interval)>, regardless of any time jumps.
2117		2352
2118	For numerical stability it is preferable that the C<offset> value is near	2353	The C<interval> I<MUST> be positive, and for numerical stability, the
2119	C<ev_now ()> (the current time), but there is no range requirement for	2354	interval value should be higher than C<1/8192> (which is around 100
2120	this value, and in fact is often specified as zero.	2355	microseconds) and C<offset> should be higher than C<0> and should have
		2356	at most a similar magnitude as the current time (say, within a factor of
		2357	ten). Typical values for offset are, in fact, C<0> or something between
		2358	C<0> and C<interval>, which is also the recommended range.
2121		2359
2122	Note also that there is an upper limit to how often a timer can fire (CPU	2360	Note also that there is an upper limit to how often a timer can fire (CPU
2123	speed for example), so if C<interval> is very small then timing stability	2361	speed for example), so if C<interval> is very small then timing stability
2124	will of course deteriorate. Libev itself tries to be exact to be about one	2362	will of course deteriorate. Libev itself tries to be exact to be about one
2125	millisecond (if the OS supports it and the machine is fast enough).	2363	millisecond (if the OS supports it and the machine is fast enough).
…		…
2155		2393
2156	NOTE: I<< This callback must always return a time that is higher than or	2394	NOTE: I<< This callback must always return a time that is higher than or
2157	equal to the passed C<now> value >>.	2395	equal to the passed C<now> value >>.
2158		2396
2159	This can be used to create very complex timers, such as a timer that	2397	This can be used to create very complex timers, such as a timer that
2160	triggers on "next midnight, local time". To do this, you would calculate the	2398	triggers on "next midnight, local time". To do this, you would calculate
2161	next midnight after C<now> and return the timestamp value for this. How	2399	the next midnight after C<now> and return the timestamp value for
2162	you do this is, again, up to you (but it is not trivial, which is the main	2400	this. Here is a (completely untested, no error checking) example on how to
2163	reason I omitted it as an example).	2401	do this:
		2402
		2403	#include <time.h>
		2404
		2405	static ev_tstamp
		2406	my_rescheduler (ev_periodic *w, ev_tstamp now)
		2407	{
		2408	time_t tnow = (time_t)now;
		2409	struct tm tm;
		2410	localtime_r (&tnow, &tm);
		2411
		2412	tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
		2413	++tm.tm_mday; // midnight next day
		2414
		2415	return mktime (&tm);
		2416	}
		2417
		2418	Note: this code might run into trouble on days that have more then two
		2419	midnights (beginning and end).
2164		2420
2165	=back	2421	=back
2166		2422
2167	=item ev_periodic_again (loop, ev_periodic *)	2423	=item ev_periodic_again (loop, ev_periodic *)
2168		2424
…		…
2233		2489
2234	ev_periodic hourly_tick;	2490	ev_periodic hourly_tick;
2235	ev_periodic_init (&hourly_tick, clock_cb,	2491	ev_periodic_init (&hourly_tick, clock_cb,
2236	fmod (ev_now (loop), 3600.), 3600., 0);	2492	fmod (ev_now (loop), 3600.), 3600., 0);
2237	ev_periodic_start (loop, &hourly_tick);	2493	ev_periodic_start (loop, &hourly_tick);
2238		2494
2239		2495
2240	=head2 C<ev_signal> - signal me when a signal gets signalled!	2496	=head2 C<ev_signal> - signal me when a signal gets signalled!
2241		2497
2242	Signal watchers will trigger an event when the process receives a specific	2498	Signal watchers will trigger an event when the process receives a specific
2243	signal one or more times. Even though signals are very asynchronous, libev	2499	signal one or more times. Even though signals are very asynchronous, libev
2244	will try it's best to deliver signals synchronously, i.e. as part of the	2500	will try its best to deliver signals synchronously, i.e. as part of the
2245	normal event processing, like any other event.	2501	normal event processing, like any other event.
2246		2502
2247	If you want signals to be delivered truly asynchronously, just use	2503	If you want signals to be delivered truly asynchronously, just use
2248	C<sigaction> as you would do without libev and forget about sharing	2504	C<sigaction> as you would do without libev and forget about sharing
2249	the signal. You can even use C<ev_async> from a signal handler to	2505	the signal. You can even use C<ev_async> from a signal handler to
…		…
2253	only within the same loop, i.e. you can watch for C<SIGINT> in your	2509	only within the same loop, i.e. you can watch for C<SIGINT> in your
2254	default loop and for C<SIGIO> in another loop, but you cannot watch for	2510	default loop and for C<SIGIO> in another loop, but you cannot watch for
2255	C<SIGINT> in both the default loop and another loop at the same time. At	2511	C<SIGINT> in both the default loop and another loop at the same time. At
2256	the moment, C<SIGCHLD> is permanently tied to the default loop.	2512	the moment, C<SIGCHLD> is permanently tied to the default loop.
2257		2513
2258	When the first watcher gets started will libev actually register something	2514	Only after the first watcher for a signal is started will libev actually
2259	with the kernel (thus it coexists with your own signal handlers as long as	2515	register something with the kernel. It thus coexists with your own signal
2260	you don't register any with libev for the same signal).	2516	handlers as long as you don't register any with libev for the same signal.
2261		2517
2262	If possible and supported, libev will install its handlers with	2518	If possible and supported, libev will install its handlers with
2263	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should	2519	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
2264	not be unduly interrupted. If you have a problem with system calls getting	2520	not be unduly interrupted. If you have a problem with system calls getting
2265	interrupted by signals you can block all signals in an C<ev_check> watcher	2521	interrupted by signals you can block all signals in an C<ev_check> watcher
…		…
2268	=head3 The special problem of inheritance over fork/execve/pthread_create	2524	=head3 The special problem of inheritance over fork/execve/pthread_create
2269		2525
2270	Both the signal mask (C<sigprocmask>) and the signal disposition	2526	Both the signal mask (C<sigprocmask>) and the signal disposition
2271	(C<sigaction>) are unspecified after starting a signal watcher (and after	2527	(C<sigaction>) are unspecified after starting a signal watcher (and after
2272	stopping it again), that is, libev might or might not block the signal,	2528	stopping it again), that is, libev might or might not block the signal,
2273	and might or might not set or restore the installed signal handler.	2529	and might or might not set or restore the installed signal handler (but
		2530	see C<EVFLAG_NOSIGMASK>).
2274		2531
2275	While this does not matter for the signal disposition (libev never	2532	While this does not matter for the signal disposition (libev never
2276	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on	2533	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
2277	C<execve>), this matters for the signal mask: many programs do not expect	2534	C<execve>), this matters for the signal mask: many programs do not expect
2278	certain signals to be blocked.	2535	certain signals to be blocked.
…		…
2291	I<has> to modify the signal mask, at least temporarily.	2548	I<has> to modify the signal mask, at least temporarily.
2292		2549
2293	So I can't stress this enough: I<If you do not reset your signal mask when	2550	So I can't stress this enough: I<If you do not reset your signal mask when
2294	you expect it to be empty, you have a race condition in your code>. This	2551	you expect it to be empty, you have a race condition in your code>. This
2295	is not a libev-specific thing, this is true for most event libraries.	2552	is not a libev-specific thing, this is true for most event libraries.
		2553
		2554	=head3 The special problem of threads signal handling
		2555
		2556	POSIX threads has problematic signal handling semantics, specifically,
		2557	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2558	threads in a process block signals, which is hard to achieve.
		2559
		2560	When you want to use sigwait (or mix libev signal handling with your own
		2561	for the same signals), you can tackle this problem by globally blocking
		2562	all signals before creating any threads (or creating them with a fully set
		2563	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2564	loops. Then designate one thread as "signal receiver thread" which handles
		2565	these signals. You can pass on any signals that libev might be interested
		2566	in by calling C<ev_feed_signal>.
2296		2567
2297	=head3 Watcher-Specific Functions and Data Members	2568	=head3 Watcher-Specific Functions and Data Members
2298		2569
2299	=over 4	2570	=over 4
2300		2571
…		…
2435		2706
2436	=head2 C<ev_stat> - did the file attributes just change?	2707	=head2 C<ev_stat> - did the file attributes just change?
2437		2708
2438	This watches a file system path for attribute changes. That is, it calls	2709	This watches a file system path for attribute changes. That is, it calls
2439	C<stat> on that path in regular intervals (or when the OS says it changed)	2710	C<stat> on that path in regular intervals (or when the OS says it changed)
2440	and sees if it changed compared to the last time, invoking the callback if	2711	and sees if it changed compared to the last time, invoking the callback
2441	it did.	2712	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2713	happen after the watcher has been started will be reported.
2442		2714
2443	The path does not need to exist: changing from "path exists" to "path does	2715	The path does not need to exist: changing from "path exists" to "path does
2444	not exist" is a status change like any other. The condition "path does not	2716	not exist" is a status change like any other. The condition "path does not
2445	exist" (or more correctly "path cannot be stat'ed") is signified by the	2717	exist" (or more correctly "path cannot be stat'ed") is signified by the
2446	C<st_nlink> field being zero (which is otherwise always forced to be at	2718	C<st_nlink> field being zero (which is otherwise always forced to be at
…		…
2676	Apart from keeping your process non-blocking (which is a useful	2948	Apart from keeping your process non-blocking (which is a useful
2677	effect on its own sometimes), idle watchers are a good place to do	2949	effect on its own sometimes), idle watchers are a good place to do
2678	"pseudo-background processing", or delay processing stuff to after the	2950	"pseudo-background processing", or delay processing stuff to after the
2679	event loop has handled all outstanding events.	2951	event loop has handled all outstanding events.
2680		2952
		2953	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2954
		2955	As long as there is at least one active idle watcher, libev will never
		2956	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2957	For this to work, the idle watcher doesn't need to be invoked at all - the
		2958	lowest priority will do.
		2959
		2960	This mode of operation can be useful together with an C<ev_check> watcher,
		2961	to do something on each event loop iteration - for example to balance load
		2962	between different connections.
		2963
		2964	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2965	example.
		2966
2681	=head3 Watcher-Specific Functions and Data Members	2967	=head3 Watcher-Specific Functions and Data Members
2682		2968
2683	=over 4	2969	=over 4
2684		2970
2685	=item ev_idle_init (ev_idle *, callback)	2971	=item ev_idle_init (ev_idle *, callback)
…		…
2696	callback, free it. Also, use no error checking, as usual.	2982	callback, free it. Also, use no error checking, as usual.
2697		2983
2698	static void	2984	static void
2699	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)	2985	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2700	{	2986	{
		2987	// stop the watcher
		2988	ev_idle_stop (loop, w);
		2989
		2990	// now we can free it
2701	free (w);	2991	free (w);
		2992
2702	// now do something you wanted to do when the program has	2993	// now do something you wanted to do when the program has
2703	// no longer anything immediate to do.	2994	// no longer anything immediate to do.
2704	}	2995	}
2705		2996
2706	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	2997	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
…		…
2708	ev_idle_start (loop, idle_watcher);	2999	ev_idle_start (loop, idle_watcher);
2709		3000
2710		3001
2711	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	3002	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2712		3003
2713	Prepare and check watchers are usually (but not always) used in pairs:	3004	Prepare and check watchers are often (but not always) used in pairs:
2714	prepare watchers get invoked before the process blocks and check watchers	3005	prepare watchers get invoked before the process blocks and check watchers
2715	afterwards.	3006	afterwards.
2716		3007
2717	You I<must not> call C<ev_run> or similar functions that enter	3008	You I<must not> call C<ev_run> (or similar functions that enter the
2718	the current event loop from either C<ev_prepare> or C<ev_check>	3009	current event loop) or C<ev_loop_fork> from either C<ev_prepare> or
2719	watchers. Other loops than the current one are fine, however. The	3010	C<ev_check> watchers. Other loops than the current one are fine,
2720	rationale behind this is that you do not need to check for recursion in	3011	however. The rationale behind this is that you do not need to check
2721	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	3012	for recursion in those watchers, i.e. the sequence will always be
2722	C<ev_check> so if you have one watcher of each kind they will always be	3013	C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
2723	called in pairs bracketing the blocking call.	3014	kind they will always be called in pairs bracketing the blocking call.
2724		3015
2725	Their main purpose is to integrate other event mechanisms into libev and	3016	Their main purpose is to integrate other event mechanisms into libev and
2726	their use is somewhat advanced. They could be used, for example, to track	3017	their use is somewhat advanced. They could be used, for example, to track
2727	variable changes, implement your own watchers, integrate net-snmp or a	3018	variable changes, implement your own watchers, integrate net-snmp or a
2728	coroutine library and lots more. They are also occasionally useful if	3019	coroutine library and lots more. They are also occasionally useful if
…		…
2746	with priority higher than or equal to the event loop and one coroutine	3037	with priority higher than or equal to the event loop and one coroutine
2747	of lower priority, but only once, using idle watchers to keep the event	3038	of lower priority, but only once, using idle watchers to keep the event
2748	loop from blocking if lower-priority coroutines are active, thus mapping	3039	loop from blocking if lower-priority coroutines are active, thus mapping
2749	low-priority coroutines to idle/background tasks).	3040	low-priority coroutines to idle/background tasks).
2750		3041
2751	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	3042	When used for this purpose, it is recommended to give C<ev_check> watchers
2752	priority, to ensure that they are being run before any other watchers	3043	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
2753	after the poll (this doesn't matter for C<ev_prepare> watchers).	3044	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		3045	watchers).
2754		3046
2755	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not	3047	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
2756	activate ("feed") events into libev. While libev fully supports this, they	3048	activate ("feed") events into libev. While libev fully supports this, they
2757	might get executed before other C<ev_check> watchers did their job. As	3049	might get executed before other C<ev_check> watchers did their job. As
2758	C<ev_check> watchers are often used to embed other (non-libev) event	3050	C<ev_check> watchers are often used to embed other (non-libev) event
2759	loops those other event loops might be in an unusable state until their	3051	loops those other event loops might be in an unusable state until their
2760	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	3052	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
2761	others).	3053	others).
		3054
		3055	=head3 Abusing an C<ev_check> watcher for its side-effect
		3056
		3057	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		3058	useful because they are called once per event loop iteration. For
		3059	example, if you want to handle a large number of connections fairly, you
		3060	normally only do a bit of work for each active connection, and if there
		3061	is more work to do, you wait for the next event loop iteration, so other
		3062	connections have a chance of making progress.
		3063
		3064	Using an C<ev_check> watcher is almost enough: it will be called on the
		3065	next event loop iteration. However, that isn't as soon as possible -
		3066	without external events, your C<ev_check> watcher will not be invoked.
		3067
		3068	This is where C<ev_idle> watchers come in handy - all you need is a
		3069	single global idle watcher that is active as long as you have one active
		3070	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		3071	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		3072	invoked. Neither watcher alone can do that.
2762		3073
2763	=head3 Watcher-Specific Functions and Data Members	3074	=head3 Watcher-Specific Functions and Data Members
2764		3075
2765	=over 4	3076	=over 4
2766		3077
…		…
2967		3278
2968	=over 4	3279	=over 4
2969		3280
2970	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3281	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
2971		3282
2972	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3283	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
2973		3284
2974	Configures the watcher to embed the given loop, which must be	3285	Configures the watcher to embed the given loop, which must be
2975	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3286	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
2976	invoked automatically, otherwise it is the responsibility of the callback	3287	invoked automatically, otherwise it is the responsibility of the callback
2977	to invoke it (it will continue to be called until the sweep has been done,	3288	to invoke it (it will continue to be called until the sweep has been done,
…		…
2998	used).	3309	used).
2999		3310
3000	struct ev_loop *loop_hi = ev_default_init (0);	3311	struct ev_loop *loop_hi = ev_default_init (0);
3001	struct ev_loop *loop_lo = 0;	3312	struct ev_loop *loop_lo = 0;
3002	ev_embed embed;	3313	ev_embed embed;
3003		3314
3004	// see if there is a chance of getting one that works	3315	// see if there is a chance of getting one that works
3005	// (remember that a flags value of 0 means autodetection)	3316	// (remember that a flags value of 0 means autodetection)
3006	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3317	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3007	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3318	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3008	: 0;	3319	: 0;
…		…
3022	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3333	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
3023		3334
3024	struct ev_loop *loop = ev_default_init (0);	3335	struct ev_loop *loop = ev_default_init (0);
3025	struct ev_loop *loop_socket = 0;	3336	struct ev_loop *loop_socket = 0;
3026	ev_embed embed;	3337	ev_embed embed;
3027		3338
3028	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3339	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3029	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3340	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3030	{	3341	{
3031	ev_embed_init (&embed, 0, loop_socket);	3342	ev_embed_init (&embed, 0, loop_socket);
3032	ev_embed_start (loop, &embed);	3343	ev_embed_start (loop, &embed);
…		…
3040		3351
3041	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3352	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
3042		3353
3043	Fork watchers are called when a C<fork ()> was detected (usually because	3354	Fork watchers are called when a C<fork ()> was detected (usually because
3044	whoever is a good citizen cared to tell libev about it by calling	3355	whoever is a good citizen cared to tell libev about it by calling
3045	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the	3356	C<ev_loop_fork>). The invocation is done before the event loop blocks next
3046	event loop blocks next and before C<ev_check> watchers are being called,	3357	and before C<ev_check> watchers are being called, and only in the child
3047	and only in the child after the fork. If whoever good citizen calling	3358	after the fork. If whoever good citizen calling C<ev_default_fork> cheats
3048	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3359	and calls it in the wrong process, the fork handlers will be invoked, too,
3049	handlers will be invoked, too, of course.	3360	of course.
3050		3361
3051	=head3 The special problem of life after fork - how is it possible?	3362	=head3 The special problem of life after fork - how is it possible?
3052		3363
3053	Most uses of C<fork()> consist of forking, then some simple calls to set	3364	Most uses of C<fork ()> consist of forking, then some simple calls to set
3054	up/change the process environment, followed by a call to C<exec()>. This	3365	up/change the process environment, followed by a call to C<exec()>. This
3055	sequence should be handled by libev without any problems.	3366	sequence should be handled by libev without any problems.
3056		3367
3057	This changes when the application actually wants to do event handling	3368	This changes when the application actually wants to do event handling
3058	in the child, or both parent in child, in effect "continuing" after the	3369	in the child, or both parent in child, in effect "continuing" after the
…		…
3074	disadvantage of having to use multiple event loops (which do not support	3385	disadvantage of having to use multiple event loops (which do not support
3075	signal watchers).	3386	signal watchers).
3076		3387
3077	When this is not possible, or you want to use the default loop for	3388	When this is not possible, or you want to use the default loop for
3078	other reasons, then in the process that wants to start "fresh", call	3389	other reasons, then in the process that wants to start "fresh", call
3079	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying	3390	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
3080	the default loop will "orphan" (not stop) all registered watchers, so you	3391	Destroying the default loop will "orphan" (not stop) all registered
3081	have to be careful not to execute code that modifies those watchers. Note	3392	watchers, so you have to be careful not to execute code that modifies
3082	also that in that case, you have to re-register any signal watchers.	3393	those watchers. Note also that in that case, you have to re-register any
		3394	signal watchers.
3083		3395
3084	=head3 Watcher-Specific Functions and Data Members	3396	=head3 Watcher-Specific Functions and Data Members
3085		3397
3086	=over 4	3398	=over 4
3087		3399
3088	=item ev_fork_init (ev_signal *, callback)	3400	=item ev_fork_init (ev_fork *, callback)
3089		3401
3090	Initialises and configures the fork watcher - it has no parameters of any	3402	Initialises and configures the fork watcher - it has no parameters of any
3091	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,	3403	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
3092	believe me.	3404	really.
3093		3405
3094	=back	3406	=back
3095		3407
3096		3408
		3409	=head2 C<ev_cleanup> - even the best things end
		3410
		3411	Cleanup watchers are called just before the event loop is being destroyed
		3412	by a call to C<ev_loop_destroy>.
		3413
		3414	While there is no guarantee that the event loop gets destroyed, cleanup
		3415	watchers provide a convenient method to install cleanup hooks for your
		3416	program, worker threads and so on - you just to make sure to destroy the
		3417	loop when you want them to be invoked.
		3418
		3419	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3420	all other watchers, they do not keep a reference to the event loop (which
		3421	makes a lot of sense if you think about it). Like all other watchers, you
		3422	can call libev functions in the callback, except C<ev_cleanup_start>.
		3423
		3424	=head3 Watcher-Specific Functions and Data Members
		3425
		3426	=over 4
		3427
		3428	=item ev_cleanup_init (ev_cleanup *, callback)
		3429
		3430	Initialises and configures the cleanup watcher - it has no parameters of
		3431	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3432	pointless, I assure you.
		3433
		3434	=back
		3435
		3436	Example: Register an atexit handler to destroy the default loop, so any
		3437	cleanup functions are called.
		3438
		3439	static void
		3440	program_exits (void)
		3441	{
		3442	ev_loop_destroy (EV_DEFAULT_UC);
		3443	}
		3444
		3445	...
		3446	atexit (program_exits);
		3447
		3448
3097	=head2 C<ev_async> - how to wake up an event loop	3449	=head2 C<ev_async> - how to wake up an event loop
3098		3450
3099	In general, you cannot use an C<ev_run> from multiple threads or other	3451	In general, you cannot use an C<ev_loop> from multiple threads or other
3100	asynchronous sources such as signal handlers (as opposed to multiple event	3452	asynchronous sources such as signal handlers (as opposed to multiple event
3101	loops - those are of course safe to use in different threads).	3453	loops - those are of course safe to use in different threads).
3102		3454
3103	Sometimes, however, you need to wake up an event loop you do not control,	3455	Sometimes, however, you need to wake up an event loop you do not control,
3104	for example because it belongs to another thread. This is what C<ev_async>	3456	for example because it belongs to another thread. This is what C<ev_async>
…		…
3106	it by calling C<ev_async_send>, which is thread- and signal safe.	3458	it by calling C<ev_async_send>, which is thread- and signal safe.
3107		3459
3108	This functionality is very similar to C<ev_signal> watchers, as signals,	3460	This functionality is very similar to C<ev_signal> watchers, as signals,
3109	too, are asynchronous in nature, and signals, too, will be compressed	3461	too, are asynchronous in nature, and signals, too, will be compressed
3110	(i.e. the number of callback invocations may be less than the number of	3462	(i.e. the number of callback invocations may be less than the number of
3111	C<ev_async_sent> calls).	3463	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
3112		3464	of "global async watchers" by using a watcher on an otherwise unused
3113	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not	3465	signal, and C<ev_feed_signal> to signal this watcher from another thread,
3114	just the default loop.	3466	even without knowing which loop owns the signal.
3115		3467
3116	=head3 Queueing	3468	=head3 Queueing
3117		3469
3118	C<ev_async> does not support queueing of data in any way. The reason	3470	C<ev_async> does not support queueing of data in any way. The reason
3119	is that the author does not know of a simple (or any) algorithm for a	3471	is that the author does not know of a simple (or any) algorithm for a
…		…
3211	trust me.	3563	trust me.
3212		3564
3213	=item ev_async_send (loop, ev_async *)	3565	=item ev_async_send (loop, ev_async *)
3214		3566
3215	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3567	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
3216	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3568	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3569	returns.
		3570
3217	C<ev_feed_event>, this call is safe to do from other threads, signal or	3571	Unlike C<ev_feed_event>, this call is safe to do from other threads,
3218	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3572	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3219	section below on what exactly this means).	3573	embedding section below on what exactly this means).
3220		3574
3221	Note that, as with other watchers in libev, multiple events might get	3575	Note that, as with other watchers in libev, multiple events might get
3222	compressed into a single callback invocation (another way to look at this	3576	compressed into a single callback invocation (another way to look at
3223	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,	3577	this is that C<ev_async> watchers are level-triggered: they are set on
3224	reset when the event loop detects that).	3578	C<ev_async_send>, reset when the event loop detects that).
3225		3579
3226	This call incurs the overhead of a system call only once per event loop	3580	This call incurs the overhead of at most one extra system call per event
3227	iteration, so while the overhead might be noticeable, it doesn't apply to	3581	loop iteration, if the event loop is blocked, and no syscall at all if
3228	repeated calls to C<ev_async_send> for the same event loop.	3582	the event loop (or your program) is processing events. That means that
		3583	repeated calls are basically free (there is no need to avoid calls for
		3584	performance reasons) and that the overhead becomes smaller (typically
		3585	zero) under load.
3229		3586
3230	=item bool = ev_async_pending (ev_async *)	3587	=item bool = ev_async_pending (ev_async *)
3231		3588
3232	Returns a non-zero value when C<ev_async_send> has been called on the	3589	Returns a non-zero value when C<ev_async_send> has been called on the
3233	watcher but the event has not yet been processed (or even noted) by the	3590	watcher but the event has not yet been processed (or even noted) by the
…		…
3250		3607
3251	There are some other functions of possible interest. Described. Here. Now.	3608	There are some other functions of possible interest. Described. Here. Now.
3252		3609
3253	=over 4	3610	=over 4
3254		3611
3255	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3612	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)
3256		3613
3257	This function combines a simple timer and an I/O watcher, calls your	3614	This function combines a simple timer and an I/O watcher, calls your
3258	callback on whichever event happens first and automatically stops both	3615	callback on whichever event happens first and automatically stops both
3259	watchers. This is useful if you want to wait for a single event on an fd	3616	watchers. This is useful if you want to wait for a single event on an fd
3260	or timeout without having to allocate/configure/start/stop/free one or	3617	or timeout without having to allocate/configure/start/stop/free one or
…		…
3288	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3645	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3289		3646
3290	=item ev_feed_fd_event (loop, int fd, int revents)	3647	=item ev_feed_fd_event (loop, int fd, int revents)
3291		3648
3292	Feed an event on the given fd, as if a file descriptor backend detected	3649	Feed an event on the given fd, as if a file descriptor backend detected
3293	the given events it.	3650	the given events.
3294		3651
3295	=item ev_feed_signal_event (loop, int signum)	3652	=item ev_feed_signal_event (loop, int signum)
3296		3653
3297	Feed an event as if the given signal occurred (C<loop> must be the default	3654	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3298	loop!).	3655	which is async-safe.
3299		3656
3300	=back	3657	=back
		3658
		3659
		3660	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3661
		3662	This section explains some common idioms that are not immediately
		3663	obvious. Note that examples are sprinkled over the whole manual, and this
		3664	section only contains stuff that wouldn't fit anywhere else.
		3665
		3666	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3667
		3668	Each watcher has, by default, a C<void *data> member that you can read
		3669	or modify at any time: libev will completely ignore it. This can be used
		3670	to associate arbitrary data with your watcher. If you need more data and
		3671	don't want to allocate memory separately and store a pointer to it in that
		3672	data member, you can also "subclass" the watcher type and provide your own
		3673	data:
		3674
		3675	struct my_io
		3676	{
		3677	ev_io io;
		3678	int otherfd;
		3679	void *somedata;
		3680	struct whatever *mostinteresting;
		3681	};
		3682
		3683	...
		3684	struct my_io w;
		3685	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3686
		3687	And since your callback will be called with a pointer to the watcher, you
		3688	can cast it back to your own type:
		3689
		3690	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3691	{
		3692	struct my_io *w = (struct my_io *)w_;
		3693	...
		3694	}
		3695
		3696	More interesting and less C-conformant ways of casting your callback
		3697	function type instead have been omitted.
		3698
		3699	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3700
		3701	Another common scenario is to use some data structure with multiple
		3702	embedded watchers, in effect creating your own watcher that combines
		3703	multiple libev event sources into one "super-watcher":
		3704
		3705	struct my_biggy
		3706	{
		3707	int some_data;
		3708	ev_timer t1;
		3709	ev_timer t2;
		3710	}
		3711
		3712	In this case getting the pointer to C<my_biggy> is a bit more
		3713	complicated: Either you store the address of your C<my_biggy> struct in
		3714	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3715	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3716	real programmers):
		3717
		3718	#include <stddef.h>
		3719
		3720	static void
		3721	t1_cb (EV_P_ ev_timer *w, int revents)
		3722	{
		3723	struct my_biggy big = (struct my_biggy *)
		3724	(((char *)w) - offsetof (struct my_biggy, t1));
		3725	}
		3726
		3727	static void
		3728	t2_cb (EV_P_ ev_timer *w, int revents)
		3729	{
		3730	struct my_biggy big = (struct my_biggy *)
		3731	(((char *)w) - offsetof (struct my_biggy, t2));
		3732	}
		3733
		3734	=head2 AVOIDING FINISHING BEFORE RETURNING
		3735
		3736	Often you have structures like this in event-based programs:
		3737
		3738	callback ()
		3739	{
		3740	free (request);
		3741	}
		3742
		3743	request = start_new_request (..., callback);
		3744
		3745	The intent is to start some "lengthy" operation. The C<request> could be
		3746	used to cancel the operation, or do other things with it.
		3747
		3748	It's not uncommon to have code paths in C<start_new_request> that
		3749	immediately invoke the callback, for example, to report errors. Or you add
		3750	some caching layer that finds that it can skip the lengthy aspects of the
		3751	operation and simply invoke the callback with the result.
		3752
		3753	The problem here is that this will happen I<before> C<start_new_request>
		3754	has returned, so C<request> is not set.
		3755
		3756	Even if you pass the request by some safer means to the callback, you
		3757	might want to do something to the request after starting it, such as
		3758	canceling it, which probably isn't working so well when the callback has
		3759	already been invoked.
		3760
		3761	A common way around all these issues is to make sure that
		3762	C<start_new_request> I<always> returns before the callback is invoked. If
		3763	C<start_new_request> immediately knows the result, it can artificially
		3764	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3765	example, or more sneakily, by reusing an existing (stopped) watcher and
		3766	pushing it into the pending queue:
		3767
		3768	ev_set_cb (watcher, callback);
		3769	ev_feed_event (EV_A_ watcher, 0);
		3770
		3771	This way, C<start_new_request> can safely return before the callback is
		3772	invoked, while not delaying callback invocation too much.
		3773
		3774	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3775
		3776	Often (especially in GUI toolkits) there are places where you have
		3777	I<modal> interaction, which is most easily implemented by recursively
		3778	invoking C<ev_run>.
		3779
		3780	This brings the problem of exiting - a callback might want to finish the
		3781	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3782	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3783	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3784	other combination: In these cases, a simple C<ev_break> will not work.
		3785
		3786	The solution is to maintain "break this loop" variable for each C<ev_run>
		3787	invocation, and use a loop around C<ev_run> until the condition is
		3788	triggered, using C<EVRUN_ONCE>:
		3789
		3790	// main loop
		3791	int exit_main_loop = 0;
		3792
		3793	while (!exit_main_loop)
		3794	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3795
		3796	// in a modal watcher
		3797	int exit_nested_loop = 0;
		3798
		3799	while (!exit_nested_loop)
		3800	ev_run (EV_A_ EVRUN_ONCE);
		3801
		3802	To exit from any of these loops, just set the corresponding exit variable:
		3803
		3804	// exit modal loop
		3805	exit_nested_loop = 1;
		3806
		3807	// exit main program, after modal loop is finished
		3808	exit_main_loop = 1;
		3809
		3810	// exit both
		3811	exit_main_loop = exit_nested_loop = 1;
		3812
		3813	=head2 THREAD LOCKING EXAMPLE
		3814
		3815	Here is a fictitious example of how to run an event loop in a different
		3816	thread from where callbacks are being invoked and watchers are
		3817	created/added/removed.
		3818
		3819	For a real-world example, see the C<EV::Loop::Async> perl module,
		3820	which uses exactly this technique (which is suited for many high-level
		3821	languages).
		3822
		3823	The example uses a pthread mutex to protect the loop data, a condition
		3824	variable to wait for callback invocations, an async watcher to notify the
		3825	event loop thread and an unspecified mechanism to wake up the main thread.
		3826
		3827	First, you need to associate some data with the event loop:
		3828
		3829	typedef struct {
		3830	mutex_t lock; /* global loop lock */
		3831	ev_async async_w;
		3832	thread_t tid;
		3833	cond_t invoke_cv;
		3834	} userdata;
		3835
		3836	void prepare_loop (EV_P)
		3837	{
		3838	// for simplicity, we use a static userdata struct.
		3839	static userdata u;
		3840
		3841	ev_async_init (&u->async_w, async_cb);
		3842	ev_async_start (EV_A_ &u->async_w);
		3843
		3844	pthread_mutex_init (&u->lock, 0);
		3845	pthread_cond_init (&u->invoke_cv, 0);
		3846
		3847	// now associate this with the loop
		3848	ev_set_userdata (EV_A_ u);
		3849	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3850	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3851
		3852	// then create the thread running ev_run
		3853	pthread_create (&u->tid, 0, l_run, EV_A);
		3854	}
		3855
		3856	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3857	solely to wake up the event loop so it takes notice of any new watchers
		3858	that might have been added:
		3859
		3860	static void
		3861	async_cb (EV_P_ ev_async *w, int revents)
		3862	{
		3863	// just used for the side effects
		3864	}
		3865
		3866	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3867	protecting the loop data, respectively.
		3868
		3869	static void
		3870	l_release (EV_P)
		3871	{
		3872	userdata *u = ev_userdata (EV_A);
		3873	pthread_mutex_unlock (&u->lock);
		3874	}
		3875
		3876	static void
		3877	l_acquire (EV_P)
		3878	{
		3879	userdata *u = ev_userdata (EV_A);
		3880	pthread_mutex_lock (&u->lock);
		3881	}
		3882
		3883	The event loop thread first acquires the mutex, and then jumps straight
		3884	into C<ev_run>:
		3885
		3886	void *
		3887	l_run (void *thr_arg)
		3888	{
		3889	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3890
		3891	l_acquire (EV_A);
		3892	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3893	ev_run (EV_A_ 0);
		3894	l_release (EV_A);
		3895
		3896	return 0;
		3897	}
		3898
		3899	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3900	signal the main thread via some unspecified mechanism (signals? pipe
		3901	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3902	have been called (in a while loop because a) spurious wakeups are possible
		3903	and b) skipping inter-thread-communication when there are no pending
		3904	watchers is very beneficial):
		3905
		3906	static void
		3907	l_invoke (EV_P)
		3908	{
		3909	userdata *u = ev_userdata (EV_A);
		3910
		3911	while (ev_pending_count (EV_A))
		3912	{
		3913	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3914	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3915	}
		3916	}
		3917
		3918	Now, whenever the main thread gets told to invoke pending watchers, it
		3919	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3920	thread to continue:
		3921
		3922	static void
		3923	real_invoke_pending (EV_P)
		3924	{
		3925	userdata *u = ev_userdata (EV_A);
		3926
		3927	pthread_mutex_lock (&u->lock);
		3928	ev_invoke_pending (EV_A);
		3929	pthread_cond_signal (&u->invoke_cv);
		3930	pthread_mutex_unlock (&u->lock);
		3931	}
		3932
		3933	Whenever you want to start/stop a watcher or do other modifications to an
		3934	event loop, you will now have to lock:
		3935
		3936	ev_timer timeout_watcher;
		3937	userdata *u = ev_userdata (EV_A);
		3938
		3939	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3940
		3941	pthread_mutex_lock (&u->lock);
		3942	ev_timer_start (EV_A_ &timeout_watcher);
		3943	ev_async_send (EV_A_ &u->async_w);
		3944	pthread_mutex_unlock (&u->lock);
		3945
		3946	Note that sending the C<ev_async> watcher is required because otherwise
		3947	an event loop currently blocking in the kernel will have no knowledge
		3948	about the newly added timer. By waking up the loop it will pick up any new
		3949	watchers in the next event loop iteration.
		3950
		3951	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3952
		3953	While the overhead of a callback that e.g. schedules a thread is small, it
		3954	is still an overhead. If you embed libev, and your main usage is with some
		3955	kind of threads or coroutines, you might want to customise libev so that
		3956	doesn't need callbacks anymore.
		3957
		3958	Imagine you have coroutines that you can switch to using a function
		3959	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3960	and that due to some magic, the currently active coroutine is stored in a
		3961	global called C<current_coro>. Then you can build your own "wait for libev
		3962	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3963	the differing C<;> conventions):
		3964
		3965	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3966	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3967
		3968	That means instead of having a C callback function, you store the
		3969	coroutine to switch to in each watcher, and instead of having libev call
		3970	your callback, you instead have it switch to that coroutine.
		3971
		3972	A coroutine might now wait for an event with a function called
		3973	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3974	matter when, or whether the watcher is active or not when this function is
		3975	called):
		3976
		3977	void
		3978	wait_for_event (ev_watcher *w)
		3979	{
		3980	ev_set_cb (w, current_coro);
		3981	switch_to (libev_coro);
		3982	}
		3983
		3984	That basically suspends the coroutine inside C<wait_for_event> and
		3985	continues the libev coroutine, which, when appropriate, switches back to
		3986	this or any other coroutine.
		3987
		3988	You can do similar tricks if you have, say, threads with an event queue -
		3989	instead of storing a coroutine, you store the queue object and instead of
		3990	switching to a coroutine, you push the watcher onto the queue and notify
		3991	any waiters.
		3992
		3993	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		3994	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3995
		3996	// my_ev.h
		3997	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3998	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3999	#include "../libev/ev.h"
		4000
		4001	// my_ev.c
		4002	#define EV_H "my_ev.h"
		4003	#include "../libev/ev.c"
		4004
		4005	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		4006	F<my_ev.c> into your project. When properly specifying include paths, you
		4007	can even use F<ev.h> as header file name directly.
3301		4008
3302		4009
3303	=head1 LIBEVENT EMULATION	4010	=head1 LIBEVENT EMULATION
3304		4011
3305	Libev offers a compatibility emulation layer for libevent. It cannot	4012	Libev offers a compatibility emulation layer for libevent. It cannot
3306	emulate the internals of libevent, so here are some usage hints:	4013	emulate the internals of libevent, so here are some usage hints:
3307		4014
3308	=over 4	4015	=over 4
		4016
		4017	=item * Only the libevent-1.4.1-beta API is being emulated.
		4018
		4019	This was the newest libevent version available when libev was implemented,
		4020	and is still mostly unchanged in 2010.
3309		4021
3310	=item * Use it by including <event.h>, as usual.	4022	=item * Use it by including <event.h>, as usual.
3311		4023
3312	=item * The following members are fully supported: ev_base, ev_callback,	4024	=item * The following members are fully supported: ev_base, ev_callback,
3313	ev_arg, ev_fd, ev_res, ev_events.	4025	ev_arg, ev_fd, ev_res, ev_events.
…		…
3319	=item * Priorities are not currently supported. Initialising priorities	4031	=item * Priorities are not currently supported. Initialising priorities
3320	will fail and all watchers will have the same priority, even though there	4032	will fail and all watchers will have the same priority, even though there
3321	is an ev_pri field.	4033	is an ev_pri field.
3322		4034
3323	=item * In libevent, the last base created gets the signals, in libev, the	4035	=item * In libevent, the last base created gets the signals, in libev, the
3324	first base created (== the default loop) gets the signals.	4036	base that registered the signal gets the signals.
3325		4037
3326	=item * Other members are not supported.	4038	=item * Other members are not supported.
3327		4039
3328	=item * The libev emulation is I<not> ABI compatible to libevent, you need	4040	=item * The libev emulation is I<not> ABI compatible to libevent, you need
3329	to use the libev header file and library.	4041	to use the libev header file and library.
3330		4042
3331	=back	4043	=back
3332		4044
3333	=head1 C++ SUPPORT	4045	=head1 C++ SUPPORT
		4046
		4047	=head2 C API
		4048
		4049	The normal C API should work fine when used from C++: both ev.h and the
		4050	libev sources can be compiled as C++. Therefore, code that uses the C API
		4051	will work fine.
		4052
		4053	Proper exception specifications might have to be added to callbacks passed
		4054	to libev: exceptions may be thrown only from watcher callbacks, all other
		4055	callbacks (allocator, syserr, loop acquire/release and periodic reschedule
		4056	callbacks) must not throw exceptions, and might need a C<noexcept>
		4057	specification. If you have code that needs to be compiled as both C and
		4058	C++ you can use the C<EV_NOEXCEPT> macro for this:
		4059
		4060	static void
		4061	fatal_error (const char *msg) EV_NOEXCEPT
		4062	{
		4063	perror (msg);
		4064	abort ();
		4065	}
		4066
		4067	...
		4068	ev_set_syserr_cb (fatal_error);
		4069
		4070	The only API functions that can currently throw exceptions are C<ev_run>,
		4071	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		4072	because it runs cleanup watchers).
		4073
		4074	Throwing exceptions in watcher callbacks is only supported if libev itself
		4075	is compiled with a C++ compiler or your C and C++ environments allow
		4076	throwing exceptions through C libraries (most do).
		4077
		4078	=head2 C++ API
3334		4079
3335	Libev comes with some simplistic wrapper classes for C++ that mainly allow	4080	Libev comes with some simplistic wrapper classes for C++ that mainly allow
3336	you to use some convenience methods to start/stop watchers and also change	4081	you to use some convenience methods to start/stop watchers and also change
3337	the callback model to a model using method callbacks on objects.	4082	the callback model to a model using method callbacks on objects.
3338		4083
3339	To use it,	4084	To use it,
3340		4085
3341	#include <ev++.h>	4086	#include <ev++.h>
3342		4087
3343	This automatically includes F<ev.h> and puts all of its definitions (many	4088	This automatically includes F<ev.h> and puts all of its definitions (many
3344	of them macros) into the global namespace. All C++ specific things are	4089	of them macros) into the global namespace. All C++ specific things are
3345	put into the C<ev> namespace. It should support all the same embedding	4090	put into the C<ev> namespace. It should support all the same embedding
…		…
3348	Care has been taken to keep the overhead low. The only data member the C++	4093	Care has been taken to keep the overhead low. The only data member the C++
3349	classes add (compared to plain C-style watchers) is the event loop pointer	4094	classes add (compared to plain C-style watchers) is the event loop pointer
3350	that the watcher is associated with (or no additional members at all if	4095	that the watcher is associated with (or no additional members at all if
3351	you disable C<EV_MULTIPLICITY> when embedding libev).	4096	you disable C<EV_MULTIPLICITY> when embedding libev).
3352		4097
3353	Currently, functions, and static and non-static member functions can be	4098	Currently, functions, static and non-static member functions and classes
3354	used as callbacks. Other types should be easy to add as long as they only	4099	with C<operator ()> can be used as callbacks. Other types should be easy
3355	need one additional pointer for context. If you need support for other	4100	to add as long as they only need one additional pointer for context. If
3356	types of functors please contact the author (preferably after implementing	4101	you need support for other types of functors please contact the author
3357	it).	4102	(preferably after implementing it).
		4103
		4104	For all this to work, your C++ compiler either has to use the same calling
		4105	conventions as your C compiler (for static member functions), or you have
		4106	to embed libev and compile libev itself as C++.
3358		4107
3359	Here is a list of things available in the C<ev> namespace:	4108	Here is a list of things available in the C<ev> namespace:
3360		4109
3361	=over 4	4110	=over 4
3362		4111
…		…
3372	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4121	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
3373		4122
3374	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4123	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
3375	the same name in the C<ev> namespace, with the exception of C<ev_signal>	4124	the same name in the C<ev> namespace, with the exception of C<ev_signal>
3376	which is called C<ev::sig> to avoid clashes with the C<signal> macro	4125	which is called C<ev::sig> to avoid clashes with the C<signal> macro
3377	defines by many implementations.	4126	defined by many implementations.
3378		4127
3379	All of those classes have these methods:	4128	All of those classes have these methods:
3380		4129
3381	=over 4	4130	=over 4
3382		4131
…		…
3444	void operator() (ev::io &w, int revents)	4193	void operator() (ev::io &w, int revents)
3445	{	4194	{
3446	...	4195	...
3447	}	4196	}
3448	}	4197	}
3449		4198
3450	myfunctor f;	4199	myfunctor f;
3451		4200
3452	ev::io w;	4201	ev::io w;
3453	w.set (&f);	4202	w.set (&f);
3454		4203
…		…
3472	Associates a different C<struct ev_loop> with this watcher. You can only	4221	Associates a different C<struct ev_loop> with this watcher. You can only
3473	do this when the watcher is inactive (and not pending either).	4222	do this when the watcher is inactive (and not pending either).
3474		4223
3475	=item w->set ([arguments])	4224	=item w->set ([arguments])
3476		4225
3477	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this	4226	Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
3478	method or a suitable start method must be called at least once. Unlike the	4227	with the same arguments. Either this method or a suitable start method
3479	C counterpart, an active watcher gets automatically stopped and restarted	4228	must be called at least once. Unlike the C counterpart, an active watcher
3480	when reconfiguring it with this method.	4229	gets automatically stopped and restarted when reconfiguring it with this
		4230	method.
		4231
		4232	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4233	clashing with the C<set (loop)> method.
3481		4234
3482	=item w->start ()	4235	=item w->start ()
3483		4236
3484	Starts the watcher. Note that there is no C<loop> argument, as the	4237	Starts the watcher. Note that there is no C<loop> argument, as the
3485	constructor already stores the event loop.	4238	constructor already stores the event loop.
…		…
3515	watchers in the constructor.	4268	watchers in the constructor.
3516		4269
3517	class myclass	4270	class myclass
3518	{	4271	{
3519	ev::io io ; void io_cb (ev::io &w, int revents);	4272	ev::io io ; void io_cb (ev::io &w, int revents);
3520	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);	4273	ev::io io2 ; void io2_cb (ev::io &w, int revents);
3521	ev::idle idle; void idle_cb (ev::idle &w, int revents);	4274	ev::idle idle; void idle_cb (ev::idle &w, int revents);
3522		4275
3523	myclass (int fd)	4276	myclass (int fd)
3524	{	4277	{
3525	io .set <myclass, &myclass::io_cb > (this);	4278	io .set <myclass, &myclass::io_cb > (this);
…		…
3576	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.	4329	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3577		4330
3578	=item D	4331	=item D
3579		4332
3580	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4333	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
3581	be found at L<http://proj.llucax.com.ar/wiki/evd>.	4334	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
3582		4335
3583	=item Ocaml	4336	=item Ocaml
3584		4337
3585	Erkki Seppala has written Ocaml bindings for libev, to be found at	4338	Erkki Seppala has written Ocaml bindings for libev, to be found at
3586	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	4339	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
…		…
3589		4342
3590	Brian Maher has written a partial interface to libev for lua (at the	4343	Brian Maher has written a partial interface to libev for lua (at the
3591	time of this writing, only C<ev_io> and C<ev_timer>), to be found at	4344	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
3592	L<http://github.com/brimworks/lua-ev>.	4345	L<http://github.com/brimworks/lua-ev>.
3593		4346
		4347	=item Javascript
		4348
		4349	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4350
		4351	=item Others
		4352
		4353	There are others, and I stopped counting.
		4354
3594	=back	4355	=back
3595		4356
3596		4357
3597	=head1 MACRO MAGIC	4358	=head1 MACRO MAGIC
3598		4359
…		…
3634	suitable for use with C<EV_A>.	4395	suitable for use with C<EV_A>.
3635		4396
3636	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4397	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
3637		4398
3638	Similar to the other two macros, this gives you the value of the default	4399	Similar to the other two macros, this gives you the value of the default
3639	loop, if multiple loops are supported ("ev loop default").	4400	loop, if multiple loops are supported ("ev loop default"). The default loop
		4401	will be initialised if it isn't already initialised.
		4402
		4403	For non-multiplicity builds, these macros do nothing, so you always have
		4404	to initialise the loop somewhere.
3640		4405
3641	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4406	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
3642		4407
3643	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4408	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
3644	default loop has been initialised (C<UC> == unchecked). Their behaviour	4409	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
3711	ev_vars.h	4476	ev_vars.h
3712	ev_wrap.h	4477	ev_wrap.h
3713		4478
3714	ev_win32.c required on win32 platforms only	4479	ev_win32.c required on win32 platforms only
3715		4480
3716	ev_select.c only when select backend is enabled (which is enabled by default)	4481	ev_select.c only when select backend is enabled
3717	ev_poll.c only when poll backend is enabled (disabled by default)	4482	ev_poll.c only when poll backend is enabled
3718	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4483	ev_epoll.c only when the epoll backend is enabled
		4484	ev_linuxaio.c only when the linux aio backend is enabled
3719	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4485	ev_kqueue.c only when the kqueue backend is enabled
3720	ev_port.c only when the solaris port backend is enabled (disabled by default)	4486	ev_port.c only when the solaris port backend is enabled
3721		4487
3722	F<ev.c> includes the backend files directly when enabled, so you only need	4488	F<ev.c> includes the backend files directly when enabled, so you only need
3723	to compile this single file.	4489	to compile this single file.
3724		4490
3725	=head3 LIBEVENT COMPATIBILITY API	4491	=head3 LIBEVENT COMPATIBILITY API
…		…
3789	supported). It will also not define any of the structs usually found in	4555	supported). It will also not define any of the structs usually found in
3790	F<event.h> that are not directly supported by the libev core alone.	4556	F<event.h> that are not directly supported by the libev core alone.
3791		4557
3792	In standalone mode, libev will still try to automatically deduce the	4558	In standalone mode, libev will still try to automatically deduce the
3793	configuration, but has to be more conservative.	4559	configuration, but has to be more conservative.
		4560
		4561	=item EV_USE_FLOOR
		4562
		4563	If defined to be C<1>, libev will use the C<floor ()> function for its
		4564	periodic reschedule calculations, otherwise libev will fall back on a
		4565	portable (slower) implementation. If you enable this, you usually have to
		4566	link against libm or something equivalent. Enabling this when the C<floor>
		4567	function is not available will fail, so the safe default is to not enable
		4568	this.
3794		4569
3795	=item EV_USE_MONOTONIC	4570	=item EV_USE_MONOTONIC
3796		4571
3797	If defined to be C<1>, libev will try to detect the availability of the	4572	If defined to be C<1>, libev will try to detect the availability of the
3798	monotonic clock option at both compile time and runtime. Otherwise no	4573	monotonic clock option at both compile time and runtime. Otherwise no
…		…
3884	If programs implement their own fd to handle mapping on win32, then this	4659	If programs implement their own fd to handle mapping on win32, then this
3885	macro can be used to override the C<close> function, useful to unregister	4660	macro can be used to override the C<close> function, useful to unregister
3886	file descriptors again. Note that the replacement function has to close	4661	file descriptors again. Note that the replacement function has to close
3887	the underlying OS handle.	4662	the underlying OS handle.
3888		4663
		4664	=item EV_USE_WSASOCKET
		4665
		4666	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4667	communication socket, which works better in some environments. Otherwise,
		4668	the normal C<socket> function will be used, which works better in other
		4669	environments.
		4670
3889	=item EV_USE_POLL	4671	=item EV_USE_POLL
3890		4672
3891	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4673	If defined to be C<1>, libev will compile in support for the C<poll>(2)
3892	backend. Otherwise it will be enabled on non-win32 platforms. It	4674	backend. Otherwise it will be enabled on non-win32 platforms. It
3893	takes precedence over select.	4675	takes precedence over select.
…		…
3897	If defined to be C<1>, libev will compile in support for the Linux	4679	If defined to be C<1>, libev will compile in support for the Linux
3898	C<epoll>(7) backend. Its availability will be detected at runtime,	4680	C<epoll>(7) backend. Its availability will be detected at runtime,
3899	otherwise another method will be used as fallback. This is the preferred	4681	otherwise another method will be used as fallback. This is the preferred
3900	backend for GNU/Linux systems. If undefined, it will be enabled if the	4682	backend for GNU/Linux systems. If undefined, it will be enabled if the
3901	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4683	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4684
		4685	=item EV_USE_LINUXAIO
		4686
		4687	If defined to be C<1>, libev will compile in support for the Linux
		4688	aio backend. Due to it's currenbt limitations it has to be requested
		4689	explicitly. If undefined, it will be enabled on linux, otherwise
		4690	disabled.
3902		4691
3903	=item EV_USE_KQUEUE	4692	=item EV_USE_KQUEUE
3904		4693
3905	If defined to be C<1>, libev will compile in support for the BSD style	4694	If defined to be C<1>, libev will compile in support for the BSD style
3906	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	4695	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
3928	If defined to be C<1>, libev will compile in support for the Linux inotify	4717	If defined to be C<1>, libev will compile in support for the Linux inotify
3929	interface to speed up C<ev_stat> watchers. Its actual availability will	4718	interface to speed up C<ev_stat> watchers. Its actual availability will
3930	be detected at runtime. If undefined, it will be enabled if the headers	4719	be detected at runtime. If undefined, it will be enabled if the headers
3931	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4720	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
3932		4721
		4722	=item EV_NO_SMP
		4723
		4724	If defined to be C<1>, libev will assume that memory is always coherent
		4725	between threads, that is, threads can be used, but threads never run on
		4726	different cpus (or different cpu cores). This reduces dependencies
		4727	and makes libev faster.
		4728
		4729	=item EV_NO_THREADS
		4730
		4731	If defined to be C<1>, libev will assume that it will never be called from
		4732	different threads (that includes signal handlers), which is a stronger
		4733	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4734	libev faster.
		4735
3933	=item EV_ATOMIC_T	4736	=item EV_ATOMIC_T
3934		4737
3935	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4738	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
3936	access is atomic with respect to other threads or signal contexts. No such	4739	access is atomic with respect to other threads or signal contexts. No
3937	type is easily found in the C language, so you can provide your own type	4740	such type is easily found in the C language, so you can provide your own
3938	that you know is safe for your purposes. It is used both for signal handler "locking"	4741	type that you know is safe for your purposes. It is used both for signal
3939	as well as for signal and thread safety in C<ev_async> watchers.	4742	handler "locking" as well as for signal and thread safety in C<ev_async>
		4743	watchers.
3940		4744
3941	In the absence of this define, libev will use C<sig_atomic_t volatile>	4745	In the absence of this define, libev will use C<sig_atomic_t volatile>
3942	(from F<signal.h>), which is usually good enough on most platforms.	4746	(from F<signal.h>), which is usually good enough on most platforms.
3943		4747
3944	=item EV_H (h)	4748	=item EV_H (h)
…		…
3971	will have the C<struct ev_loop *> as first argument, and you can create	4775	will have the C<struct ev_loop *> as first argument, and you can create
3972	additional independent event loops. Otherwise there will be no support	4776	additional independent event loops. Otherwise there will be no support
3973	for multiple event loops and there is no first event loop pointer	4777	for multiple event loops and there is no first event loop pointer
3974	argument. Instead, all functions act on the single default loop.	4778	argument. Instead, all functions act on the single default loop.
3975		4779
		4780	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4781	default loop when multiplicity is switched off - you always have to
		4782	initialise the loop manually in this case.
		4783
3976	=item EV_MINPRI	4784	=item EV_MINPRI
3977		4785
3978	=item EV_MAXPRI	4786	=item EV_MAXPRI
3979		4787
3980	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4788	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
4016	#define EV_USE_POLL 1	4824	#define EV_USE_POLL 1
4017	#define EV_CHILD_ENABLE 1	4825	#define EV_CHILD_ENABLE 1
4018	#define EV_ASYNC_ENABLE 1	4826	#define EV_ASYNC_ENABLE 1
4019		4827
4020	The actual value is a bitset, it can be a combination of the following	4828	The actual value is a bitset, it can be a combination of the following
4021	values:	4829	values (by default, all of these are enabled):
4022		4830
4023	=over 4	4831	=over 4
4024		4832
4025	=item C<1> - faster/larger code	4833	=item C<1> - faster/larger code
4026		4834
…		…
4030	code size by roughly 30% on amd64).	4838	code size by roughly 30% on amd64).
4031		4839
4032	When optimising for size, use of compiler flags such as C<-Os> with	4840	When optimising for size, use of compiler flags such as C<-Os> with
4033	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of	4841	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
4034	assertions.	4842	assertions.
		4843
		4844	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4845	(e.g. gcc with C<-Os>).
4035		4846
4036	=item C<2> - faster/larger data structures	4847	=item C<2> - faster/larger data structures
4037		4848
4038	Replaces the small 2-heap for timer management by a faster 4-heap, larger	4849	Replaces the small 2-heap for timer management by a faster 4-heap, larger
4039	hash table sizes and so on. This will usually further increase code size	4850	hash table sizes and so on. This will usually further increase code size
4040	and can additionally have an effect on the size of data structures at	4851	and can additionally have an effect on the size of data structures at
4041	runtime.	4852	runtime.
4042		4853
		4854	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4855	(e.g. gcc with C<-Os>).
		4856
4043	=item C<4> - full API configuration	4857	=item C<4> - full API configuration
4044		4858
4045	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and	4859	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
4046	enables multiplicity (C<EV_MULTIPLICITY>=1).	4860	enables multiplicity (C<EV_MULTIPLICITY>=1).
4047		4861
…		…
4077		4891
4078	With an intelligent-enough linker (gcc+binutils are intelligent enough	4892	With an intelligent-enough linker (gcc+binutils are intelligent enough
4079	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by	4893	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
4080	your program might be left out as well - a binary starting a timer and an	4894	your program might be left out as well - a binary starting a timer and an
4081	I/O watcher then might come out at only 5Kb.	4895	I/O watcher then might come out at only 5Kb.
		4896
		4897	=item EV_API_STATIC
		4898
		4899	If this symbol is defined (by default it is not), then all identifiers
		4900	will have static linkage. This means that libev will not export any
		4901	identifiers, and you cannot link against libev anymore. This can be useful
		4902	when you embed libev, only want to use libev functions in a single file,
		4903	and do not want its identifiers to be visible.
		4904
		4905	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4906	wants to use libev.
		4907
		4908	This option only works when libev is compiled with a C compiler, as C++
		4909	doesn't support the required declaration syntax.
4082		4910
4083	=item EV_AVOID_STDIO	4911	=item EV_AVOID_STDIO
4084		4912
4085	If this is set to C<1> at compiletime, then libev will avoid using stdio	4913	If this is set to C<1> at compiletime, then libev will avoid using stdio
4086	functions (printf, scanf, perror etc.). This will increase the code size	4914	functions (printf, scanf, perror etc.). This will increase the code size
…		…
4230	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	5058	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4231		5059
4232	#include "ev_cpp.h"	5060	#include "ev_cpp.h"
4233	#include "ev.c"	5061	#include "ev.c"
4234		5062
4235	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	5063	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4236		5064
4237	=head2 THREADS AND COROUTINES	5065	=head2 THREADS AND COROUTINES
4238		5066
4239	=head3 THREADS	5067	=head3 THREADS
4240		5068
…		…
4291	default loop and triggering an C<ev_async> watcher from the default loop	5119	default loop and triggering an C<ev_async> watcher from the default loop
4292	watcher callback into the event loop interested in the signal.	5120	watcher callback into the event loop interested in the signal.
4293		5121
4294	=back	5122	=back
4295		5123
4296	=head4 THREAD LOCKING EXAMPLE	5124	See also L</THREAD LOCKING EXAMPLE>.
4297
4298	Here is a fictitious example of how to run an event loop in a different
4299	thread than where callbacks are being invoked and watchers are
4300	created/added/removed.
4301
4302	For a real-world example, see the C<EV::Loop::Async> perl module,
4303	which uses exactly this technique (which is suited for many high-level
4304	languages).
4305
4306	The example uses a pthread mutex to protect the loop data, a condition
4307	variable to wait for callback invocations, an async watcher to notify the
4308	event loop thread and an unspecified mechanism to wake up the main thread.
4309
4310	First, you need to associate some data with the event loop:
4311
4312	typedef struct {
4313	mutex_t lock; /* global loop lock */
4314	ev_async async_w;
4315	thread_t tid;
4316	cond_t invoke_cv;
4317	} userdata;
4318
4319	void prepare_loop (EV_P)
4320	{
4321	// for simplicity, we use a static userdata struct.
4322	static userdata u;
4323
4324	ev_async_init (&u->async_w, async_cb);
4325	ev_async_start (EV_A_ &u->async_w);
4326
4327	pthread_mutex_init (&u->lock, 0);
4328	pthread_cond_init (&u->invoke_cv, 0);
4329
4330	// now associate this with the loop
4331	ev_set_userdata (EV_A_ u);
4332	ev_set_invoke_pending_cb (EV_A_ l_invoke);
4333	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4334
4335	// then create the thread running ev_loop
4336	pthread_create (&u->tid, 0, l_run, EV_A);
4337	}
4338
4339	The callback for the C<ev_async> watcher does nothing: the watcher is used
4340	solely to wake up the event loop so it takes notice of any new watchers
4341	that might have been added:
4342
4343	static void
4344	async_cb (EV_P_ ev_async *w, int revents)
4345	{
4346	// just used for the side effects
4347	}
4348
4349	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
4350	protecting the loop data, respectively.
4351
4352	static void
4353	l_release (EV_P)
4354	{
4355	userdata *u = ev_userdata (EV_A);
4356	pthread_mutex_unlock (&u->lock);
4357	}
4358
4359	static void
4360	l_acquire (EV_P)
4361	{
4362	userdata *u = ev_userdata (EV_A);
4363	pthread_mutex_lock (&u->lock);
4364	}
4365
4366	The event loop thread first acquires the mutex, and then jumps straight
4367	into C<ev_run>:
4368
4369	void *
4370	l_run (void *thr_arg)
4371	{
4372	struct ev_loop *loop = (struct ev_loop *)thr_arg;
4373
4374	l_acquire (EV_A);
4375	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4376	ev_run (EV_A_ 0);
4377	l_release (EV_A);
4378
4379	return 0;
4380	}
4381
4382	Instead of invoking all pending watchers, the C<l_invoke> callback will
4383	signal the main thread via some unspecified mechanism (signals? pipe
4384	writes? C<Async::Interrupt>?) and then waits until all pending watchers
4385	have been called (in a while loop because a) spurious wakeups are possible
4386	and b) skipping inter-thread-communication when there are no pending
4387	watchers is very beneficial):
4388
4389	static void
4390	l_invoke (EV_P)
4391	{
4392	userdata *u = ev_userdata (EV_A);
4393
4394	while (ev_pending_count (EV_A))
4395	{
4396	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4397	pthread_cond_wait (&u->invoke_cv, &u->lock);
4398	}
4399	}
4400
4401	Now, whenever the main thread gets told to invoke pending watchers, it
4402	will grab the lock, call C<ev_invoke_pending> and then signal the loop
4403	thread to continue:
4404
4405	static void
4406	real_invoke_pending (EV_P)
4407	{
4408	userdata *u = ev_userdata (EV_A);
4409
4410	pthread_mutex_lock (&u->lock);
4411	ev_invoke_pending (EV_A);
4412	pthread_cond_signal (&u->invoke_cv);
4413	pthread_mutex_unlock (&u->lock);
4414	}
4415
4416	Whenever you want to start/stop a watcher or do other modifications to an
4417	event loop, you will now have to lock:
4418
4419	ev_timer timeout_watcher;
4420	userdata *u = ev_userdata (EV_A);
4421
4422	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4423
4424	pthread_mutex_lock (&u->lock);
4425	ev_timer_start (EV_A_ &timeout_watcher);
4426	ev_async_send (EV_A_ &u->async_w);
4427	pthread_mutex_unlock (&u->lock);
4428
4429	Note that sending the C<ev_async> watcher is required because otherwise
4430	an event loop currently blocking in the kernel will have no knowledge
4431	about the newly added timer. By waking up the loop it will pick up any new
4432	watchers in the next event loop iteration.
4433		5125
4434	=head3 COROUTINES	5126	=head3 COROUTINES
4435		5127
4436	Libev is very accommodating to coroutines ("cooperative threads"):	5128	Libev is very accommodating to coroutines ("cooperative threads"):
4437	libev fully supports nesting calls to its functions from different	5129	libev fully supports nesting calls to its functions from different
…		…
4602	requires, and its I/O model is fundamentally incompatible with the POSIX	5294	requires, and its I/O model is fundamentally incompatible with the POSIX
4603	model. Libev still offers limited functionality on this platform in	5295	model. Libev still offers limited functionality on this platform in
4604	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5296	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
4605	descriptors. This only applies when using Win32 natively, not when using	5297	descriptors. This only applies when using Win32 natively, not when using
4606	e.g. cygwin. Actually, it only applies to the microsofts own compilers,	5298	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4607	as every compielr comes with a slightly differently broken/incompatible	5299	as every compiler comes with a slightly differently broken/incompatible
4608	environment.	5300	environment.
4609		5301
4610	Lifting these limitations would basically require the full	5302	Lifting these limitations would basically require the full
4611	re-implementation of the I/O system. If you are into this kind of thing,	5303	re-implementation of the I/O system. If you are into this kind of thing,
4612	then note that glib does exactly that for you in a very portable way (note	5304	then note that glib does exactly that for you in a very portable way (note
…		…
4706	structure (guaranteed by POSIX but not by ISO C for example), but it also	5398	structure (guaranteed by POSIX but not by ISO C for example), but it also
4707	assumes that the same (machine) code can be used to call any watcher	5399	assumes that the same (machine) code can be used to call any watcher
4708	callback: The watcher callbacks have different type signatures, but libev	5400	callback: The watcher callbacks have different type signatures, but libev
4709	calls them using an C<ev_watcher *> internally.	5401	calls them using an C<ev_watcher *> internally.
4710		5402
		5403	=item null pointers and integer zero are represented by 0 bytes
		5404
		5405	Libev uses C<memset> to initialise structs and arrays to C<0> bytes, and
		5406	relies on this setting pointers and integers to null.
		5407
		5408	=item pointer accesses must be thread-atomic
		5409
		5410	Accessing a pointer value must be atomic, it must both be readable and
		5411	writable in one piece - this is the case on all current architectures.
		5412
4711	=item C<sig_atomic_t volatile> must be thread-atomic as well	5413	=item C<sig_atomic_t volatile> must be thread-atomic as well
4712		5414
4713	The type C<sig_atomic_t volatile> (or whatever is defined as	5415	The type C<sig_atomic_t volatile> (or whatever is defined as
4714	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different	5416	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
4715	threads. This is not part of the specification for C<sig_atomic_t>, but is	5417	threads. This is not part of the specification for C<sig_atomic_t>, but is
…		…
4723	thread" or will block signals process-wide, both behaviours would	5425	thread" or will block signals process-wide, both behaviours would
4724	be compatible with libev. Interaction between C<sigprocmask> and	5426	be compatible with libev. Interaction between C<sigprocmask> and
4725	C<pthread_sigmask> could complicate things, however.	5427	C<pthread_sigmask> could complicate things, however.
4726		5428
4727	The most portable way to handle signals is to block signals in all threads	5429	The most portable way to handle signals is to block signals in all threads
4728	except the initial one, and run the default loop in the initial thread as	5430	except the initial one, and run the signal handling loop in the initial
4729	well.	5431	thread as well.
4730		5432
4731	=item C<long> must be large enough for common memory allocation sizes	5433	=item C<long> must be large enough for common memory allocation sizes
4732		5434
4733	To improve portability and simplify its API, libev uses C<long> internally	5435	To improve portability and simplify its API, libev uses C<long> internally
4734	instead of C<size_t> when allocating its data structures. On non-POSIX	5436	instead of C<size_t> when allocating its data structures. On non-POSIX
…		…
4740		5442
4741	The type C<double> is used to represent timestamps. It is required to	5443	The type C<double> is used to represent timestamps. It is required to
4742	have at least 51 bits of mantissa (and 9 bits of exponent), which is	5444	have at least 51 bits of mantissa (and 9 bits of exponent), which is
4743	good enough for at least into the year 4000 with millisecond accuracy	5445	good enough for at least into the year 4000 with millisecond accuracy
4744	(the design goal for libev). This requirement is overfulfilled by	5446	(the design goal for libev). This requirement is overfulfilled by
4745	implementations using IEEE 754, which is basically all existing ones. With	5447	implementations using IEEE 754, which is basically all existing ones.
		5448
4746	IEEE 754 doubles, you get microsecond accuracy until at least 2200.	5449	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5450	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5451	is either obsolete or somebody patched it to use C<long double> or
		5452	something like that, just kidding).
4747		5453
4748	=back	5454	=back
4749		5455
4750	If you know of other additional requirements drop me a note.	5456	If you know of other additional requirements drop me a note.
4751		5457
…		…
4813	=item Processing ev_async_send: O(number_of_async_watchers)	5519	=item Processing ev_async_send: O(number_of_async_watchers)
4814		5520
4815	=item Processing signals: O(max_signal_number)	5521	=item Processing signals: O(max_signal_number)
4816		5522
4817	Sending involves a system call I<iff> there were no other C<ev_async_send>	5523	Sending involves a system call I<iff> there were no other C<ev_async_send>
4818	calls in the current loop iteration. Checking for async and signal events	5524	calls in the current loop iteration and the loop is currently
		5525	blocked. Checking for async and signal events involves iterating over all
4819	involves iterating over all running async watchers or all signal numbers.	5526	running async watchers or all signal numbers.
4820		5527
4821	=back	5528	=back
4822		5529
4823		5530
4824	=head1 PORTING FROM LIBEV 3.X TO 4.X	5531	=head1 PORTING FROM LIBEV 3.X TO 4.X
4825		5532
4826	The major version 4 introduced some minor incompatible changes to the API.	5533	The major version 4 introduced some incompatible changes to the API.
4827		5534
4828	At the moment, the C<ev.h> header file tries to implement superficial	5535	At the moment, the C<ev.h> header file provides compatibility definitions
4829	compatibility, so most programs should still compile. Those might be	5536	for all changes, so most programs should still compile. The compatibility
4830	removed in later versions of libev, so better update early than late.	5537	layer might be removed in later versions of libev, so better update to the
		5538	new API early than late.
4831		5539
4832	=over 4	5540	=over 4
		5541
		5542	=item C<EV_COMPAT3> backwards compatibility mechanism
		5543
		5544	The backward compatibility mechanism can be controlled by
		5545	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
		5546	section.
		5547
		5548	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5549
		5550	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5551
		5552	ev_loop_destroy (EV_DEFAULT_UC);
		5553	ev_loop_fork (EV_DEFAULT);
4833		5554
4834	=item function/symbol renames	5555	=item function/symbol renames
4835		5556
4836	A number of functions and symbols have been renamed:	5557	A number of functions and symbols have been renamed:
4837		5558
…		…
4856	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme	5577	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
4857	as all other watcher types. Note that C<ev_loop_fork> is still called	5578	as all other watcher types. Note that C<ev_loop_fork> is still called
4858	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>	5579	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
4859	typedef.	5580	typedef.
4860		5581
4861	=item C<EV_COMPAT3> backwards compatibility mechanism
4862
4863	The backward compatibility mechanism can be controlled by
4864	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
4865	section.
4866
4867	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>	5582	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
4868		5583
4869	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different	5584	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
4870	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile	5585	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
4871	and work, but the library code will of course be larger.	5586	and work, but the library code will of course be larger.
…		…
4878	=over 4	5593	=over 4
4879		5594
4880	=item active	5595	=item active
4881		5596
4882	A watcher is active as long as it has been started and not yet stopped.	5597	A watcher is active as long as it has been started and not yet stopped.
4883	See L<WATCHER STATES> for details.	5598	See L</WATCHER STATES> for details.
4884		5599
4885	=item application	5600	=item application
4886		5601
4887	In this document, an application is whatever is using libev.	5602	In this document, an application is whatever is using libev.
4888		5603
…		…
4924	watchers and events.	5639	watchers and events.
4925		5640
4926	=item pending	5641	=item pending
4927		5642
4928	A watcher is pending as soon as the corresponding event has been	5643	A watcher is pending as soon as the corresponding event has been
4929	detected. See L<WATCHER STATES> for details.	5644	detected. See L</WATCHER STATES> for details.
4930		5645
4931	=item real time	5646	=item real time
4932		5647
4933	The physical time that is observed. It is apparently strictly monotonic :)	5648	The physical time that is observed. It is apparently strictly monotonic :)
4934		5649
4935	=item wall-clock time	5650	=item wall-clock time
4936		5651
4937	The time and date as shown on clocks. Unlike real time, it can actually	5652	The time and date as shown on clocks. Unlike real time, it can actually
4938	be wrong and jump forwards and backwards, e.g. when the you adjust your	5653	be wrong and jump forwards and backwards, e.g. when you adjust your
4939	clock.	5654	clock.
4940		5655
4941	=item watcher	5656	=item watcher
4942		5657
4943	A data structure that describes interest in certain events. Watchers need	5658	A data structure that describes interest in certain events. Watchers need
…		…
4945		5660
4946	=back	5661	=back
4947		5662
4948	=head1 AUTHOR	5663	=head1 AUTHOR
4949		5664
4950	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.	5665	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5666	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
4951		5667

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