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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
…		…
9	=head2 EXAMPLE PROGRAM	11	=head2 EXAMPLE PROGRAM
10		12
11	// a single header file is required	13	// a single header file is required
12	#include <ev.h>	14	#include <ev.h>
13		15
		16	#include <stdio.h> // for puts
		17
14	// every watcher type has its own typedef'd struct	18	// every watcher type has its own typedef'd struct
15	// with the name ev_<type>	19	// with the name ev_TYPE
16	ev_io stdin_watcher;	20	ev_io stdin_watcher;
17	ev_timer timeout_watcher;	21	ev_timer timeout_watcher;
18		22
19	// all watcher callbacks have a similar signature	23	// all watcher callbacks have a similar signature
20	// this callback is called when data is readable on stdin	24	// this callback is called when data is readable on stdin
21	static void	25	static void
22	stdin_cb (EV_P_ struct ev_io *w, int revents)	26	stdin_cb (EV_P_ ev_io *w, int revents)
23	{	27	{
24	puts ("stdin ready");	28	puts ("stdin ready");
25	// for one-shot events, one must manually stop the watcher	29	// for one-shot events, one must manually stop the watcher
26	// with its corresponding stop function.	30	// with its corresponding stop function.
27	ev_io_stop (EV_A_ w);	31	ev_io_stop (EV_A_ w);
28		32
29	// this causes all nested ev_loop's to stop iterating	33	// this causes all nested ev_run's to stop iterating
30	ev_unloop (EV_A_ EVUNLOOP_ALL);	34	ev_break (EV_A_ EVBREAK_ALL);
31	}	35	}
32		36
33	// another callback, this time for a time-out	37	// another callback, this time for a time-out
34	static void	38	static void
35	timeout_cb (EV_P_ struct ev_timer *w, int revents)	39	timeout_cb (EV_P_ ev_timer *w, int revents)
36	{	40	{
37	puts ("timeout");	41	puts ("timeout");
38	// this causes the innermost ev_loop to stop iterating	42	// this causes the innermost ev_run to stop iterating
39	ev_unloop (EV_A_ EVUNLOOP_ONE);	43	ev_break (EV_A_ EVBREAK_ONE);
40	}	44	}
41		45
42	int	46	int
43	main (void)	47	main (void)
44	{	48	{
45	// use the default event loop unless you have special needs	49	// use the default event loop unless you have special needs
46	struct ev_loop *loop = ev_default_loop (0);	50	struct ev_loop *loop = EV_DEFAULT;
47		51
48	// initialise an io watcher, then start it	52	// initialise an io watcher, then start it
49	// this one will watch for stdin to become readable	53	// this one will watch for stdin to become readable
50	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);
51	ev_io_start (loop, &stdin_watcher);	55	ev_io_start (loop, &stdin_watcher);
…		…
54	// simple non-repeating 5.5 second timeout	58	// simple non-repeating 5.5 second timeout
55	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);	59	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
56	ev_timer_start (loop, &timeout_watcher);	60	ev_timer_start (loop, &timeout_watcher);
57		61
58	// now wait for events to arrive	62	// now wait for events to arrive
59	ev_loop (loop, 0);	63	ev_run (loop, 0);
60		64
61	// unloop was called, so exit	65	// break was called, so exit
62	return 0;	66	return 0;
63	}	67	}
64		68
65	=head1 DESCRIPTION	69	=head1 ABOUT THIS DOCUMENT
		70
		71	This document documents the libev software package.
66		72
67	The newest version of this document is also available as an html-formatted	73	The newest version of this document is also available as an html-formatted
68	web page you might find easier to navigate when reading it for the first	74	web page you might find easier to navigate when reading it for the first
69	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.	75	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		76
		77	While this document tries to be as complete as possible in documenting
		78	libev, its usage and the rationale behind its design, it is not a tutorial
		79	on event-based programming, nor will it introduce event-based programming
		80	with libev.
		81
		82	Familiarity with event based programming techniques in general is assumed
		83	throughout this document.
		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
		93	=head1 ABOUT LIBEV
70		94
71	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
72	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
73	these event sources and provide your program with events.	97	these event sources and provide your program with events.
74		98
…		…
81	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
82	watcher.	106	watcher.
83		107
84	=head2 FEATURES	108	=head2 FEATURES
85		109
86	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>
87	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	111	interfaces, the BSD-specific C<kqueue> and the Solaris-specific event port
88	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>
89	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	113	interface (for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
90	with customised rescheduling (C<ev_periodic>), synchronous signals	114	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
91	(C<ev_signal>), process status change events (C<ev_child>), and event	115	timers (C<ev_timer>), absolute timers with customised rescheduling
92	watchers dealing with the event loop mechanism itself (C<ev_idle>,	116	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
93	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as	117	change events (C<ev_child>), and event watchers dealing with the event
94	file watchers (C<ev_stat>) and even limited support for fork events	118	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
95	(C<ev_fork>).	119	C<ev_check> watchers) as well as file watchers (C<ev_stat>) and even
		120	limited support for fork events (C<ev_fork>).
96		121
97	It also is quite fast (see this	122	It also is quite fast (see this
98	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent	123	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
99	for example).	124	for example).
100		125
…		…
108	name C<loop> (which is always of type C<struct ev_loop *>) will not have	133	name C<loop> (which is always of type C<struct ev_loop *>) will not have
109	this argument.	134	this argument.
110		135
111	=head2 TIME REPRESENTATION	136	=head2 TIME REPRESENTATION
112		137
113	Libev represents time as a single floating point number, representing the	138	Libev represents time as a single floating point number, representing
114	(fractional) number of seconds since the (POSIX) epoch (somewhere near	139	the (fractional) number of seconds since the (POSIX) epoch (in practice
115	the beginning of 1970, details are complicated, don't ask). This type is	140	somewhere near the beginning of 1970, details are complicated, don't
116	called C<ev_tstamp>, which is what you should use too. It usually aliases	141	ask). This type is called C<ev_tstamp>, which is what you should use
117	to the C<double> type in C, and when you need to do any calculations on	142	too. It usually aliases to the C<double> type in C. When you need to do
118	it, you should treat it as some floating point value. Unlike the name	143	any calculations on it, you should treat it as some floating point value.
		144
119	component C<stamp> might indicate, it is also used for time differences	145	Unlike the name component C<stamp> might indicate, it is also used for
120	throughout libev.	146	time differences (e.g. delays) throughout libev.
121		147
122	=head1 ERROR HANDLING	148	=head1 ERROR HANDLING
123		149
124	Libev knows three classes of errors: operating system errors, usage errors	150	Libev knows three classes of errors: operating system errors, usage errors
125	and internal errors (bugs).	151	and internal errors (bugs).
…		…
149		175
150	=item ev_tstamp ev_time ()	176	=item ev_tstamp ev_time ()
151		177
152	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
153	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
154	you actually want to know.	180	you actually want to know. Also interesting is the combination of
		181	C<ev_now_update> and C<ev_now>.
155		182
156	=item ev_sleep (ev_tstamp interval)	183	=item ev_sleep (ev_tstamp interval)
157		184
158	Sleep for the given interval: The current thread will be blocked until	185	Sleep for the given interval: The current thread will be blocked
159	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
160	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 >>).
161		194
162	=item int ev_version_major ()	195	=item int ev_version_major ()
163		196
164	=item int ev_version_minor ()	197	=item int ev_version_minor ()
165		198
…		…
176	as this indicates an incompatible change. Minor versions are usually	209	as this indicates an incompatible change. Minor versions are usually
177	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
178	not a problem.	211	not a problem.
179		212
180	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
181	version.	214	version (note, however, that this will not detect other ABI mismatches,
		215	such as LFS or reentrancy).
182		216
183	assert (("libev version mismatch",	217	assert (("libev version mismatch",
184	ev_version_major () == EV_VERSION_MAJOR	218	ev_version_major () == EV_VERSION_MAJOR
185	&& ev_version_minor () >= EV_VERSION_MINOR));	219	&& ev_version_minor () >= EV_VERSION_MINOR));
186		220
…		…
197	assert (("sorry, no epoll, no sex",	231	assert (("sorry, no epoll, no sex",
198	ev_supported_backends () & EVBACKEND_EPOLL));	232	ev_supported_backends () & EVBACKEND_EPOLL));
199		233
200	=item unsigned int ev_recommended_backends ()	234	=item unsigned int ev_recommended_backends ()
201		235
202	Return the set of all backends compiled into this binary of libev and also	236	Return the set of all backends compiled into this binary of libev and
203	recommended for this platform. This set is often smaller than the one	237	also recommended for this platform, meaning it will work for most file
		238	descriptor types. This set is often smaller than the one returned by
204	returned by C<ev_supported_backends>, as for example kqueue is broken on	239	C<ev_supported_backends>, as for example kqueue is broken on most BSDs
205	most BSDs and will not be auto-detected unless you explicitly request it	240	and will not be auto-detected unless you explicitly request it (assuming
206	(assuming you know what you are doing). This is the set of backends that	241	you know what you are doing). This is the set of backends that libev will
207	libev will probe for if you specify no backends explicitly.	242	probe for if you specify no backends explicitly.
208		243
209	=item unsigned int ev_embeddable_backends ()	244	=item unsigned int ev_embeddable_backends ()
210		245
211	Returns the set of backends that are embeddable in other event loops. This	246	Returns the set of backends that are embeddable in other event loops. This
212	is the theoretical, all-platform, value. To find which backends	247	value is platform-specific but can include backends not available on the
213	might be supported on the current system, you would need to look at	248	current system. To find which embeddable backends might be supported on
214	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	249	the current system, you would need to look at C<ev_embeddable_backends ()
215	recommended ones.	250	& ev_supported_backends ()>, likewise for recommended ones.
216		251
217	See the description of C<ev_embed> watchers for more info.	252	See the description of C<ev_embed> watchers for more info.
218		253
219	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	254	=item ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())
220		255
221	Sets the allocation function to use (the prototype is similar - the	256	Sets the allocation function to use (the prototype is similar - the
222	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
223	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
224	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
…		…
230		265
231	You could override this function in high-availability programs to, say,	266	You could override this function in high-availability programs to, say,
232	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,
233	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.
234		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
235	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
236	retries (example requires a standards-compliant C<realloc>).	285	retries.
237		286
238	static void *	287	static void *
239	persistent_realloc (void *ptr, size_t size)	288	persistent_realloc (void *ptr, size_t size)
240	{	289	{
		290	if (!size)
		291	{
		292	free (ptr);
		293	return 0;
		294	}
		295
241	for (;;)	296	for (;;)
242	{	297	{
243	void *newptr = realloc (ptr, size);	298	void *newptr = realloc (ptr, size);
244		299
245	if (newptr)	300	if (newptr)
…		…
250	}	305	}
251		306
252	...	307	...
253	ev_set_allocator (persistent_realloc);	308	ev_set_allocator (persistent_realloc);
254		309
255	=item ev_set_syserr_cb (void (*cb)(const char *msg));	310	=item ev_set_syserr_cb (void (*cb)(const char *msg) throw ())
256		311
257	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
258	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
259	indicating the system call or subsystem causing the problem. If this	314	indicating the system call or subsystem causing the problem. If this
260	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
…		…
272	}	327	}
273		328
274	...	329	...
275	ev_set_syserr_cb (fatal_error);	330	ev_set_syserr_cb (fatal_error);
276		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
277	=back	345	=back
278		346
279	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	347	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
280		348
281	An event loop is described by a C<struct ev_loop *>. The library knows two	349	An event loop is described by a C<struct ev_loop *> (the C<struct> is
282	types of such loops, the I<default> loop, which supports signals and child	350	I<not> optional in this case unless libev 3 compatibility is disabled, as
283	events, and dynamically created loops which do not.	351	libev 3 had an C<ev_loop> function colliding with the struct name).
		352
		353	The library knows two types of such loops, the I<default> loop, which
		354	supports child process events, and dynamically created event loops which
		355	do not.
284		356
285	=over 4	357	=over 4
286		358
287	=item struct ev_loop *ev_default_loop (unsigned int flags)	359	=item struct ev_loop *ev_default_loop (unsigned int flags)
288		360
289	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
290	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
291	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
292	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".
293		371
294	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
295	function.	373	function (or via the C<EV_DEFAULT> macro).
296		374
297	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
298	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
299	as loops cannot bes hared easily between threads anyway).	377	that this case is unlikely, as loops cannot be shared easily between
		378	threads anyway).
300		379
301	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,
302	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
303	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
304	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
305	can simply overwrite the C<SIGCHLD> signal handler I<after> calling	384	C<SIGCHLD> signal handler I<after> calling C<ev_default_init>.
306	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.
307		404
308	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
309	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>).
310		407
311	The following flags are supported:	408	The following flags are supported:
…		…
321		418
322	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
323	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
324	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	421	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
325	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
326	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
327	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).
328		427
329	=item C<EVFLAG_FORKCHECK>	428	=item C<EVFLAG_FORKCHECK>
330		429
331	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after	430	Instead of calling C<ev_loop_fork> manually after a fork, you can also
332	a fork, you can also make libev check for a fork in each iteration by	431	make libev check for a fork in each iteration by enabling this flag.
333	enabling this flag.
334		432
335	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,
336	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
337	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
338	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
339	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
340	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).
341		440
342	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
343	forget about forgetting to tell libev about forking) when you use this	442	forget about forgetting to tell libev about forking, although you still
344	flag.	443	have to ignore C<SIGPIPE>) when you use this flag.
345		444
346	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>
347	environment variable.	446	environment variable.
		447
		448	=item C<EVFLAG_NOINOTIFY>
		449
		450	When this flag is specified, then libev will not attempt to use the
		451	I<inotify> API for its C<ev_stat> watchers. Apart from debugging and
		452	testing, this flag can be useful to conserve inotify file descriptors, as
		453	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		454
		455	=item C<EVFLAG_SIGNALFD>
		456
		457	When this flag is specified, then libev will attempt to use the
		458	I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API
		459	delivers signals synchronously, which makes it both faster and might make
		460	it possible to get the queued signal data. It can also simplify signal
		461	handling with threads, as long as you properly block signals in your
		462	threads that are not interested in handling them.
		463
		464	Signalfd will not be used by default as this changes your signal mask, and
		465	there are a lot of shoddy libraries and programs (glib's threadpool for
		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.
348		482
349	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	483	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
350		484
351	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
352	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,
…		…
359	writing a server, you should C<accept ()> in a loop to accept as many	493	writing a server, you should C<accept ()> in a loop to accept as many
360	connections as possible during one iteration. You might also want to have	494	connections as possible during one iteration. You might also want to have
361	a look at C<ev_set_io_collect_interval ()> to increase the amount of	495	a look at C<ev_set_io_collect_interval ()> to increase the amount of
362	readiness notifications you get per iteration.	496	readiness notifications you get per iteration.
363		497
		498	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		499	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		500	C<exceptfds> set on that platform).
		501
364	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	502	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
365		503
366	And this is your standard poll(2) backend. It's more complicated	504	And this is your standard poll(2) backend. It's more complicated
367	than select, but handles sparse fds better and has no artificial	505	than select, but handles sparse fds better and has no artificial
368	limit on the number of fds you can use (except it will slow down	506	limit on the number of fds you can use (except it will slow down
369	considerably with a lot of inactive fds). It scales similarly to select,	507	considerably with a lot of inactive fds). It scales similarly to select,
370	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for	508	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
371	performance tips.	509	performance tips.
372		510
		511	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		512	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
		513
373	=item C<EVBACKEND_EPOLL> (value 4, Linux)	514	=item C<EVBACKEND_EPOLL> (value 4, Linux)
374		515
		516	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		517	kernels).
		518
375	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
376	but it scales phenomenally better. While poll and select usually scale	520	it scales phenomenally better. While poll and select usually scale like
377	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
378	epoll scales either O(1) or O(active_fds). The epoll design has a number	522	fd), epoll scales either O(1) or O(active_fds).
379	of shortcomings, such as silently dropping events in some hard-to-detect	523
380	cases and requiring a system call per fd change, no fork support and bad	524	The epoll mechanism deserves honorable mention as the most misdesigned
381	support for dup.	525	of the more advanced event mechanisms: mere annoyances include silently
		526	dropping file descriptors, requiring a system call per change per file
		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
		530	0.1ms) and so on. The biggest issue is fork races, however - if a program
		531	forks then I<both> parent and child process have to recreate the epoll
		532	set, which can take considerable time (one syscall per file descriptor)
		533	and is of course hard to detect.
		534
		535	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
		536	but of course I<doesn't>, and epoll just loves to report events for
		537	totally I<different> file descriptors (even already closed ones, so
		538	one cannot even remove them from the set) than registered in the set
		539	(especially on SMP systems). Libev tries to counter these spurious
		540	notifications by employing an additional generation counter and comparing
		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
		545	not least, it also refuses to work with some file descriptors which work
		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...
382		551
383	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
384	will result in some caching, there is still a system call per such incident	553	will result in some caching, there is still a system call per such
385	(because the fd could point to a different file description now), so its	554	incident (because the same I<file descriptor> could point to a different
386	best to avoid that. Also, C<dup ()>'ed file descriptors might not work	555	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
387	very well if you register events for both fds.	556	file descriptors might not work very well if you register events for both
388		557	file descriptors.
389	Please note that epoll sometimes generates spurious notifications, so you
390	need to use non-blocking I/O or other means to avoid blocking when no data
391	(or space) is available.
392		558
393	Best performance from this backend is achieved by not unregistering all	559	Best performance from this backend is achieved by not unregistering all
394	watchers for a file descriptor until it has been closed, if possible, i.e.	560	watchers for a file descriptor until it has been closed, if possible,
395	keep at least one watcher active per fd at all times.	561	i.e. keep at least one watcher active per fd at all times. Stopping and
		562	starting a watcher (without re-setting it) also usually doesn't cause
		563	extra overhead. A fork can both result in spurious notifications as well
		564	as in libev having to destroy and recreate the epoll object, which can
		565	take considerable time and thus should be avoided.
		566
		567	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		568	faster than epoll for maybe up to a hundred file descriptors, depending on
		569	the usage. So sad.
396		570
397	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
398	all kernel versions tested so far.	572	a lot of kernel revisions, but probably(!) works in current versions.
		573
		574	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		575	C<EVBACKEND_POLL>.
		576
		577	=item C<EVBACKEND_LINUXAIO> (value 64, Linux)
		578
		579	Use the linux-specific linux aio (I<not> C<< aio(7) >>) event interface
		580	available in post-4.18 kernels.
		581
		582	If this backend works for you (as of this writing, it was very
		583	experimental and only supports a subset of file types), it is the best
		584	event interface available on linux and might be well worth it enabling it
		585	- if it isn't available in your kernel this will be detected and another
		586	backend will be chosen.
		587
		588	This backend can batch oneshot requests and uses a user-space ring buffer
		589	to receive events. It also doesn't suffer from most of the design problems
		590	of epoll (such as not being able to remove event sources from the epoll
		591	set), and generally sounds too good to be true. Because, this being the
		592	linux kernel, of course it suffers from a whole new set of limitations.
		593
		594	For one, it is not easily embeddable (but probably could be done using
		595	an event fd at some extra overhead). It also is subject to various
		596	arbitrary limits that can be configured in F</proc/sys/fs/aio-max-nr>
		597	and F</proc/sys/fs/aio-nr>), which could lead to it being skipped during
		598	initialisation.
		599
		600	Most problematic in practise, however, is that, like kqueue, it requires
		601	special support from drivers, and, not surprisingly, not all drivers
		602	implement it. For example, in linux 4.19, tcp sockets, pipes, event fds,
		603	files, F</dev/null> and a few others are supported, but ttys are not, so
		604	this is not (yet?) a generic event polling interface but is probably still
		605	be very useful in a web server or similar program.
		606
		607	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		608	C<EVBACKEND_POLL>.
399		609
400	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	610	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
401		611
402	Kqueue deserves special mention, as at the time of this writing, it	612	Kqueue deserves special mention, as at the time of this writing, it
403	was broken on all BSDs except NetBSD (usually it doesn't work reliably	613	was broken on all BSDs except NetBSD (usually it doesn't work reliably
404	with anything but sockets and pipes, except on Darwin, where of course	614	with anything but sockets and pipes, except on Darwin, where of course
405	it's completely useless). For this reason it's not being "auto-detected"	615	it's completely useless). Unlike epoll, however, whose brokenness
		616	is by design, these kqueue bugs can (and eventually will) be fixed
		617	without API changes to existing programs. For this reason it's not being
406	unless you explicitly specify it explicitly in the flags (i.e. using	618	"auto-detected" unless you explicitly specify it in the flags (i.e. using
407	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)	619	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
408	system like NetBSD.	620	system like NetBSD.
409		621
410	You still can embed kqueue into a normal poll or select backend and use it	622	You still can embed kqueue into a normal poll or select backend and use it
411	only for sockets (after having made sure that sockets work with kqueue on	623	only for sockets (after having made sure that sockets work with kqueue on
…		…
413		625
414	It scales in the same way as the epoll backend, but the interface to the	626	It scales in the same way as the epoll backend, but the interface to the
415	kernel is more efficient (which says nothing about its actual speed, of	627	kernel is more efficient (which says nothing about its actual speed, of
416	course). While stopping, setting and starting an I/O watcher does never	628	course). While stopping, setting and starting an I/O watcher does never
417	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to	629	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
418	two event changes per incident, support for C<fork ()> is very bad and it	630	two event changes per incident. Support for C<fork ()> is very bad (you
		631	might have to leak fd's on fork, but it's more sane than epoll) and it
419	drops fds silently in similarly hard-to-detect cases.	632	drops fds silently in similarly hard-to-detect cases.
420		633
421	This backend usually performs well under most conditions.	634	This backend usually performs well under most conditions.
422		635
423	While nominally embeddable in other event loops, this doesn't work	636	While nominally embeddable in other event loops, this doesn't work
424	everywhere, so you might need to test for this. And since it is broken	637	everywhere, so you might need to test for this. And since it is broken
425	almost everywhere, you should only use it when you have a lot of sockets	638	almost everywhere, you should only use it when you have a lot of sockets
426	(for which it usually works), by embedding it into another event loop	639	(for which it usually works), by embedding it into another event loop
427	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for	640	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
428	sockets.	641	also broken on OS X)) and, did I mention it, using it only for sockets.
		642
		643	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		644	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		645	C<NOTE_EOF>.
429		646
430	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	647	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
431		648
432	This is not implemented yet (and might never be, unless you send me an	649	This is not implemented yet (and might never be, unless you send me an
433	implementation). According to reports, C</dev/poll> only supports sockets	650	implementation). According to reports, C</dev/poll> only supports sockets
…		…
437	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	654	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
438		655
439	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	656	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
440	it's really slow, but it still scales very well (O(active_fds)).	657	it's really slow, but it still scales very well (O(active_fds)).
441		658
442	Please note that Solaris event ports can deliver a lot of spurious
443	notifications, so you need to use non-blocking I/O or other means to avoid
444	blocking when no data (or space) is available.
445
446	While this backend scales well, it requires one system call per active	659	While this backend scales well, it requires one system call per active
447	file descriptor per loop iteration. For small and medium numbers of file	660	file descriptor per loop iteration. For small and medium numbers of file
448	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	661	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
449	might perform better.	662	might perform better.
450		663
451	On the positive side, ignoring the spurious readiness notifications, this	664	On the positive side, this backend actually performed fully to
452	backend actually performed to specification in all tests and is fully	665	specification in all tests and is fully embeddable, which is a rare feat
453	embeddable, which is a rare feat among the OS-specific backends.	666	among the OS-specific backends (I vastly prefer correctness over speed
		667	hacks).
		668
		669	On the negative side, the interface is I<bizarre> - so bizarre that
		670	even sun itself gets it wrong in their code examples: The event polling
		671	function sometimes returns events to the caller even though an error
		672	occurred, but with no indication whether it has done so or not (yes, it's
		673	even documented that way) - deadly for edge-triggered interfaces where you
		674	absolutely have to know whether an event occurred or not because you have
		675	to re-arm the watcher.
		676
		677	Fortunately libev seems to be able to work around these idiocies.
		678
		679	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		680	C<EVBACKEND_POLL>.
454		681
455	=item C<EVBACKEND_ALL>	682	=item C<EVBACKEND_ALL>
456		683
457	Try all backends (even potentially broken ones that wouldn't be tried	684	Try all backends (even potentially broken ones that wouldn't be tried
458	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	685	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
459	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	686	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
460		687
461	It is definitely not recommended to use this flag.	688	It is definitely not recommended to use this flag, use whatever
		689	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		690	at all.
		691
		692	=item C<EVBACKEND_MASK>
		693
		694	Not a backend at all, but a mask to select all backend bits from a
		695	C<flags> value, in case you want to mask out any backends from a flags
		696	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
462		697
463	=back	698	=back
464		699
465	If one or more of these are or'ed into the flags value, then only these	700	If one or more of the backend flags are or'ed into the flags value,
466	backends will be tried (in the reverse order as listed here). If none are	701	then only these backends will be tried (in the reverse order as listed
467	specified, all backends in C<ev_recommended_backends ()> will be tried.	702	here). If none are specified, all backends in C<ev_recommended_backends
468		703	()> will be tried.
469	The most typical usage is like this:
470
471	if (!ev_default_loop (0))
472	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
473
474	Restrict libev to the select and poll backends, and do not allow
475	environment settings to be taken into account:
476
477	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
478
479	Use whatever libev has to offer, but make sure that kqueue is used if
480	available (warning, breaks stuff, best use only with your own private
481	event loop and only if you know the OS supports your types of fds):
482
483	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
484
485	=item struct ev_loop *ev_loop_new (unsigned int flags)
486
487	Similar to C<ev_default_loop>, but always creates a new event loop that is
488	always distinct from the default loop. Unlike the default loop, it cannot
489	handle signal and child watchers, and attempts to do so will be greeted by
490	undefined behaviour (or a failed assertion if assertions are enabled).
491
492	Note that this function I<is> thread-safe, and the recommended way to use
493	libev with threads is indeed to create one loop per thread, and using the
494	default loop in the "main" or "initial" thread.
495		704
496	Example: Try to create a event loop that uses epoll and nothing else.	705	Example: Try to create a event loop that uses epoll and nothing else.
497		706
498	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	707	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
499	if (!epoller)	708	if (!epoller)
500	fatal ("no epoll found here, maybe it hides under your chair");	709	fatal ("no epoll found here, maybe it hides under your chair");
501		710
		711	Example: Use whatever libev has to offer, but make sure that kqueue is
		712	used if available.
		713
		714	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		715
		716	Example: Similarly, on linux, you mgiht want to take advantage of the
		717	linux aio backend if possible, but fall back to something else if that
		718	isn't available.
		719
		720	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_LINUXAIO);
		721
502	=item ev_default_destroy ()	722	=item ev_loop_destroy (loop)
503		723
504	Destroys the default loop again (frees all memory and kernel state	724	Destroys an event loop object (frees all memory and kernel state
505	etc.). None of the active event watchers will be stopped in the normal	725	etc.). None of the active event watchers will be stopped in the normal
506	sense, so e.g. C<ev_is_active> might still return true. It is your	726	sense, so e.g. C<ev_is_active> might still return true. It is your
507	responsibility to either stop all watchers cleanly yourself I<before>	727	responsibility to either stop all watchers cleanly yourself I<before>
508	calling this function, or cope with the fact afterwards (which is usually	728	calling this function, or cope with the fact afterwards (which is usually
509	the easiest thing, you can just ignore the watchers and/or C<free ()> them	729	the easiest thing, you can just ignore the watchers and/or C<free ()> them
510	for example).	730	for example).
511		731
512	Note that certain global state, such as signal state, will not be freed by	732	Note that certain global state, such as signal state (and installed signal
513	this function, and related watchers (such as signal and child watchers)	733	handlers), will not be freed by this function, and related watchers (such
514	would need to be stopped manually.	734	as signal and child watchers) would need to be stopped manually.
515		735
516	In general it is not advisable to call this function except in the	736	This function is normally used on loop objects allocated by
517	rare occasion where you really need to free e.g. the signal handling	737	C<ev_loop_new>, but it can also be used on the default loop returned by
		738	C<ev_default_loop>, in which case it is not thread-safe.
		739
		740	Note that it is not advisable to call this function on the default loop
		741	except in the rare occasion where you really need to free its resources.
518	pipe fds. If you need dynamically allocated loops it is better to use	742	If you need dynamically allocated loops it is better to use C<ev_loop_new>
519	C<ev_loop_new> and C<ev_loop_destroy>).	743	and C<ev_loop_destroy>.
520		744
521	=item ev_loop_destroy (loop)	745	=item ev_loop_fork (loop)
522		746
523	Like C<ev_default_destroy>, but destroys an event loop created by an
524	earlier call to C<ev_loop_new>.
525
526	=item ev_default_fork ()
527
528	This function sets a flag that causes subsequent C<ev_loop> iterations	747	This function sets a flag that causes subsequent C<ev_run> iterations
529	to reinitialise the kernel state for backends that have one. Despite the	748	to reinitialise the kernel state for backends that have one. Despite
530	name, you can call it anytime, but it makes most sense after forking, in	749	the name, you can call it anytime you are allowed to start or stop
531	the child process (or both child and parent, but that again makes little	750	watchers (except inside an C<ev_prepare> callback), but it makes most
532	sense). You I<must> call it in the child before using any of the libev	751	sense after forking, in the child process. You I<must> call it (or use
533	functions, and it will only take effect at the next C<ev_loop> iteration.	752	C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.
		753
		754	In addition, if you want to reuse a loop (via this function or
		755	C<EVFLAG_FORKCHECK>), you I<also> have to ignore C<SIGPIPE>.
		756
		757	Again, you I<have> to call it on I<any> loop that you want to re-use after
		758	a fork, I<even if you do not plan to use the loop in the parent>. This is
		759	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		760	during fork.
534		761
535	On the other hand, you only need to call this function in the child	762	On the other hand, you only need to call this function in the child
536	process if and only if you want to use the event library in the child. If	763	process if and only if you want to use the event loop in the child. If
537	you just fork+exec, you don't have to call it at all.	764	you just fork+exec or create a new loop in the child, you don't have to
		765	call it at all (in fact, C<epoll> is so badly broken that it makes a
		766	difference, but libev will usually detect this case on its own and do a
		767	costly reset of the backend).
538		768
539	The function itself is quite fast and it's usually not a problem to call	769	The function itself is quite fast and it's usually not a problem to call
540	it just in case after a fork. To make this easy, the function will fit in	770	it just in case after a fork.
541	quite nicely into a call to C<pthread_atfork>:
542		771
		772	Example: Automate calling C<ev_loop_fork> on the default loop when
		773	using pthreads.
		774
		775	static void
		776	post_fork_child (void)
		777	{
		778	ev_loop_fork (EV_DEFAULT);
		779	}
		780
		781	...
543	pthread_atfork (0, 0, ev_default_fork);	782	pthread_atfork (0, 0, post_fork_child);
544
545	=item ev_loop_fork (loop)
546
547	Like C<ev_default_fork>, but acts on an event loop created by
548	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
549	after fork, and how you do this is entirely your own problem.
550		783
551	=item int ev_is_default_loop (loop)	784	=item int ev_is_default_loop (loop)
552		785
553	Returns true when the given loop actually is the default loop, false otherwise.	786	Returns true when the given loop is, in fact, the default loop, and false
		787	otherwise.
554		788
555	=item unsigned int ev_loop_count (loop)	789	=item unsigned int ev_iteration (loop)
556		790
557	Returns the count of loop iterations for the loop, which is identical to	791	Returns the current iteration count for the event loop, which is identical
558	the number of times libev did poll for new events. It starts at C<0> and	792	to the number of times libev did poll for new events. It starts at C<0>
559	happily wraps around with enough iterations.	793	and happily wraps around with enough iterations.
560		794
561	This value can sometimes be useful as a generation counter of sorts (it	795	This value can sometimes be useful as a generation counter of sorts (it
562	"ticks" the number of loop iterations), as it roughly corresponds with	796	"ticks" the number of loop iterations), as it roughly corresponds with
563	C<ev_prepare> and C<ev_check> calls.	797	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		798	prepare and check phases.
		799
		800	=item unsigned int ev_depth (loop)
		801
		802	Returns the number of times C<ev_run> was entered minus the number of
		803	times C<ev_run> was exited normally, in other words, the recursion depth.
		804
		805	Outside C<ev_run>, this number is zero. In a callback, this number is
		806	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
		807	in which case it is higher.
		808
		809	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
		810	throwing an exception etc.), doesn't count as "exit" - consider this
		811	as a hint to avoid such ungentleman-like behaviour unless it's really
		812	convenient, in which case it is fully supported.
564		813
565	=item unsigned int ev_backend (loop)	814	=item unsigned int ev_backend (loop)
566		815
567	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	816	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
568	use.	817	use.
…		…
577		826
578	=item ev_now_update (loop)	827	=item ev_now_update (loop)
579		828
580	Establishes the current time by querying the kernel, updating the time	829	Establishes the current time by querying the kernel, updating the time
581	returned by C<ev_now ()> in the progress. This is a costly operation and	830	returned by C<ev_now ()> in the progress. This is a costly operation and
582	is usually done automatically within C<ev_loop ()>.	831	is usually done automatically within C<ev_run ()>.
583		832
584	This function is rarely useful, but when some event callback runs for a	833	This function is rarely useful, but when some event callback runs for a
585	very long time without entering the event loop, updating libev's idea of	834	very long time without entering the event loop, updating libev's idea of
586	the current time is a good idea.	835	the current time is a good idea.
587		836
588	See also "The special problem of time updates" in the C<ev_timer> section.	837	See also L</The special problem of time updates> in the C<ev_timer> section.
589		838
		839	=item ev_suspend (loop)
		840
		841	=item ev_resume (loop)
		842
		843	These two functions suspend and resume an event loop, for use when the
		844	loop is not used for a while and timeouts should not be processed.
		845
		846	A typical use case would be an interactive program such as a game: When
		847	the user presses C<^Z> to suspend the game and resumes it an hour later it
		848	would be best to handle timeouts as if no time had actually passed while
		849	the program was suspended. This can be achieved by calling C<ev_suspend>
		850	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		851	C<ev_resume> directly afterwards to resume timer processing.
		852
		853	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		854	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		855	will be rescheduled (that is, they will lose any events that would have
		856	occurred while suspended).
		857
		858	After calling C<ev_suspend> you B<must not> call I<any> function on the
		859	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		860	without a previous call to C<ev_suspend>.
		861
		862	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		863	event loop time (see C<ev_now_update>).
		864
590	=item ev_loop (loop, int flags)	865	=item bool ev_run (loop, int flags)
591		866
592	Finally, this is it, the event handler. This function usually is called	867	Finally, this is it, the event handler. This function usually is called
593	after you initialised all your watchers and you want to start handling	868	after you have initialised all your watchers and you want to start
594	events.	869	handling events. It will ask the operating system for any new events, call
		870	the watcher callbacks, and then repeat the whole process indefinitely: This
		871	is why event loops are called I<loops>.
595		872
596	If the flags argument is specified as C<0>, it will not return until	873	If the flags argument is specified as C<0>, it will keep handling events
597	either no event watchers are active anymore or C<ev_unloop> was called.	874	until either no event watchers are active anymore or C<ev_break> was
		875	called.
598		876
		877	The return value is false if there are no more active watchers (which
		878	usually means "all jobs done" or "deadlock"), and true in all other cases
		879	(which usually means " you should call C<ev_run> again").
		880
599	Please note that an explicit C<ev_unloop> is usually better than	881	Please note that an explicit C<ev_break> is usually better than
600	relying on all watchers to be stopped when deciding when a program has	882	relying on all watchers to be stopped when deciding when a program has
601	finished (especially in interactive programs), but having a program that	883	finished (especially in interactive programs), but having a program
602	automatically loops as long as it has to and no longer by virtue of	884	that automatically loops as long as it has to and no longer by virtue
603	relying on its watchers stopping correctly is a thing of beauty.	885	of relying on its watchers stopping correctly, that is truly a thing of
		886	beauty.
604		887
		888	This function is I<mostly> exception-safe - you can break out of a
		889	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		890	exception and so on. This does not decrement the C<ev_depth> value, nor
		891	will it clear any outstanding C<EVBREAK_ONE> breaks.
		892
605	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	893	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
606	those events and any outstanding ones, but will not block your process in	894	those events and any already outstanding ones, but will not wait and
607	case there are no events and will return after one iteration of the loop.	895	block your process in case there are no events and will return after one
		896	iteration of the loop. This is sometimes useful to poll and handle new
		897	events while doing lengthy calculations, to keep the program responsive.
608		898
609	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	899	A flags value of C<EVRUN_ONCE> will look for new events (waiting if
610	necessary) and will handle those and any outstanding ones. It will block	900	necessary) and will handle those and any already outstanding ones. It
611	your process until at least one new event arrives, and will return after	901	will block your process until at least one new event arrives (which could
612	one iteration of the loop. This is useful if you are waiting for some	902	be an event internal to libev itself, so there is no guarantee that a
613	external event in conjunction with something not expressible using other	903	user-registered callback will be called), and will return after one
		904	iteration of the loop.
		905
		906	This is useful if you are waiting for some external event in conjunction
		907	with something not expressible using other libev watchers (i.e. "roll your
614	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	908	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
615	usually a better approach for this kind of thing.	909	usually a better approach for this kind of thing.
616		910
617	Here are the gory details of what C<ev_loop> does:	911	Here are the gory details of what C<ev_run> does (this is for your
		912	understanding, not a guarantee that things will work exactly like this in
		913	future versions):
618		914
		915	- Increment loop depth.
		916	- Reset the ev_break status.
619	- Before the first iteration, call any pending watchers.	917	- Before the first iteration, call any pending watchers.
		918	LOOP:
620	* If EVFLAG_FORKCHECK was used, check for a fork.	919	- If EVFLAG_FORKCHECK was used, check for a fork.
621	- If a fork was detected (by any means), queue and call all fork watchers.	920	- If a fork was detected (by any means), queue and call all fork watchers.
622	- Queue and call all prepare watchers.	921	- Queue and call all prepare watchers.
		922	- If ev_break was called, goto FINISH.
623	- If we have been forked, detach and recreate the kernel state	923	- If we have been forked, detach and recreate the kernel state
624	as to not disturb the other process.	924	as to not disturb the other process.
625	- Update the kernel state with all outstanding changes.	925	- Update the kernel state with all outstanding changes.
626	- Update the "event loop time" (ev_now ()).	926	- Update the "event loop time" (ev_now ()).
627	- Calculate for how long to sleep or block, if at all	927	- Calculate for how long to sleep or block, if at all
628	(active idle watchers, EVLOOP_NONBLOCK or not having	928	(active idle watchers, EVRUN_NOWAIT or not having
629	any active watchers at all will result in not sleeping).	929	any active watchers at all will result in not sleeping).
630	- Sleep if the I/O and timer collect interval say so.	930	- Sleep if the I/O and timer collect interval say so.
		931	- Increment loop iteration counter.
631	- Block the process, waiting for any events.	932	- Block the process, waiting for any events.
632	- Queue all outstanding I/O (fd) events.	933	- Queue all outstanding I/O (fd) events.
633	- Update the "event loop time" (ev_now ()), and do time jump adjustments.	934	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
634	- Queue all outstanding timers.	935	- Queue all expired timers.
635	- Queue all outstanding periodics.	936	- Queue all expired periodics.
636	- Unless any events are pending now, queue all idle watchers.	937	- Queue all idle watchers with priority higher than that of pending events.
637	- Queue all check watchers.	938	- Queue all check watchers.
638	- Call all queued watchers in reverse order (i.e. check watchers first).	939	- Call all queued watchers in reverse order (i.e. check watchers first).
639	Signals and child watchers are implemented as I/O watchers, and will	940	Signals and child watchers are implemented as I/O watchers, and will
640	be handled here by queueing them when their watcher gets executed.	941	be handled here by queueing them when their watcher gets executed.
641	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	942	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
642	were used, or there are no active watchers, return, otherwise	943	were used, or there are no active watchers, goto FINISH, otherwise
643	continue with step *.	944	continue with step LOOP.
		945	FINISH:
		946	- Reset the ev_break status iff it was EVBREAK_ONE.
		947	- Decrement the loop depth.
		948	- Return.
644		949
645	Example: Queue some jobs and then loop until no events are outstanding	950	Example: Queue some jobs and then loop until no events are outstanding
646	anymore.	951	anymore.
647		952
648	... queue jobs here, make sure they register event watchers as long	953	... queue jobs here, make sure they register event watchers as long
649	... as they still have work to do (even an idle watcher will do..)	954	... as they still have work to do (even an idle watcher will do..)
650	ev_loop (my_loop, 0);	955	ev_run (my_loop, 0);
651	... jobs done or somebody called unloop. yeah!	956	... jobs done or somebody called break. yeah!
652		957
653	=item ev_unloop (loop, how)	958	=item ev_break (loop, how)
654		959
655	Can be used to make a call to C<ev_loop> return early (but only after it	960	Can be used to make a call to C<ev_run> return early (but only after it
656	has processed all outstanding events). The C<how> argument must be either	961	has processed all outstanding events). The C<how> argument must be either
657	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	962	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
658	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	963	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
659		964
660	This "unloop state" will be cleared when entering C<ev_loop> again.	965	This "break state" will be cleared on the next call to C<ev_run>.
		966
		967	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		968	which case it will have no effect.
661		969
662	=item ev_ref (loop)	970	=item ev_ref (loop)
663		971
664	=item ev_unref (loop)	972	=item ev_unref (loop)
665		973
666	Ref/unref can be used to add or remove a reference count on the event	974	Ref/unref can be used to add or remove a reference count on the event
667	loop: Every watcher keeps one reference, and as long as the reference	975	loop: Every watcher keeps one reference, and as long as the reference
668	count is nonzero, C<ev_loop> will not return on its own. If you have	976	count is nonzero, C<ev_run> will not return on its own.
669	a watcher you never unregister that should not keep C<ev_loop> from	977
670	returning, ev_unref() after starting, and ev_ref() before stopping it. For	978	This is useful when you have a watcher that you never intend to
		979	unregister, but that nevertheless should not keep C<ev_run> from
		980	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		981	before stopping it.
		982
671	example, libev itself uses this for its internal signal pipe: It is not	983	As an example, libev itself uses this for its internal signal pipe: It
672	visible to the libev user and should not keep C<ev_loop> from exiting if	984	is not visible to the libev user and should not keep C<ev_run> from
673	no event watchers registered by it are active. It is also an excellent	985	exiting if no event watchers registered by it are active. It is also an
674	way to do this for generic recurring timers or from within third-party	986	excellent way to do this for generic recurring timers or from within
675	libraries. Just remember to I<unref after start> and I<ref before stop>	987	third-party libraries. Just remember to I<unref after start> and I<ref
676	(but only if the watcher wasn't active before, or was active before,	988	before stop> (but only if the watcher wasn't active before, or was active
677	respectively).	989	before, respectively. Note also that libev might stop watchers itself
		990	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		991	in the callback).
678		992
679	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	993	Example: Create a signal watcher, but keep it from keeping C<ev_run>
680	running when nothing else is active.	994	running when nothing else is active.
681		995
682	struct ev_signal exitsig;	996	ev_signal exitsig;
683	ev_signal_init (&exitsig, sig_cb, SIGINT);	997	ev_signal_init (&exitsig, sig_cb, SIGINT);
684	ev_signal_start (loop, &exitsig);	998	ev_signal_start (loop, &exitsig);
685	evf_unref (loop);	999	ev_unref (loop);
686		1000
687	Example: For some weird reason, unregister the above signal handler again.	1001	Example: For some weird reason, unregister the above signal handler again.
688		1002
689	ev_ref (loop);	1003	ev_ref (loop);
690	ev_signal_stop (loop, &exitsig);	1004	ev_signal_stop (loop, &exitsig);
…		…
701	Setting these to a higher value (the C<interval> I<must> be >= C<0>)	1015	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
702	allows libev to delay invocation of I/O and timer/periodic callbacks	1016	allows libev to delay invocation of I/O and timer/periodic callbacks
703	to increase efficiency of loop iterations (or to increase power-saving	1017	to increase efficiency of loop iterations (or to increase power-saving
704	opportunities).	1018	opportunities).
705		1019
706	The background is that sometimes your program runs just fast enough to	1020	The idea is that sometimes your program runs just fast enough to handle
707	handle one (or very few) event(s) per loop iteration. While this makes	1021	one (or very few) event(s) per loop iteration. While this makes the
708	the program responsive, it also wastes a lot of CPU time to poll for new	1022	program responsive, it also wastes a lot of CPU time to poll for new
709	events, especially with backends like C<select ()> which have a high	1023	events, especially with backends like C<select ()> which have a high
710	overhead for the actual polling but can deliver many events at once.	1024	overhead for the actual polling but can deliver many events at once.
711		1025
712	By setting a higher I<io collect interval> you allow libev to spend more	1026	By setting a higher I<io collect interval> you allow libev to spend more
713	time collecting I/O events, so you can handle more events per iteration,	1027	time collecting I/O events, so you can handle more events per iteration,
714	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	1028	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
715	C<ev_timer>) will be not affected. Setting this to a non-null value will	1029	C<ev_timer>) will not be affected. Setting this to a non-null value will
716	introduce an additional C<ev_sleep ()> call into most loop iterations.	1030	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		1031	sleep time ensures that libev will not poll for I/O events more often then
		1032	once per this interval, on average (as long as the host time resolution is
		1033	good enough).
717		1034
718	Likewise, by setting a higher I<timeout collect interval> you allow libev	1035	Likewise, by setting a higher I<timeout collect interval> you allow libev
719	to spend more time collecting timeouts, at the expense of increased	1036	to spend more time collecting timeouts, at the expense of increased
720	latency (the watcher callback will be called later). C<ev_io> watchers	1037	latency/jitter/inexactness (the watcher callback will be called
721	will not be affected. Setting this to a non-null value will not introduce	1038	later). C<ev_io> watchers will not be affected. Setting this to a non-null
722	any overhead in libev.	1039	value will not introduce any overhead in libev.
723		1040
724	Many (busy) programs can usually benefit by setting the I/O collect	1041	Many (busy) programs can usually benefit by setting the I/O collect
725	interval to a value near C<0.1> or so, which is often enough for	1042	interval to a value near C<0.1> or so, which is often enough for
726	interactive servers (of course not for games), likewise for timeouts. It	1043	interactive servers (of course not for games), likewise for timeouts. It
727	usually doesn't make much sense to set it to a lower value than C<0.01>,	1044	usually doesn't make much sense to set it to a lower value than C<0.01>,
728	as this approaches the timing granularity of most systems.	1045	as this approaches the timing granularity of most systems. Note that if
		1046	you do transactions with the outside world and you can't increase the
		1047	parallelity, then this setting will limit your transaction rate (if you
		1048	need to poll once per transaction and the I/O collect interval is 0.01,
		1049	then you can't do more than 100 transactions per second).
729		1050
730	Setting the I<timeout collect interval> can improve the opportunity for	1051	Setting the I<timeout collect interval> can improve the opportunity for
731	saving power, as the program will "bundle" timer callback invocations that	1052	saving power, as the program will "bundle" timer callback invocations that
732	are "near" in time together, by delaying some, thus reducing the number of	1053	are "near" in time together, by delaying some, thus reducing the number of
733	times the process sleeps and wakes up again. Another useful technique to	1054	times the process sleeps and wakes up again. Another useful technique to
734	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure	1055	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
735	they fire on, say, one-second boundaries only.	1056	they fire on, say, one-second boundaries only.
736		1057
		1058	Example: we only need 0.1s timeout granularity, and we wish not to poll
		1059	more often than 100 times per second:
		1060
		1061	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		1062	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		1063
		1064	=item ev_invoke_pending (loop)
		1065
		1066	This call will simply invoke all pending watchers while resetting their
		1067	pending state. Normally, C<ev_run> does this automatically when required,
		1068	but when overriding the invoke callback this call comes handy. This
		1069	function can be invoked from a watcher - this can be useful for example
		1070	when you want to do some lengthy calculation and want to pass further
		1071	event handling to another thread (you still have to make sure only one
		1072	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
		1073
		1074	=item int ev_pending_count (loop)
		1075
		1076	Returns the number of pending watchers - zero indicates that no watchers
		1077	are pending.
		1078
		1079	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		1080
		1081	This overrides the invoke pending functionality of the loop: Instead of
		1082	invoking all pending watchers when there are any, C<ev_run> will call
		1083	this callback instead. This is useful, for example, when you want to
		1084	invoke the actual watchers inside another context (another thread etc.).
		1085
		1086	If you want to reset the callback, use C<ev_invoke_pending> as new
		1087	callback.
		1088
		1089	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
		1090
		1091	Sometimes you want to share the same loop between multiple threads. This
		1092	can be done relatively simply by putting mutex_lock/unlock calls around
		1093	each call to a libev function.
		1094
		1095	However, C<ev_run> can run an indefinite time, so it is not feasible
		1096	to wait for it to return. One way around this is to wake up the event
		1097	loop via C<ev_break> and C<ev_async_send>, another way is to set these
		1098	I<release> and I<acquire> callbacks on the loop.
		1099
		1100	When set, then C<release> will be called just before the thread is
		1101	suspended waiting for new events, and C<acquire> is called just
		1102	afterwards.
		1103
		1104	Ideally, C<release> will just call your mutex_unlock function, and
		1105	C<acquire> will just call the mutex_lock function again.
		1106
		1107	While event loop modifications are allowed between invocations of
		1108	C<release> and C<acquire> (that's their only purpose after all), no
		1109	modifications done will affect the event loop, i.e. adding watchers will
		1110	have no effect on the set of file descriptors being watched, or the time
		1111	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		1112	to take note of any changes you made.
		1113
		1114	In theory, threads executing C<ev_run> will be async-cancel safe between
		1115	invocations of C<release> and C<acquire>.
		1116
		1117	See also the locking example in the C<THREADS> section later in this
		1118	document.
		1119
		1120	=item ev_set_userdata (loop, void *data)
		1121
		1122	=item void *ev_userdata (loop)
		1123
		1124	Set and retrieve a single C<void *> associated with a loop. When
		1125	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		1126	C<0>.
		1127
		1128	These two functions can be used to associate arbitrary data with a loop,
		1129	and are intended solely for the C<invoke_pending_cb>, C<release> and
		1130	C<acquire> callbacks described above, but of course can be (ab-)used for
		1131	any other purpose as well.
		1132
737	=item ev_loop_verify (loop)	1133	=item ev_verify (loop)
738		1134
739	This function only does something when C<EV_VERIFY> support has been	1135	This function only does something when C<EV_VERIFY> support has been
740	compiled in. It tries to go through all internal structures and checks	1136	compiled in, which is the default for non-minimal builds. It tries to go
741	them for validity. If anything is found to be inconsistent, it will print	1137	through all internal structures and checks them for validity. If anything
742	an error message to standard error and call C<abort ()>.	1138	is found to be inconsistent, it will print an error message to standard
		1139	error and call C<abort ()>.
743		1140
744	This can be used to catch bugs inside libev itself: under normal	1141	This can be used to catch bugs inside libev itself: under normal
745	circumstances, this function will never abort as of course libev keeps its	1142	circumstances, this function will never abort as of course libev keeps its
746	data structures consistent.	1143	data structures consistent.
747		1144
748	=back	1145	=back
749		1146
750		1147
751	=head1 ANATOMY OF A WATCHER	1148	=head1 ANATOMY OF A WATCHER
752		1149
		1150	In the following description, uppercase C<TYPE> in names stands for the
		1151	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		1152	watchers and C<ev_io_start> for I/O watchers.
		1153
753	A watcher is a structure that you create and register to record your	1154	A watcher is an opaque structure that you allocate and register to record
754	interest in some event. For instance, if you want to wait for STDIN to	1155	your interest in some event. To make a concrete example, imagine you want
755	become readable, you would create an C<ev_io> watcher for that:	1156	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1157	for that:
756		1158
757	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1159	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
758	{	1160	{
759	ev_io_stop (w);	1161	ev_io_stop (w);
760	ev_unloop (loop, EVUNLOOP_ALL);	1162	ev_break (loop, EVBREAK_ALL);
761	}	1163	}
762		1164
763	struct ev_loop *loop = ev_default_loop (0);	1165	struct ev_loop *loop = ev_default_loop (0);
		1166
764	struct ev_io stdin_watcher;	1167	ev_io stdin_watcher;
		1168
765	ev_init (&stdin_watcher, my_cb);	1169	ev_init (&stdin_watcher, my_cb);
766	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1170	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
767	ev_io_start (loop, &stdin_watcher);	1171	ev_io_start (loop, &stdin_watcher);
		1172
768	ev_loop (loop, 0);	1173	ev_run (loop, 0);
769		1174
770	As you can see, you are responsible for allocating the memory for your	1175	As you can see, you are responsible for allocating the memory for your
771	watcher structures (and it is usually a bad idea to do this on the stack,	1176	watcher structures (and it is I<usually> a bad idea to do this on the
772	although this can sometimes be quite valid).	1177	stack).
773		1178
		1179	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1180	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1181
774	Each watcher structure must be initialised by a call to C<ev_init	1182	Each watcher structure must be initialised by a call to C<ev_init (watcher
775	(watcher *, callback)>, which expects a callback to be provided. This	1183	*, callback)>, which expects a callback to be provided. This callback is
776	callback gets invoked each time the event occurs (or, in the case of I/O	1184	invoked each time the event occurs (or, in the case of I/O watchers, each
777	watchers, each time the event loop detects that the file descriptor given	1185	time the event loop detects that the file descriptor given is readable
778	is readable and/or writable).	1186	and/or writable).
779		1187
780	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1188	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
781	with arguments specific to this watcher type. There is also a macro	1189	macro to configure it, with arguments specific to the watcher type. There
782	to combine initialisation and setting in one call: C<< ev_<type>_init	1190	is also a macro to combine initialisation and setting in one call: C<<
783	(watcher *, callback, ...) >>.	1191	ev_TYPE_init (watcher *, callback, ...) >>.
784		1192
785	To make the watcher actually watch out for events, you have to start it	1193	To make the watcher actually watch out for events, you have to start it
786	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1194	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
787	*) >>), and you can stop watching for events at any time by calling the	1195	*) >>), and you can stop watching for events at any time by calling the
788	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1196	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
789		1197
790	As long as your watcher is active (has been started but not stopped) you	1198	As long as your watcher is active (has been started but not stopped) you
791	must not touch the values stored in it. Most specifically you must never	1199	must not touch the values stored in it. Most specifically you must never
792	reinitialise it or call its C<set> macro.	1200	reinitialise it or call its C<ev_TYPE_set> macro.
793		1201
794	Each and every callback receives the event loop pointer as first, the	1202	Each and every callback receives the event loop pointer as first, the
795	registered watcher structure as second, and a bitset of received events as	1203	registered watcher structure as second, and a bitset of received events as
796	third argument.	1204	third argument.
797		1205
…		…
806	=item C<EV_WRITE>	1214	=item C<EV_WRITE>
807		1215
808	The file descriptor in the C<ev_io> watcher has become readable and/or	1216	The file descriptor in the C<ev_io> watcher has become readable and/or
809	writable.	1217	writable.
810		1218
811	=item C<EV_TIMEOUT>	1219	=item C<EV_TIMER>
812		1220
813	The C<ev_timer> watcher has timed out.	1221	The C<ev_timer> watcher has timed out.
814		1222
815	=item C<EV_PERIODIC>	1223	=item C<EV_PERIODIC>
816		1224
…		…
834		1242
835	=item C<EV_PREPARE>	1243	=item C<EV_PREPARE>
836		1244
837	=item C<EV_CHECK>	1245	=item C<EV_CHECK>
838		1246
839	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts	1247	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts to
840	to gather new events, and all C<ev_check> watchers are invoked just after	1248	gather new events, and all C<ev_check> watchers are queued (not invoked)
841	C<ev_loop> has gathered them, but before it invokes any callbacks for any	1249	just after C<ev_run> has gathered them, but before it queues any callbacks
		1250	for any received events. That means C<ev_prepare> watchers are the last
		1251	watchers invoked before the event loop sleeps or polls for new events, and
		1252	C<ev_check> watchers will be invoked before any other watchers of the same
		1253	or lower priority within an event loop iteration.
		1254
842	received events. Callbacks of both watcher types can start and stop as	1255	Callbacks of both watcher types can start and stop as many watchers as
843	many watchers as they want, and all of them will be taken into account	1256	they want, and all of them will be taken into account (for example, a
844	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1257	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
845	C<ev_loop> from blocking).	1258	blocking).
846		1259
847	=item C<EV_EMBED>	1260	=item C<EV_EMBED>
848		1261
849	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1262	The embedded event loop specified in the C<ev_embed> watcher needs attention.
850		1263
851	=item C<EV_FORK>	1264	=item C<EV_FORK>
852		1265
853	The event loop has been resumed in the child process after fork (see	1266	The event loop has been resumed in the child process after fork (see
854	C<ev_fork>).	1267	C<ev_fork>).
855		1268
		1269	=item C<EV_CLEANUP>
		1270
		1271	The event loop is about to be destroyed (see C<ev_cleanup>).
		1272
856	=item C<EV_ASYNC>	1273	=item C<EV_ASYNC>
857		1274
858	The given async watcher has been asynchronously notified (see C<ev_async>).	1275	The given async watcher has been asynchronously notified (see C<ev_async>).
		1276
		1277	=item C<EV_CUSTOM>
		1278
		1279	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1280	by libev users to signal watchers (e.g. via C<ev_feed_event>).
859		1281
860	=item C<EV_ERROR>	1282	=item C<EV_ERROR>
861		1283
862	An unspecified error has occurred, the watcher has been stopped. This might	1284	An unspecified error has occurred, the watcher has been stopped. This might
863	happen because the watcher could not be properly started because libev	1285	happen because the watcher could not be properly started because libev
864	ran out of memory, a file descriptor was found to be closed or any other	1286	ran out of memory, a file descriptor was found to be closed or any other
		1287	problem. Libev considers these application bugs.
		1288
865	problem. You best act on it by reporting the problem and somehow coping	1289	You best act on it by reporting the problem and somehow coping with the
866	with the watcher being stopped.	1290	watcher being stopped. Note that well-written programs should not receive
		1291	an error ever, so when your watcher receives it, this usually indicates a
		1292	bug in your program.
867		1293
868	Libev will usually signal a few "dummy" events together with an error,	1294	Libev will usually signal a few "dummy" events together with an error, for
869	for example it might indicate that a fd is readable or writable, and if	1295	example it might indicate that a fd is readable or writable, and if your
870	your callbacks is well-written it can just attempt the operation and cope	1296	callbacks is well-written it can just attempt the operation and cope with
871	with the error from read() or write(). This will not work in multi-threaded	1297	the error from read() or write(). This will not work in multi-threaded
872	programs, though, so beware.	1298	programs, though, as the fd could already be closed and reused for another
		1299	thing, so beware.
873		1300
874	=back	1301	=back
875		1302
876	=head2 GENERIC WATCHER FUNCTIONS	1303	=head2 GENERIC WATCHER FUNCTIONS
877
878	In the following description, C<TYPE> stands for the watcher type,
879	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
880		1304
881	=over 4	1305	=over 4
882		1306
883	=item C<ev_init> (ev_TYPE *watcher, callback)	1307	=item C<ev_init> (ev_TYPE *watcher, callback)
884		1308
…		…
890	which rolls both calls into one.	1314	which rolls both calls into one.
891		1315
892	You can reinitialise a watcher at any time as long as it has been stopped	1316	You can reinitialise a watcher at any time as long as it has been stopped
893	(or never started) and there are no pending events outstanding.	1317	(or never started) and there are no pending events outstanding.
894		1318
895	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1319	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
896	int revents)>.	1320	int revents)>.
897		1321
		1322	Example: Initialise an C<ev_io> watcher in two steps.
		1323
		1324	ev_io w;
		1325	ev_init (&w, my_cb);
		1326	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1327
898	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1328	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
899		1329
900	This macro initialises the type-specific parts of a watcher. You need to	1330	This macro initialises the type-specific parts of a watcher. You need to
901	call C<ev_init> at least once before you call this macro, but you can	1331	call C<ev_init> at least once before you call this macro, but you can
902	call C<ev_TYPE_set> any number of times. You must not, however, call this	1332	call C<ev_TYPE_set> any number of times. You must not, however, call this
903	macro on a watcher that is active (it can be pending, however, which is a	1333	macro on a watcher that is active (it can be pending, however, which is a
904	difference to the C<ev_init> macro).	1334	difference to the C<ev_init> macro).
905		1335
906	Although some watcher types do not have type-specific arguments	1336	Although some watcher types do not have type-specific arguments
907	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1337	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
908		1338
		1339	See C<ev_init>, above, for an example.
		1340
909	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1341	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
910		1342
911	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1343	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
912	calls into a single call. This is the most convenient method to initialise	1344	calls into a single call. This is the most convenient method to initialise
913	a watcher. The same limitations apply, of course.	1345	a watcher. The same limitations apply, of course.
914		1346
		1347	Example: Initialise and set an C<ev_io> watcher in one step.
		1348
		1349	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1350
915	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1351	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
916		1352
917	Starts (activates) the given watcher. Only active watchers will receive	1353	Starts (activates) the given watcher. Only active watchers will receive
918	events. If the watcher is already active nothing will happen.	1354	events. If the watcher is already active nothing will happen.
919		1355
		1356	Example: Start the C<ev_io> watcher that is being abused as example in this
		1357	whole section.
		1358
		1359	ev_io_start (EV_DEFAULT_UC, &w);
		1360
920	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1361	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
921		1362
922	Stops the given watcher again (if active) and clears the pending	1363	Stops the given watcher if active, and clears the pending status (whether
		1364	the watcher was active or not).
		1365
923	status. It is possible that stopped watchers are pending (for example,	1366	It is possible that stopped watchers are pending - for example,
924	non-repeating timers are being stopped when they become pending), but	1367	non-repeating timers are being stopped when they become pending - but
925	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1368	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
926	you want to free or reuse the memory used by the watcher it is therefore a	1369	pending. If you want to free or reuse the memory used by the watcher it is
927	good idea to always call its C<ev_TYPE_stop> function.	1370	therefore a good idea to always call its C<ev_TYPE_stop> function.
928		1371
929	=item bool ev_is_active (ev_TYPE *watcher)	1372	=item bool ev_is_active (ev_TYPE *watcher)
930		1373
931	Returns a true value iff the watcher is active (i.e. it has been started	1374	Returns a true value iff the watcher is active (i.e. it has been started
932	and not yet been stopped). As long as a watcher is active you must not modify	1375	and not yet been stopped). As long as a watcher is active you must not modify
…		…
943		1386
944	=item callback ev_cb (ev_TYPE *watcher)	1387	=item callback ev_cb (ev_TYPE *watcher)
945		1388
946	Returns the callback currently set on the watcher.	1389	Returns the callback currently set on the watcher.
947		1390
948	=item ev_cb_set (ev_TYPE *watcher, callback)	1391	=item ev_set_cb (ev_TYPE *watcher, callback)
949		1392
950	Change the callback. You can change the callback at virtually any time	1393	Change the callback. You can change the callback at virtually any time
951	(modulo threads).	1394	(modulo threads).
952		1395
953	=item ev_set_priority (ev_TYPE *watcher, priority)	1396	=item ev_set_priority (ev_TYPE *watcher, int priority)
954		1397
955	=item int ev_priority (ev_TYPE *watcher)	1398	=item int ev_priority (ev_TYPE *watcher)
956		1399
957	Set and query the priority of the watcher. The priority is a small	1400	Set and query the priority of the watcher. The priority is a small
958	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1401	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
959	(default: C<-2>). Pending watchers with higher priority will be invoked	1402	(default: C<-2>). Pending watchers with higher priority will be invoked
960	before watchers with lower priority, but priority will not keep watchers	1403	before watchers with lower priority, but priority will not keep watchers
961	from being executed (except for C<ev_idle> watchers).	1404	from being executed (except for C<ev_idle> watchers).
962		1405
963	This means that priorities are I<only> used for ordering callback
964	invocation after new events have been received. This is useful, for
965	example, to reduce latency after idling, or more often, to bind two
966	watchers on the same event and make sure one is called first.
967
968	If you need to suppress invocation when higher priority events are pending	1406	If you need to suppress invocation when higher priority events are pending
969	you need to look at C<ev_idle> watchers, which provide this functionality.	1407	you need to look at C<ev_idle> watchers, which provide this functionality.
970		1408
971	You I<must not> change the priority of a watcher as long as it is active or	1409	You I<must not> change the priority of a watcher as long as it is active or
972	pending.	1410	pending.
973		1411
		1412	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1413	fine, as long as you do not mind that the priority value you query might
		1414	or might not have been clamped to the valid range.
		1415
974	The default priority used by watchers when no priority has been set is	1416	The default priority used by watchers when no priority has been set is
975	always C<0>, which is supposed to not be too high and not be too low :).	1417	always C<0>, which is supposed to not be too high and not be too low :).
976		1418
977	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1419	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
978	fine, as long as you do not mind that the priority value you query might	1420	priorities.
979	or might not have been adjusted to be within valid range.
980		1421
981	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1422	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
982		1423
983	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1424	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
984	C<loop> nor C<revents> need to be valid as long as the watcher callback	1425	C<loop> nor C<revents> need to be valid as long as the watcher callback
985	can deal with that fact.	1426	can deal with that fact, as both are simply passed through to the
		1427	callback.
986		1428
987	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1429	=item int ev_clear_pending (loop, ev_TYPE *watcher)
988		1430
989	If the watcher is pending, this function returns clears its pending status	1431	If the watcher is pending, this function clears its pending status and
990	and returns its C<revents> bitset (as if its callback was invoked). If the	1432	returns its C<revents> bitset (as if its callback was invoked). If the
991	watcher isn't pending it does nothing and returns C<0>.	1433	watcher isn't pending it does nothing and returns C<0>.
992		1434
		1435	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1436	callback to be invoked, which can be accomplished with this function.
		1437
		1438	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1439
		1440	Feeds the given event set into the event loop, as if the specified event
		1441	had happened for the specified watcher (which must be a pointer to an
		1442	initialised but not necessarily started event watcher). Obviously you must
		1443	not free the watcher as long as it has pending events.
		1444
		1445	Stopping the watcher, letting libev invoke it, or calling
		1446	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1447	not started in the first place.
		1448
		1449	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1450	functions that do not need a watcher.
		1451
993	=back	1452	=back
994		1453
		1454	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
		1455	OWN COMPOSITE WATCHERS> idioms.
995		1456
996	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1457	=head2 WATCHER STATES
997		1458
998	Each watcher has, by default, a member C<void *data> that you can change	1459	There are various watcher states mentioned throughout this manual -
999	and read at any time, libev will completely ignore it. This can be used	1460	active, pending and so on. In this section these states and the rules to
1000	to associate arbitrary data with your watcher. If you need more data and	1461	transition between them will be described in more detail - and while these
1001	don't want to allocate memory and store a pointer to it in that data	1462	rules might look complicated, they usually do "the right thing".
1002	member, you can also "subclass" the watcher type and provide your own
1003	data:
1004		1463
1005	struct my_io	1464	=over 4
		1465
		1466	=item initialised
		1467
		1468	Before a watcher can be registered with the event loop it has to be
		1469	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
		1470	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
		1471
		1472	In this state it is simply some block of memory that is suitable for
		1473	use in an event loop. It can be moved around, freed, reused etc. at
		1474	will - as long as you either keep the memory contents intact, or call
		1475	C<ev_TYPE_init> again.
		1476
		1477	=item started/running/active
		1478
		1479	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
		1480	property of the event loop, and is actively waiting for events. While in
		1481	this state it cannot be accessed (except in a few documented ways), moved,
		1482	freed or anything else - the only legal thing is to keep a pointer to it,
		1483	and call libev functions on it that are documented to work on active watchers.
		1484
		1485	=item pending
		1486
		1487	If a watcher is active and libev determines that an event it is interested
		1488	in has occurred (such as a timer expiring), it will become pending. It will
		1489	stay in this pending state until either it is stopped or its callback is
		1490	about to be invoked, so it is not normally pending inside the watcher
		1491	callback.
		1492
		1493	The watcher might or might not be active while it is pending (for example,
		1494	an expired non-repeating timer can be pending but no longer active). If it
		1495	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1496	but it is still property of the event loop at this time, so cannot be
		1497	moved, freed or reused. And if it is active the rules described in the
		1498	previous item still apply.
		1499
		1500	It is also possible to feed an event on a watcher that is not active (e.g.
		1501	via C<ev_feed_event>), in which case it becomes pending without being
		1502	active.
		1503
		1504	=item stopped
		1505
		1506	A watcher can be stopped implicitly by libev (in which case it might still
		1507	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1508	latter will clear any pending state the watcher might be in, regardless
		1509	of whether it was active or not, so stopping a watcher explicitly before
		1510	freeing it is often a good idea.
		1511
		1512	While stopped (and not pending) the watcher is essentially in the
		1513	initialised state, that is, it can be reused, moved, modified in any way
		1514	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1515	it again).
		1516
		1517	=back
		1518
		1519	=head2 WATCHER PRIORITY MODELS
		1520
		1521	Many event loops support I<watcher priorities>, which are usually small
		1522	integers that influence the ordering of event callback invocation
		1523	between watchers in some way, all else being equal.
		1524
		1525	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1526	description for the more technical details such as the actual priority
		1527	range.
		1528
		1529	There are two common ways how these these priorities are being interpreted
		1530	by event loops:
		1531
		1532	In the more common lock-out model, higher priorities "lock out" invocation
		1533	of lower priority watchers, which means as long as higher priority
		1534	watchers receive events, lower priority watchers are not being invoked.
		1535
		1536	The less common only-for-ordering model uses priorities solely to order
		1537	callback invocation within a single event loop iteration: Higher priority
		1538	watchers are invoked before lower priority ones, but they all get invoked
		1539	before polling for new events.
		1540
		1541	Libev uses the second (only-for-ordering) model for all its watchers
		1542	except for idle watchers (which use the lock-out model).
		1543
		1544	The rationale behind this is that implementing the lock-out model for
		1545	watchers is not well supported by most kernel interfaces, and most event
		1546	libraries will just poll for the same events again and again as long as
		1547	their callbacks have not been executed, which is very inefficient in the
		1548	common case of one high-priority watcher locking out a mass of lower
		1549	priority ones.
		1550
		1551	Static (ordering) priorities are most useful when you have two or more
		1552	watchers handling the same resource: a typical usage example is having an
		1553	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1554	timeouts. Under load, data might be received while the program handles
		1555	other jobs, but since timers normally get invoked first, the timeout
		1556	handler will be executed before checking for data. In that case, giving
		1557	the timer a lower priority than the I/O watcher ensures that I/O will be
		1558	handled first even under adverse conditions (which is usually, but not
		1559	always, what you want).
		1560
		1561	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1562	will only be executed when no same or higher priority watchers have
		1563	received events, they can be used to implement the "lock-out" model when
		1564	required.
		1565
		1566	For example, to emulate how many other event libraries handle priorities,
		1567	you can associate an C<ev_idle> watcher to each such watcher, and in
		1568	the normal watcher callback, you just start the idle watcher. The real
		1569	processing is done in the idle watcher callback. This causes libev to
		1570	continuously poll and process kernel event data for the watcher, but when
		1571	the lock-out case is known to be rare (which in turn is rare :), this is
		1572	workable.
		1573
		1574	Usually, however, the lock-out model implemented that way will perform
		1575	miserably under the type of load it was designed to handle. In that case,
		1576	it might be preferable to stop the real watcher before starting the
		1577	idle watcher, so the kernel will not have to process the event in case
		1578	the actual processing will be delayed for considerable time.
		1579
		1580	Here is an example of an I/O watcher that should run at a strictly lower
		1581	priority than the default, and which should only process data when no
		1582	other events are pending:
		1583
		1584	ev_idle idle; // actual processing watcher
		1585	ev_io io; // actual event watcher
		1586
		1587	static void
		1588	io_cb (EV_P_ ev_io *w, int revents)
1006	{	1589	{
1007	struct ev_io io;	1590	// stop the I/O watcher, we received the event, but
1008	int otherfd;	1591	// are not yet ready to handle it.
1009	void *somedata;	1592	ev_io_stop (EV_A_ w);
1010	struct whatever *mostinteresting;	1593
		1594	// start the idle watcher to handle the actual event.
		1595	// it will not be executed as long as other watchers
		1596	// with the default priority are receiving events.
		1597	ev_idle_start (EV_A_ &idle);
1011	};	1598	}
1012		1599
1013	...	1600	static void
1014	struct my_io w;	1601	idle_cb (EV_P_ ev_idle *w, int revents)
1015	ev_io_init (&w.io, my_cb, fd, EV_READ);
1016
1017	And since your callback will be called with a pointer to the watcher, you
1018	can cast it back to your own type:
1019
1020	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
1021	{	1602	{
1022	struct my_io *w = (struct my_io *)w_;	1603	// actual processing
1023	...	1604	read (STDIN_FILENO, ...);
		1605
		1606	// have to start the I/O watcher again, as
		1607	// we have handled the event
		1608	ev_io_start (EV_P_ &io);
1024	}	1609	}
1025		1610
1026	More interesting and less C-conformant ways of casting your callback type	1611	// initialisation
1027	instead have been omitted.	1612	ev_idle_init (&idle, idle_cb);
		1613	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1614	ev_io_start (EV_DEFAULT_ &io);
1028		1615
1029	Another common scenario is to use some data structure with multiple	1616	In the "real" world, it might also be beneficial to start a timer, so that
1030	embedded watchers:	1617	low-priority connections can not be locked out forever under load. This
1031		1618	enables your program to keep a lower latency for important connections
1032	struct my_biggy	1619	during short periods of high load, while not completely locking out less
1033	{	1620	important ones.
1034	int some_data;
1035	ev_timer t1;
1036	ev_timer t2;
1037	}
1038
1039	In this case getting the pointer to C<my_biggy> is a bit more
1040	complicated: Either you store the address of your C<my_biggy> struct
1041	in the C<data> member of the watcher, or you need to use some pointer
1042	arithmetic using C<offsetof> inside your watchers:
1043
1044	#include <stddef.h>
1045
1046	static void
1047	t1_cb (EV_P_ struct ev_timer *w, int revents)
1048	{
1049	struct my_biggy big = (struct my_biggy *
1050	(((char *)w) - offsetof (struct my_biggy, t1));
1051	}
1052
1053	static void
1054	t2_cb (EV_P_ struct ev_timer *w, int revents)
1055	{
1056	struct my_biggy big = (struct my_biggy *
1057	(((char *)w) - offsetof (struct my_biggy, t2));
1058	}
1059		1621
1060		1622
1061	=head1 WATCHER TYPES	1623	=head1 WATCHER TYPES
1062		1624
1063	This section describes each watcher in detail, but will not repeat	1625	This section describes each watcher in detail, but will not repeat
…		…
1087	In general you can register as many read and/or write event watchers per	1649	In general you can register as many read and/or write event watchers per
1088	fd as you want (as long as you don't confuse yourself). Setting all file	1650	fd as you want (as long as you don't confuse yourself). Setting all file
1089	descriptors to non-blocking mode is also usually a good idea (but not	1651	descriptors to non-blocking mode is also usually a good idea (but not
1090	required if you know what you are doing).	1652	required if you know what you are doing).
1091		1653
1092	If you must do this, then force the use of a known-to-be-good backend
1093	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
1094	C<EVBACKEND_POLL>).
1095
1096	Another thing you have to watch out for is that it is quite easy to	1654	Another thing you have to watch out for is that it is quite easy to
1097	receive "spurious" readiness notifications, that is your callback might	1655	receive "spurious" readiness notifications, that is, your callback might
1098	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1656	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1099	because there is no data. Not only are some backends known to create a	1657	because there is no data. It is very easy to get into this situation even
1100	lot of those (for example Solaris ports), it is very easy to get into	1658	with a relatively standard program structure. Thus it is best to always
1101	this situation even with a relatively standard program structure. Thus	1659	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1102	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1103	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1660	preferable to a program hanging until some data arrives.
1104		1661
1105	If you cannot run the fd in non-blocking mode (for example you should not	1662	If you cannot run the fd in non-blocking mode (for example you should
1106	play around with an Xlib connection), then you have to separately re-test	1663	not play around with an Xlib connection), then you have to separately
1107	whether a file descriptor is really ready with a known-to-be good interface	1664	re-test whether a file descriptor is really ready with a known-to-be good
1108	such as poll (fortunately in our Xlib example, Xlib already does this on	1665	interface such as poll (fortunately in the case of Xlib, it already does
1109	its own, so its quite safe to use).	1666	this on its own, so its quite safe to use). Some people additionally
		1667	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1668	indefinitely.
		1669
		1670	But really, best use non-blocking mode.
1110		1671
1111	=head3 The special problem of disappearing file descriptors	1672	=head3 The special problem of disappearing file descriptors
1112		1673
1113	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1674	Some backends (e.g. kqueue, epoll, linuxaio) need to be told about closing
1114	descriptor (either by calling C<close> explicitly or by any other means,	1675	a file descriptor (either due to calling C<close> explicitly or any other
1115	such as C<dup>). The reason is that you register interest in some file	1676	means, such as C<dup2>). The reason is that you register interest in some
1116	descriptor, but when it goes away, the operating system will silently drop	1677	file descriptor, but when it goes away, the operating system will silently
1117	this interest. If another file descriptor with the same number then is	1678	drop this interest. If another file descriptor with the same number then
1118	registered with libev, there is no efficient way to see that this is, in	1679	is registered with libev, there is no efficient way to see that this is,
1119	fact, a different file descriptor.	1680	in fact, a different file descriptor.
1120		1681
1121	To avoid having to explicitly tell libev about such cases, libev follows	1682	To avoid having to explicitly tell libev about such cases, libev follows
1122	the following policy: Each time C<ev_io_set> is being called, libev	1683	the following policy: Each time C<ev_io_set> is being called, libev
1123	will assume that this is potentially a new file descriptor, otherwise	1684	will assume that this is potentially a new file descriptor, otherwise
1124	it is assumed that the file descriptor stays the same. That means that	1685	it is assumed that the file descriptor stays the same. That means that
…		…
1138		1699
1139	There is no workaround possible except not registering events	1700	There is no workaround possible except not registering events
1140	for potentially C<dup ()>'ed file descriptors, or to resort to	1701	for potentially C<dup ()>'ed file descriptors, or to resort to
1141	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1702	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1142		1703
		1704	=head3 The special problem of files
		1705
		1706	Many people try to use C<select> (or libev) on file descriptors
		1707	representing files, and expect it to become ready when their program
		1708	doesn't block on disk accesses (which can take a long time on their own).
		1709
		1710	However, this cannot ever work in the "expected" way - you get a readiness
		1711	notification as soon as the kernel knows whether and how much data is
		1712	there, and in the case of open files, that's always the case, so you
		1713	always get a readiness notification instantly, and your read (or possibly
		1714	write) will still block on the disk I/O.
		1715
		1716	Another way to view it is that in the case of sockets, pipes, character
		1717	devices and so on, there is another party (the sender) that delivers data
		1718	on its own, but in the case of files, there is no such thing: the disk
		1719	will not send data on its own, simply because it doesn't know what you
		1720	wish to read - you would first have to request some data.
		1721
		1722	Since files are typically not-so-well supported by advanced notification
		1723	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1724	to files, even though you should not use it. The reason for this is
		1725	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1726	usually a tty, often a pipe, but also sometimes files or special devices
		1727	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1728	F</dev/urandom>), and even though the file might better be served with
		1729	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1730	it "just works" instead of freezing.
		1731
		1732	So avoid file descriptors pointing to files when you know it (e.g. use
		1733	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1734	when you rarely read from a file instead of from a socket, and want to
		1735	reuse the same code path.
		1736
1143	=head3 The special problem of fork	1737	=head3 The special problem of fork
1144		1738
1145	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1739	Some backends (epoll, kqueue, probably linuxaio) do not support C<fork ()>
1146	useless behaviour. Libev fully supports fork, but needs to be told about	1740	at all or exhibit useless behaviour. Libev fully supports fork, but needs
1147	it in the child.	1741	to be told about it in the child if you want to continue to use it in the
		1742	child.
1148		1743
1149	To support fork in your programs, you either have to call	1744	To support fork in your child processes, you have to call C<ev_loop_fork
1150	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1745	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1151	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1746	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1152	C<EVBACKEND_POLL>.
1153		1747
1154	=head3 The special problem of SIGPIPE	1748	=head3 The special problem of SIGPIPE
1155		1749
1156	While not really specific to libev, it is easy to forget about SIGPIPE:	1750	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1157	when writing to a pipe whose other end has been closed, your program gets	1751	when writing to a pipe whose other end has been closed, your program gets
1158	send a SIGPIPE, which, by default, aborts your program. For most programs	1752	sent a SIGPIPE, which, by default, aborts your program. For most programs
1159	this is sensible behaviour, for daemons, this is usually undesirable.	1753	this is sensible behaviour, for daemons, this is usually undesirable.
1160		1754
1161	So when you encounter spurious, unexplained daemon exits, make sure you	1755	So when you encounter spurious, unexplained daemon exits, make sure you
1162	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon	1756	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
1163	somewhere, as that would have given you a big clue).	1757	somewhere, as that would have given you a big clue).
1164		1758
		1759	=head3 The special problem of accept()ing when you can't
		1760
		1761	Many implementations of the POSIX C<accept> function (for example,
		1762	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1763	connection from the pending queue in all error cases.
		1764
		1765	For example, larger servers often run out of file descriptors (because
		1766	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1767	rejecting the connection, leading to libev signalling readiness on
		1768	the next iteration again (the connection still exists after all), and
		1769	typically causing the program to loop at 100% CPU usage.
		1770
		1771	Unfortunately, the set of errors that cause this issue differs between
		1772	operating systems, there is usually little the app can do to remedy the
		1773	situation, and no known thread-safe method of removing the connection to
		1774	cope with overload is known (to me).
		1775
		1776	One of the easiest ways to handle this situation is to just ignore it
		1777	- when the program encounters an overload, it will just loop until the
		1778	situation is over. While this is a form of busy waiting, no OS offers an
		1779	event-based way to handle this situation, so it's the best one can do.
		1780
		1781	A better way to handle the situation is to log any errors other than
		1782	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1783	messages, and continue as usual, which at least gives the user an idea of
		1784	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1785	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1786	usage.
		1787
		1788	If your program is single-threaded, then you could also keep a dummy file
		1789	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1790	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1791	close that fd, and create a new dummy fd. This will gracefully refuse
		1792	clients under typical overload conditions.
		1793
		1794	The last way to handle it is to simply log the error and C<exit>, as
		1795	is often done with C<malloc> failures, but this results in an easy
		1796	opportunity for a DoS attack.
1165		1797
1166	=head3 Watcher-Specific Functions	1798	=head3 Watcher-Specific Functions
1167		1799
1168	=over 4	1800	=over 4
1169		1801
1170	=item ev_io_init (ev_io *, callback, int fd, int events)	1802	=item ev_io_init (ev_io *, callback, int fd, int events)
1171		1803
1172	=item ev_io_set (ev_io *, int fd, int events)	1804	=item ev_io_set (ev_io *, int fd, int events)
1173		1805
1174	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1806	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1175	receive events for and events is either C<EV_READ>, C<EV_WRITE> or	1807	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
1176	C<EV_READ | EV_WRITE> to receive the given events.	1808	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1177		1809
1178	=item int fd [read-only]	1810	=item int fd [read-only]
1179		1811
1180	The file descriptor being watched.	1812	The file descriptor being watched.
1181		1813
…		…
1190	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1822	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1191	readable, but only once. Since it is likely line-buffered, you could	1823	readable, but only once. Since it is likely line-buffered, you could
1192	attempt to read a whole line in the callback.	1824	attempt to read a whole line in the callback.
1193		1825
1194	static void	1826	static void
1195	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1827	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1196	{	1828	{
1197	ev_io_stop (loop, w);	1829	ev_io_stop (loop, w);
1198	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1830	.. read from stdin here (or from w->fd) and handle any I/O errors
1199	}	1831	}
1200		1832
1201	...	1833	...
1202	struct ev_loop *loop = ev_default_init (0);	1834	struct ev_loop *loop = ev_default_init (0);
1203	struct ev_io stdin_readable;	1835	ev_io stdin_readable;
1204	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1836	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1205	ev_io_start (loop, &stdin_readable);	1837	ev_io_start (loop, &stdin_readable);
1206	ev_loop (loop, 0);	1838	ev_run (loop, 0);
1207		1839
1208		1840
1209	=head2 C<ev_timer> - relative and optionally repeating timeouts	1841	=head2 C<ev_timer> - relative and optionally repeating timeouts
1210		1842
1211	Timer watchers are simple relative timers that generate an event after a	1843	Timer watchers are simple relative timers that generate an event after a
1212	given time, and optionally repeating in regular intervals after that.	1844	given time, and optionally repeating in regular intervals after that.
1213		1845
1214	The timers are based on real time, that is, if you register an event that	1846	The timers are based on real time, that is, if you register an event that
1215	times out after an hour and you reset your system clock to January last	1847	times out after an hour and you reset your system clock to January last
1216	year, it will still time out after (roughly) and hour. "Roughly" because	1848	year, it will still time out after (roughly) one hour. "Roughly" because
1217	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1849	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1218	monotonic clock option helps a lot here).	1850	monotonic clock option helps a lot here).
1219		1851
1220	The callback is guaranteed to be invoked only after its timeout has passed,	1852	The callback is guaranteed to be invoked only I<after> its timeout has
1221	but if multiple timers become ready during the same loop iteration then	1853	passed (not I<at>, so on systems with very low-resolution clocks this
1222	order of execution is undefined.	1854	might introduce a small delay, see "the special problem of being too
		1855	early", below). If multiple timers become ready during the same loop
		1856	iteration then the ones with earlier time-out values are invoked before
		1857	ones of the same priority with later time-out values (but this is no
		1858	longer true when a callback calls C<ev_run> recursively).
		1859
		1860	=head3 Be smart about timeouts
		1861
		1862	Many real-world problems involve some kind of timeout, usually for error
		1863	recovery. A typical example is an HTTP request - if the other side hangs,
		1864	you want to raise some error after a while.
		1865
		1866	What follows are some ways to handle this problem, from obvious and
		1867	inefficient to smart and efficient.
		1868
		1869	In the following, a 60 second activity timeout is assumed - a timeout that
		1870	gets reset to 60 seconds each time there is activity (e.g. each time some
		1871	data or other life sign was received).
		1872
		1873	=over 4
		1874
		1875	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1876
		1877	This is the most obvious, but not the most simple way: In the beginning,
		1878	start the watcher:
		1879
		1880	ev_timer_init (timer, callback, 60., 0.);
		1881	ev_timer_start (loop, timer);
		1882
		1883	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1884	and start it again:
		1885
		1886	ev_timer_stop (loop, timer);
		1887	ev_timer_set (timer, 60., 0.);
		1888	ev_timer_start (loop, timer);
		1889
		1890	This is relatively simple to implement, but means that each time there is
		1891	some activity, libev will first have to remove the timer from its internal
		1892	data structure and then add it again. Libev tries to be fast, but it's
		1893	still not a constant-time operation.
		1894
		1895	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1896
		1897	This is the easiest way, and involves using C<ev_timer_again> instead of
		1898	C<ev_timer_start>.
		1899
		1900	To implement this, configure an C<ev_timer> with a C<repeat> value
		1901	of C<60> and then call C<ev_timer_again> at start and each time you
		1902	successfully read or write some data. If you go into an idle state where
		1903	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1904	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1905
		1906	That means you can ignore both the C<ev_timer_start> function and the
		1907	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1908	member and C<ev_timer_again>.
		1909
		1910	At start:
		1911
		1912	ev_init (timer, callback);
		1913	timer->repeat = 60.;
		1914	ev_timer_again (loop, timer);
		1915
		1916	Each time there is some activity:
		1917
		1918	ev_timer_again (loop, timer);
		1919
		1920	It is even possible to change the time-out on the fly, regardless of
		1921	whether the watcher is active or not:
		1922
		1923	timer->repeat = 30.;
		1924	ev_timer_again (loop, timer);
		1925
		1926	This is slightly more efficient then stopping/starting the timer each time
		1927	you want to modify its timeout value, as libev does not have to completely
		1928	remove and re-insert the timer from/into its internal data structure.
		1929
		1930	It is, however, even simpler than the "obvious" way to do it.
		1931
		1932	=item 3. Let the timer time out, but then re-arm it as required.
		1933
		1934	This method is more tricky, but usually most efficient: Most timeouts are
		1935	relatively long compared to the intervals between other activity - in
		1936	our example, within 60 seconds, there are usually many I/O events with
		1937	associated activity resets.
		1938
		1939	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1940	but remember the time of last activity, and check for a real timeout only
		1941	within the callback:
		1942
		1943	ev_tstamp timeout = 60.;
		1944	ev_tstamp last_activity; // time of last activity
		1945	ev_timer timer;
		1946
		1947	static void
		1948	callback (EV_P_ ev_timer *w, int revents)
		1949	{
		1950	// calculate when the timeout would happen
		1951	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
		1952
		1953	// if negative, it means we the timeout already occurred
		1954	if (after < 0.)
		1955	{
		1956	// timeout occurred, take action
		1957	}
		1958	else
		1959	{
		1960	// callback was invoked, but there was some recent
		1961	// activity. simply restart the timer to time out
		1962	// after "after" seconds, which is the earliest time
		1963	// the timeout can occur.
		1964	ev_timer_set (w, after, 0.);
		1965	ev_timer_start (EV_A_ w);
		1966	}
		1967	}
		1968
		1969	To summarise the callback: first calculate in how many seconds the
		1970	timeout will occur (by calculating the absolute time when it would occur,
		1971	C<last_activity + timeout>, and subtracting the current time, C<ev_now
		1972	(EV_A)> from that).
		1973
		1974	If this value is negative, then we are already past the timeout, i.e. we
		1975	timed out, and need to do whatever is needed in this case.
		1976
		1977	Otherwise, we now the earliest time at which the timeout would trigger,
		1978	and simply start the timer with this timeout value.
		1979
		1980	In other words, each time the callback is invoked it will check whether
		1981	the timeout occurred. If not, it will simply reschedule itself to check
		1982	again at the earliest time it could time out. Rinse. Repeat.
		1983
		1984	This scheme causes more callback invocations (about one every 60 seconds
		1985	minus half the average time between activity), but virtually no calls to
		1986	libev to change the timeout.
		1987
		1988	To start the machinery, simply initialise the watcher and set
		1989	C<last_activity> to the current time (meaning there was some activity just
		1990	now), then call the callback, which will "do the right thing" and start
		1991	the timer:
		1992
		1993	last_activity = ev_now (EV_A);
		1994	ev_init (&timer, callback);
		1995	callback (EV_A_ &timer, 0);
		1996
		1997	When there is some activity, simply store the current time in
		1998	C<last_activity>, no libev calls at all:
		1999
		2000	if (activity detected)
		2001	last_activity = ev_now (EV_A);
		2002
		2003	When your timeout value changes, then the timeout can be changed by simply
		2004	providing a new value, stopping the timer and calling the callback, which
		2005	will again do the right thing (for example, time out immediately :).
		2006
		2007	timeout = new_value;
		2008	ev_timer_stop (EV_A_ &timer);
		2009	callback (EV_A_ &timer, 0);
		2010
		2011	This technique is slightly more complex, but in most cases where the
		2012	time-out is unlikely to be triggered, much more efficient.
		2013
		2014	=item 4. Wee, just use a double-linked list for your timeouts.
		2015
		2016	If there is not one request, but many thousands (millions...), all
		2017	employing some kind of timeout with the same timeout value, then one can
		2018	do even better:
		2019
		2020	When starting the timeout, calculate the timeout value and put the timeout
		2021	at the I<end> of the list.
		2022
		2023	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		2024	the list is expected to fire (for example, using the technique #3).
		2025
		2026	When there is some activity, remove the timer from the list, recalculate
		2027	the timeout, append it to the end of the list again, and make sure to
		2028	update the C<ev_timer> if it was taken from the beginning of the list.
		2029
		2030	This way, one can manage an unlimited number of timeouts in O(1) time for
		2031	starting, stopping and updating the timers, at the expense of a major
		2032	complication, and having to use a constant timeout. The constant timeout
		2033	ensures that the list stays sorted.
		2034
		2035	=back
		2036
		2037	So which method the best?
		2038
		2039	Method #2 is a simple no-brain-required solution that is adequate in most
		2040	situations. Method #3 requires a bit more thinking, but handles many cases
		2041	better, and isn't very complicated either. In most case, choosing either
		2042	one is fine, with #3 being better in typical situations.
		2043
		2044	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		2045	rather complicated, but extremely efficient, something that really pays
		2046	off after the first million or so of active timers, i.e. it's usually
		2047	overkill :)
		2048
		2049	=head3 The special problem of being too early
		2050
		2051	If you ask a timer to call your callback after three seconds, then
		2052	you expect it to be invoked after three seconds - but of course, this
		2053	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		2054	guaranteed to any precision by libev - imagine somebody suspending the
		2055	process with a STOP signal for a few hours for example.
		2056
		2057	So, libev tries to invoke your callback as soon as possible I<after> the
		2058	delay has occurred, but cannot guarantee this.
		2059
		2060	A less obvious failure mode is calling your callback too early: many event
		2061	loops compare timestamps with a "elapsed delay >= requested delay", but
		2062	this can cause your callback to be invoked much earlier than you would
		2063	expect.
		2064
		2065	To see why, imagine a system with a clock that only offers full second
		2066	resolution (think windows if you can't come up with a broken enough OS
		2067	yourself). If you schedule a one-second timer at the time 500.9, then the
		2068	event loop will schedule your timeout to elapse at a system time of 500
		2069	(500.9 truncated to the resolution) + 1, or 501.
		2070
		2071	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2072	501" and invoke the callback 0.1s after it was started, even though a
		2073	one-second delay was requested - this is being "too early", despite best
		2074	intentions.
		2075
		2076	This is the reason why libev will never invoke the callback if the elapsed
		2077	delay equals the requested delay, but only when the elapsed delay is
		2078	larger than the requested delay. In the example above, libev would only invoke
		2079	the callback at system time 502, or 1.1s after the timer was started.
		2080
		2081	So, while libev cannot guarantee that your callback will be invoked
		2082	exactly when requested, it I<can> and I<does> guarantee that the requested
		2083	delay has actually elapsed, or in other words, it always errs on the "too
		2084	late" side of things.
1223		2085
1224	=head3 The special problem of time updates	2086	=head3 The special problem of time updates
1225		2087
1226	Establishing the current time is a costly operation (it usually takes at	2088	Establishing the current time is a costly operation (it usually takes
1227	least two system calls): EV therefore updates its idea of the current	2089	at least one system call): EV therefore updates its idea of the current
1228	time only before and after C<ev_loop> polls for new events, which causes	2090	time only before and after C<ev_run> collects new events, which causes a
1229	a growing difference between C<ev_now ()> and C<ev_time ()> when handling	2091	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1230	lots of events.	2092	lots of events in one iteration.
1231		2093
1232	The relative timeouts are calculated relative to the C<ev_now ()>	2094	The relative timeouts are calculated relative to the C<ev_now ()>
1233	time. This is usually the right thing as this timestamp refers to the time	2095	time. This is usually the right thing as this timestamp refers to the time
1234	of the event triggering whatever timeout you are modifying/starting. If	2096	of the event triggering whatever timeout you are modifying/starting. If
1235	you suspect event processing to be delayed and you I<need> to base the	2097	you suspect event processing to be delayed and you I<need> to base the
1236	timeout on the current time, use something like this to adjust for this:	2098	timeout on the current time, use something like the following to adjust
		2099	for it:
1237		2100
1238	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2101	ev_timer_set (&timer, after + (ev_time () - ev_now ()), 0.);
1239		2102
1240	If the event loop is suspended for a long time, you can also force an	2103	If the event loop is suspended for a long time, you can also force an
1241	update of the time returned by C<ev_now ()> by calling C<ev_now_update	2104	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1242	()>.	2105	()>, although that will push the event time of all outstanding events
		2106	further into the future.
		2107
		2108	=head3 The special problem of unsynchronised clocks
		2109
		2110	Modern systems have a variety of clocks - libev itself uses the normal
		2111	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2112	jumps).
		2113
		2114	Neither of these clocks is synchronised with each other or any other clock
		2115	on the system, so C<ev_time ()> might return a considerably different time
		2116	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2117	a call to C<gettimeofday> might return a second count that is one higher
		2118	than a directly following call to C<time>.
		2119
		2120	The moral of this is to only compare libev-related timestamps with
		2121	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2122	a second or so.
		2123
		2124	One more problem arises due to this lack of synchronisation: if libev uses
		2125	the system monotonic clock and you compare timestamps from C<ev_time>
		2126	or C<ev_now> from when you started your timer and when your callback is
		2127	invoked, you will find that sometimes the callback is a bit "early".
		2128
		2129	This is because C<ev_timer>s work in real time, not wall clock time, so
		2130	libev makes sure your callback is not invoked before the delay happened,
		2131	I<measured according to the real time>, not the system clock.
		2132
		2133	If your timeouts are based on a physical timescale (e.g. "time out this
		2134	connection after 100 seconds") then this shouldn't bother you as it is
		2135	exactly the right behaviour.
		2136
		2137	If you want to compare wall clock/system timestamps to your timers, then
		2138	you need to use C<ev_periodic>s, as these are based on the wall clock
		2139	time, where your comparisons will always generate correct results.
		2140
		2141	=head3 The special problems of suspended animation
		2142
		2143	When you leave the server world it is quite customary to hit machines that
		2144	can suspend/hibernate - what happens to the clocks during such a suspend?
		2145
		2146	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		2147	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		2148	to run until the system is suspended, but they will not advance while the
		2149	system is suspended. That means, on resume, it will be as if the program
		2150	was frozen for a few seconds, but the suspend time will not be counted
		2151	towards C<ev_timer> when a monotonic clock source is used. The real time
		2152	clock advanced as expected, but if it is used as sole clocksource, then a
		2153	long suspend would be detected as a time jump by libev, and timers would
		2154	be adjusted accordingly.
		2155
		2156	I would not be surprised to see different behaviour in different between
		2157	operating systems, OS versions or even different hardware.
		2158
		2159	The other form of suspend (job control, or sending a SIGSTOP) will see a
		2160	time jump in the monotonic clocks and the realtime clock. If the program
		2161	is suspended for a very long time, and monotonic clock sources are in use,
		2162	then you can expect C<ev_timer>s to expire as the full suspension time
		2163	will be counted towards the timers. When no monotonic clock source is in
		2164	use, then libev will again assume a timejump and adjust accordingly.
		2165
		2166	It might be beneficial for this latter case to call C<ev_suspend>
		2167	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		2168	deterministic behaviour in this case (you can do nothing against
		2169	C<SIGSTOP>).
1243		2170
1244	=head3 Watcher-Specific Functions and Data Members	2171	=head3 Watcher-Specific Functions and Data Members
1245		2172
1246	=over 4	2173	=over 4
1247		2174
1248	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2175	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1249		2176
1250	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2177	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1251		2178
1252	Configure the timer to trigger after C<after> seconds. If C<repeat>	2179	Configure the timer to trigger after C<after> seconds (fractional and
1253	is C<0.>, then it will automatically be stopped once the timeout is	2180	negative values are supported). If C<repeat> is C<0.>, then it will
1254	reached. If it is positive, then the timer will automatically be	2181	automatically be stopped once the timeout is reached. If it is positive,
1255	configured to trigger again C<repeat> seconds later, again, and again,	2182	then the timer will automatically be configured to trigger again C<repeat>
1256	until stopped manually.	2183	seconds later, again, and again, until stopped manually.
1257		2184
1258	The timer itself will do a best-effort at avoiding drift, that is, if	2185	The timer itself will do a best-effort at avoiding drift, that is, if
1259	you configure a timer to trigger every 10 seconds, then it will normally	2186	you configure a timer to trigger every 10 seconds, then it will normally
1260	trigger at exactly 10 second intervals. If, however, your program cannot	2187	trigger at exactly 10 second intervals. If, however, your program cannot
1261	keep up with the timer (because it takes longer than those 10 seconds to	2188	keep up with the timer (because it takes longer than those 10 seconds to
1262	do stuff) the timer will not fire more than once per event loop iteration.	2189	do stuff) the timer will not fire more than once per event loop iteration.
1263		2190
1264	=item ev_timer_again (loop, ev_timer *)	2191	=item ev_timer_again (loop, ev_timer *)
1265		2192
1266	This will act as if the timer timed out and restart it again if it is	2193	This will act as if the timer timed out, and restarts it again if it is
1267	repeating. The exact semantics are:	2194	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2195	timeout to the C<repeat> value and calling C<ev_timer_start>.
1268		2196
		2197	The exact semantics are as in the following rules, all of which will be
		2198	applied to the watcher:
		2199
		2200	=over 4
		2201
1269	If the timer is pending, its pending status is cleared.	2202	=item If the timer is pending, the pending status is always cleared.
1270		2203
1271	If the timer is started but non-repeating, stop it (as if it timed out).	2204	=item If the timer is started but non-repeating, stop it (as if it timed
		2205	out, without invoking it).
1272		2206
1273	If the timer is repeating, either start it if necessary (with the	2207	=item If the timer is repeating, make the C<repeat> value the new timeout
1274	C<repeat> value), or reset the running timer to the C<repeat> value.	2208	and start the timer, if necessary.
1275		2209
1276	This sounds a bit complicated, but here is a useful and typical	2210	=back
1277	example: Imagine you have a TCP connection and you want a so-called idle
1278	timeout, that is, you want to be called when there have been, say, 60
1279	seconds of inactivity on the socket. The easiest way to do this is to
1280	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1281	C<ev_timer_again> each time you successfully read or write some data. If
1282	you go into an idle state where you do not expect data to travel on the
1283	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1284	automatically restart it if need be.
1285		2211
1286	That means you can ignore the C<after> value and C<ev_timer_start>	2212	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
1287	altogether and only ever use the C<repeat> value and C<ev_timer_again>:	2213	usage example.
1288		2214
1289	ev_timer_init (timer, callback, 0., 5.);	2215	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1290	ev_timer_again (loop, timer);
1291	...
1292	timer->again = 17.;
1293	ev_timer_again (loop, timer);
1294	...
1295	timer->again = 10.;
1296	ev_timer_again (loop, timer);
1297		2216
1298	This is more slightly efficient then stopping/starting the timer each time	2217	Returns the remaining time until a timer fires. If the timer is active,
1299	you want to modify its timeout value.	2218	then this time is relative to the current event loop time, otherwise it's
		2219	the timeout value currently configured.
		2220
		2221	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
		2222	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		2223	will return C<4>. When the timer expires and is restarted, it will return
		2224	roughly C<7> (likely slightly less as callback invocation takes some time,
		2225	too), and so on.
1300		2226
1301	=item ev_tstamp repeat [read-write]	2227	=item ev_tstamp repeat [read-write]
1302		2228
1303	The current C<repeat> value. Will be used each time the watcher times out	2229	The current C<repeat> value. Will be used each time the watcher times out
1304	or C<ev_timer_again> is called and determines the next timeout (if any),	2230	or C<ev_timer_again> is called, and determines the next timeout (if any),
1305	which is also when any modifications are taken into account.	2231	which is also when any modifications are taken into account.
1306		2232
1307	=back	2233	=back
1308		2234
1309	=head3 Examples	2235	=head3 Examples
1310		2236
1311	Example: Create a timer that fires after 60 seconds.	2237	Example: Create a timer that fires after 60 seconds.
1312		2238
1313	static void	2239	static void
1314	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2240	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1315	{	2241	{
1316	.. one minute over, w is actually stopped right here	2242	.. one minute over, w is actually stopped right here
1317	}	2243	}
1318		2244
1319	struct ev_timer mytimer;	2245	ev_timer mytimer;
1320	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	2246	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1321	ev_timer_start (loop, &mytimer);	2247	ev_timer_start (loop, &mytimer);
1322		2248
1323	Example: Create a timeout timer that times out after 10 seconds of	2249	Example: Create a timeout timer that times out after 10 seconds of
1324	inactivity.	2250	inactivity.
1325		2251
1326	static void	2252	static void
1327	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2253	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1328	{	2254	{
1329	.. ten seconds without any activity	2255	.. ten seconds without any activity
1330	}	2256	}
1331		2257
1332	struct ev_timer mytimer;	2258	ev_timer mytimer;
1333	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	2259	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1334	ev_timer_again (&mytimer); /* start timer */	2260	ev_timer_again (&mytimer); /* start timer */
1335	ev_loop (loop, 0);	2261	ev_run (loop, 0);
1336		2262
1337	// and in some piece of code that gets executed on any "activity":	2263	// and in some piece of code that gets executed on any "activity":
1338	// reset the timeout to start ticking again at 10 seconds	2264	// reset the timeout to start ticking again at 10 seconds
1339	ev_timer_again (&mytimer);	2265	ev_timer_again (&mytimer);
1340		2266
…		…
1342	=head2 C<ev_periodic> - to cron or not to cron?	2268	=head2 C<ev_periodic> - to cron or not to cron?
1343		2269
1344	Periodic watchers are also timers of a kind, but they are very versatile	2270	Periodic watchers are also timers of a kind, but they are very versatile
1345	(and unfortunately a bit complex).	2271	(and unfortunately a bit complex).
1346		2272
1347	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2273	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1348	but on wall clock time (absolute time). You can tell a periodic watcher	2274	relative time, the physical time that passes) but on wall clock time
1349	to trigger after some specific point in time. For example, if you tell a	2275	(absolute time, the thing you can read on your calendar or clock). The
1350	periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now ()	2276	difference is that wall clock time can run faster or slower than real
1351	+ 10.>, that is, an absolute time not a delay) and then reset your system	2277	time, and time jumps are not uncommon (e.g. when you adjust your
1352	clock to January of the previous year, then it will take more than year	2278	wrist-watch).
1353	to trigger the event (unlike an C<ev_timer>, which would still trigger
1354	roughly 10 seconds later as it uses a relative timeout).
1355		2279
		2280	You can tell a periodic watcher to trigger after some specific point
		2281	in time: for example, if you tell a periodic watcher to trigger "in 10
		2282	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2283	not a delay) and then reset your system clock to January of the previous
		2284	year, then it will take a year or more to trigger the event (unlike an
		2285	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2286	it, as it uses a relative timeout).
		2287
1356	C<ev_periodic>s can also be used to implement vastly more complex timers,	2288	C<ev_periodic> watchers can also be used to implement vastly more complex
1357	such as triggering an event on each "midnight, local time", or other	2289	timers, such as triggering an event on each "midnight, local time", or
1358	complicated, rules.	2290	other complicated rules. This cannot easily be done with C<ev_timer>
		2291	watchers, as those cannot react to time jumps.
1359		2292
1360	As with timers, the callback is guaranteed to be invoked only when the	2293	As with timers, the callback is guaranteed to be invoked only when the
1361	time (C<at>) has passed, but if multiple periodic timers become ready	2294	point in time where it is supposed to trigger has passed. If multiple
1362	during the same loop iteration then order of execution is undefined.	2295	timers become ready during the same loop iteration then the ones with
		2296	earlier time-out values are invoked before ones with later time-out values
		2297	(but this is no longer true when a callback calls C<ev_run> recursively).
1363		2298
1364	=head3 Watcher-Specific Functions and Data Members	2299	=head3 Watcher-Specific Functions and Data Members
1365		2300
1366	=over 4	2301	=over 4
1367		2302
1368	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2303	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1369		2304
1370	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2305	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1371		2306
1372	Lots of arguments, lets sort it out... There are basically three modes of	2307	Lots of arguments, let's sort it out... There are basically three modes of
1373	operation, and we will explain them from simplest to complex:	2308	operation, and we will explain them from simplest to most complex:
1374		2309
1375	=over 4	2310	=over 4
1376		2311
1377	=item * absolute timer (at = time, interval = reschedule_cb = 0)	2312	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1378		2313
1379	In this configuration the watcher triggers an event after the wall clock	2314	In this configuration the watcher triggers an event after the wall clock
1380	time C<at> has passed and doesn't repeat. It will not adjust when a time	2315	time C<offset> has passed. It will not repeat and will not adjust when a
1381	jump occurs, that is, if it is to be run at January 1st 2011 then it will	2316	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1382	run when the system time reaches or surpasses this time.	2317	will be stopped and invoked when the system clock reaches or surpasses
		2318	this point in time.
1383		2319
1384	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	2320	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1385		2321
1386	In this mode the watcher will always be scheduled to time out at the next	2322	In this mode the watcher will always be scheduled to time out at the next
1387	C<at + N * interval> time (for some integer N, which can also be negative)	2323	C<offset + N * interval> time (for some integer N, which can also be
1388	and then repeat, regardless of any time jumps.	2324	negative) and then repeat, regardless of any time jumps. The C<offset>
		2325	argument is merely an offset into the C<interval> periods.
1389		2326
1390	This can be used to create timers that do not drift with respect to system	2327	This can be used to create timers that do not drift with respect to the
1391	time, for example, here is a C<ev_periodic> that triggers each hour, on	2328	system clock, for example, here is an C<ev_periodic> that triggers each
1392	the hour:	2329	hour, on the hour (with respect to UTC):
1393		2330
1394	ev_periodic_set (&periodic, 0., 3600., 0);	2331	ev_periodic_set (&periodic, 0., 3600., 0);
1395		2332
1396	This doesn't mean there will always be 3600 seconds in between triggers,	2333	This doesn't mean there will always be 3600 seconds in between triggers,
1397	but only that the callback will be called when the system time shows a	2334	but only that the callback will be called when the system time shows a
1398	full hour (UTC), or more correctly, when the system time is evenly divisible	2335	full hour (UTC), or more correctly, when the system time is evenly divisible
1399	by 3600.	2336	by 3600.
1400		2337
1401	Another way to think about it (for the mathematically inclined) is that	2338	Another way to think about it (for the mathematically inclined) is that
1402	C<ev_periodic> will try to run the callback in this mode at the next possible	2339	C<ev_periodic> will try to run the callback in this mode at the next possible
1403	time where C<time = at (mod interval)>, regardless of any time jumps.	2340	time where C<time = offset (mod interval)>, regardless of any time jumps.
1404		2341
1405	For numerical stability it is preferable that the C<at> value is near	2342	The C<interval> I<MUST> be positive, and for numerical stability, the
1406	C<ev_now ()> (the current time), but there is no range requirement for	2343	interval value should be higher than C<1/8192> (which is around 100
1407	this value, and in fact is often specified as zero.	2344	microseconds) and C<offset> should be higher than C<0> and should have
		2345	at most a similar magnitude as the current time (say, within a factor of
		2346	ten). Typical values for offset are, in fact, C<0> or something between
		2347	C<0> and C<interval>, which is also the recommended range.
1408		2348
1409	Note also that there is an upper limit to how often a timer can fire (CPU	2349	Note also that there is an upper limit to how often a timer can fire (CPU
1410	speed for example), so if C<interval> is very small then timing stability	2350	speed for example), so if C<interval> is very small then timing stability
1411	will of course deteriorate. Libev itself tries to be exact to be about one	2351	will of course deteriorate. Libev itself tries to be exact to be about one
1412	millisecond (if the OS supports it and the machine is fast enough).	2352	millisecond (if the OS supports it and the machine is fast enough).
1413		2353
1414	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	2354	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1415		2355
1416	In this mode the values for C<interval> and C<at> are both being	2356	In this mode the values for C<interval> and C<offset> are both being
1417	ignored. Instead, each time the periodic watcher gets scheduled, the	2357	ignored. Instead, each time the periodic watcher gets scheduled, the
1418	reschedule callback will be called with the watcher as first, and the	2358	reschedule callback will be called with the watcher as first, and the
1419	current time as second argument.	2359	current time as second argument.
1420		2360
1421	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2361	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1422	ever, or make ANY event loop modifications whatsoever>.	2362	or make ANY other event loop modifications whatsoever, unless explicitly
		2363	allowed by documentation here>.
1423		2364
1424	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop	2365	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
1425	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the	2366	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
1426	only event loop modification you are allowed to do).	2367	only event loop modification you are allowed to do).
1427		2368
1428	The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic	2369	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1429	*w, ev_tstamp now)>, e.g.:	2370	*w, ev_tstamp now)>, e.g.:
1430		2371
		2372	static ev_tstamp
1431	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2373	my_rescheduler (ev_periodic *w, ev_tstamp now)
1432	{	2374	{
1433	return now + 60.;	2375	return now + 60.;
1434	}	2376	}
1435		2377
1436	It must return the next time to trigger, based on the passed time value	2378	It must return the next time to trigger, based on the passed time value
…		…
1440		2382
1441	NOTE: I<< This callback must always return a time that is higher than or	2383	NOTE: I<< This callback must always return a time that is higher than or
1442	equal to the passed C<now> value >>.	2384	equal to the passed C<now> value >>.
1443		2385
1444	This can be used to create very complex timers, such as a timer that	2386	This can be used to create very complex timers, such as a timer that
1445	triggers on "next midnight, local time". To do this, you would calculate the	2387	triggers on "next midnight, local time". To do this, you would calculate
1446	next midnight after C<now> and return the timestamp value for this. How	2388	the next midnight after C<now> and return the timestamp value for
1447	you do this is, again, up to you (but it is not trivial, which is the main	2389	this. Here is a (completely untested, no error checking) example on how to
1448	reason I omitted it as an example).	2390	do this:
		2391
		2392	#include <time.h>
		2393
		2394	static ev_tstamp
		2395	my_rescheduler (ev_periodic *w, ev_tstamp now)
		2396	{
		2397	time_t tnow = (time_t)now;
		2398	struct tm tm;
		2399	localtime_r (&tnow, &tm);
		2400
		2401	tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
		2402	++tm.tm_mday; // midnight next day
		2403
		2404	return mktime (&tm);
		2405	}
		2406
		2407	Note: this code might run into trouble on days that have more then two
		2408	midnights (beginning and end).
1449		2409
1450	=back	2410	=back
1451		2411
1452	=item ev_periodic_again (loop, ev_periodic *)	2412	=item ev_periodic_again (loop, ev_periodic *)
1453		2413
…		…
1456	a different time than the last time it was called (e.g. in a crond like	2416	a different time than the last time it was called (e.g. in a crond like
1457	program when the crontabs have changed).	2417	program when the crontabs have changed).
1458		2418
1459	=item ev_tstamp ev_periodic_at (ev_periodic *)	2419	=item ev_tstamp ev_periodic_at (ev_periodic *)
1460		2420
1461	When active, returns the absolute time that the watcher is supposed to	2421	When active, returns the absolute time that the watcher is supposed
1462	trigger next.	2422	to trigger next. This is not the same as the C<offset> argument to
		2423	C<ev_periodic_set>, but indeed works even in interval and manual
		2424	rescheduling modes.
1463		2425
1464	=item ev_tstamp offset [read-write]	2426	=item ev_tstamp offset [read-write]
1465		2427
1466	When repeating, this contains the offset value, otherwise this is the	2428	When repeating, this contains the offset value, otherwise this is the
1467	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2429	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2430	although libev might modify this value for better numerical stability).
1468		2431
1469	Can be modified any time, but changes only take effect when the periodic	2432	Can be modified any time, but changes only take effect when the periodic
1470	timer fires or C<ev_periodic_again> is being called.	2433	timer fires or C<ev_periodic_again> is being called.
1471		2434
1472	=item ev_tstamp interval [read-write]	2435	=item ev_tstamp interval [read-write]
1473		2436
1474	The current interval value. Can be modified any time, but changes only	2437	The current interval value. Can be modified any time, but changes only
1475	take effect when the periodic timer fires or C<ev_periodic_again> is being	2438	take effect when the periodic timer fires or C<ev_periodic_again> is being
1476	called.	2439	called.
1477		2440
1478	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2441	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1479		2442
1480	The current reschedule callback, or C<0>, if this functionality is	2443	The current reschedule callback, or C<0>, if this functionality is
1481	switched off. Can be changed any time, but changes only take effect when	2444	switched off. Can be changed any time, but changes only take effect when
1482	the periodic timer fires or C<ev_periodic_again> is being called.	2445	the periodic timer fires or C<ev_periodic_again> is being called.
1483		2446
1484	=back	2447	=back
1485		2448
1486	=head3 Examples	2449	=head3 Examples
1487		2450
1488	Example: Call a callback every hour, or, more precisely, whenever the	2451	Example: Call a callback every hour, or, more precisely, whenever the
1489	system clock is divisible by 3600. The callback invocation times have	2452	system time is divisible by 3600. The callback invocation times have
1490	potentially a lot of jitter, but good long-term stability.	2453	potentially a lot of jitter, but good long-term stability.
1491		2454
1492	static void	2455	static void
1493	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2456	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1494	{	2457	{
1495	... its now a full hour (UTC, or TAI or whatever your clock follows)	2458	... its now a full hour (UTC, or TAI or whatever your clock follows)
1496	}	2459	}
1497		2460
1498	struct ev_periodic hourly_tick;	2461	ev_periodic hourly_tick;
1499	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2462	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1500	ev_periodic_start (loop, &hourly_tick);	2463	ev_periodic_start (loop, &hourly_tick);
1501		2464
1502	Example: The same as above, but use a reschedule callback to do it:	2465	Example: The same as above, but use a reschedule callback to do it:
1503		2466
1504	#include <math.h>	2467	#include <math.h>
1505		2468
1506	static ev_tstamp	2469	static ev_tstamp
1507	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2470	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1508	{	2471	{
1509	return fmod (now, 3600.) + 3600.;	2472	return now + (3600. - fmod (now, 3600.));
1510	}	2473	}
1511		2474
1512	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2475	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1513		2476
1514	Example: Call a callback every hour, starting now:	2477	Example: Call a callback every hour, starting now:
1515		2478
1516	struct ev_periodic hourly_tick;	2479	ev_periodic hourly_tick;
1517	ev_periodic_init (&hourly_tick, clock_cb,	2480	ev_periodic_init (&hourly_tick, clock_cb,
1518	fmod (ev_now (loop), 3600.), 3600., 0);	2481	fmod (ev_now (loop), 3600.), 3600., 0);
1519	ev_periodic_start (loop, &hourly_tick);	2482	ev_periodic_start (loop, &hourly_tick);
1520		2483
1521		2484
1522	=head2 C<ev_signal> - signal me when a signal gets signalled!	2485	=head2 C<ev_signal> - signal me when a signal gets signalled!
1523		2486
1524	Signal watchers will trigger an event when the process receives a specific	2487	Signal watchers will trigger an event when the process receives a specific
1525	signal one or more times. Even though signals are very asynchronous, libev	2488	signal one or more times. Even though signals are very asynchronous, libev
1526	will try it's best to deliver signals synchronously, i.e. as part of the	2489	will try its best to deliver signals synchronously, i.e. as part of the
1527	normal event processing, like any other event.	2490	normal event processing, like any other event.
1528		2491
		2492	If you want signals to be delivered truly asynchronously, just use
		2493	C<sigaction> as you would do without libev and forget about sharing
		2494	the signal. You can even use C<ev_async> from a signal handler to
		2495	synchronously wake up an event loop.
		2496
1529	You can configure as many watchers as you like per signal. Only when the	2497	You can configure as many watchers as you like for the same signal, but
1530	first watcher gets started will libev actually register a signal watcher	2498	only within the same loop, i.e. you can watch for C<SIGINT> in your
1531	with the kernel (thus it coexists with your own signal handlers as long	2499	default loop and for C<SIGIO> in another loop, but you cannot watch for
1532	as you don't register any with libev). Similarly, when the last signal	2500	C<SIGINT> in both the default loop and another loop at the same time. At
1533	watcher for a signal is stopped libev will reset the signal handler to	2501	the moment, C<SIGCHLD> is permanently tied to the default loop.
1534	SIG_DFL (regardless of what it was set to before).	2502
		2503	Only after the first watcher for a signal is started will libev actually
		2504	register something with the kernel. It thus coexists with your own signal
		2505	handlers as long as you don't register any with libev for the same signal.
1535		2506
1536	If possible and supported, libev will install its handlers with	2507	If possible and supported, libev will install its handlers with
1537	C<SA_RESTART> behaviour enabled, so system calls should not be unduly	2508	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
1538	interrupted. If you have a problem with system calls getting interrupted by	2509	not be unduly interrupted. If you have a problem with system calls getting
1539	signals you can block all signals in an C<ev_check> watcher and unblock	2510	interrupted by signals you can block all signals in an C<ev_check> watcher
1540	them in an C<ev_prepare> watcher.	2511	and unblock them in an C<ev_prepare> watcher.
		2512
		2513	=head3 The special problem of inheritance over fork/execve/pthread_create
		2514
		2515	Both the signal mask (C<sigprocmask>) and the signal disposition
		2516	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2517	stopping it again), that is, libev might or might not block the signal,
		2518	and might or might not set or restore the installed signal handler (but
		2519	see C<EVFLAG_NOSIGMASK>).
		2520
		2521	While this does not matter for the signal disposition (libev never
		2522	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2523	C<execve>), this matters for the signal mask: many programs do not expect
		2524	certain signals to be blocked.
		2525
		2526	This means that before calling C<exec> (from the child) you should reset
		2527	the signal mask to whatever "default" you expect (all clear is a good
		2528	choice usually).
		2529
		2530	The simplest way to ensure that the signal mask is reset in the child is
		2531	to install a fork handler with C<pthread_atfork> that resets it. That will
		2532	catch fork calls done by libraries (such as the libc) as well.
		2533
		2534	In current versions of libev, the signal will not be blocked indefinitely
		2535	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2536	the window of opportunity for problems, it will not go away, as libev
		2537	I<has> to modify the signal mask, at least temporarily.
		2538
		2539	So I can't stress this enough: I<If you do not reset your signal mask when
		2540	you expect it to be empty, you have a race condition in your code>. This
		2541	is not a libev-specific thing, this is true for most event libraries.
		2542
		2543	=head3 The special problem of threads signal handling
		2544
		2545	POSIX threads has problematic signal handling semantics, specifically,
		2546	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2547	threads in a process block signals, which is hard to achieve.
		2548
		2549	When you want to use sigwait (or mix libev signal handling with your own
		2550	for the same signals), you can tackle this problem by globally blocking
		2551	all signals before creating any threads (or creating them with a fully set
		2552	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2553	loops. Then designate one thread as "signal receiver thread" which handles
		2554	these signals. You can pass on any signals that libev might be interested
		2555	in by calling C<ev_feed_signal>.
1541		2556
1542	=head3 Watcher-Specific Functions and Data Members	2557	=head3 Watcher-Specific Functions and Data Members
1543		2558
1544	=over 4	2559	=over 4
1545		2560
…		…
1556		2571
1557	=back	2572	=back
1558		2573
1559	=head3 Examples	2574	=head3 Examples
1560		2575
1561	Example: Try to exit cleanly on SIGINT and SIGTERM.	2576	Example: Try to exit cleanly on SIGINT.
1562		2577
1563	static void	2578	static void
1564	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2579	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
1565	{	2580	{
1566	ev_unloop (loop, EVUNLOOP_ALL);	2581	ev_break (loop, EVBREAK_ALL);
1567	}	2582	}
1568		2583
1569	struct ev_signal signal_watcher;	2584	ev_signal signal_watcher;
1570	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2585	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1571	ev_signal_start (loop, &sigint_cb);	2586	ev_signal_start (loop, &signal_watcher);
1572		2587
1573		2588
1574	=head2 C<ev_child> - watch out for process status changes	2589	=head2 C<ev_child> - watch out for process status changes
1575		2590
1576	Child watchers trigger when your process receives a SIGCHLD in response to	2591	Child watchers trigger when your process receives a SIGCHLD in response to
1577	some child status changes (most typically when a child of yours dies). It	2592	some child status changes (most typically when a child of yours dies or
1578	is permissible to install a child watcher I<after> the child has been	2593	exits). It is permissible to install a child watcher I<after> the child
1579	forked (which implies it might have already exited), as long as the event	2594	has been forked (which implies it might have already exited), as long
1580	loop isn't entered (or is continued from a watcher).	2595	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2596	forking and then immediately registering a watcher for the child is fine,
		2597	but forking and registering a watcher a few event loop iterations later or
		2598	in the next callback invocation is not.
1581		2599
1582	Only the default event loop is capable of handling signals, and therefore	2600	Only the default event loop is capable of handling signals, and therefore
1583	you can only register child watchers in the default event loop.	2601	you can only register child watchers in the default event loop.
1584		2602
		2603	Due to some design glitches inside libev, child watchers will always be
		2604	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2605	libev)
		2606
1585	=head3 Process Interaction	2607	=head3 Process Interaction
1586		2608
1587	Libev grabs C<SIGCHLD> as soon as the default event loop is	2609	Libev grabs C<SIGCHLD> as soon as the default event loop is
1588	initialised. This is necessary to guarantee proper behaviour even if	2610	initialised. This is necessary to guarantee proper behaviour even if the
1589	the first child watcher is started after the child exits. The occurrence	2611	first child watcher is started after the child exits. The occurrence
1590	of C<SIGCHLD> is recorded asynchronously, but child reaping is done	2612	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
1591	synchronously as part of the event loop processing. Libev always reaps all	2613	synchronously as part of the event loop processing. Libev always reaps all
1592	children, even ones not watched.	2614	children, even ones not watched.
1593		2615
1594	=head3 Overriding the Built-In Processing	2616	=head3 Overriding the Built-In Processing
…		…
1604	=head3 Stopping the Child Watcher	2626	=head3 Stopping the Child Watcher
1605		2627
1606	Currently, the child watcher never gets stopped, even when the	2628	Currently, the child watcher never gets stopped, even when the
1607	child terminates, so normally one needs to stop the watcher in the	2629	child terminates, so normally one needs to stop the watcher in the
1608	callback. Future versions of libev might stop the watcher automatically	2630	callback. Future versions of libev might stop the watcher automatically
1609	when a child exit is detected.	2631	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2632	problem).
1610		2633
1611	=head3 Watcher-Specific Functions and Data Members	2634	=head3 Watcher-Specific Functions and Data Members
1612		2635
1613	=over 4	2636	=over 4
1614		2637
…		…
1646	its completion.	2669	its completion.
1647		2670
1648	ev_child cw;	2671	ev_child cw;
1649		2672
1650	static void	2673	static void
1651	child_cb (EV_P_ struct ev_child *w, int revents)	2674	child_cb (EV_P_ ev_child *w, int revents)
1652	{	2675	{
1653	ev_child_stop (EV_A_ w);	2676	ev_child_stop (EV_A_ w);
1654	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);	2677	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1655	}	2678	}
1656		2679
…		…
1671		2694
1672		2695
1673	=head2 C<ev_stat> - did the file attributes just change?	2696	=head2 C<ev_stat> - did the file attributes just change?
1674		2697
1675	This watches a file system path for attribute changes. That is, it calls	2698	This watches a file system path for attribute changes. That is, it calls
1676	C<stat> regularly (or when the OS says it changed) and sees if it changed	2699	C<stat> on that path in regular intervals (or when the OS says it changed)
1677	compared to the last time, invoking the callback if it did.	2700	and sees if it changed compared to the last time, invoking the callback
		2701	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2702	happen after the watcher has been started will be reported.
1678		2703
1679	The path does not need to exist: changing from "path exists" to "path does	2704	The path does not need to exist: changing from "path exists" to "path does
1680	not exist" is a status change like any other. The condition "path does	2705	not exist" is a status change like any other. The condition "path does not
1681	not exist" is signified by the C<st_nlink> field being zero (which is	2706	exist" (or more correctly "path cannot be stat'ed") is signified by the
1682	otherwise always forced to be at least one) and all the other fields of	2707	C<st_nlink> field being zero (which is otherwise always forced to be at
1683	the stat buffer having unspecified contents.	2708	least one) and all the other fields of the stat buffer having unspecified
		2709	contents.
1684		2710
1685	The path I<should> be absolute and I<must not> end in a slash. If it is	2711	The path I<must not> end in a slash or contain special components such as
		2712	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1686	relative and your working directory changes, the behaviour is undefined.	2713	your working directory changes, then the behaviour is undefined.
1687		2714
1688	Since there is no standard to do this, the portable implementation simply	2715	Since there is no portable change notification interface available, the
1689	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2716	portable implementation simply calls C<stat(2)> regularly on the path
1690	can specify a recommended polling interval for this case. If you specify	2717	to see if it changed somehow. You can specify a recommended polling
1691	a polling interval of C<0> (highly recommended!) then a I<suitable,	2718	interval for this case. If you specify a polling interval of C<0> (highly
1692	unspecified default> value will be used (which you can expect to be around	2719	recommended!) then a I<suitable, unspecified default> value will be used
1693	five seconds, although this might change dynamically). Libev will also	2720	(which you can expect to be around five seconds, although this might
1694	impose a minimum interval which is currently around C<0.1>, but thats	2721	change dynamically). Libev will also impose a minimum interval which is
1695	usually overkill.	2722	currently around C<0.1>, but that's usually overkill.
1696		2723
1697	This watcher type is not meant for massive numbers of stat watchers,	2724	This watcher type is not meant for massive numbers of stat watchers,
1698	as even with OS-supported change notifications, this can be	2725	as even with OS-supported change notifications, this can be
1699	resource-intensive.	2726	resource-intensive.
1700		2727
1701	At the time of this writing, only the Linux inotify interface is	2728	At the time of this writing, the only OS-specific interface implemented
1702	implemented (implementing kqueue support is left as an exercise for the	2729	is the Linux inotify interface (implementing kqueue support is left as an
1703	reader, note, however, that the author sees no way of implementing ev_stat	2730	exercise for the reader. Note, however, that the author sees no way of
1704	semantics with kqueue). Inotify will be used to give hints only and should	2731	implementing C<ev_stat> semantics with kqueue, except as a hint).
1705	not change the semantics of C<ev_stat> watchers, which means that libev
1706	sometimes needs to fall back to regular polling again even with inotify,
1707	but changes are usually detected immediately, and if the file exists there
1708	will be no polling.
1709		2732
1710	=head3 ABI Issues (Largefile Support)	2733	=head3 ABI Issues (Largefile Support)
1711		2734
1712	Libev by default (unless the user overrides this) uses the default	2735	Libev by default (unless the user overrides this) uses the default
1713	compilation environment, which means that on systems with large file	2736	compilation environment, which means that on systems with large file
1714	support disabled by default, you get the 32 bit version of the stat	2737	support disabled by default, you get the 32 bit version of the stat
1715	structure. When using the library from programs that change the ABI to	2738	structure. When using the library from programs that change the ABI to
1716	use 64 bit file offsets the programs will fail. In that case you have to	2739	use 64 bit file offsets the programs will fail. In that case you have to
1717	compile libev with the same flags to get binary compatibility. This is	2740	compile libev with the same flags to get binary compatibility. This is
1718	obviously the case with any flags that change the ABI, but the problem is	2741	obviously the case with any flags that change the ABI, but the problem is
1719	most noticeably disabled with ev_stat and large file support.	2742	most noticeably displayed with ev_stat and large file support.
1720		2743
1721	The solution for this is to lobby your distribution maker to make large	2744	The solution for this is to lobby your distribution maker to make large
1722	file interfaces available by default (as e.g. FreeBSD does) and not	2745	file interfaces available by default (as e.g. FreeBSD does) and not
1723	optional. Libev cannot simply switch on large file support because it has	2746	optional. Libev cannot simply switch on large file support because it has
1724	to exchange stat structures with application programs compiled using the	2747	to exchange stat structures with application programs compiled using the
1725	default compilation environment.	2748	default compilation environment.
1726		2749
1727	=head3 Inotify	2750	=head3 Inotify and Kqueue
1728		2751
1729	When C<inotify (7)> support has been compiled into libev (generally only	2752	When C<inotify (7)> support has been compiled into libev and present at
1730	available on Linux) and present at runtime, it will be used to speed up	2753	runtime, it will be used to speed up change detection where possible. The
1731	change detection where possible. The inotify descriptor will be created lazily	2754	inotify descriptor will be created lazily when the first C<ev_stat>
1732	when the first C<ev_stat> watcher is being started.	2755	watcher is being started.
1733		2756
1734	Inotify presence does not change the semantics of C<ev_stat> watchers	2757	Inotify presence does not change the semantics of C<ev_stat> watchers
1735	except that changes might be detected earlier, and in some cases, to avoid	2758	except that changes might be detected earlier, and in some cases, to avoid
1736	making regular C<stat> calls. Even in the presence of inotify support	2759	making regular C<stat> calls. Even in the presence of inotify support
1737	there are many cases where libev has to resort to regular C<stat> polling.	2760	there are many cases where libev has to resort to regular C<stat> polling,
		2761	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2762	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2763	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2764	xfs are fully working) libev usually gets away without polling.
1738		2765
1739	(There is no support for kqueue, as apparently it cannot be used to	2766	There is no support for kqueue, as apparently it cannot be used to
1740	implement this functionality, due to the requirement of having a file	2767	implement this functionality, due to the requirement of having a file
1741	descriptor open on the object at all times).	2768	descriptor open on the object at all times, and detecting renames, unlinks
		2769	etc. is difficult.
		2770
		2771	=head3 C<stat ()> is a synchronous operation
		2772
		2773	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2774	the process. The exception are C<ev_stat> watchers - those call C<stat
		2775	()>, which is a synchronous operation.
		2776
		2777	For local paths, this usually doesn't matter: unless the system is very
		2778	busy or the intervals between stat's are large, a stat call will be fast,
		2779	as the path data is usually in memory already (except when starting the
		2780	watcher).
		2781
		2782	For networked file systems, calling C<stat ()> can block an indefinite
		2783	time due to network issues, and even under good conditions, a stat call
		2784	often takes multiple milliseconds.
		2785
		2786	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2787	paths, although this is fully supported by libev.
1742		2788
1743	=head3 The special problem of stat time resolution	2789	=head3 The special problem of stat time resolution
1744		2790
1745	The C<stat ()> system call only supports full-second resolution portably, and	2791	The C<stat ()> system call only supports full-second resolution portably,
1746	even on systems where the resolution is higher, many file systems still	2792	and even on systems where the resolution is higher, most file systems
1747	only support whole seconds.	2793	still only support whole seconds.
1748		2794
1749	That means that, if the time is the only thing that changes, you can	2795	That means that, if the time is the only thing that changes, you can
1750	easily miss updates: on the first update, C<ev_stat> detects a change and	2796	easily miss updates: on the first update, C<ev_stat> detects a change and
1751	calls your callback, which does something. When there is another update	2797	calls your callback, which does something. When there is another update
1752	within the same second, C<ev_stat> will be unable to detect it as the stat	2798	within the same second, C<ev_stat> will be unable to detect unless the
1753	data does not change.	2799	stat data does change in other ways (e.g. file size).
1754		2800
1755	The solution to this is to delay acting on a change for slightly more	2801	The solution to this is to delay acting on a change for slightly more
1756	than a second (or till slightly after the next full second boundary), using	2802	than a second (or till slightly after the next full second boundary), using
1757	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);	2803	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
1758	ev_timer_again (loop, w)>).	2804	ev_timer_again (loop, w)>).
…		…
1778	C<path>. The C<interval> is a hint on how quickly a change is expected to	2824	C<path>. The C<interval> is a hint on how quickly a change is expected to
1779	be detected and should normally be specified as C<0> to let libev choose	2825	be detected and should normally be specified as C<0> to let libev choose
1780	a suitable value. The memory pointed to by C<path> must point to the same	2826	a suitable value. The memory pointed to by C<path> must point to the same
1781	path for as long as the watcher is active.	2827	path for as long as the watcher is active.
1782		2828
1783	The callback will receive C<EV_STAT> when a change was detected, relative	2829	The callback will receive an C<EV_STAT> event when a change was detected,
1784	to the attributes at the time the watcher was started (or the last change	2830	relative to the attributes at the time the watcher was started (or the
1785	was detected).	2831	last change was detected).
1786		2832
1787	=item ev_stat_stat (loop, ev_stat *)	2833	=item ev_stat_stat (loop, ev_stat *)
1788		2834
1789	Updates the stat buffer immediately with new values. If you change the	2835	Updates the stat buffer immediately with new values. If you change the
1790	watched path in your callback, you could call this function to avoid	2836	watched path in your callback, you could call this function to avoid
…		…
1873		2919
1874		2920
1875	=head2 C<ev_idle> - when you've got nothing better to do...	2921	=head2 C<ev_idle> - when you've got nothing better to do...
1876		2922
1877	Idle watchers trigger events when no other events of the same or higher	2923	Idle watchers trigger events when no other events of the same or higher
1878	priority are pending (prepare, check and other idle watchers do not	2924	priority are pending (prepare, check and other idle watchers do not count
1879	count).	2925	as receiving "events").
1880		2926
1881	That is, as long as your process is busy handling sockets or timeouts	2927	That is, as long as your process is busy handling sockets or timeouts
1882	(or even signals, imagine) of the same or higher priority it will not be	2928	(or even signals, imagine) of the same or higher priority it will not be
1883	triggered. But when your process is idle (or only lower-priority watchers	2929	triggered. But when your process is idle (or only lower-priority watchers
1884	are pending), the idle watchers are being called once per event loop	2930	are pending), the idle watchers are being called once per event loop
…		…
1891	Apart from keeping your process non-blocking (which is a useful	2937	Apart from keeping your process non-blocking (which is a useful
1892	effect on its own sometimes), idle watchers are a good place to do	2938	effect on its own sometimes), idle watchers are a good place to do
1893	"pseudo-background processing", or delay processing stuff to after the	2939	"pseudo-background processing", or delay processing stuff to after the
1894	event loop has handled all outstanding events.	2940	event loop has handled all outstanding events.
1895		2941
		2942	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2943
		2944	As long as there is at least one active idle watcher, libev will never
		2945	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2946	For this to work, the idle watcher doesn't need to be invoked at all - the
		2947	lowest priority will do.
		2948
		2949	This mode of operation can be useful together with an C<ev_check> watcher,
		2950	to do something on each event loop iteration - for example to balance load
		2951	between different connections.
		2952
		2953	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2954	example.
		2955
1896	=head3 Watcher-Specific Functions and Data Members	2956	=head3 Watcher-Specific Functions and Data Members
1897		2957
1898	=over 4	2958	=over 4
1899		2959
1900	=item ev_idle_init (ev_signal *, callback)	2960	=item ev_idle_init (ev_idle *, callback)
1901		2961
1902	Initialises and configures the idle watcher - it has no parameters of any	2962	Initialises and configures the idle watcher - it has no parameters of any
1903	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2963	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1904	believe me.	2964	believe me.
1905		2965
…		…
1909		2969
1910	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2970	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1911	callback, free it. Also, use no error checking, as usual.	2971	callback, free it. Also, use no error checking, as usual.
1912		2972
1913	static void	2973	static void
1914	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2974	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1915	{	2975	{
		2976	// stop the watcher
		2977	ev_idle_stop (loop, w);
		2978
		2979	// now we can free it
1916	free (w);	2980	free (w);
		2981
1917	// now do something you wanted to do when the program has	2982	// now do something you wanted to do when the program has
1918	// no longer anything immediate to do.	2983	// no longer anything immediate to do.
1919	}	2984	}
1920		2985
1921	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2986	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1922	ev_idle_init (idle_watcher, idle_cb);	2987	ev_idle_init (idle_watcher, idle_cb);
1923	ev_idle_start (loop, idle_cb);	2988	ev_idle_start (loop, idle_watcher);
1924		2989
1925		2990
1926	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2991	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1927		2992
1928	Prepare and check watchers are usually (but not always) used in tandem:	2993	Prepare and check watchers are often (but not always) used in pairs:
1929	prepare watchers get invoked before the process blocks and check watchers	2994	prepare watchers get invoked before the process blocks and check watchers
1930	afterwards.	2995	afterwards.
1931		2996
1932	You I<must not> call C<ev_loop> or similar functions that enter	2997	You I<must not> call C<ev_run> (or similar functions that enter the
1933	the current event loop from either C<ev_prepare> or C<ev_check>	2998	current event loop) or C<ev_loop_fork> from either C<ev_prepare> or
1934	watchers. Other loops than the current one are fine, however. The	2999	C<ev_check> watchers. Other loops than the current one are fine,
1935	rationale behind this is that you do not need to check for recursion in	3000	however. The rationale behind this is that you do not need to check
1936	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	3001	for recursion in those watchers, i.e. the sequence will always be
1937	C<ev_check> so if you have one watcher of each kind they will always be	3002	C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
1938	called in pairs bracketing the blocking call.	3003	kind they will always be called in pairs bracketing the blocking call.
1939		3004
1940	Their main purpose is to integrate other event mechanisms into libev and	3005	Their main purpose is to integrate other event mechanisms into libev and
1941	their use is somewhat advanced. This could be used, for example, to track	3006	their use is somewhat advanced. They could be used, for example, to track
1942	variable changes, implement your own watchers, integrate net-snmp or a	3007	variable changes, implement your own watchers, integrate net-snmp or a
1943	coroutine library and lots more. They are also occasionally useful if	3008	coroutine library and lots more. They are also occasionally useful if
1944	you cache some data and want to flush it before blocking (for example,	3009	you cache some data and want to flush it before blocking (for example,
1945	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	3010	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1946	watcher).	3011	watcher).
1947		3012
1948	This is done by examining in each prepare call which file descriptors need	3013	This is done by examining in each prepare call which file descriptors
1949	to be watched by the other library, registering C<ev_io> watchers for	3014	need to be watched by the other library, registering C<ev_io> watchers
1950	them and starting an C<ev_timer> watcher for any timeouts (many libraries	3015	for them and starting an C<ev_timer> watcher for any timeouts (many
1951	provide just this functionality). Then, in the check watcher you check for	3016	libraries provide exactly this functionality). Then, in the check watcher,
1952	any events that occurred (by checking the pending status of all watchers	3017	you check for any events that occurred (by checking the pending status
1953	and stopping them) and call back into the library. The I/O and timer	3018	of all watchers and stopping them) and call back into the library. The
1954	callbacks will never actually be called (but must be valid nevertheless,	3019	I/O and timer callbacks will never actually be called (but must be valid
1955	because you never know, you know?).	3020	nevertheless, because you never know, you know?).
1956		3021
1957	As another example, the Perl Coro module uses these hooks to integrate	3022	As another example, the Perl Coro module uses these hooks to integrate
1958	coroutines into libev programs, by yielding to other active coroutines	3023	coroutines into libev programs, by yielding to other active coroutines
1959	during each prepare and only letting the process block if no coroutines	3024	during each prepare and only letting the process block if no coroutines
1960	are ready to run (it's actually more complicated: it only runs coroutines	3025	are ready to run (it's actually more complicated: it only runs coroutines
1961	with priority higher than or equal to the event loop and one coroutine	3026	with priority higher than or equal to the event loop and one coroutine
1962	of lower priority, but only once, using idle watchers to keep the event	3027	of lower priority, but only once, using idle watchers to keep the event
1963	loop from blocking if lower-priority coroutines are active, thus mapping	3028	loop from blocking if lower-priority coroutines are active, thus mapping
1964	low-priority coroutines to idle/background tasks).	3029	low-priority coroutines to idle/background tasks).
1965		3030
1966	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	3031	When used for this purpose, it is recommended to give C<ev_check> watchers
1967	priority, to ensure that they are being run before any other watchers	3032	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
		3033	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		3034	watchers).
		3035
1968	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	3036	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1969	too) should not activate ("feed") events into libev. While libev fully	3037	activate ("feed") events into libev. While libev fully supports this, they
1970	supports this, they might get executed before other C<ev_check> watchers	3038	might get executed before other C<ev_check> watchers did their job. As
1971	did their job. As C<ev_check> watchers are often used to embed other	3039	C<ev_check> watchers are often used to embed other (non-libev) event
1972	(non-libev) event loops those other event loops might be in an unusable	3040	loops those other event loops might be in an unusable state until their
1973	state until their C<ev_check> watcher ran (always remind yourself to	3041	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1974	coexist peacefully with others).	3042	others).
		3043
		3044	=head3 Abusing an C<ev_check> watcher for its side-effect
		3045
		3046	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		3047	useful because they are called once per event loop iteration. For
		3048	example, if you want to handle a large number of connections fairly, you
		3049	normally only do a bit of work for each active connection, and if there
		3050	is more work to do, you wait for the next event loop iteration, so other
		3051	connections have a chance of making progress.
		3052
		3053	Using an C<ev_check> watcher is almost enough: it will be called on the
		3054	next event loop iteration. However, that isn't as soon as possible -
		3055	without external events, your C<ev_check> watcher will not be invoked.
		3056
		3057	This is where C<ev_idle> watchers come in handy - all you need is a
		3058	single global idle watcher that is active as long as you have one active
		3059	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		3060	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		3061	invoked. Neither watcher alone can do that.
1975		3062
1976	=head3 Watcher-Specific Functions and Data Members	3063	=head3 Watcher-Specific Functions and Data Members
1977		3064
1978	=over 4	3065	=over 4
1979		3066
…		…
1981		3068
1982	=item ev_check_init (ev_check *, callback)	3069	=item ev_check_init (ev_check *, callback)
1983		3070
1984	Initialises and configures the prepare or check watcher - they have no	3071	Initialises and configures the prepare or check watcher - they have no
1985	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	3072	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1986	macros, but using them is utterly, utterly and completely pointless.	3073	macros, but using them is utterly, utterly, utterly and completely
		3074	pointless.
1987		3075
1988	=back	3076	=back
1989		3077
1990	=head3 Examples	3078	=head3 Examples
1991		3079
…		…
2004		3092
2005	static ev_io iow [nfd];	3093	static ev_io iow [nfd];
2006	static ev_timer tw;	3094	static ev_timer tw;
2007		3095
2008	static void	3096	static void
2009	io_cb (ev_loop *loop, ev_io *w, int revents)	3097	io_cb (struct ev_loop *loop, ev_io *w, int revents)
2010	{	3098	{
2011	}	3099	}
2012		3100
2013	// create io watchers for each fd and a timer before blocking	3101	// create io watchers for each fd and a timer before blocking
2014	static void	3102	static void
2015	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	3103	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
2016	{	3104	{
2017	int timeout = 3600000;	3105	int timeout = 3600000;
2018	struct pollfd fds [nfd];	3106	struct pollfd fds [nfd];
2019	// actual code will need to loop here and realloc etc.	3107	// actual code will need to loop here and realloc etc.
2020	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	3108	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2021		3109
2022	/* the callback is illegal, but won't be called as we stop during check */	3110	/* the callback is illegal, but won't be called as we stop during check */
2023	ev_timer_init (&tw, 0, timeout * 1e-3);	3111	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
2024	ev_timer_start (loop, &tw);	3112	ev_timer_start (loop, &tw);
2025		3113
2026	// create one ev_io per pollfd	3114	// create one ev_io per pollfd
2027	for (int i = 0; i < nfd; ++i)	3115	for (int i = 0; i < nfd; ++i)
2028	{	3116	{
…		…
2035	}	3123	}
2036	}	3124	}
2037		3125
2038	// stop all watchers after blocking	3126	// stop all watchers after blocking
2039	static void	3127	static void
2040	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	3128	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
2041	{	3129	{
2042	ev_timer_stop (loop, &tw);	3130	ev_timer_stop (loop, &tw);
2043		3131
2044	for (int i = 0; i < nfd; ++i)	3132	for (int i = 0; i < nfd; ++i)
2045	{	3133	{
…		…
2084	}	3172	}
2085		3173
2086	// do not ever call adns_afterpoll	3174	// do not ever call adns_afterpoll
2087		3175
2088	Method 4: Do not use a prepare or check watcher because the module you	3176	Method 4: Do not use a prepare or check watcher because the module you
2089	want to embed is too inflexible to support it. Instead, you can override	3177	want to embed is not flexible enough to support it. Instead, you can
2090	their poll function. The drawback with this solution is that the main	3178	override their poll function. The drawback with this solution is that the
2091	loop is now no longer controllable by EV. The C<Glib::EV> module does	3179	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
2092	this.	3180	this approach, effectively embedding EV as a client into the horrible
		3181	libglib event loop.
2093		3182
2094	static gint	3183	static gint
2095	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	3184	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
2096	{	3185	{
2097	int got_events = 0;	3186	int got_events = 0;
…		…
2101		3190
2102	if (timeout >= 0)	3191	if (timeout >= 0)
2103	// create/start timer	3192	// create/start timer
2104		3193
2105	// poll	3194	// poll
2106	ev_loop (EV_A_ 0);	3195	ev_run (EV_A_ 0);
2107		3196
2108	// stop timer again	3197	// stop timer again
2109	if (timeout >= 0)	3198	if (timeout >= 0)
2110	ev_timer_stop (EV_A_ &to);	3199	ev_timer_stop (EV_A_ &to);
2111		3200
…		…
2128	prioritise I/O.	3217	prioritise I/O.
2129		3218
2130	As an example for a bug workaround, the kqueue backend might only support	3219	As an example for a bug workaround, the kqueue backend might only support
2131	sockets on some platform, so it is unusable as generic backend, but you	3220	sockets on some platform, so it is unusable as generic backend, but you
2132	still want to make use of it because you have many sockets and it scales	3221	still want to make use of it because you have many sockets and it scales
2133	so nicely. In this case, you would create a kqueue-based loop and embed it	3222	so nicely. In this case, you would create a kqueue-based loop and embed
2134	into your default loop (which might use e.g. poll). Overall operation will	3223	it into your default loop (which might use e.g. poll). Overall operation
2135	be a bit slower because first libev has to poll and then call kevent, but	3224	will be a bit slower because first libev has to call C<poll> and then
2136	at least you can use both at what they are best.	3225	C<kevent>, but at least you can use both mechanisms for what they are
		3226	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
2137		3227
2138	As for prioritising I/O: rarely you have the case where some fds have	3228	As for prioritising I/O: under rare circumstances you have the case where
2139	to be watched and handled very quickly (with low latency), and even	3229	some fds have to be watched and handled very quickly (with low latency),
2140	priorities and idle watchers might have too much overhead. In this case	3230	and even priorities and idle watchers might have too much overhead. In
2141	you would put all the high priority stuff in one loop and all the rest in	3231	this case you would put all the high priority stuff in one loop and all
2142	a second one, and embed the second one in the first.	3232	the rest in a second one, and embed the second one in the first.
2143		3233
2144	As long as the watcher is active, the callback will be invoked every time	3234	As long as the watcher is active, the callback will be invoked every
2145	there might be events pending in the embedded loop. The callback must then	3235	time there might be events pending in the embedded loop. The callback
2146	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	3236	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
2147	their callbacks (you could also start an idle watcher to give the embedded	3237	sweep and invoke their callbacks (the callback doesn't need to invoke the
2148	loop strictly lower priority for example). You can also set the callback	3238	C<ev_embed_sweep> function directly, it could also start an idle watcher
2149	to C<0>, in which case the embed watcher will automatically execute the	3239	to give the embedded loop strictly lower priority for example).
2150	embedded loop sweep.
2151		3240
2152	As long as the watcher is started it will automatically handle events. The	3241	You can also set the callback to C<0>, in which case the embed watcher
2153	callback will be invoked whenever some events have been handled. You can	3242	will automatically execute the embedded loop sweep whenever necessary.
2154	set the callback to C<0> to avoid having to specify one if you are not
2155	interested in that.
2156		3243
2157	Also, there have not currently been made special provisions for forking:	3244	Fork detection will be handled transparently while the C<ev_embed> watcher
2158	when you fork, you not only have to call C<ev_loop_fork> on both loops,	3245	is active, i.e., the embedded loop will automatically be forked when the
2159	but you will also have to stop and restart any C<ev_embed> watchers	3246	embedding loop forks. In other cases, the user is responsible for calling
2160	yourself.	3247	C<ev_loop_fork> on the embedded loop.
2161		3248
2162	Unfortunately, not all backends are embeddable, only the ones returned by	3249	Unfortunately, not all backends are embeddable: only the ones returned by
2163	C<ev_embeddable_backends> are, which, unfortunately, does not include any	3250	C<ev_embeddable_backends> are, which, unfortunately, does not include any
2164	portable one.	3251	portable one.
2165		3252
2166	So when you want to use this feature you will always have to be prepared	3253	So when you want to use this feature you will always have to be prepared
2167	that you cannot get an embeddable loop. The recommended way to get around	3254	that you cannot get an embeddable loop. The recommended way to get around
2168	this is to have a separate variables for your embeddable loop, try to	3255	this is to have a separate variables for your embeddable loop, try to
2169	create it, and if that fails, use the normal loop for everything.	3256	create it, and if that fails, use the normal loop for everything.
2170		3257
		3258	=head3 C<ev_embed> and fork
		3259
		3260	While the C<ev_embed> watcher is running, forks in the embedding loop will
		3261	automatically be applied to the embedded loop as well, so no special
		3262	fork handling is required in that case. When the watcher is not running,
		3263	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		3264	as applicable.
		3265
2171	=head3 Watcher-Specific Functions and Data Members	3266	=head3 Watcher-Specific Functions and Data Members
2172		3267
2173	=over 4	3268	=over 4
2174		3269
2175	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3270	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
2176		3271
2177	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3272	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
2178		3273
2179	Configures the watcher to embed the given loop, which must be	3274	Configures the watcher to embed the given loop, which must be
2180	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3275	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
2181	invoked automatically, otherwise it is the responsibility of the callback	3276	invoked automatically, otherwise it is the responsibility of the callback
2182	to invoke it (it will continue to be called until the sweep has been done,	3277	to invoke it (it will continue to be called until the sweep has been done,
2183	if you do not want that, you need to temporarily stop the embed watcher).	3278	if you do not want that, you need to temporarily stop the embed watcher).
2184		3279
2185	=item ev_embed_sweep (loop, ev_embed *)	3280	=item ev_embed_sweep (loop, ev_embed *)
2186		3281
2187	Make a single, non-blocking sweep over the embedded loop. This works	3282	Make a single, non-blocking sweep over the embedded loop. This works
2188	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	3283	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
2189	appropriate way for embedded loops.	3284	appropriate way for embedded loops.
2190		3285
2191	=item struct ev_loop *other [read-only]	3286	=item struct ev_loop *other [read-only]
2192		3287
2193	The embedded event loop.	3288	The embedded event loop.
…		…
2202	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be	3297	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
2203	used).	3298	used).
2204		3299
2205	struct ev_loop *loop_hi = ev_default_init (0);	3300	struct ev_loop *loop_hi = ev_default_init (0);
2206	struct ev_loop *loop_lo = 0;	3301	struct ev_loop *loop_lo = 0;
2207	struct ev_embed embed;	3302	ev_embed embed;
2208		3303
2209	// see if there is a chance of getting one that works	3304	// see if there is a chance of getting one that works
2210	// (remember that a flags value of 0 means autodetection)	3305	// (remember that a flags value of 0 means autodetection)
2211	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3306	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2212	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3307	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
2213	: 0;	3308	: 0;
…		…
2226	kqueue implementation). Store the kqueue/socket-only event loop in	3321	kqueue implementation). Store the kqueue/socket-only event loop in
2227	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3322	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2228		3323
2229	struct ev_loop *loop = ev_default_init (0);	3324	struct ev_loop *loop = ev_default_init (0);
2230	struct ev_loop *loop_socket = 0;	3325	struct ev_loop *loop_socket = 0;
2231	struct ev_embed embed;	3326	ev_embed embed;
2232		3327
2233	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3328	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2234	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3329	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2235	{	3330	{
2236	ev_embed_init (&embed, 0, loop_socket);	3331	ev_embed_init (&embed, 0, loop_socket);
2237	ev_embed_start (loop, &embed);	3332	ev_embed_start (loop, &embed);
…		…
2245		3340
2246	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3341	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
2247		3342
2248	Fork watchers are called when a C<fork ()> was detected (usually because	3343	Fork watchers are called when a C<fork ()> was detected (usually because
2249	whoever is a good citizen cared to tell libev about it by calling	3344	whoever is a good citizen cared to tell libev about it by calling
2250	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the	3345	C<ev_loop_fork>). The invocation is done before the event loop blocks next
2251	event loop blocks next and before C<ev_check> watchers are being called,	3346	and before C<ev_check> watchers are being called, and only in the child
2252	and only in the child after the fork. If whoever good citizen calling	3347	after the fork. If whoever good citizen calling C<ev_default_fork> cheats
2253	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3348	and calls it in the wrong process, the fork handlers will be invoked, too,
2254	handlers will be invoked, too, of course.	3349	of course.
		3350
		3351	=head3 The special problem of life after fork - how is it possible?
		3352
		3353	Most uses of C<fork ()> consist of forking, then some simple calls to set
		3354	up/change the process environment, followed by a call to C<exec()>. This
		3355	sequence should be handled by libev without any problems.
		3356
		3357	This changes when the application actually wants to do event handling
		3358	in the child, or both parent in child, in effect "continuing" after the
		3359	fork.
		3360
		3361	The default mode of operation (for libev, with application help to detect
		3362	forks) is to duplicate all the state in the child, as would be expected
		3363	when I<either> the parent I<or> the child process continues.
		3364
		3365	When both processes want to continue using libev, then this is usually the
		3366	wrong result. In that case, usually one process (typically the parent) is
		3367	supposed to continue with all watchers in place as before, while the other
		3368	process typically wants to start fresh, i.e. without any active watchers.
		3369
		3370	The cleanest and most efficient way to achieve that with libev is to
		3371	simply create a new event loop, which of course will be "empty", and
		3372	use that for new watchers. This has the advantage of not touching more
		3373	memory than necessary, and thus avoiding the copy-on-write, and the
		3374	disadvantage of having to use multiple event loops (which do not support
		3375	signal watchers).
		3376
		3377	When this is not possible, or you want to use the default loop for
		3378	other reasons, then in the process that wants to start "fresh", call
		3379	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
		3380	Destroying the default loop will "orphan" (not stop) all registered
		3381	watchers, so you have to be careful not to execute code that modifies
		3382	those watchers. Note also that in that case, you have to re-register any
		3383	signal watchers.
2255		3384
2256	=head3 Watcher-Specific Functions and Data Members	3385	=head3 Watcher-Specific Functions and Data Members
2257		3386
2258	=over 4	3387	=over 4
2259		3388
2260	=item ev_fork_init (ev_signal *, callback)	3389	=item ev_fork_init (ev_fork *, callback)
2261		3390
2262	Initialises and configures the fork watcher - it has no parameters of any	3391	Initialises and configures the fork watcher - it has no parameters of any
2263	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,	3392	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
2264	believe me.	3393	really.
2265		3394
2266	=back	3395	=back
2267		3396
2268		3397
		3398	=head2 C<ev_cleanup> - even the best things end
		3399
		3400	Cleanup watchers are called just before the event loop is being destroyed
		3401	by a call to C<ev_loop_destroy>.
		3402
		3403	While there is no guarantee that the event loop gets destroyed, cleanup
		3404	watchers provide a convenient method to install cleanup hooks for your
		3405	program, worker threads and so on - you just to make sure to destroy the
		3406	loop when you want them to be invoked.
		3407
		3408	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3409	all other watchers, they do not keep a reference to the event loop (which
		3410	makes a lot of sense if you think about it). Like all other watchers, you
		3411	can call libev functions in the callback, except C<ev_cleanup_start>.
		3412
		3413	=head3 Watcher-Specific Functions and Data Members
		3414
		3415	=over 4
		3416
		3417	=item ev_cleanup_init (ev_cleanup *, callback)
		3418
		3419	Initialises and configures the cleanup watcher - it has no parameters of
		3420	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3421	pointless, I assure you.
		3422
		3423	=back
		3424
		3425	Example: Register an atexit handler to destroy the default loop, so any
		3426	cleanup functions are called.
		3427
		3428	static void
		3429	program_exits (void)
		3430	{
		3431	ev_loop_destroy (EV_DEFAULT_UC);
		3432	}
		3433
		3434	...
		3435	atexit (program_exits);
		3436
		3437
2269	=head2 C<ev_async> - how to wake up another event loop	3438	=head2 C<ev_async> - how to wake up an event loop
2270		3439
2271	In general, you cannot use an C<ev_loop> from multiple threads or other	3440	In general, you cannot use an C<ev_loop> from multiple threads or other
2272	asynchronous sources such as signal handlers (as opposed to multiple event	3441	asynchronous sources such as signal handlers (as opposed to multiple event
2273	loops - those are of course safe to use in different threads).	3442	loops - those are of course safe to use in different threads).
2274		3443
2275	Sometimes, however, you need to wake up another event loop you do not	3444	Sometimes, however, you need to wake up an event loop you do not control,
2276	control, for example because it belongs to another thread. This is what	3445	for example because it belongs to another thread. This is what C<ev_async>
2277	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you	3446	watchers do: as long as the C<ev_async> watcher is active, you can signal
2278	can signal it by calling C<ev_async_send>, which is thread- and signal	3447	it by calling C<ev_async_send>, which is thread- and signal safe.
2279	safe.
2280		3448
2281	This functionality is very similar to C<ev_signal> watchers, as signals,	3449	This functionality is very similar to C<ev_signal> watchers, as signals,
2282	too, are asynchronous in nature, and signals, too, will be compressed	3450	too, are asynchronous in nature, and signals, too, will be compressed
2283	(i.e. the number of callback invocations may be less than the number of	3451	(i.e. the number of callback invocations may be less than the number of
2284	C<ev_async_sent> calls).	3452	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
2285		3453	of "global async watchers" by using a watcher on an otherwise unused
2286	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not	3454	signal, and C<ev_feed_signal> to signal this watcher from another thread,
2287	just the default loop.	3455	even without knowing which loop owns the signal.
2288		3456
2289	=head3 Queueing	3457	=head3 Queueing
2290		3458
2291	C<ev_async> does not support queueing of data in any way. The reason	3459	C<ev_async> does not support queueing of data in any way. The reason
2292	is that the author does not know of a simple (or any) algorithm for a	3460	is that the author does not know of a simple (or any) algorithm for a
2293	multiple-writer-single-reader queue that works in all cases and doesn't	3461	multiple-writer-single-reader queue that works in all cases and doesn't
2294	need elaborate support such as pthreads.	3462	need elaborate support such as pthreads or unportable memory access
		3463	semantics.
2295		3464
2296	That means that if you want to queue data, you have to provide your own	3465	That means that if you want to queue data, you have to provide your own
2297	queue. But at least I can tell you would implement locking around your	3466	queue. But at least I can tell you how to implement locking around your
2298	queue:	3467	queue:
2299		3468
2300	=over 4	3469	=over 4
2301		3470
2302	=item queueing from a signal handler context	3471	=item queueing from a signal handler context
2303		3472
2304	To implement race-free queueing, you simply add to the queue in the signal	3473	To implement race-free queueing, you simply add to the queue in the signal
2305	handler but you block the signal handler in the watcher callback. Here is an example that does that for	3474	handler but you block the signal handler in the watcher callback. Here is
2306	some fictitious SIGUSR1 handler:	3475	an example that does that for some fictitious SIGUSR1 handler:
2307		3476
2308	static ev_async mysig;	3477	static ev_async mysig;
2309		3478
2310	static void	3479	static void
2311	sigusr1_handler (void)	3480	sigusr1_handler (void)
…		…
2377	=over 4	3546	=over 4
2378		3547
2379	=item ev_async_init (ev_async *, callback)	3548	=item ev_async_init (ev_async *, callback)
2380		3549
2381	Initialises and configures the async watcher - it has no parameters of any	3550	Initialises and configures the async watcher - it has no parameters of any
2382	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,	3551	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
2383	believe me.	3552	trust me.
2384		3553
2385	=item ev_async_send (loop, ev_async *)	3554	=item ev_async_send (loop, ev_async *)
2386		3555
2387	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3556	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
2388	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3557	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3558	returns.
		3559
2389	C<ev_feed_event>, this call is safe to do in other threads, signal or	3560	Unlike C<ev_feed_event>, this call is safe to do from other threads,
2390	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3561	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
2391	section below on what exactly this means).	3562	embedding section below on what exactly this means).
2392		3563
2393	This call incurs the overhead of a system call only once per loop iteration,	3564	Note that, as with other watchers in libev, multiple events might get
2394	so while the overhead might be noticeable, it doesn't apply to repeated	3565	compressed into a single callback invocation (another way to look at
2395	calls to C<ev_async_send>.	3566	this is that C<ev_async> watchers are level-triggered: they are set on
		3567	C<ev_async_send>, reset when the event loop detects that).
		3568
		3569	This call incurs the overhead of at most one extra system call per event
		3570	loop iteration, if the event loop is blocked, and no syscall at all if
		3571	the event loop (or your program) is processing events. That means that
		3572	repeated calls are basically free (there is no need to avoid calls for
		3573	performance reasons) and that the overhead becomes smaller (typically
		3574	zero) under load.
2396		3575
2397	=item bool = ev_async_pending (ev_async *)	3576	=item bool = ev_async_pending (ev_async *)
2398		3577
2399	Returns a non-zero value when C<ev_async_send> has been called on the	3578	Returns a non-zero value when C<ev_async_send> has been called on the
2400	watcher but the event has not yet been processed (or even noted) by the	3579	watcher but the event has not yet been processed (or even noted) by the
…		…
2403	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When	3582	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
2404	the loop iterates next and checks for the watcher to have become active,	3583	the loop iterates next and checks for the watcher to have become active,
2405	it will reset the flag again. C<ev_async_pending> can be used to very	3584	it will reset the flag again. C<ev_async_pending> can be used to very
2406	quickly check whether invoking the loop might be a good idea.	3585	quickly check whether invoking the loop might be a good idea.
2407		3586
2408	Not that this does I<not> check whether the watcher itself is pending, only	3587	Not that this does I<not> check whether the watcher itself is pending,
2409	whether it has been requested to make this watcher pending.	3588	only whether it has been requested to make this watcher pending: there
		3589	is a time window between the event loop checking and resetting the async
		3590	notification, and the callback being invoked.
2410		3591
2411	=back	3592	=back
2412		3593
2413		3594
2414	=head1 OTHER FUNCTIONS	3595	=head1 OTHER FUNCTIONS
2415		3596
2416	There are some other functions of possible interest. Described. Here. Now.	3597	There are some other functions of possible interest. Described. Here. Now.
2417		3598
2418	=over 4	3599	=over 4
2419		3600
2420	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3601	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)
2421		3602
2422	This function combines a simple timer and an I/O watcher, calls your	3603	This function combines a simple timer and an I/O watcher, calls your
2423	callback on whichever event happens first and automatically stop both	3604	callback on whichever event happens first and automatically stops both
2424	watchers. This is useful if you want to wait for a single event on an fd	3605	watchers. This is useful if you want to wait for a single event on an fd
2425	or timeout without having to allocate/configure/start/stop/free one or	3606	or timeout without having to allocate/configure/start/stop/free one or
2426	more watchers yourself.	3607	more watchers yourself.
2427		3608
2428	If C<fd> is less than 0, then no I/O watcher will be started and events	3609	If C<fd> is less than 0, then no I/O watcher will be started and the
2429	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3610	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
2430	C<events> set will be created and started.	3611	the given C<fd> and C<events> set will be created and started.
2431		3612
2432	If C<timeout> is less than 0, then no timeout watcher will be	3613	If C<timeout> is less than 0, then no timeout watcher will be
2433	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3614	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
2434	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3615	repeat = 0) will be started. C<0> is a valid timeout.
2435	dubious value.
2436		3616
2437	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3617	The callback has the type C<void (*cb)(int revents, void *arg)> and is
2438	passed an C<revents> set like normal event callbacks (a combination of	3618	passed an C<revents> set like normal event callbacks (a combination of
2439	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3619	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
2440	value passed to C<ev_once>:	3620	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3621	a timeout and an io event at the same time - you probably should give io
		3622	events precedence.
		3623
		3624	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
2441		3625
2442	static void stdin_ready (int revents, void *arg)	3626	static void stdin_ready (int revents, void *arg)
2443	{	3627	{
		3628	if (revents & EV_READ)
		3629	/* stdin might have data for us, joy! */;
2444	if (revents & EV_TIMEOUT)	3630	else if (revents & EV_TIMER)
2445	/* doh, nothing entered */;	3631	/* doh, nothing entered */;
2446	else if (revents & EV_READ)
2447	/* stdin might have data for us, joy! */;
2448	}	3632	}
2449		3633
2450	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3634	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2451		3635
2452	=item ev_feed_event (ev_loop *, watcher *, int revents)
2453
2454	Feeds the given event set into the event loop, as if the specified event
2455	had happened for the specified watcher (which must be a pointer to an
2456	initialised but not necessarily started event watcher).
2457
2458	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3636	=item ev_feed_fd_event (loop, int fd, int revents)
2459		3637
2460	Feed an event on the given fd, as if a file descriptor backend detected	3638	Feed an event on the given fd, as if a file descriptor backend detected
2461	the given events it.	3639	the given events.
2462		3640
2463	=item ev_feed_signal_event (ev_loop *loop, int signum)	3641	=item ev_feed_signal_event (loop, int signum)
2464		3642
2465	Feed an event as if the given signal occurred (C<loop> must be the default	3643	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
2466	loop!).	3644	which is async-safe.
2467		3645
2468	=back	3646	=back
		3647
		3648
		3649	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3650
		3651	This section explains some common idioms that are not immediately
		3652	obvious. Note that examples are sprinkled over the whole manual, and this
		3653	section only contains stuff that wouldn't fit anywhere else.
		3654
		3655	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3656
		3657	Each watcher has, by default, a C<void *data> member that you can read
		3658	or modify at any time: libev will completely ignore it. This can be used
		3659	to associate arbitrary data with your watcher. If you need more data and
		3660	don't want to allocate memory separately and store a pointer to it in that
		3661	data member, you can also "subclass" the watcher type and provide your own
		3662	data:
		3663
		3664	struct my_io
		3665	{
		3666	ev_io io;
		3667	int otherfd;
		3668	void *somedata;
		3669	struct whatever *mostinteresting;
		3670	};
		3671
		3672	...
		3673	struct my_io w;
		3674	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3675
		3676	And since your callback will be called with a pointer to the watcher, you
		3677	can cast it back to your own type:
		3678
		3679	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3680	{
		3681	struct my_io *w = (struct my_io *)w_;
		3682	...
		3683	}
		3684
		3685	More interesting and less C-conformant ways of casting your callback
		3686	function type instead have been omitted.
		3687
		3688	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3689
		3690	Another common scenario is to use some data structure with multiple
		3691	embedded watchers, in effect creating your own watcher that combines
		3692	multiple libev event sources into one "super-watcher":
		3693
		3694	struct my_biggy
		3695	{
		3696	int some_data;
		3697	ev_timer t1;
		3698	ev_timer t2;
		3699	}
		3700
		3701	In this case getting the pointer to C<my_biggy> is a bit more
		3702	complicated: Either you store the address of your C<my_biggy> struct in
		3703	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3704	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3705	real programmers):
		3706
		3707	#include <stddef.h>
		3708
		3709	static void
		3710	t1_cb (EV_P_ ev_timer *w, int revents)
		3711	{
		3712	struct my_biggy big = (struct my_biggy *)
		3713	(((char *)w) - offsetof (struct my_biggy, t1));
		3714	}
		3715
		3716	static void
		3717	t2_cb (EV_P_ ev_timer *w, int revents)
		3718	{
		3719	struct my_biggy big = (struct my_biggy *)
		3720	(((char *)w) - offsetof (struct my_biggy, t2));
		3721	}
		3722
		3723	=head2 AVOIDING FINISHING BEFORE RETURNING
		3724
		3725	Often you have structures like this in event-based programs:
		3726
		3727	callback ()
		3728	{
		3729	free (request);
		3730	}
		3731
		3732	request = start_new_request (..., callback);
		3733
		3734	The intent is to start some "lengthy" operation. The C<request> could be
		3735	used to cancel the operation, or do other things with it.
		3736
		3737	It's not uncommon to have code paths in C<start_new_request> that
		3738	immediately invoke the callback, for example, to report errors. Or you add
		3739	some caching layer that finds that it can skip the lengthy aspects of the
		3740	operation and simply invoke the callback with the result.
		3741
		3742	The problem here is that this will happen I<before> C<start_new_request>
		3743	has returned, so C<request> is not set.
		3744
		3745	Even if you pass the request by some safer means to the callback, you
		3746	might want to do something to the request after starting it, such as
		3747	canceling it, which probably isn't working so well when the callback has
		3748	already been invoked.
		3749
		3750	A common way around all these issues is to make sure that
		3751	C<start_new_request> I<always> returns before the callback is invoked. If
		3752	C<start_new_request> immediately knows the result, it can artificially
		3753	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3754	example, or more sneakily, by reusing an existing (stopped) watcher and
		3755	pushing it into the pending queue:
		3756
		3757	ev_set_cb (watcher, callback);
		3758	ev_feed_event (EV_A_ watcher, 0);
		3759
		3760	This way, C<start_new_request> can safely return before the callback is
		3761	invoked, while not delaying callback invocation too much.
		3762
		3763	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3764
		3765	Often (especially in GUI toolkits) there are places where you have
		3766	I<modal> interaction, which is most easily implemented by recursively
		3767	invoking C<ev_run>.
		3768
		3769	This brings the problem of exiting - a callback might want to finish the
		3770	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3771	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3772	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3773	other combination: In these cases, a simple C<ev_break> will not work.
		3774
		3775	The solution is to maintain "break this loop" variable for each C<ev_run>
		3776	invocation, and use a loop around C<ev_run> until the condition is
		3777	triggered, using C<EVRUN_ONCE>:
		3778
		3779	// main loop
		3780	int exit_main_loop = 0;
		3781
		3782	while (!exit_main_loop)
		3783	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3784
		3785	// in a modal watcher
		3786	int exit_nested_loop = 0;
		3787
		3788	while (!exit_nested_loop)
		3789	ev_run (EV_A_ EVRUN_ONCE);
		3790
		3791	To exit from any of these loops, just set the corresponding exit variable:
		3792
		3793	// exit modal loop
		3794	exit_nested_loop = 1;
		3795
		3796	// exit main program, after modal loop is finished
		3797	exit_main_loop = 1;
		3798
		3799	// exit both
		3800	exit_main_loop = exit_nested_loop = 1;
		3801
		3802	=head2 THREAD LOCKING EXAMPLE
		3803
		3804	Here is a fictitious example of how to run an event loop in a different
		3805	thread from where callbacks are being invoked and watchers are
		3806	created/added/removed.
		3807
		3808	For a real-world example, see the C<EV::Loop::Async> perl module,
		3809	which uses exactly this technique (which is suited for many high-level
		3810	languages).
		3811
		3812	The example uses a pthread mutex to protect the loop data, a condition
		3813	variable to wait for callback invocations, an async watcher to notify the
		3814	event loop thread and an unspecified mechanism to wake up the main thread.
		3815
		3816	First, you need to associate some data with the event loop:
		3817
		3818	typedef struct {
		3819	mutex_t lock; /* global loop lock */
		3820	ev_async async_w;
		3821	thread_t tid;
		3822	cond_t invoke_cv;
		3823	} userdata;
		3824
		3825	void prepare_loop (EV_P)
		3826	{
		3827	// for simplicity, we use a static userdata struct.
		3828	static userdata u;
		3829
		3830	ev_async_init (&u->async_w, async_cb);
		3831	ev_async_start (EV_A_ &u->async_w);
		3832
		3833	pthread_mutex_init (&u->lock, 0);
		3834	pthread_cond_init (&u->invoke_cv, 0);
		3835
		3836	// now associate this with the loop
		3837	ev_set_userdata (EV_A_ u);
		3838	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3839	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3840
		3841	// then create the thread running ev_run
		3842	pthread_create (&u->tid, 0, l_run, EV_A);
		3843	}
		3844
		3845	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3846	solely to wake up the event loop so it takes notice of any new watchers
		3847	that might have been added:
		3848
		3849	static void
		3850	async_cb (EV_P_ ev_async *w, int revents)
		3851	{
		3852	// just used for the side effects
		3853	}
		3854
		3855	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3856	protecting the loop data, respectively.
		3857
		3858	static void
		3859	l_release (EV_P)
		3860	{
		3861	userdata *u = ev_userdata (EV_A);
		3862	pthread_mutex_unlock (&u->lock);
		3863	}
		3864
		3865	static void
		3866	l_acquire (EV_P)
		3867	{
		3868	userdata *u = ev_userdata (EV_A);
		3869	pthread_mutex_lock (&u->lock);
		3870	}
		3871
		3872	The event loop thread first acquires the mutex, and then jumps straight
		3873	into C<ev_run>:
		3874
		3875	void *
		3876	l_run (void *thr_arg)
		3877	{
		3878	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3879
		3880	l_acquire (EV_A);
		3881	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3882	ev_run (EV_A_ 0);
		3883	l_release (EV_A);
		3884
		3885	return 0;
		3886	}
		3887
		3888	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3889	signal the main thread via some unspecified mechanism (signals? pipe
		3890	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3891	have been called (in a while loop because a) spurious wakeups are possible
		3892	and b) skipping inter-thread-communication when there are no pending
		3893	watchers is very beneficial):
		3894
		3895	static void
		3896	l_invoke (EV_P)
		3897	{
		3898	userdata *u = ev_userdata (EV_A);
		3899
		3900	while (ev_pending_count (EV_A))
		3901	{
		3902	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3903	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3904	}
		3905	}
		3906
		3907	Now, whenever the main thread gets told to invoke pending watchers, it
		3908	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3909	thread to continue:
		3910
		3911	static void
		3912	real_invoke_pending (EV_P)
		3913	{
		3914	userdata *u = ev_userdata (EV_A);
		3915
		3916	pthread_mutex_lock (&u->lock);
		3917	ev_invoke_pending (EV_A);
		3918	pthread_cond_signal (&u->invoke_cv);
		3919	pthread_mutex_unlock (&u->lock);
		3920	}
		3921
		3922	Whenever you want to start/stop a watcher or do other modifications to an
		3923	event loop, you will now have to lock:
		3924
		3925	ev_timer timeout_watcher;
		3926	userdata *u = ev_userdata (EV_A);
		3927
		3928	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3929
		3930	pthread_mutex_lock (&u->lock);
		3931	ev_timer_start (EV_A_ &timeout_watcher);
		3932	ev_async_send (EV_A_ &u->async_w);
		3933	pthread_mutex_unlock (&u->lock);
		3934
		3935	Note that sending the C<ev_async> watcher is required because otherwise
		3936	an event loop currently blocking in the kernel will have no knowledge
		3937	about the newly added timer. By waking up the loop it will pick up any new
		3938	watchers in the next event loop iteration.
		3939
		3940	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3941
		3942	While the overhead of a callback that e.g. schedules a thread is small, it
		3943	is still an overhead. If you embed libev, and your main usage is with some
		3944	kind of threads or coroutines, you might want to customise libev so that
		3945	doesn't need callbacks anymore.
		3946
		3947	Imagine you have coroutines that you can switch to using a function
		3948	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3949	and that due to some magic, the currently active coroutine is stored in a
		3950	global called C<current_coro>. Then you can build your own "wait for libev
		3951	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3952	the differing C<;> conventions):
		3953
		3954	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3955	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3956
		3957	That means instead of having a C callback function, you store the
		3958	coroutine to switch to in each watcher, and instead of having libev call
		3959	your callback, you instead have it switch to that coroutine.
		3960
		3961	A coroutine might now wait for an event with a function called
		3962	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3963	matter when, or whether the watcher is active or not when this function is
		3964	called):
		3965
		3966	void
		3967	wait_for_event (ev_watcher *w)
		3968	{
		3969	ev_set_cb (w, current_coro);
		3970	switch_to (libev_coro);
		3971	}
		3972
		3973	That basically suspends the coroutine inside C<wait_for_event> and
		3974	continues the libev coroutine, which, when appropriate, switches back to
		3975	this or any other coroutine.
		3976
		3977	You can do similar tricks if you have, say, threads with an event queue -
		3978	instead of storing a coroutine, you store the queue object and instead of
		3979	switching to a coroutine, you push the watcher onto the queue and notify
		3980	any waiters.
		3981
		3982	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		3983	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3984
		3985	// my_ev.h
		3986	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3987	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3988	#include "../libev/ev.h"
		3989
		3990	// my_ev.c
		3991	#define EV_H "my_ev.h"
		3992	#include "../libev/ev.c"
		3993
		3994	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3995	F<my_ev.c> into your project. When properly specifying include paths, you
		3996	can even use F<ev.h> as header file name directly.
2469		3997
2470		3998
2471	=head1 LIBEVENT EMULATION	3999	=head1 LIBEVENT EMULATION
2472		4000
2473	Libev offers a compatibility emulation layer for libevent. It cannot	4001	Libev offers a compatibility emulation layer for libevent. It cannot
2474	emulate the internals of libevent, so here are some usage hints:	4002	emulate the internals of libevent, so here are some usage hints:
2475		4003
2476	=over 4	4004	=over 4
		4005
		4006	=item * Only the libevent-1.4.1-beta API is being emulated.
		4007
		4008	This was the newest libevent version available when libev was implemented,
		4009	and is still mostly unchanged in 2010.
2477		4010
2478	=item * Use it by including <event.h>, as usual.	4011	=item * Use it by including <event.h>, as usual.
2479		4012
2480	=item * The following members are fully supported: ev_base, ev_callback,	4013	=item * The following members are fully supported: ev_base, ev_callback,
2481	ev_arg, ev_fd, ev_res, ev_events.	4014	ev_arg, ev_fd, ev_res, ev_events.
…		…
2487	=item * Priorities are not currently supported. Initialising priorities	4020	=item * Priorities are not currently supported. Initialising priorities
2488	will fail and all watchers will have the same priority, even though there	4021	will fail and all watchers will have the same priority, even though there
2489	is an ev_pri field.	4022	is an ev_pri field.
2490		4023
2491	=item * In libevent, the last base created gets the signals, in libev, the	4024	=item * In libevent, the last base created gets the signals, in libev, the
2492	first base created (== the default loop) gets the signals.	4025	base that registered the signal gets the signals.
2493		4026
2494	=item * Other members are not supported.	4027	=item * Other members are not supported.
2495		4028
2496	=item * The libev emulation is I<not> ABI compatible to libevent, you need	4029	=item * The libev emulation is I<not> ABI compatible to libevent, you need
2497	to use the libev header file and library.	4030	to use the libev header file and library.
2498		4031
2499	=back	4032	=back
2500		4033
2501	=head1 C++ SUPPORT	4034	=head1 C++ SUPPORT
		4035
		4036	=head2 C API
		4037
		4038	The normal C API should work fine when used from C++: both ev.h and the
		4039	libev sources can be compiled as C++. Therefore, code that uses the C API
		4040	will work fine.
		4041
		4042	Proper exception specifications might have to be added to callbacks passed
		4043	to libev: exceptions may be thrown only from watcher callbacks, all other
		4044	callbacks (allocator, syserr, loop acquire/release and periodic reschedule
		4045	callbacks) must not throw exceptions, and might need a C<noexcept>
		4046	specification. If you have code that needs to be compiled as both C and
		4047	C++ you can use the C<EV_NOEXCEPT> macro for this:
		4048
		4049	static void
		4050	fatal_error (const char *msg) EV_NOEXCEPT
		4051	{
		4052	perror (msg);
		4053	abort ();
		4054	}
		4055
		4056	...
		4057	ev_set_syserr_cb (fatal_error);
		4058
		4059	The only API functions that can currently throw exceptions are C<ev_run>,
		4060	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		4061	because it runs cleanup watchers).
		4062
		4063	Throwing exceptions in watcher callbacks is only supported if libev itself
		4064	is compiled with a C++ compiler or your C and C++ environments allow
		4065	throwing exceptions through C libraries (most do).
		4066
		4067	=head2 C++ API
2502		4068
2503	Libev comes with some simplistic wrapper classes for C++ that mainly allow	4069	Libev comes with some simplistic wrapper classes for C++ that mainly allow
2504	you to use some convenience methods to start/stop watchers and also change	4070	you to use some convenience methods to start/stop watchers and also change
2505	the callback model to a model using method callbacks on objects.	4071	the callback model to a model using method callbacks on objects.
2506		4072
2507	To use it,	4073	To use it,
2508		4074
2509	#include <ev++.h>	4075	#include <ev++.h>
2510		4076
2511	This automatically includes F<ev.h> and puts all of its definitions (many	4077	This automatically includes F<ev.h> and puts all of its definitions (many
2512	of them macros) into the global namespace. All C++ specific things are	4078	of them macros) into the global namespace. All C++ specific things are
2513	put into the C<ev> namespace. It should support all the same embedding	4079	put into the C<ev> namespace. It should support all the same embedding
…		…
2516	Care has been taken to keep the overhead low. The only data member the C++	4082	Care has been taken to keep the overhead low. The only data member the C++
2517	classes add (compared to plain C-style watchers) is the event loop pointer	4083	classes add (compared to plain C-style watchers) is the event loop pointer
2518	that the watcher is associated with (or no additional members at all if	4084	that the watcher is associated with (or no additional members at all if
2519	you disable C<EV_MULTIPLICITY> when embedding libev).	4085	you disable C<EV_MULTIPLICITY> when embedding libev).
2520		4086
2521	Currently, functions, and static and non-static member functions can be	4087	Currently, functions, static and non-static member functions and classes
2522	used as callbacks. Other types should be easy to add as long as they only	4088	with C<operator ()> can be used as callbacks. Other types should be easy
2523	need one additional pointer for context. If you need support for other	4089	to add as long as they only need one additional pointer for context. If
2524	types of functors please contact the author (preferably after implementing	4090	you need support for other types of functors please contact the author
2525	it).	4091	(preferably after implementing it).
		4092
		4093	For all this to work, your C++ compiler either has to use the same calling
		4094	conventions as your C compiler (for static member functions), or you have
		4095	to embed libev and compile libev itself as C++.
2526		4096
2527	Here is a list of things available in the C<ev> namespace:	4097	Here is a list of things available in the C<ev> namespace:
2528		4098
2529	=over 4	4099	=over 4
2530		4100
…		…
2540	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4110	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
2541		4111
2542	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4112	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
2543	the same name in the C<ev> namespace, with the exception of C<ev_signal>	4113	the same name in the C<ev> namespace, with the exception of C<ev_signal>
2544	which is called C<ev::sig> to avoid clashes with the C<signal> macro	4114	which is called C<ev::sig> to avoid clashes with the C<signal> macro
2545	defines by many implementations.	4115	defined by many implementations.
2546		4116
2547	All of those classes have these methods:	4117	All of those classes have these methods:
2548		4118
2549	=over 4	4119	=over 4
2550		4120
2551	=item ev::TYPE::TYPE ()	4121	=item ev::TYPE::TYPE ()
2552		4122
2553	=item ev::TYPE::TYPE (struct ev_loop *)	4123	=item ev::TYPE::TYPE (loop)
2554		4124
2555	=item ev::TYPE::~TYPE	4125	=item ev::TYPE::~TYPE
2556		4126
2557	The constructor (optionally) takes an event loop to associate the watcher	4127	The constructor (optionally) takes an event loop to associate the watcher
2558	with. If it is omitted, it will use C<EV_DEFAULT>.	4128	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
2590		4160
2591	myclass obj;	4161	myclass obj;
2592	ev::io iow;	4162	ev::io iow;
2593	iow.set <myclass, &myclass::io_cb> (&obj);	4163	iow.set <myclass, &myclass::io_cb> (&obj);
2594		4164
		4165	=item w->set (object *)
		4166
		4167	This is a variation of a method callback - leaving out the method to call
		4168	will default the method to C<operator ()>, which makes it possible to use
		4169	functor objects without having to manually specify the C<operator ()> all
		4170	the time. Incidentally, you can then also leave out the template argument
		4171	list.
		4172
		4173	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		4174	int revents)>.
		4175
		4176	See the method-C<set> above for more details.
		4177
		4178	Example: use a functor object as callback.
		4179
		4180	struct myfunctor
		4181	{
		4182	void operator() (ev::io &w, int revents)
		4183	{
		4184	...
		4185	}
		4186	}
		4187
		4188	myfunctor f;
		4189
		4190	ev::io w;
		4191	w.set (&f);
		4192
2595	=item w->set<function> (void *data = 0)	4193	=item w->set<function> (void *data = 0)
2596		4194
2597	Also sets a callback, but uses a static method or plain function as	4195	Also sets a callback, but uses a static method or plain function as
2598	callback. The optional C<data> argument will be stored in the watcher's	4196	callback. The optional C<data> argument will be stored in the watcher's
2599	C<data> member and is free for you to use.	4197	C<data> member and is free for you to use.
2600		4198
2601	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	4199	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2602		4200
2603	See the method-C<set> above for more details.	4201	See the method-C<set> above for more details.
2604		4202
2605	Example:	4203	Example: Use a plain function as callback.
2606		4204
2607	static void io_cb (ev::io &w, int revents) { }	4205	static void io_cb (ev::io &w, int revents) { }
2608	iow.set <io_cb> ();	4206	iow.set <io_cb> ();
2609		4207
2610	=item w->set (struct ev_loop *)	4208	=item w->set (loop)
2611		4209
2612	Associates a different C<struct ev_loop> with this watcher. You can only	4210	Associates a different C<struct ev_loop> with this watcher. You can only
2613	do this when the watcher is inactive (and not pending either).	4211	do this when the watcher is inactive (and not pending either).
2614		4212
2615	=item w->set ([arguments])	4213	=item w->set ([arguments])
2616		4214
2617	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be	4215	Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
		4216	with the same arguments. Either this method or a suitable start method
2618	called at least once. Unlike the C counterpart, an active watcher gets	4217	must be called at least once. Unlike the C counterpart, an active watcher
2619	automatically stopped and restarted when reconfiguring it with this	4218	gets automatically stopped and restarted when reconfiguring it with this
2620	method.	4219	method.
		4220
		4221	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4222	clashing with the C<set (loop)> method.
2621		4223
2622	=item w->start ()	4224	=item w->start ()
2623		4225
2624	Starts the watcher. Note that there is no C<loop> argument, as the	4226	Starts the watcher. Note that there is no C<loop> argument, as the
2625	constructor already stores the event loop.	4227	constructor already stores the event loop.
2626		4228
		4229	=item w->start ([arguments])
		4230
		4231	Instead of calling C<set> and C<start> methods separately, it is often
		4232	convenient to wrap them in one call. Uses the same type of arguments as
		4233	the configure C<set> method of the watcher.
		4234
2627	=item w->stop ()	4235	=item w->stop ()
2628		4236
2629	Stops the watcher if it is active. Again, no C<loop> argument.	4237	Stops the watcher if it is active. Again, no C<loop> argument.
2630		4238
2631	=item w->again () (C<ev::timer>, C<ev::periodic> only)	4239	=item w->again () (C<ev::timer>, C<ev::periodic> only)
…		…
2643		4251
2644	=back	4252	=back
2645		4253
2646	=back	4254	=back
2647		4255
2648	Example: Define a class with an IO and idle watcher, start one of them in	4256	Example: Define a class with two I/O and idle watchers, start the I/O
2649	the constructor.	4257	watchers in the constructor.
2650		4258
2651	class myclass	4259	class myclass
2652	{	4260	{
2653	ev::io io; void io_cb (ev::io &w, int revents);	4261	ev::io io ; void io_cb (ev::io &w, int revents);
		4262	ev::io io2 ; void io2_cb (ev::io &w, int revents);
2654	ev:idle idle void idle_cb (ev::idle &w, int revents);	4263	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2655		4264
2656	myclass (int fd)	4265	myclass (int fd)
2657	{	4266	{
2658	io .set <myclass, &myclass::io_cb > (this);	4267	io .set <myclass, &myclass::io_cb > (this);
		4268	io2 .set <myclass, &myclass::io2_cb > (this);
2659	idle.set <myclass, &myclass::idle_cb> (this);	4269	idle.set <myclass, &myclass::idle_cb> (this);
2660		4270
2661	io.start (fd, ev::READ);	4271	io.set (fd, ev::WRITE); // configure the watcher
		4272	io.start (); // start it whenever convenient
		4273
		4274	io2.start (fd, ev::READ); // set + start in one call
2662	}	4275	}
2663	};	4276	};
2664		4277
2665		4278
2666	=head1 OTHER LANGUAGE BINDINGS	4279	=head1 OTHER LANGUAGE BINDINGS
…		…
2675	=item Perl	4288	=item Perl
2676		4289
2677	The EV module implements the full libev API and is actually used to test	4290	The EV module implements the full libev API and is actually used to test
2678	libev. EV is developed together with libev. Apart from the EV core module,	4291	libev. EV is developed together with libev. Apart from the EV core module,
2679	there are additional modules that implement libev-compatible interfaces	4292	there are additional modules that implement libev-compatible interfaces
2680	to C<libadns> (C<EV::ADNS>), C<Net::SNMP> (C<Net::SNMP::EV>) and the	4293	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
2681	C<libglib> event core (C<Glib::EV> and C<EV::Glib>).	4294	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		4295	and C<EV::Glib>).
2682		4296
2683	It can be found and installed via CPAN, its homepage is at	4297	It can be found and installed via CPAN, its homepage is at
2684	L<http://software.schmorp.de/pkg/EV>.	4298	L<http://software.schmorp.de/pkg/EV>.
2685		4299
2686	=item Python	4300	=item Python
2687		4301
2688	Python bindings can be found at L<http://code.google.com/p/pyev/>. It	4302	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
2689	seems to be quite complete and well-documented. Note, however, that the	4303	seems to be quite complete and well-documented.
2690	patch they require for libev is outright dangerous as it breaks the ABI
2691	for everybody else, and therefore, should never be applied in an installed
2692	libev (if python requires an incompatible ABI then it needs to embed
2693	libev).
2694		4304
2695	=item Ruby	4305	=item Ruby
2696		4306
2697	Tony Arcieri has written a ruby extension that offers access to a subset	4307	Tony Arcieri has written a ruby extension that offers access to a subset
2698	of the libev API and adds file handle abstractions, asynchronous DNS and	4308	of the libev API and adds file handle abstractions, asynchronous DNS and
2699	more on top of it. It can be found via gem servers. Its homepage is at	4309	more on top of it. It can be found via gem servers. Its homepage is at
2700	L<http://rev.rubyforge.org/>.	4310	L<http://rev.rubyforge.org/>.
2701		4311
		4312	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		4313	makes rev work even on mingw.
		4314
		4315	=item Haskell
		4316
		4317	A haskell binding to libev is available at
		4318	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		4319
2702	=item D	4320	=item D
2703		4321
2704	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4322	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
2705	be found at L<http://proj.llucax.com.ar/wiki/evd>.	4323	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
		4324
		4325	=item Ocaml
		4326
		4327	Erkki Seppala has written Ocaml bindings for libev, to be found at
		4328	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		4329
		4330	=item Lua
		4331
		4332	Brian Maher has written a partial interface to libev for lua (at the
		4333	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		4334	L<http://github.com/brimworks/lua-ev>.
		4335
		4336	=item Javascript
		4337
		4338	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4339
		4340	=item Others
		4341
		4342	There are others, and I stopped counting.
2706		4343
2707	=back	4344	=back
2708		4345
2709		4346
2710	=head1 MACRO MAGIC	4347	=head1 MACRO MAGIC
…		…
2724	loop argument"). The C<EV_A> form is used when this is the sole argument,	4361	loop argument"). The C<EV_A> form is used when this is the sole argument,
2725	C<EV_A_> is used when other arguments are following. Example:	4362	C<EV_A_> is used when other arguments are following. Example:
2726		4363
2727	ev_unref (EV_A);	4364	ev_unref (EV_A);
2728	ev_timer_add (EV_A_ watcher);	4365	ev_timer_add (EV_A_ watcher);
2729	ev_loop (EV_A_ 0);	4366	ev_run (EV_A_ 0);
2730		4367
2731	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	4368	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2732	which is often provided by the following macro.	4369	which is often provided by the following macro.
2733		4370
2734	=item C<EV_P>, C<EV_P_>	4371	=item C<EV_P>, C<EV_P_>
…		…
2747	suitable for use with C<EV_A>.	4384	suitable for use with C<EV_A>.
2748		4385
2749	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4386	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2750		4387
2751	Similar to the other two macros, this gives you the value of the default	4388	Similar to the other two macros, this gives you the value of the default
2752	loop, if multiple loops are supported ("ev loop default").	4389	loop, if multiple loops are supported ("ev loop default"). The default loop
		4390	will be initialised if it isn't already initialised.
		4391
		4392	For non-multiplicity builds, these macros do nothing, so you always have
		4393	to initialise the loop somewhere.
2753		4394
2754	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4395	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
2755		4396
2756	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4397	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
2757	default loop has been initialised (C<UC> == unchecked). Their behaviour	4398	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
2774	}	4415	}
2775		4416
2776	ev_check check;	4417	ev_check check;
2777	ev_check_init (&check, check_cb);	4418	ev_check_init (&check, check_cb);
2778	ev_check_start (EV_DEFAULT_ &check);	4419	ev_check_start (EV_DEFAULT_ &check);
2779	ev_loop (EV_DEFAULT_ 0);	4420	ev_run (EV_DEFAULT_ 0);
2780		4421
2781	=head1 EMBEDDING	4422	=head1 EMBEDDING
2782		4423
2783	Libev can (and often is) directly embedded into host	4424	Libev can (and often is) directly embedded into host
2784	applications. Examples of applications that embed it include the Deliantra	4425	applications. Examples of applications that embed it include the Deliantra
…		…
2811		4452
2812	#define EV_STANDALONE 1	4453	#define EV_STANDALONE 1
2813	#include "ev.h"	4454	#include "ev.h"
2814		4455
2815	Both header files and implementation files can be compiled with a C++	4456	Both header files and implementation files can be compiled with a C++
2816	compiler (at least, thats a stated goal, and breakage will be treated	4457	compiler (at least, that's a stated goal, and breakage will be treated
2817	as a bug).	4458	as a bug).
2818		4459
2819	You need the following files in your source tree, or in a directory	4460	You need the following files in your source tree, or in a directory
2820	in your include path (e.g. in libev/ when using -Ilibev):	4461	in your include path (e.g. in libev/ when using -Ilibev):
2821		4462
…		…
2824	ev_vars.h	4465	ev_vars.h
2825	ev_wrap.h	4466	ev_wrap.h
2826		4467
2827	ev_win32.c required on win32 platforms only	4468	ev_win32.c required on win32 platforms only
2828		4469
2829	ev_select.c only when select backend is enabled (which is enabled by default)	4470	ev_select.c only when select backend is enabled
2830	ev_poll.c only when poll backend is enabled (disabled by default)	4471	ev_poll.c only when poll backend is enabled
2831	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4472	ev_epoll.c only when the epoll backend is enabled
		4473	ev_linuxaio.c only when the linux aio backend is enabled
2832	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4474	ev_kqueue.c only when the kqueue backend is enabled
2833	ev_port.c only when the solaris port backend is enabled (disabled by default)	4475	ev_port.c only when the solaris port backend is enabled
2834		4476
2835	F<ev.c> includes the backend files directly when enabled, so you only need	4477	F<ev.c> includes the backend files directly when enabled, so you only need
2836	to compile this single file.	4478	to compile this single file.
2837		4479
2838	=head3 LIBEVENT COMPATIBILITY API	4480	=head3 LIBEVENT COMPATIBILITY API
…		…
2864	libev.m4	4506	libev.m4
2865		4507
2866	=head2 PREPROCESSOR SYMBOLS/MACROS	4508	=head2 PREPROCESSOR SYMBOLS/MACROS
2867		4509
2868	Libev can be configured via a variety of preprocessor symbols you have to	4510	Libev can be configured via a variety of preprocessor symbols you have to
2869	define before including any of its files. The default in the absence of	4511	define before including (or compiling) any of its files. The default in
2870	autoconf is noted for every option.	4512	the absence of autoconf is documented for every option.
		4513
		4514	Symbols marked with "(h)" do not change the ABI, and can have different
		4515	values when compiling libev vs. including F<ev.h>, so it is permissible
		4516	to redefine them before including F<ev.h> without breaking compatibility
		4517	to a compiled library. All other symbols change the ABI, which means all
		4518	users of libev and the libev code itself must be compiled with compatible
		4519	settings.
2871		4520
2872	=over 4	4521	=over 4
2873		4522
		4523	=item EV_COMPAT3 (h)
		4524
		4525	Backwards compatibility is a major concern for libev. This is why this
		4526	release of libev comes with wrappers for the functions and symbols that
		4527	have been renamed between libev version 3 and 4.
		4528
		4529	You can disable these wrappers (to test compatibility with future
		4530	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		4531	sources. This has the additional advantage that you can drop the C<struct>
		4532	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		4533	typedef in that case.
		4534
		4535	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		4536	and in some even more future version the compatibility code will be
		4537	removed completely.
		4538
2874	=item EV_STANDALONE	4539	=item EV_STANDALONE (h)
2875		4540
2876	Must always be C<1> if you do not use autoconf configuration, which	4541	Must always be C<1> if you do not use autoconf configuration, which
2877	keeps libev from including F<config.h>, and it also defines dummy	4542	keeps libev from including F<config.h>, and it also defines dummy
2878	implementations for some libevent functions (such as logging, which is not	4543	implementations for some libevent functions (such as logging, which is not
2879	supported). It will also not define any of the structs usually found in	4544	supported). It will also not define any of the structs usually found in
2880	F<event.h> that are not directly supported by the libev core alone.	4545	F<event.h> that are not directly supported by the libev core alone.
2881		4546
		4547	In standalone mode, libev will still try to automatically deduce the
		4548	configuration, but has to be more conservative.
		4549
		4550	=item EV_USE_FLOOR
		4551
		4552	If defined to be C<1>, libev will use the C<floor ()> function for its
		4553	periodic reschedule calculations, otherwise libev will fall back on a
		4554	portable (slower) implementation. If you enable this, you usually have to
		4555	link against libm or something equivalent. Enabling this when the C<floor>
		4556	function is not available will fail, so the safe default is to not enable
		4557	this.
		4558
2882	=item EV_USE_MONOTONIC	4559	=item EV_USE_MONOTONIC
2883		4560
2884	If defined to be C<1>, libev will try to detect the availability of the	4561	If defined to be C<1>, libev will try to detect the availability of the
2885	monotonic clock option at both compile time and runtime. Otherwise no use	4562	monotonic clock option at both compile time and runtime. Otherwise no
2886	of the monotonic clock option will be attempted. If you enable this, you	4563	use of the monotonic clock option will be attempted. If you enable this,
2887	usually have to link against librt or something similar. Enabling it when	4564	you usually have to link against librt or something similar. Enabling it
2888	the functionality isn't available is safe, though, although you have	4565	when the functionality isn't available is safe, though, although you have
2889	to make sure you link against any libraries where the C<clock_gettime>	4566	to make sure you link against any libraries where the C<clock_gettime>
2890	function is hiding in (often F<-lrt>).	4567	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2891		4568
2892	=item EV_USE_REALTIME	4569	=item EV_USE_REALTIME
2893		4570
2894	If defined to be C<1>, libev will try to detect the availability of the	4571	If defined to be C<1>, libev will try to detect the availability of the
2895	real-time clock option at compile time (and assume its availability at	4572	real-time clock option at compile time (and assume its availability
2896	runtime if successful). Otherwise no use of the real-time clock option will	4573	at runtime if successful). Otherwise no use of the real-time clock
2897	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	4574	option will be attempted. This effectively replaces C<gettimeofday>
2898	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	4575	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2899	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	4576	correctness. See the note about libraries in the description of
		4577	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		4578	C<EV_USE_CLOCK_SYSCALL>.
		4579
		4580	=item EV_USE_CLOCK_SYSCALL
		4581
		4582	If defined to be C<1>, libev will try to use a direct syscall instead
		4583	of calling the system-provided C<clock_gettime> function. This option
		4584	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		4585	unconditionally pulls in C<libpthread>, slowing down single-threaded
		4586	programs needlessly. Using a direct syscall is slightly slower (in
		4587	theory), because no optimised vdso implementation can be used, but avoids
		4588	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		4589	higher, as it simplifies linking (no need for C<-lrt>).
2900		4590
2901	=item EV_USE_NANOSLEEP	4591	=item EV_USE_NANOSLEEP
2902		4592
2903	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	4593	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2904	and will use it for delays. Otherwise it will use C<select ()>.	4594	and will use it for delays. Otherwise it will use C<select ()>.
…		…
2920		4610
2921	=item EV_SELECT_USE_FD_SET	4611	=item EV_SELECT_USE_FD_SET
2922		4612
2923	If defined to C<1>, then the select backend will use the system C<fd_set>	4613	If defined to C<1>, then the select backend will use the system C<fd_set>
2924	structure. This is useful if libev doesn't compile due to a missing	4614	structure. This is useful if libev doesn't compile due to a missing
2925	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on	4615	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2926	exotic systems. This usually limits the range of file descriptors to some	4616	on exotic systems. This usually limits the range of file descriptors to
2927	low limit such as 1024 or might have other limitations (winsocket only	4617	some low limit such as 1024 or might have other limitations (winsocket
2928	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	4618	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2929	influence the size of the C<fd_set> used.	4619	configures the maximum size of the C<fd_set>.
2930		4620
2931	=item EV_SELECT_IS_WINSOCKET	4621	=item EV_SELECT_IS_WINSOCKET
2932		4622
2933	When defined to C<1>, the select backend will assume that	4623	When defined to C<1>, the select backend will assume that
2934	select/socket/connect etc. don't understand file descriptors but	4624	select/socket/connect etc. don't understand file descriptors but
…		…
2936	be used is the winsock select). This means that it will call	4626	be used is the winsock select). This means that it will call
2937	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	4627	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2938	it is assumed that all these functions actually work on fds, even	4628	it is assumed that all these functions actually work on fds, even
2939	on win32. Should not be defined on non-win32 platforms.	4629	on win32. Should not be defined on non-win32 platforms.
2940		4630
2941	=item EV_FD_TO_WIN32_HANDLE	4631	=item EV_FD_TO_WIN32_HANDLE(fd)
2942		4632
2943	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map	4633	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
2944	file descriptors to socket handles. When not defining this symbol (the	4634	file descriptors to socket handles. When not defining this symbol (the
2945	default), then libev will call C<_get_osfhandle>, which is usually	4635	default), then libev will call C<_get_osfhandle>, which is usually
2946	correct. In some cases, programs use their own file descriptor management,	4636	correct. In some cases, programs use their own file descriptor management,
2947	in which case they can provide this function to map fds to socket handles.	4637	in which case they can provide this function to map fds to socket handles.
2948		4638
		4639	=item EV_WIN32_HANDLE_TO_FD(handle)
		4640
		4641	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		4642	using the standard C<_open_osfhandle> function. For programs implementing
		4643	their own fd to handle mapping, overwriting this function makes it easier
		4644	to do so. This can be done by defining this macro to an appropriate value.
		4645
		4646	=item EV_WIN32_CLOSE_FD(fd)
		4647
		4648	If programs implement their own fd to handle mapping on win32, then this
		4649	macro can be used to override the C<close> function, useful to unregister
		4650	file descriptors again. Note that the replacement function has to close
		4651	the underlying OS handle.
		4652
		4653	=item EV_USE_WSASOCKET
		4654
		4655	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4656	communication socket, which works better in some environments. Otherwise,
		4657	the normal C<socket> function will be used, which works better in other
		4658	environments.
		4659
2949	=item EV_USE_POLL	4660	=item EV_USE_POLL
2950		4661
2951	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4662	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2952	backend. Otherwise it will be enabled on non-win32 platforms. It	4663	backend. Otherwise it will be enabled on non-win32 platforms. It
2953	takes precedence over select.	4664	takes precedence over select.
…		…
2957	If defined to be C<1>, libev will compile in support for the Linux	4668	If defined to be C<1>, libev will compile in support for the Linux
2958	C<epoll>(7) backend. Its availability will be detected at runtime,	4669	C<epoll>(7) backend. Its availability will be detected at runtime,
2959	otherwise another method will be used as fallback. This is the preferred	4670	otherwise another method will be used as fallback. This is the preferred
2960	backend for GNU/Linux systems. If undefined, it will be enabled if the	4671	backend for GNU/Linux systems. If undefined, it will be enabled if the
2961	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4672	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4673
		4674	=item EV_USE_LINUXAIO
		4675
		4676	If defined to be C<1>, libev will compile in support for the Linux
		4677	aio backend. Due to it's currenbt limitations it has to be requested
		4678	explicitly. If undefined, it will be enabled on linux, otherwise
		4679	disabled.
2962		4680
2963	=item EV_USE_KQUEUE	4681	=item EV_USE_KQUEUE
2964		4682
2965	If defined to be C<1>, libev will compile in support for the BSD style	4683	If defined to be C<1>, libev will compile in support for the BSD style
2966	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	4684	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2988	If defined to be C<1>, libev will compile in support for the Linux inotify	4706	If defined to be C<1>, libev will compile in support for the Linux inotify
2989	interface to speed up C<ev_stat> watchers. Its actual availability will	4707	interface to speed up C<ev_stat> watchers. Its actual availability will
2990	be detected at runtime. If undefined, it will be enabled if the headers	4708	be detected at runtime. If undefined, it will be enabled if the headers
2991	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4709	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2992		4710
		4711	=item EV_NO_SMP
		4712
		4713	If defined to be C<1>, libev will assume that memory is always coherent
		4714	between threads, that is, threads can be used, but threads never run on
		4715	different cpus (or different cpu cores). This reduces dependencies
		4716	and makes libev faster.
		4717
		4718	=item EV_NO_THREADS
		4719
		4720	If defined to be C<1>, libev will assume that it will never be called from
		4721	different threads (that includes signal handlers), which is a stronger
		4722	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4723	libev faster.
		4724
2993	=item EV_ATOMIC_T	4725	=item EV_ATOMIC_T
2994		4726
2995	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4727	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
2996	access is atomic with respect to other threads or signal contexts. No such	4728	access is atomic with respect to other threads or signal contexts. No
2997	type is easily found in the C language, so you can provide your own type	4729	such type is easily found in the C language, so you can provide your own
2998	that you know is safe for your purposes. It is used both for signal handler "locking"	4730	type that you know is safe for your purposes. It is used both for signal
2999	as well as for signal and thread safety in C<ev_async> watchers.	4731	handler "locking" as well as for signal and thread safety in C<ev_async>
		4732	watchers.
3000		4733
3001	In the absence of this define, libev will use C<sig_atomic_t volatile>	4734	In the absence of this define, libev will use C<sig_atomic_t volatile>
3002	(from F<signal.h>), which is usually good enough on most platforms.	4735	(from F<signal.h>), which is usually good enough on most platforms.
3003		4736
3004	=item EV_H	4737	=item EV_H (h)
3005		4738
3006	The name of the F<ev.h> header file used to include it. The default if	4739	The name of the F<ev.h> header file used to include it. The default if
3007	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be	4740	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
3008	used to virtually rename the F<ev.h> header file in case of conflicts.	4741	used to virtually rename the F<ev.h> header file in case of conflicts.
3009		4742
3010	=item EV_CONFIG_H	4743	=item EV_CONFIG_H (h)
3011		4744
3012	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	4745	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
3013	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	4746	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
3014	C<EV_H>, above.	4747	C<EV_H>, above.
3015		4748
3016	=item EV_EVENT_H	4749	=item EV_EVENT_H (h)
3017		4750
3018	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	4751	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
3019	of how the F<event.h> header can be found, the default is C<"event.h">.	4752	of how the F<event.h> header can be found, the default is C<"event.h">.
3020		4753
3021	=item EV_PROTOTYPES	4754	=item EV_PROTOTYPES (h)
3022		4755
3023	If defined to be C<0>, then F<ev.h> will not define any function	4756	If defined to be C<0>, then F<ev.h> will not define any function
3024	prototypes, but still define all the structs and other symbols. This is	4757	prototypes, but still define all the structs and other symbols. This is
3025	occasionally useful if you want to provide your own wrapper functions	4758	occasionally useful if you want to provide your own wrapper functions
3026	around libev functions.	4759	around libev functions.
…		…
3031	will have the C<struct ev_loop *> as first argument, and you can create	4764	will have the C<struct ev_loop *> as first argument, and you can create
3032	additional independent event loops. Otherwise there will be no support	4765	additional independent event loops. Otherwise there will be no support
3033	for multiple event loops and there is no first event loop pointer	4766	for multiple event loops and there is no first event loop pointer
3034	argument. Instead, all functions act on the single default loop.	4767	argument. Instead, all functions act on the single default loop.
3035		4768
		4769	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4770	default loop when multiplicity is switched off - you always have to
		4771	initialise the loop manually in this case.
		4772
3036	=item EV_MINPRI	4773	=item EV_MINPRI
3037		4774
3038	=item EV_MAXPRI	4775	=item EV_MAXPRI
3039		4776
3040	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4777	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
3045	When doing priority-based operations, libev usually has to linearly search	4782	When doing priority-based operations, libev usually has to linearly search
3046	all the priorities, so having many of them (hundreds) uses a lot of space	4783	all the priorities, so having many of them (hundreds) uses a lot of space
3047	and time, so using the defaults of five priorities (-2 .. +2) is usually	4784	and time, so using the defaults of five priorities (-2 .. +2) is usually
3048	fine.	4785	fine.
3049		4786
3050	If your embedding application does not need any priorities, defining these both to	4787	If your embedding application does not need any priorities, defining these
3051	C<0> will save some memory and CPU.	4788	both to C<0> will save some memory and CPU.
3052		4789
3053	=item EV_PERIODIC_ENABLE	4790	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		4791	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		4792	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
3054		4793
3055	If undefined or defined to be C<1>, then periodic timers are supported. If	4794	If undefined or defined to be C<1> (and the platform supports it), then
3056	defined to be C<0>, then they are not. Disabling them saves a few kB of	4795	the respective watcher type is supported. If defined to be C<0>, then it
3057	code.	4796	is not. Disabling watcher types mainly saves code size.
3058		4797
3059	=item EV_IDLE_ENABLE	4798	=item EV_FEATURES
3060
3061	If undefined or defined to be C<1>, then idle watchers are supported. If
3062	defined to be C<0>, then they are not. Disabling them saves a few kB of
3063	code.
3064
3065	=item EV_EMBED_ENABLE
3066
3067	If undefined or defined to be C<1>, then embed watchers are supported. If
3068	defined to be C<0>, then they are not.
3069
3070	=item EV_STAT_ENABLE
3071
3072	If undefined or defined to be C<1>, then stat watchers are supported. If
3073	defined to be C<0>, then they are not.
3074
3075	=item EV_FORK_ENABLE
3076
3077	If undefined or defined to be C<1>, then fork watchers are supported. If
3078	defined to be C<0>, then they are not.
3079
3080	=item EV_ASYNC_ENABLE
3081
3082	If undefined or defined to be C<1>, then async watchers are supported. If
3083	defined to be C<0>, then they are not.
3084
3085	=item EV_MINIMAL
3086		4799
3087	If you need to shave off some kilobytes of code at the expense of some	4800	If you need to shave off some kilobytes of code at the expense of some
3088	speed, define this symbol to C<1>. Currently this is used to override some	4801	speed (but with the full API), you can define this symbol to request
3089	inlining decisions, saves roughly 30% code size on amd64. It also selects a	4802	certain subsets of functionality. The default is to enable all features
3090	much smaller 2-heap for timer management over the default 4-heap.	4803	that can be enabled on the platform.
		4804
		4805	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4806	with some broad features you want) and then selectively re-enable
		4807	additional parts you want, for example if you want everything minimal,
		4808	but multiple event loop support, async and child watchers and the poll
		4809	backend, use this:
		4810
		4811	#define EV_FEATURES 0
		4812	#define EV_MULTIPLICITY 1
		4813	#define EV_USE_POLL 1
		4814	#define EV_CHILD_ENABLE 1
		4815	#define EV_ASYNC_ENABLE 1
		4816
		4817	The actual value is a bitset, it can be a combination of the following
		4818	values (by default, all of these are enabled):
		4819
		4820	=over 4
		4821
		4822	=item C<1> - faster/larger code
		4823
		4824	Use larger code to speed up some operations.
		4825
		4826	Currently this is used to override some inlining decisions (enlarging the
		4827	code size by roughly 30% on amd64).
		4828
		4829	When optimising for size, use of compiler flags such as C<-Os> with
		4830	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4831	assertions.
		4832
		4833	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4834	(e.g. gcc with C<-Os>).
		4835
		4836	=item C<2> - faster/larger data structures
		4837
		4838	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4839	hash table sizes and so on. This will usually further increase code size
		4840	and can additionally have an effect on the size of data structures at
		4841	runtime.
		4842
		4843	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4844	(e.g. gcc with C<-Os>).
		4845
		4846	=item C<4> - full API configuration
		4847
		4848	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4849	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4850
		4851	=item C<8> - full API
		4852
		4853	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4854	details on which parts of the API are still available without this
		4855	feature, and do not complain if this subset changes over time.
		4856
		4857	=item C<16> - enable all optional watcher types
		4858
		4859	Enables all optional watcher types. If you want to selectively enable
		4860	only some watcher types other than I/O and timers (e.g. prepare,
		4861	embed, async, child...) you can enable them manually by defining
		4862	C<EV_watchertype_ENABLE> to C<1> instead.
		4863
		4864	=item C<32> - enable all backends
		4865
		4866	This enables all backends - without this feature, you need to enable at
		4867	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4868
		4869	=item C<64> - enable OS-specific "helper" APIs
		4870
		4871	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4872	default.
		4873
		4874	=back
		4875
		4876	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4877	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4878	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4879	watchers, timers and monotonic clock support.
		4880
		4881	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4882	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4883	your program might be left out as well - a binary starting a timer and an
		4884	I/O watcher then might come out at only 5Kb.
		4885
		4886	=item EV_API_STATIC
		4887
		4888	If this symbol is defined (by default it is not), then all identifiers
		4889	will have static linkage. This means that libev will not export any
		4890	identifiers, and you cannot link against libev anymore. This can be useful
		4891	when you embed libev, only want to use libev functions in a single file,
		4892	and do not want its identifiers to be visible.
		4893
		4894	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4895	wants to use libev.
		4896
		4897	This option only works when libev is compiled with a C compiler, as C++
		4898	doesn't support the required declaration syntax.
		4899
		4900	=item EV_AVOID_STDIO
		4901
		4902	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4903	functions (printf, scanf, perror etc.). This will increase the code size
		4904	somewhat, but if your program doesn't otherwise depend on stdio and your
		4905	libc allows it, this avoids linking in the stdio library which is quite
		4906	big.
		4907
		4908	Note that error messages might become less precise when this option is
		4909	enabled.
		4910
		4911	=item EV_NSIG
		4912
		4913	The highest supported signal number, +1 (or, the number of
		4914	signals): Normally, libev tries to deduce the maximum number of signals
		4915	automatically, but sometimes this fails, in which case it can be
		4916	specified. Also, using a lower number than detected (C<32> should be
		4917	good for about any system in existence) can save some memory, as libev
		4918	statically allocates some 12-24 bytes per signal number.
3091		4919
3092	=item EV_PID_HASHSIZE	4920	=item EV_PID_HASHSIZE
3093		4921
3094	C<ev_child> watchers use a small hash table to distribute workload by	4922	C<ev_child> watchers use a small hash table to distribute workload by
3095	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	4923	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
3096	than enough. If you need to manage thousands of children you might want to	4924	usually more than enough. If you need to manage thousands of children you
3097	increase this value (I<must> be a power of two).	4925	might want to increase this value (I<must> be a power of two).
3098		4926
3099	=item EV_INOTIFY_HASHSIZE	4927	=item EV_INOTIFY_HASHSIZE
3100		4928
3101	C<ev_stat> watchers use a small hash table to distribute workload by	4929	C<ev_stat> watchers use a small hash table to distribute workload by
3102	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	4930	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
3103	usually more than enough. If you need to manage thousands of C<ev_stat>	4931	disabled), usually more than enough. If you need to manage thousands of
3104	watchers you might want to increase this value (I<must> be a power of	4932	C<ev_stat> watchers you might want to increase this value (I<must> be a
3105	two).	4933	power of two).
3106		4934
3107	=item EV_USE_4HEAP	4935	=item EV_USE_4HEAP
3108		4936
3109	Heaps are not very cache-efficient. To improve the cache-efficiency of the	4937	Heaps are not very cache-efficient. To improve the cache-efficiency of the
3110	timer and periodics heap, libev uses a 4-heap when this symbol is defined	4938	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
3111	to C<1>. The 4-heap uses more complicated (longer) code but has	4939	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
3112	noticeably faster performance with many (thousands) of watchers.	4940	faster performance with many (thousands) of watchers.
3113		4941
3114	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	4942	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3115	(disabled).	4943	will be C<0>.
3116		4944
3117	=item EV_HEAP_CACHE_AT	4945	=item EV_HEAP_CACHE_AT
3118		4946
3119	Heaps are not very cache-efficient. To improve the cache-efficiency of the	4947	Heaps are not very cache-efficient. To improve the cache-efficiency of the
3120	timer and periodics heap, libev can cache the timestamp (I<at>) within	4948	timer and periodics heaps, libev can cache the timestamp (I<at>) within
3121	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),	4949	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
3122	which uses 8-12 bytes more per watcher and a few hundred bytes more code,	4950	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
3123	but avoids random read accesses on heap changes. This improves performance	4951	but avoids random read accesses on heap changes. This improves performance
3124	noticeably with with many (hundreds) of watchers.	4952	noticeably with many (hundreds) of watchers.
3125		4953
3126	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	4954	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3127	(disabled).	4955	will be C<0>.
3128		4956
3129	=item EV_VERIFY	4957	=item EV_VERIFY
3130		4958
3131	Controls how much internal verification (see C<ev_loop_verify ()>) will	4959	Controls how much internal verification (see C<ev_verify ()>) will
3132	be done: If set to C<0>, no internal verification code will be compiled	4960	be done: If set to C<0>, no internal verification code will be compiled
3133	in. If set to C<1>, then verification code will be compiled in, but not	4961	in. If set to C<1>, then verification code will be compiled in, but not
3134	called. If set to C<2>, then the internal verification code will be	4962	called. If set to C<2>, then the internal verification code will be
3135	called once per loop, which can slow down libev. If set to C<3>, then the	4963	called once per loop, which can slow down libev. If set to C<3>, then the
3136	verification code will be called very frequently, which will slow down	4964	verification code will be called very frequently, which will slow down
3137	libev considerably.	4965	libev considerably.
3138		4966
3139	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be	4967	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3140	C<0.>	4968	will be C<0>.
3141		4969
3142	=item EV_COMMON	4970	=item EV_COMMON
3143		4971
3144	By default, all watchers have a C<void *data> member. By redefining	4972	By default, all watchers have a C<void *data> member. By redefining
3145	this macro to a something else you can include more and other types of	4973	this macro to something else you can include more and other types of
3146	members. You have to define it each time you include one of the files,	4974	members. You have to define it each time you include one of the files,
3147	though, and it must be identical each time.	4975	though, and it must be identical each time.
3148		4976
3149	For example, the perl EV module uses something like this:	4977	For example, the perl EV module uses something like this:
3150		4978
…		…
3162	and the way callbacks are invoked and set. Must expand to a struct member	4990	and the way callbacks are invoked and set. Must expand to a struct member
3163	definition and a statement, respectively. See the F<ev.h> header file for	4991	definition and a statement, respectively. See the F<ev.h> header file for
3164	their default definitions. One possible use for overriding these is to	4992	their default definitions. One possible use for overriding these is to
3165	avoid the C<struct ev_loop *> as first argument in all cases, or to use	4993	avoid the C<struct ev_loop *> as first argument in all cases, or to use
3166	method calls instead of plain function calls in C++.	4994	method calls instead of plain function calls in C++.
		4995
		4996	=back
3167		4997
3168	=head2 EXPORTED API SYMBOLS	4998	=head2 EXPORTED API SYMBOLS
3169		4999
3170	If you need to re-export the API (e.g. via a DLL) and you need a list of	5000	If you need to re-export the API (e.g. via a DLL) and you need a list of
3171	exported symbols, you can use the provided F<Symbol.*> files which list	5001	exported symbols, you can use the provided F<Symbol.*> files which list
…		…
3201	file.	5031	file.
3202		5032
3203	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	5033	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
3204	that everybody includes and which overrides some configure choices:	5034	that everybody includes and which overrides some configure choices:
3205		5035
3206	#define EV_MINIMAL 1	5036	#define EV_FEATURES 8
3207	#define EV_USE_POLL 0	5037	#define EV_USE_SELECT 1
3208	#define EV_MULTIPLICITY 0
3209	#define EV_PERIODIC_ENABLE 0	5038	#define EV_PREPARE_ENABLE 1
		5039	#define EV_IDLE_ENABLE 1
3210	#define EV_STAT_ENABLE 0	5040	#define EV_SIGNAL_ENABLE 1
3211	#define EV_FORK_ENABLE 0	5041	#define EV_CHILD_ENABLE 1
		5042	#define EV_USE_STDEXCEPT 0
3212	#define EV_CONFIG_H <config.h>	5043	#define EV_CONFIG_H <config.h>
3213	#define EV_MINPRI 0
3214	#define EV_MAXPRI 0
3215		5044
3216	#include "ev++.h"	5045	#include "ev++.h"
3217		5046
3218	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	5047	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
3219		5048
3220	#include "ev_cpp.h"	5049	#include "ev_cpp.h"
3221	#include "ev.c"	5050	#include "ev.c"
3222		5051
		5052	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
3223		5053
3224	=head1 THREADS AND COROUTINES	5054	=head2 THREADS AND COROUTINES
3225		5055
3226	=head2 THREADS	5056	=head3 THREADS
3227		5057
3228	Libev itself is completely thread-safe, but it uses no locking. This	5058	All libev functions are reentrant and thread-safe unless explicitly
		5059	documented otherwise, but libev implements no locking itself. This means
3229	means that you can use as many loops as you want in parallel, as long as	5060	that you can use as many loops as you want in parallel, as long as there
3230	only one thread ever calls into one libev function with the same loop	5061	are no concurrent calls into any libev function with the same loop
3231	parameter.	5062	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		5063	of course): libev guarantees that different event loops share no data
		5064	structures that need any locking.
3232		5065
3233	Or put differently: calls with different loop parameters can be done in	5066	Or to put it differently: calls with different loop parameters can be done
3234	parallel from multiple threads, calls with the same loop parameter must be	5067	concurrently from multiple threads, calls with the same loop parameter
3235	done serially (but can be done from different threads, as long as only one	5068	must be done serially (but can be done from different threads, as long as
3236	thread ever is inside a call at any point in time, e.g. by using a mutex	5069	only one thread ever is inside a call at any point in time, e.g. by using
3237	per loop).	5070	a mutex per loop).
		5071
		5072	Specifically to support threads (and signal handlers), libev implements
		5073	so-called C<ev_async> watchers, which allow some limited form of
		5074	concurrency on the same event loop, namely waking it up "from the
		5075	outside".
3238		5076
3239	If you want to know which design (one loop, locking, or multiple loops	5077	If you want to know which design (one loop, locking, or multiple loops
3240	without or something else still) is best for your problem, then I cannot	5078	without or something else still) is best for your problem, then I cannot
3241	help you. I can give some generic advice however:	5079	help you, but here is some generic advice:
3242		5080
3243	=over 4	5081	=over 4
3244		5082
3245	=item * most applications have a main thread: use the default libev loop	5083	=item * most applications have a main thread: use the default libev loop
3246	in that thread, or create a separate thread running only the default loop.	5084	in that thread, or create a separate thread running only the default loop.
…		…
3258		5096
3259	Choosing a model is hard - look around, learn, know that usually you can do	5097	Choosing a model is hard - look around, learn, know that usually you can do
3260	better than you currently do :-)	5098	better than you currently do :-)
3261		5099
3262	=item * often you need to talk to some other thread which blocks in the	5100	=item * often you need to talk to some other thread which blocks in the
		5101	event loop.
		5102
3263	event loop - C<ev_async> watchers can be used to wake them up from other	5103	C<ev_async> watchers can be used to wake them up from other threads safely
3264	threads safely (or from signal contexts...).	5104	(or from signal contexts...).
		5105
		5106	An example use would be to communicate signals or other events that only
		5107	work in the default loop by registering the signal watcher with the
		5108	default loop and triggering an C<ev_async> watcher from the default loop
		5109	watcher callback into the event loop interested in the signal.
3265		5110
3266	=back	5111	=back
3267		5112
		5113	See also L</THREAD LOCKING EXAMPLE>.
		5114
3268	=head2 COROUTINES	5115	=head3 COROUTINES
3269		5116
3270	Libev is much more accommodating to coroutines ("cooperative threads"):	5117	Libev is very accommodating to coroutines ("cooperative threads"):
3271	libev fully supports nesting calls to it's functions from different	5118	libev fully supports nesting calls to its functions from different
3272	coroutines (e.g. you can call C<ev_loop> on the same loop from two	5119	coroutines (e.g. you can call C<ev_run> on the same loop from two
3273	different coroutines and switch freely between both coroutines running the	5120	different coroutines, and switch freely between both coroutines running
3274	loop, as long as you don't confuse yourself). The only exception is that	5121	the loop, as long as you don't confuse yourself). The only exception is
3275	you must not do this from C<ev_periodic> reschedule callbacks.	5122	that you must not do this from C<ev_periodic> reschedule callbacks.
3276		5123
3277	Care has been invested into making sure that libev does not keep local	5124	Care has been taken to ensure that libev does not keep local state inside
3278	state inside C<ev_loop>, and other calls do not usually allow coroutine	5125	C<ev_run>, and other calls do not usually allow for coroutine switches as
3279	switches.	5126	they do not call any callbacks.
3280		5127
		5128	=head2 COMPILER WARNINGS
3281		5129
3282	=head1 COMPLEXITIES	5130	Depending on your compiler and compiler settings, you might get no or a
		5131	lot of warnings when compiling libev code. Some people are apparently
		5132	scared by this.
3283		5133
3284	In this section the complexities of (many of) the algorithms used inside	5134	However, these are unavoidable for many reasons. For one, each compiler
3285	libev will be explained. For complexity discussions about backends see the	5135	has different warnings, and each user has different tastes regarding
3286	documentation for C<ev_default_init>.	5136	warning options. "Warn-free" code therefore cannot be a goal except when
		5137	targeting a specific compiler and compiler-version.
3287		5138
3288	All of the following are about amortised time: If an array needs to be	5139	Another reason is that some compiler warnings require elaborate
3289	extended, libev needs to realloc and move the whole array, but this	5140	workarounds, or other changes to the code that make it less clear and less
3290	happens asymptotically never with higher number of elements, so O(1) might	5141	maintainable.
3291	mean it might do a lengthy realloc operation in rare cases, but on average
3292	it is much faster and asymptotically approaches constant time.
3293		5142
3294	=over 4	5143	And of course, some compiler warnings are just plain stupid, or simply
		5144	wrong (because they don't actually warn about the condition their message
		5145	seems to warn about). For example, certain older gcc versions had some
		5146	warnings that resulted in an extreme number of false positives. These have
		5147	been fixed, but some people still insist on making code warn-free with
		5148	such buggy versions.
3295		5149
3296	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	5150	While libev is written to generate as few warnings as possible,
		5151	"warn-free" code is not a goal, and it is recommended not to build libev
		5152	with any compiler warnings enabled unless you are prepared to cope with
		5153	them (e.g. by ignoring them). Remember that warnings are just that:
		5154	warnings, not errors, or proof of bugs.
3297		5155
3298	This means that, when you have a watcher that triggers in one hour and
3299	there are 100 watchers that would trigger before that then inserting will
3300	have to skip roughly seven (C<ld 100>) of these watchers.
3301		5156
3302	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)	5157	=head2 VALGRIND
3303		5158
3304	That means that changing a timer costs less than removing/adding them	5159	Valgrind has a special section here because it is a popular tool that is
3305	as only the relative motion in the event queue has to be paid for.	5160	highly useful. Unfortunately, valgrind reports are very hard to interpret.
3306		5161
3307	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)	5162	If you think you found a bug (memory leak, uninitialised data access etc.)
		5163	in libev, then check twice: If valgrind reports something like:
3308		5164
3309	These just add the watcher into an array or at the head of a list.	5165	==2274== definitely lost: 0 bytes in 0 blocks.
		5166	==2274== possibly lost: 0 bytes in 0 blocks.
		5167	==2274== still reachable: 256 bytes in 1 blocks.
3310		5168
3311	=item Stopping check/prepare/idle/fork/async watchers: O(1)	5169	Then there is no memory leak, just as memory accounted to global variables
		5170	is not a memleak - the memory is still being referenced, and didn't leak.
3312		5171
3313	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	5172	Similarly, under some circumstances, valgrind might report kernel bugs
		5173	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		5174	although an acceptable workaround has been found here), or it might be
		5175	confused.
3314		5176
3315	These watchers are stored in lists then need to be walked to find the	5177	Keep in mind that valgrind is a very good tool, but only a tool. Don't
3316	correct watcher to remove. The lists are usually short (you don't usually	5178	make it into some kind of religion.
3317	have many watchers waiting for the same fd or signal).
3318		5179
3319	=item Finding the next timer in each loop iteration: O(1)	5180	If you are unsure about something, feel free to contact the mailing list
		5181	with the full valgrind report and an explanation on why you think this
		5182	is a bug in libev (best check the archives, too :). However, don't be
		5183	annoyed when you get a brisk "this is no bug" answer and take the chance
		5184	of learning how to interpret valgrind properly.
3320		5185
3321	By virtue of using a binary or 4-heap, the next timer is always found at a	5186	If you need, for some reason, empty reports from valgrind for your project
3322	fixed position in the storage array.	5187	I suggest using suppression lists.
3323		5188
3324	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
3325		5189
3326	A change means an I/O watcher gets started or stopped, which requires	5190	=head1 PORTABILITY NOTES
3327	libev to recalculate its status (and possibly tell the kernel, depending
3328	on backend and whether C<ev_io_set> was used).
3329		5191
3330	=item Activating one watcher (putting it into the pending state): O(1)	5192	=head2 GNU/LINUX 32 BIT LIMITATIONS
3331		5193
3332	=item Priority handling: O(number_of_priorities)	5194	GNU/Linux is the only common platform that supports 64 bit file/large file
		5195	interfaces but I<disables> them by default.
3333		5196
3334	Priorities are implemented by allocating some space for each	5197	That means that libev compiled in the default environment doesn't support
3335	priority. When doing priority-based operations, libev usually has to	5198	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
3336	linearly search all the priorities, but starting/stopping and activating
3337	watchers becomes O(1) w.r.t. priority handling.
3338		5199
3339	=item Sending an ev_async: O(1)	5200	Unfortunately, many programs try to work around this GNU/Linux issue
		5201	by enabling the large file API, which makes them incompatible with the
		5202	standard libev compiled for their system.
3340		5203
3341	=item Processing ev_async_send: O(number_of_async_watchers)	5204	Likewise, libev cannot enable the large file API itself as this would
		5205	suddenly make it incompatible to the default compile time environment,
		5206	i.e. all programs not using special compile switches.
3342		5207
3343	=item Processing signals: O(max_signal_number)	5208	=head2 OS/X AND DARWIN BUGS
3344		5209
3345	Sending involves a system call I<iff> there were no other C<ev_async_send>	5210	The whole thing is a bug if you ask me - basically any system interface
3346	calls in the current loop iteration. Checking for async and signal events	5211	you touch is broken, whether it is locales, poll, kqueue or even the
3347	involves iterating over all running async watchers or all signal numbers.	5212	OpenGL drivers.
3348		5213
3349	=back	5214	=head3 C<kqueue> is buggy
3350		5215
		5216	The kqueue syscall is broken in all known versions - most versions support
		5217	only sockets, many support pipes.
3351		5218
		5219	Libev tries to work around this by not using C<kqueue> by default on this
		5220	rotten platform, but of course you can still ask for it when creating a
		5221	loop - embedding a socket-only kqueue loop into a select-based one is
		5222	probably going to work well.
		5223
		5224	=head3 C<poll> is buggy
		5225
		5226	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		5227	implementation by something calling C<kqueue> internally around the 10.5.6
		5228	release, so now C<kqueue> I<and> C<poll> are broken.
		5229
		5230	Libev tries to work around this by not using C<poll> by default on
		5231	this rotten platform, but of course you can still ask for it when creating
		5232	a loop.
		5233
		5234	=head3 C<select> is buggy
		5235
		5236	All that's left is C<select>, and of course Apple found a way to fuck this
		5237	one up as well: On OS/X, C<select> actively limits the number of file
		5238	descriptors you can pass in to 1024 - your program suddenly crashes when
		5239	you use more.
		5240
		5241	There is an undocumented "workaround" for this - defining
		5242	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		5243	work on OS/X.
		5244
		5245	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		5246
		5247	=head3 C<errno> reentrancy
		5248
		5249	The default compile environment on Solaris is unfortunately so
		5250	thread-unsafe that you can't even use components/libraries compiled
		5251	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		5252	defined by default. A valid, if stupid, implementation choice.
		5253
		5254	If you want to use libev in threaded environments you have to make sure
		5255	it's compiled with C<_REENTRANT> defined.
		5256
		5257	=head3 Event port backend
		5258
		5259	The scalable event interface for Solaris is called "event
		5260	ports". Unfortunately, this mechanism is very buggy in all major
		5261	releases. If you run into high CPU usage, your program freezes or you get
		5262	a large number of spurious wakeups, make sure you have all the relevant
		5263	and latest kernel patches applied. No, I don't know which ones, but there
		5264	are multiple ones to apply, and afterwards, event ports actually work
		5265	great.
		5266
		5267	If you can't get it to work, you can try running the program by setting
		5268	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		5269	C<select> backends.
		5270
		5271	=head2 AIX POLL BUG
		5272
		5273	AIX unfortunately has a broken C<poll.h> header. Libev works around
		5274	this by trying to avoid the poll backend altogether (i.e. it's not even
		5275	compiled in), which normally isn't a big problem as C<select> works fine
		5276	with large bitsets on AIX, and AIX is dead anyway.
		5277
3352	=head1 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS	5278	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		5279
		5280	=head3 General issues
3353		5281
3354	Win32 doesn't support any of the standards (e.g. POSIX) that libev	5282	Win32 doesn't support any of the standards (e.g. POSIX) that libev
3355	requires, and its I/O model is fundamentally incompatible with the POSIX	5283	requires, and its I/O model is fundamentally incompatible with the POSIX
3356	model. Libev still offers limited functionality on this platform in	5284	model. Libev still offers limited functionality on this platform in
3357	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5285	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
3358	descriptors. This only applies when using Win32 natively, not when using	5286	descriptors. This only applies when using Win32 natively, not when using
3359	e.g. cygwin.	5287	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		5288	as every compiler comes with a slightly differently broken/incompatible
		5289	environment.
3360		5290
3361	Lifting these limitations would basically require the full	5291	Lifting these limitations would basically require the full
3362	re-implementation of the I/O system. If you are into these kinds of	5292	re-implementation of the I/O system. If you are into this kind of thing,
3363	things, then note that glib does exactly that for you in a very portable	5293	then note that glib does exactly that for you in a very portable way (note
3364	way (note also that glib is the slowest event library known to man).	5294	also that glib is the slowest event library known to man).
3365		5295
3366	There is no supported compilation method available on windows except	5296	There is no supported compilation method available on windows except
3367	embedding it into other applications.	5297	embedding it into other applications.
		5298
		5299	Sensible signal handling is officially unsupported by Microsoft - libev
		5300	tries its best, but under most conditions, signals will simply not work.
3368		5301
3369	Not a libev limitation but worth mentioning: windows apparently doesn't	5302	Not a libev limitation but worth mentioning: windows apparently doesn't
3370	accept large writes: instead of resulting in a partial write, windows will	5303	accept large writes: instead of resulting in a partial write, windows will
3371	either accept everything or return C<ENOBUFS> if the buffer is too large,	5304	either accept everything or return C<ENOBUFS> if the buffer is too large,
3372	so make sure you only write small amounts into your sockets (less than a	5305	so make sure you only write small amounts into your sockets (less than a
3373	megabyte seems safe, but thsi apparently depends on the amount of memory	5306	megabyte seems safe, but this apparently depends on the amount of memory
3374	available).	5307	available).
3375		5308
3376	Due to the many, low, and arbitrary limits on the win32 platform and	5309	Due to the many, low, and arbitrary limits on the win32 platform and
3377	the abysmal performance of winsockets, using a large number of sockets	5310	the abysmal performance of winsockets, using a large number of sockets
3378	is not recommended (and not reasonable). If your program needs to use	5311	is not recommended (and not reasonable). If your program needs to use
3379	more than a hundred or so sockets, then likely it needs to use a totally	5312	more than a hundred or so sockets, then likely it needs to use a totally
3380	different implementation for windows, as libev offers the POSIX readiness	5313	different implementation for windows, as libev offers the POSIX readiness
3381	notification model, which cannot be implemented efficiently on windows	5314	notification model, which cannot be implemented efficiently on windows
3382	(Microsoft monopoly games).	5315	(due to Microsoft monopoly games).
3383		5316
3384	A typical way to use libev under windows is to embed it (see the embedding	5317	A typical way to use libev under windows is to embed it (see the embedding
3385	section for details) and use the following F<evwrap.h> header file instead	5318	section for details) and use the following F<evwrap.h> header file instead
3386	of F<ev.h>:	5319	of F<ev.h>:
3387		5320
…		…
3389	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */	5322	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
3390		5323
3391	#include "ev.h"	5324	#include "ev.h"
3392		5325
3393	And compile the following F<evwrap.c> file into your project (make sure	5326	And compile the following F<evwrap.c> file into your project (make sure
3394	you do I<not> compile the F<ev.c> or any other embedded soruce files!):	5327	you do I<not> compile the F<ev.c> or any other embedded source files!):
3395		5328
3396	#include "evwrap.h"	5329	#include "evwrap.h"
3397	#include "ev.c"	5330	#include "ev.c"
3398		5331
3399	=over 4
3400
3401	=item The winsocket select function	5332	=head3 The winsocket C<select> function
3402		5333
3403	The winsocket C<select> function doesn't follow POSIX in that it	5334	The winsocket C<select> function doesn't follow POSIX in that it
3404	requires socket I<handles> and not socket I<file descriptors> (it is	5335	requires socket I<handles> and not socket I<file descriptors> (it is
3405	also extremely buggy). This makes select very inefficient, and also	5336	also extremely buggy). This makes select very inefficient, and also
3406	requires a mapping from file descriptors to socket handles (the Microsoft	5337	requires a mapping from file descriptors to socket handles (the Microsoft
…		…
3415	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */	5346	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
3416		5347
3417	Note that winsockets handling of fd sets is O(n), so you can easily get a	5348	Note that winsockets handling of fd sets is O(n), so you can easily get a
3418	complexity in the O(n²) range when using win32.	5349	complexity in the O(n²) range when using win32.
3419		5350
3420	=item Limited number of file descriptors	5351	=head3 Limited number of file descriptors
3421		5352
3422	Windows has numerous arbitrary (and low) limits on things.	5353	Windows has numerous arbitrary (and low) limits on things.
3423		5354
3424	Early versions of winsocket's select only supported waiting for a maximum	5355	Early versions of winsocket's select only supported waiting for a maximum
3425	of C<64> handles (probably owning to the fact that all windows kernels	5356	of C<64> handles (probably owning to the fact that all windows kernels
3426	can only wait for C<64> things at the same time internally; Microsoft	5357	can only wait for C<64> things at the same time internally; Microsoft
3427	recommends spawning a chain of threads and wait for 63 handles and the	5358	recommends spawning a chain of threads and wait for 63 handles and the
3428	previous thread in each. Great).	5359	previous thread in each. Sounds great!).
3429		5360
3430	Newer versions support more handles, but you need to define C<FD_SETSIZE>	5361	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3431	to some high number (e.g. C<2048>) before compiling the winsocket select	5362	to some high number (e.g. C<2048>) before compiling the winsocket select
3432	call (which might be in libev or elsewhere, for example, perl does its own	5363	call (which might be in libev or elsewhere, for example, perl and many
3433	select emulation on windows).	5364	other interpreters do their own select emulation on windows).
3434		5365
3435	Another limit is the number of file descriptors in the Microsoft runtime	5366	Another limit is the number of file descriptors in the Microsoft runtime
3436	libraries, which by default is C<64> (there must be a hidden I<64> fetish	5367	libraries, which by default is C<64> (there must be a hidden I<64>
3437	or something like this inside Microsoft). You can increase this by calling	5368	fetish or something like this inside Microsoft). You can increase this
3438	C<_setmaxstdio>, which can increase this limit to C<2048> (another	5369	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
3439	arbitrary limit), but is broken in many versions of the Microsoft runtime	5370	(another arbitrary limit), but is broken in many versions of the Microsoft
3440	libraries.
3441
3442	This might get you to about C<512> or C<2048> sockets (depending on	5371	runtime libraries. This might get you to about C<512> or C<2048> sockets
3443	windows version and/or the phase of the moon). To get more, you need to	5372	(depending on windows version and/or the phase of the moon). To get more,
3444	wrap all I/O functions and provide your own fd management, but the cost of	5373	you need to wrap all I/O functions and provide your own fd management, but
3445	calling select (O(n²)) will likely make this unworkable.	5374	the cost of calling select (O(n²)) will likely make this unworkable.
3446		5375
3447	=back
3448
3449
3450	=head1 PORTABILITY REQUIREMENTS	5376	=head2 PORTABILITY REQUIREMENTS
3451		5377
3452	In addition to a working ISO-C implementation, libev relies on a few	5378	In addition to a working ISO-C implementation and of course the
3453	additional extensions:	5379	backend-specific APIs, libev relies on a few additional extensions:
3454		5380
3455	=over 4	5381	=over 4
3456		5382
3457	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible	5383	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
3458	calling conventions regardless of C<ev_watcher_type *>.	5384	calling conventions regardless of C<ev_watcher_type *>.
…		…
3461	structure (guaranteed by POSIX but not by ISO C for example), but it also	5387	structure (guaranteed by POSIX but not by ISO C for example), but it also
3462	assumes that the same (machine) code can be used to call any watcher	5388	assumes that the same (machine) code can be used to call any watcher
3463	callback: The watcher callbacks have different type signatures, but libev	5389	callback: The watcher callbacks have different type signatures, but libev
3464	calls them using an C<ev_watcher *> internally.	5390	calls them using an C<ev_watcher *> internally.
3465		5391
		5392	=item null pointers and integer zero are represented by 0 bytes
		5393
		5394	Libev uses C<memset> to initialise structs and arrays to C<0> bytes, and
		5395	relies on this setting pointers and integers to null.
		5396
		5397	=item pointer accesses must be thread-atomic
		5398
		5399	Accessing a pointer value must be atomic, it must both be readable and
		5400	writable in one piece - this is the case on all current architectures.
		5401
3466	=item C<sig_atomic_t volatile> must be thread-atomic as well	5402	=item C<sig_atomic_t volatile> must be thread-atomic as well
3467		5403
3468	The type C<sig_atomic_t volatile> (or whatever is defined as	5404	The type C<sig_atomic_t volatile> (or whatever is defined as
3469	C<EV_ATOMIC_T>) must be atomic w.r.t. accesses from different	5405	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
3470	threads. This is not part of the specification for C<sig_atomic_t>, but is	5406	threads. This is not part of the specification for C<sig_atomic_t>, but is
3471	believed to be sufficiently portable.	5407	believed to be sufficiently portable.
3472		5408
3473	=item C<sigprocmask> must work in a threaded environment	5409	=item C<sigprocmask> must work in a threaded environment
3474		5410
…		…
3478	thread" or will block signals process-wide, both behaviours would	5414	thread" or will block signals process-wide, both behaviours would
3479	be compatible with libev. Interaction between C<sigprocmask> and	5415	be compatible with libev. Interaction between C<sigprocmask> and
3480	C<pthread_sigmask> could complicate things, however.	5416	C<pthread_sigmask> could complicate things, however.
3481		5417
3482	The most portable way to handle signals is to block signals in all threads	5418	The most portable way to handle signals is to block signals in all threads
3483	except the initial one, and run the default loop in the initial thread as	5419	except the initial one, and run the signal handling loop in the initial
3484	well.	5420	thread as well.
3485		5421
3486	=item C<long> must be large enough for common memory allocation sizes	5422	=item C<long> must be large enough for common memory allocation sizes
3487		5423
3488	To improve portability and simplify using libev, libev uses C<long>	5424	To improve portability and simplify its API, libev uses C<long> internally
3489	internally instead of C<size_t> when allocating its data structures. On	5425	instead of C<size_t> when allocating its data structures. On non-POSIX
3490	non-POSIX systems (Microsoft...) this might be unexpectedly low, but	5426	systems (Microsoft...) this might be unexpectedly low, but is still at
3491	is still at least 31 bits everywhere, which is enough for hundreds of	5427	least 31 bits everywhere, which is enough for hundreds of millions of
3492	millions of watchers.	5428	watchers.
3493		5429
3494	=item C<double> must hold a time value in seconds with enough accuracy	5430	=item C<double> must hold a time value in seconds with enough accuracy
3495		5431
3496	The type C<double> is used to represent timestamps. It is required to	5432	The type C<double> is used to represent timestamps. It is required to
3497	have at least 51 bits of mantissa (and 9 bits of exponent), which is good	5433	have at least 51 bits of mantissa (and 9 bits of exponent), which is
3498	enough for at least into the year 4000. This requirement is fulfilled by	5434	good enough for at least into the year 4000 with millisecond accuracy
		5435	(the design goal for libev). This requirement is overfulfilled by
3499	implementations implementing IEEE 754 (basically all existing ones).	5436	implementations using IEEE 754, which is basically all existing ones.
		5437
		5438	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5439	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5440	is either obsolete or somebody patched it to use C<long double> or
		5441	something like that, just kidding).
3500		5442
3501	=back	5443	=back
3502		5444
3503	If you know of other additional requirements drop me a note.	5445	If you know of other additional requirements drop me a note.
3504		5446
3505		5447
3506	=head1 COMPILER WARNINGS	5448	=head1 ALGORITHMIC COMPLEXITIES
3507		5449
3508	Depending on your compiler and compiler settings, you might get no or a	5450	In this section the complexities of (many of) the algorithms used inside
3509	lot of warnings when compiling libev code. Some people are apparently	5451	libev will be documented. For complexity discussions about backends see
3510	scared by this.	5452	the documentation for C<ev_default_init>.
3511		5453
3512	However, these are unavoidable for many reasons. For one, each compiler	5454	All of the following are about amortised time: If an array needs to be
3513	has different warnings, and each user has different tastes regarding	5455	extended, libev needs to realloc and move the whole array, but this
3514	warning options. "Warn-free" code therefore cannot be a goal except when	5456	happens asymptotically rarer with higher number of elements, so O(1) might
3515	targeting a specific compiler and compiler-version.	5457	mean that libev does a lengthy realloc operation in rare cases, but on
		5458	average it is much faster and asymptotically approaches constant time.
3516		5459
3517	Another reason is that some compiler warnings require elaborate	5460	=over 4
3518	workarounds, or other changes to the code that make it less clear and less
3519	maintainable.
3520		5461
3521	And of course, some compiler warnings are just plain stupid, or simply	5462	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
3522	wrong (because they don't actually warn about the condition their message
3523	seems to warn about).
3524		5463
3525	While libev is written to generate as few warnings as possible,	5464	This means that, when you have a watcher that triggers in one hour and
3526	"warn-free" code is not a goal, and it is recommended not to build libev	5465	there are 100 watchers that would trigger before that, then inserting will
3527	with any compiler warnings enabled unless you are prepared to cope with	5466	have to skip roughly seven (C<ld 100>) of these watchers.
3528	them (e.g. by ignoring them). Remember that warnings are just that:
3529	warnings, not errors, or proof of bugs.
3530		5467
		5468	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
3531		5469
3532	=head1 VALGRIND	5470	That means that changing a timer costs less than removing/adding them,
		5471	as only the relative motion in the event queue has to be paid for.
3533		5472
3534	Valgrind has a special section here because it is a popular tool that is	5473	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
3535	highly useful, but valgrind reports are very hard to interpret.
3536		5474
3537	If you think you found a bug (memory leak, uninitialised data access etc.)	5475	These just add the watcher into an array or at the head of a list.
3538	in libev, then check twice: If valgrind reports something like:
3539		5476
3540	==2274== definitely lost: 0 bytes in 0 blocks.	5477	=item Stopping check/prepare/idle/fork/async watchers: O(1)
3541	==2274== possibly lost: 0 bytes in 0 blocks.
3542	==2274== still reachable: 256 bytes in 1 blocks.
3543		5478
3544	Then there is no memory leak. Similarly, under some circumstances,	5479	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
3545	valgrind might report kernel bugs as if it were a bug in libev, or it
3546	might be confused (it is a very good tool, but only a tool).
3547		5480
3548	If you are unsure about something, feel free to contact the mailing list	5481	These watchers are stored in lists, so they need to be walked to find the
3549	with the full valgrind report and an explanation on why you think this is	5482	correct watcher to remove. The lists are usually short (you don't usually
3550	a bug in libev. However, don't be annoyed when you get a brisk "this is	5483	have many watchers waiting for the same fd or signal: one is typical, two
3551	no bug" answer and take the chance of learning how to interpret valgrind	5484	is rare).
3552	properly.
3553		5485
3554	If you need, for some reason, empty reports from valgrind for your project	5486	=item Finding the next timer in each loop iteration: O(1)
3555	I suggest using suppression lists.
3556		5487
		5488	By virtue of using a binary or 4-heap, the next timer is always found at a
		5489	fixed position in the storage array.
		5490
		5491	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		5492
		5493	A change means an I/O watcher gets started or stopped, which requires
		5494	libev to recalculate its status (and possibly tell the kernel, depending
		5495	on backend and whether C<ev_io_set> was used).
		5496
		5497	=item Activating one watcher (putting it into the pending state): O(1)
		5498
		5499	=item Priority handling: O(number_of_priorities)
		5500
		5501	Priorities are implemented by allocating some space for each
		5502	priority. When doing priority-based operations, libev usually has to
		5503	linearly search all the priorities, but starting/stopping and activating
		5504	watchers becomes O(1) with respect to priority handling.
		5505
		5506	=item Sending an ev_async: O(1)
		5507
		5508	=item Processing ev_async_send: O(number_of_async_watchers)
		5509
		5510	=item Processing signals: O(max_signal_number)
		5511
		5512	Sending involves a system call I<iff> there were no other C<ev_async_send>
		5513	calls in the current loop iteration and the loop is currently
		5514	blocked. Checking for async and signal events involves iterating over all
		5515	running async watchers or all signal numbers.
		5516
		5517	=back
		5518
		5519
		5520	=head1 PORTING FROM LIBEV 3.X TO 4.X
		5521
		5522	The major version 4 introduced some incompatible changes to the API.
		5523
		5524	At the moment, the C<ev.h> header file provides compatibility definitions
		5525	for all changes, so most programs should still compile. The compatibility
		5526	layer might be removed in later versions of libev, so better update to the
		5527	new API early than late.
		5528
		5529	=over 4
		5530
		5531	=item C<EV_COMPAT3> backwards compatibility mechanism
		5532
		5533	The backward compatibility mechanism can be controlled by
		5534	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
		5535	section.
		5536
		5537	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5538
		5539	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5540
		5541	ev_loop_destroy (EV_DEFAULT_UC);
		5542	ev_loop_fork (EV_DEFAULT);
		5543
		5544	=item function/symbol renames
		5545
		5546	A number of functions and symbols have been renamed:
		5547
		5548	ev_loop => ev_run
		5549	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		5550	EVLOOP_ONESHOT => EVRUN_ONCE
		5551
		5552	ev_unloop => ev_break
		5553	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		5554	EVUNLOOP_ONE => EVBREAK_ONE
		5555	EVUNLOOP_ALL => EVBREAK_ALL
		5556
		5557	EV_TIMEOUT => EV_TIMER
		5558
		5559	ev_loop_count => ev_iteration
		5560	ev_loop_depth => ev_depth
		5561	ev_loop_verify => ev_verify
		5562
		5563	Most functions working on C<struct ev_loop> objects don't have an
		5564	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		5565	associated constants have been renamed to not collide with the C<struct
		5566	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		5567	as all other watcher types. Note that C<ev_loop_fork> is still called
		5568	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		5569	typedef.
		5570
		5571	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		5572
		5573	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		5574	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		5575	and work, but the library code will of course be larger.
		5576
		5577	=back
		5578
		5579
		5580	=head1 GLOSSARY
		5581
		5582	=over 4
		5583
		5584	=item active
		5585
		5586	A watcher is active as long as it has been started and not yet stopped.
		5587	See L</WATCHER STATES> for details.
		5588
		5589	=item application
		5590
		5591	In this document, an application is whatever is using libev.
		5592
		5593	=item backend
		5594
		5595	The part of the code dealing with the operating system interfaces.
		5596
		5597	=item callback
		5598
		5599	The address of a function that is called when some event has been
		5600	detected. Callbacks are being passed the event loop, the watcher that
		5601	received the event, and the actual event bitset.
		5602
		5603	=item callback/watcher invocation
		5604
		5605	The act of calling the callback associated with a watcher.
		5606
		5607	=item event
		5608
		5609	A change of state of some external event, such as data now being available
		5610	for reading on a file descriptor, time having passed or simply not having
		5611	any other events happening anymore.
		5612
		5613	In libev, events are represented as single bits (such as C<EV_READ> or
		5614	C<EV_TIMER>).
		5615
		5616	=item event library
		5617
		5618	A software package implementing an event model and loop.
		5619
		5620	=item event loop
		5621
		5622	An entity that handles and processes external events and converts them
		5623	into callback invocations.
		5624
		5625	=item event model
		5626
		5627	The model used to describe how an event loop handles and processes
		5628	watchers and events.
		5629
		5630	=item pending
		5631
		5632	A watcher is pending as soon as the corresponding event has been
		5633	detected. See L</WATCHER STATES> for details.
		5634
		5635	=item real time
		5636
		5637	The physical time that is observed. It is apparently strictly monotonic :)
		5638
		5639	=item wall-clock time
		5640
		5641	The time and date as shown on clocks. Unlike real time, it can actually
		5642	be wrong and jump forwards and backwards, e.g. when you adjust your
		5643	clock.
		5644
		5645	=item watcher
		5646
		5647	A data structure that describes interest in certain events. Watchers need
		5648	to be started (attached to an event loop) before they can receive events.
		5649
		5650	=back
3557		5651
3558	=head1 AUTHOR	5652	=head1 AUTHOR
3559		5653
3560	Marc Lehmann <libev@schmorp.de>.	5654	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5655	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
3561		5656

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