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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
…		…
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 C<epoll>, the
87	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	111	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
88	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	112	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
89	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	113	(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	all kernel versions tested so far.
		573
		574	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		575	C<EVBACKEND_POLL>.
399		576
400	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	577	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
401		578
402	Kqueue deserves special mention, as at the time of this writing, it	579	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	580	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	581	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"	582	it's completely useless). Unlike epoll, however, whose brokenness
		583	is by design, these kqueue bugs can (and eventually will) be fixed
		584	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	585	"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)	586	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
408	system like NetBSD.	587	system like NetBSD.
409		588
410	You still can embed kqueue into a normal poll or select backend and use it	589	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	590	only for sockets (after having made sure that sockets work with kqueue on
…		…
413		592
414	It scales in the same way as the epoll backend, but the interface to the	593	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	594	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	595	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	596	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	597	two event changes per incident. Support for C<fork ()> is very bad (you
		598	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.	599	drops fds silently in similarly hard-to-detect cases.
420		600
421	This backend usually performs well under most conditions.	601	This backend usually performs well under most conditions.
422		602
423	While nominally embeddable in other event loops, this doesn't work	603	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	604	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	605	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	606	(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	607	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
428	sockets.	608	also broken on OS X)) and, did I mention it, using it only for sockets.
		609
		610	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		611	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		612	C<NOTE_EOF>.
429		613
430	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	614	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
431		615
432	This is not implemented yet (and might never be, unless you send me an	616	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	617	implementation). According to reports, C</dev/poll> only supports sockets
…		…
437	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	621	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
438		622
439	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	623	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)).	624	it's really slow, but it still scales very well (O(active_fds)).
441		625
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	626	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	627	file descriptor per loop iteration. For small and medium numbers of file
448	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	628	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
449	might perform better.	629	might perform better.
450		630
451	On the positive side, ignoring the spurious readiness notifications, this	631	On the positive side, this backend actually performed fully to
452	backend actually performed to specification in all tests and is fully	632	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.	633	among the OS-specific backends (I vastly prefer correctness over speed
		634	hacks).
		635
		636	On the negative side, the interface is I<bizarre> - so bizarre that
		637	even sun itself gets it wrong in their code examples: The event polling
		638	function sometimes returns events to the caller even though an error
		639	occurred, but with no indication whether it has done so or not (yes, it's
		640	even documented that way) - deadly for edge-triggered interfaces where you
		641	absolutely have to know whether an event occurred or not because you have
		642	to re-arm the watcher.
		643
		644	Fortunately libev seems to be able to work around these idiocies.
		645
		646	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		647	C<EVBACKEND_POLL>.
454		648
455	=item C<EVBACKEND_ALL>	649	=item C<EVBACKEND_ALL>
456		650
457	Try all backends (even potentially broken ones that wouldn't be tried	651	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	652	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
459	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	653	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
460		654
461	It is definitely not recommended to use this flag.	655	It is definitely not recommended to use this flag, use whatever
		656	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		657	at all.
		658
		659	=item C<EVBACKEND_MASK>
		660
		661	Not a backend at all, but a mask to select all backend bits from a
		662	C<flags> value, in case you want to mask out any backends from a flags
		663	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
462		664
463	=back	665	=back
464		666
465	If one or more of these are or'ed into the flags value, then only these	667	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	668	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.	669	here). If none are specified, all backends in C<ev_recommended_backends
468		670	()> 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		671
496	Example: Try to create a event loop that uses epoll and nothing else.	672	Example: Try to create a event loop that uses epoll and nothing else.
497		673
498	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	674	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
499	if (!epoller)	675	if (!epoller)
500	fatal ("no epoll found here, maybe it hides under your chair");	676	fatal ("no epoll found here, maybe it hides under your chair");
501		677
		678	Example: Use whatever libev has to offer, but make sure that kqueue is
		679	used if available.
		680
		681	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		682
502	=item ev_default_destroy ()	683	=item ev_loop_destroy (loop)
503		684
504	Destroys the default loop again (frees all memory and kernel state	685	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	686	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	687	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>	688	responsibility to either stop all watchers cleanly yourself I<before>
508	calling this function, or cope with the fact afterwards (which is usually	689	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	690	the easiest thing, you can just ignore the watchers and/or C<free ()> them
510	for example).	691	for example).
511		692
512	Note that certain global state, such as signal state, will not be freed by	693	Note that certain global state, such as signal state (and installed signal
513	this function, and related watchers (such as signal and child watchers)	694	handlers), will not be freed by this function, and related watchers (such
514	would need to be stopped manually.	695	as signal and child watchers) would need to be stopped manually.
515		696
516	In general it is not advisable to call this function except in the	697	This function is normally used on loop objects allocated by
517	rare occasion where you really need to free e.g. the signal handling	698	C<ev_loop_new>, but it can also be used on the default loop returned by
		699	C<ev_default_loop>, in which case it is not thread-safe.
		700
		701	Note that it is not advisable to call this function on the default loop
		702	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	703	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>).	704	and C<ev_loop_destroy>.
520		705
521	=item ev_loop_destroy (loop)	706	=item ev_loop_fork (loop)
522		707
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	708	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	709	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	710	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	711	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	712	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.	713	C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.
		714
		715	In addition, if you want to reuse a loop (via this function or
		716	C<EVFLAG_FORKCHECK>), you I<also> have to ignore C<SIGPIPE>.
		717
		718	Again, you I<have> to call it on I<any> loop that you want to re-use after
		719	a fork, I<even if you do not plan to use the loop in the parent>. This is
		720	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		721	during fork.
534		722
535	On the other hand, you only need to call this function in the child	723	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	724	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.	725	you just fork+exec or create a new loop in the child, you don't have to
		726	call it at all (in fact, C<epoll> is so badly broken that it makes a
		727	difference, but libev will usually detect this case on its own and do a
		728	costly reset of the backend).
538		729
539	The function itself is quite fast and it's usually not a problem to call	730	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	731	it just in case after a fork.
541	quite nicely into a call to C<pthread_atfork>:
542		732
		733	Example: Automate calling C<ev_loop_fork> on the default loop when
		734	using pthreads.
		735
		736	static void
		737	post_fork_child (void)
		738	{
		739	ev_loop_fork (EV_DEFAULT);
		740	}
		741
		742	...
543	pthread_atfork (0, 0, ev_default_fork);	743	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		744
551	=item int ev_is_default_loop (loop)	745	=item int ev_is_default_loop (loop)
552		746
553	Returns true when the given loop actually is the default loop, false otherwise.	747	Returns true when the given loop is, in fact, the default loop, and false
		748	otherwise.
554		749
555	=item unsigned int ev_loop_count (loop)	750	=item unsigned int ev_iteration (loop)
556		751
557	Returns the count of loop iterations for the loop, which is identical to	752	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	753	to the number of times libev did poll for new events. It starts at C<0>
559	happily wraps around with enough iterations.	754	and happily wraps around with enough iterations.
560		755
561	This value can sometimes be useful as a generation counter of sorts (it	756	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	757	"ticks" the number of loop iterations), as it roughly corresponds with
563	C<ev_prepare> and C<ev_check> calls.	758	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		759	prepare and check phases.
		760
		761	=item unsigned int ev_depth (loop)
		762
		763	Returns the number of times C<ev_run> was entered minus the number of
		764	times C<ev_run> was exited normally, in other words, the recursion depth.
		765
		766	Outside C<ev_run>, this number is zero. In a callback, this number is
		767	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
		768	in which case it is higher.
		769
		770	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
		771	throwing an exception etc.), doesn't count as "exit" - consider this
		772	as a hint to avoid such ungentleman-like behaviour unless it's really
		773	convenient, in which case it is fully supported.
564		774
565	=item unsigned int ev_backend (loop)	775	=item unsigned int ev_backend (loop)
566		776
567	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	777	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
568	use.	778	use.
…		…
573	received events and started processing them. This timestamp does not	783	received events and started processing them. This timestamp does not
574	change as long as callbacks are being processed, and this is also the base	784	change as long as callbacks are being processed, and this is also the base
575	time used for relative timers. You can treat it as the timestamp of the	785	time used for relative timers. You can treat it as the timestamp of the
576	event occurring (or more correctly, libev finding out about it).	786	event occurring (or more correctly, libev finding out about it).
577		787
		788	=item ev_now_update (loop)
		789
		790	Establishes the current time by querying the kernel, updating the time
		791	returned by C<ev_now ()> in the progress. This is a costly operation and
		792	is usually done automatically within C<ev_run ()>.
		793
		794	This function is rarely useful, but when some event callback runs for a
		795	very long time without entering the event loop, updating libev's idea of
		796	the current time is a good idea.
		797
		798	See also L</The special problem of time updates> in the C<ev_timer> section.
		799
		800	=item ev_suspend (loop)
		801
		802	=item ev_resume (loop)
		803
		804	These two functions suspend and resume an event loop, for use when the
		805	loop is not used for a while and timeouts should not be processed.
		806
		807	A typical use case would be an interactive program such as a game: When
		808	the user presses C<^Z> to suspend the game and resumes it an hour later it
		809	would be best to handle timeouts as if no time had actually passed while
		810	the program was suspended. This can be achieved by calling C<ev_suspend>
		811	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		812	C<ev_resume> directly afterwards to resume timer processing.
		813
		814	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		815	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		816	will be rescheduled (that is, they will lose any events that would have
		817	occurred while suspended).
		818
		819	After calling C<ev_suspend> you B<must not> call I<any> function on the
		820	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		821	without a previous call to C<ev_suspend>.
		822
		823	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		824	event loop time (see C<ev_now_update>).
		825
578	=item ev_loop (loop, int flags)	826	=item bool ev_run (loop, int flags)
579		827
580	Finally, this is it, the event handler. This function usually is called	828	Finally, this is it, the event handler. This function usually is called
581	after you initialised all your watchers and you want to start handling	829	after you have initialised all your watchers and you want to start
582	events.	830	handling events. It will ask the operating system for any new events, call
		831	the watcher callbacks, and then repeat the whole process indefinitely: This
		832	is why event loops are called I<loops>.
583		833
584	If the flags argument is specified as C<0>, it will not return until	834	If the flags argument is specified as C<0>, it will keep handling events
585	either no event watchers are active anymore or C<ev_unloop> was called.	835	until either no event watchers are active anymore or C<ev_break> was
		836	called.
586		837
		838	The return value is false if there are no more active watchers (which
		839	usually means "all jobs done" or "deadlock"), and true in all other cases
		840	(which usually means " you should call C<ev_run> again").
		841
587	Please note that an explicit C<ev_unloop> is usually better than	842	Please note that an explicit C<ev_break> is usually better than
588	relying on all watchers to be stopped when deciding when a program has	843	relying on all watchers to be stopped when deciding when a program has
589	finished (especially in interactive programs), but having a program that	844	finished (especially in interactive programs), but having a program
590	automatically loops as long as it has to and no longer by virtue of	845	that automatically loops as long as it has to and no longer by virtue
591	relying on its watchers stopping correctly is a thing of beauty.	846	of relying on its watchers stopping correctly, that is truly a thing of
		847	beauty.
592		848
		849	This function is I<mostly> exception-safe - you can break out of a
		850	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		851	exception and so on. This does not decrement the C<ev_depth> value, nor
		852	will it clear any outstanding C<EVBREAK_ONE> breaks.
		853
593	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	854	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
594	those events and any outstanding ones, but will not block your process in	855	those events and any already outstanding ones, but will not wait and
595	case there are no events and will return after one iteration of the loop.	856	block your process in case there are no events and will return after one
		857	iteration of the loop. This is sometimes useful to poll and handle new
		858	events while doing lengthy calculations, to keep the program responsive.
596		859
597	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	860	A flags value of C<EVRUN_ONCE> will look for new events (waiting if
598	necessary) and will handle those and any outstanding ones. It will block	861	necessary) and will handle those and any already outstanding ones. It
599	your process until at least one new event arrives, and will return after	862	will block your process until at least one new event arrives (which could
600	one iteration of the loop. This is useful if you are waiting for some	863	be an event internal to libev itself, so there is no guarantee that a
601	external event in conjunction with something not expressible using other	864	user-registered callback will be called), and will return after one
		865	iteration of the loop.
		866
		867	This is useful if you are waiting for some external event in conjunction
		868	with something not expressible using other libev watchers (i.e. "roll your
602	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	869	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
603	usually a better approach for this kind of thing.	870	usually a better approach for this kind of thing.
604		871
605	Here are the gory details of what C<ev_loop> does:	872	Here are the gory details of what C<ev_run> does (this is for your
		873	understanding, not a guarantee that things will work exactly like this in
		874	future versions):
606		875
		876	- Increment loop depth.
		877	- Reset the ev_break status.
607	- Before the first iteration, call any pending watchers.	878	- Before the first iteration, call any pending watchers.
		879	LOOP:
608	* If EVFLAG_FORKCHECK was used, check for a fork.	880	- If EVFLAG_FORKCHECK was used, check for a fork.
609	- If a fork was detected (by any means), queue and call all fork watchers.	881	- If a fork was detected (by any means), queue and call all fork watchers.
610	- Queue and call all prepare watchers.	882	- Queue and call all prepare watchers.
		883	- If ev_break was called, goto FINISH.
611	- If we have been forked, detach and recreate the kernel state	884	- If we have been forked, detach and recreate the kernel state
612	as to not disturb the other process.	885	as to not disturb the other process.
613	- Update the kernel state with all outstanding changes.	886	- Update the kernel state with all outstanding changes.
614	- Update the "event loop time" (ev_now ()).	887	- Update the "event loop time" (ev_now ()).
615	- Calculate for how long to sleep or block, if at all	888	- Calculate for how long to sleep or block, if at all
616	(active idle watchers, EVLOOP_NONBLOCK or not having	889	(active idle watchers, EVRUN_NOWAIT or not having
617	any active watchers at all will result in not sleeping).	890	any active watchers at all will result in not sleeping).
618	- Sleep if the I/O and timer collect interval say so.	891	- Sleep if the I/O and timer collect interval say so.
		892	- Increment loop iteration counter.
619	- Block the process, waiting for any events.	893	- Block the process, waiting for any events.
620	- Queue all outstanding I/O (fd) events.	894	- Queue all outstanding I/O (fd) events.
621	- Update the "event loop time" (ev_now ()), and do time jump adjustments.	895	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
622	- Queue all outstanding timers.	896	- Queue all expired timers.
623	- Queue all outstanding periodics.	897	- Queue all expired periodics.
624	- Unless any events are pending now, queue all idle watchers.	898	- Queue all idle watchers with priority higher than that of pending events.
625	- Queue all check watchers.	899	- Queue all check watchers.
626	- Call all queued watchers in reverse order (i.e. check watchers first).	900	- Call all queued watchers in reverse order (i.e. check watchers first).
627	Signals and child watchers are implemented as I/O watchers, and will	901	Signals and child watchers are implemented as I/O watchers, and will
628	be handled here by queueing them when their watcher gets executed.	902	be handled here by queueing them when their watcher gets executed.
629	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	903	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
630	were used, or there are no active watchers, return, otherwise	904	were used, or there are no active watchers, goto FINISH, otherwise
631	continue with step *.	905	continue with step LOOP.
		906	FINISH:
		907	- Reset the ev_break status iff it was EVBREAK_ONE.
		908	- Decrement the loop depth.
		909	- Return.
632		910
633	Example: Queue some jobs and then loop until no events are outstanding	911	Example: Queue some jobs and then loop until no events are outstanding
634	anymore.	912	anymore.
635		913
636	... queue jobs here, make sure they register event watchers as long	914	... queue jobs here, make sure they register event watchers as long
637	... as they still have work to do (even an idle watcher will do..)	915	... as they still have work to do (even an idle watcher will do..)
638	ev_loop (my_loop, 0);	916	ev_run (my_loop, 0);
639	... jobs done or somebody called unloop. yeah!	917	... jobs done or somebody called break. yeah!
640		918
641	=item ev_unloop (loop, how)	919	=item ev_break (loop, how)
642		920
643	Can be used to make a call to C<ev_loop> return early (but only after it	921	Can be used to make a call to C<ev_run> return early (but only after it
644	has processed all outstanding events). The C<how> argument must be either	922	has processed all outstanding events). The C<how> argument must be either
645	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	923	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
646	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	924	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
647		925
648	This "unloop state" will be cleared when entering C<ev_loop> again.	926	This "break state" will be cleared on the next call to C<ev_run>.
		927
		928	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		929	which case it will have no effect.
649		930
650	=item ev_ref (loop)	931	=item ev_ref (loop)
651		932
652	=item ev_unref (loop)	933	=item ev_unref (loop)
653		934
654	Ref/unref can be used to add or remove a reference count on the event	935	Ref/unref can be used to add or remove a reference count on the event
655	loop: Every watcher keeps one reference, and as long as the reference	936	loop: Every watcher keeps one reference, and as long as the reference
656	count is nonzero, C<ev_loop> will not return on its own. If you have	937	count is nonzero, C<ev_run> will not return on its own.
657	a watcher you never unregister that should not keep C<ev_loop> from	938
658	returning, ev_unref() after starting, and ev_ref() before stopping it. For	939	This is useful when you have a watcher that you never intend to
		940	unregister, but that nevertheless should not keep C<ev_run> from
		941	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		942	before stopping it.
		943
659	example, libev itself uses this for its internal signal pipe: It is not	944	As an example, libev itself uses this for its internal signal pipe: It
660	visible to the libev user and should not keep C<ev_loop> from exiting if	945	is not visible to the libev user and should not keep C<ev_run> from
661	no event watchers registered by it are active. It is also an excellent	946	exiting if no event watchers registered by it are active. It is also an
662	way to do this for generic recurring timers or from within third-party	947	excellent way to do this for generic recurring timers or from within
663	libraries. Just remember to I<unref after start> and I<ref before stop>	948	third-party libraries. Just remember to I<unref after start> and I<ref
664	(but only if the watcher wasn't active before, or was active before,	949	before stop> (but only if the watcher wasn't active before, or was active
665	respectively).	950	before, respectively. Note also that libev might stop watchers itself
		951	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		952	in the callback).
666		953
667	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	954	Example: Create a signal watcher, but keep it from keeping C<ev_run>
668	running when nothing else is active.	955	running when nothing else is active.
669		956
670	struct ev_signal exitsig;	957	ev_signal exitsig;
671	ev_signal_init (&exitsig, sig_cb, SIGINT);	958	ev_signal_init (&exitsig, sig_cb, SIGINT);
672	ev_signal_start (loop, &exitsig);	959	ev_signal_start (loop, &exitsig);
673	evf_unref (loop);	960	ev_unref (loop);
674		961
675	Example: For some weird reason, unregister the above signal handler again.	962	Example: For some weird reason, unregister the above signal handler again.
676		963
677	ev_ref (loop);	964	ev_ref (loop);
678	ev_signal_stop (loop, &exitsig);	965	ev_signal_stop (loop, &exitsig);
…		…
689	Setting these to a higher value (the C<interval> I<must> be >= C<0>)	976	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
690	allows libev to delay invocation of I/O and timer/periodic callbacks	977	allows libev to delay invocation of I/O and timer/periodic callbacks
691	to increase efficiency of loop iterations (or to increase power-saving	978	to increase efficiency of loop iterations (or to increase power-saving
692	opportunities).	979	opportunities).
693		980
694	The background is that sometimes your program runs just fast enough to	981	The idea is that sometimes your program runs just fast enough to handle
695	handle one (or very few) event(s) per loop iteration. While this makes	982	one (or very few) event(s) per loop iteration. While this makes the
696	the program responsive, it also wastes a lot of CPU time to poll for new	983	program responsive, it also wastes a lot of CPU time to poll for new
697	events, especially with backends like C<select ()> which have a high	984	events, especially with backends like C<select ()> which have a high
698	overhead for the actual polling but can deliver many events at once.	985	overhead for the actual polling but can deliver many events at once.
699		986
700	By setting a higher I<io collect interval> you allow libev to spend more	987	By setting a higher I<io collect interval> you allow libev to spend more
701	time collecting I/O events, so you can handle more events per iteration,	988	time collecting I/O events, so you can handle more events per iteration,
702	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	989	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
703	C<ev_timer>) will be not affected. Setting this to a non-null value will	990	C<ev_timer>) will not be affected. Setting this to a non-null value will
704	introduce an additional C<ev_sleep ()> call into most loop iterations.	991	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		992	sleep time ensures that libev will not poll for I/O events more often then
		993	once per this interval, on average (as long as the host time resolution is
		994	good enough).
705		995
706	Likewise, by setting a higher I<timeout collect interval> you allow libev	996	Likewise, by setting a higher I<timeout collect interval> you allow libev
707	to spend more time collecting timeouts, at the expense of increased	997	to spend more time collecting timeouts, at the expense of increased
708	latency (the watcher callback will be called later). C<ev_io> watchers	998	latency/jitter/inexactness (the watcher callback will be called
709	will not be affected. Setting this to a non-null value will not introduce	999	later). C<ev_io> watchers will not be affected. Setting this to a non-null
710	any overhead in libev.	1000	value will not introduce any overhead in libev.
711		1001
712	Many (busy) programs can usually benefit by setting the I/O collect	1002	Many (busy) programs can usually benefit by setting the I/O collect
713	interval to a value near C<0.1> or so, which is often enough for	1003	interval to a value near C<0.1> or so, which is often enough for
714	interactive servers (of course not for games), likewise for timeouts. It	1004	interactive servers (of course not for games), likewise for timeouts. It
715	usually doesn't make much sense to set it to a lower value than C<0.01>,	1005	usually doesn't make much sense to set it to a lower value than C<0.01>,
716	as this approaches the timing granularity of most systems.	1006	as this approaches the timing granularity of most systems. Note that if
		1007	you do transactions with the outside world and you can't increase the
		1008	parallelity, then this setting will limit your transaction rate (if you
		1009	need to poll once per transaction and the I/O collect interval is 0.01,
		1010	then you can't do more than 100 transactions per second).
717		1011
718	Setting the I<timeout collect interval> can improve the opportunity for	1012	Setting the I<timeout collect interval> can improve the opportunity for
719	saving power, as the program will "bundle" timer callback invocations that	1013	saving power, as the program will "bundle" timer callback invocations that
720	are "near" in time together, by delaying some, thus reducing the number of	1014	are "near" in time together, by delaying some, thus reducing the number of
721	times the process sleeps and wakes up again. Another useful technique to	1015	times the process sleeps and wakes up again. Another useful technique to
722	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure	1016	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
723	they fire on, say, one-second boundaries only.	1017	they fire on, say, one-second boundaries only.
724		1018
		1019	Example: we only need 0.1s timeout granularity, and we wish not to poll
		1020	more often than 100 times per second:
		1021
		1022	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		1023	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		1024
		1025	=item ev_invoke_pending (loop)
		1026
		1027	This call will simply invoke all pending watchers while resetting their
		1028	pending state. Normally, C<ev_run> does this automatically when required,
		1029	but when overriding the invoke callback this call comes handy. This
		1030	function can be invoked from a watcher - this can be useful for example
		1031	when you want to do some lengthy calculation and want to pass further
		1032	event handling to another thread (you still have to make sure only one
		1033	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
		1034
		1035	=item int ev_pending_count (loop)
		1036
		1037	Returns the number of pending watchers - zero indicates that no watchers
		1038	are pending.
		1039
		1040	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		1041
		1042	This overrides the invoke pending functionality of the loop: Instead of
		1043	invoking all pending watchers when there are any, C<ev_run> will call
		1044	this callback instead. This is useful, for example, when you want to
		1045	invoke the actual watchers inside another context (another thread etc.).
		1046
		1047	If you want to reset the callback, use C<ev_invoke_pending> as new
		1048	callback.
		1049
		1050	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
		1051
		1052	Sometimes you want to share the same loop between multiple threads. This
		1053	can be done relatively simply by putting mutex_lock/unlock calls around
		1054	each call to a libev function.
		1055
		1056	However, C<ev_run> can run an indefinite time, so it is not feasible
		1057	to wait for it to return. One way around this is to wake up the event
		1058	loop via C<ev_break> and C<ev_async_send>, another way is to set these
		1059	I<release> and I<acquire> callbacks on the loop.
		1060
		1061	When set, then C<release> will be called just before the thread is
		1062	suspended waiting for new events, and C<acquire> is called just
		1063	afterwards.
		1064
		1065	Ideally, C<release> will just call your mutex_unlock function, and
		1066	C<acquire> will just call the mutex_lock function again.
		1067
		1068	While event loop modifications are allowed between invocations of
		1069	C<release> and C<acquire> (that's their only purpose after all), no
		1070	modifications done will affect the event loop, i.e. adding watchers will
		1071	have no effect on the set of file descriptors being watched, or the time
		1072	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		1073	to take note of any changes you made.
		1074
		1075	In theory, threads executing C<ev_run> will be async-cancel safe between
		1076	invocations of C<release> and C<acquire>.
		1077
		1078	See also the locking example in the C<THREADS> section later in this
		1079	document.
		1080
		1081	=item ev_set_userdata (loop, void *data)
		1082
		1083	=item void *ev_userdata (loop)
		1084
		1085	Set and retrieve a single C<void *> associated with a loop. When
		1086	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		1087	C<0>.
		1088
		1089	These two functions can be used to associate arbitrary data with a loop,
		1090	and are intended solely for the C<invoke_pending_cb>, C<release> and
		1091	C<acquire> callbacks described above, but of course can be (ab-)used for
		1092	any other purpose as well.
		1093
725	=item ev_loop_verify (loop)	1094	=item ev_verify (loop)
726		1095
727	This function only does something when C<EV_VERIFY> support has been	1096	This function only does something when C<EV_VERIFY> support has been
728	compiled in. It tries to go through all internal structures and checks	1097	compiled in, which is the default for non-minimal builds. It tries to go
729	them for validity. If anything is found to be inconsistent, it will print	1098	through all internal structures and checks them for validity. If anything
730	an error message to standard error and call C<abort ()>.	1099	is found to be inconsistent, it will print an error message to standard
		1100	error and call C<abort ()>.
731		1101
732	This can be used to catch bugs inside libev itself: under normal	1102	This can be used to catch bugs inside libev itself: under normal
733	circumstances, this function will never abort as of course libev keeps its	1103	circumstances, this function will never abort as of course libev keeps its
734	data structures consistent.	1104	data structures consistent.
735		1105
736	=back	1106	=back
737		1107
738		1108
739	=head1 ANATOMY OF A WATCHER	1109	=head1 ANATOMY OF A WATCHER
740		1110
		1111	In the following description, uppercase C<TYPE> in names stands for the
		1112	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		1113	watchers and C<ev_io_start> for I/O watchers.
		1114
741	A watcher is a structure that you create and register to record your	1115	A watcher is an opaque structure that you allocate and register to record
742	interest in some event. For instance, if you want to wait for STDIN to	1116	your interest in some event. To make a concrete example, imagine you want
743	become readable, you would create an C<ev_io> watcher for that:	1117	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1118	for that:
744		1119
745	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1120	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
746	{	1121	{
747	ev_io_stop (w);	1122	ev_io_stop (w);
748	ev_unloop (loop, EVUNLOOP_ALL);	1123	ev_break (loop, EVBREAK_ALL);
749	}	1124	}
750		1125
751	struct ev_loop *loop = ev_default_loop (0);	1126	struct ev_loop *loop = ev_default_loop (0);
		1127
752	struct ev_io stdin_watcher;	1128	ev_io stdin_watcher;
		1129
753	ev_init (&stdin_watcher, my_cb);	1130	ev_init (&stdin_watcher, my_cb);
754	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1131	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
755	ev_io_start (loop, &stdin_watcher);	1132	ev_io_start (loop, &stdin_watcher);
		1133
756	ev_loop (loop, 0);	1134	ev_run (loop, 0);
757		1135
758	As you can see, you are responsible for allocating the memory for your	1136	As you can see, you are responsible for allocating the memory for your
759	watcher structures (and it is usually a bad idea to do this on the stack,	1137	watcher structures (and it is I<usually> a bad idea to do this on the
760	although this can sometimes be quite valid).	1138	stack).
761		1139
		1140	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1141	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1142
762	Each watcher structure must be initialised by a call to C<ev_init	1143	Each watcher structure must be initialised by a call to C<ev_init (watcher
763	(watcher *, callback)>, which expects a callback to be provided. This	1144	*, callback)>, which expects a callback to be provided. This callback is
764	callback gets invoked each time the event occurs (or, in the case of I/O	1145	invoked each time the event occurs (or, in the case of I/O watchers, each
765	watchers, each time the event loop detects that the file descriptor given	1146	time the event loop detects that the file descriptor given is readable
766	is readable and/or writable).	1147	and/or writable).
767		1148
768	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1149	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
769	with arguments specific to this watcher type. There is also a macro	1150	macro to configure it, with arguments specific to the watcher type. There
770	to combine initialisation and setting in one call: C<< ev_<type>_init	1151	is also a macro to combine initialisation and setting in one call: C<<
771	(watcher *, callback, ...) >>.	1152	ev_TYPE_init (watcher *, callback, ...) >>.
772		1153
773	To make the watcher actually watch out for events, you have to start it	1154	To make the watcher actually watch out for events, you have to start it
774	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1155	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
775	*) >>), and you can stop watching for events at any time by calling the	1156	*) >>), and you can stop watching for events at any time by calling the
776	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1157	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
777		1158
778	As long as your watcher is active (has been started but not stopped) you	1159	As long as your watcher is active (has been started but not stopped) you
779	must not touch the values stored in it. Most specifically you must never	1160	must not touch the values stored in it. Most specifically you must never
780	reinitialise it or call its C<set> macro.	1161	reinitialise it or call its C<ev_TYPE_set> macro.
781		1162
782	Each and every callback receives the event loop pointer as first, the	1163	Each and every callback receives the event loop pointer as first, the
783	registered watcher structure as second, and a bitset of received events as	1164	registered watcher structure as second, and a bitset of received events as
784	third argument.	1165	third argument.
785		1166
…		…
794	=item C<EV_WRITE>	1175	=item C<EV_WRITE>
795		1176
796	The file descriptor in the C<ev_io> watcher has become readable and/or	1177	The file descriptor in the C<ev_io> watcher has become readable and/or
797	writable.	1178	writable.
798		1179
799	=item C<EV_TIMEOUT>	1180	=item C<EV_TIMER>
800		1181
801	The C<ev_timer> watcher has timed out.	1182	The C<ev_timer> watcher has timed out.
802		1183
803	=item C<EV_PERIODIC>	1184	=item C<EV_PERIODIC>
804		1185
…		…
822		1203
823	=item C<EV_PREPARE>	1204	=item C<EV_PREPARE>
824		1205
825	=item C<EV_CHECK>	1206	=item C<EV_CHECK>
826		1207
827	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts	1208	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts to
828	to gather new events, and all C<ev_check> watchers are invoked just after	1209	gather new events, and all C<ev_check> watchers are queued (not invoked)
829	C<ev_loop> has gathered them, but before it invokes any callbacks for any	1210	just after C<ev_run> has gathered them, but before it queues any callbacks
		1211	for any received events. That means C<ev_prepare> watchers are the last
		1212	watchers invoked before the event loop sleeps or polls for new events, and
		1213	C<ev_check> watchers will be invoked before any other watchers of the same
		1214	or lower priority within an event loop iteration.
		1215
830	received events. Callbacks of both watcher types can start and stop as	1216	Callbacks of both watcher types can start and stop as many watchers as
831	many watchers as they want, and all of them will be taken into account	1217	they want, and all of them will be taken into account (for example, a
832	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1218	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
833	C<ev_loop> from blocking).	1219	blocking).
834		1220
835	=item C<EV_EMBED>	1221	=item C<EV_EMBED>
836		1222
837	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1223	The embedded event loop specified in the C<ev_embed> watcher needs attention.
838		1224
839	=item C<EV_FORK>	1225	=item C<EV_FORK>
840		1226
841	The event loop has been resumed in the child process after fork (see	1227	The event loop has been resumed in the child process after fork (see
842	C<ev_fork>).	1228	C<ev_fork>).
843		1229
		1230	=item C<EV_CLEANUP>
		1231
		1232	The event loop is about to be destroyed (see C<ev_cleanup>).
		1233
844	=item C<EV_ASYNC>	1234	=item C<EV_ASYNC>
845		1235
846	The given async watcher has been asynchronously notified (see C<ev_async>).	1236	The given async watcher has been asynchronously notified (see C<ev_async>).
		1237
		1238	=item C<EV_CUSTOM>
		1239
		1240	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1241	by libev users to signal watchers (e.g. via C<ev_feed_event>).
847		1242
848	=item C<EV_ERROR>	1243	=item C<EV_ERROR>
849		1244
850	An unspecified error has occurred, the watcher has been stopped. This might	1245	An unspecified error has occurred, the watcher has been stopped. This might
851	happen because the watcher could not be properly started because libev	1246	happen because the watcher could not be properly started because libev
852	ran out of memory, a file descriptor was found to be closed or any other	1247	ran out of memory, a file descriptor was found to be closed or any other
		1248	problem. Libev considers these application bugs.
		1249
853	problem. You best act on it by reporting the problem and somehow coping	1250	You best act on it by reporting the problem and somehow coping with the
854	with the watcher being stopped.	1251	watcher being stopped. Note that well-written programs should not receive
		1252	an error ever, so when your watcher receives it, this usually indicates a
		1253	bug in your program.
855		1254
856	Libev will usually signal a few "dummy" events together with an error,	1255	Libev will usually signal a few "dummy" events together with an error, for
857	for example it might indicate that a fd is readable or writable, and if	1256	example it might indicate that a fd is readable or writable, and if your
858	your callbacks is well-written it can just attempt the operation and cope	1257	callbacks is well-written it can just attempt the operation and cope with
859	with the error from read() or write(). This will not work in multi-threaded	1258	the error from read() or write(). This will not work in multi-threaded
860	programs, though, so beware.	1259	programs, though, as the fd could already be closed and reused for another
		1260	thing, so beware.
861		1261
862	=back	1262	=back
863		1263
864	=head2 GENERIC WATCHER FUNCTIONS	1264	=head2 GENERIC WATCHER FUNCTIONS
865
866	In the following description, C<TYPE> stands for the watcher type,
867	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
868		1265
869	=over 4	1266	=over 4
870		1267
871	=item C<ev_init> (ev_TYPE *watcher, callback)	1268	=item C<ev_init> (ev_TYPE *watcher, callback)
872		1269
…		…
878	which rolls both calls into one.	1275	which rolls both calls into one.
879		1276
880	You can reinitialise a watcher at any time as long as it has been stopped	1277	You can reinitialise a watcher at any time as long as it has been stopped
881	(or never started) and there are no pending events outstanding.	1278	(or never started) and there are no pending events outstanding.
882		1279
883	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1280	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
884	int revents)>.	1281	int revents)>.
885		1282
		1283	Example: Initialise an C<ev_io> watcher in two steps.
		1284
		1285	ev_io w;
		1286	ev_init (&w, my_cb);
		1287	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1288
886	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1289	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
887		1290
888	This macro initialises the type-specific parts of a watcher. You need to	1291	This macro initialises the type-specific parts of a watcher. You need to
889	call C<ev_init> at least once before you call this macro, but you can	1292	call C<ev_init> at least once before you call this macro, but you can
890	call C<ev_TYPE_set> any number of times. You must not, however, call this	1293	call C<ev_TYPE_set> any number of times. You must not, however, call this
891	macro on a watcher that is active (it can be pending, however, which is a	1294	macro on a watcher that is active (it can be pending, however, which is a
892	difference to the C<ev_init> macro).	1295	difference to the C<ev_init> macro).
893		1296
894	Although some watcher types do not have type-specific arguments	1297	Although some watcher types do not have type-specific arguments
895	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1298	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
896		1299
		1300	See C<ev_init>, above, for an example.
		1301
897	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1302	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
898		1303
899	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1304	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
900	calls into a single call. This is the most convenient method to initialise	1305	calls into a single call. This is the most convenient method to initialise
901	a watcher. The same limitations apply, of course.	1306	a watcher. The same limitations apply, of course.
902		1307
		1308	Example: Initialise and set an C<ev_io> watcher in one step.
		1309
		1310	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1311
903	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1312	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
904		1313
905	Starts (activates) the given watcher. Only active watchers will receive	1314	Starts (activates) the given watcher. Only active watchers will receive
906	events. If the watcher is already active nothing will happen.	1315	events. If the watcher is already active nothing will happen.
907		1316
		1317	Example: Start the C<ev_io> watcher that is being abused as example in this
		1318	whole section.
		1319
		1320	ev_io_start (EV_DEFAULT_UC, &w);
		1321
908	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1322	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
909		1323
910	Stops the given watcher again (if active) and clears the pending	1324	Stops the given watcher if active, and clears the pending status (whether
		1325	the watcher was active or not).
		1326
911	status. It is possible that stopped watchers are pending (for example,	1327	It is possible that stopped watchers are pending - for example,
912	non-repeating timers are being stopped when they become pending), but	1328	non-repeating timers are being stopped when they become pending - but
913	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1329	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
914	you want to free or reuse the memory used by the watcher it is therefore a	1330	pending. If you want to free or reuse the memory used by the watcher it is
915	good idea to always call its C<ev_TYPE_stop> function.	1331	therefore a good idea to always call its C<ev_TYPE_stop> function.
916		1332
917	=item bool ev_is_active (ev_TYPE *watcher)	1333	=item bool ev_is_active (ev_TYPE *watcher)
918		1334
919	Returns a true value iff the watcher is active (i.e. it has been started	1335	Returns a true value iff the watcher is active (i.e. it has been started
920	and not yet been stopped). As long as a watcher is active you must not modify	1336	and not yet been stopped). As long as a watcher is active you must not modify
…		…
931		1347
932	=item callback ev_cb (ev_TYPE *watcher)	1348	=item callback ev_cb (ev_TYPE *watcher)
933		1349
934	Returns the callback currently set on the watcher.	1350	Returns the callback currently set on the watcher.
935		1351
936	=item ev_cb_set (ev_TYPE *watcher, callback)	1352	=item ev_set_cb (ev_TYPE *watcher, callback)
937		1353
938	Change the callback. You can change the callback at virtually any time	1354	Change the callback. You can change the callback at virtually any time
939	(modulo threads).	1355	(modulo threads).
940		1356
941	=item ev_set_priority (ev_TYPE *watcher, priority)	1357	=item ev_set_priority (ev_TYPE *watcher, int priority)
942		1358
943	=item int ev_priority (ev_TYPE *watcher)	1359	=item int ev_priority (ev_TYPE *watcher)
944		1360
945	Set and query the priority of the watcher. The priority is a small	1361	Set and query the priority of the watcher. The priority is a small
946	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1362	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
947	(default: C<-2>). Pending watchers with higher priority will be invoked	1363	(default: C<-2>). Pending watchers with higher priority will be invoked
948	before watchers with lower priority, but priority will not keep watchers	1364	before watchers with lower priority, but priority will not keep watchers
949	from being executed (except for C<ev_idle> watchers).	1365	from being executed (except for C<ev_idle> watchers).
950		1366
951	This means that priorities are I<only> used for ordering callback
952	invocation after new events have been received. This is useful, for
953	example, to reduce latency after idling, or more often, to bind two
954	watchers on the same event and make sure one is called first.
955
956	If you need to suppress invocation when higher priority events are pending	1367	If you need to suppress invocation when higher priority events are pending
957	you need to look at C<ev_idle> watchers, which provide this functionality.	1368	you need to look at C<ev_idle> watchers, which provide this functionality.
958		1369
959	You I<must not> change the priority of a watcher as long as it is active or	1370	You I<must not> change the priority of a watcher as long as it is active or
960	pending.	1371	pending.
961		1372
		1373	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1374	fine, as long as you do not mind that the priority value you query might
		1375	or might not have been clamped to the valid range.
		1376
962	The default priority used by watchers when no priority has been set is	1377	The default priority used by watchers when no priority has been set is
963	always C<0>, which is supposed to not be too high and not be too low :).	1378	always C<0>, which is supposed to not be too high and not be too low :).
964		1379
965	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1380	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
966	fine, as long as you do not mind that the priority value you query might	1381	priorities.
967	or might not have been adjusted to be within valid range.
968		1382
969	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1383	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
970		1384
971	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1385	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
972	C<loop> nor C<revents> need to be valid as long as the watcher callback	1386	C<loop> nor C<revents> need to be valid as long as the watcher callback
973	can deal with that fact.	1387	can deal with that fact, as both are simply passed through to the
		1388	callback.
974		1389
975	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1390	=item int ev_clear_pending (loop, ev_TYPE *watcher)
976		1391
977	If the watcher is pending, this function returns clears its pending status	1392	If the watcher is pending, this function clears its pending status and
978	and returns its C<revents> bitset (as if its callback was invoked). If the	1393	returns its C<revents> bitset (as if its callback was invoked). If the
979	watcher isn't pending it does nothing and returns C<0>.	1394	watcher isn't pending it does nothing and returns C<0>.
980		1395
		1396	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1397	callback to be invoked, which can be accomplished with this function.
		1398
		1399	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1400
		1401	Feeds the given event set into the event loop, as if the specified event
		1402	had happened for the specified watcher (which must be a pointer to an
		1403	initialised but not necessarily started event watcher). Obviously you must
		1404	not free the watcher as long as it has pending events.
		1405
		1406	Stopping the watcher, letting libev invoke it, or calling
		1407	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1408	not started in the first place.
		1409
		1410	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1411	functions that do not need a watcher.
		1412
981	=back	1413	=back
982		1414
		1415	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
		1416	OWN COMPOSITE WATCHERS> idioms.
983		1417
984	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1418	=head2 WATCHER STATES
985		1419
986	Each watcher has, by default, a member C<void *data> that you can change	1420	There are various watcher states mentioned throughout this manual -
987	and read at any time, libev will completely ignore it. This can be used	1421	active, pending and so on. In this section these states and the rules to
988	to associate arbitrary data with your watcher. If you need more data and	1422	transition between them will be described in more detail - and while these
989	don't want to allocate memory and store a pointer to it in that data	1423	rules might look complicated, they usually do "the right thing".
990	member, you can also "subclass" the watcher type and provide your own
991	data:
992		1424
993	struct my_io	1425	=over 4
		1426
		1427	=item initialised
		1428
		1429	Before a watcher can be registered with the event loop it has to be
		1430	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
		1431	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
		1432
		1433	In this state it is simply some block of memory that is suitable for
		1434	use in an event loop. It can be moved around, freed, reused etc. at
		1435	will - as long as you either keep the memory contents intact, or call
		1436	C<ev_TYPE_init> again.
		1437
		1438	=item started/running/active
		1439
		1440	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
		1441	property of the event loop, and is actively waiting for events. While in
		1442	this state it cannot be accessed (except in a few documented ways), moved,
		1443	freed or anything else - the only legal thing is to keep a pointer to it,
		1444	and call libev functions on it that are documented to work on active watchers.
		1445
		1446	=item pending
		1447
		1448	If a watcher is active and libev determines that an event it is interested
		1449	in has occurred (such as a timer expiring), it will become pending. It will
		1450	stay in this pending state until either it is stopped or its callback is
		1451	about to be invoked, so it is not normally pending inside the watcher
		1452	callback.
		1453
		1454	The watcher might or might not be active while it is pending (for example,
		1455	an expired non-repeating timer can be pending but no longer active). If it
		1456	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1457	but it is still property of the event loop at this time, so cannot be
		1458	moved, freed or reused. And if it is active the rules described in the
		1459	previous item still apply.
		1460
		1461	It is also possible to feed an event on a watcher that is not active (e.g.
		1462	via C<ev_feed_event>), in which case it becomes pending without being
		1463	active.
		1464
		1465	=item stopped
		1466
		1467	A watcher can be stopped implicitly by libev (in which case it might still
		1468	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1469	latter will clear any pending state the watcher might be in, regardless
		1470	of whether it was active or not, so stopping a watcher explicitly before
		1471	freeing it is often a good idea.
		1472
		1473	While stopped (and not pending) the watcher is essentially in the
		1474	initialised state, that is, it can be reused, moved, modified in any way
		1475	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1476	it again).
		1477
		1478	=back
		1479
		1480	=head2 WATCHER PRIORITY MODELS
		1481
		1482	Many event loops support I<watcher priorities>, which are usually small
		1483	integers that influence the ordering of event callback invocation
		1484	between watchers in some way, all else being equal.
		1485
		1486	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1487	description for the more technical details such as the actual priority
		1488	range.
		1489
		1490	There are two common ways how these these priorities are being interpreted
		1491	by event loops:
		1492
		1493	In the more common lock-out model, higher priorities "lock out" invocation
		1494	of lower priority watchers, which means as long as higher priority
		1495	watchers receive events, lower priority watchers are not being invoked.
		1496
		1497	The less common only-for-ordering model uses priorities solely to order
		1498	callback invocation within a single event loop iteration: Higher priority
		1499	watchers are invoked before lower priority ones, but they all get invoked
		1500	before polling for new events.
		1501
		1502	Libev uses the second (only-for-ordering) model for all its watchers
		1503	except for idle watchers (which use the lock-out model).
		1504
		1505	The rationale behind this is that implementing the lock-out model for
		1506	watchers is not well supported by most kernel interfaces, and most event
		1507	libraries will just poll for the same events again and again as long as
		1508	their callbacks have not been executed, which is very inefficient in the
		1509	common case of one high-priority watcher locking out a mass of lower
		1510	priority ones.
		1511
		1512	Static (ordering) priorities are most useful when you have two or more
		1513	watchers handling the same resource: a typical usage example is having an
		1514	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1515	timeouts. Under load, data might be received while the program handles
		1516	other jobs, but since timers normally get invoked first, the timeout
		1517	handler will be executed before checking for data. In that case, giving
		1518	the timer a lower priority than the I/O watcher ensures that I/O will be
		1519	handled first even under adverse conditions (which is usually, but not
		1520	always, what you want).
		1521
		1522	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1523	will only be executed when no same or higher priority watchers have
		1524	received events, they can be used to implement the "lock-out" model when
		1525	required.
		1526
		1527	For example, to emulate how many other event libraries handle priorities,
		1528	you can associate an C<ev_idle> watcher to each such watcher, and in
		1529	the normal watcher callback, you just start the idle watcher. The real
		1530	processing is done in the idle watcher callback. This causes libev to
		1531	continuously poll and process kernel event data for the watcher, but when
		1532	the lock-out case is known to be rare (which in turn is rare :), this is
		1533	workable.
		1534
		1535	Usually, however, the lock-out model implemented that way will perform
		1536	miserably under the type of load it was designed to handle. In that case,
		1537	it might be preferable to stop the real watcher before starting the
		1538	idle watcher, so the kernel will not have to process the event in case
		1539	the actual processing will be delayed for considerable time.
		1540
		1541	Here is an example of an I/O watcher that should run at a strictly lower
		1542	priority than the default, and which should only process data when no
		1543	other events are pending:
		1544
		1545	ev_idle idle; // actual processing watcher
		1546	ev_io io; // actual event watcher
		1547
		1548	static void
		1549	io_cb (EV_P_ ev_io *w, int revents)
994	{	1550	{
995	struct ev_io io;	1551	// stop the I/O watcher, we received the event, but
996	int otherfd;	1552	// are not yet ready to handle it.
997	void *somedata;	1553	ev_io_stop (EV_A_ w);
998	struct whatever *mostinteresting;	1554
		1555	// start the idle watcher to handle the actual event.
		1556	// it will not be executed as long as other watchers
		1557	// with the default priority are receiving events.
		1558	ev_idle_start (EV_A_ &idle);
999	}	1559	}
1000		1560
1001	And since your callback will be called with a pointer to the watcher, you	1561	static void
1002	can cast it back to your own type:	1562	idle_cb (EV_P_ ev_idle *w, int revents)
1003
1004	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
1005	{	1563	{
1006	struct my_io *w = (struct my_io *)w_;	1564	// actual processing
1007	...	1565	read (STDIN_FILENO, ...);
		1566
		1567	// have to start the I/O watcher again, as
		1568	// we have handled the event
		1569	ev_io_start (EV_P_ &io);
1008	}	1570	}
1009		1571
1010	More interesting and less C-conformant ways of casting your callback type	1572	// initialisation
1011	instead have been omitted.	1573	ev_idle_init (&idle, idle_cb);
		1574	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1575	ev_io_start (EV_DEFAULT_ &io);
1012		1576
1013	Another common scenario is having some data structure with multiple	1577	In the "real" world, it might also be beneficial to start a timer, so that
1014	watchers:	1578	low-priority connections can not be locked out forever under load. This
1015		1579	enables your program to keep a lower latency for important connections
1016	struct my_biggy	1580	during short periods of high load, while not completely locking out less
1017	{	1581	important ones.
1018	int some_data;
1019	ev_timer t1;
1020	ev_timer t2;
1021	}
1022
1023	In this case getting the pointer to C<my_biggy> is a bit more complicated,
1024	you need to use C<offsetof>:
1025
1026	#include <stddef.h>
1027
1028	static void
1029	t1_cb (EV_P_ struct ev_timer *w, int revents)
1030	{
1031	struct my_biggy big = (struct my_biggy *
1032	(((char *)w) - offsetof (struct my_biggy, t1));
1033	}
1034
1035	static void
1036	t2_cb (EV_P_ struct ev_timer *w, int revents)
1037	{
1038	struct my_biggy big = (struct my_biggy *
1039	(((char *)w) - offsetof (struct my_biggy, t2));
1040	}
1041		1582
1042		1583
1043	=head1 WATCHER TYPES	1584	=head1 WATCHER TYPES
1044		1585
1045	This section describes each watcher in detail, but will not repeat	1586	This section describes each watcher in detail, but will not repeat
…		…
1069	In general you can register as many read and/or write event watchers per	1610	In general you can register as many read and/or write event watchers per
1070	fd as you want (as long as you don't confuse yourself). Setting all file	1611	fd as you want (as long as you don't confuse yourself). Setting all file
1071	descriptors to non-blocking mode is also usually a good idea (but not	1612	descriptors to non-blocking mode is also usually a good idea (but not
1072	required if you know what you are doing).	1613	required if you know what you are doing).
1073		1614
1074	If you must do this, then force the use of a known-to-be-good backend
1075	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
1076	C<EVBACKEND_POLL>).
1077
1078	Another thing you have to watch out for is that it is quite easy to	1615	Another thing you have to watch out for is that it is quite easy to
1079	receive "spurious" readiness notifications, that is your callback might	1616	receive "spurious" readiness notifications, that is, your callback might
1080	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1617	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1081	because there is no data. Not only are some backends known to create a	1618	because there is no data. It is very easy to get into this situation even
1082	lot of those (for example Solaris ports), it is very easy to get into	1619	with a relatively standard program structure. Thus it is best to always
1083	this situation even with a relatively standard program structure. Thus	1620	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1084	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1085	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1621	preferable to a program hanging until some data arrives.
1086		1622
1087	If you cannot run the fd in non-blocking mode (for example you should not	1623	If you cannot run the fd in non-blocking mode (for example you should
1088	play around with an Xlib connection), then you have to separately re-test	1624	not play around with an Xlib connection), then you have to separately
1089	whether a file descriptor is really ready with a known-to-be good interface	1625	re-test whether a file descriptor is really ready with a known-to-be good
1090	such as poll (fortunately in our Xlib example, Xlib already does this on	1626	interface such as poll (fortunately in the case of Xlib, it already does
1091	its own, so its quite safe to use).	1627	this on its own, so its quite safe to use). Some people additionally
		1628	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1629	indefinitely.
		1630
		1631	But really, best use non-blocking mode.
1092		1632
1093	=head3 The special problem of disappearing file descriptors	1633	=head3 The special problem of disappearing file descriptors
1094		1634
1095	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1635	Some backends (e.g. kqueue, epoll) need to be told about closing a file
1096	descriptor (either by calling C<close> explicitly or by any other means,	1636	descriptor (either due to calling C<close> explicitly or any other means,
1097	such as C<dup>). The reason is that you register interest in some file	1637	such as C<dup2>). The reason is that you register interest in some file
1098	descriptor, but when it goes away, the operating system will silently drop	1638	descriptor, but when it goes away, the operating system will silently drop
1099	this interest. If another file descriptor with the same number then is	1639	this interest. If another file descriptor with the same number then is
1100	registered with libev, there is no efficient way to see that this is, in	1640	registered with libev, there is no efficient way to see that this is, in
1101	fact, a different file descriptor.	1641	fact, a different file descriptor.
1102		1642
…		…
1120		1660
1121	There is no workaround possible except not registering events	1661	There is no workaround possible except not registering events
1122	for potentially C<dup ()>'ed file descriptors, or to resort to	1662	for potentially C<dup ()>'ed file descriptors, or to resort to
1123	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1663	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1124		1664
		1665	=head3 The special problem of files
		1666
		1667	Many people try to use C<select> (or libev) on file descriptors
		1668	representing files, and expect it to become ready when their program
		1669	doesn't block on disk accesses (which can take a long time on their own).
		1670
		1671	However, this cannot ever work in the "expected" way - you get a readiness
		1672	notification as soon as the kernel knows whether and how much data is
		1673	there, and in the case of open files, that's always the case, so you
		1674	always get a readiness notification instantly, and your read (or possibly
		1675	write) will still block on the disk I/O.
		1676
		1677	Another way to view it is that in the case of sockets, pipes, character
		1678	devices and so on, there is another party (the sender) that delivers data
		1679	on its own, but in the case of files, there is no such thing: the disk
		1680	will not send data on its own, simply because it doesn't know what you
		1681	wish to read - you would first have to request some data.
		1682
		1683	Since files are typically not-so-well supported by advanced notification
		1684	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1685	to files, even though you should not use it. The reason for this is
		1686	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1687	usually a tty, often a pipe, but also sometimes files or special devices
		1688	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1689	F</dev/urandom>), and even though the file might better be served with
		1690	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1691	it "just works" instead of freezing.
		1692
		1693	So avoid file descriptors pointing to files when you know it (e.g. use
		1694	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1695	when you rarely read from a file instead of from a socket, and want to
		1696	reuse the same code path.
		1697
1125	=head3 The special problem of fork	1698	=head3 The special problem of fork
1126		1699
1127	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1700	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
1128	useless behaviour. Libev fully supports fork, but needs to be told about	1701	useless behaviour. Libev fully supports fork, but needs to be told about
1129	it in the child.	1702	it in the child if you want to continue to use it in the child.
1130		1703
1131	To support fork in your programs, you either have to call	1704	To support fork in your child processes, you have to call C<ev_loop_fork
1132	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1705	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1133	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1706	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1134	C<EVBACKEND_POLL>.
1135		1707
1136	=head3 The special problem of SIGPIPE	1708	=head3 The special problem of SIGPIPE
1137		1709
1138	While not really specific to libev, it is easy to forget about SIGPIPE:	1710	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1139	when reading from a pipe whose other end has been closed, your program	1711	when writing to a pipe whose other end has been closed, your program gets
1140	gets send a SIGPIPE, which, by default, aborts your program. For most	1712	sent a SIGPIPE, which, by default, aborts your program. For most programs
1141	programs this is sensible behaviour, for daemons, this is usually	1713	this is sensible behaviour, for daemons, this is usually undesirable.
1142	undesirable.
1143		1714
1144	So when you encounter spurious, unexplained daemon exits, make sure you	1715	So when you encounter spurious, unexplained daemon exits, make sure you
1145	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon	1716	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
1146	somewhere, as that would have given you a big clue).	1717	somewhere, as that would have given you a big clue).
1147		1718
		1719	=head3 The special problem of accept()ing when you can't
		1720
		1721	Many implementations of the POSIX C<accept> function (for example,
		1722	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1723	connection from the pending queue in all error cases.
		1724
		1725	For example, larger servers often run out of file descriptors (because
		1726	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1727	rejecting the connection, leading to libev signalling readiness on
		1728	the next iteration again (the connection still exists after all), and
		1729	typically causing the program to loop at 100% CPU usage.
		1730
		1731	Unfortunately, the set of errors that cause this issue differs between
		1732	operating systems, there is usually little the app can do to remedy the
		1733	situation, and no known thread-safe method of removing the connection to
		1734	cope with overload is known (to me).
		1735
		1736	One of the easiest ways to handle this situation is to just ignore it
		1737	- when the program encounters an overload, it will just loop until the
		1738	situation is over. While this is a form of busy waiting, no OS offers an
		1739	event-based way to handle this situation, so it's the best one can do.
		1740
		1741	A better way to handle the situation is to log any errors other than
		1742	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1743	messages, and continue as usual, which at least gives the user an idea of
		1744	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1745	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1746	usage.
		1747
		1748	If your program is single-threaded, then you could also keep a dummy file
		1749	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1750	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1751	close that fd, and create a new dummy fd. This will gracefully refuse
		1752	clients under typical overload conditions.
		1753
		1754	The last way to handle it is to simply log the error and C<exit>, as
		1755	is often done with C<malloc> failures, but this results in an easy
		1756	opportunity for a DoS attack.
1148		1757
1149	=head3 Watcher-Specific Functions	1758	=head3 Watcher-Specific Functions
1150		1759
1151	=over 4	1760	=over 4
1152		1761
1153	=item ev_io_init (ev_io *, callback, int fd, int events)	1762	=item ev_io_init (ev_io *, callback, int fd, int events)
1154		1763
1155	=item ev_io_set (ev_io *, int fd, int events)	1764	=item ev_io_set (ev_io *, int fd, int events)
1156		1765
1157	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1766	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1158	receive events for and events is either C<EV_READ>, C<EV_WRITE> or	1767	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
1159	C<EV_READ | EV_WRITE> to receive the given events.	1768	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1160		1769
1161	=item int fd [read-only]	1770	=item int fd [read-only]
1162		1771
1163	The file descriptor being watched.	1772	The file descriptor being watched.
1164		1773
…		…
1173	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1782	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1174	readable, but only once. Since it is likely line-buffered, you could	1783	readable, but only once. Since it is likely line-buffered, you could
1175	attempt to read a whole line in the callback.	1784	attempt to read a whole line in the callback.
1176		1785
1177	static void	1786	static void
1178	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1787	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1179	{	1788	{
1180	ev_io_stop (loop, w);	1789	ev_io_stop (loop, w);
1181	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1790	.. read from stdin here (or from w->fd) and handle any I/O errors
1182	}	1791	}
1183		1792
1184	...	1793	...
1185	struct ev_loop *loop = ev_default_init (0);	1794	struct ev_loop *loop = ev_default_init (0);
1186	struct ev_io stdin_readable;	1795	ev_io stdin_readable;
1187	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1796	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1188	ev_io_start (loop, &stdin_readable);	1797	ev_io_start (loop, &stdin_readable);
1189	ev_loop (loop, 0);	1798	ev_run (loop, 0);
1190		1799
1191		1800
1192	=head2 C<ev_timer> - relative and optionally repeating timeouts	1801	=head2 C<ev_timer> - relative and optionally repeating timeouts
1193		1802
1194	Timer watchers are simple relative timers that generate an event after a	1803	Timer watchers are simple relative timers that generate an event after a
1195	given time, and optionally repeating in regular intervals after that.	1804	given time, and optionally repeating in regular intervals after that.
1196		1805
1197	The timers are based on real time, that is, if you register an event that	1806	The timers are based on real time, that is, if you register an event that
1198	times out after an hour and you reset your system clock to January last	1807	times out after an hour and you reset your system clock to January last
1199	year, it will still time out after (roughly) and hour. "Roughly" because	1808	year, it will still time out after (roughly) one hour. "Roughly" because
1200	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1809	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1201	monotonic clock option helps a lot here).	1810	monotonic clock option helps a lot here).
		1811
		1812	The callback is guaranteed to be invoked only I<after> its timeout has
		1813	passed (not I<at>, so on systems with very low-resolution clocks this
		1814	might introduce a small delay, see "the special problem of being too
		1815	early", below). If multiple timers become ready during the same loop
		1816	iteration then the ones with earlier time-out values are invoked before
		1817	ones of the same priority with later time-out values (but this is no
		1818	longer true when a callback calls C<ev_run> recursively).
		1819
		1820	=head3 Be smart about timeouts
		1821
		1822	Many real-world problems involve some kind of timeout, usually for error
		1823	recovery. A typical example is an HTTP request - if the other side hangs,
		1824	you want to raise some error after a while.
		1825
		1826	What follows are some ways to handle this problem, from obvious and
		1827	inefficient to smart and efficient.
		1828
		1829	In the following, a 60 second activity timeout is assumed - a timeout that
		1830	gets reset to 60 seconds each time there is activity (e.g. each time some
		1831	data or other life sign was received).
		1832
		1833	=over 4
		1834
		1835	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1836
		1837	This is the most obvious, but not the most simple way: In the beginning,
		1838	start the watcher:
		1839
		1840	ev_timer_init (timer, callback, 60., 0.);
		1841	ev_timer_start (loop, timer);
		1842
		1843	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1844	and start it again:
		1845
		1846	ev_timer_stop (loop, timer);
		1847	ev_timer_set (timer, 60., 0.);
		1848	ev_timer_start (loop, timer);
		1849
		1850	This is relatively simple to implement, but means that each time there is
		1851	some activity, libev will first have to remove the timer from its internal
		1852	data structure and then add it again. Libev tries to be fast, but it's
		1853	still not a constant-time operation.
		1854
		1855	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1856
		1857	This is the easiest way, and involves using C<ev_timer_again> instead of
		1858	C<ev_timer_start>.
		1859
		1860	To implement this, configure an C<ev_timer> with a C<repeat> value
		1861	of C<60> and then call C<ev_timer_again> at start and each time you
		1862	successfully read or write some data. If you go into an idle state where
		1863	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1864	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1865
		1866	That means you can ignore both the C<ev_timer_start> function and the
		1867	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1868	member and C<ev_timer_again>.
		1869
		1870	At start:
		1871
		1872	ev_init (timer, callback);
		1873	timer->repeat = 60.;
		1874	ev_timer_again (loop, timer);
		1875
		1876	Each time there is some activity:
		1877
		1878	ev_timer_again (loop, timer);
		1879
		1880	It is even possible to change the time-out on the fly, regardless of
		1881	whether the watcher is active or not:
		1882
		1883	timer->repeat = 30.;
		1884	ev_timer_again (loop, timer);
		1885
		1886	This is slightly more efficient then stopping/starting the timer each time
		1887	you want to modify its timeout value, as libev does not have to completely
		1888	remove and re-insert the timer from/into its internal data structure.
		1889
		1890	It is, however, even simpler than the "obvious" way to do it.
		1891
		1892	=item 3. Let the timer time out, but then re-arm it as required.
		1893
		1894	This method is more tricky, but usually most efficient: Most timeouts are
		1895	relatively long compared to the intervals between other activity - in
		1896	our example, within 60 seconds, there are usually many I/O events with
		1897	associated activity resets.
		1898
		1899	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1900	but remember the time of last activity, and check for a real timeout only
		1901	within the callback:
		1902
		1903	ev_tstamp timeout = 60.;
		1904	ev_tstamp last_activity; // time of last activity
		1905	ev_timer timer;
		1906
		1907	static void
		1908	callback (EV_P_ ev_timer *w, int revents)
		1909	{
		1910	// calculate when the timeout would happen
		1911	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
		1912
		1913	// if negative, it means we the timeout already occurred
		1914	if (after < 0.)
		1915	{
		1916	// timeout occurred, take action
		1917	}
		1918	else
		1919	{
		1920	// callback was invoked, but there was some recent
		1921	// activity. simply restart the timer to time out
		1922	// after "after" seconds, which is the earliest time
		1923	// the timeout can occur.
		1924	ev_timer_set (w, after, 0.);
		1925	ev_timer_start (EV_A_ w);
		1926	}
		1927	}
		1928
		1929	To summarise the callback: first calculate in how many seconds the
		1930	timeout will occur (by calculating the absolute time when it would occur,
		1931	C<last_activity + timeout>, and subtracting the current time, C<ev_now
		1932	(EV_A)> from that).
		1933
		1934	If this value is negative, then we are already past the timeout, i.e. we
		1935	timed out, and need to do whatever is needed in this case.
		1936
		1937	Otherwise, we now the earliest time at which the timeout would trigger,
		1938	and simply start the timer with this timeout value.
		1939
		1940	In other words, each time the callback is invoked it will check whether
		1941	the timeout occurred. If not, it will simply reschedule itself to check
		1942	again at the earliest time it could time out. Rinse. Repeat.
		1943
		1944	This scheme causes more callback invocations (about one every 60 seconds
		1945	minus half the average time between activity), but virtually no calls to
		1946	libev to change the timeout.
		1947
		1948	To start the machinery, simply initialise the watcher and set
		1949	C<last_activity> to the current time (meaning there was some activity just
		1950	now), then call the callback, which will "do the right thing" and start
		1951	the timer:
		1952
		1953	last_activity = ev_now (EV_A);
		1954	ev_init (&timer, callback);
		1955	callback (EV_A_ &timer, 0);
		1956
		1957	When there is some activity, simply store the current time in
		1958	C<last_activity>, no libev calls at all:
		1959
		1960	if (activity detected)
		1961	last_activity = ev_now (EV_A);
		1962
		1963	When your timeout value changes, then the timeout can be changed by simply
		1964	providing a new value, stopping the timer and calling the callback, which
		1965	will again do the right thing (for example, time out immediately :).
		1966
		1967	timeout = new_value;
		1968	ev_timer_stop (EV_A_ &timer);
		1969	callback (EV_A_ &timer, 0);
		1970
		1971	This technique is slightly more complex, but in most cases where the
		1972	time-out is unlikely to be triggered, much more efficient.
		1973
		1974	=item 4. Wee, just use a double-linked list for your timeouts.
		1975
		1976	If there is not one request, but many thousands (millions...), all
		1977	employing some kind of timeout with the same timeout value, then one can
		1978	do even better:
		1979
		1980	When starting the timeout, calculate the timeout value and put the timeout
		1981	at the I<end> of the list.
		1982
		1983	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1984	the list is expected to fire (for example, using the technique #3).
		1985
		1986	When there is some activity, remove the timer from the list, recalculate
		1987	the timeout, append it to the end of the list again, and make sure to
		1988	update the C<ev_timer> if it was taken from the beginning of the list.
		1989
		1990	This way, one can manage an unlimited number of timeouts in O(1) time for
		1991	starting, stopping and updating the timers, at the expense of a major
		1992	complication, and having to use a constant timeout. The constant timeout
		1993	ensures that the list stays sorted.
		1994
		1995	=back
		1996
		1997	So which method the best?
		1998
		1999	Method #2 is a simple no-brain-required solution that is adequate in most
		2000	situations. Method #3 requires a bit more thinking, but handles many cases
		2001	better, and isn't very complicated either. In most case, choosing either
		2002	one is fine, with #3 being better in typical situations.
		2003
		2004	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		2005	rather complicated, but extremely efficient, something that really pays
		2006	off after the first million or so of active timers, i.e. it's usually
		2007	overkill :)
		2008
		2009	=head3 The special problem of being too early
		2010
		2011	If you ask a timer to call your callback after three seconds, then
		2012	you expect it to be invoked after three seconds - but of course, this
		2013	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		2014	guaranteed to any precision by libev - imagine somebody suspending the
		2015	process with a STOP signal for a few hours for example.
		2016
		2017	So, libev tries to invoke your callback as soon as possible I<after> the
		2018	delay has occurred, but cannot guarantee this.
		2019
		2020	A less obvious failure mode is calling your callback too early: many event
		2021	loops compare timestamps with a "elapsed delay >= requested delay", but
		2022	this can cause your callback to be invoked much earlier than you would
		2023	expect.
		2024
		2025	To see why, imagine a system with a clock that only offers full second
		2026	resolution (think windows if you can't come up with a broken enough OS
		2027	yourself). If you schedule a one-second timer at the time 500.9, then the
		2028	event loop will schedule your timeout to elapse at a system time of 500
		2029	(500.9 truncated to the resolution) + 1, or 501.
		2030
		2031	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2032	501" and invoke the callback 0.1s after it was started, even though a
		2033	one-second delay was requested - this is being "too early", despite best
		2034	intentions.
		2035
		2036	This is the reason why libev will never invoke the callback if the elapsed
		2037	delay equals the requested delay, but only when the elapsed delay is
		2038	larger than the requested delay. In the example above, libev would only invoke
		2039	the callback at system time 502, or 1.1s after the timer was started.
		2040
		2041	So, while libev cannot guarantee that your callback will be invoked
		2042	exactly when requested, it I<can> and I<does> guarantee that the requested
		2043	delay has actually elapsed, or in other words, it always errs on the "too
		2044	late" side of things.
		2045
		2046	=head3 The special problem of time updates
		2047
		2048	Establishing the current time is a costly operation (it usually takes
		2049	at least one system call): EV therefore updates its idea of the current
		2050	time only before and after C<ev_run> collects new events, which causes a
		2051	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		2052	lots of events in one iteration.
1202		2053
1203	The relative timeouts are calculated relative to the C<ev_now ()>	2054	The relative timeouts are calculated relative to the C<ev_now ()>
1204	time. This is usually the right thing as this timestamp refers to the time	2055	time. This is usually the right thing as this timestamp refers to the time
1205	of the event triggering whatever timeout you are modifying/starting. If	2056	of the event triggering whatever timeout you are modifying/starting. If
1206	you suspect event processing to be delayed and you I<need> to base the timeout	2057	you suspect event processing to be delayed and you I<need> to base the
1207	on the current time, use something like this to adjust for this:	2058	timeout on the current time, use something like the following to adjust
		2059	for it:
1208		2060
1209	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2061	ev_timer_set (&timer, after + (ev_time () - ev_now ()), 0.);
1210		2062
1211	The callback is guaranteed to be invoked only after its timeout has passed,	2063	If the event loop is suspended for a long time, you can also force an
1212	but if multiple timers become ready during the same loop iteration then	2064	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1213	order of execution is undefined.	2065	()>, although that will push the event time of all outstanding events
		2066	further into the future.
		2067
		2068	=head3 The special problem of unsynchronised clocks
		2069
		2070	Modern systems have a variety of clocks - libev itself uses the normal
		2071	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2072	jumps).
		2073
		2074	Neither of these clocks is synchronised with each other or any other clock
		2075	on the system, so C<ev_time ()> might return a considerably different time
		2076	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2077	a call to C<gettimeofday> might return a second count that is one higher
		2078	than a directly following call to C<time>.
		2079
		2080	The moral of this is to only compare libev-related timestamps with
		2081	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2082	a second or so.
		2083
		2084	One more problem arises due to this lack of synchronisation: if libev uses
		2085	the system monotonic clock and you compare timestamps from C<ev_time>
		2086	or C<ev_now> from when you started your timer and when your callback is
		2087	invoked, you will find that sometimes the callback is a bit "early".
		2088
		2089	This is because C<ev_timer>s work in real time, not wall clock time, so
		2090	libev makes sure your callback is not invoked before the delay happened,
		2091	I<measured according to the real time>, not the system clock.
		2092
		2093	If your timeouts are based on a physical timescale (e.g. "time out this
		2094	connection after 100 seconds") then this shouldn't bother you as it is
		2095	exactly the right behaviour.
		2096
		2097	If you want to compare wall clock/system timestamps to your timers, then
		2098	you need to use C<ev_periodic>s, as these are based on the wall clock
		2099	time, where your comparisons will always generate correct results.
		2100
		2101	=head3 The special problems of suspended animation
		2102
		2103	When you leave the server world it is quite customary to hit machines that
		2104	can suspend/hibernate - what happens to the clocks during such a suspend?
		2105
		2106	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		2107	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		2108	to run until the system is suspended, but they will not advance while the
		2109	system is suspended. That means, on resume, it will be as if the program
		2110	was frozen for a few seconds, but the suspend time will not be counted
		2111	towards C<ev_timer> when a monotonic clock source is used. The real time
		2112	clock advanced as expected, but if it is used as sole clocksource, then a
		2113	long suspend would be detected as a time jump by libev, and timers would
		2114	be adjusted accordingly.
		2115
		2116	I would not be surprised to see different behaviour in different between
		2117	operating systems, OS versions or even different hardware.
		2118
		2119	The other form of suspend (job control, or sending a SIGSTOP) will see a
		2120	time jump in the monotonic clocks and the realtime clock. If the program
		2121	is suspended for a very long time, and monotonic clock sources are in use,
		2122	then you can expect C<ev_timer>s to expire as the full suspension time
		2123	will be counted towards the timers. When no monotonic clock source is in
		2124	use, then libev will again assume a timejump and adjust accordingly.
		2125
		2126	It might be beneficial for this latter case to call C<ev_suspend>
		2127	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		2128	deterministic behaviour in this case (you can do nothing against
		2129	C<SIGSTOP>).
1214		2130
1215	=head3 Watcher-Specific Functions and Data Members	2131	=head3 Watcher-Specific Functions and Data Members
1216		2132
1217	=over 4	2133	=over 4
1218		2134
1219	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2135	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1220		2136
1221	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2137	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1222		2138
1223	Configure the timer to trigger after C<after> seconds. If C<repeat>	2139	Configure the timer to trigger after C<after> seconds (fractional and
1224	is C<0.>, then it will automatically be stopped once the timeout is	2140	negative values are supported). If C<repeat> is C<0.>, then it will
1225	reached. If it is positive, then the timer will automatically be	2141	automatically be stopped once the timeout is reached. If it is positive,
1226	configured to trigger again C<repeat> seconds later, again, and again,	2142	then the timer will automatically be configured to trigger again C<repeat>
1227	until stopped manually.	2143	seconds later, again, and again, until stopped manually.
1228		2144
1229	The timer itself will do a best-effort at avoiding drift, that is, if	2145	The timer itself will do a best-effort at avoiding drift, that is, if
1230	you configure a timer to trigger every 10 seconds, then it will normally	2146	you configure a timer to trigger every 10 seconds, then it will normally
1231	trigger at exactly 10 second intervals. If, however, your program cannot	2147	trigger at exactly 10 second intervals. If, however, your program cannot
1232	keep up with the timer (because it takes longer than those 10 seconds to	2148	keep up with the timer (because it takes longer than those 10 seconds to
1233	do stuff) the timer will not fire more than once per event loop iteration.	2149	do stuff) the timer will not fire more than once per event loop iteration.
1234		2150
1235	=item ev_timer_again (loop, ev_timer *)	2151	=item ev_timer_again (loop, ev_timer *)
1236		2152
1237	This will act as if the timer timed out and restart it again if it is	2153	This will act as if the timer timed out, and restarts it again if it is
1238	repeating. The exact semantics are:	2154	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2155	timeout to the C<repeat> value and calling C<ev_timer_start>.
1239		2156
		2157	The exact semantics are as in the following rules, all of which will be
		2158	applied to the watcher:
		2159
		2160	=over 4
		2161
1240	If the timer is pending, its pending status is cleared.	2162	=item If the timer is pending, the pending status is always cleared.
1241		2163
1242	If the timer is started but non-repeating, stop it (as if it timed out).	2164	=item If the timer is started but non-repeating, stop it (as if it timed
		2165	out, without invoking it).
1243		2166
1244	If the timer is repeating, either start it if necessary (with the	2167	=item If the timer is repeating, make the C<repeat> value the new timeout
1245	C<repeat> value), or reset the running timer to the C<repeat> value.	2168	and start the timer, if necessary.
1246		2169
1247	This sounds a bit complicated, but here is a useful and typical	2170	=back
1248	example: Imagine you have a TCP connection and you want a so-called idle
1249	timeout, that is, you want to be called when there have been, say, 60
1250	seconds of inactivity on the socket. The easiest way to do this is to
1251	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1252	C<ev_timer_again> each time you successfully read or write some data. If
1253	you go into an idle state where you do not expect data to travel on the
1254	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1255	automatically restart it if need be.
1256		2171
1257	That means you can ignore the C<after> value and C<ev_timer_start>	2172	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
1258	altogether and only ever use the C<repeat> value and C<ev_timer_again>:	2173	usage example.
1259		2174
1260	ev_timer_init (timer, callback, 0., 5.);	2175	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1261	ev_timer_again (loop, timer);
1262	...
1263	timer->again = 17.;
1264	ev_timer_again (loop, timer);
1265	...
1266	timer->again = 10.;
1267	ev_timer_again (loop, timer);
1268		2176
1269	This is more slightly efficient then stopping/starting the timer each time	2177	Returns the remaining time until a timer fires. If the timer is active,
1270	you want to modify its timeout value.	2178	then this time is relative to the current event loop time, otherwise it's
		2179	the timeout value currently configured.
		2180
		2181	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
		2182	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		2183	will return C<4>. When the timer expires and is restarted, it will return
		2184	roughly C<7> (likely slightly less as callback invocation takes some time,
		2185	too), and so on.
1271		2186
1272	=item ev_tstamp repeat [read-write]	2187	=item ev_tstamp repeat [read-write]
1273		2188
1274	The current C<repeat> value. Will be used each time the watcher times out	2189	The current C<repeat> value. Will be used each time the watcher times out
1275	or C<ev_timer_again> is called and determines the next timeout (if any),	2190	or C<ev_timer_again> is called, and determines the next timeout (if any),
1276	which is also when any modifications are taken into account.	2191	which is also when any modifications are taken into account.
1277		2192
1278	=back	2193	=back
1279		2194
1280	=head3 Examples	2195	=head3 Examples
1281		2196
1282	Example: Create a timer that fires after 60 seconds.	2197	Example: Create a timer that fires after 60 seconds.
1283		2198
1284	static void	2199	static void
1285	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2200	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1286	{	2201	{
1287	.. one minute over, w is actually stopped right here	2202	.. one minute over, w is actually stopped right here
1288	}	2203	}
1289		2204
1290	struct ev_timer mytimer;	2205	ev_timer mytimer;
1291	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	2206	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1292	ev_timer_start (loop, &mytimer);	2207	ev_timer_start (loop, &mytimer);
1293		2208
1294	Example: Create a timeout timer that times out after 10 seconds of	2209	Example: Create a timeout timer that times out after 10 seconds of
1295	inactivity.	2210	inactivity.
1296		2211
1297	static void	2212	static void
1298	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2213	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1299	{	2214	{
1300	.. ten seconds without any activity	2215	.. ten seconds without any activity
1301	}	2216	}
1302		2217
1303	struct ev_timer mytimer;	2218	ev_timer mytimer;
1304	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	2219	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1305	ev_timer_again (&mytimer); /* start timer */	2220	ev_timer_again (&mytimer); /* start timer */
1306	ev_loop (loop, 0);	2221	ev_run (loop, 0);
1307		2222
1308	// and in some piece of code that gets executed on any "activity":	2223	// and in some piece of code that gets executed on any "activity":
1309	// reset the timeout to start ticking again at 10 seconds	2224	// reset the timeout to start ticking again at 10 seconds
1310	ev_timer_again (&mytimer);	2225	ev_timer_again (&mytimer);
1311		2226
…		…
1313	=head2 C<ev_periodic> - to cron or not to cron?	2228	=head2 C<ev_periodic> - to cron or not to cron?
1314		2229
1315	Periodic watchers are also timers of a kind, but they are very versatile	2230	Periodic watchers are also timers of a kind, but they are very versatile
1316	(and unfortunately a bit complex).	2231	(and unfortunately a bit complex).
1317		2232
1318	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2233	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1319	but on wall clock time (absolute time). You can tell a periodic watcher	2234	relative time, the physical time that passes) but on wall clock time
1320	to trigger after some specific point in time. For example, if you tell a	2235	(absolute time, the thing you can read on your calendar or clock). The
1321	periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now ()	2236	difference is that wall clock time can run faster or slower than real
1322	+ 10.>, that is, an absolute time not a delay) and then reset your system	2237	time, and time jumps are not uncommon (e.g. when you adjust your
1323	clock to January of the previous year, then it will take more than year	2238	wrist-watch).
1324	to trigger the event (unlike an C<ev_timer>, which would still trigger
1325	roughly 10 seconds later as it uses a relative timeout).
1326		2239
		2240	You can tell a periodic watcher to trigger after some specific point
		2241	in time: for example, if you tell a periodic watcher to trigger "in 10
		2242	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2243	not a delay) and then reset your system clock to January of the previous
		2244	year, then it will take a year or more to trigger the event (unlike an
		2245	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2246	it, as it uses a relative timeout).
		2247
1327	C<ev_periodic>s can also be used to implement vastly more complex timers,	2248	C<ev_periodic> watchers can also be used to implement vastly more complex
1328	such as triggering an event on each "midnight, local time", or other	2249	timers, such as triggering an event on each "midnight, local time", or
1329	complicated, rules.	2250	other complicated rules. This cannot easily be done with C<ev_timer>
		2251	watchers, as those cannot react to time jumps.
1330		2252
1331	As with timers, the callback is guaranteed to be invoked only when the	2253	As with timers, the callback is guaranteed to be invoked only when the
1332	time (C<at>) has passed, but if multiple periodic timers become ready	2254	point in time where it is supposed to trigger has passed. If multiple
1333	during the same loop iteration then order of execution is undefined.	2255	timers become ready during the same loop iteration then the ones with
		2256	earlier time-out values are invoked before ones with later time-out values
		2257	(but this is no longer true when a callback calls C<ev_run> recursively).
1334		2258
1335	=head3 Watcher-Specific Functions and Data Members	2259	=head3 Watcher-Specific Functions and Data Members
1336		2260
1337	=over 4	2261	=over 4
1338		2262
1339	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2263	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1340		2264
1341	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2265	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1342		2266
1343	Lots of arguments, lets sort it out... There are basically three modes of	2267	Lots of arguments, let's sort it out... There are basically three modes of
1344	operation, and we will explain them from simplest to complex:	2268	operation, and we will explain them from simplest to most complex:
1345		2269
1346	=over 4	2270	=over 4
1347		2271
1348	=item * absolute timer (at = time, interval = reschedule_cb = 0)	2272	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1349		2273
1350	In this configuration the watcher triggers an event after the wall clock	2274	In this configuration the watcher triggers an event after the wall clock
1351	time C<at> has passed and doesn't repeat. It will not adjust when a time	2275	time C<offset> has passed. It will not repeat and will not adjust when a
1352	jump occurs, that is, if it is to be run at January 1st 2011 then it will	2276	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1353	run when the system time reaches or surpasses this time.	2277	will be stopped and invoked when the system clock reaches or surpasses
		2278	this point in time.
1354		2279
1355	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	2280	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1356		2281
1357	In this mode the watcher will always be scheduled to time out at the next	2282	In this mode the watcher will always be scheduled to time out at the next
1358	C<at + N * interval> time (for some integer N, which can also be negative)	2283	C<offset + N * interval> time (for some integer N, which can also be
1359	and then repeat, regardless of any time jumps.	2284	negative) and then repeat, regardless of any time jumps. The C<offset>
		2285	argument is merely an offset into the C<interval> periods.
1360		2286
1361	This can be used to create timers that do not drift with respect to system	2287	This can be used to create timers that do not drift with respect to the
1362	time, for example, here is a C<ev_periodic> that triggers each hour, on	2288	system clock, for example, here is an C<ev_periodic> that triggers each
1363	the hour:	2289	hour, on the hour (with respect to UTC):
1364		2290
1365	ev_periodic_set (&periodic, 0., 3600., 0);	2291	ev_periodic_set (&periodic, 0., 3600., 0);
1366		2292
1367	This doesn't mean there will always be 3600 seconds in between triggers,	2293	This doesn't mean there will always be 3600 seconds in between triggers,
1368	but only that the callback will be called when the system time shows a	2294	but only that the callback will be called when the system time shows a
1369	full hour (UTC), or more correctly, when the system time is evenly divisible	2295	full hour (UTC), or more correctly, when the system time is evenly divisible
1370	by 3600.	2296	by 3600.
1371		2297
1372	Another way to think about it (for the mathematically inclined) is that	2298	Another way to think about it (for the mathematically inclined) is that
1373	C<ev_periodic> will try to run the callback in this mode at the next possible	2299	C<ev_periodic> will try to run the callback in this mode at the next possible
1374	time where C<time = at (mod interval)>, regardless of any time jumps.	2300	time where C<time = offset (mod interval)>, regardless of any time jumps.
1375		2301
1376	For numerical stability it is preferable that the C<at> value is near	2302	The C<interval> I<MUST> be positive, and for numerical stability, the
1377	C<ev_now ()> (the current time), but there is no range requirement for	2303	interval value should be higher than C<1/8192> (which is around 100
1378	this value, and in fact is often specified as zero.	2304	microseconds) and C<offset> should be higher than C<0> and should have
		2305	at most a similar magnitude as the current time (say, within a factor of
		2306	ten). Typical values for offset are, in fact, C<0> or something between
		2307	C<0> and C<interval>, which is also the recommended range.
1379		2308
1380	Note also that there is an upper limit to how often a timer can fire (CPU	2309	Note also that there is an upper limit to how often a timer can fire (CPU
1381	speed for example), so if C<interval> is very small then timing stability	2310	speed for example), so if C<interval> is very small then timing stability
1382	will of course deteriorate. Libev itself tries to be exact to be about one	2311	will of course deteriorate. Libev itself tries to be exact to be about one
1383	millisecond (if the OS supports it and the machine is fast enough).	2312	millisecond (if the OS supports it and the machine is fast enough).
1384		2313
1385	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	2314	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1386		2315
1387	In this mode the values for C<interval> and C<at> are both being	2316	In this mode the values for C<interval> and C<offset> are both being
1388	ignored. Instead, each time the periodic watcher gets scheduled, the	2317	ignored. Instead, each time the periodic watcher gets scheduled, the
1389	reschedule callback will be called with the watcher as first, and the	2318	reschedule callback will be called with the watcher as first, and the
1390	current time as second argument.	2319	current time as second argument.
1391		2320
1392	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2321	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1393	ever, or make ANY event loop modifications whatsoever>.	2322	or make ANY other event loop modifications whatsoever, unless explicitly
		2323	allowed by documentation here>.
1394		2324
1395	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop	2325	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
1396	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the	2326	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
1397	only event loop modification you are allowed to do).	2327	only event loop modification you are allowed to do).
1398		2328
1399	The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic	2329	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1400	*w, ev_tstamp now)>, e.g.:	2330	*w, ev_tstamp now)>, e.g.:
1401		2331
		2332	static ev_tstamp
1402	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2333	my_rescheduler (ev_periodic *w, ev_tstamp now)
1403	{	2334	{
1404	return now + 60.;	2335	return now + 60.;
1405	}	2336	}
1406		2337
1407	It must return the next time to trigger, based on the passed time value	2338	It must return the next time to trigger, based on the passed time value
…		…
1411		2342
1412	NOTE: I<< This callback must always return a time that is higher than or	2343	NOTE: I<< This callback must always return a time that is higher than or
1413	equal to the passed C<now> value >>.	2344	equal to the passed C<now> value >>.
1414		2345
1415	This can be used to create very complex timers, such as a timer that	2346	This can be used to create very complex timers, such as a timer that
1416	triggers on "next midnight, local time". To do this, you would calculate the	2347	triggers on "next midnight, local time". To do this, you would calculate
1417	next midnight after C<now> and return the timestamp value for this. How	2348	the next midnight after C<now> and return the timestamp value for
1418	you do this is, again, up to you (but it is not trivial, which is the main	2349	this. Here is a (completely untested, no error checking) example on how to
1419	reason I omitted it as an example).	2350	do this:
		2351
		2352	#include <time.h>
		2353
		2354	static ev_tstamp
		2355	my_rescheduler (ev_periodic *w, ev_tstamp now)
		2356	{
		2357	time_t tnow = (time_t)now;
		2358	struct tm tm;
		2359	localtime_r (&tnow, &tm);
		2360
		2361	tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
		2362	++tm.tm_mday; // midnight next day
		2363
		2364	return mktime (&tm);
		2365	}
		2366
		2367	Note: this code might run into trouble on days that have more then two
		2368	midnights (beginning and end).
1420		2369
1421	=back	2370	=back
1422		2371
1423	=item ev_periodic_again (loop, ev_periodic *)	2372	=item ev_periodic_again (loop, ev_periodic *)
1424		2373
…		…
1427	a different time than the last time it was called (e.g. in a crond like	2376	a different time than the last time it was called (e.g. in a crond like
1428	program when the crontabs have changed).	2377	program when the crontabs have changed).
1429		2378
1430	=item ev_tstamp ev_periodic_at (ev_periodic *)	2379	=item ev_tstamp ev_periodic_at (ev_periodic *)
1431		2380
1432	When active, returns the absolute time that the watcher is supposed to	2381	When active, returns the absolute time that the watcher is supposed
1433	trigger next.	2382	to trigger next. This is not the same as the C<offset> argument to
		2383	C<ev_periodic_set>, but indeed works even in interval and manual
		2384	rescheduling modes.
1434		2385
1435	=item ev_tstamp offset [read-write]	2386	=item ev_tstamp offset [read-write]
1436		2387
1437	When repeating, this contains the offset value, otherwise this is the	2388	When repeating, this contains the offset value, otherwise this is the
1438	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2389	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2390	although libev might modify this value for better numerical stability).
1439		2391
1440	Can be modified any time, but changes only take effect when the periodic	2392	Can be modified any time, but changes only take effect when the periodic
1441	timer fires or C<ev_periodic_again> is being called.	2393	timer fires or C<ev_periodic_again> is being called.
1442		2394
1443	=item ev_tstamp interval [read-write]	2395	=item ev_tstamp interval [read-write]
1444		2396
1445	The current interval value. Can be modified any time, but changes only	2397	The current interval value. Can be modified any time, but changes only
1446	take effect when the periodic timer fires or C<ev_periodic_again> is being	2398	take effect when the periodic timer fires or C<ev_periodic_again> is being
1447	called.	2399	called.
1448		2400
1449	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2401	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1450		2402
1451	The current reschedule callback, or C<0>, if this functionality is	2403	The current reschedule callback, or C<0>, if this functionality is
1452	switched off. Can be changed any time, but changes only take effect when	2404	switched off. Can be changed any time, but changes only take effect when
1453	the periodic timer fires or C<ev_periodic_again> is being called.	2405	the periodic timer fires or C<ev_periodic_again> is being called.
1454		2406
1455	=back	2407	=back
1456		2408
1457	=head3 Examples	2409	=head3 Examples
1458		2410
1459	Example: Call a callback every hour, or, more precisely, whenever the	2411	Example: Call a callback every hour, or, more precisely, whenever the
1460	system clock is divisible by 3600. The callback invocation times have	2412	system time is divisible by 3600. The callback invocation times have
1461	potentially a lot of jitter, but good long-term stability.	2413	potentially a lot of jitter, but good long-term stability.
1462		2414
1463	static void	2415	static void
1464	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2416	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1465	{	2417	{
1466	... its now a full hour (UTC, or TAI or whatever your clock follows)	2418	... its now a full hour (UTC, or TAI or whatever your clock follows)
1467	}	2419	}
1468		2420
1469	struct ev_periodic hourly_tick;	2421	ev_periodic hourly_tick;
1470	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2422	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1471	ev_periodic_start (loop, &hourly_tick);	2423	ev_periodic_start (loop, &hourly_tick);
1472		2424
1473	Example: The same as above, but use a reschedule callback to do it:	2425	Example: The same as above, but use a reschedule callback to do it:
1474		2426
1475	#include <math.h>	2427	#include <math.h>
1476		2428
1477	static ev_tstamp	2429	static ev_tstamp
1478	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2430	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1479	{	2431	{
1480	return fmod (now, 3600.) + 3600.;	2432	return now + (3600. - fmod (now, 3600.));
1481	}	2433	}
1482		2434
1483	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2435	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1484		2436
1485	Example: Call a callback every hour, starting now:	2437	Example: Call a callback every hour, starting now:
1486		2438
1487	struct ev_periodic hourly_tick;	2439	ev_periodic hourly_tick;
1488	ev_periodic_init (&hourly_tick, clock_cb,	2440	ev_periodic_init (&hourly_tick, clock_cb,
1489	fmod (ev_now (loop), 3600.), 3600., 0);	2441	fmod (ev_now (loop), 3600.), 3600., 0);
1490	ev_periodic_start (loop, &hourly_tick);	2442	ev_periodic_start (loop, &hourly_tick);
1491		2443
1492		2444
1493	=head2 C<ev_signal> - signal me when a signal gets signalled!	2445	=head2 C<ev_signal> - signal me when a signal gets signalled!
1494		2446
1495	Signal watchers will trigger an event when the process receives a specific	2447	Signal watchers will trigger an event when the process receives a specific
1496	signal one or more times. Even though signals are very asynchronous, libev	2448	signal one or more times. Even though signals are very asynchronous, libev
1497	will try it's best to deliver signals synchronously, i.e. as part of the	2449	will try its best to deliver signals synchronously, i.e. as part of the
1498	normal event processing, like any other event.	2450	normal event processing, like any other event.
1499		2451
		2452	If you want signals to be delivered truly asynchronously, just use
		2453	C<sigaction> as you would do without libev and forget about sharing
		2454	the signal. You can even use C<ev_async> from a signal handler to
		2455	synchronously wake up an event loop.
		2456
1500	You can configure as many watchers as you like per signal. Only when the	2457	You can configure as many watchers as you like for the same signal, but
1501	first watcher gets started will libev actually register a signal watcher	2458	only within the same loop, i.e. you can watch for C<SIGINT> in your
1502	with the kernel (thus it coexists with your own signal handlers as long	2459	default loop and for C<SIGIO> in another loop, but you cannot watch for
1503	as you don't register any with libev). Similarly, when the last signal	2460	C<SIGINT> in both the default loop and another loop at the same time. At
1504	watcher for a signal is stopped libev will reset the signal handler to	2461	the moment, C<SIGCHLD> is permanently tied to the default loop.
1505	SIG_DFL (regardless of what it was set to before).	2462
		2463	Only after the first watcher for a signal is started will libev actually
		2464	register something with the kernel. It thus coexists with your own signal
		2465	handlers as long as you don't register any with libev for the same signal.
1506		2466
1507	If possible and supported, libev will install its handlers with	2467	If possible and supported, libev will install its handlers with
1508	C<SA_RESTART> behaviour enabled, so system calls should not be unduly	2468	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
1509	interrupted. If you have a problem with system calls getting interrupted by	2469	not be unduly interrupted. If you have a problem with system calls getting
1510	signals you can block all signals in an C<ev_check> watcher and unblock	2470	interrupted by signals you can block all signals in an C<ev_check> watcher
1511	them in an C<ev_prepare> watcher.	2471	and unblock them in an C<ev_prepare> watcher.
		2472
		2473	=head3 The special problem of inheritance over fork/execve/pthread_create
		2474
		2475	Both the signal mask (C<sigprocmask>) and the signal disposition
		2476	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2477	stopping it again), that is, libev might or might not block the signal,
		2478	and might or might not set or restore the installed signal handler (but
		2479	see C<EVFLAG_NOSIGMASK>).
		2480
		2481	While this does not matter for the signal disposition (libev never
		2482	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2483	C<execve>), this matters for the signal mask: many programs do not expect
		2484	certain signals to be blocked.
		2485
		2486	This means that before calling C<exec> (from the child) you should reset
		2487	the signal mask to whatever "default" you expect (all clear is a good
		2488	choice usually).
		2489
		2490	The simplest way to ensure that the signal mask is reset in the child is
		2491	to install a fork handler with C<pthread_atfork> that resets it. That will
		2492	catch fork calls done by libraries (such as the libc) as well.
		2493
		2494	In current versions of libev, the signal will not be blocked indefinitely
		2495	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2496	the window of opportunity for problems, it will not go away, as libev
		2497	I<has> to modify the signal mask, at least temporarily.
		2498
		2499	So I can't stress this enough: I<If you do not reset your signal mask when
		2500	you expect it to be empty, you have a race condition in your code>. This
		2501	is not a libev-specific thing, this is true for most event libraries.
		2502
		2503	=head3 The special problem of threads signal handling
		2504
		2505	POSIX threads has problematic signal handling semantics, specifically,
		2506	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2507	threads in a process block signals, which is hard to achieve.
		2508
		2509	When you want to use sigwait (or mix libev signal handling with your own
		2510	for the same signals), you can tackle this problem by globally blocking
		2511	all signals before creating any threads (or creating them with a fully set
		2512	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2513	loops. Then designate one thread as "signal receiver thread" which handles
		2514	these signals. You can pass on any signals that libev might be interested
		2515	in by calling C<ev_feed_signal>.
1512		2516
1513	=head3 Watcher-Specific Functions and Data Members	2517	=head3 Watcher-Specific Functions and Data Members
1514		2518
1515	=over 4	2519	=over 4
1516		2520
…		…
1527		2531
1528	=back	2532	=back
1529		2533
1530	=head3 Examples	2534	=head3 Examples
1531		2535
1532	Example: Try to exit cleanly on SIGINT and SIGTERM.	2536	Example: Try to exit cleanly on SIGINT.
1533		2537
1534	static void	2538	static void
1535	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2539	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
1536	{	2540	{
1537	ev_unloop (loop, EVUNLOOP_ALL);	2541	ev_break (loop, EVBREAK_ALL);
1538	}	2542	}
1539		2543
1540	struct ev_signal signal_watcher;	2544	ev_signal signal_watcher;
1541	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2545	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1542	ev_signal_start (loop, &sigint_cb);	2546	ev_signal_start (loop, &signal_watcher);
1543		2547
1544		2548
1545	=head2 C<ev_child> - watch out for process status changes	2549	=head2 C<ev_child> - watch out for process status changes
1546		2550
1547	Child watchers trigger when your process receives a SIGCHLD in response to	2551	Child watchers trigger when your process receives a SIGCHLD in response to
1548	some child status changes (most typically when a child of yours dies). It	2552	some child status changes (most typically when a child of yours dies or
1549	is permissible to install a child watcher I<after> the child has been	2553	exits). It is permissible to install a child watcher I<after> the child
1550	forked (which implies it might have already exited), as long as the event	2554	has been forked (which implies it might have already exited), as long
1551	loop isn't entered (or is continued from a watcher).	2555	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2556	forking and then immediately registering a watcher for the child is fine,
		2557	but forking and registering a watcher a few event loop iterations later or
		2558	in the next callback invocation is not.
1552		2559
1553	Only the default event loop is capable of handling signals, and therefore	2560	Only the default event loop is capable of handling signals, and therefore
1554	you can only register child watchers in the default event loop.	2561	you can only register child watchers in the default event loop.
1555		2562
		2563	Due to some design glitches inside libev, child watchers will always be
		2564	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2565	libev)
		2566
1556	=head3 Process Interaction	2567	=head3 Process Interaction
1557		2568
1558	Libev grabs C<SIGCHLD> as soon as the default event loop is	2569	Libev grabs C<SIGCHLD> as soon as the default event loop is
1559	initialised. This is necessary to guarantee proper behaviour even if	2570	initialised. This is necessary to guarantee proper behaviour even if the
1560	the first child watcher is started after the child exits. The occurrence	2571	first child watcher is started after the child exits. The occurrence
1561	of C<SIGCHLD> is recorded asynchronously, but child reaping is done	2572	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
1562	synchronously as part of the event loop processing. Libev always reaps all	2573	synchronously as part of the event loop processing. Libev always reaps all
1563	children, even ones not watched.	2574	children, even ones not watched.
1564		2575
1565	=head3 Overriding the Built-In Processing	2576	=head3 Overriding the Built-In Processing
…		…
1569	handler, you can override it easily by installing your own handler for	2580	handler, you can override it easily by installing your own handler for
1570	C<SIGCHLD> after initialising the default loop, and making sure the	2581	C<SIGCHLD> after initialising the default loop, and making sure the
1571	default loop never gets destroyed. You are encouraged, however, to use an	2582	default loop never gets destroyed. You are encouraged, however, to use an
1572	event-based approach to child reaping and thus use libev's support for	2583	event-based approach to child reaping and thus use libev's support for
1573	that, so other libev users can use C<ev_child> watchers freely.	2584	that, so other libev users can use C<ev_child> watchers freely.
		2585
		2586	=head3 Stopping the Child Watcher
		2587
		2588	Currently, the child watcher never gets stopped, even when the
		2589	child terminates, so normally one needs to stop the watcher in the
		2590	callback. Future versions of libev might stop the watcher automatically
		2591	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2592	problem).
1574		2593
1575	=head3 Watcher-Specific Functions and Data Members	2594	=head3 Watcher-Specific Functions and Data Members
1576		2595
1577	=over 4	2596	=over 4
1578		2597
…		…
1610	its completion.	2629	its completion.
1611		2630
1612	ev_child cw;	2631	ev_child cw;
1613		2632
1614	static void	2633	static void
1615	child_cb (EV_P_ struct ev_child *w, int revents)	2634	child_cb (EV_P_ ev_child *w, int revents)
1616	{	2635	{
1617	ev_child_stop (EV_A_ w);	2636	ev_child_stop (EV_A_ w);
1618	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);	2637	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1619	}	2638	}
1620		2639
…		…
1635		2654
1636		2655
1637	=head2 C<ev_stat> - did the file attributes just change?	2656	=head2 C<ev_stat> - did the file attributes just change?
1638		2657
1639	This watches a file system path for attribute changes. That is, it calls	2658	This watches a file system path for attribute changes. That is, it calls
1640	C<stat> regularly (or when the OS says it changed) and sees if it changed	2659	C<stat> on that path in regular intervals (or when the OS says it changed)
1641	compared to the last time, invoking the callback if it did.	2660	and sees if it changed compared to the last time, invoking the callback
		2661	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2662	happen after the watcher has been started will be reported.
1642		2663
1643	The path does not need to exist: changing from "path exists" to "path does	2664	The path does not need to exist: changing from "path exists" to "path does
1644	not exist" is a status change like any other. The condition "path does	2665	not exist" is a status change like any other. The condition "path does not
1645	not exist" is signified by the C<st_nlink> field being zero (which is	2666	exist" (or more correctly "path cannot be stat'ed") is signified by the
1646	otherwise always forced to be at least one) and all the other fields of	2667	C<st_nlink> field being zero (which is otherwise always forced to be at
1647	the stat buffer having unspecified contents.	2668	least one) and all the other fields of the stat buffer having unspecified
		2669	contents.
1648		2670
1649	The path I<should> be absolute and I<must not> end in a slash. If it is	2671	The path I<must not> end in a slash or contain special components such as
		2672	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1650	relative and your working directory changes, the behaviour is undefined.	2673	your working directory changes, then the behaviour is undefined.
1651		2674
1652	Since there is no standard to do this, the portable implementation simply	2675	Since there is no portable change notification interface available, the
1653	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2676	portable implementation simply calls C<stat(2)> regularly on the path
1654	can specify a recommended polling interval for this case. If you specify	2677	to see if it changed somehow. You can specify a recommended polling
1655	a polling interval of C<0> (highly recommended!) then a I<suitable,	2678	interval for this case. If you specify a polling interval of C<0> (highly
1656	unspecified default> value will be used (which you can expect to be around	2679	recommended!) then a I<suitable, unspecified default> value will be used
1657	five seconds, although this might change dynamically). Libev will also	2680	(which you can expect to be around five seconds, although this might
1658	impose a minimum interval which is currently around C<0.1>, but thats	2681	change dynamically). Libev will also impose a minimum interval which is
1659	usually overkill.	2682	currently around C<0.1>, but that's usually overkill.
1660		2683
1661	This watcher type is not meant for massive numbers of stat watchers,	2684	This watcher type is not meant for massive numbers of stat watchers,
1662	as even with OS-supported change notifications, this can be	2685	as even with OS-supported change notifications, this can be
1663	resource-intensive.	2686	resource-intensive.
1664		2687
1665	At the time of this writing, only the Linux inotify interface is	2688	At the time of this writing, the only OS-specific interface implemented
1666	implemented (implementing kqueue support is left as an exercise for the	2689	is the Linux inotify interface (implementing kqueue support is left as an
1667	reader, note, however, that the author sees no way of implementing ev_stat	2690	exercise for the reader. Note, however, that the author sees no way of
1668	semantics with kqueue). Inotify will be used to give hints only and should	2691	implementing C<ev_stat> semantics with kqueue, except as a hint).
1669	not change the semantics of C<ev_stat> watchers, which means that libev
1670	sometimes needs to fall back to regular polling again even with inotify,
1671	but changes are usually detected immediately, and if the file exists there
1672	will be no polling.
1673		2692
1674	=head3 ABI Issues (Largefile Support)	2693	=head3 ABI Issues (Largefile Support)
1675		2694
1676	Libev by default (unless the user overrides this) uses the default	2695	Libev by default (unless the user overrides this) uses the default
1677	compilation environment, which means that on systems with large file	2696	compilation environment, which means that on systems with large file
1678	support disabled by default, you get the 32 bit version of the stat	2697	support disabled by default, you get the 32 bit version of the stat
1679	structure. When using the library from programs that change the ABI to	2698	structure. When using the library from programs that change the ABI to
1680	use 64 bit file offsets the programs will fail. In that case you have to	2699	use 64 bit file offsets the programs will fail. In that case you have to
1681	compile libev with the same flags to get binary compatibility. This is	2700	compile libev with the same flags to get binary compatibility. This is
1682	obviously the case with any flags that change the ABI, but the problem is	2701	obviously the case with any flags that change the ABI, but the problem is
1683	most noticeably disabled with ev_stat and large file support.	2702	most noticeably displayed with ev_stat and large file support.
1684		2703
1685	The solution for this is to lobby your distribution maker to make large	2704	The solution for this is to lobby your distribution maker to make large
1686	file interfaces available by default (as e.g. FreeBSD does) and not	2705	file interfaces available by default (as e.g. FreeBSD does) and not
1687	optional. Libev cannot simply switch on large file support because it has	2706	optional. Libev cannot simply switch on large file support because it has
1688	to exchange stat structures with application programs compiled using the	2707	to exchange stat structures with application programs compiled using the
1689	default compilation environment.	2708	default compilation environment.
1690		2709
1691	=head3 Inotify	2710	=head3 Inotify and Kqueue
1692		2711
1693	When C<inotify (7)> support has been compiled into libev (generally only	2712	When C<inotify (7)> support has been compiled into libev and present at
1694	available on Linux) and present at runtime, it will be used to speed up	2713	runtime, it will be used to speed up change detection where possible. The
1695	change detection where possible. The inotify descriptor will be created lazily	2714	inotify descriptor will be created lazily when the first C<ev_stat>
1696	when the first C<ev_stat> watcher is being started.	2715	watcher is being started.
1697		2716
1698	Inotify presence does not change the semantics of C<ev_stat> watchers	2717	Inotify presence does not change the semantics of C<ev_stat> watchers
1699	except that changes might be detected earlier, and in some cases, to avoid	2718	except that changes might be detected earlier, and in some cases, to avoid
1700	making regular C<stat> calls. Even in the presence of inotify support	2719	making regular C<stat> calls. Even in the presence of inotify support
1701	there are many cases where libev has to resort to regular C<stat> polling.	2720	there are many cases where libev has to resort to regular C<stat> polling,
		2721	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2722	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2723	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2724	xfs are fully working) libev usually gets away without polling.
1702		2725
1703	(There is no support for kqueue, as apparently it cannot be used to	2726	There is no support for kqueue, as apparently it cannot be used to
1704	implement this functionality, due to the requirement of having a file	2727	implement this functionality, due to the requirement of having a file
1705	descriptor open on the object at all times).	2728	descriptor open on the object at all times, and detecting renames, unlinks
		2729	etc. is difficult.
		2730
		2731	=head3 C<stat ()> is a synchronous operation
		2732
		2733	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2734	the process. The exception are C<ev_stat> watchers - those call C<stat
		2735	()>, which is a synchronous operation.
		2736
		2737	For local paths, this usually doesn't matter: unless the system is very
		2738	busy or the intervals between stat's are large, a stat call will be fast,
		2739	as the path data is usually in memory already (except when starting the
		2740	watcher).
		2741
		2742	For networked file systems, calling C<stat ()> can block an indefinite
		2743	time due to network issues, and even under good conditions, a stat call
		2744	often takes multiple milliseconds.
		2745
		2746	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2747	paths, although this is fully supported by libev.
1706		2748
1707	=head3 The special problem of stat time resolution	2749	=head3 The special problem of stat time resolution
1708		2750
1709	The C<stat ()> system call only supports full-second resolution portably, and	2751	The C<stat ()> system call only supports full-second resolution portably,
1710	even on systems where the resolution is higher, many file systems still	2752	and even on systems where the resolution is higher, most file systems
1711	only support whole seconds.	2753	still only support whole seconds.
1712		2754
1713	That means that, if the time is the only thing that changes, you can	2755	That means that, if the time is the only thing that changes, you can
1714	easily miss updates: on the first update, C<ev_stat> detects a change and	2756	easily miss updates: on the first update, C<ev_stat> detects a change and
1715	calls your callback, which does something. When there is another update	2757	calls your callback, which does something. When there is another update
1716	within the same second, C<ev_stat> will be unable to detect it as the stat	2758	within the same second, C<ev_stat> will be unable to detect unless the
1717	data does not change.	2759	stat data does change in other ways (e.g. file size).
1718		2760
1719	The solution to this is to delay acting on a change for slightly more	2761	The solution to this is to delay acting on a change for slightly more
1720	than a second (or till slightly after the next full second boundary), using	2762	than a second (or till slightly after the next full second boundary), using
1721	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);	2763	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
1722	ev_timer_again (loop, w)>).	2764	ev_timer_again (loop, w)>).
…		…
1742	C<path>. The C<interval> is a hint on how quickly a change is expected to	2784	C<path>. The C<interval> is a hint on how quickly a change is expected to
1743	be detected and should normally be specified as C<0> to let libev choose	2785	be detected and should normally be specified as C<0> to let libev choose
1744	a suitable value. The memory pointed to by C<path> must point to the same	2786	a suitable value. The memory pointed to by C<path> must point to the same
1745	path for as long as the watcher is active.	2787	path for as long as the watcher is active.
1746		2788
1747	The callback will receive C<EV_STAT> when a change was detected, relative	2789	The callback will receive an C<EV_STAT> event when a change was detected,
1748	to the attributes at the time the watcher was started (or the last change	2790	relative to the attributes at the time the watcher was started (or the
1749	was detected).	2791	last change was detected).
1750		2792
1751	=item ev_stat_stat (loop, ev_stat *)	2793	=item ev_stat_stat (loop, ev_stat *)
1752		2794
1753	Updates the stat buffer immediately with new values. If you change the	2795	Updates the stat buffer immediately with new values. If you change the
1754	watched path in your callback, you could call this function to avoid	2796	watched path in your callback, you could call this function to avoid
…		…
1837		2879
1838		2880
1839	=head2 C<ev_idle> - when you've got nothing better to do...	2881	=head2 C<ev_idle> - when you've got nothing better to do...
1840		2882
1841	Idle watchers trigger events when no other events of the same or higher	2883	Idle watchers trigger events when no other events of the same or higher
1842	priority are pending (prepare, check and other idle watchers do not	2884	priority are pending (prepare, check and other idle watchers do not count
1843	count).	2885	as receiving "events").
1844		2886
1845	That is, as long as your process is busy handling sockets or timeouts	2887	That is, as long as your process is busy handling sockets or timeouts
1846	(or even signals, imagine) of the same or higher priority it will not be	2888	(or even signals, imagine) of the same or higher priority it will not be
1847	triggered. But when your process is idle (or only lower-priority watchers	2889	triggered. But when your process is idle (or only lower-priority watchers
1848	are pending), the idle watchers are being called once per event loop	2890	are pending), the idle watchers are being called once per event loop
…		…
1855	Apart from keeping your process non-blocking (which is a useful	2897	Apart from keeping your process non-blocking (which is a useful
1856	effect on its own sometimes), idle watchers are a good place to do	2898	effect on its own sometimes), idle watchers are a good place to do
1857	"pseudo-background processing", or delay processing stuff to after the	2899	"pseudo-background processing", or delay processing stuff to after the
1858	event loop has handled all outstanding events.	2900	event loop has handled all outstanding events.
1859		2901
		2902	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2903
		2904	As long as there is at least one active idle watcher, libev will never
		2905	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2906	For this to work, the idle watcher doesn't need to be invoked at all - the
		2907	lowest priority will do.
		2908
		2909	This mode of operation can be useful together with an C<ev_check> watcher,
		2910	to do something on each event loop iteration - for example to balance load
		2911	between different connections.
		2912
		2913	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2914	example.
		2915
1860	=head3 Watcher-Specific Functions and Data Members	2916	=head3 Watcher-Specific Functions and Data Members
1861		2917
1862	=over 4	2918	=over 4
1863		2919
1864	=item ev_idle_init (ev_signal *, callback)	2920	=item ev_idle_init (ev_idle *, callback)
1865		2921
1866	Initialises and configures the idle watcher - it has no parameters of any	2922	Initialises and configures the idle watcher - it has no parameters of any
1867	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2923	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1868	believe me.	2924	believe me.
1869		2925
…		…
1873		2929
1874	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2930	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1875	callback, free it. Also, use no error checking, as usual.	2931	callback, free it. Also, use no error checking, as usual.
1876		2932
1877	static void	2933	static void
1878	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2934	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1879	{	2935	{
		2936	// stop the watcher
		2937	ev_idle_stop (loop, w);
		2938
		2939	// now we can free it
1880	free (w);	2940	free (w);
		2941
1881	// now do something you wanted to do when the program has	2942	// now do something you wanted to do when the program has
1882	// no longer anything immediate to do.	2943	// no longer anything immediate to do.
1883	}	2944	}
1884		2945
1885	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2946	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1886	ev_idle_init (idle_watcher, idle_cb);	2947	ev_idle_init (idle_watcher, idle_cb);
1887	ev_idle_start (loop, idle_cb);	2948	ev_idle_start (loop, idle_watcher);
1888		2949
1889		2950
1890	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2951	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1891		2952
1892	Prepare and check watchers are usually (but not always) used in tandem:	2953	Prepare and check watchers are often (but not always) used in pairs:
1893	prepare watchers get invoked before the process blocks and check watchers	2954	prepare watchers get invoked before the process blocks and check watchers
1894	afterwards.	2955	afterwards.
1895		2956
1896	You I<must not> call C<ev_loop> or similar functions that enter	2957	You I<must not> call C<ev_run> (or similar functions that enter the
1897	the current event loop from either C<ev_prepare> or C<ev_check>	2958	current event loop) or C<ev_loop_fork> from either C<ev_prepare> or
1898	watchers. Other loops than the current one are fine, however. The	2959	C<ev_check> watchers. Other loops than the current one are fine,
1899	rationale behind this is that you do not need to check for recursion in	2960	however. The rationale behind this is that you do not need to check
1900	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2961	for recursion in those watchers, i.e. the sequence will always be
1901	C<ev_check> so if you have one watcher of each kind they will always be	2962	C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
1902	called in pairs bracketing the blocking call.	2963	kind they will always be called in pairs bracketing the blocking call.
1903		2964
1904	Their main purpose is to integrate other event mechanisms into libev and	2965	Their main purpose is to integrate other event mechanisms into libev and
1905	their use is somewhat advanced. This could be used, for example, to track	2966	their use is somewhat advanced. They could be used, for example, to track
1906	variable changes, implement your own watchers, integrate net-snmp or a	2967	variable changes, implement your own watchers, integrate net-snmp or a
1907	coroutine library and lots more. They are also occasionally useful if	2968	coroutine library and lots more. They are also occasionally useful if
1908	you cache some data and want to flush it before blocking (for example,	2969	you cache some data and want to flush it before blocking (for example,
1909	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2970	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1910	watcher).	2971	watcher).
1911		2972
1912	This is done by examining in each prepare call which file descriptors need	2973	This is done by examining in each prepare call which file descriptors
1913	to be watched by the other library, registering C<ev_io> watchers for	2974	need to be watched by the other library, registering C<ev_io> watchers
1914	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2975	for them and starting an C<ev_timer> watcher for any timeouts (many
1915	provide just this functionality). Then, in the check watcher you check for	2976	libraries provide exactly this functionality). Then, in the check watcher,
1916	any events that occurred (by checking the pending status of all watchers	2977	you check for any events that occurred (by checking the pending status
1917	and stopping them) and call back into the library. The I/O and timer	2978	of all watchers and stopping them) and call back into the library. The
1918	callbacks will never actually be called (but must be valid nevertheless,	2979	I/O and timer callbacks will never actually be called (but must be valid
1919	because you never know, you know?).	2980	nevertheless, because you never know, you know?).
1920		2981
1921	As another example, the Perl Coro module uses these hooks to integrate	2982	As another example, the Perl Coro module uses these hooks to integrate
1922	coroutines into libev programs, by yielding to other active coroutines	2983	coroutines into libev programs, by yielding to other active coroutines
1923	during each prepare and only letting the process block if no coroutines	2984	during each prepare and only letting the process block if no coroutines
1924	are ready to run (it's actually more complicated: it only runs coroutines	2985	are ready to run (it's actually more complicated: it only runs coroutines
1925	with priority higher than or equal to the event loop and one coroutine	2986	with priority higher than or equal to the event loop and one coroutine
1926	of lower priority, but only once, using idle watchers to keep the event	2987	of lower priority, but only once, using idle watchers to keep the event
1927	loop from blocking if lower-priority coroutines are active, thus mapping	2988	loop from blocking if lower-priority coroutines are active, thus mapping
1928	low-priority coroutines to idle/background tasks).	2989	low-priority coroutines to idle/background tasks).
1929		2990
1930	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2991	When used for this purpose, it is recommended to give C<ev_check> watchers
1931	priority, to ensure that they are being run before any other watchers	2992	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
		2993	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		2994	watchers).
		2995
1932	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2996	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1933	too) should not activate ("feed") events into libev. While libev fully	2997	activate ("feed") events into libev. While libev fully supports this, they
1934	supports this, they might get executed before other C<ev_check> watchers	2998	might get executed before other C<ev_check> watchers did their job. As
1935	did their job. As C<ev_check> watchers are often used to embed other	2999	C<ev_check> watchers are often used to embed other (non-libev) event
1936	(non-libev) event loops those other event loops might be in an unusable	3000	loops those other event loops might be in an unusable state until their
1937	state until their C<ev_check> watcher ran (always remind yourself to	3001	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1938	coexist peacefully with others).	3002	others).
		3003
		3004	=head3 Abusing an C<ev_check> watcher for its side-effect
		3005
		3006	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		3007	useful because they are called once per event loop iteration. For
		3008	example, if you want to handle a large number of connections fairly, you
		3009	normally only do a bit of work for each active connection, and if there
		3010	is more work to do, you wait for the next event loop iteration, so other
		3011	connections have a chance of making progress.
		3012
		3013	Using an C<ev_check> watcher is almost enough: it will be called on the
		3014	next event loop iteration. However, that isn't as soon as possible -
		3015	without external events, your C<ev_check> watcher will not be invoked.
		3016
		3017	This is where C<ev_idle> watchers come in handy - all you need is a
		3018	single global idle watcher that is active as long as you have one active
		3019	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		3020	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		3021	invoked. Neither watcher alone can do that.
1939		3022
1940	=head3 Watcher-Specific Functions and Data Members	3023	=head3 Watcher-Specific Functions and Data Members
1941		3024
1942	=over 4	3025	=over 4
1943		3026
…		…
1945		3028
1946	=item ev_check_init (ev_check *, callback)	3029	=item ev_check_init (ev_check *, callback)
1947		3030
1948	Initialises and configures the prepare or check watcher - they have no	3031	Initialises and configures the prepare or check watcher - they have no
1949	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	3032	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1950	macros, but using them is utterly, utterly and completely pointless.	3033	macros, but using them is utterly, utterly, utterly and completely
		3034	pointless.
1951		3035
1952	=back	3036	=back
1953		3037
1954	=head3 Examples	3038	=head3 Examples
1955		3039
…		…
1968		3052
1969	static ev_io iow [nfd];	3053	static ev_io iow [nfd];
1970	static ev_timer tw;	3054	static ev_timer tw;
1971		3055
1972	static void	3056	static void
1973	io_cb (ev_loop *loop, ev_io *w, int revents)	3057	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1974	{	3058	{
1975	}	3059	}
1976		3060
1977	// create io watchers for each fd and a timer before blocking	3061	// create io watchers for each fd and a timer before blocking
1978	static void	3062	static void
1979	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	3063	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1980	{	3064	{
1981	int timeout = 3600000;	3065	int timeout = 3600000;
1982	struct pollfd fds [nfd];	3066	struct pollfd fds [nfd];
1983	// actual code will need to loop here and realloc etc.	3067	// actual code will need to loop here and realloc etc.
1984	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	3068	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1985		3069
1986	/* the callback is illegal, but won't be called as we stop during check */	3070	/* the callback is illegal, but won't be called as we stop during check */
1987	ev_timer_init (&tw, 0, timeout * 1e-3);	3071	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1988	ev_timer_start (loop, &tw);	3072	ev_timer_start (loop, &tw);
1989		3073
1990	// create one ev_io per pollfd	3074	// create one ev_io per pollfd
1991	for (int i = 0; i < nfd; ++i)	3075	for (int i = 0; i < nfd; ++i)
1992	{	3076	{
…		…
1999	}	3083	}
2000	}	3084	}
2001		3085
2002	// stop all watchers after blocking	3086	// stop all watchers after blocking
2003	static void	3087	static void
2004	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	3088	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
2005	{	3089	{
2006	ev_timer_stop (loop, &tw);	3090	ev_timer_stop (loop, &tw);
2007		3091
2008	for (int i = 0; i < nfd; ++i)	3092	for (int i = 0; i < nfd; ++i)
2009	{	3093	{
…		…
2048	}	3132	}
2049		3133
2050	// do not ever call adns_afterpoll	3134	// do not ever call adns_afterpoll
2051		3135
2052	Method 4: Do not use a prepare or check watcher because the module you	3136	Method 4: Do not use a prepare or check watcher because the module you
2053	want to embed is too inflexible to support it. Instead, you can override	3137	want to embed is not flexible enough to support it. Instead, you can
2054	their poll function. The drawback with this solution is that the main	3138	override their poll function. The drawback with this solution is that the
2055	loop is now no longer controllable by EV. The C<Glib::EV> module does	3139	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
2056	this.	3140	this approach, effectively embedding EV as a client into the horrible
		3141	libglib event loop.
2057		3142
2058	static gint	3143	static gint
2059	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	3144	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
2060	{	3145	{
2061	int got_events = 0;	3146	int got_events = 0;
…		…
2065		3150
2066	if (timeout >= 0)	3151	if (timeout >= 0)
2067	// create/start timer	3152	// create/start timer
2068		3153
2069	// poll	3154	// poll
2070	ev_loop (EV_A_ 0);	3155	ev_run (EV_A_ 0);
2071		3156
2072	// stop timer again	3157	// stop timer again
2073	if (timeout >= 0)	3158	if (timeout >= 0)
2074	ev_timer_stop (EV_A_ &to);	3159	ev_timer_stop (EV_A_ &to);
2075		3160
…		…
2092	prioritise I/O.	3177	prioritise I/O.
2093		3178
2094	As an example for a bug workaround, the kqueue backend might only support	3179	As an example for a bug workaround, the kqueue backend might only support
2095	sockets on some platform, so it is unusable as generic backend, but you	3180	sockets on some platform, so it is unusable as generic backend, but you
2096	still want to make use of it because you have many sockets and it scales	3181	still want to make use of it because you have many sockets and it scales
2097	so nicely. In this case, you would create a kqueue-based loop and embed it	3182	so nicely. In this case, you would create a kqueue-based loop and embed
2098	into your default loop (which might use e.g. poll). Overall operation will	3183	it into your default loop (which might use e.g. poll). Overall operation
2099	be a bit slower because first libev has to poll and then call kevent, but	3184	will be a bit slower because first libev has to call C<poll> and then
2100	at least you can use both at what they are best.	3185	C<kevent>, but at least you can use both mechanisms for what they are
		3186	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
2101		3187
2102	As for prioritising I/O: rarely you have the case where some fds have	3188	As for prioritising I/O: under rare circumstances you have the case where
2103	to be watched and handled very quickly (with low latency), and even	3189	some fds have to be watched and handled very quickly (with low latency),
2104	priorities and idle watchers might have too much overhead. In this case	3190	and even priorities and idle watchers might have too much overhead. In
2105	you would put all the high priority stuff in one loop and all the rest in	3191	this case you would put all the high priority stuff in one loop and all
2106	a second one, and embed the second one in the first.	3192	the rest in a second one, and embed the second one in the first.
2107		3193
2108	As long as the watcher is active, the callback will be invoked every time	3194	As long as the watcher is active, the callback will be invoked every
2109	there might be events pending in the embedded loop. The callback must then	3195	time there might be events pending in the embedded loop. The callback
2110	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	3196	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
2111	their callbacks (you could also start an idle watcher to give the embedded	3197	sweep and invoke their callbacks (the callback doesn't need to invoke the
2112	loop strictly lower priority for example). You can also set the callback	3198	C<ev_embed_sweep> function directly, it could also start an idle watcher
2113	to C<0>, in which case the embed watcher will automatically execute the	3199	to give the embedded loop strictly lower priority for example).
2114	embedded loop sweep.
2115		3200
2116	As long as the watcher is started it will automatically handle events. The	3201	You can also set the callback to C<0>, in which case the embed watcher
2117	callback will be invoked whenever some events have been handled. You can	3202	will automatically execute the embedded loop sweep whenever necessary.
2118	set the callback to C<0> to avoid having to specify one if you are not
2119	interested in that.
2120		3203
2121	Also, there have not currently been made special provisions for forking:	3204	Fork detection will be handled transparently while the C<ev_embed> watcher
2122	when you fork, you not only have to call C<ev_loop_fork> on both loops,	3205	is active, i.e., the embedded loop will automatically be forked when the
2123	but you will also have to stop and restart any C<ev_embed> watchers	3206	embedding loop forks. In other cases, the user is responsible for calling
2124	yourself.	3207	C<ev_loop_fork> on the embedded loop.
2125		3208
2126	Unfortunately, not all backends are embeddable, only the ones returned by	3209	Unfortunately, not all backends are embeddable: only the ones returned by
2127	C<ev_embeddable_backends> are, which, unfortunately, does not include any	3210	C<ev_embeddable_backends> are, which, unfortunately, does not include any
2128	portable one.	3211	portable one.
2129		3212
2130	So when you want to use this feature you will always have to be prepared	3213	So when you want to use this feature you will always have to be prepared
2131	that you cannot get an embeddable loop. The recommended way to get around	3214	that you cannot get an embeddable loop. The recommended way to get around
2132	this is to have a separate variables for your embeddable loop, try to	3215	this is to have a separate variables for your embeddable loop, try to
2133	create it, and if that fails, use the normal loop for everything.	3216	create it, and if that fails, use the normal loop for everything.
2134		3217
		3218	=head3 C<ev_embed> and fork
		3219
		3220	While the C<ev_embed> watcher is running, forks in the embedding loop will
		3221	automatically be applied to the embedded loop as well, so no special
		3222	fork handling is required in that case. When the watcher is not running,
		3223	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		3224	as applicable.
		3225
2135	=head3 Watcher-Specific Functions and Data Members	3226	=head3 Watcher-Specific Functions and Data Members
2136		3227
2137	=over 4	3228	=over 4
2138		3229
2139	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3230	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
2140		3231
2141	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3232	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
2142		3233
2143	Configures the watcher to embed the given loop, which must be	3234	Configures the watcher to embed the given loop, which must be
2144	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3235	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
2145	invoked automatically, otherwise it is the responsibility of the callback	3236	invoked automatically, otherwise it is the responsibility of the callback
2146	to invoke it (it will continue to be called until the sweep has been done,	3237	to invoke it (it will continue to be called until the sweep has been done,
2147	if you do not want that, you need to temporarily stop the embed watcher).	3238	if you do not want that, you need to temporarily stop the embed watcher).
2148		3239
2149	=item ev_embed_sweep (loop, ev_embed *)	3240	=item ev_embed_sweep (loop, ev_embed *)
2150		3241
2151	Make a single, non-blocking sweep over the embedded loop. This works	3242	Make a single, non-blocking sweep over the embedded loop. This works
2152	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	3243	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
2153	appropriate way for embedded loops.	3244	appropriate way for embedded loops.
2154		3245
2155	=item struct ev_loop *other [read-only]	3246	=item struct ev_loop *other [read-only]
2156		3247
2157	The embedded event loop.	3248	The embedded event loop.
…		…
2166	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be	3257	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
2167	used).	3258	used).
2168		3259
2169	struct ev_loop *loop_hi = ev_default_init (0);	3260	struct ev_loop *loop_hi = ev_default_init (0);
2170	struct ev_loop *loop_lo = 0;	3261	struct ev_loop *loop_lo = 0;
2171	struct ev_embed embed;	3262	ev_embed embed;
2172		3263
2173	// see if there is a chance of getting one that works	3264	// see if there is a chance of getting one that works
2174	// (remember that a flags value of 0 means autodetection)	3265	// (remember that a flags value of 0 means autodetection)
2175	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3266	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2176	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3267	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
2177	: 0;	3268	: 0;
…		…
2190	kqueue implementation). Store the kqueue/socket-only event loop in	3281	kqueue implementation). Store the kqueue/socket-only event loop in
2191	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3282	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2192		3283
2193	struct ev_loop *loop = ev_default_init (0);	3284	struct ev_loop *loop = ev_default_init (0);
2194	struct ev_loop *loop_socket = 0;	3285	struct ev_loop *loop_socket = 0;
2195	struct ev_embed embed;	3286	ev_embed embed;
2196		3287
2197	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3288	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2198	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3289	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2199	{	3290	{
2200	ev_embed_init (&embed, 0, loop_socket);	3291	ev_embed_init (&embed, 0, loop_socket);
2201	ev_embed_start (loop, &embed);	3292	ev_embed_start (loop, &embed);
…		…
2209		3300
2210	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3301	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
2211		3302
2212	Fork watchers are called when a C<fork ()> was detected (usually because	3303	Fork watchers are called when a C<fork ()> was detected (usually because
2213	whoever is a good citizen cared to tell libev about it by calling	3304	whoever is a good citizen cared to tell libev about it by calling
2214	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the	3305	C<ev_loop_fork>). The invocation is done before the event loop blocks next
2215	event loop blocks next and before C<ev_check> watchers are being called,	3306	and before C<ev_check> watchers are being called, and only in the child
2216	and only in the child after the fork. If whoever good citizen calling	3307	after the fork. If whoever good citizen calling C<ev_default_fork> cheats
2217	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3308	and calls it in the wrong process, the fork handlers will be invoked, too,
2218	handlers will be invoked, too, of course.	3309	of course.
		3310
		3311	=head3 The special problem of life after fork - how is it possible?
		3312
		3313	Most uses of C<fork ()> consist of forking, then some simple calls to set
		3314	up/change the process environment, followed by a call to C<exec()>. This
		3315	sequence should be handled by libev without any problems.
		3316
		3317	This changes when the application actually wants to do event handling
		3318	in the child, or both parent in child, in effect "continuing" after the
		3319	fork.
		3320
		3321	The default mode of operation (for libev, with application help to detect
		3322	forks) is to duplicate all the state in the child, as would be expected
		3323	when I<either> the parent I<or> the child process continues.
		3324
		3325	When both processes want to continue using libev, then this is usually the
		3326	wrong result. In that case, usually one process (typically the parent) is
		3327	supposed to continue with all watchers in place as before, while the other
		3328	process typically wants to start fresh, i.e. without any active watchers.
		3329
		3330	The cleanest and most efficient way to achieve that with libev is to
		3331	simply create a new event loop, which of course will be "empty", and
		3332	use that for new watchers. This has the advantage of not touching more
		3333	memory than necessary, and thus avoiding the copy-on-write, and the
		3334	disadvantage of having to use multiple event loops (which do not support
		3335	signal watchers).
		3336
		3337	When this is not possible, or you want to use the default loop for
		3338	other reasons, then in the process that wants to start "fresh", call
		3339	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
		3340	Destroying the default loop will "orphan" (not stop) all registered
		3341	watchers, so you have to be careful not to execute code that modifies
		3342	those watchers. Note also that in that case, you have to re-register any
		3343	signal watchers.
2219		3344
2220	=head3 Watcher-Specific Functions and Data Members	3345	=head3 Watcher-Specific Functions and Data Members
2221		3346
2222	=over 4	3347	=over 4
2223		3348
2224	=item ev_fork_init (ev_signal *, callback)	3349	=item ev_fork_init (ev_fork *, callback)
2225		3350
2226	Initialises and configures the fork watcher - it has no parameters of any	3351	Initialises and configures the fork watcher - it has no parameters of any
2227	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,	3352	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
2228	believe me.	3353	really.
2229		3354
2230	=back	3355	=back
2231		3356
2232		3357
		3358	=head2 C<ev_cleanup> - even the best things end
		3359
		3360	Cleanup watchers are called just before the event loop is being destroyed
		3361	by a call to C<ev_loop_destroy>.
		3362
		3363	While there is no guarantee that the event loop gets destroyed, cleanup
		3364	watchers provide a convenient method to install cleanup hooks for your
		3365	program, worker threads and so on - you just to make sure to destroy the
		3366	loop when you want them to be invoked.
		3367
		3368	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3369	all other watchers, they do not keep a reference to the event loop (which
		3370	makes a lot of sense if you think about it). Like all other watchers, you
		3371	can call libev functions in the callback, except C<ev_cleanup_start>.
		3372
		3373	=head3 Watcher-Specific Functions and Data Members
		3374
		3375	=over 4
		3376
		3377	=item ev_cleanup_init (ev_cleanup *, callback)
		3378
		3379	Initialises and configures the cleanup watcher - it has no parameters of
		3380	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3381	pointless, I assure you.
		3382
		3383	=back
		3384
		3385	Example: Register an atexit handler to destroy the default loop, so any
		3386	cleanup functions are called.
		3387
		3388	static void
		3389	program_exits (void)
		3390	{
		3391	ev_loop_destroy (EV_DEFAULT_UC);
		3392	}
		3393
		3394	...
		3395	atexit (program_exits);
		3396
		3397
2233	=head2 C<ev_async> - how to wake up another event loop	3398	=head2 C<ev_async> - how to wake up an event loop
2234		3399
2235	In general, you cannot use an C<ev_loop> from multiple threads or other	3400	In general, you cannot use an C<ev_loop> from multiple threads or other
2236	asynchronous sources such as signal handlers (as opposed to multiple event	3401	asynchronous sources such as signal handlers (as opposed to multiple event
2237	loops - those are of course safe to use in different threads).	3402	loops - those are of course safe to use in different threads).
2238		3403
2239	Sometimes, however, you need to wake up another event loop you do not	3404	Sometimes, however, you need to wake up an event loop you do not control,
2240	control, for example because it belongs to another thread. This is what	3405	for example because it belongs to another thread. This is what C<ev_async>
2241	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you	3406	watchers do: as long as the C<ev_async> watcher is active, you can signal
2242	can signal it by calling C<ev_async_send>, which is thread- and signal	3407	it by calling C<ev_async_send>, which is thread- and signal safe.
2243	safe.
2244		3408
2245	This functionality is very similar to C<ev_signal> watchers, as signals,	3409	This functionality is very similar to C<ev_signal> watchers, as signals,
2246	too, are asynchronous in nature, and signals, too, will be compressed	3410	too, are asynchronous in nature, and signals, too, will be compressed
2247	(i.e. the number of callback invocations may be less than the number of	3411	(i.e. the number of callback invocations may be less than the number of
2248	C<ev_async_sent> calls).	3412	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
2249		3413	of "global async watchers" by using a watcher on an otherwise unused
2250	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not	3414	signal, and C<ev_feed_signal> to signal this watcher from another thread,
2251	just the default loop.	3415	even without knowing which loop owns the signal.
2252		3416
2253	=head3 Queueing	3417	=head3 Queueing
2254		3418
2255	C<ev_async> does not support queueing of data in any way. The reason	3419	C<ev_async> does not support queueing of data in any way. The reason
2256	is that the author does not know of a simple (or any) algorithm for a	3420	is that the author does not know of a simple (or any) algorithm for a
2257	multiple-writer-single-reader queue that works in all cases and doesn't	3421	multiple-writer-single-reader queue that works in all cases and doesn't
2258	need elaborate support such as pthreads.	3422	need elaborate support such as pthreads or unportable memory access
		3423	semantics.
2259		3424
2260	That means that if you want to queue data, you have to provide your own	3425	That means that if you want to queue data, you have to provide your own
2261	queue. But at least I can tell you would implement locking around your	3426	queue. But at least I can tell you how to implement locking around your
2262	queue:	3427	queue:
2263		3428
2264	=over 4	3429	=over 4
2265		3430
2266	=item queueing from a signal handler context	3431	=item queueing from a signal handler context
2267		3432
2268	To implement race-free queueing, you simply add to the queue in the signal	3433	To implement race-free queueing, you simply add to the queue in the signal
2269	handler but you block the signal handler in the watcher callback. Here is an example that does that for	3434	handler but you block the signal handler in the watcher callback. Here is
2270	some fictitious SIGUSR1 handler:	3435	an example that does that for some fictitious SIGUSR1 handler:
2271		3436
2272	static ev_async mysig;	3437	static ev_async mysig;
2273		3438
2274	static void	3439	static void
2275	sigusr1_handler (void)	3440	sigusr1_handler (void)
…		…
2341	=over 4	3506	=over 4
2342		3507
2343	=item ev_async_init (ev_async *, callback)	3508	=item ev_async_init (ev_async *, callback)
2344		3509
2345	Initialises and configures the async watcher - it has no parameters of any	3510	Initialises and configures the async watcher - it has no parameters of any
2346	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,	3511	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
2347	believe me.	3512	trust me.
2348		3513
2349	=item ev_async_send (loop, ev_async *)	3514	=item ev_async_send (loop, ev_async *)
2350		3515
2351	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3516	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
2352	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3517	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3518	returns.
		3519
2353	C<ev_feed_event>, this call is safe to do in other threads, signal or	3520	Unlike C<ev_feed_event>, this call is safe to do from other threads,
2354	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3521	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
2355	section below on what exactly this means).	3522	embedding section below on what exactly this means).
2356		3523
2357	This call incurs the overhead of a system call only once per loop iteration,	3524	Note that, as with other watchers in libev, multiple events might get
2358	so while the overhead might be noticeable, it doesn't apply to repeated	3525	compressed into a single callback invocation (another way to look at
2359	calls to C<ev_async_send>.	3526	this is that C<ev_async> watchers are level-triggered: they are set on
		3527	C<ev_async_send>, reset when the event loop detects that).
		3528
		3529	This call incurs the overhead of at most one extra system call per event
		3530	loop iteration, if the event loop is blocked, and no syscall at all if
		3531	the event loop (or your program) is processing events. That means that
		3532	repeated calls are basically free (there is no need to avoid calls for
		3533	performance reasons) and that the overhead becomes smaller (typically
		3534	zero) under load.
2360		3535
2361	=item bool = ev_async_pending (ev_async *)	3536	=item bool = ev_async_pending (ev_async *)
2362		3537
2363	Returns a non-zero value when C<ev_async_send> has been called on the	3538	Returns a non-zero value when C<ev_async_send> has been called on the
2364	watcher but the event has not yet been processed (or even noted) by the	3539	watcher but the event has not yet been processed (or even noted) by the
…		…
2367	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When	3542	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
2368	the loop iterates next and checks for the watcher to have become active,	3543	the loop iterates next and checks for the watcher to have become active,
2369	it will reset the flag again. C<ev_async_pending> can be used to very	3544	it will reset the flag again. C<ev_async_pending> can be used to very
2370	quickly check whether invoking the loop might be a good idea.	3545	quickly check whether invoking the loop might be a good idea.
2371		3546
2372	Not that this does I<not> check whether the watcher itself is pending, only	3547	Not that this does I<not> check whether the watcher itself is pending,
2373	whether it has been requested to make this watcher pending.	3548	only whether it has been requested to make this watcher pending: there
		3549	is a time window between the event loop checking and resetting the async
		3550	notification, and the callback being invoked.
2374		3551
2375	=back	3552	=back
2376		3553
2377		3554
2378	=head1 OTHER FUNCTIONS	3555	=head1 OTHER FUNCTIONS
2379		3556
2380	There are some other functions of possible interest. Described. Here. Now.	3557	There are some other functions of possible interest. Described. Here. Now.
2381		3558
2382	=over 4	3559	=over 4
2383		3560
2384	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3561	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)
2385		3562
2386	This function combines a simple timer and an I/O watcher, calls your	3563	This function combines a simple timer and an I/O watcher, calls your
2387	callback on whichever event happens first and automatically stop both	3564	callback on whichever event happens first and automatically stops both
2388	watchers. This is useful if you want to wait for a single event on an fd	3565	watchers. This is useful if you want to wait for a single event on an fd
2389	or timeout without having to allocate/configure/start/stop/free one or	3566	or timeout without having to allocate/configure/start/stop/free one or
2390	more watchers yourself.	3567	more watchers yourself.
2391		3568
2392	If C<fd> is less than 0, then no I/O watcher will be started and events	3569	If C<fd> is less than 0, then no I/O watcher will be started and the
2393	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3570	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
2394	C<events> set will be created and started.	3571	the given C<fd> and C<events> set will be created and started.
2395		3572
2396	If C<timeout> is less than 0, then no timeout watcher will be	3573	If C<timeout> is less than 0, then no timeout watcher will be
2397	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3574	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
2398	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3575	repeat = 0) will be started. C<0> is a valid timeout.
2399	dubious value.
2400		3576
2401	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3577	The callback has the type C<void (*cb)(int revents, void *arg)> and is
2402	passed an C<revents> set like normal event callbacks (a combination of	3578	passed an C<revents> set like normal event callbacks (a combination of
2403	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3579	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
2404	value passed to C<ev_once>:	3580	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3581	a timeout and an io event at the same time - you probably should give io
		3582	events precedence.
		3583
		3584	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
2405		3585
2406	static void stdin_ready (int revents, void *arg)	3586	static void stdin_ready (int revents, void *arg)
2407	{	3587	{
		3588	if (revents & EV_READ)
		3589	/* stdin might have data for us, joy! */;
2408	if (revents & EV_TIMEOUT)	3590	else if (revents & EV_TIMER)
2409	/* doh, nothing entered */;	3591	/* doh, nothing entered */;
2410	else if (revents & EV_READ)
2411	/* stdin might have data for us, joy! */;
2412	}	3592	}
2413		3593
2414	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3594	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2415		3595
2416	=item ev_feed_event (ev_loop *, watcher *, int revents)
2417
2418	Feeds the given event set into the event loop, as if the specified event
2419	had happened for the specified watcher (which must be a pointer to an
2420	initialised but not necessarily started event watcher).
2421
2422	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3596	=item ev_feed_fd_event (loop, int fd, int revents)
2423		3597
2424	Feed an event on the given fd, as if a file descriptor backend detected	3598	Feed an event on the given fd, as if a file descriptor backend detected
2425	the given events it.	3599	the given events.
2426		3600
2427	=item ev_feed_signal_event (ev_loop *loop, int signum)	3601	=item ev_feed_signal_event (loop, int signum)
2428		3602
2429	Feed an event as if the given signal occurred (C<loop> must be the default	3603	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
2430	loop!).	3604	which is async-safe.
2431		3605
2432	=back	3606	=back
		3607
		3608
		3609	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3610
		3611	This section explains some common idioms that are not immediately
		3612	obvious. Note that examples are sprinkled over the whole manual, and this
		3613	section only contains stuff that wouldn't fit anywhere else.
		3614
		3615	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3616
		3617	Each watcher has, by default, a C<void *data> member that you can read
		3618	or modify at any time: libev will completely ignore it. This can be used
		3619	to associate arbitrary data with your watcher. If you need more data and
		3620	don't want to allocate memory separately and store a pointer to it in that
		3621	data member, you can also "subclass" the watcher type and provide your own
		3622	data:
		3623
		3624	struct my_io
		3625	{
		3626	ev_io io;
		3627	int otherfd;
		3628	void *somedata;
		3629	struct whatever *mostinteresting;
		3630	};
		3631
		3632	...
		3633	struct my_io w;
		3634	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3635
		3636	And since your callback will be called with a pointer to the watcher, you
		3637	can cast it back to your own type:
		3638
		3639	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3640	{
		3641	struct my_io *w = (struct my_io *)w_;
		3642	...
		3643	}
		3644
		3645	More interesting and less C-conformant ways of casting your callback
		3646	function type instead have been omitted.
		3647
		3648	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3649
		3650	Another common scenario is to use some data structure with multiple
		3651	embedded watchers, in effect creating your own watcher that combines
		3652	multiple libev event sources into one "super-watcher":
		3653
		3654	struct my_biggy
		3655	{
		3656	int some_data;
		3657	ev_timer t1;
		3658	ev_timer t2;
		3659	}
		3660
		3661	In this case getting the pointer to C<my_biggy> is a bit more
		3662	complicated: Either you store the address of your C<my_biggy> struct in
		3663	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3664	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3665	real programmers):
		3666
		3667	#include <stddef.h>
		3668
		3669	static void
		3670	t1_cb (EV_P_ ev_timer *w, int revents)
		3671	{
		3672	struct my_biggy big = (struct my_biggy *)
		3673	(((char *)w) - offsetof (struct my_biggy, t1));
		3674	}
		3675
		3676	static void
		3677	t2_cb (EV_P_ ev_timer *w, int revents)
		3678	{
		3679	struct my_biggy big = (struct my_biggy *)
		3680	(((char *)w) - offsetof (struct my_biggy, t2));
		3681	}
		3682
		3683	=head2 AVOIDING FINISHING BEFORE RETURNING
		3684
		3685	Often you have structures like this in event-based programs:
		3686
		3687	callback ()
		3688	{
		3689	free (request);
		3690	}
		3691
		3692	request = start_new_request (..., callback);
		3693
		3694	The intent is to start some "lengthy" operation. The C<request> could be
		3695	used to cancel the operation, or do other things with it.
		3696
		3697	It's not uncommon to have code paths in C<start_new_request> that
		3698	immediately invoke the callback, for example, to report errors. Or you add
		3699	some caching layer that finds that it can skip the lengthy aspects of the
		3700	operation and simply invoke the callback with the result.
		3701
		3702	The problem here is that this will happen I<before> C<start_new_request>
		3703	has returned, so C<request> is not set.
		3704
		3705	Even if you pass the request by some safer means to the callback, you
		3706	might want to do something to the request after starting it, such as
		3707	canceling it, which probably isn't working so well when the callback has
		3708	already been invoked.
		3709
		3710	A common way around all these issues is to make sure that
		3711	C<start_new_request> I<always> returns before the callback is invoked. If
		3712	C<start_new_request> immediately knows the result, it can artificially
		3713	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3714	example, or more sneakily, by reusing an existing (stopped) watcher and
		3715	pushing it into the pending queue:
		3716
		3717	ev_set_cb (watcher, callback);
		3718	ev_feed_event (EV_A_ watcher, 0);
		3719
		3720	This way, C<start_new_request> can safely return before the callback is
		3721	invoked, while not delaying callback invocation too much.
		3722
		3723	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3724
		3725	Often (especially in GUI toolkits) there are places where you have
		3726	I<modal> interaction, which is most easily implemented by recursively
		3727	invoking C<ev_run>.
		3728
		3729	This brings the problem of exiting - a callback might want to finish the
		3730	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3731	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3732	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3733	other combination: In these cases, a simple C<ev_break> will not work.
		3734
		3735	The solution is to maintain "break this loop" variable for each C<ev_run>
		3736	invocation, and use a loop around C<ev_run> until the condition is
		3737	triggered, using C<EVRUN_ONCE>:
		3738
		3739	// main loop
		3740	int exit_main_loop = 0;
		3741
		3742	while (!exit_main_loop)
		3743	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3744
		3745	// in a modal watcher
		3746	int exit_nested_loop = 0;
		3747
		3748	while (!exit_nested_loop)
		3749	ev_run (EV_A_ EVRUN_ONCE);
		3750
		3751	To exit from any of these loops, just set the corresponding exit variable:
		3752
		3753	// exit modal loop
		3754	exit_nested_loop = 1;
		3755
		3756	// exit main program, after modal loop is finished
		3757	exit_main_loop = 1;
		3758
		3759	// exit both
		3760	exit_main_loop = exit_nested_loop = 1;
		3761
		3762	=head2 THREAD LOCKING EXAMPLE
		3763
		3764	Here is a fictitious example of how to run an event loop in a different
		3765	thread from where callbacks are being invoked and watchers are
		3766	created/added/removed.
		3767
		3768	For a real-world example, see the C<EV::Loop::Async> perl module,
		3769	which uses exactly this technique (which is suited for many high-level
		3770	languages).
		3771
		3772	The example uses a pthread mutex to protect the loop data, a condition
		3773	variable to wait for callback invocations, an async watcher to notify the
		3774	event loop thread and an unspecified mechanism to wake up the main thread.
		3775
		3776	First, you need to associate some data with the event loop:
		3777
		3778	typedef struct {
		3779	mutex_t lock; /* global loop lock */
		3780	ev_async async_w;
		3781	thread_t tid;
		3782	cond_t invoke_cv;
		3783	} userdata;
		3784
		3785	void prepare_loop (EV_P)
		3786	{
		3787	// for simplicity, we use a static userdata struct.
		3788	static userdata u;
		3789
		3790	ev_async_init (&u->async_w, async_cb);
		3791	ev_async_start (EV_A_ &u->async_w);
		3792
		3793	pthread_mutex_init (&u->lock, 0);
		3794	pthread_cond_init (&u->invoke_cv, 0);
		3795
		3796	// now associate this with the loop
		3797	ev_set_userdata (EV_A_ u);
		3798	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3799	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3800
		3801	// then create the thread running ev_run
		3802	pthread_create (&u->tid, 0, l_run, EV_A);
		3803	}
		3804
		3805	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3806	solely to wake up the event loop so it takes notice of any new watchers
		3807	that might have been added:
		3808
		3809	static void
		3810	async_cb (EV_P_ ev_async *w, int revents)
		3811	{
		3812	// just used for the side effects
		3813	}
		3814
		3815	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3816	protecting the loop data, respectively.
		3817
		3818	static void
		3819	l_release (EV_P)
		3820	{
		3821	userdata *u = ev_userdata (EV_A);
		3822	pthread_mutex_unlock (&u->lock);
		3823	}
		3824
		3825	static void
		3826	l_acquire (EV_P)
		3827	{
		3828	userdata *u = ev_userdata (EV_A);
		3829	pthread_mutex_lock (&u->lock);
		3830	}
		3831
		3832	The event loop thread first acquires the mutex, and then jumps straight
		3833	into C<ev_run>:
		3834
		3835	void *
		3836	l_run (void *thr_arg)
		3837	{
		3838	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3839
		3840	l_acquire (EV_A);
		3841	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3842	ev_run (EV_A_ 0);
		3843	l_release (EV_A);
		3844
		3845	return 0;
		3846	}
		3847
		3848	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3849	signal the main thread via some unspecified mechanism (signals? pipe
		3850	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3851	have been called (in a while loop because a) spurious wakeups are possible
		3852	and b) skipping inter-thread-communication when there are no pending
		3853	watchers is very beneficial):
		3854
		3855	static void
		3856	l_invoke (EV_P)
		3857	{
		3858	userdata *u = ev_userdata (EV_A);
		3859
		3860	while (ev_pending_count (EV_A))
		3861	{
		3862	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3863	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3864	}
		3865	}
		3866
		3867	Now, whenever the main thread gets told to invoke pending watchers, it
		3868	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3869	thread to continue:
		3870
		3871	static void
		3872	real_invoke_pending (EV_P)
		3873	{
		3874	userdata *u = ev_userdata (EV_A);
		3875
		3876	pthread_mutex_lock (&u->lock);
		3877	ev_invoke_pending (EV_A);
		3878	pthread_cond_signal (&u->invoke_cv);
		3879	pthread_mutex_unlock (&u->lock);
		3880	}
		3881
		3882	Whenever you want to start/stop a watcher or do other modifications to an
		3883	event loop, you will now have to lock:
		3884
		3885	ev_timer timeout_watcher;
		3886	userdata *u = ev_userdata (EV_A);
		3887
		3888	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3889
		3890	pthread_mutex_lock (&u->lock);
		3891	ev_timer_start (EV_A_ &timeout_watcher);
		3892	ev_async_send (EV_A_ &u->async_w);
		3893	pthread_mutex_unlock (&u->lock);
		3894
		3895	Note that sending the C<ev_async> watcher is required because otherwise
		3896	an event loop currently blocking in the kernel will have no knowledge
		3897	about the newly added timer. By waking up the loop it will pick up any new
		3898	watchers in the next event loop iteration.
		3899
		3900	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3901
		3902	While the overhead of a callback that e.g. schedules a thread is small, it
		3903	is still an overhead. If you embed libev, and your main usage is with some
		3904	kind of threads or coroutines, you might want to customise libev so that
		3905	doesn't need callbacks anymore.
		3906
		3907	Imagine you have coroutines that you can switch to using a function
		3908	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3909	and that due to some magic, the currently active coroutine is stored in a
		3910	global called C<current_coro>. Then you can build your own "wait for libev
		3911	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3912	the differing C<;> conventions):
		3913
		3914	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3915	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3916
		3917	That means instead of having a C callback function, you store the
		3918	coroutine to switch to in each watcher, and instead of having libev call
		3919	your callback, you instead have it switch to that coroutine.
		3920
		3921	A coroutine might now wait for an event with a function called
		3922	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3923	matter when, or whether the watcher is active or not when this function is
		3924	called):
		3925
		3926	void
		3927	wait_for_event (ev_watcher *w)
		3928	{
		3929	ev_set_cb (w, current_coro);
		3930	switch_to (libev_coro);
		3931	}
		3932
		3933	That basically suspends the coroutine inside C<wait_for_event> and
		3934	continues the libev coroutine, which, when appropriate, switches back to
		3935	this or any other coroutine.
		3936
		3937	You can do similar tricks if you have, say, threads with an event queue -
		3938	instead of storing a coroutine, you store the queue object and instead of
		3939	switching to a coroutine, you push the watcher onto the queue and notify
		3940	any waiters.
		3941
		3942	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		3943	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3944
		3945	// my_ev.h
		3946	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3947	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3948	#include "../libev/ev.h"
		3949
		3950	// my_ev.c
		3951	#define EV_H "my_ev.h"
		3952	#include "../libev/ev.c"
		3953
		3954	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3955	F<my_ev.c> into your project. When properly specifying include paths, you
		3956	can even use F<ev.h> as header file name directly.
2433		3957
2434		3958
2435	=head1 LIBEVENT EMULATION	3959	=head1 LIBEVENT EMULATION
2436		3960
2437	Libev offers a compatibility emulation layer for libevent. It cannot	3961	Libev offers a compatibility emulation layer for libevent. It cannot
2438	emulate the internals of libevent, so here are some usage hints:	3962	emulate the internals of libevent, so here are some usage hints:
2439		3963
2440	=over 4	3964	=over 4
		3965
		3966	=item * Only the libevent-1.4.1-beta API is being emulated.
		3967
		3968	This was the newest libevent version available when libev was implemented,
		3969	and is still mostly unchanged in 2010.
2441		3970
2442	=item * Use it by including <event.h>, as usual.	3971	=item * Use it by including <event.h>, as usual.
2443		3972
2444	=item * The following members are fully supported: ev_base, ev_callback,	3973	=item * The following members are fully supported: ev_base, ev_callback,
2445	ev_arg, ev_fd, ev_res, ev_events.	3974	ev_arg, ev_fd, ev_res, ev_events.
…		…
2451	=item * Priorities are not currently supported. Initialising priorities	3980	=item * Priorities are not currently supported. Initialising priorities
2452	will fail and all watchers will have the same priority, even though there	3981	will fail and all watchers will have the same priority, even though there
2453	is an ev_pri field.	3982	is an ev_pri field.
2454		3983
2455	=item * In libevent, the last base created gets the signals, in libev, the	3984	=item * In libevent, the last base created gets the signals, in libev, the
2456	first base created (== the default loop) gets the signals.	3985	base that registered the signal gets the signals.
2457		3986
2458	=item * Other members are not supported.	3987	=item * Other members are not supported.
2459		3988
2460	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3989	=item * The libev emulation is I<not> ABI compatible to libevent, you need
2461	to use the libev header file and library.	3990	to use the libev header file and library.
2462		3991
2463	=back	3992	=back
2464		3993
2465	=head1 C++ SUPPORT	3994	=head1 C++ SUPPORT
		3995
		3996	=head2 C API
		3997
		3998	The normal C API should work fine when used from C++: both ev.h and the
		3999	libev sources can be compiled as C++. Therefore, code that uses the C API
		4000	will work fine.
		4001
		4002	Proper exception specifications might have to be added to callbacks passed
		4003	to libev: exceptions may be thrown only from watcher callbacks, all other
		4004	callbacks (allocator, syserr, loop acquire/release and periodic reschedule
		4005	callbacks) must not throw exceptions, and might need a C<noexcept>
		4006	specification. If you have code that needs to be compiled as both C and
		4007	C++ you can use the C<EV_NOEXCEPT> macro for this:
		4008
		4009	static void
		4010	fatal_error (const char *msg) EV_NOEXCEPT
		4011	{
		4012	perror (msg);
		4013	abort ();
		4014	}
		4015
		4016	...
		4017	ev_set_syserr_cb (fatal_error);
		4018
		4019	The only API functions that can currently throw exceptions are C<ev_run>,
		4020	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		4021	because it runs cleanup watchers).
		4022
		4023	Throwing exceptions in watcher callbacks is only supported if libev itself
		4024	is compiled with a C++ compiler or your C and C++ environments allow
		4025	throwing exceptions through C libraries (most do).
		4026
		4027	=head2 C++ API
2466		4028
2467	Libev comes with some simplistic wrapper classes for C++ that mainly allow	4029	Libev comes with some simplistic wrapper classes for C++ that mainly allow
2468	you to use some convenience methods to start/stop watchers and also change	4030	you to use some convenience methods to start/stop watchers and also change
2469	the callback model to a model using method callbacks on objects.	4031	the callback model to a model using method callbacks on objects.
2470		4032
2471	To use it,	4033	To use it,
2472		4034
2473	#include <ev++.h>	4035	#include <ev++.h>
2474		4036
2475	This automatically includes F<ev.h> and puts all of its definitions (many	4037	This automatically includes F<ev.h> and puts all of its definitions (many
2476	of them macros) into the global namespace. All C++ specific things are	4038	of them macros) into the global namespace. All C++ specific things are
2477	put into the C<ev> namespace. It should support all the same embedding	4039	put into the C<ev> namespace. It should support all the same embedding
…		…
2480	Care has been taken to keep the overhead low. The only data member the C++	4042	Care has been taken to keep the overhead low. The only data member the C++
2481	classes add (compared to plain C-style watchers) is the event loop pointer	4043	classes add (compared to plain C-style watchers) is the event loop pointer
2482	that the watcher is associated with (or no additional members at all if	4044	that the watcher is associated with (or no additional members at all if
2483	you disable C<EV_MULTIPLICITY> when embedding libev).	4045	you disable C<EV_MULTIPLICITY> when embedding libev).
2484		4046
2485	Currently, functions, and static and non-static member functions can be	4047	Currently, functions, static and non-static member functions and classes
2486	used as callbacks. Other types should be easy to add as long as they only	4048	with C<operator ()> can be used as callbacks. Other types should be easy
2487	need one additional pointer for context. If you need support for other	4049	to add as long as they only need one additional pointer for context. If
2488	types of functors please contact the author (preferably after implementing	4050	you need support for other types of functors please contact the author
2489	it).	4051	(preferably after implementing it).
		4052
		4053	For all this to work, your C++ compiler either has to use the same calling
		4054	conventions as your C compiler (for static member functions), or you have
		4055	to embed libev and compile libev itself as C++.
2490		4056
2491	Here is a list of things available in the C<ev> namespace:	4057	Here is a list of things available in the C<ev> namespace:
2492		4058
2493	=over 4	4059	=over 4
2494		4060
…		…
2504	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4070	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
2505		4071
2506	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4072	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
2507	the same name in the C<ev> namespace, with the exception of C<ev_signal>	4073	the same name in the C<ev> namespace, with the exception of C<ev_signal>
2508	which is called C<ev::sig> to avoid clashes with the C<signal> macro	4074	which is called C<ev::sig> to avoid clashes with the C<signal> macro
2509	defines by many implementations.	4075	defined by many implementations.
2510		4076
2511	All of those classes have these methods:	4077	All of those classes have these methods:
2512		4078
2513	=over 4	4079	=over 4
2514		4080
2515	=item ev::TYPE::TYPE ()	4081	=item ev::TYPE::TYPE ()
2516		4082
2517	=item ev::TYPE::TYPE (struct ev_loop *)	4083	=item ev::TYPE::TYPE (loop)
2518		4084
2519	=item ev::TYPE::~TYPE	4085	=item ev::TYPE::~TYPE
2520		4086
2521	The constructor (optionally) takes an event loop to associate the watcher	4087	The constructor (optionally) takes an event loop to associate the watcher
2522	with. If it is omitted, it will use C<EV_DEFAULT>.	4088	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
2554		4120
2555	myclass obj;	4121	myclass obj;
2556	ev::io iow;	4122	ev::io iow;
2557	iow.set <myclass, &myclass::io_cb> (&obj);	4123	iow.set <myclass, &myclass::io_cb> (&obj);
2558		4124
		4125	=item w->set (object *)
		4126
		4127	This is a variation of a method callback - leaving out the method to call
		4128	will default the method to C<operator ()>, which makes it possible to use
		4129	functor objects without having to manually specify the C<operator ()> all
		4130	the time. Incidentally, you can then also leave out the template argument
		4131	list.
		4132
		4133	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		4134	int revents)>.
		4135
		4136	See the method-C<set> above for more details.
		4137
		4138	Example: use a functor object as callback.
		4139
		4140	struct myfunctor
		4141	{
		4142	void operator() (ev::io &w, int revents)
		4143	{
		4144	...
		4145	}
		4146	}
		4147
		4148	myfunctor f;
		4149
		4150	ev::io w;
		4151	w.set (&f);
		4152
2559	=item w->set<function> (void *data = 0)	4153	=item w->set<function> (void *data = 0)
2560		4154
2561	Also sets a callback, but uses a static method or plain function as	4155	Also sets a callback, but uses a static method or plain function as
2562	callback. The optional C<data> argument will be stored in the watcher's	4156	callback. The optional C<data> argument will be stored in the watcher's
2563	C<data> member and is free for you to use.	4157	C<data> member and is free for you to use.
2564		4158
2565	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	4159	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2566		4160
2567	See the method-C<set> above for more details.	4161	See the method-C<set> above for more details.
2568		4162
2569	Example:	4163	Example: Use a plain function as callback.
2570		4164
2571	static void io_cb (ev::io &w, int revents) { }	4165	static void io_cb (ev::io &w, int revents) { }
2572	iow.set <io_cb> ();	4166	iow.set <io_cb> ();
2573		4167
2574	=item w->set (struct ev_loop *)	4168	=item w->set (loop)
2575		4169
2576	Associates a different C<struct ev_loop> with this watcher. You can only	4170	Associates a different C<struct ev_loop> with this watcher. You can only
2577	do this when the watcher is inactive (and not pending either).	4171	do this when the watcher is inactive (and not pending either).
2578		4172
2579	=item w->set ([arguments])	4173	=item w->set ([arguments])
2580		4174
2581	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be	4175	Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
		4176	with the same arguments. Either this method or a suitable start method
2582	called at least once. Unlike the C counterpart, an active watcher gets	4177	must be called at least once. Unlike the C counterpart, an active watcher
2583	automatically stopped and restarted when reconfiguring it with this	4178	gets automatically stopped and restarted when reconfiguring it with this
2584	method.	4179	method.
		4180
		4181	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4182	clashing with the C<set (loop)> method.
2585		4183
2586	=item w->start ()	4184	=item w->start ()
2587		4185
2588	Starts the watcher. Note that there is no C<loop> argument, as the	4186	Starts the watcher. Note that there is no C<loop> argument, as the
2589	constructor already stores the event loop.	4187	constructor already stores the event loop.
2590		4188
		4189	=item w->start ([arguments])
		4190
		4191	Instead of calling C<set> and C<start> methods separately, it is often
		4192	convenient to wrap them in one call. Uses the same type of arguments as
		4193	the configure C<set> method of the watcher.
		4194
2591	=item w->stop ()	4195	=item w->stop ()
2592		4196
2593	Stops the watcher if it is active. Again, no C<loop> argument.	4197	Stops the watcher if it is active. Again, no C<loop> argument.
2594		4198
2595	=item w->again () (C<ev::timer>, C<ev::periodic> only)	4199	=item w->again () (C<ev::timer>, C<ev::periodic> only)
…		…
2607		4211
2608	=back	4212	=back
2609		4213
2610	=back	4214	=back
2611		4215
2612	Example: Define a class with an IO and idle watcher, start one of them in	4216	Example: Define a class with two I/O and idle watchers, start the I/O
2613	the constructor.	4217	watchers in the constructor.
2614		4218
2615	class myclass	4219	class myclass
2616	{	4220	{
2617	ev::io io; void io_cb (ev::io &w, int revents);	4221	ev::io io ; void io_cb (ev::io &w, int revents);
		4222	ev::io io2 ; void io2_cb (ev::io &w, int revents);
2618	ev:idle idle void idle_cb (ev::idle &w, int revents);	4223	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2619		4224
2620	myclass (int fd)	4225	myclass (int fd)
2621	{	4226	{
2622	io .set <myclass, &myclass::io_cb > (this);	4227	io .set <myclass, &myclass::io_cb > (this);
		4228	io2 .set <myclass, &myclass::io2_cb > (this);
2623	idle.set <myclass, &myclass::idle_cb> (this);	4229	idle.set <myclass, &myclass::idle_cb> (this);
2624		4230
2625	io.start (fd, ev::READ);	4231	io.set (fd, ev::WRITE); // configure the watcher
		4232	io.start (); // start it whenever convenient
		4233
		4234	io2.start (fd, ev::READ); // set + start in one call
2626	}	4235	}
2627	};	4236	};
2628		4237
2629		4238
2630	=head1 OTHER LANGUAGE BINDINGS	4239	=head1 OTHER LANGUAGE BINDINGS
…		…
2639	=item Perl	4248	=item Perl
2640		4249
2641	The EV module implements the full libev API and is actually used to test	4250	The EV module implements the full libev API and is actually used to test
2642	libev. EV is developed together with libev. Apart from the EV core module,	4251	libev. EV is developed together with libev. Apart from the EV core module,
2643	there are additional modules that implement libev-compatible interfaces	4252	there are additional modules that implement libev-compatible interfaces
2644	to C<libadns> (C<EV::ADNS>), C<Net::SNMP> (C<Net::SNMP::EV>) and the	4253	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
2645	C<libglib> event core (C<Glib::EV> and C<EV::Glib>).	4254	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		4255	and C<EV::Glib>).
2646		4256
2647	It can be found and installed via CPAN, its homepage is at	4257	It can be found and installed via CPAN, its homepage is at
2648	L<http://software.schmorp.de/pkg/EV>.	4258	L<http://software.schmorp.de/pkg/EV>.
2649		4259
2650	=item Python	4260	=item Python
2651		4261
2652	Python bindings can be found at L<http://code.google.com/p/pyev/>. It	4262	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
2653	seems to be quite complete and well-documented. Note, however, that the	4263	seems to be quite complete and well-documented.
2654	patch they require for libev is outright dangerous as it breaks the ABI
2655	for everybody else, and therefore, should never be applied in an installed
2656	libev (if python requires an incompatible ABI then it needs to embed
2657	libev).
2658		4264
2659	=item Ruby	4265	=item Ruby
2660		4266
2661	Tony Arcieri has written a ruby extension that offers access to a subset	4267	Tony Arcieri has written a ruby extension that offers access to a subset
2662	of the libev API and adds file handle abstractions, asynchronous DNS and	4268	of the libev API and adds file handle abstractions, asynchronous DNS and
2663	more on top of it. It can be found via gem servers. Its homepage is at	4269	more on top of it. It can be found via gem servers. Its homepage is at
2664	L<http://rev.rubyforge.org/>.	4270	L<http://rev.rubyforge.org/>.
2665		4271
		4272	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		4273	makes rev work even on mingw.
		4274
		4275	=item Haskell
		4276
		4277	A haskell binding to libev is available at
		4278	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		4279
2666	=item D	4280	=item D
2667		4281
2668	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4282	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
2669	be found at L<http://proj.llucax.com.ar/wiki/evd>.	4283	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
		4284
		4285	=item Ocaml
		4286
		4287	Erkki Seppala has written Ocaml bindings for libev, to be found at
		4288	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		4289
		4290	=item Lua
		4291
		4292	Brian Maher has written a partial interface to libev for lua (at the
		4293	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		4294	L<http://github.com/brimworks/lua-ev>.
		4295
		4296	=item Javascript
		4297
		4298	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4299
		4300	=item Others
		4301
		4302	There are others, and I stopped counting.
2670		4303
2671	=back	4304	=back
2672		4305
2673		4306
2674	=head1 MACRO MAGIC	4307	=head1 MACRO MAGIC
…		…
2688	loop argument"). The C<EV_A> form is used when this is the sole argument,	4321	loop argument"). The C<EV_A> form is used when this is the sole argument,
2689	C<EV_A_> is used when other arguments are following. Example:	4322	C<EV_A_> is used when other arguments are following. Example:
2690		4323
2691	ev_unref (EV_A);	4324	ev_unref (EV_A);
2692	ev_timer_add (EV_A_ watcher);	4325	ev_timer_add (EV_A_ watcher);
2693	ev_loop (EV_A_ 0);	4326	ev_run (EV_A_ 0);
2694		4327
2695	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	4328	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2696	which is often provided by the following macro.	4329	which is often provided by the following macro.
2697		4330
2698	=item C<EV_P>, C<EV_P_>	4331	=item C<EV_P>, C<EV_P_>
…		…
2711	suitable for use with C<EV_A>.	4344	suitable for use with C<EV_A>.
2712		4345
2713	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4346	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2714		4347
2715	Similar to the other two macros, this gives you the value of the default	4348	Similar to the other two macros, this gives you the value of the default
2716	loop, if multiple loops are supported ("ev loop default").	4349	loop, if multiple loops are supported ("ev loop default"). The default loop
		4350	will be initialised if it isn't already initialised.
		4351
		4352	For non-multiplicity builds, these macros do nothing, so you always have
		4353	to initialise the loop somewhere.
2717		4354
2718	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4355	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
2719		4356
2720	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4357	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
2721	default loop has been initialised (C<UC> == unchecked). Their behaviour	4358	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
2738	}	4375	}
2739		4376
2740	ev_check check;	4377	ev_check check;
2741	ev_check_init (&check, check_cb);	4378	ev_check_init (&check, check_cb);
2742	ev_check_start (EV_DEFAULT_ &check);	4379	ev_check_start (EV_DEFAULT_ &check);
2743	ev_loop (EV_DEFAULT_ 0);	4380	ev_run (EV_DEFAULT_ 0);
2744		4381
2745	=head1 EMBEDDING	4382	=head1 EMBEDDING
2746		4383
2747	Libev can (and often is) directly embedded into host	4384	Libev can (and often is) directly embedded into host
2748	applications. Examples of applications that embed it include the Deliantra	4385	applications. Examples of applications that embed it include the Deliantra
…		…
2775		4412
2776	#define EV_STANDALONE 1	4413	#define EV_STANDALONE 1
2777	#include "ev.h"	4414	#include "ev.h"
2778		4415
2779	Both header files and implementation files can be compiled with a C++	4416	Both header files and implementation files can be compiled with a C++
2780	compiler (at least, thats a stated goal, and breakage will be treated	4417	compiler (at least, that's a stated goal, and breakage will be treated
2781	as a bug).	4418	as a bug).
2782		4419
2783	You need the following files in your source tree, or in a directory	4420	You need the following files in your source tree, or in a directory
2784	in your include path (e.g. in libev/ when using -Ilibev):	4421	in your include path (e.g. in libev/ when using -Ilibev):
2785		4422
…		…
2788	ev_vars.h	4425	ev_vars.h
2789	ev_wrap.h	4426	ev_wrap.h
2790		4427
2791	ev_win32.c required on win32 platforms only	4428	ev_win32.c required on win32 platforms only
2792		4429
2793	ev_select.c only when select backend is enabled (which is enabled by default)	4430	ev_select.c only when select backend is enabled
2794	ev_poll.c only when poll backend is enabled (disabled by default)	4431	ev_poll.c only when poll backend is enabled
2795	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4432	ev_epoll.c only when the epoll backend is enabled
2796	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4433	ev_kqueue.c only when the kqueue backend is enabled
2797	ev_port.c only when the solaris port backend is enabled (disabled by default)	4434	ev_port.c only when the solaris port backend is enabled
2798		4435
2799	F<ev.c> includes the backend files directly when enabled, so you only need	4436	F<ev.c> includes the backend files directly when enabled, so you only need
2800	to compile this single file.	4437	to compile this single file.
2801		4438
2802	=head3 LIBEVENT COMPATIBILITY API	4439	=head3 LIBEVENT COMPATIBILITY API
…		…
2828	libev.m4	4465	libev.m4
2829		4466
2830	=head2 PREPROCESSOR SYMBOLS/MACROS	4467	=head2 PREPROCESSOR SYMBOLS/MACROS
2831		4468
2832	Libev can be configured via a variety of preprocessor symbols you have to	4469	Libev can be configured via a variety of preprocessor symbols you have to
2833	define before including any of its files. The default in the absence of	4470	define before including (or compiling) any of its files. The default in
2834	autoconf is noted for every option.	4471	the absence of autoconf is documented for every option.
		4472
		4473	Symbols marked with "(h)" do not change the ABI, and can have different
		4474	values when compiling libev vs. including F<ev.h>, so it is permissible
		4475	to redefine them before including F<ev.h> without breaking compatibility
		4476	to a compiled library. All other symbols change the ABI, which means all
		4477	users of libev and the libev code itself must be compiled with compatible
		4478	settings.
2835		4479
2836	=over 4	4480	=over 4
2837		4481
		4482	=item EV_COMPAT3 (h)
		4483
		4484	Backwards compatibility is a major concern for libev. This is why this
		4485	release of libev comes with wrappers for the functions and symbols that
		4486	have been renamed between libev version 3 and 4.
		4487
		4488	You can disable these wrappers (to test compatibility with future
		4489	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		4490	sources. This has the additional advantage that you can drop the C<struct>
		4491	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		4492	typedef in that case.
		4493
		4494	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		4495	and in some even more future version the compatibility code will be
		4496	removed completely.
		4497
2838	=item EV_STANDALONE	4498	=item EV_STANDALONE (h)
2839		4499
2840	Must always be C<1> if you do not use autoconf configuration, which	4500	Must always be C<1> if you do not use autoconf configuration, which
2841	keeps libev from including F<config.h>, and it also defines dummy	4501	keeps libev from including F<config.h>, and it also defines dummy
2842	implementations for some libevent functions (such as logging, which is not	4502	implementations for some libevent functions (such as logging, which is not
2843	supported). It will also not define any of the structs usually found in	4503	supported). It will also not define any of the structs usually found in
2844	F<event.h> that are not directly supported by the libev core alone.	4504	F<event.h> that are not directly supported by the libev core alone.
2845		4505
		4506	In standalone mode, libev will still try to automatically deduce the
		4507	configuration, but has to be more conservative.
		4508
		4509	=item EV_USE_FLOOR
		4510
		4511	If defined to be C<1>, libev will use the C<floor ()> function for its
		4512	periodic reschedule calculations, otherwise libev will fall back on a
		4513	portable (slower) implementation. If you enable this, you usually have to
		4514	link against libm or something equivalent. Enabling this when the C<floor>
		4515	function is not available will fail, so the safe default is to not enable
		4516	this.
		4517
2846	=item EV_USE_MONOTONIC	4518	=item EV_USE_MONOTONIC
2847		4519
2848	If defined to be C<1>, libev will try to detect the availability of the	4520	If defined to be C<1>, libev will try to detect the availability of the
2849	monotonic clock option at both compile time and runtime. Otherwise no use	4521	monotonic clock option at both compile time and runtime. Otherwise no
2850	of the monotonic clock option will be attempted. If you enable this, you	4522	use of the monotonic clock option will be attempted. If you enable this,
2851	usually have to link against librt or something similar. Enabling it when	4523	you usually have to link against librt or something similar. Enabling it
2852	the functionality isn't available is safe, though, although you have	4524	when the functionality isn't available is safe, though, although you have
2853	to make sure you link against any libraries where the C<clock_gettime>	4525	to make sure you link against any libraries where the C<clock_gettime>
2854	function is hiding in (often F<-lrt>).	4526	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2855		4527
2856	=item EV_USE_REALTIME	4528	=item EV_USE_REALTIME
2857		4529
2858	If defined to be C<1>, libev will try to detect the availability of the	4530	If defined to be C<1>, libev will try to detect the availability of the
2859	real-time clock option at compile time (and assume its availability at	4531	real-time clock option at compile time (and assume its availability
2860	runtime if successful). Otherwise no use of the real-time clock option will	4532	at runtime if successful). Otherwise no use of the real-time clock
2861	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	4533	option will be attempted. This effectively replaces C<gettimeofday>
2862	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	4534	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2863	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	4535	correctness. See the note about libraries in the description of
		4536	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		4537	C<EV_USE_CLOCK_SYSCALL>.
		4538
		4539	=item EV_USE_CLOCK_SYSCALL
		4540
		4541	If defined to be C<1>, libev will try to use a direct syscall instead
		4542	of calling the system-provided C<clock_gettime> function. This option
		4543	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		4544	unconditionally pulls in C<libpthread>, slowing down single-threaded
		4545	programs needlessly. Using a direct syscall is slightly slower (in
		4546	theory), because no optimised vdso implementation can be used, but avoids
		4547	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		4548	higher, as it simplifies linking (no need for C<-lrt>).
2864		4549
2865	=item EV_USE_NANOSLEEP	4550	=item EV_USE_NANOSLEEP
2866		4551
2867	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	4552	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2868	and will use it for delays. Otherwise it will use C<select ()>.	4553	and will use it for delays. Otherwise it will use C<select ()>.
…		…
2884		4569
2885	=item EV_SELECT_USE_FD_SET	4570	=item EV_SELECT_USE_FD_SET
2886		4571
2887	If defined to C<1>, then the select backend will use the system C<fd_set>	4572	If defined to C<1>, then the select backend will use the system C<fd_set>
2888	structure. This is useful if libev doesn't compile due to a missing	4573	structure. This is useful if libev doesn't compile due to a missing
2889	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on	4574	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2890	exotic systems. This usually limits the range of file descriptors to some	4575	on exotic systems. This usually limits the range of file descriptors to
2891	low limit such as 1024 or might have other limitations (winsocket only	4576	some low limit such as 1024 or might have other limitations (winsocket
2892	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	4577	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2893	influence the size of the C<fd_set> used.	4578	configures the maximum size of the C<fd_set>.
2894		4579
2895	=item EV_SELECT_IS_WINSOCKET	4580	=item EV_SELECT_IS_WINSOCKET
2896		4581
2897	When defined to C<1>, the select backend will assume that	4582	When defined to C<1>, the select backend will assume that
2898	select/socket/connect etc. don't understand file descriptors but	4583	select/socket/connect etc. don't understand file descriptors but
…		…
2900	be used is the winsock select). This means that it will call	4585	be used is the winsock select). This means that it will call
2901	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	4586	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2902	it is assumed that all these functions actually work on fds, even	4587	it is assumed that all these functions actually work on fds, even
2903	on win32. Should not be defined on non-win32 platforms.	4588	on win32. Should not be defined on non-win32 platforms.
2904		4589
2905	=item EV_FD_TO_WIN32_HANDLE	4590	=item EV_FD_TO_WIN32_HANDLE(fd)
2906		4591
2907	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map	4592	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
2908	file descriptors to socket handles. When not defining this symbol (the	4593	file descriptors to socket handles. When not defining this symbol (the
2909	default), then libev will call C<_get_osfhandle>, which is usually	4594	default), then libev will call C<_get_osfhandle>, which is usually
2910	correct. In some cases, programs use their own file descriptor management,	4595	correct. In some cases, programs use their own file descriptor management,
2911	in which case they can provide this function to map fds to socket handles.	4596	in which case they can provide this function to map fds to socket handles.
		4597
		4598	=item EV_WIN32_HANDLE_TO_FD(handle)
		4599
		4600	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		4601	using the standard C<_open_osfhandle> function. For programs implementing
		4602	their own fd to handle mapping, overwriting this function makes it easier
		4603	to do so. This can be done by defining this macro to an appropriate value.
		4604
		4605	=item EV_WIN32_CLOSE_FD(fd)
		4606
		4607	If programs implement their own fd to handle mapping on win32, then this
		4608	macro can be used to override the C<close> function, useful to unregister
		4609	file descriptors again. Note that the replacement function has to close
		4610	the underlying OS handle.
		4611
		4612	=item EV_USE_WSASOCKET
		4613
		4614	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4615	communication socket, which works better in some environments. Otherwise,
		4616	the normal C<socket> function will be used, which works better in other
		4617	environments.
2912		4618
2913	=item EV_USE_POLL	4619	=item EV_USE_POLL
2914		4620
2915	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4621	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2916	backend. Otherwise it will be enabled on non-win32 platforms. It	4622	backend. Otherwise it will be enabled on non-win32 platforms. It
…		…
2952	If defined to be C<1>, libev will compile in support for the Linux inotify	4658	If defined to be C<1>, libev will compile in support for the Linux inotify
2953	interface to speed up C<ev_stat> watchers. Its actual availability will	4659	interface to speed up C<ev_stat> watchers. Its actual availability will
2954	be detected at runtime. If undefined, it will be enabled if the headers	4660	be detected at runtime. If undefined, it will be enabled if the headers
2955	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4661	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2956		4662
		4663	=item EV_NO_SMP
		4664
		4665	If defined to be C<1>, libev will assume that memory is always coherent
		4666	between threads, that is, threads can be used, but threads never run on
		4667	different cpus (or different cpu cores). This reduces dependencies
		4668	and makes libev faster.
		4669
		4670	=item EV_NO_THREADS
		4671
		4672	If defined to be C<1>, libev will assume that it will never be called from
		4673	different threads (that includes signal handlers), which is a stronger
		4674	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4675	libev faster.
		4676
2957	=item EV_ATOMIC_T	4677	=item EV_ATOMIC_T
2958		4678
2959	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4679	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
2960	access is atomic with respect to other threads or signal contexts. No such	4680	access is atomic with respect to other threads or signal contexts. No
2961	type is easily found in the C language, so you can provide your own type	4681	such type is easily found in the C language, so you can provide your own
2962	that you know is safe for your purposes. It is used both for signal handler "locking"	4682	type that you know is safe for your purposes. It is used both for signal
2963	as well as for signal and thread safety in C<ev_async> watchers.	4683	handler "locking" as well as for signal and thread safety in C<ev_async>
		4684	watchers.
2964		4685
2965	In the absence of this define, libev will use C<sig_atomic_t volatile>	4686	In the absence of this define, libev will use C<sig_atomic_t volatile>
2966	(from F<signal.h>), which is usually good enough on most platforms.	4687	(from F<signal.h>), which is usually good enough on most platforms.
2967		4688
2968	=item EV_H	4689	=item EV_H (h)
2969		4690
2970	The name of the F<ev.h> header file used to include it. The default if	4691	The name of the F<ev.h> header file used to include it. The default if
2971	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be	4692	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2972	used to virtually rename the F<ev.h> header file in case of conflicts.	4693	used to virtually rename the F<ev.h> header file in case of conflicts.
2973		4694
2974	=item EV_CONFIG_H	4695	=item EV_CONFIG_H (h)
2975		4696
2976	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	4697	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2977	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	4698	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2978	C<EV_H>, above.	4699	C<EV_H>, above.
2979		4700
2980	=item EV_EVENT_H	4701	=item EV_EVENT_H (h)
2981		4702
2982	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	4703	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2983	of how the F<event.h> header can be found, the default is C<"event.h">.	4704	of how the F<event.h> header can be found, the default is C<"event.h">.
2984		4705
2985	=item EV_PROTOTYPES	4706	=item EV_PROTOTYPES (h)
2986		4707
2987	If defined to be C<0>, then F<ev.h> will not define any function	4708	If defined to be C<0>, then F<ev.h> will not define any function
2988	prototypes, but still define all the structs and other symbols. This is	4709	prototypes, but still define all the structs and other symbols. This is
2989	occasionally useful if you want to provide your own wrapper functions	4710	occasionally useful if you want to provide your own wrapper functions
2990	around libev functions.	4711	around libev functions.
…		…
2995	will have the C<struct ev_loop *> as first argument, and you can create	4716	will have the C<struct ev_loop *> as first argument, and you can create
2996	additional independent event loops. Otherwise there will be no support	4717	additional independent event loops. Otherwise there will be no support
2997	for multiple event loops and there is no first event loop pointer	4718	for multiple event loops and there is no first event loop pointer
2998	argument. Instead, all functions act on the single default loop.	4719	argument. Instead, all functions act on the single default loop.
2999		4720
		4721	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4722	default loop when multiplicity is switched off - you always have to
		4723	initialise the loop manually in this case.
		4724
3000	=item EV_MINPRI	4725	=item EV_MINPRI
3001		4726
3002	=item EV_MAXPRI	4727	=item EV_MAXPRI
3003		4728
3004	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4729	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
3009	When doing priority-based operations, libev usually has to linearly search	4734	When doing priority-based operations, libev usually has to linearly search
3010	all the priorities, so having many of them (hundreds) uses a lot of space	4735	all the priorities, so having many of them (hundreds) uses a lot of space
3011	and time, so using the defaults of five priorities (-2 .. +2) is usually	4736	and time, so using the defaults of five priorities (-2 .. +2) is usually
3012	fine.	4737	fine.
3013		4738
3014	If your embedding application does not need any priorities, defining these both to	4739	If your embedding application does not need any priorities, defining these
3015	C<0> will save some memory and CPU.	4740	both to C<0> will save some memory and CPU.
3016		4741
3017	=item EV_PERIODIC_ENABLE	4742	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		4743	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		4744	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
3018		4745
3019	If undefined or defined to be C<1>, then periodic timers are supported. If	4746	If undefined or defined to be C<1> (and the platform supports it), then
3020	defined to be C<0>, then they are not. Disabling them saves a few kB of	4747	the respective watcher type is supported. If defined to be C<0>, then it
3021	code.	4748	is not. Disabling watcher types mainly saves code size.
3022		4749
3023	=item EV_IDLE_ENABLE	4750	=item EV_FEATURES
3024
3025	If undefined or defined to be C<1>, then idle watchers are supported. If
3026	defined to be C<0>, then they are not. Disabling them saves a few kB of
3027	code.
3028
3029	=item EV_EMBED_ENABLE
3030
3031	If undefined or defined to be C<1>, then embed watchers are supported. If
3032	defined to be C<0>, then they are not.
3033
3034	=item EV_STAT_ENABLE
3035
3036	If undefined or defined to be C<1>, then stat watchers are supported. If
3037	defined to be C<0>, then they are not.
3038
3039	=item EV_FORK_ENABLE
3040
3041	If undefined or defined to be C<1>, then fork watchers are supported. If
3042	defined to be C<0>, then they are not.
3043
3044	=item EV_ASYNC_ENABLE
3045
3046	If undefined or defined to be C<1>, then async watchers are supported. If
3047	defined to be C<0>, then they are not.
3048
3049	=item EV_MINIMAL
3050		4751
3051	If you need to shave off some kilobytes of code at the expense of some	4752	If you need to shave off some kilobytes of code at the expense of some
3052	speed, define this symbol to C<1>. Currently this is used to override some	4753	speed (but with the full API), you can define this symbol to request
3053	inlining decisions, saves roughly 30% code size on amd64. It also selects a	4754	certain subsets of functionality. The default is to enable all features
3054	much smaller 2-heap for timer management over the default 4-heap.	4755	that can be enabled on the platform.
		4756
		4757	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4758	with some broad features you want) and then selectively re-enable
		4759	additional parts you want, for example if you want everything minimal,
		4760	but multiple event loop support, async and child watchers and the poll
		4761	backend, use this:
		4762
		4763	#define EV_FEATURES 0
		4764	#define EV_MULTIPLICITY 1
		4765	#define EV_USE_POLL 1
		4766	#define EV_CHILD_ENABLE 1
		4767	#define EV_ASYNC_ENABLE 1
		4768
		4769	The actual value is a bitset, it can be a combination of the following
		4770	values (by default, all of these are enabled):
		4771
		4772	=over 4
		4773
		4774	=item C<1> - faster/larger code
		4775
		4776	Use larger code to speed up some operations.
		4777
		4778	Currently this is used to override some inlining decisions (enlarging the
		4779	code size by roughly 30% on amd64).
		4780
		4781	When optimising for size, use of compiler flags such as C<-Os> with
		4782	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4783	assertions.
		4784
		4785	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4786	(e.g. gcc with C<-Os>).
		4787
		4788	=item C<2> - faster/larger data structures
		4789
		4790	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4791	hash table sizes and so on. This will usually further increase code size
		4792	and can additionally have an effect on the size of data structures at
		4793	runtime.
		4794
		4795	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4796	(e.g. gcc with C<-Os>).
		4797
		4798	=item C<4> - full API configuration
		4799
		4800	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4801	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4802
		4803	=item C<8> - full API
		4804
		4805	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4806	details on which parts of the API are still available without this
		4807	feature, and do not complain if this subset changes over time.
		4808
		4809	=item C<16> - enable all optional watcher types
		4810
		4811	Enables all optional watcher types. If you want to selectively enable
		4812	only some watcher types other than I/O and timers (e.g. prepare,
		4813	embed, async, child...) you can enable them manually by defining
		4814	C<EV_watchertype_ENABLE> to C<1> instead.
		4815
		4816	=item C<32> - enable all backends
		4817
		4818	This enables all backends - without this feature, you need to enable at
		4819	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4820
		4821	=item C<64> - enable OS-specific "helper" APIs
		4822
		4823	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4824	default.
		4825
		4826	=back
		4827
		4828	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4829	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4830	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4831	watchers, timers and monotonic clock support.
		4832
		4833	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4834	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4835	your program might be left out as well - a binary starting a timer and an
		4836	I/O watcher then might come out at only 5Kb.
		4837
		4838	=item EV_API_STATIC
		4839
		4840	If this symbol is defined (by default it is not), then all identifiers
		4841	will have static linkage. This means that libev will not export any
		4842	identifiers, and you cannot link against libev anymore. This can be useful
		4843	when you embed libev, only want to use libev functions in a single file,
		4844	and do not want its identifiers to be visible.
		4845
		4846	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4847	wants to use libev.
		4848
		4849	This option only works when libev is compiled with a C compiler, as C++
		4850	doesn't support the required declaration syntax.
		4851
		4852	=item EV_AVOID_STDIO
		4853
		4854	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4855	functions (printf, scanf, perror etc.). This will increase the code size
		4856	somewhat, but if your program doesn't otherwise depend on stdio and your
		4857	libc allows it, this avoids linking in the stdio library which is quite
		4858	big.
		4859
		4860	Note that error messages might become less precise when this option is
		4861	enabled.
		4862
		4863	=item EV_NSIG
		4864
		4865	The highest supported signal number, +1 (or, the number of
		4866	signals): Normally, libev tries to deduce the maximum number of signals
		4867	automatically, but sometimes this fails, in which case it can be
		4868	specified. Also, using a lower number than detected (C<32> should be
		4869	good for about any system in existence) can save some memory, as libev
		4870	statically allocates some 12-24 bytes per signal number.
3055		4871
3056	=item EV_PID_HASHSIZE	4872	=item EV_PID_HASHSIZE
3057		4873
3058	C<ev_child> watchers use a small hash table to distribute workload by	4874	C<ev_child> watchers use a small hash table to distribute workload by
3059	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	4875	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
3060	than enough. If you need to manage thousands of children you might want to	4876	usually more than enough. If you need to manage thousands of children you
3061	increase this value (I<must> be a power of two).	4877	might want to increase this value (I<must> be a power of two).
3062		4878
3063	=item EV_INOTIFY_HASHSIZE	4879	=item EV_INOTIFY_HASHSIZE
3064		4880
3065	C<ev_stat> watchers use a small hash table to distribute workload by	4881	C<ev_stat> watchers use a small hash table to distribute workload by
3066	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	4882	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
3067	usually more than enough. If you need to manage thousands of C<ev_stat>	4883	disabled), usually more than enough. If you need to manage thousands of
3068	watchers you might want to increase this value (I<must> be a power of	4884	C<ev_stat> watchers you might want to increase this value (I<must> be a
3069	two).	4885	power of two).
3070		4886
3071	=item EV_USE_4HEAP	4887	=item EV_USE_4HEAP
3072		4888
3073	Heaps are not very cache-efficient. To improve the cache-efficiency of the	4889	Heaps are not very cache-efficient. To improve the cache-efficiency of the
3074	timer and periodics heap, libev uses a 4-heap when this symbol is defined	4890	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
3075	to C<1>. The 4-heap uses more complicated (longer) code but has	4891	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
3076	noticeably faster performance with many (thousands) of watchers.	4892	faster performance with many (thousands) of watchers.
3077		4893
3078	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	4894	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3079	(disabled).	4895	will be C<0>.
3080		4896
3081	=item EV_HEAP_CACHE_AT	4897	=item EV_HEAP_CACHE_AT
3082		4898
3083	Heaps are not very cache-efficient. To improve the cache-efficiency of the	4899	Heaps are not very cache-efficient. To improve the cache-efficiency of the
3084	timer and periodics heap, libev can cache the timestamp (I<at>) within	4900	timer and periodics heaps, libev can cache the timestamp (I<at>) within
3085	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),	4901	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
3086	which uses 8-12 bytes more per watcher and a few hundred bytes more code,	4902	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
3087	but avoids random read accesses on heap changes. This improves performance	4903	but avoids random read accesses on heap changes. This improves performance
3088	noticeably with with many (hundreds) of watchers.	4904	noticeably with many (hundreds) of watchers.
3089		4905
3090	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	4906	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3091	(disabled).	4907	will be C<0>.
3092		4908
3093	=item EV_VERIFY	4909	=item EV_VERIFY
3094		4910
3095	Controls how much internal verification (see C<ev_loop_verify ()>) will	4911	Controls how much internal verification (see C<ev_verify ()>) will
3096	be done: If set to C<0>, no internal verification code will be compiled	4912	be done: If set to C<0>, no internal verification code will be compiled
3097	in. If set to C<1>, then verification code will be compiled in, but not	4913	in. If set to C<1>, then verification code will be compiled in, but not
3098	called. If set to C<2>, then the internal verification code will be	4914	called. If set to C<2>, then the internal verification code will be
3099	called once per loop, which can slow down libev. If set to C<3>, then the	4915	called once per loop, which can slow down libev. If set to C<3>, then the
3100	verification code will be called very frequently, which will slow down	4916	verification code will be called very frequently, which will slow down
3101	libev considerably.	4917	libev considerably.
3102		4918
3103	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be	4919	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3104	C<0.>	4920	will be C<0>.
3105		4921
3106	=item EV_COMMON	4922	=item EV_COMMON
3107		4923
3108	By default, all watchers have a C<void *data> member. By redefining	4924	By default, all watchers have a C<void *data> member. By redefining
3109	this macro to a something else you can include more and other types of	4925	this macro to something else you can include more and other types of
3110	members. You have to define it each time you include one of the files,	4926	members. You have to define it each time you include one of the files,
3111	though, and it must be identical each time.	4927	though, and it must be identical each time.
3112		4928
3113	For example, the perl EV module uses something like this:	4929	For example, the perl EV module uses something like this:
3114		4930
…		…
3126	and the way callbacks are invoked and set. Must expand to a struct member	4942	and the way callbacks are invoked and set. Must expand to a struct member
3127	definition and a statement, respectively. See the F<ev.h> header file for	4943	definition and a statement, respectively. See the F<ev.h> header file for
3128	their default definitions. One possible use for overriding these is to	4944	their default definitions. One possible use for overriding these is to
3129	avoid the C<struct ev_loop *> as first argument in all cases, or to use	4945	avoid the C<struct ev_loop *> as first argument in all cases, or to use
3130	method calls instead of plain function calls in C++.	4946	method calls instead of plain function calls in C++.
		4947
		4948	=back
3131		4949
3132	=head2 EXPORTED API SYMBOLS	4950	=head2 EXPORTED API SYMBOLS
3133		4951
3134	If you need to re-export the API (e.g. via a DLL) and you need a list of	4952	If you need to re-export the API (e.g. via a DLL) and you need a list of
3135	exported symbols, you can use the provided F<Symbol.*> files which list	4953	exported symbols, you can use the provided F<Symbol.*> files which list
…		…
3165	file.	4983	file.
3166		4984
3167	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	4985	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
3168	that everybody includes and which overrides some configure choices:	4986	that everybody includes and which overrides some configure choices:
3169		4987
3170	#define EV_MINIMAL 1	4988	#define EV_FEATURES 8
3171	#define EV_USE_POLL 0	4989	#define EV_USE_SELECT 1
3172	#define EV_MULTIPLICITY 0
3173	#define EV_PERIODIC_ENABLE 0	4990	#define EV_PREPARE_ENABLE 1
		4991	#define EV_IDLE_ENABLE 1
3174	#define EV_STAT_ENABLE 0	4992	#define EV_SIGNAL_ENABLE 1
3175	#define EV_FORK_ENABLE 0	4993	#define EV_CHILD_ENABLE 1
		4994	#define EV_USE_STDEXCEPT 0
3176	#define EV_CONFIG_H <config.h>	4995	#define EV_CONFIG_H <config.h>
3177	#define EV_MINPRI 0
3178	#define EV_MAXPRI 0
3179		4996
3180	#include "ev++.h"	4997	#include "ev++.h"
3181		4998
3182	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4999	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
3183		5000
3184	#include "ev_cpp.h"	5001	#include "ev_cpp.h"
3185	#include "ev.c"	5002	#include "ev.c"
3186		5003
		5004	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
3187		5005
3188	=head1 THREADS AND COROUTINES	5006	=head2 THREADS AND COROUTINES
3189		5007
3190	=head2 THREADS	5008	=head3 THREADS
3191		5009
3192	Libev itself is completely thread-safe, but it uses no locking. This	5010	All libev functions are reentrant and thread-safe unless explicitly
		5011	documented otherwise, but libev implements no locking itself. This means
3193	means that you can use as many loops as you want in parallel, as long as	5012	that you can use as many loops as you want in parallel, as long as there
3194	only one thread ever calls into one libev function with the same loop	5013	are no concurrent calls into any libev function with the same loop
3195	parameter.	5014	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		5015	of course): libev guarantees that different event loops share no data
		5016	structures that need any locking.
3196		5017
3197	Or put differently: calls with different loop parameters can be done in	5018	Or to put it differently: calls with different loop parameters can be done
3198	parallel from multiple threads, calls with the same loop parameter must be	5019	concurrently from multiple threads, calls with the same loop parameter
3199	done serially (but can be done from different threads, as long as only one	5020	must be done serially (but can be done from different threads, as long as
3200	thread ever is inside a call at any point in time, e.g. by using a mutex	5021	only one thread ever is inside a call at any point in time, e.g. by using
3201	per loop).	5022	a mutex per loop).
		5023
		5024	Specifically to support threads (and signal handlers), libev implements
		5025	so-called C<ev_async> watchers, which allow some limited form of
		5026	concurrency on the same event loop, namely waking it up "from the
		5027	outside".
3202		5028
3203	If you want to know which design (one loop, locking, or multiple loops	5029	If you want to know which design (one loop, locking, or multiple loops
3204	without or something else still) is best for your problem, then I cannot	5030	without or something else still) is best for your problem, then I cannot
3205	help you. I can give some generic advice however:	5031	help you, but here is some generic advice:
3206		5032
3207	=over 4	5033	=over 4
3208		5034
3209	=item * most applications have a main thread: use the default libev loop	5035	=item * most applications have a main thread: use the default libev loop
3210	in that thread, or create a separate thread running only the default loop.	5036	in that thread, or create a separate thread running only the default loop.
…		…
3222		5048
3223	Choosing a model is hard - look around, learn, know that usually you can do	5049	Choosing a model is hard - look around, learn, know that usually you can do
3224	better than you currently do :-)	5050	better than you currently do :-)
3225		5051
3226	=item * often you need to talk to some other thread which blocks in the	5052	=item * often you need to talk to some other thread which blocks in the
		5053	event loop.
		5054
3227	event loop - C<ev_async> watchers can be used to wake them up from other	5055	C<ev_async> watchers can be used to wake them up from other threads safely
3228	threads safely (or from signal contexts...).	5056	(or from signal contexts...).
		5057
		5058	An example use would be to communicate signals or other events that only
		5059	work in the default loop by registering the signal watcher with the
		5060	default loop and triggering an C<ev_async> watcher from the default loop
		5061	watcher callback into the event loop interested in the signal.
3229		5062
3230	=back	5063	=back
3231		5064
		5065	See also L</THREAD LOCKING EXAMPLE>.
		5066
3232	=head2 COROUTINES	5067	=head3 COROUTINES
3233		5068
3234	Libev is much more accommodating to coroutines ("cooperative threads"):	5069	Libev is very accommodating to coroutines ("cooperative threads"):
3235	libev fully supports nesting calls to it's functions from different	5070	libev fully supports nesting calls to its functions from different
3236	coroutines (e.g. you can call C<ev_loop> on the same loop from two	5071	coroutines (e.g. you can call C<ev_run> on the same loop from two
3237	different coroutines and switch freely between both coroutines running the	5072	different coroutines, and switch freely between both coroutines running
3238	loop, as long as you don't confuse yourself). The only exception is that	5073	the loop, as long as you don't confuse yourself). The only exception is
3239	you must not do this from C<ev_periodic> reschedule callbacks.	5074	that you must not do this from C<ev_periodic> reschedule callbacks.
3240		5075
3241	Care has been invested into making sure that libev does not keep local	5076	Care has been taken to ensure that libev does not keep local state inside
3242	state inside C<ev_loop>, and other calls do not usually allow coroutine	5077	C<ev_run>, and other calls do not usually allow for coroutine switches as
3243	switches.	5078	they do not call any callbacks.
3244		5079
		5080	=head2 COMPILER WARNINGS
3245		5081
3246	=head1 COMPLEXITIES	5082	Depending on your compiler and compiler settings, you might get no or a
		5083	lot of warnings when compiling libev code. Some people are apparently
		5084	scared by this.
3247		5085
3248	In this section the complexities of (many of) the algorithms used inside	5086	However, these are unavoidable for many reasons. For one, each compiler
3249	libev will be explained. For complexity discussions about backends see the	5087	has different warnings, and each user has different tastes regarding
3250	documentation for C<ev_default_init>.	5088	warning options. "Warn-free" code therefore cannot be a goal except when
		5089	targeting a specific compiler and compiler-version.
3251		5090
3252	All of the following are about amortised time: If an array needs to be	5091	Another reason is that some compiler warnings require elaborate
3253	extended, libev needs to realloc and move the whole array, but this	5092	workarounds, or other changes to the code that make it less clear and less
3254	happens asymptotically never with higher number of elements, so O(1) might	5093	maintainable.
3255	mean it might do a lengthy realloc operation in rare cases, but on average
3256	it is much faster and asymptotically approaches constant time.
3257		5094
3258	=over 4	5095	And of course, some compiler warnings are just plain stupid, or simply
		5096	wrong (because they don't actually warn about the condition their message
		5097	seems to warn about). For example, certain older gcc versions had some
		5098	warnings that resulted in an extreme number of false positives. These have
		5099	been fixed, but some people still insist on making code warn-free with
		5100	such buggy versions.
3259		5101
3260	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	5102	While libev is written to generate as few warnings as possible,
		5103	"warn-free" code is not a goal, and it is recommended not to build libev
		5104	with any compiler warnings enabled unless you are prepared to cope with
		5105	them (e.g. by ignoring them). Remember that warnings are just that:
		5106	warnings, not errors, or proof of bugs.
3261		5107
3262	This means that, when you have a watcher that triggers in one hour and
3263	there are 100 watchers that would trigger before that then inserting will
3264	have to skip roughly seven (C<ld 100>) of these watchers.
3265		5108
3266	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)	5109	=head2 VALGRIND
3267		5110
3268	That means that changing a timer costs less than removing/adding them	5111	Valgrind has a special section here because it is a popular tool that is
3269	as only the relative motion in the event queue has to be paid for.	5112	highly useful. Unfortunately, valgrind reports are very hard to interpret.
3270		5113
3271	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)	5114	If you think you found a bug (memory leak, uninitialised data access etc.)
		5115	in libev, then check twice: If valgrind reports something like:
3272		5116
3273	These just add the watcher into an array or at the head of a list.	5117	==2274== definitely lost: 0 bytes in 0 blocks.
		5118	==2274== possibly lost: 0 bytes in 0 blocks.
		5119	==2274== still reachable: 256 bytes in 1 blocks.
3274		5120
3275	=item Stopping check/prepare/idle/fork/async watchers: O(1)	5121	Then there is no memory leak, just as memory accounted to global variables
		5122	is not a memleak - the memory is still being referenced, and didn't leak.
3276		5123
3277	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	5124	Similarly, under some circumstances, valgrind might report kernel bugs
		5125	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		5126	although an acceptable workaround has been found here), or it might be
		5127	confused.
3278		5128
3279	These watchers are stored in lists then need to be walked to find the	5129	Keep in mind that valgrind is a very good tool, but only a tool. Don't
3280	correct watcher to remove. The lists are usually short (you don't usually	5130	make it into some kind of religion.
3281	have many watchers waiting for the same fd or signal).
3282		5131
3283	=item Finding the next timer in each loop iteration: O(1)	5132	If you are unsure about something, feel free to contact the mailing list
		5133	with the full valgrind report and an explanation on why you think this
		5134	is a bug in libev (best check the archives, too :). However, don't be
		5135	annoyed when you get a brisk "this is no bug" answer and take the chance
		5136	of learning how to interpret valgrind properly.
3284		5137
3285	By virtue of using a binary or 4-heap, the next timer is always found at a	5138	If you need, for some reason, empty reports from valgrind for your project
3286	fixed position in the storage array.	5139	I suggest using suppression lists.
3287		5140
3288	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
3289		5141
3290	A change means an I/O watcher gets started or stopped, which requires	5142	=head1 PORTABILITY NOTES
3291	libev to recalculate its status (and possibly tell the kernel, depending
3292	on backend and whether C<ev_io_set> was used).
3293		5143
3294	=item Activating one watcher (putting it into the pending state): O(1)	5144	=head2 GNU/LINUX 32 BIT LIMITATIONS
3295		5145
3296	=item Priority handling: O(number_of_priorities)	5146	GNU/Linux is the only common platform that supports 64 bit file/large file
		5147	interfaces but I<disables> them by default.
3297		5148
3298	Priorities are implemented by allocating some space for each	5149	That means that libev compiled in the default environment doesn't support
3299	priority. When doing priority-based operations, libev usually has to	5150	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
3300	linearly search all the priorities, but starting/stopping and activating
3301	watchers becomes O(1) w.r.t. priority handling.
3302		5151
3303	=item Sending an ev_async: O(1)	5152	Unfortunately, many programs try to work around this GNU/Linux issue
		5153	by enabling the large file API, which makes them incompatible with the
		5154	standard libev compiled for their system.
3304		5155
3305	=item Processing ev_async_send: O(number_of_async_watchers)	5156	Likewise, libev cannot enable the large file API itself as this would
		5157	suddenly make it incompatible to the default compile time environment,
		5158	i.e. all programs not using special compile switches.
3306		5159
3307	=item Processing signals: O(max_signal_number)	5160	=head2 OS/X AND DARWIN BUGS
3308		5161
3309	Sending involves a system call I<iff> there were no other C<ev_async_send>	5162	The whole thing is a bug if you ask me - basically any system interface
3310	calls in the current loop iteration. Checking for async and signal events	5163	you touch is broken, whether it is locales, poll, kqueue or even the
3311	involves iterating over all running async watchers or all signal numbers.	5164	OpenGL drivers.
3312		5165
3313	=back	5166	=head3 C<kqueue> is buggy
3314		5167
		5168	The kqueue syscall is broken in all known versions - most versions support
		5169	only sockets, many support pipes.
3315		5170
		5171	Libev tries to work around this by not using C<kqueue> by default on this
		5172	rotten platform, but of course you can still ask for it when creating a
		5173	loop - embedding a socket-only kqueue loop into a select-based one is
		5174	probably going to work well.
		5175
		5176	=head3 C<poll> is buggy
		5177
		5178	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		5179	implementation by something calling C<kqueue> internally around the 10.5.6
		5180	release, so now C<kqueue> I<and> C<poll> are broken.
		5181
		5182	Libev tries to work around this by not using C<poll> by default on
		5183	this rotten platform, but of course you can still ask for it when creating
		5184	a loop.
		5185
		5186	=head3 C<select> is buggy
		5187
		5188	All that's left is C<select>, and of course Apple found a way to fuck this
		5189	one up as well: On OS/X, C<select> actively limits the number of file
		5190	descriptors you can pass in to 1024 - your program suddenly crashes when
		5191	you use more.
		5192
		5193	There is an undocumented "workaround" for this - defining
		5194	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		5195	work on OS/X.
		5196
		5197	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		5198
		5199	=head3 C<errno> reentrancy
		5200
		5201	The default compile environment on Solaris is unfortunately so
		5202	thread-unsafe that you can't even use components/libraries compiled
		5203	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		5204	defined by default. A valid, if stupid, implementation choice.
		5205
		5206	If you want to use libev in threaded environments you have to make sure
		5207	it's compiled with C<_REENTRANT> defined.
		5208
		5209	=head3 Event port backend
		5210
		5211	The scalable event interface for Solaris is called "event
		5212	ports". Unfortunately, this mechanism is very buggy in all major
		5213	releases. If you run into high CPU usage, your program freezes or you get
		5214	a large number of spurious wakeups, make sure you have all the relevant
		5215	and latest kernel patches applied. No, I don't know which ones, but there
		5216	are multiple ones to apply, and afterwards, event ports actually work
		5217	great.
		5218
		5219	If you can't get it to work, you can try running the program by setting
		5220	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		5221	C<select> backends.
		5222
		5223	=head2 AIX POLL BUG
		5224
		5225	AIX unfortunately has a broken C<poll.h> header. Libev works around
		5226	this by trying to avoid the poll backend altogether (i.e. it's not even
		5227	compiled in), which normally isn't a big problem as C<select> works fine
		5228	with large bitsets on AIX, and AIX is dead anyway.
		5229
3316	=head1 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS	5230	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		5231
		5232	=head3 General issues
3317		5233
3318	Win32 doesn't support any of the standards (e.g. POSIX) that libev	5234	Win32 doesn't support any of the standards (e.g. POSIX) that libev
3319	requires, and its I/O model is fundamentally incompatible with the POSIX	5235	requires, and its I/O model is fundamentally incompatible with the POSIX
3320	model. Libev still offers limited functionality on this platform in	5236	model. Libev still offers limited functionality on this platform in
3321	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5237	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
3322	descriptors. This only applies when using Win32 natively, not when using	5238	descriptors. This only applies when using Win32 natively, not when using
3323	e.g. cygwin.	5239	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		5240	as every compiler comes with a slightly differently broken/incompatible
		5241	environment.
3324		5242
3325	Lifting these limitations would basically require the full	5243	Lifting these limitations would basically require the full
3326	re-implementation of the I/O system. If you are into these kinds of	5244	re-implementation of the I/O system. If you are into this kind of thing,
3327	things, then note that glib does exactly that for you in a very portable	5245	then note that glib does exactly that for you in a very portable way (note
3328	way (note also that glib is the slowest event library known to man).	5246	also that glib is the slowest event library known to man).
3329		5247
3330	There is no supported compilation method available on windows except	5248	There is no supported compilation method available on windows except
3331	embedding it into other applications.	5249	embedding it into other applications.
		5250
		5251	Sensible signal handling is officially unsupported by Microsoft - libev
		5252	tries its best, but under most conditions, signals will simply not work.
3332		5253
3333	Not a libev limitation but worth mentioning: windows apparently doesn't	5254	Not a libev limitation but worth mentioning: windows apparently doesn't
3334	accept large writes: instead of resulting in a partial write, windows will	5255	accept large writes: instead of resulting in a partial write, windows will
3335	either accept everything or return C<ENOBUFS> if the buffer is too large,	5256	either accept everything or return C<ENOBUFS> if the buffer is too large,
3336	so make sure you only write small amounts into your sockets (less than a	5257	so make sure you only write small amounts into your sockets (less than a
3337	megabyte seems safe, but thsi apparently depends on the amount of memory	5258	megabyte seems safe, but this apparently depends on the amount of memory
3338	available).	5259	available).
3339		5260
3340	Due to the many, low, and arbitrary limits on the win32 platform and	5261	Due to the many, low, and arbitrary limits on the win32 platform and
3341	the abysmal performance of winsockets, using a large number of sockets	5262	the abysmal performance of winsockets, using a large number of sockets
3342	is not recommended (and not reasonable). If your program needs to use	5263	is not recommended (and not reasonable). If your program needs to use
3343	more than a hundred or so sockets, then likely it needs to use a totally	5264	more than a hundred or so sockets, then likely it needs to use a totally
3344	different implementation for windows, as libev offers the POSIX readiness	5265	different implementation for windows, as libev offers the POSIX readiness
3345	notification model, which cannot be implemented efficiently on windows	5266	notification model, which cannot be implemented efficiently on windows
3346	(Microsoft monopoly games).	5267	(due to Microsoft monopoly games).
3347		5268
3348	A typical way to use libev under windows is to embed it (see the embedding	5269	A typical way to use libev under windows is to embed it (see the embedding
3349	section for details) and use the following F<evwrap.h> header file instead	5270	section for details) and use the following F<evwrap.h> header file instead
3350	of F<ev.h>:	5271	of F<ev.h>:
3351		5272
…		…
3353	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */	5274	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
3354		5275
3355	#include "ev.h"	5276	#include "ev.h"
3356		5277
3357	And compile the following F<evwrap.c> file into your project (make sure	5278	And compile the following F<evwrap.c> file into your project (make sure
3358	you do I<not> compile the F<ev.c> or any other embedded soruce files!):	5279	you do I<not> compile the F<ev.c> or any other embedded source files!):
3359		5280
3360	#include "evwrap.h"	5281	#include "evwrap.h"
3361	#include "ev.c"	5282	#include "ev.c"
3362		5283
3363	=over 4
3364
3365	=item The winsocket select function	5284	=head3 The winsocket C<select> function
3366		5285
3367	The winsocket C<select> function doesn't follow POSIX in that it	5286	The winsocket C<select> function doesn't follow POSIX in that it
3368	requires socket I<handles> and not socket I<file descriptors> (it is	5287	requires socket I<handles> and not socket I<file descriptors> (it is
3369	also extremely buggy). This makes select very inefficient, and also	5288	also extremely buggy). This makes select very inefficient, and also
3370	requires a mapping from file descriptors to socket handles (the Microsoft	5289	requires a mapping from file descriptors to socket handles (the Microsoft
…		…
3379	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */	5298	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
3380		5299
3381	Note that winsockets handling of fd sets is O(n), so you can easily get a	5300	Note that winsockets handling of fd sets is O(n), so you can easily get a
3382	complexity in the O(n²) range when using win32.	5301	complexity in the O(n²) range when using win32.
3383		5302
3384	=item Limited number of file descriptors	5303	=head3 Limited number of file descriptors
3385		5304
3386	Windows has numerous arbitrary (and low) limits on things.	5305	Windows has numerous arbitrary (and low) limits on things.
3387		5306
3388	Early versions of winsocket's select only supported waiting for a maximum	5307	Early versions of winsocket's select only supported waiting for a maximum
3389	of C<64> handles (probably owning to the fact that all windows kernels	5308	of C<64> handles (probably owning to the fact that all windows kernels
3390	can only wait for C<64> things at the same time internally; Microsoft	5309	can only wait for C<64> things at the same time internally; Microsoft
3391	recommends spawning a chain of threads and wait for 63 handles and the	5310	recommends spawning a chain of threads and wait for 63 handles and the
3392	previous thread in each. Great).	5311	previous thread in each. Sounds great!).
3393		5312
3394	Newer versions support more handles, but you need to define C<FD_SETSIZE>	5313	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3395	to some high number (e.g. C<2048>) before compiling the winsocket select	5314	to some high number (e.g. C<2048>) before compiling the winsocket select
3396	call (which might be in libev or elsewhere, for example, perl does its own	5315	call (which might be in libev or elsewhere, for example, perl and many
3397	select emulation on windows).	5316	other interpreters do their own select emulation on windows).
3398		5317
3399	Another limit is the number of file descriptors in the Microsoft runtime	5318	Another limit is the number of file descriptors in the Microsoft runtime
3400	libraries, which by default is C<64> (there must be a hidden I<64> fetish	5319	libraries, which by default is C<64> (there must be a hidden I<64>
3401	or something like this inside Microsoft). You can increase this by calling	5320	fetish or something like this inside Microsoft). You can increase this
3402	C<_setmaxstdio>, which can increase this limit to C<2048> (another	5321	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
3403	arbitrary limit), but is broken in many versions of the Microsoft runtime	5322	(another arbitrary limit), but is broken in many versions of the Microsoft
3404	libraries.
3405
3406	This might get you to about C<512> or C<2048> sockets (depending on	5323	runtime libraries. This might get you to about C<512> or C<2048> sockets
3407	windows version and/or the phase of the moon). To get more, you need to	5324	(depending on windows version and/or the phase of the moon). To get more,
3408	wrap all I/O functions and provide your own fd management, but the cost of	5325	you need to wrap all I/O functions and provide your own fd management, but
3409	calling select (O(n²)) will likely make this unworkable.	5326	the cost of calling select (O(n²)) will likely make this unworkable.
3410		5327
3411	=back
3412
3413
3414	=head1 PORTABILITY REQUIREMENTS	5328	=head2 PORTABILITY REQUIREMENTS
3415		5329
3416	In addition to a working ISO-C implementation, libev relies on a few	5330	In addition to a working ISO-C implementation and of course the
3417	additional extensions:	5331	backend-specific APIs, libev relies on a few additional extensions:
3418		5332
3419	=over 4	5333	=over 4
3420		5334
3421	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible	5335	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
3422	calling conventions regardless of C<ev_watcher_type *>.	5336	calling conventions regardless of C<ev_watcher_type *>.
…		…
3425	structure (guaranteed by POSIX but not by ISO C for example), but it also	5339	structure (guaranteed by POSIX but not by ISO C for example), but it also
3426	assumes that the same (machine) code can be used to call any watcher	5340	assumes that the same (machine) code can be used to call any watcher
3427	callback: The watcher callbacks have different type signatures, but libev	5341	callback: The watcher callbacks have different type signatures, but libev
3428	calls them using an C<ev_watcher *> internally.	5342	calls them using an C<ev_watcher *> internally.
3429		5343
		5344	=item null pointers and integer zero are represented by 0 bytes
		5345
		5346	Libev uses C<memset> to initialise structs and arrays to C<0> bytes, and
		5347	relies on this setting pointers and integers to null.
		5348
		5349	=item pointer accesses must be thread-atomic
		5350
		5351	Accessing a pointer value must be atomic, it must both be readable and
		5352	writable in one piece - this is the case on all current architectures.
		5353
3430	=item C<sig_atomic_t volatile> must be thread-atomic as well	5354	=item C<sig_atomic_t volatile> must be thread-atomic as well
3431		5355
3432	The type C<sig_atomic_t volatile> (or whatever is defined as	5356	The type C<sig_atomic_t volatile> (or whatever is defined as
3433	C<EV_ATOMIC_T>) must be atomic w.r.t. accesses from different	5357	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
3434	threads. This is not part of the specification for C<sig_atomic_t>, but is	5358	threads. This is not part of the specification for C<sig_atomic_t>, but is
3435	believed to be sufficiently portable.	5359	believed to be sufficiently portable.
3436		5360
3437	=item C<sigprocmask> must work in a threaded environment	5361	=item C<sigprocmask> must work in a threaded environment
3438		5362
…		…
3442	thread" or will block signals process-wide, both behaviours would	5366	thread" or will block signals process-wide, both behaviours would
3443	be compatible with libev. Interaction between C<sigprocmask> and	5367	be compatible with libev. Interaction between C<sigprocmask> and
3444	C<pthread_sigmask> could complicate things, however.	5368	C<pthread_sigmask> could complicate things, however.
3445		5369
3446	The most portable way to handle signals is to block signals in all threads	5370	The most portable way to handle signals is to block signals in all threads
3447	except the initial one, and run the default loop in the initial thread as	5371	except the initial one, and run the signal handling loop in the initial
3448	well.	5372	thread as well.
3449		5373
3450	=item C<long> must be large enough for common memory allocation sizes	5374	=item C<long> must be large enough for common memory allocation sizes
3451		5375
3452	To improve portability and simplify using libev, libev uses C<long>	5376	To improve portability and simplify its API, libev uses C<long> internally
3453	internally instead of C<size_t> when allocating its data structures. On	5377	instead of C<size_t> when allocating its data structures. On non-POSIX
3454	non-POSIX systems (Microsoft...) this might be unexpectedly low, but	5378	systems (Microsoft...) this might be unexpectedly low, but is still at
3455	is still at least 31 bits everywhere, which is enough for hundreds of	5379	least 31 bits everywhere, which is enough for hundreds of millions of
3456	millions of watchers.	5380	watchers.
3457		5381
3458	=item C<double> must hold a time value in seconds with enough accuracy	5382	=item C<double> must hold a time value in seconds with enough accuracy
3459		5383
3460	The type C<double> is used to represent timestamps. It is required to	5384	The type C<double> is used to represent timestamps. It is required to
3461	have at least 51 bits of mantissa (and 9 bits of exponent), which is good	5385	have at least 51 bits of mantissa (and 9 bits of exponent), which is
3462	enough for at least into the year 4000. This requirement is fulfilled by	5386	good enough for at least into the year 4000 with millisecond accuracy
		5387	(the design goal for libev). This requirement is overfulfilled by
3463	implementations implementing IEEE 754 (basically all existing ones).	5388	implementations using IEEE 754, which is basically all existing ones.
		5389
		5390	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5391	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5392	is either obsolete or somebody patched it to use C<long double> or
		5393	something like that, just kidding).
3464		5394
3465	=back	5395	=back
3466		5396
3467	If you know of other additional requirements drop me a note.	5397	If you know of other additional requirements drop me a note.
3468		5398
3469		5399
3470	=head1 COMPILER WARNINGS	5400	=head1 ALGORITHMIC COMPLEXITIES
3471		5401
3472	Depending on your compiler and compiler settings, you might get no or a	5402	In this section the complexities of (many of) the algorithms used inside
3473	lot of warnings when compiling libev code. Some people are apparently	5403	libev will be documented. For complexity discussions about backends see
3474	scared by this.	5404	the documentation for C<ev_default_init>.
3475		5405
3476	However, these are unavoidable for many reasons. For one, each compiler	5406	All of the following are about amortised time: If an array needs to be
3477	has different warnings, and each user has different tastes regarding	5407	extended, libev needs to realloc and move the whole array, but this
3478	warning options. "Warn-free" code therefore cannot be a goal except when	5408	happens asymptotically rarer with higher number of elements, so O(1) might
3479	targeting a specific compiler and compiler-version.	5409	mean that libev does a lengthy realloc operation in rare cases, but on
		5410	average it is much faster and asymptotically approaches constant time.
3480		5411
3481	Another reason is that some compiler warnings require elaborate	5412	=over 4
3482	workarounds, or other changes to the code that make it less clear and less
3483	maintainable.
3484		5413
3485	And of course, some compiler warnings are just plain stupid, or simply	5414	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
3486	wrong (because they don't actually warn about the condition their message
3487	seems to warn about).
3488		5415
3489	While libev is written to generate as few warnings as possible,	5416	This means that, when you have a watcher that triggers in one hour and
3490	"warn-free" code is not a goal, and it is recommended not to build libev	5417	there are 100 watchers that would trigger before that, then inserting will
3491	with any compiler warnings enabled unless you are prepared to cope with	5418	have to skip roughly seven (C<ld 100>) of these watchers.
3492	them (e.g. by ignoring them). Remember that warnings are just that:
3493	warnings, not errors, or proof of bugs.
3494		5419
		5420	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
3495		5421
3496	=head1 VALGRIND	5422	That means that changing a timer costs less than removing/adding them,
		5423	as only the relative motion in the event queue has to be paid for.
3497		5424
3498	Valgrind has a special section here because it is a popular tool that is	5425	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
3499	highly useful, but valgrind reports are very hard to interpret.
3500		5426
3501	If you think you found a bug (memory leak, uninitialised data access etc.)	5427	These just add the watcher into an array or at the head of a list.
3502	in libev, then check twice: If valgrind reports something like:
3503		5428
3504	==2274== definitely lost: 0 bytes in 0 blocks.	5429	=item Stopping check/prepare/idle/fork/async watchers: O(1)
3505	==2274== possibly lost: 0 bytes in 0 blocks.
3506	==2274== still reachable: 256 bytes in 1 blocks.
3507		5430
3508	Then there is no memory leak. Similarly, under some circumstances,	5431	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
3509	valgrind might report kernel bugs as if it were a bug in libev, or it
3510	might be confused (it is a very good tool, but only a tool).
3511		5432
3512	If you are unsure about something, feel free to contact the mailing list	5433	These watchers are stored in lists, so they need to be walked to find the
3513	with the full valgrind report and an explanation on why you think this is	5434	correct watcher to remove. The lists are usually short (you don't usually
3514	a bug in libev. However, don't be annoyed when you get a brisk "this is	5435	have many watchers waiting for the same fd or signal: one is typical, two
3515	no bug" answer and take the chance of learning how to interpret valgrind	5436	is rare).
3516	properly.
3517		5437
3518	If you need, for some reason, empty reports from valgrind for your project	5438	=item Finding the next timer in each loop iteration: O(1)
3519	I suggest using suppression lists.
3520		5439
		5440	By virtue of using a binary or 4-heap, the next timer is always found at a
		5441	fixed position in the storage array.
		5442
		5443	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		5444
		5445	A change means an I/O watcher gets started or stopped, which requires
		5446	libev to recalculate its status (and possibly tell the kernel, depending
		5447	on backend and whether C<ev_io_set> was used).
		5448
		5449	=item Activating one watcher (putting it into the pending state): O(1)
		5450
		5451	=item Priority handling: O(number_of_priorities)
		5452
		5453	Priorities are implemented by allocating some space for each
		5454	priority. When doing priority-based operations, libev usually has to
		5455	linearly search all the priorities, but starting/stopping and activating
		5456	watchers becomes O(1) with respect to priority handling.
		5457
		5458	=item Sending an ev_async: O(1)
		5459
		5460	=item Processing ev_async_send: O(number_of_async_watchers)
		5461
		5462	=item Processing signals: O(max_signal_number)
		5463
		5464	Sending involves a system call I<iff> there were no other C<ev_async_send>
		5465	calls in the current loop iteration and the loop is currently
		5466	blocked. Checking for async and signal events involves iterating over all
		5467	running async watchers or all signal numbers.
		5468
		5469	=back
		5470
		5471
		5472	=head1 PORTING FROM LIBEV 3.X TO 4.X
		5473
		5474	The major version 4 introduced some incompatible changes to the API.
		5475
		5476	At the moment, the C<ev.h> header file provides compatibility definitions
		5477	for all changes, so most programs should still compile. The compatibility
		5478	layer might be removed in later versions of libev, so better update to the
		5479	new API early than late.
		5480
		5481	=over 4
		5482
		5483	=item C<EV_COMPAT3> backwards compatibility mechanism
		5484
		5485	The backward compatibility mechanism can be controlled by
		5486	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
		5487	section.
		5488
		5489	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5490
		5491	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5492
		5493	ev_loop_destroy (EV_DEFAULT_UC);
		5494	ev_loop_fork (EV_DEFAULT);
		5495
		5496	=item function/symbol renames
		5497
		5498	A number of functions and symbols have been renamed:
		5499
		5500	ev_loop => ev_run
		5501	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		5502	EVLOOP_ONESHOT => EVRUN_ONCE
		5503
		5504	ev_unloop => ev_break
		5505	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		5506	EVUNLOOP_ONE => EVBREAK_ONE
		5507	EVUNLOOP_ALL => EVBREAK_ALL
		5508
		5509	EV_TIMEOUT => EV_TIMER
		5510
		5511	ev_loop_count => ev_iteration
		5512	ev_loop_depth => ev_depth
		5513	ev_loop_verify => ev_verify
		5514
		5515	Most functions working on C<struct ev_loop> objects don't have an
		5516	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		5517	associated constants have been renamed to not collide with the C<struct
		5518	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		5519	as all other watcher types. Note that C<ev_loop_fork> is still called
		5520	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		5521	typedef.
		5522
		5523	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		5524
		5525	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		5526	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		5527	and work, but the library code will of course be larger.
		5528
		5529	=back
		5530
		5531
		5532	=head1 GLOSSARY
		5533
		5534	=over 4
		5535
		5536	=item active
		5537
		5538	A watcher is active as long as it has been started and not yet stopped.
		5539	See L</WATCHER STATES> for details.
		5540
		5541	=item application
		5542
		5543	In this document, an application is whatever is using libev.
		5544
		5545	=item backend
		5546
		5547	The part of the code dealing with the operating system interfaces.
		5548
		5549	=item callback
		5550
		5551	The address of a function that is called when some event has been
		5552	detected. Callbacks are being passed the event loop, the watcher that
		5553	received the event, and the actual event bitset.
		5554
		5555	=item callback/watcher invocation
		5556
		5557	The act of calling the callback associated with a watcher.
		5558
		5559	=item event
		5560
		5561	A change of state of some external event, such as data now being available
		5562	for reading on a file descriptor, time having passed or simply not having
		5563	any other events happening anymore.
		5564
		5565	In libev, events are represented as single bits (such as C<EV_READ> or
		5566	C<EV_TIMER>).
		5567
		5568	=item event library
		5569
		5570	A software package implementing an event model and loop.
		5571
		5572	=item event loop
		5573
		5574	An entity that handles and processes external events and converts them
		5575	into callback invocations.
		5576
		5577	=item event model
		5578
		5579	The model used to describe how an event loop handles and processes
		5580	watchers and events.
		5581
		5582	=item pending
		5583
		5584	A watcher is pending as soon as the corresponding event has been
		5585	detected. See L</WATCHER STATES> for details.
		5586
		5587	=item real time
		5588
		5589	The physical time that is observed. It is apparently strictly monotonic :)
		5590
		5591	=item wall-clock time
		5592
		5593	The time and date as shown on clocks. Unlike real time, it can actually
		5594	be wrong and jump forwards and backwards, e.g. when you adjust your
		5595	clock.
		5596
		5597	=item watcher
		5598
		5599	A data structure that describes interest in certain events. Watchers need
		5600	to be started (attached to an event loop) before they can receive events.
		5601
		5602	=back
3521		5603
3522	=head1 AUTHOR	5604	=head1 AUTHOR
3523		5605
3524	Marc Lehmann <libev@schmorp.de>.	5606	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5607	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
3525		5608

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