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Revision 1.159 by root, Thu May 22 02:44:57 2008 UTC vs.
Revision 1.406 by root, Thu May 3 16:00:47 2012 UTC

…		…
2		2
3	libev - a high performance full-featured event loop written in C	3	libev - a high performance full-featured event loop written in C
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
8		8
9	=head2 EXAMPLE PROGRAM	9	=head2 EXAMPLE PROGRAM
10		10
11	// a single header file is required	11	// a single header file is required
12	#include <ev.h>	12	#include <ev.h>
13		13
		14	#include <stdio.h> // for puts
		15
14	// every watcher type has its own typedef'd struct	16	// every watcher type has its own typedef'd struct
15	// with the name ev_<type>	17	// with the name ev_TYPE
16	ev_io stdin_watcher;	18	ev_io stdin_watcher;
17	ev_timer timeout_watcher;	19	ev_timer timeout_watcher;
18		20
19	// all watcher callbacks have a similar signature	21	// all watcher callbacks have a similar signature
20	// this callback is called when data is readable on stdin	22	// this callback is called when data is readable on stdin
21	static void	23	static void
22	stdin_cb (EV_P_ struct ev_io *w, int revents)	24	stdin_cb (EV_P_ ev_io *w, int revents)
23	{	25	{
24	puts ("stdin ready");	26	puts ("stdin ready");
25	// for one-shot events, one must manually stop the watcher	27	// for one-shot events, one must manually stop the watcher
26	// with its corresponding stop function.	28	// with its corresponding stop function.
27	ev_io_stop (EV_A_ w);	29	ev_io_stop (EV_A_ w);
28		30
29	// this causes all nested ev_loop's to stop iterating	31	// this causes all nested ev_run's to stop iterating
30	ev_unloop (EV_A_ EVUNLOOP_ALL);	32	ev_break (EV_A_ EVBREAK_ALL);
31	}	33	}
32		34
33	// another callback, this time for a time-out	35	// another callback, this time for a time-out
34	static void	36	static void
35	timeout_cb (EV_P_ struct ev_timer *w, int revents)	37	timeout_cb (EV_P_ ev_timer *w, int revents)
36	{	38	{
37	puts ("timeout");	39	puts ("timeout");
38	// this causes the innermost ev_loop to stop iterating	40	// this causes the innermost ev_run to stop iterating
39	ev_unloop (EV_A_ EVUNLOOP_ONE);	41	ev_break (EV_A_ EVBREAK_ONE);
40	}	42	}
41		43
42	int	44	int
43	main (void)	45	main (void)
44	{	46	{
45	// use the default event loop unless you have special needs	47	// use the default event loop unless you have special needs
46	struct ev_loop *loop = ev_default_loop (0);	48	struct ev_loop *loop = EV_DEFAULT;
47		49
48	// initialise an io watcher, then start it	50	// initialise an io watcher, then start it
49	// this one will watch for stdin to become readable	51	// this one will watch for stdin to become readable
50	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
51	ev_io_start (loop, &stdin_watcher);	53	ev_io_start (loop, &stdin_watcher);
52		54
53	// initialise a timer watcher, then start it	55	// initialise a timer watcher, then start it
54	// simple non-repeating 5.5 second timeout	56	// simple non-repeating 5.5 second timeout
55	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);	57	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
56	ev_timer_start (loop, &timeout_watcher);	58	ev_timer_start (loop, &timeout_watcher);
57		59
58	// now wait for events to arrive	60	// now wait for events to arrive
59	ev_loop (loop, 0);	61	ev_run (loop, 0);
60		62
61	// unloop was called, so exit	63	// break was called, so exit
62	return 0;	64	return 0;
63	}	65	}
64		66
65	=head1 DESCRIPTION	67	=head1 ABOUT THIS DOCUMENT
		68
		69	This document documents the libev software package.
66		70
67	The newest version of this document is also available as an html-formatted	71	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	72	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>.	73	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		74
		75	While this document tries to be as complete as possible in documenting
		76	libev, its usage and the rationale behind its design, it is not a tutorial
		77	on event-based programming, nor will it introduce event-based programming
		78	with libev.
		79
		80	Familiarity with event based programming techniques in general is assumed
		81	throughout this document.
		82
		83	=head1 WHAT TO READ WHEN IN A HURRY
		84
		85	This manual tries to be very detailed, but unfortunately, this also makes
		86	it very long. If you just want to know the basics of libev, I suggest
		87	reading L<ANATOMY OF A WATCHER>, then the L<EXAMPLE PROGRAM> above and
		88	look up the missing functions in L<GLOBAL FUNCTIONS> and the C<ev_io> and
		89	C<ev_timer> sections in L<WATCHER TYPES>.
		90
		91	=head1 ABOUT LIBEV
70		92
71	Libev is an event loop: you register interest in certain events (such as a	93	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	94	file descriptor being readable or a timeout occurring), and it will manage
73	these event sources and provide your program with events.	95	these event sources and provide your program with events.
74		96
…		…
84	=head2 FEATURES	106	=head2 FEATURES
85		107
86	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	108	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
87	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	109	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
88	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	110	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
89	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	111	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
90	with customised rescheduling (C<ev_periodic>), synchronous signals	112	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	113	timers (C<ev_timer>), absolute timers with customised rescheduling
92	watchers dealing with the event loop mechanism itself (C<ev_idle>,	114	(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	115	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	116	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
95	(C<ev_fork>).	117	C<ev_check> watchers) as well as file watchers (C<ev_stat>) and even
		118	limited support for fork events (C<ev_fork>).
96		119
97	It also is quite fast (see this	120	It also is quite fast (see this
98	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent	121	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
99	for example).	122	for example).
100		123
…		…
108	name C<loop> (which is always of type C<struct ev_loop *>) will not have	131	name C<loop> (which is always of type C<struct ev_loop *>) will not have
109	this argument.	132	this argument.
110		133
111	=head2 TIME REPRESENTATION	134	=head2 TIME REPRESENTATION
112		135
113	Libev represents time as a single floating point number, representing the	136	Libev represents time as a single floating point number, representing
114	(fractional) number of seconds since the (POSIX) epoch (somewhere near	137	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	138	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	139	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	140	too. It usually aliases to the C<double> type in C. When you need to do
118	it, you should treat it as some floatingpoint value. Unlike the name	141	any calculations on it, you should treat it as some floating point value.
		142
119	component C<stamp> might indicate, it is also used for time differences	143	Unlike the name component C<stamp> might indicate, it is also used for
120	throughout libev.	144	time differences (e.g. delays) throughout libev.
		145
		146	=head1 ERROR HANDLING
		147
		148	Libev knows three classes of errors: operating system errors, usage errors
		149	and internal errors (bugs).
		150
		151	When libev catches an operating system error it cannot handle (for example
		152	a system call indicating a condition libev cannot fix), it calls the callback
		153	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		154	abort. The default is to print a diagnostic message and to call C<abort
		155	()>.
		156
		157	When libev detects a usage error such as a negative timer interval, then
		158	it will print a diagnostic message and abort (via the C<assert> mechanism,
		159	so C<NDEBUG> will disable this checking): these are programming errors in
		160	the libev caller and need to be fixed there.
		161
		162	Libev also has a few internal error-checking C<assert>ions, and also has
		163	extensive consistency checking code. These do not trigger under normal
		164	circumstances, as they indicate either a bug in libev or worse.
		165
121		166
122	=head1 GLOBAL FUNCTIONS	167	=head1 GLOBAL FUNCTIONS
123		168
124	These functions can be called anytime, even before initialising the	169	These functions can be called anytime, even before initialising the
125	library in any way.	170	library in any way.
…		…
128		173
129	=item ev_tstamp ev_time ()	174	=item ev_tstamp ev_time ()
130		175
131	Returns the current time as libev would use it. Please note that the	176	Returns the current time as libev would use it. Please note that the
132	C<ev_now> function is usually faster and also often returns the timestamp	177	C<ev_now> function is usually faster and also often returns the timestamp
133	you actually want to know.	178	you actually want to know. Also interesting is the combination of
		179	C<ev_now_update> and C<ev_now>.
134		180
135	=item ev_sleep (ev_tstamp interval)	181	=item ev_sleep (ev_tstamp interval)
136		182
137	Sleep for the given interval: The current thread will be blocked until	183	Sleep for the given interval: The current thread will be blocked
138	either it is interrupted or the given time interval has passed. Basically	184	until either it is interrupted or the given time interval has
		185	passed (approximately - it might return a bit earlier even if not
		186	interrupted). Returns immediately if C<< interval <= 0 >>.
		187
139	this is a subsecond-resolution C<sleep ()>.	188	Basically this is a sub-second-resolution C<sleep ()>.
		189
		190	The range of the C<interval> is limited - libev only guarantees to work
		191	with sleep times of up to one day (C<< interval <= 86400 >>).
140		192
141	=item int ev_version_major ()	193	=item int ev_version_major ()
142		194
143	=item int ev_version_minor ()	195	=item int ev_version_minor ()
144		196
…		…
155	as this indicates an incompatible change. Minor versions are usually	207	as this indicates an incompatible change. Minor versions are usually
156	compatible to older versions, so a larger minor version alone is usually	208	compatible to older versions, so a larger minor version alone is usually
157	not a problem.	209	not a problem.
158		210
159	Example: Make sure we haven't accidentally been linked against the wrong	211	Example: Make sure we haven't accidentally been linked against the wrong
160	version.	212	version (note, however, that this will not detect other ABI mismatches,
		213	such as LFS or reentrancy).
161		214
162	assert (("libev version mismatch",	215	assert (("libev version mismatch",
163	ev_version_major () == EV_VERSION_MAJOR	216	ev_version_major () == EV_VERSION_MAJOR
164	&& ev_version_minor () >= EV_VERSION_MINOR));	217	&& ev_version_minor () >= EV_VERSION_MINOR));
165		218
166	=item unsigned int ev_supported_backends ()	219	=item unsigned int ev_supported_backends ()
167		220
168	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	221	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
169	value) compiled into this binary of libev (independent of their	222	value) compiled into this binary of libev (independent of their
…		…
171	a description of the set values.	224	a description of the set values.
172		225
173	Example: make sure we have the epoll method, because yeah this is cool and	226	Example: make sure we have the epoll method, because yeah this is cool and
174	a must have and can we have a torrent of it please!!!11	227	a must have and can we have a torrent of it please!!!11
175		228
176	assert (("sorry, no epoll, no sex",	229	assert (("sorry, no epoll, no sex",
177	ev_supported_backends () & EVBACKEND_EPOLL));	230	ev_supported_backends () & EVBACKEND_EPOLL));
178		231
179	=item unsigned int ev_recommended_backends ()	232	=item unsigned int ev_recommended_backends ()
180		233
181	Return the set of all backends compiled into this binary of libev and also	234	Return the set of all backends compiled into this binary of libev and
182	recommended for this platform. This set is often smaller than the one	235	also recommended for this platform, meaning it will work for most file
		236	descriptor types. This set is often smaller than the one returned by
183	returned by C<ev_supported_backends>, as for example kqueue is broken on	237	C<ev_supported_backends>, as for example kqueue is broken on most BSDs
184	most BSDs and will not be autodetected unless you explicitly request it	238	and will not be auto-detected unless you explicitly request it (assuming
185	(assuming you know what you are doing). This is the set of backends that	239	you know what you are doing). This is the set of backends that libev will
186	libev will probe for if you specify no backends explicitly.	240	probe for if you specify no backends explicitly.
187		241
188	=item unsigned int ev_embeddable_backends ()	242	=item unsigned int ev_embeddable_backends ()
189		243
190	Returns the set of backends that are embeddable in other event loops. This	244	Returns the set of backends that are embeddable in other event loops. This
191	is the theoretical, all-platform, value. To find which backends	245	value is platform-specific but can include backends not available on the
192	might be supported on the current system, you would need to look at	246	current system. To find which embeddable backends might be supported on
193	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	247	the current system, you would need to look at C<ev_embeddable_backends ()
194	recommended ones.	248	& ev_supported_backends ()>, likewise for recommended ones.
195		249
196	See the description of C<ev_embed> watchers for more info.	250	See the description of C<ev_embed> watchers for more info.
197		251
198	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	252	=item ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())
199		253
200	Sets the allocation function to use (the prototype is similar - the	254	Sets the allocation function to use (the prototype is similar - the
201	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is	255	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
202	used to allocate and free memory (no surprises here). If it returns zero	256	used to allocate and free memory (no surprises here). If it returns zero
203	when memory needs to be allocated (C<size != 0>), the library might abort	257	when memory needs to be allocated (C<size != 0>), the library might abort
…		…
229	}	283	}
230		284
231	...	285	...
232	ev_set_allocator (persistent_realloc);	286	ev_set_allocator (persistent_realloc);
233		287
234	=item ev_set_syserr_cb (void (*cb)(const char *msg));	288	=item ev_set_syserr_cb (void (*cb)(const char *msg) throw ())
235		289
236	Set the callback function to call on a retryable syscall error (such	290	Set the callback function to call on a retryable system call error (such
237	as failed select, poll, epoll_wait). The message is a printable string	291	as failed select, poll, epoll_wait). The message is a printable string
238	indicating the system call or subsystem causing the problem. If this	292	indicating the system call or subsystem causing the problem. If this
239	callback is set, then libev will expect it to remedy the sitution, no	293	callback is set, then libev will expect it to remedy the situation, no
240	matter what, when it returns. That is, libev will generally retry the	294	matter what, when it returns. That is, libev will generally retry the
241	requested operation, or, if the condition doesn't go away, do bad stuff	295	requested operation, or, if the condition doesn't go away, do bad stuff
242	(such as abort).	296	(such as abort).
243		297
244	Example: This is basically the same thing that libev does internally, too.	298	Example: This is basically the same thing that libev does internally, too.
…		…
251	}	305	}
252		306
253	...	307	...
254	ev_set_syserr_cb (fatal_error);	308	ev_set_syserr_cb (fatal_error);
255		309
		310	=item ev_feed_signal (int signum)
		311
		312	This function can be used to "simulate" a signal receive. It is completely
		313	safe to call this function at any time, from any context, including signal
		314	handlers or random threads.
		315
		316	Its main use is to customise signal handling in your process, especially
		317	in the presence of threads. For example, you could block signals
		318	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		319	creating any loops), and in one thread, use C<sigwait> or any other
		320	mechanism to wait for signals, then "deliver" them to libev by calling
		321	C<ev_feed_signal>.
		322
256	=back	323	=back
257		324
258	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	325	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
259		326
260	An event loop is described by a C<struct ev_loop *>. The library knows two	327	An event loop is described by a C<struct ev_loop *> (the C<struct> is
261	types of such loops, the I<default> loop, which supports signals and child	328	I<not> optional in this case unless libev 3 compatibility is disabled, as
262	events, and dynamically created loops which do not.	329	libev 3 had an C<ev_loop> function colliding with the struct name).
		330
		331	The library knows two types of such loops, the I<default> loop, which
		332	supports child process events, and dynamically created event loops which
		333	do not.
263		334
264	=over 4	335	=over 4
265		336
266	=item struct ev_loop *ev_default_loop (unsigned int flags)	337	=item struct ev_loop *ev_default_loop (unsigned int flags)
267		338
268	This will initialise the default event loop if it hasn't been initialised	339	This returns the "default" event loop object, which is what you should
269	yet and return it. If the default loop could not be initialised, returns	340	normally use when you just need "the event loop". Event loop objects and
270	false. If it already was initialised it simply returns it (and ignores the	341	the C<flags> parameter are described in more detail in the entry for
271	flags. If that is troubling you, check C<ev_backend ()> afterwards).	342	C<ev_loop_new>.
		343
		344	If the default loop is already initialised then this function simply
		345	returns it (and ignores the flags. If that is troubling you, check
		346	C<ev_backend ()> afterwards). Otherwise it will create it with the given
		347	flags, which should almost always be C<0>, unless the caller is also the
		348	one calling C<ev_run> or otherwise qualifies as "the main program".
272		349
273	If you don't know what event loop to use, use the one returned from this	350	If you don't know what event loop to use, use the one returned from this
274	function.	351	function (or via the C<EV_DEFAULT> macro).
275		352
276	Note that this function is I<not> thread-safe, so if you want to use it	353	Note that this function is I<not> thread-safe, so if you want to use it
277	from multiple threads, you have to lock (note also that this is unlikely,	354	from multiple threads, you have to employ some kind of mutex (note also
278	as loops cannot bes hared easily between threads anyway).	355	that this case is unlikely, as loops cannot be shared easily between
		356	threads anyway).
279		357
280	The default loop is the only loop that can handle C<ev_signal> and	358	The default loop is the only loop that can handle C<ev_child> watchers,
281	C<ev_child> watchers, and to do this, it always registers a handler	359	and to do this, it always registers a handler for C<SIGCHLD>. If this is
282	for C<SIGCHLD>. If this is a problem for your app you can either	360	a problem for your application you can either create a dynamic loop with
283	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you	361	C<ev_loop_new> which doesn't do that, or you can simply overwrite the
284	can simply overwrite the C<SIGCHLD> signal handler I<after> calling	362	C<SIGCHLD> signal handler I<after> calling C<ev_default_init>.
285	C<ev_default_init>.	363
		364	Example: This is the most typical usage.
		365
		366	if (!ev_default_loop (0))
		367	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		368
		369	Example: Restrict libev to the select and poll backends, and do not allow
		370	environment settings to be taken into account:
		371
		372	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		373
		374	=item struct ev_loop *ev_loop_new (unsigned int flags)
		375
		376	This will create and initialise a new event loop object. If the loop
		377	could not be initialised, returns false.
		378
		379	This function is thread-safe, and one common way to use libev with
		380	threads is indeed to create one loop per thread, and using the default
		381	loop in the "main" or "initial" thread.
286		382
287	The flags argument can be used to specify special behaviour or specific	383	The flags argument can be used to specify special behaviour or specific
288	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	384	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
289		385
290	The following flags are supported:	386	The following flags are supported:
…		…
296	The default flags value. Use this if you have no clue (it's the right	392	The default flags value. Use this if you have no clue (it's the right
297	thing, believe me).	393	thing, believe me).
298		394
299	=item C<EVFLAG_NOENV>	395	=item C<EVFLAG_NOENV>
300		396
301	If this flag bit is ored into the flag value (or the program runs setuid	397	If this flag bit is or'ed into the flag value (or the program runs setuid
302	or setgid) then libev will I<not> look at the environment variable	398	or setgid) then libev will I<not> look at the environment variable
303	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	399	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
304	override the flags completely if it is found in the environment. This is	400	override the flags completely if it is found in the environment. This is
305	useful to try out specific backends to test their performance, or to work	401	useful to try out specific backends to test their performance, or to work
306	around bugs.	402	around bugs.
307		403
308	=item C<EVFLAG_FORKCHECK>	404	=item C<EVFLAG_FORKCHECK>
309		405
310	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after	406	Instead of calling C<ev_loop_fork> manually after a fork, you can also
311	a fork, you can also make libev check for a fork in each iteration by	407	make libev check for a fork in each iteration by enabling this flag.
312	enabling this flag.
313		408
314	This works by calling C<getpid ()> on every iteration of the loop,	409	This works by calling C<getpid ()> on every iteration of the loop,
315	and thus this might slow down your event loop if you do a lot of loop	410	and thus this might slow down your event loop if you do a lot of loop
316	iterations and little real work, but is usually not noticeable (on my	411	iterations and little real work, but is usually not noticeable (on my
317	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence	412	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
318	without a syscall and thus I<very> fast, but my GNU/Linux system also has	413	without a system call and thus I<very> fast, but my GNU/Linux system also has
319	C<pthread_atfork> which is even faster).	414	C<pthread_atfork> which is even faster).
320		415
321	The big advantage of this flag is that you can forget about fork (and	416	The big advantage of this flag is that you can forget about fork (and
322	forget about forgetting to tell libev about forking) when you use this	417	forget about forgetting to tell libev about forking) when you use this
323	flag.	418	flag.
324		419
325	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>	420	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
326	environment variable.	421	environment variable.
		422
		423	=item C<EVFLAG_NOINOTIFY>
		424
		425	When this flag is specified, then libev will not attempt to use the
		426	I<inotify> API for its C<ev_stat> watchers. Apart from debugging and
		427	testing, this flag can be useful to conserve inotify file descriptors, as
		428	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		429
		430	=item C<EVFLAG_SIGNALFD>
		431
		432	When this flag is specified, then libev will attempt to use the
		433	I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API
		434	delivers signals synchronously, which makes it both faster and might make
		435	it possible to get the queued signal data. It can also simplify signal
		436	handling with threads, as long as you properly block signals in your
		437	threads that are not interested in handling them.
		438
		439	Signalfd will not be used by default as this changes your signal mask, and
		440	there are a lot of shoddy libraries and programs (glib's threadpool for
		441	example) that can't properly initialise their signal masks.
		442
		443	=item C<EVFLAG_NOSIGMASK>
		444
		445	When this flag is specified, then libev will avoid to modify the signal
		446	mask. Specifically, this means you have to make sure signals are unblocked
		447	when you want to receive them.
		448
		449	This behaviour is useful when you want to do your own signal handling, or
		450	want to handle signals only in specific threads and want to avoid libev
		451	unblocking the signals.
		452
		453	It's also required by POSIX in a threaded program, as libev calls
		454	C<sigprocmask>, whose behaviour is officially unspecified.
		455
		456	This flag's behaviour will become the default in future versions of libev.
327		457
328	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	458	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
329		459
330	This is your standard select(2) backend. Not I<completely> standard, as	460	This is your standard select(2) backend. Not I<completely> standard, as
331	libev tries to roll its own fd_set with no limits on the number of fds,	461	libev tries to roll its own fd_set with no limits on the number of fds,
332	but if that fails, expect a fairly low limit on the number of fds when	462	but if that fails, expect a fairly low limit on the number of fds when
333	using this backend. It doesn't scale too well (O(highest_fd)), but its	463	using this backend. It doesn't scale too well (O(highest_fd)), but its
334	usually the fastest backend for a low number of (low-numbered :) fds.	464	usually the fastest backend for a low number of (low-numbered :) fds.
335		465
336	To get good performance out of this backend you need a high amount of	466	To get good performance out of this backend you need a high amount of
337	parallelity (most of the file descriptors should be busy). If you are	467	parallelism (most of the file descriptors should be busy). If you are
338	writing a server, you should C<accept ()> in a loop to accept as many	468	writing a server, you should C<accept ()> in a loop to accept as many
339	connections as possible during one iteration. You might also want to have	469	connections as possible during one iteration. You might also want to have
340	a look at C<ev_set_io_collect_interval ()> to increase the amount of	470	a look at C<ev_set_io_collect_interval ()> to increase the amount of
341	readiness notifications you get per iteration.	471	readiness notifications you get per iteration.
		472
		473	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		474	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		475	C<exceptfds> set on that platform).
342		476
343	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	477	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
344		478
345	And this is your standard poll(2) backend. It's more complicated	479	And this is your standard poll(2) backend. It's more complicated
346	than select, but handles sparse fds better and has no artificial	480	than select, but handles sparse fds better and has no artificial
347	limit on the number of fds you can use (except it will slow down	481	limit on the number of fds you can use (except it will slow down
348	considerably with a lot of inactive fds). It scales similarly to select,	482	considerably with a lot of inactive fds). It scales similarly to select,
349	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for	483	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
350	performance tips.	484	performance tips.
351		485
		486	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		487	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
		488
352	=item C<EVBACKEND_EPOLL> (value 4, Linux)	489	=item C<EVBACKEND_EPOLL> (value 4, Linux)
353		490
		491	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		492	kernels).
		493
354	For few fds, this backend is a bit little slower than poll and select,	494	For few fds, this backend is a bit little slower than poll and select, but
355	but it scales phenomenally better. While poll and select usually scale	495	it scales phenomenally better. While poll and select usually scale like
356	like O(total_fds) where n is the total number of fds (or the highest fd),	496	O(total_fds) where total_fds is the total number of fds (or the highest
357	epoll scales either O(1) or O(active_fds). The epoll design has a number	497	fd), epoll scales either O(1) or O(active_fds).
358	of shortcomings, such as silently dropping events in some hard-to-detect	498
359	cases and requiring a syscall per fd change, no fork support and bad	499	The epoll mechanism deserves honorable mention as the most misdesigned
360	support for dup.	500	of the more advanced event mechanisms: mere annoyances include silently
		501	dropping file descriptors, requiring a system call per change per file
		502	descriptor (and unnecessary guessing of parameters), problems with dup,
		503	returning before the timeout value, resulting in additional iterations
		504	(and only giving 5ms accuracy while select on the same platform gives
		505	0.1ms) and so on. The biggest issue is fork races, however - if a program
		506	forks then I<both> parent and child process have to recreate the epoll
		507	set, which can take considerable time (one syscall per file descriptor)
		508	and is of course hard to detect.
		509
		510	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
		511	but of course I<doesn't>, and epoll just loves to report events for
		512	totally I<different> file descriptors (even already closed ones, so
		513	one cannot even remove them from the set) than registered in the set
		514	(especially on SMP systems). Libev tries to counter these spurious
		515	notifications by employing an additional generation counter and comparing
		516	that against the events to filter out spurious ones, recreating the set
		517	when required. Epoll also erroneously rounds down timeouts, but gives you
		518	no way to know when and by how much, so sometimes you have to busy-wait
		519	because epoll returns immediately despite a nonzero timeout. And last
		520	not least, it also refuses to work with some file descriptors which work
		521	perfectly fine with C<select> (files, many character devices...).
		522
		523	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		524	cobbled together in a hurry, no thought to design or interaction with
		525	others. Oh, the pain, will it ever stop...
361		526
362	While stopping, setting and starting an I/O watcher in the same iteration	527	While stopping, setting and starting an I/O watcher in the same iteration
363	will result in some caching, there is still a syscall per such incident	528	will result in some caching, there is still a system call per such
364	(because the fd could point to a different file description now), so its	529	incident (because the same I<file descriptor> could point to a different
365	best to avoid that. Also, C<dup ()>'ed file descriptors might not work	530	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
366	very well if you register events for both fds.	531	file descriptors might not work very well if you register events for both
367		532	file descriptors.
368	Please note that epoll sometimes generates spurious notifications, so you
369	need to use non-blocking I/O or other means to avoid blocking when no data
370	(or space) is available.
371		533
372	Best performance from this backend is achieved by not unregistering all	534	Best performance from this backend is achieved by not unregistering all
373	watchers for a file descriptor until it has been closed, if possible, i.e.	535	watchers for a file descriptor until it has been closed, if possible,
374	keep at least one watcher active per fd at all times.	536	i.e. keep at least one watcher active per fd at all times. Stopping and
		537	starting a watcher (without re-setting it) also usually doesn't cause
		538	extra overhead. A fork can both result in spurious notifications as well
		539	as in libev having to destroy and recreate the epoll object, which can
		540	take considerable time and thus should be avoided.
375		541
		542	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		543	faster than epoll for maybe up to a hundred file descriptors, depending on
		544	the usage. So sad.
		545
376	While nominally embeddeble in other event loops, this feature is broken in	546	While nominally embeddable in other event loops, this feature is broken in
377	all kernel versions tested so far.	547	all kernel versions tested so far.
		548
		549	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		550	C<EVBACKEND_POLL>.
378		551
379	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	552	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
380		553
381	Kqueue deserves special mention, as at the time of this writing, it	554	Kqueue deserves special mention, as at the time of this writing, it
382	was broken on all BSDs except NetBSD (usually it doesn't work reliably	555	was broken on all BSDs except NetBSD (usually it doesn't work reliably
383	with anything but sockets and pipes, except on Darwin, where of course	556	with anything but sockets and pipes, except on Darwin, where of course
384	it's completely useless). For this reason it's not being "autodetected"	557	it's completely useless). Unlike epoll, however, whose brokenness
		558	is by design, these kqueue bugs can (and eventually will) be fixed
		559	without API changes to existing programs. For this reason it's not being
385	unless you explicitly specify it explicitly in the flags (i.e. using	560	"auto-detected" unless you explicitly specify it in the flags (i.e. using
386	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)	561	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
387	system like NetBSD.	562	system like NetBSD.
388		563
389	You still can embed kqueue into a normal poll or select backend and use it	564	You still can embed kqueue into a normal poll or select backend and use it
390	only for sockets (after having made sure that sockets work with kqueue on	565	only for sockets (after having made sure that sockets work with kqueue on
391	the target platform). See C<ev_embed> watchers for more info.	566	the target platform). See C<ev_embed> watchers for more info.
392		567
393	It scales in the same way as the epoll backend, but the interface to the	568	It scales in the same way as the epoll backend, but the interface to the
394	kernel is more efficient (which says nothing about its actual speed, of	569	kernel is more efficient (which says nothing about its actual speed, of
395	course). While stopping, setting and starting an I/O watcher does never	570	course). While stopping, setting and starting an I/O watcher does never
396	cause an extra syscall as with C<EVBACKEND_EPOLL>, it still adds up to	571	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
397	two event changes per incident, support for C<fork ()> is very bad and it	572	two event changes per incident. Support for C<fork ()> is very bad (you
		573	might have to leak fd's on fork, but it's more sane than epoll) and it
398	drops fds silently in similarly hard-to-detect cases.	574	drops fds silently in similarly hard-to-detect cases
399		575
400	This backend usually performs well under most conditions.	576	This backend usually performs well under most conditions.
401		577
402	While nominally embeddable in other event loops, this doesn't work	578	While nominally embeddable in other event loops, this doesn't work
403	everywhere, so you might need to test for this. And since it is broken	579	everywhere, so you might need to test for this. And since it is broken
404	almost everywhere, you should only use it when you have a lot of sockets	580	almost everywhere, you should only use it when you have a lot of sockets
405	(for which it usually works), by embedding it into another event loop	581	(for which it usually works), by embedding it into another event loop
406	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for	582	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
407	sockets.	583	also broken on OS X)) and, did I mention it, using it only for sockets.
		584
		585	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		586	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		587	C<NOTE_EOF>.
408		588
409	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	589	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
410		590
411	This is not implemented yet (and might never be, unless you send me an	591	This is not implemented yet (and might never be, unless you send me an
412	implementation). According to reports, C</dev/poll> only supports sockets	592	implementation). According to reports, C</dev/poll> only supports sockets
…		…
416	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	596	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
417		597
418	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	598	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
419	it's really slow, but it still scales very well (O(active_fds)).	599	it's really slow, but it still scales very well (O(active_fds)).
420		600
421	Please note that solaris event ports can deliver a lot of spurious
422	notifications, so you need to use non-blocking I/O or other means to avoid
423	blocking when no data (or space) is available.
424
425	While this backend scales well, it requires one system call per active	601	While this backend scales well, it requires one system call per active
426	file descriptor per loop iteration. For small and medium numbers of file	602	file descriptor per loop iteration. For small and medium numbers of file
427	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	603	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
428	might perform better.	604	might perform better.
429		605
430	On the positive side, ignoring the spurious readiness notifications, this	606	On the positive side, this backend actually performed fully to
431	backend actually performed to specification in all tests and is fully	607	specification in all tests and is fully embeddable, which is a rare feat
432	embeddable, which is a rare feat among the OS-specific backends.	608	among the OS-specific backends (I vastly prefer correctness over speed
		609	hacks).
		610
		611	On the negative side, the interface is I<bizarre> - so bizarre that
		612	even sun itself gets it wrong in their code examples: The event polling
		613	function sometimes returns events to the caller even though an error
		614	occurred, but with no indication whether it has done so or not (yes, it's
		615	even documented that way) - deadly for edge-triggered interfaces where you
		616	absolutely have to know whether an event occurred or not because you have
		617	to re-arm the watcher.
		618
		619	Fortunately libev seems to be able to work around these idiocies.
		620
		621	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		622	C<EVBACKEND_POLL>.
433		623
434	=item C<EVBACKEND_ALL>	624	=item C<EVBACKEND_ALL>
435		625
436	Try all backends (even potentially broken ones that wouldn't be tried	626	Try all backends (even potentially broken ones that wouldn't be tried
437	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	627	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
438	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	628	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
439		629
440	It is definitely not recommended to use this flag.	630	It is definitely not recommended to use this flag, use whatever
		631	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		632	at all.
		633
		634	=item C<EVBACKEND_MASK>
		635
		636	Not a backend at all, but a mask to select all backend bits from a
		637	C<flags> value, in case you want to mask out any backends from a flags
		638	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
441		639
442	=back	640	=back
443		641
444	If one or more of these are ored into the flags value, then only these	642	If one or more of the backend flags are or'ed into the flags value,
445	backends will be tried (in the reverse order as listed here). If none are	643	then only these backends will be tried (in the reverse order as listed
446	specified, all backends in C<ev_recommended_backends ()> will be tried.	644	here). If none are specified, all backends in C<ev_recommended_backends
447		645	()> will be tried.
448	The most typical usage is like this:
449
450	if (!ev_default_loop (0))
451	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
452
453	Restrict libev to the select and poll backends, and do not allow
454	environment settings to be taken into account:
455
456	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
457
458	Use whatever libev has to offer, but make sure that kqueue is used if
459	available (warning, breaks stuff, best use only with your own private
460	event loop and only if you know the OS supports your types of fds):
461
462	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
463
464	=item struct ev_loop *ev_loop_new (unsigned int flags)
465
466	Similar to C<ev_default_loop>, but always creates a new event loop that is
467	always distinct from the default loop. Unlike the default loop, it cannot
468	handle signal and child watchers, and attempts to do so will be greeted by
469	undefined behaviour (or a failed assertion if assertions are enabled).
470
471	Note that this function I<is> thread-safe, and the recommended way to use
472	libev with threads is indeed to create one loop per thread, and using the
473	default loop in the "main" or "initial" thread.
474		646
475	Example: Try to create a event loop that uses epoll and nothing else.	647	Example: Try to create a event loop that uses epoll and nothing else.
476		648
477	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	649	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
478	if (!epoller)	650	if (!epoller)
479	fatal ("no epoll found here, maybe it hides under your chair");	651	fatal ("no epoll found here, maybe it hides under your chair");
480		652
		653	Example: Use whatever libev has to offer, but make sure that kqueue is
		654	used if available.
		655
		656	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		657
481	=item ev_default_destroy ()	658	=item ev_loop_destroy (loop)
482		659
483	Destroys the default loop again (frees all memory and kernel state	660	Destroys an event loop object (frees all memory and kernel state
484	etc.). None of the active event watchers will be stopped in the normal	661	etc.). None of the active event watchers will be stopped in the normal
485	sense, so e.g. C<ev_is_active> might still return true. It is your	662	sense, so e.g. C<ev_is_active> might still return true. It is your
486	responsibility to either stop all watchers cleanly yoursef I<before>	663	responsibility to either stop all watchers cleanly yourself I<before>
487	calling this function, or cope with the fact afterwards (which is usually	664	calling this function, or cope with the fact afterwards (which is usually
488	the easiest thing, you can just ignore the watchers and/or C<free ()> them	665	the easiest thing, you can just ignore the watchers and/or C<free ()> them
489	for example).	666	for example).
490		667
491	Note that certain global state, such as signal state, will not be freed by	668	Note that certain global state, such as signal state (and installed signal
492	this function, and related watchers (such as signal and child watchers)	669	handlers), will not be freed by this function, and related watchers (such
493	would need to be stopped manually.	670	as signal and child watchers) would need to be stopped manually.
494		671
495	In general it is not advisable to call this function except in the	672	This function is normally used on loop objects allocated by
496	rare occasion where you really need to free e.g. the signal handling	673	C<ev_loop_new>, but it can also be used on the default loop returned by
		674	C<ev_default_loop>, in which case it is not thread-safe.
		675
		676	Note that it is not advisable to call this function on the default loop
		677	except in the rare occasion where you really need to free its resources.
497	pipe fds. If you need dynamically allocated loops it is better to use	678	If you need dynamically allocated loops it is better to use C<ev_loop_new>
498	C<ev_loop_new> and C<ev_loop_destroy>).	679	and C<ev_loop_destroy>.
499		680
500	=item ev_loop_destroy (loop)	681	=item ev_loop_fork (loop)
501		682
502	Like C<ev_default_destroy>, but destroys an event loop created by an
503	earlier call to C<ev_loop_new>.
504
505	=item ev_default_fork ()
506
507	This function sets a flag that causes subsequent C<ev_loop> iterations	683	This function sets a flag that causes subsequent C<ev_run> iterations to
508	to reinitialise the kernel state for backends that have one. Despite the	684	reinitialise the kernel state for backends that have one. Despite the
509	name, you can call it anytime, but it makes most sense after forking, in	685	name, you can call it anytime, but it makes most sense after forking, in
510	the child process (or both child and parent, but that again makes little	686	the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the
511	sense). You I<must> call it in the child before using any of the libev	687	child before resuming or calling C<ev_run>.
512	functions, and it will only take effect at the next C<ev_loop> iteration.	688
		689	Again, you I<have> to call it on I<any> loop that you want to re-use after
		690	a fork, I<even if you do not plan to use the loop in the parent>. This is
		691	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		692	during fork.
513		693
514	On the other hand, you only need to call this function in the child	694	On the other hand, you only need to call this function in the child
515	process if and only if you want to use the event library in the child. If	695	process if and only if you want to use the event loop in the child. If
516	you just fork+exec, you don't have to call it at all.	696	you just fork+exec or create a new loop in the child, you don't have to
		697	call it at all (in fact, C<epoll> is so badly broken that it makes a
		698	difference, but libev will usually detect this case on its own and do a
		699	costly reset of the backend).
517		700
518	The function itself is quite fast and it's usually not a problem to call	701	The function itself is quite fast and it's usually not a problem to call
519	it just in case after a fork. To make this easy, the function will fit in	702	it just in case after a fork.
520	quite nicely into a call to C<pthread_atfork>:
521		703
		704	Example: Automate calling C<ev_loop_fork> on the default loop when
		705	using pthreads.
		706
		707	static void
		708	post_fork_child (void)
		709	{
		710	ev_loop_fork (EV_DEFAULT);
		711	}
		712
		713	...
522	pthread_atfork (0, 0, ev_default_fork);	714	pthread_atfork (0, 0, post_fork_child);
523
524	=item ev_loop_fork (loop)
525
526	Like C<ev_default_fork>, but acts on an event loop created by
527	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
528	after fork, and how you do this is entirely your own problem.
529		715
530	=item int ev_is_default_loop (loop)	716	=item int ev_is_default_loop (loop)
531		717
532	Returns true when the given loop actually is the default loop, false otherwise.	718	Returns true when the given loop is, in fact, the default loop, and false
		719	otherwise.
533		720
534	=item unsigned int ev_loop_count (loop)	721	=item unsigned int ev_iteration (loop)
535		722
536	Returns the count of loop iterations for the loop, which is identical to	723	Returns the current iteration count for the event loop, which is identical
537	the number of times libev did poll for new events. It starts at C<0> and	724	to the number of times libev did poll for new events. It starts at C<0>
538	happily wraps around with enough iterations.	725	and happily wraps around with enough iterations.
539		726
540	This value can sometimes be useful as a generation counter of sorts (it	727	This value can sometimes be useful as a generation counter of sorts (it
541	"ticks" the number of loop iterations), as it roughly corresponds with	728	"ticks" the number of loop iterations), as it roughly corresponds with
542	C<ev_prepare> and C<ev_check> calls.	729	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		730	prepare and check phases.
		731
		732	=item unsigned int ev_depth (loop)
		733
		734	Returns the number of times C<ev_run> was entered minus the number of
		735	times C<ev_run> was exited normally, in other words, the recursion depth.
		736
		737	Outside C<ev_run>, this number is zero. In a callback, this number is
		738	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
		739	in which case it is higher.
		740
		741	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
		742	throwing an exception etc.), doesn't count as "exit" - consider this
		743	as a hint to avoid such ungentleman-like behaviour unless it's really
		744	convenient, in which case it is fully supported.
543		745
544	=item unsigned int ev_backend (loop)	746	=item unsigned int ev_backend (loop)
545		747
546	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	748	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
547	use.	749	use.
…		…
552	received events and started processing them. This timestamp does not	754	received events and started processing them. This timestamp does not
553	change as long as callbacks are being processed, and this is also the base	755	change as long as callbacks are being processed, and this is also the base
554	time used for relative timers. You can treat it as the timestamp of the	756	time used for relative timers. You can treat it as the timestamp of the
555	event occurring (or more correctly, libev finding out about it).	757	event occurring (or more correctly, libev finding out about it).
556		758
		759	=item ev_now_update (loop)
		760
		761	Establishes the current time by querying the kernel, updating the time
		762	returned by C<ev_now ()> in the progress. This is a costly operation and
		763	is usually done automatically within C<ev_run ()>.
		764
		765	This function is rarely useful, but when some event callback runs for a
		766	very long time without entering the event loop, updating libev's idea of
		767	the current time is a good idea.
		768
		769	See also L<The special problem of time updates> in the C<ev_timer> section.
		770
		771	=item ev_suspend (loop)
		772
		773	=item ev_resume (loop)
		774
		775	These two functions suspend and resume an event loop, for use when the
		776	loop is not used for a while and timeouts should not be processed.
		777
		778	A typical use case would be an interactive program such as a game: When
		779	the user presses C<^Z> to suspend the game and resumes it an hour later it
		780	would be best to handle timeouts as if no time had actually passed while
		781	the program was suspended. This can be achieved by calling C<ev_suspend>
		782	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		783	C<ev_resume> directly afterwards to resume timer processing.
		784
		785	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		786	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		787	will be rescheduled (that is, they will lose any events that would have
		788	occurred while suspended).
		789
		790	After calling C<ev_suspend> you B<must not> call I<any> function on the
		791	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		792	without a previous call to C<ev_suspend>.
		793
		794	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		795	event loop time (see C<ev_now_update>).
		796
557	=item ev_loop (loop, int flags)	797	=item bool ev_run (loop, int flags)
558		798
559	Finally, this is it, the event handler. This function usually is called	799	Finally, this is it, the event handler. This function usually is called
560	after you initialised all your watchers and you want to start handling	800	after you have initialised all your watchers and you want to start
561	events.	801	handling events. It will ask the operating system for any new events, call
		802	the watcher callbacks, and then repeat the whole process indefinitely: This
		803	is why event loops are called I<loops>.
562		804
563	If the flags argument is specified as C<0>, it will not return until	805	If the flags argument is specified as C<0>, it will keep handling events
564	either no event watchers are active anymore or C<ev_unloop> was called.	806	until either no event watchers are active anymore or C<ev_break> was
		807	called.
565		808
		809	The return value is false if there are no more active watchers (which
		810	usually means "all jobs done" or "deadlock"), and true in all other cases
		811	(which usually means " you should call C<ev_run> again").
		812
566	Please note that an explicit C<ev_unloop> is usually better than	813	Please note that an explicit C<ev_break> is usually better than
567	relying on all watchers to be stopped when deciding when a program has	814	relying on all watchers to be stopped when deciding when a program has
568	finished (especially in interactive programs), but having a program that	815	finished (especially in interactive programs), but having a program
569	automatically loops as long as it has to and no longer by virtue of	816	that automatically loops as long as it has to and no longer by virtue
570	relying on its watchers stopping correctly is a thing of beauty.	817	of relying on its watchers stopping correctly, that is truly a thing of
		818	beauty.
571		819
		820	This function is I<mostly> exception-safe - you can break out of a
		821	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		822	exception and so on. This does not decrement the C<ev_depth> value, nor
		823	will it clear any outstanding C<EVBREAK_ONE> breaks.
		824
572	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	825	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
573	those events and any outstanding ones, but will not block your process in	826	those events and any already outstanding ones, but will not wait and
574	case there are no events and will return after one iteration of the loop.	827	block your process in case there are no events and will return after one
		828	iteration of the loop. This is sometimes useful to poll and handle new
		829	events while doing lengthy calculations, to keep the program responsive.
575		830
576	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	831	A flags value of C<EVRUN_ONCE> will look for new events (waiting if
577	neccessary) and will handle those and any outstanding ones. It will block	832	necessary) and will handle those and any already outstanding ones. It
578	your process until at least one new event arrives, and will return after	833	will block your process until at least one new event arrives (which could
579	one iteration of the loop. This is useful if you are waiting for some	834	be an event internal to libev itself, so there is no guarantee that a
580	external event in conjunction with something not expressible using other	835	user-registered callback will be called), and will return after one
		836	iteration of the loop.
		837
		838	This is useful if you are waiting for some external event in conjunction
		839	with something not expressible using other libev watchers (i.e. "roll your
581	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	840	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
582	usually a better approach for this kind of thing.	841	usually a better approach for this kind of thing.
583		842
584	Here are the gory details of what C<ev_loop> does:	843	Here are the gory details of what C<ev_run> does (this is for your
		844	understanding, not a guarantee that things will work exactly like this in
		845	future versions):
585		846
		847	- Increment loop depth.
		848	- Reset the ev_break status.
586	- Before the first iteration, call any pending watchers.	849	- Before the first iteration, call any pending watchers.
		850	LOOP:
587	* If EVFLAG_FORKCHECK was used, check for a fork.	851	- If EVFLAG_FORKCHECK was used, check for a fork.
588	- If a fork was detected, queue and call all fork watchers.	852	- If a fork was detected (by any means), queue and call all fork watchers.
589	- Queue and call all prepare watchers.	853	- Queue and call all prepare watchers.
		854	- If ev_break was called, goto FINISH.
590	- If we have been forked, recreate the kernel state.	855	- If we have been forked, detach and recreate the kernel state
		856	as to not disturb the other process.
591	- Update the kernel state with all outstanding changes.	857	- Update the kernel state with all outstanding changes.
592	- Update the "event loop time".	858	- Update the "event loop time" (ev_now ()).
593	- Calculate for how long to sleep or block, if at all	859	- Calculate for how long to sleep or block, if at all
594	(active idle watchers, EVLOOP_NONBLOCK or not having	860	(active idle watchers, EVRUN_NOWAIT or not having
595	any active watchers at all will result in not sleeping).	861	any active watchers at all will result in not sleeping).
596	- Sleep if the I/O and timer collect interval say so.	862	- Sleep if the I/O and timer collect interval say so.
		863	- Increment loop iteration counter.
597	- Block the process, waiting for any events.	864	- Block the process, waiting for any events.
598	- Queue all outstanding I/O (fd) events.	865	- Queue all outstanding I/O (fd) events.
599	- Update the "event loop time" and do time jump handling.	866	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
600	- Queue all outstanding timers.	867	- Queue all expired timers.
601	- Queue all outstanding periodics.	868	- Queue all expired periodics.
602	- If no events are pending now, queue all idle watchers.	869	- Queue all idle watchers with priority higher than that of pending events.
603	- Queue all check watchers.	870	- Queue all check watchers.
604	- Call all queued watchers in reverse order (i.e. check watchers first).	871	- Call all queued watchers in reverse order (i.e. check watchers first).
605	Signals and child watchers are implemented as I/O watchers, and will	872	Signals and child watchers are implemented as I/O watchers, and will
606	be handled here by queueing them when their watcher gets executed.	873	be handled here by queueing them when their watcher gets executed.
607	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	874	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
608	were used, or there are no active watchers, return, otherwise	875	were used, or there are no active watchers, goto FINISH, otherwise
609	continue with step *.	876	continue with step LOOP.
		877	FINISH:
		878	- Reset the ev_break status iff it was EVBREAK_ONE.
		879	- Decrement the loop depth.
		880	- Return.
610		881
611	Example: Queue some jobs and then loop until no events are outstanding	882	Example: Queue some jobs and then loop until no events are outstanding
612	anymore.	883	anymore.
613		884
614	... queue jobs here, make sure they register event watchers as long	885	... queue jobs here, make sure they register event watchers as long
615	... as they still have work to do (even an idle watcher will do..)	886	... as they still have work to do (even an idle watcher will do..)
616	ev_loop (my_loop, 0);	887	ev_run (my_loop, 0);
617	... jobs done. yeah!	888	... jobs done or somebody called break. yeah!
618		889
619	=item ev_unloop (loop, how)	890	=item ev_break (loop, how)
620		891
621	Can be used to make a call to C<ev_loop> return early (but only after it	892	Can be used to make a call to C<ev_run> return early (but only after it
622	has processed all outstanding events). The C<how> argument must be either	893	has processed all outstanding events). The C<how> argument must be either
623	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	894	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
624	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	895	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
625		896
626	This "unloop state" will be cleared when entering C<ev_loop> again.	897	This "break state" will be cleared on the next call to C<ev_run>.
		898
		899	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		900	which case it will have no effect.
627		901
628	=item ev_ref (loop)	902	=item ev_ref (loop)
629		903
630	=item ev_unref (loop)	904	=item ev_unref (loop)
631		905
632	Ref/unref can be used to add or remove a reference count on the event	906	Ref/unref can be used to add or remove a reference count on the event
633	loop: Every watcher keeps one reference, and as long as the reference	907	loop: Every watcher keeps one reference, and as long as the reference
634	count is nonzero, C<ev_loop> will not return on its own. If you have	908	count is nonzero, C<ev_run> will not return on its own.
635	a watcher you never unregister that should not keep C<ev_loop> from	909
636	returning, ev_unref() after starting, and ev_ref() before stopping it. For	910	This is useful when you have a watcher that you never intend to
		911	unregister, but that nevertheless should not keep C<ev_run> from
		912	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		913	before stopping it.
		914
637	example, libev itself uses this for its internal signal pipe: It is not	915	As an example, libev itself uses this for its internal signal pipe: It
638	visible to the libev user and should not keep C<ev_loop> from exiting if	916	is not visible to the libev user and should not keep C<ev_run> from
639	no event watchers registered by it are active. It is also an excellent	917	exiting if no event watchers registered by it are active. It is also an
640	way to do this for generic recurring timers or from within third-party	918	excellent way to do this for generic recurring timers or from within
641	libraries. Just remember to I<unref after start> and I<ref before stop>	919	third-party libraries. Just remember to I<unref after start> and I<ref
642	(but only if the watcher wasn't active before, or was active before,	920	before stop> (but only if the watcher wasn't active before, or was active
643	respectively).	921	before, respectively. Note also that libev might stop watchers itself
		922	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		923	in the callback).
644		924
645	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	925	Example: Create a signal watcher, but keep it from keeping C<ev_run>
646	running when nothing else is active.	926	running when nothing else is active.
647		927
648	struct ev_signal exitsig;	928	ev_signal exitsig;
649	ev_signal_init (&exitsig, sig_cb, SIGINT);	929	ev_signal_init (&exitsig, sig_cb, SIGINT);
650	ev_signal_start (loop, &exitsig);	930	ev_signal_start (loop, &exitsig);
651	evf_unref (loop);	931	ev_unref (loop);
652		932
653	Example: For some weird reason, unregister the above signal handler again.	933	Example: For some weird reason, unregister the above signal handler again.
654		934
655	ev_ref (loop);	935	ev_ref (loop);
656	ev_signal_stop (loop, &exitsig);	936	ev_signal_stop (loop, &exitsig);
657		937
658	=item ev_set_io_collect_interval (loop, ev_tstamp interval)	938	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
659		939
660	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)	940	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
661		941
662	These advanced functions influence the time that libev will spend waiting	942	These advanced functions influence the time that libev will spend waiting
663	for events. Both are by default C<0>, meaning that libev will try to	943	for events. Both time intervals are by default C<0>, meaning that libev
664	invoke timer/periodic callbacks and I/O callbacks with minimum latency.	944	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		945	latency.
665		946
666	Setting these to a higher value (the C<interval> I<must> be >= C<0>)	947	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
667	allows libev to delay invocation of I/O and timer/periodic callbacks to	948	allows libev to delay invocation of I/O and timer/periodic callbacks
668	increase efficiency of loop iterations.	949	to increase efficiency of loop iterations (or to increase power-saving
		950	opportunities).
669		951
670	The background is that sometimes your program runs just fast enough to	952	The idea is that sometimes your program runs just fast enough to handle
671	handle one (or very few) event(s) per loop iteration. While this makes	953	one (or very few) event(s) per loop iteration. While this makes the
672	the program responsive, it also wastes a lot of CPU time to poll for new	954	program responsive, it also wastes a lot of CPU time to poll for new
673	events, especially with backends like C<select ()> which have a high	955	events, especially with backends like C<select ()> which have a high
674	overhead for the actual polling but can deliver many events at once.	956	overhead for the actual polling but can deliver many events at once.
675		957
676	By setting a higher I<io collect interval> you allow libev to spend more	958	By setting a higher I<io collect interval> you allow libev to spend more
677	time collecting I/O events, so you can handle more events per iteration,	959	time collecting I/O events, so you can handle more events per iteration,
678	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	960	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
679	C<ev_timer>) will be not affected. Setting this to a non-null value will	961	C<ev_timer>) will not be affected. Setting this to a non-null value will
680	introduce an additional C<ev_sleep ()> call into most loop iterations.	962	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		963	sleep time ensures that libev will not poll for I/O events more often then
		964	once per this interval, on average (as long as the host time resolution is
		965	good enough).
681		966
682	Likewise, by setting a higher I<timeout collect interval> you allow libev	967	Likewise, by setting a higher I<timeout collect interval> you allow libev
683	to spend more time collecting timeouts, at the expense of increased	968	to spend more time collecting timeouts, at the expense of increased
684	latency (the watcher callback will be called later). C<ev_io> watchers	969	latency/jitter/inexactness (the watcher callback will be called
685	will not be affected. Setting this to a non-null value will not introduce	970	later). C<ev_io> watchers will not be affected. Setting this to a non-null
686	any overhead in libev.	971	value will not introduce any overhead in libev.
687		972
688	Many (busy) programs can usually benefit by setting the io collect	973	Many (busy) programs can usually benefit by setting the I/O collect
689	interval to a value near C<0.1> or so, which is often enough for	974	interval to a value near C<0.1> or so, which is often enough for
690	interactive servers (of course not for games), likewise for timeouts. It	975	interactive servers (of course not for games), likewise for timeouts. It
691	usually doesn't make much sense to set it to a lower value than C<0.01>,	976	usually doesn't make much sense to set it to a lower value than C<0.01>,
692	as this approsaches the timing granularity of most systems.	977	as this approaches the timing granularity of most systems. Note that if
		978	you do transactions with the outside world and you can't increase the
		979	parallelity, then this setting will limit your transaction rate (if you
		980	need to poll once per transaction and the I/O collect interval is 0.01,
		981	then you can't do more than 100 transactions per second).
693		982
		983	Setting the I<timeout collect interval> can improve the opportunity for
		984	saving power, as the program will "bundle" timer callback invocations that
		985	are "near" in time together, by delaying some, thus reducing the number of
		986	times the process sleeps and wakes up again. Another useful technique to
		987	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		988	they fire on, say, one-second boundaries only.
		989
		990	Example: we only need 0.1s timeout granularity, and we wish not to poll
		991	more often than 100 times per second:
		992
		993	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		994	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		995
		996	=item ev_invoke_pending (loop)
		997
		998	This call will simply invoke all pending watchers while resetting their
		999	pending state. Normally, C<ev_run> does this automatically when required,
		1000	but when overriding the invoke callback this call comes handy. This
		1001	function can be invoked from a watcher - this can be useful for example
		1002	when you want to do some lengthy calculation and want to pass further
		1003	event handling to another thread (you still have to make sure only one
		1004	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
		1005
		1006	=item int ev_pending_count (loop)
		1007
		1008	Returns the number of pending watchers - zero indicates that no watchers
		1009	are pending.
		1010
		1011	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		1012
		1013	This overrides the invoke pending functionality of the loop: Instead of
		1014	invoking all pending watchers when there are any, C<ev_run> will call
		1015	this callback instead. This is useful, for example, when you want to
		1016	invoke the actual watchers inside another context (another thread etc.).
		1017
		1018	If you want to reset the callback, use C<ev_invoke_pending> as new
		1019	callback.
		1020
		1021	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
		1022
		1023	Sometimes you want to share the same loop between multiple threads. This
		1024	can be done relatively simply by putting mutex_lock/unlock calls around
		1025	each call to a libev function.
		1026
		1027	However, C<ev_run> can run an indefinite time, so it is not feasible
		1028	to wait for it to return. One way around this is to wake up the event
		1029	loop via C<ev_break> and C<ev_async_send>, another way is to set these
		1030	I<release> and I<acquire> callbacks on the loop.
		1031
		1032	When set, then C<release> will be called just before the thread is
		1033	suspended waiting for new events, and C<acquire> is called just
		1034	afterwards.
		1035
		1036	Ideally, C<release> will just call your mutex_unlock function, and
		1037	C<acquire> will just call the mutex_lock function again.
		1038
		1039	While event loop modifications are allowed between invocations of
		1040	C<release> and C<acquire> (that's their only purpose after all), no
		1041	modifications done will affect the event loop, i.e. adding watchers will
		1042	have no effect on the set of file descriptors being watched, or the time
		1043	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		1044	to take note of any changes you made.
		1045
		1046	In theory, threads executing C<ev_run> will be async-cancel safe between
		1047	invocations of C<release> and C<acquire>.
		1048
		1049	See also the locking example in the C<THREADS> section later in this
		1050	document.
		1051
		1052	=item ev_set_userdata (loop, void *data)
		1053
		1054	=item void *ev_userdata (loop)
		1055
		1056	Set and retrieve a single C<void *> associated with a loop. When
		1057	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		1058	C<0>.
		1059
		1060	These two functions can be used to associate arbitrary data with a loop,
		1061	and are intended solely for the C<invoke_pending_cb>, C<release> and
		1062	C<acquire> callbacks described above, but of course can be (ab-)used for
		1063	any other purpose as well.
		1064
694	=item ev_loop_verify (loop)	1065	=item ev_verify (loop)
695		1066
696	This function only does something when C<EV_VERIFY> support has been	1067	This function only does something when C<EV_VERIFY> support has been
697	compiled in. It tries to go through all internal structures and checks	1068	compiled in, which is the default for non-minimal builds. It tries to go
698	them for validity. If anything is found to be inconsistent, it will print	1069	through all internal structures and checks them for validity. If anything
699	an error message to standard error and call C<abort ()>.	1070	is found to be inconsistent, it will print an error message to standard
		1071	error and call C<abort ()>.
700		1072
701	This can be used to catch bugs inside libev itself: under normal	1073	This can be used to catch bugs inside libev itself: under normal
702	circumstances, this function will never abort as of course libev keeps its	1074	circumstances, this function will never abort as of course libev keeps its
703	data structures consistent.	1075	data structures consistent.
704		1076
705	=back	1077	=back
706		1078
707		1079
708	=head1 ANATOMY OF A WATCHER	1080	=head1 ANATOMY OF A WATCHER
709		1081
		1082	In the following description, uppercase C<TYPE> in names stands for the
		1083	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		1084	watchers and C<ev_io_start> for I/O watchers.
		1085
710	A watcher is a structure that you create and register to record your	1086	A watcher is an opaque structure that you allocate and register to record
711	interest in some event. For instance, if you want to wait for STDIN to	1087	your interest in some event. To make a concrete example, imagine you want
712	become readable, you would create an C<ev_io> watcher for that:	1088	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1089	for that:
713		1090
714	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1091	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
715	{	1092	{
716	ev_io_stop (w);	1093	ev_io_stop (w);
717	ev_unloop (loop, EVUNLOOP_ALL);	1094	ev_break (loop, EVBREAK_ALL);
718	}	1095	}
719		1096
720	struct ev_loop *loop = ev_default_loop (0);	1097	struct ev_loop *loop = ev_default_loop (0);
		1098
721	struct ev_io stdin_watcher;	1099	ev_io stdin_watcher;
		1100
722	ev_init (&stdin_watcher, my_cb);	1101	ev_init (&stdin_watcher, my_cb);
723	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1102	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
724	ev_io_start (loop, &stdin_watcher);	1103	ev_io_start (loop, &stdin_watcher);
		1104
725	ev_loop (loop, 0);	1105	ev_run (loop, 0);
726		1106
727	As you can see, you are responsible for allocating the memory for your	1107	As you can see, you are responsible for allocating the memory for your
728	watcher structures (and it is usually a bad idea to do this on the stack,	1108	watcher structures (and it is I<usually> a bad idea to do this on the
729	although this can sometimes be quite valid).	1109	stack).
730		1110
		1111	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1112	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1113
731	Each watcher structure must be initialised by a call to C<ev_init	1114	Each watcher structure must be initialised by a call to C<ev_init (watcher
732	(watcher *, callback)>, which expects a callback to be provided. This	1115	*, callback)>, which expects a callback to be provided. This callback is
733	callback gets invoked each time the event occurs (or, in the case of io	1116	invoked each time the event occurs (or, in the case of I/O watchers, each
734	watchers, each time the event loop detects that the file descriptor given	1117	time the event loop detects that the file descriptor given is readable
735	is readable and/or writable).	1118	and/or writable).
736		1119
737	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1120	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
738	with arguments specific to this watcher type. There is also a macro	1121	macro to configure it, with arguments specific to the watcher type. There
739	to combine initialisation and setting in one call: C<< ev_<type>_init	1122	is also a macro to combine initialisation and setting in one call: C<<
740	(watcher *, callback, ...) >>.	1123	ev_TYPE_init (watcher *, callback, ...) >>.
741		1124
742	To make the watcher actually watch out for events, you have to start it	1125	To make the watcher actually watch out for events, you have to start it
743	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1126	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
744	*) >>), and you can stop watching for events at any time by calling the	1127	*) >>), and you can stop watching for events at any time by calling the
745	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1128	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
746		1129
747	As long as your watcher is active (has been started but not stopped) you	1130	As long as your watcher is active (has been started but not stopped) you
748	must not touch the values stored in it. Most specifically you must never	1131	must not touch the values stored in it. Most specifically you must never
749	reinitialise it or call its C<set> macro.	1132	reinitialise it or call its C<ev_TYPE_set> macro.
750		1133
751	Each and every callback receives the event loop pointer as first, the	1134	Each and every callback receives the event loop pointer as first, the
752	registered watcher structure as second, and a bitset of received events as	1135	registered watcher structure as second, and a bitset of received events as
753	third argument.	1136	third argument.
754		1137
…		…
763	=item C<EV_WRITE>	1146	=item C<EV_WRITE>
764		1147
765	The file descriptor in the C<ev_io> watcher has become readable and/or	1148	The file descriptor in the C<ev_io> watcher has become readable and/or
766	writable.	1149	writable.
767		1150
768	=item C<EV_TIMEOUT>	1151	=item C<EV_TIMER>
769		1152
770	The C<ev_timer> watcher has timed out.	1153	The C<ev_timer> watcher has timed out.
771		1154
772	=item C<EV_PERIODIC>	1155	=item C<EV_PERIODIC>
773		1156
…		…
791		1174
792	=item C<EV_PREPARE>	1175	=item C<EV_PREPARE>
793		1176
794	=item C<EV_CHECK>	1177	=item C<EV_CHECK>
795		1178
796	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts	1179	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts to
797	to gather new events, and all C<ev_check> watchers are invoked just after	1180	gather new events, and all C<ev_check> watchers are queued (not invoked)
798	C<ev_loop> has gathered them, but before it invokes any callbacks for any	1181	just after C<ev_run> has gathered them, but before it queues any callbacks
		1182	for any received events. That means C<ev_prepare> watchers are the last
		1183	watchers invoked before the event loop sleeps or polls for new events, and
		1184	C<ev_check> watchers will be invoked before any other watchers of the same
		1185	or lower priority within an event loop iteration.
		1186
799	received events. Callbacks of both watcher types can start and stop as	1187	Callbacks of both watcher types can start and stop as many watchers as
800	many watchers as they want, and all of them will be taken into account	1188	they want, and all of them will be taken into account (for example, a
801	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1189	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
802	C<ev_loop> from blocking).	1190	blocking).
803		1191
804	=item C<EV_EMBED>	1192	=item C<EV_EMBED>
805		1193
806	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1194	The embedded event loop specified in the C<ev_embed> watcher needs attention.
807		1195
808	=item C<EV_FORK>	1196	=item C<EV_FORK>
809		1197
810	The event loop has been resumed in the child process after fork (see	1198	The event loop has been resumed in the child process after fork (see
811	C<ev_fork>).	1199	C<ev_fork>).
812		1200
		1201	=item C<EV_CLEANUP>
		1202
		1203	The event loop is about to be destroyed (see C<ev_cleanup>).
		1204
813	=item C<EV_ASYNC>	1205	=item C<EV_ASYNC>
814		1206
815	The given async watcher has been asynchronously notified (see C<ev_async>).	1207	The given async watcher has been asynchronously notified (see C<ev_async>).
816		1208
		1209	=item C<EV_CUSTOM>
		1210
		1211	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1212	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1213
817	=item C<EV_ERROR>	1214	=item C<EV_ERROR>
818		1215
819	An unspecified error has occured, the watcher has been stopped. This might	1216	An unspecified error has occurred, the watcher has been stopped. This might
820	happen because the watcher could not be properly started because libev	1217	happen because the watcher could not be properly started because libev
821	ran out of memory, a file descriptor was found to be closed or any other	1218	ran out of memory, a file descriptor was found to be closed or any other
		1219	problem. Libev considers these application bugs.
		1220
822	problem. You best act on it by reporting the problem and somehow coping	1221	You best act on it by reporting the problem and somehow coping with the
823	with the watcher being stopped.	1222	watcher being stopped. Note that well-written programs should not receive
		1223	an error ever, so when your watcher receives it, this usually indicates a
		1224	bug in your program.
824		1225
825	Libev will usually signal a few "dummy" events together with an error,	1226	Libev will usually signal a few "dummy" events together with an error, for
826	for example it might indicate that a fd is readable or writable, and if	1227	example it might indicate that a fd is readable or writable, and if your
827	your callbacks is well-written it can just attempt the operation and cope	1228	callbacks is well-written it can just attempt the operation and cope with
828	with the error from read() or write(). This will not work in multithreaded	1229	the error from read() or write(). This will not work in multi-threaded
829	programs, though, so beware.	1230	programs, though, as the fd could already be closed and reused for another
		1231	thing, so beware.
830		1232
831	=back	1233	=back
832		1234
833	=head2 GENERIC WATCHER FUNCTIONS	1235	=head2 GENERIC WATCHER FUNCTIONS
834
835	In the following description, C<TYPE> stands for the watcher type,
836	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
837		1236
838	=over 4	1237	=over 4
839		1238
840	=item C<ev_init> (ev_TYPE *watcher, callback)	1239	=item C<ev_init> (ev_TYPE *watcher, callback)
841		1240
…		…
847	which rolls both calls into one.	1246	which rolls both calls into one.
848		1247
849	You can reinitialise a watcher at any time as long as it has been stopped	1248	You can reinitialise a watcher at any time as long as it has been stopped
850	(or never started) and there are no pending events outstanding.	1249	(or never started) and there are no pending events outstanding.
851		1250
852	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1251	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
853	int revents)>.	1252	int revents)>.
854		1253
		1254	Example: Initialise an C<ev_io> watcher in two steps.
		1255
		1256	ev_io w;
		1257	ev_init (&w, my_cb);
		1258	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1259
855	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1260	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
856		1261
857	This macro initialises the type-specific parts of a watcher. You need to	1262	This macro initialises the type-specific parts of a watcher. You need to
858	call C<ev_init> at least once before you call this macro, but you can	1263	call C<ev_init> at least once before you call this macro, but you can
859	call C<ev_TYPE_set> any number of times. You must not, however, call this	1264	call C<ev_TYPE_set> any number of times. You must not, however, call this
860	macro on a watcher that is active (it can be pending, however, which is a	1265	macro on a watcher that is active (it can be pending, however, which is a
861	difference to the C<ev_init> macro).	1266	difference to the C<ev_init> macro).
862		1267
863	Although some watcher types do not have type-specific arguments	1268	Although some watcher types do not have type-specific arguments
864	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1269	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
865		1270
		1271	See C<ev_init>, above, for an example.
		1272
866	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1273	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
867		1274
868	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1275	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
869	calls into a single call. This is the most convinient method to initialise	1276	calls into a single call. This is the most convenient method to initialise
870	a watcher. The same limitations apply, of course.	1277	a watcher. The same limitations apply, of course.
871		1278
		1279	Example: Initialise and set an C<ev_io> watcher in one step.
		1280
		1281	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1282
872	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1283	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
873		1284
874	Starts (activates) the given watcher. Only active watchers will receive	1285	Starts (activates) the given watcher. Only active watchers will receive
875	events. If the watcher is already active nothing will happen.	1286	events. If the watcher is already active nothing will happen.
876		1287
		1288	Example: Start the C<ev_io> watcher that is being abused as example in this
		1289	whole section.
		1290
		1291	ev_io_start (EV_DEFAULT_UC, &w);
		1292
877	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1293	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
878		1294
879	Stops the given watcher again (if active) and clears the pending	1295	Stops the given watcher if active, and clears the pending status (whether
		1296	the watcher was active or not).
		1297
880	status. It is possible that stopped watchers are pending (for example,	1298	It is possible that stopped watchers are pending - for example,
881	non-repeating timers are being stopped when they become pending), but	1299	non-repeating timers are being stopped when they become pending - but
882	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1300	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
883	you want to free or reuse the memory used by the watcher it is therefore a	1301	pending. If you want to free or reuse the memory used by the watcher it is
884	good idea to always call its C<ev_TYPE_stop> function.	1302	therefore a good idea to always call its C<ev_TYPE_stop> function.
885		1303
886	=item bool ev_is_active (ev_TYPE *watcher)	1304	=item bool ev_is_active (ev_TYPE *watcher)
887		1305
888	Returns a true value iff the watcher is active (i.e. it has been started	1306	Returns a true value iff the watcher is active (i.e. it has been started
889	and not yet been stopped). As long as a watcher is active you must not modify	1307	and not yet been stopped). As long as a watcher is active you must not modify
…		…
905	=item ev_cb_set (ev_TYPE *watcher, callback)	1323	=item ev_cb_set (ev_TYPE *watcher, callback)
906		1324
907	Change the callback. You can change the callback at virtually any time	1325	Change the callback. You can change the callback at virtually any time
908	(modulo threads).	1326	(modulo threads).
909		1327
910	=item ev_set_priority (ev_TYPE *watcher, priority)	1328	=item ev_set_priority (ev_TYPE *watcher, int priority)
911		1329
912	=item int ev_priority (ev_TYPE *watcher)	1330	=item int ev_priority (ev_TYPE *watcher)
913		1331
914	Set and query the priority of the watcher. The priority is a small	1332	Set and query the priority of the watcher. The priority is a small
915	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1333	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
916	(default: C<-2>). Pending watchers with higher priority will be invoked	1334	(default: C<-2>). Pending watchers with higher priority will be invoked
917	before watchers with lower priority, but priority will not keep watchers	1335	before watchers with lower priority, but priority will not keep watchers
918	from being executed (except for C<ev_idle> watchers).	1336	from being executed (except for C<ev_idle> watchers).
919		1337
920	This means that priorities are I<only> used for ordering callback
921	invocation after new events have been received. This is useful, for
922	example, to reduce latency after idling, or more often, to bind two
923	watchers on the same event and make sure one is called first.
924
925	If you need to suppress invocation when higher priority events are pending	1338	If you need to suppress invocation when higher priority events are pending
926	you need to look at C<ev_idle> watchers, which provide this functionality.	1339	you need to look at C<ev_idle> watchers, which provide this functionality.
927		1340
928	You I<must not> change the priority of a watcher as long as it is active or	1341	You I<must not> change the priority of a watcher as long as it is active or
929	pending.	1342	pending.
930		1343
		1344	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1345	fine, as long as you do not mind that the priority value you query might
		1346	or might not have been clamped to the valid range.
		1347
931	The default priority used by watchers when no priority has been set is	1348	The default priority used by watchers when no priority has been set is
932	always C<0>, which is supposed to not be too high and not be too low :).	1349	always C<0>, which is supposed to not be too high and not be too low :).
933		1350
934	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1351	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
935	fine, as long as you do not mind that the priority value you query might	1352	priorities.
936	or might not have been adjusted to be within valid range.
937		1353
938	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1354	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
939		1355
940	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1356	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
941	C<loop> nor C<revents> need to be valid as long as the watcher callback	1357	C<loop> nor C<revents> need to be valid as long as the watcher callback
942	can deal with that fact.	1358	can deal with that fact, as both are simply passed through to the
		1359	callback.
943		1360
944	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1361	=item int ev_clear_pending (loop, ev_TYPE *watcher)
945		1362
946	If the watcher is pending, this function returns clears its pending status	1363	If the watcher is pending, this function clears its pending status and
947	and returns its C<revents> bitset (as if its callback was invoked). If the	1364	returns its C<revents> bitset (as if its callback was invoked). If the
948	watcher isn't pending it does nothing and returns C<0>.	1365	watcher isn't pending it does nothing and returns C<0>.
949		1366
		1367	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1368	callback to be invoked, which can be accomplished with this function.
		1369
		1370	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1371
		1372	Feeds the given event set into the event loop, as if the specified event
		1373	had happened for the specified watcher (which must be a pointer to an
		1374	initialised but not necessarily started event watcher). Obviously you must
		1375	not free the watcher as long as it has pending events.
		1376
		1377	Stopping the watcher, letting libev invoke it, or calling
		1378	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1379	not started in the first place.
		1380
		1381	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1382	functions that do not need a watcher.
		1383
950	=back	1384	=back
951		1385
		1386	See also the L<ASSOCIATING CUSTOM DATA WITH A WATCHER> and L<BUILDING YOUR
		1387	OWN COMPOSITE WATCHERS> idioms.
952		1388
953	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1389	=head2 WATCHER STATES
954		1390
955	Each watcher has, by default, a member C<void *data> that you can change	1391	There are various watcher states mentioned throughout this manual -
956	and read at any time, libev will completely ignore it. This can be used	1392	active, pending and so on. In this section these states and the rules to
957	to associate arbitrary data with your watcher. If you need more data and	1393	transition between them will be described in more detail - and while these
958	don't want to allocate memory and store a pointer to it in that data	1394	rules might look complicated, they usually do "the right thing".
959	member, you can also "subclass" the watcher type and provide your own
960	data:
961		1395
962	struct my_io	1396	=over 4
963	{
964	struct ev_io io;
965	int otherfd;
966	void *somedata;
967	struct whatever *mostinteresting;
968	}
969		1397
970	And since your callback will be called with a pointer to the watcher, you	1398	=item initialiased
971	can cast it back to your own type:
972		1399
973	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1400	Before a watcher can be registered with the event loop it has to be
974	{	1401	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
975	struct my_io *w = (struct my_io *)w_;	1402	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
976	...
977	}
978		1403
979	More interesting and less C-conformant ways of casting your callback type	1404	In this state it is simply some block of memory that is suitable for
980	instead have been omitted.	1405	use in an event loop. It can be moved around, freed, reused etc. at
		1406	will - as long as you either keep the memory contents intact, or call
		1407	C<ev_TYPE_init> again.
981		1408
982	Another common scenario is having some data structure with multiple	1409	=item started/running/active
983	watchers:
984		1410
985	struct my_biggy	1411	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
986	{	1412	property of the event loop, and is actively waiting for events. While in
987	int some_data;	1413	this state it cannot be accessed (except in a few documented ways), moved,
988	ev_timer t1;	1414	freed or anything else - the only legal thing is to keep a pointer to it,
989	ev_timer t2;	1415	and call libev functions on it that are documented to work on active watchers.
990	}
991		1416
992	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1417	=item pending
993	you need to use C<offsetof>:
994		1418
995	#include <stddef.h>	1419	If a watcher is active and libev determines that an event it is interested
		1420	in has occurred (such as a timer expiring), it will become pending. It will
		1421	stay in this pending state until either it is stopped or its callback is
		1422	about to be invoked, so it is not normally pending inside the watcher
		1423	callback.
996		1424
		1425	The watcher might or might not be active while it is pending (for example,
		1426	an expired non-repeating timer can be pending but no longer active). If it
		1427	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1428	but it is still property of the event loop at this time, so cannot be
		1429	moved, freed or reused. And if it is active the rules described in the
		1430	previous item still apply.
		1431
		1432	It is also possible to feed an event on a watcher that is not active (e.g.
		1433	via C<ev_feed_event>), in which case it becomes pending without being
		1434	active.
		1435
		1436	=item stopped
		1437
		1438	A watcher can be stopped implicitly by libev (in which case it might still
		1439	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1440	latter will clear any pending state the watcher might be in, regardless
		1441	of whether it was active or not, so stopping a watcher explicitly before
		1442	freeing it is often a good idea.
		1443
		1444	While stopped (and not pending) the watcher is essentially in the
		1445	initialised state, that is, it can be reused, moved, modified in any way
		1446	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1447	it again).
		1448
		1449	=back
		1450
		1451	=head2 WATCHER PRIORITY MODELS
		1452
		1453	Many event loops support I<watcher priorities>, which are usually small
		1454	integers that influence the ordering of event callback invocation
		1455	between watchers in some way, all else being equal.
		1456
		1457	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1458	description for the more technical details such as the actual priority
		1459	range.
		1460
		1461	There are two common ways how these these priorities are being interpreted
		1462	by event loops:
		1463
		1464	In the more common lock-out model, higher priorities "lock out" invocation
		1465	of lower priority watchers, which means as long as higher priority
		1466	watchers receive events, lower priority watchers are not being invoked.
		1467
		1468	The less common only-for-ordering model uses priorities solely to order
		1469	callback invocation within a single event loop iteration: Higher priority
		1470	watchers are invoked before lower priority ones, but they all get invoked
		1471	before polling for new events.
		1472
		1473	Libev uses the second (only-for-ordering) model for all its watchers
		1474	except for idle watchers (which use the lock-out model).
		1475
		1476	The rationale behind this is that implementing the lock-out model for
		1477	watchers is not well supported by most kernel interfaces, and most event
		1478	libraries will just poll for the same events again and again as long as
		1479	their callbacks have not been executed, which is very inefficient in the
		1480	common case of one high-priority watcher locking out a mass of lower
		1481	priority ones.
		1482
		1483	Static (ordering) priorities are most useful when you have two or more
		1484	watchers handling the same resource: a typical usage example is having an
		1485	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1486	timeouts. Under load, data might be received while the program handles
		1487	other jobs, but since timers normally get invoked first, the timeout
		1488	handler will be executed before checking for data. In that case, giving
		1489	the timer a lower priority than the I/O watcher ensures that I/O will be
		1490	handled first even under adverse conditions (which is usually, but not
		1491	always, what you want).
		1492
		1493	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1494	will only be executed when no same or higher priority watchers have
		1495	received events, they can be used to implement the "lock-out" model when
		1496	required.
		1497
		1498	For example, to emulate how many other event libraries handle priorities,
		1499	you can associate an C<ev_idle> watcher to each such watcher, and in
		1500	the normal watcher callback, you just start the idle watcher. The real
		1501	processing is done in the idle watcher callback. This causes libev to
		1502	continuously poll and process kernel event data for the watcher, but when
		1503	the lock-out case is known to be rare (which in turn is rare :), this is
		1504	workable.
		1505
		1506	Usually, however, the lock-out model implemented that way will perform
		1507	miserably under the type of load it was designed to handle. In that case,
		1508	it might be preferable to stop the real watcher before starting the
		1509	idle watcher, so the kernel will not have to process the event in case
		1510	the actual processing will be delayed for considerable time.
		1511
		1512	Here is an example of an I/O watcher that should run at a strictly lower
		1513	priority than the default, and which should only process data when no
		1514	other events are pending:
		1515
		1516	ev_idle idle; // actual processing watcher
		1517	ev_io io; // actual event watcher
		1518
997	static void	1519	static void
998	t1_cb (EV_P_ struct ev_timer *w, int revents)	1520	io_cb (EV_P_ ev_io *w, int revents)
999	{	1521	{
1000	struct my_biggy big = (struct my_biggy *	1522	// stop the I/O watcher, we received the event, but
1001	(((char *)w) - offsetof (struct my_biggy, t1));	1523	// are not yet ready to handle it.
		1524	ev_io_stop (EV_A_ w);
		1525
		1526	// start the idle watcher to handle the actual event.
		1527	// it will not be executed as long as other watchers
		1528	// with the default priority are receiving events.
		1529	ev_idle_start (EV_A_ &idle);
1002	}	1530	}
1003		1531
1004	static void	1532	static void
1005	t2_cb (EV_P_ struct ev_timer *w, int revents)	1533	idle_cb (EV_P_ ev_idle *w, int revents)
1006	{	1534	{
1007	struct my_biggy big = (struct my_biggy *	1535	// actual processing
1008	(((char *)w) - offsetof (struct my_biggy, t2));	1536	read (STDIN_FILENO, ...);
		1537
		1538	// have to start the I/O watcher again, as
		1539	// we have handled the event
		1540	ev_io_start (EV_P_ &io);
1009	}	1541	}
		1542
		1543	// initialisation
		1544	ev_idle_init (&idle, idle_cb);
		1545	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1546	ev_io_start (EV_DEFAULT_ &io);
		1547
		1548	In the "real" world, it might also be beneficial to start a timer, so that
		1549	low-priority connections can not be locked out forever under load. This
		1550	enables your program to keep a lower latency for important connections
		1551	during short periods of high load, while not completely locking out less
		1552	important ones.
1010		1553
1011		1554
1012	=head1 WATCHER TYPES	1555	=head1 WATCHER TYPES
1013		1556
1014	This section describes each watcher in detail, but will not repeat	1557	This section describes each watcher in detail, but will not repeat
…		…
1038	In general you can register as many read and/or write event watchers per	1581	In general you can register as many read and/or write event watchers per
1039	fd as you want (as long as you don't confuse yourself). Setting all file	1582	fd as you want (as long as you don't confuse yourself). Setting all file
1040	descriptors to non-blocking mode is also usually a good idea (but not	1583	descriptors to non-blocking mode is also usually a good idea (but not
1041	required if you know what you are doing).	1584	required if you know what you are doing).
1042		1585
1043	If you must do this, then force the use of a known-to-be-good backend
1044	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
1045	C<EVBACKEND_POLL>).
1046
1047	Another thing you have to watch out for is that it is quite easy to	1586	Another thing you have to watch out for is that it is quite easy to
1048	receive "spurious" readiness notifications, that is your callback might	1587	receive "spurious" readiness notifications, that is, your callback might
1049	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1588	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1050	because there is no data. Not only are some backends known to create a	1589	because there is no data. It is very easy to get into this situation even
1051	lot of those (for example solaris ports), it is very easy to get into	1590	with a relatively standard program structure. Thus it is best to always
1052	this situation even with a relatively standard program structure. Thus	1591	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1053	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1054	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1592	preferable to a program hanging until some data arrives.
1055		1593
1056	If you cannot run the fd in non-blocking mode (for example you should not	1594	If you cannot run the fd in non-blocking mode (for example you should
1057	play around with an Xlib connection), then you have to seperately re-test	1595	not play around with an Xlib connection), then you have to separately
1058	whether a file descriptor is really ready with a known-to-be good interface	1596	re-test whether a file descriptor is really ready with a known-to-be good
1059	such as poll (fortunately in our Xlib example, Xlib already does this on	1597	interface such as poll (fortunately in the case of Xlib, it already does
1060	its own, so its quite safe to use).	1598	this on its own, so its quite safe to use). Some people additionally
		1599	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1600	indefinitely.
		1601
		1602	But really, best use non-blocking mode.
1061		1603
1062	=head3 The special problem of disappearing file descriptors	1604	=head3 The special problem of disappearing file descriptors
1063		1605
1064	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1606	Some backends (e.g. kqueue, epoll) need to be told about closing a file
1065	descriptor (either by calling C<close> explicitly or by any other means,	1607	descriptor (either due to calling C<close> explicitly or any other means,
1066	such as C<dup>). The reason is that you register interest in some file	1608	such as C<dup2>). The reason is that you register interest in some file
1067	descriptor, but when it goes away, the operating system will silently drop	1609	descriptor, but when it goes away, the operating system will silently drop
1068	this interest. If another file descriptor with the same number then is	1610	this interest. If another file descriptor with the same number then is
1069	registered with libev, there is no efficient way to see that this is, in	1611	registered with libev, there is no efficient way to see that this is, in
1070	fact, a different file descriptor.	1612	fact, a different file descriptor.
1071		1613
…		…
1089		1631
1090	There is no workaround possible except not registering events	1632	There is no workaround possible except not registering events
1091	for potentially C<dup ()>'ed file descriptors, or to resort to	1633	for potentially C<dup ()>'ed file descriptors, or to resort to
1092	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1634	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1093		1635
		1636	=head3 The special problem of files
		1637
		1638	Many people try to use C<select> (or libev) on file descriptors
		1639	representing files, and expect it to become ready when their program
		1640	doesn't block on disk accesses (which can take a long time on their own).
		1641
		1642	However, this cannot ever work in the "expected" way - you get a readiness
		1643	notification as soon as the kernel knows whether and how much data is
		1644	there, and in the case of open files, that's always the case, so you
		1645	always get a readiness notification instantly, and your read (or possibly
		1646	write) will still block on the disk I/O.
		1647
		1648	Another way to view it is that in the case of sockets, pipes, character
		1649	devices and so on, there is another party (the sender) that delivers data
		1650	on its own, but in the case of files, there is no such thing: the disk
		1651	will not send data on its own, simply because it doesn't know what you
		1652	wish to read - you would first have to request some data.
		1653
		1654	Since files are typically not-so-well supported by advanced notification
		1655	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1656	to files, even though you should not use it. The reason for this is
		1657	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1658	usually a tty, often a pipe, but also sometimes files or special devices
		1659	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1660	F</dev/urandom>), and even though the file might better be served with
		1661	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1662	it "just works" instead of freezing.
		1663
		1664	So avoid file descriptors pointing to files when you know it (e.g. use
		1665	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1666	when you rarely read from a file instead of from a socket, and want to
		1667	reuse the same code path.
		1668
1094	=head3 The special problem of fork	1669	=head3 The special problem of fork
1095		1670
1096	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1671	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
1097	useless behaviour. Libev fully supports fork, but needs to be told about	1672	useless behaviour. Libev fully supports fork, but needs to be told about
1098	it in the child.	1673	it in the child if you want to continue to use it in the child.
1099		1674
1100	To support fork in your programs, you either have to call	1675	To support fork in your child processes, you have to call C<ev_loop_fork
1101	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1676	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1102	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1677	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1103	C<EVBACKEND_POLL>.
1104		1678
1105	=head3 The special problem of SIGPIPE	1679	=head3 The special problem of SIGPIPE
1106		1680
1107	While not really specific to libev, it is easy to forget about SIGPIPE:	1681	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1108	when reading from a pipe whose other end has been closed, your program	1682	when writing to a pipe whose other end has been closed, your program gets
1109	gets send a SIGPIPE, which, by default, aborts your program. For most	1683	sent a SIGPIPE, which, by default, aborts your program. For most programs
1110	programs this is sensible behaviour, for daemons, this is usually	1684	this is sensible behaviour, for daemons, this is usually undesirable.
1111	undesirable.
1112		1685
1113	So when you encounter spurious, unexplained daemon exits, make sure you	1686	So when you encounter spurious, unexplained daemon exits, make sure you
1114	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon	1687	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
1115	somewhere, as that would have given you a big clue).	1688	somewhere, as that would have given you a big clue).
1116		1689
		1690	=head3 The special problem of accept()ing when you can't
		1691
		1692	Many implementations of the POSIX C<accept> function (for example,
		1693	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1694	connection from the pending queue in all error cases.
		1695
		1696	For example, larger servers often run out of file descriptors (because
		1697	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1698	rejecting the connection, leading to libev signalling readiness on
		1699	the next iteration again (the connection still exists after all), and
		1700	typically causing the program to loop at 100% CPU usage.
		1701
		1702	Unfortunately, the set of errors that cause this issue differs between
		1703	operating systems, there is usually little the app can do to remedy the
		1704	situation, and no known thread-safe method of removing the connection to
		1705	cope with overload is known (to me).
		1706
		1707	One of the easiest ways to handle this situation is to just ignore it
		1708	- when the program encounters an overload, it will just loop until the
		1709	situation is over. While this is a form of busy waiting, no OS offers an
		1710	event-based way to handle this situation, so it's the best one can do.
		1711
		1712	A better way to handle the situation is to log any errors other than
		1713	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1714	messages, and continue as usual, which at least gives the user an idea of
		1715	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1716	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1717	usage.
		1718
		1719	If your program is single-threaded, then you could also keep a dummy file
		1720	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1721	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1722	close that fd, and create a new dummy fd. This will gracefully refuse
		1723	clients under typical overload conditions.
		1724
		1725	The last way to handle it is to simply log the error and C<exit>, as
		1726	is often done with C<malloc> failures, but this results in an easy
		1727	opportunity for a DoS attack.
1117		1728
1118	=head3 Watcher-Specific Functions	1729	=head3 Watcher-Specific Functions
1119		1730
1120	=over 4	1731	=over 4
1121		1732
1122	=item ev_io_init (ev_io *, callback, int fd, int events)	1733	=item ev_io_init (ev_io *, callback, int fd, int events)
1123		1734
1124	=item ev_io_set (ev_io *, int fd, int events)	1735	=item ev_io_set (ev_io *, int fd, int events)
1125		1736
1126	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1737	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1127	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1738	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
1128	C<EV_READ | EV_WRITE> to receive the given events.	1739	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1129		1740
1130	=item int fd [read-only]	1741	=item int fd [read-only]
1131		1742
1132	The file descriptor being watched.	1743	The file descriptor being watched.
1133		1744
…		…
1141		1752
1142	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1753	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1143	readable, but only once. Since it is likely line-buffered, you could	1754	readable, but only once. Since it is likely line-buffered, you could
1144	attempt to read a whole line in the callback.	1755	attempt to read a whole line in the callback.
1145		1756
1146	static void	1757	static void
1147	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1758	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1148	{	1759	{
1149	ev_io_stop (loop, w);	1760	ev_io_stop (loop, w);
1150	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1761	.. read from stdin here (or from w->fd) and handle any I/O errors
1151	}	1762	}
1152		1763
1153	...	1764	...
1154	struct ev_loop *loop = ev_default_init (0);	1765	struct ev_loop *loop = ev_default_init (0);
1155	struct ev_io stdin_readable;	1766	ev_io stdin_readable;
1156	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1767	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1157	ev_io_start (loop, &stdin_readable);	1768	ev_io_start (loop, &stdin_readable);
1158	ev_loop (loop, 0);	1769	ev_run (loop, 0);
1159		1770
1160		1771
1161	=head2 C<ev_timer> - relative and optionally repeating timeouts	1772	=head2 C<ev_timer> - relative and optionally repeating timeouts
1162		1773
1163	Timer watchers are simple relative timers that generate an event after a	1774	Timer watchers are simple relative timers that generate an event after a
1164	given time, and optionally repeating in regular intervals after that.	1775	given time, and optionally repeating in regular intervals after that.
1165		1776
1166	The timers are based on real time, that is, if you register an event that	1777	The timers are based on real time, that is, if you register an event that
1167	times out after an hour and you reset your system clock to january last	1778	times out after an hour and you reset your system clock to January last
1168	year, it will still time out after (roughly) and hour. "Roughly" because	1779	year, it will still time out after (roughly) one hour. "Roughly" because
1169	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1780	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1170	monotonic clock option helps a lot here).	1781	monotonic clock option helps a lot here).
		1782
		1783	The callback is guaranteed to be invoked only I<after> its timeout has
		1784	passed (not I<at>, so on systems with very low-resolution clocks this
		1785	might introduce a small delay, see "the special problem of being too
		1786	early", below). If multiple timers become ready during the same loop
		1787	iteration then the ones with earlier time-out values are invoked before
		1788	ones of the same priority with later time-out values (but this is no
		1789	longer true when a callback calls C<ev_run> recursively).
		1790
		1791	=head3 Be smart about timeouts
		1792
		1793	Many real-world problems involve some kind of timeout, usually for error
		1794	recovery. A typical example is an HTTP request - if the other side hangs,
		1795	you want to raise some error after a while.
		1796
		1797	What follows are some ways to handle this problem, from obvious and
		1798	inefficient to smart and efficient.
		1799
		1800	In the following, a 60 second activity timeout is assumed - a timeout that
		1801	gets reset to 60 seconds each time there is activity (e.g. each time some
		1802	data or other life sign was received).
		1803
		1804	=over 4
		1805
		1806	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1807
		1808	This is the most obvious, but not the most simple way: In the beginning,
		1809	start the watcher:
		1810
		1811	ev_timer_init (timer, callback, 60., 0.);
		1812	ev_timer_start (loop, timer);
		1813
		1814	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1815	and start it again:
		1816
		1817	ev_timer_stop (loop, timer);
		1818	ev_timer_set (timer, 60., 0.);
		1819	ev_timer_start (loop, timer);
		1820
		1821	This is relatively simple to implement, but means that each time there is
		1822	some activity, libev will first have to remove the timer from its internal
		1823	data structure and then add it again. Libev tries to be fast, but it's
		1824	still not a constant-time operation.
		1825
		1826	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1827
		1828	This is the easiest way, and involves using C<ev_timer_again> instead of
		1829	C<ev_timer_start>.
		1830
		1831	To implement this, configure an C<ev_timer> with a C<repeat> value
		1832	of C<60> and then call C<ev_timer_again> at start and each time you
		1833	successfully read or write some data. If you go into an idle state where
		1834	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1835	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1836
		1837	That means you can ignore both the C<ev_timer_start> function and the
		1838	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1839	member and C<ev_timer_again>.
		1840
		1841	At start:
		1842
		1843	ev_init (timer, callback);
		1844	timer->repeat = 60.;
		1845	ev_timer_again (loop, timer);
		1846
		1847	Each time there is some activity:
		1848
		1849	ev_timer_again (loop, timer);
		1850
		1851	It is even possible to change the time-out on the fly, regardless of
		1852	whether the watcher is active or not:
		1853
		1854	timer->repeat = 30.;
		1855	ev_timer_again (loop, timer);
		1856
		1857	This is slightly more efficient then stopping/starting the timer each time
		1858	you want to modify its timeout value, as libev does not have to completely
		1859	remove and re-insert the timer from/into its internal data structure.
		1860
		1861	It is, however, even simpler than the "obvious" way to do it.
		1862
		1863	=item 3. Let the timer time out, but then re-arm it as required.
		1864
		1865	This method is more tricky, but usually most efficient: Most timeouts are
		1866	relatively long compared to the intervals between other activity - in
		1867	our example, within 60 seconds, there are usually many I/O events with
		1868	associated activity resets.
		1869
		1870	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1871	but remember the time of last activity, and check for a real timeout only
		1872	within the callback:
		1873
		1874	ev_tstamp timeout = 60.;
		1875	ev_tstamp last_activity; // time of last activity
		1876	ev_timer timer;
		1877
		1878	static void
		1879	callback (EV_P_ ev_timer *w, int revents)
		1880	{
		1881	// calculate when the timeout would happen
		1882	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
		1883
		1884	// if negative, it means we the timeout already occurred
		1885	if (after < 0.)
		1886	{
		1887	// timeout occurred, take action
		1888	}
		1889	else
		1890	{
		1891	// callback was invoked, but there was some recent
		1892	// activity. simply restart the timer to time out
		1893	// after "after" seconds, which is the earliest time
		1894	// the timeout can occur.
		1895	ev_timer_set (w, after, 0.);
		1896	ev_timer_start (EV_A_ w);
		1897	}
		1898	}
		1899
		1900	To summarise the callback: first calculate in how many seconds the
		1901	timeout will occur (by calculating the absolute time when it would occur,
		1902	C<last_activity + timeout>, and subtracting the current time, C<ev_now
		1903	(EV_A)> from that).
		1904
		1905	If this value is negative, then we are already past the timeout, i.e. we
		1906	timed out, and need to do whatever is needed in this case.
		1907
		1908	Otherwise, we now the earliest time at which the timeout would trigger,
		1909	and simply start the timer with this timeout value.
		1910
		1911	In other words, each time the callback is invoked it will check whether
		1912	the timeout occurred. If not, it will simply reschedule itself to check
		1913	again at the earliest time it could time out. Rinse. Repeat.
		1914
		1915	This scheme causes more callback invocations (about one every 60 seconds
		1916	minus half the average time between activity), but virtually no calls to
		1917	libev to change the timeout.
		1918
		1919	To start the machinery, simply initialise the watcher and set
		1920	C<last_activity> to the current time (meaning there was some activity just
		1921	now), then call the callback, which will "do the right thing" and start
		1922	the timer:
		1923
		1924	last_activity = ev_now (EV_A);
		1925	ev_init (&timer, callback);
		1926	callback (EV_A_ &timer, 0);
		1927
		1928	When there is some activity, simply store the current time in
		1929	C<last_activity>, no libev calls at all:
		1930
		1931	if (activity detected)
		1932	last_activity = ev_now (EV_A);
		1933
		1934	When your timeout value changes, then the timeout can be changed by simply
		1935	providing a new value, stopping the timer and calling the callback, which
		1936	will again do the right thing (for example, time out immediately :).
		1937
		1938	timeout = new_value;
		1939	ev_timer_stop (EV_A_ &timer);
		1940	callback (EV_A_ &timer, 0);
		1941
		1942	This technique is slightly more complex, but in most cases where the
		1943	time-out is unlikely to be triggered, much more efficient.
		1944
		1945	=item 4. Wee, just use a double-linked list for your timeouts.
		1946
		1947	If there is not one request, but many thousands (millions...), all
		1948	employing some kind of timeout with the same timeout value, then one can
		1949	do even better:
		1950
		1951	When starting the timeout, calculate the timeout value and put the timeout
		1952	at the I<end> of the list.
		1953
		1954	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1955	the list is expected to fire (for example, using the technique #3).
		1956
		1957	When there is some activity, remove the timer from the list, recalculate
		1958	the timeout, append it to the end of the list again, and make sure to
		1959	update the C<ev_timer> if it was taken from the beginning of the list.
		1960
		1961	This way, one can manage an unlimited number of timeouts in O(1) time for
		1962	starting, stopping and updating the timers, at the expense of a major
		1963	complication, and having to use a constant timeout. The constant timeout
		1964	ensures that the list stays sorted.
		1965
		1966	=back
		1967
		1968	So which method the best?
		1969
		1970	Method #2 is a simple no-brain-required solution that is adequate in most
		1971	situations. Method #3 requires a bit more thinking, but handles many cases
		1972	better, and isn't very complicated either. In most case, choosing either
		1973	one is fine, with #3 being better in typical situations.
		1974
		1975	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1976	rather complicated, but extremely efficient, something that really pays
		1977	off after the first million or so of active timers, i.e. it's usually
		1978	overkill :)
		1979
		1980	=head3 The special problem of being too early
		1981
		1982	If you ask a timer to call your callback after three seconds, then
		1983	you expect it to be invoked after three seconds - but of course, this
		1984	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		1985	guaranteed to any precision by libev - imagine somebody suspending the
		1986	process with a STOP signal for a few hours for example.
		1987
		1988	So, libev tries to invoke your callback as soon as possible I<after> the
		1989	delay has occurred, but cannot guarantee this.
		1990
		1991	A less obvious failure mode is calling your callback too early: many event
		1992	loops compare timestamps with a "elapsed delay >= requested delay", but
		1993	this can cause your callback to be invoked much earlier than you would
		1994	expect.
		1995
		1996	To see why, imagine a system with a clock that only offers full second
		1997	resolution (think windows if you can't come up with a broken enough OS
		1998	yourself). If you schedule a one-second timer at the time 500.9, then the
		1999	event loop will schedule your timeout to elapse at a system time of 500
		2000	(500.9 truncated to the resolution) + 1, or 501.
		2001
		2002	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2003	501" and invoke the callback 0.1s after it was started, even though a
		2004	one-second delay was requested - this is being "too early", despite best
		2005	intentions.
		2006
		2007	This is the reason why libev will never invoke the callback if the elapsed
		2008	delay equals the requested delay, but only when the elapsed delay is
		2009	larger than the requested delay. In the example above, libev would only invoke
		2010	the callback at system time 502, or 1.1s after the timer was started.
		2011
		2012	So, while libev cannot guarantee that your callback will be invoked
		2013	exactly when requested, it I<can> and I<does> guarantee that the requested
		2014	delay has actually elapsed, or in other words, it always errs on the "too
		2015	late" side of things.
		2016
		2017	=head3 The special problem of time updates
		2018
		2019	Establishing the current time is a costly operation (it usually takes
		2020	at least one system call): EV therefore updates its idea of the current
		2021	time only before and after C<ev_run> collects new events, which causes a
		2022	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		2023	lots of events in one iteration.
1171		2024
1172	The relative timeouts are calculated relative to the C<ev_now ()>	2025	The relative timeouts are calculated relative to the C<ev_now ()>
1173	time. This is usually the right thing as this timestamp refers to the time	2026	time. This is usually the right thing as this timestamp refers to the time
1174	of the event triggering whatever timeout you are modifying/starting. If	2027	of the event triggering whatever timeout you are modifying/starting. If
1175	you suspect event processing to be delayed and you I<need> to base the timeout	2028	you suspect event processing to be delayed and you I<need> to base the
1176	on the current time, use something like this to adjust for this:	2029	timeout on the current time, use something like this to adjust for this:
1177		2030
1178	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2031	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1179		2032
1180	The callback is guarenteed to be invoked only after its timeout has passed,	2033	If the event loop is suspended for a long time, you can also force an
1181	but if multiple timers become ready during the same loop iteration then	2034	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1182	order of execution is undefined.	2035	()>.
		2036
		2037	=head3 The special problem of unsynchronised clocks
		2038
		2039	Modern systems have a variety of clocks - libev itself uses the normal
		2040	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2041	jumps).
		2042
		2043	Neither of these clocks is synchronised with each other or any other clock
		2044	on the system, so C<ev_time ()> might return a considerably different time
		2045	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2046	a call to C<gettimeofday> might return a second count that is one higher
		2047	than a directly following call to C<time>.
		2048
		2049	The moral of this is to only compare libev-related timestamps with
		2050	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2051	a second or so.
		2052
		2053	One more problem arises due to this lack of synchronisation: if libev uses
		2054	the system monotonic clock and you compare timestamps from C<ev_time>
		2055	or C<ev_now> from when you started your timer and when your callback is
		2056	invoked, you will find that sometimes the callback is a bit "early".
		2057
		2058	This is because C<ev_timer>s work in real time, not wall clock time, so
		2059	libev makes sure your callback is not invoked before the delay happened,
		2060	I<measured according to the real time>, not the system clock.
		2061
		2062	If your timeouts are based on a physical timescale (e.g. "time out this
		2063	connection after 100 seconds") then this shouldn't bother you as it is
		2064	exactly the right behaviour.
		2065
		2066	If you want to compare wall clock/system timestamps to your timers, then
		2067	you need to use C<ev_periodic>s, as these are based on the wall clock
		2068	time, where your comparisons will always generate correct results.
		2069
		2070	=head3 The special problems of suspended animation
		2071
		2072	When you leave the server world it is quite customary to hit machines that
		2073	can suspend/hibernate - what happens to the clocks during such a suspend?
		2074
		2075	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		2076	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		2077	to run until the system is suspended, but they will not advance while the
		2078	system is suspended. That means, on resume, it will be as if the program
		2079	was frozen for a few seconds, but the suspend time will not be counted
		2080	towards C<ev_timer> when a monotonic clock source is used. The real time
		2081	clock advanced as expected, but if it is used as sole clocksource, then a
		2082	long suspend would be detected as a time jump by libev, and timers would
		2083	be adjusted accordingly.
		2084
		2085	I would not be surprised to see different behaviour in different between
		2086	operating systems, OS versions or even different hardware.
		2087
		2088	The other form of suspend (job control, or sending a SIGSTOP) will see a
		2089	time jump in the monotonic clocks and the realtime clock. If the program
		2090	is suspended for a very long time, and monotonic clock sources are in use,
		2091	then you can expect C<ev_timer>s to expire as the full suspension time
		2092	will be counted towards the timers. When no monotonic clock source is in
		2093	use, then libev will again assume a timejump and adjust accordingly.
		2094
		2095	It might be beneficial for this latter case to call C<ev_suspend>
		2096	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		2097	deterministic behaviour in this case (you can do nothing against
		2098	C<SIGSTOP>).
1183		2099
1184	=head3 Watcher-Specific Functions and Data Members	2100	=head3 Watcher-Specific Functions and Data Members
1185		2101
1186	=over 4	2102	=over 4
1187		2103
…		…
1201	keep up with the timer (because it takes longer than those 10 seconds to	2117	keep up with the timer (because it takes longer than those 10 seconds to
1202	do stuff) the timer will not fire more than once per event loop iteration.	2118	do stuff) the timer will not fire more than once per event loop iteration.
1203		2119
1204	=item ev_timer_again (loop, ev_timer *)	2120	=item ev_timer_again (loop, ev_timer *)
1205		2121
1206	This will act as if the timer timed out and restart it again if it is	2122	This will act as if the timer timed out, and restarts it again if it is
1207	repeating. The exact semantics are:	2123	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2124	timeout to the C<repeat> value and calling C<ev_timer_start>.
1208		2125
		2126	The exact semantics are as in the following rules, all of which will be
		2127	applied to the watcher:
		2128
		2129	=over 4
		2130
1209	If the timer is pending, its pending status is cleared.	2131	=item If the timer is pending, the pending status is always cleared.
1210		2132
1211	If the timer is started but nonrepeating, stop it (as if it timed out).	2133	=item If the timer is started but non-repeating, stop it (as if it timed
		2134	out, without invoking it).
1212		2135
1213	If the timer is repeating, either start it if necessary (with the	2136	=item If the timer is repeating, make the C<repeat> value the new timeout
1214	C<repeat> value), or reset the running timer to the C<repeat> value.	2137	and start the timer, if necessary.
1215		2138
1216	This sounds a bit complicated, but here is a useful and typical	2139	=back
1217	example: Imagine you have a tcp connection and you want a so-called idle
1218	timeout, that is, you want to be called when there have been, say, 60
1219	seconds of inactivity on the socket. The easiest way to do this is to
1220	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1221	C<ev_timer_again> each time you successfully read or write some data. If
1222	you go into an idle state where you do not expect data to travel on the
1223	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1224	automatically restart it if need be.
1225		2140
1226	That means you can ignore the C<after> value and C<ev_timer_start>	2141	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1227	altogether and only ever use the C<repeat> value and C<ev_timer_again>:	2142	usage example.
1228		2143
1229	ev_timer_init (timer, callback, 0., 5.);	2144	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1230	ev_timer_again (loop, timer);
1231	...
1232	timer->again = 17.;
1233	ev_timer_again (loop, timer);
1234	...
1235	timer->again = 10.;
1236	ev_timer_again (loop, timer);
1237		2145
1238	This is more slightly efficient then stopping/starting the timer each time	2146	Returns the remaining time until a timer fires. If the timer is active,
1239	you want to modify its timeout value.	2147	then this time is relative to the current event loop time, otherwise it's
		2148	the timeout value currently configured.
		2149
		2150	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
		2151	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		2152	will return C<4>. When the timer expires and is restarted, it will return
		2153	roughly C<7> (likely slightly less as callback invocation takes some time,
		2154	too), and so on.
1240		2155
1241	=item ev_tstamp repeat [read-write]	2156	=item ev_tstamp repeat [read-write]
1242		2157
1243	The current C<repeat> value. Will be used each time the watcher times out	2158	The current C<repeat> value. Will be used each time the watcher times out
1244	or C<ev_timer_again> is called and determines the next timeout (if any),	2159	or C<ev_timer_again> is called, and determines the next timeout (if any),
1245	which is also when any modifications are taken into account.	2160	which is also when any modifications are taken into account.
1246		2161
1247	=back	2162	=back
1248		2163
1249	=head3 Examples	2164	=head3 Examples
1250		2165
1251	Example: Create a timer that fires after 60 seconds.	2166	Example: Create a timer that fires after 60 seconds.
1252		2167
1253	static void	2168	static void
1254	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2169	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1255	{	2170	{
1256	.. one minute over, w is actually stopped right here	2171	.. one minute over, w is actually stopped right here
1257	}	2172	}
1258		2173
1259	struct ev_timer mytimer;	2174	ev_timer mytimer;
1260	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	2175	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1261	ev_timer_start (loop, &mytimer);	2176	ev_timer_start (loop, &mytimer);
1262		2177
1263	Example: Create a timeout timer that times out after 10 seconds of	2178	Example: Create a timeout timer that times out after 10 seconds of
1264	inactivity.	2179	inactivity.
1265		2180
1266	static void	2181	static void
1267	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2182	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1268	{	2183	{
1269	.. ten seconds without any activity	2184	.. ten seconds without any activity
1270	}	2185	}
1271		2186
1272	struct ev_timer mytimer;	2187	ev_timer mytimer;
1273	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	2188	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1274	ev_timer_again (&mytimer); /* start timer */	2189	ev_timer_again (&mytimer); /* start timer */
1275	ev_loop (loop, 0);	2190	ev_run (loop, 0);
1276		2191
1277	// and in some piece of code that gets executed on any "activity":	2192	// and in some piece of code that gets executed on any "activity":
1278	// reset the timeout to start ticking again at 10 seconds	2193	// reset the timeout to start ticking again at 10 seconds
1279	ev_timer_again (&mytimer);	2194	ev_timer_again (&mytimer);
1280		2195
1281		2196
1282	=head2 C<ev_periodic> - to cron or not to cron?	2197	=head2 C<ev_periodic> - to cron or not to cron?
1283		2198
1284	Periodic watchers are also timers of a kind, but they are very versatile	2199	Periodic watchers are also timers of a kind, but they are very versatile
1285	(and unfortunately a bit complex).	2200	(and unfortunately a bit complex).
1286		2201
1287	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2202	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1288	but on wallclock time (absolute time). You can tell a periodic watcher	2203	relative time, the physical time that passes) but on wall clock time
1289	to trigger after some specific point in time. For example, if you tell a	2204	(absolute time, the thing you can read on your calender or clock). The
1290	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	2205	difference is that wall clock time can run faster or slower than real
1291	+ 10.>, that is, an absolute time not a delay) and then reset your system	2206	time, and time jumps are not uncommon (e.g. when you adjust your
1292	clock to january of the previous year, then it will take more than year	2207	wrist-watch).
1293	to trigger the event (unlike an C<ev_timer>, which would still trigger
1294	roughly 10 seconds later as it uses a relative timeout).
1295		2208
		2209	You can tell a periodic watcher to trigger after some specific point
		2210	in time: for example, if you tell a periodic watcher to trigger "in 10
		2211	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2212	not a delay) and then reset your system clock to January of the previous
		2213	year, then it will take a year or more to trigger the event (unlike an
		2214	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2215	it, as it uses a relative timeout).
		2216
1296	C<ev_periodic>s can also be used to implement vastly more complex timers,	2217	C<ev_periodic> watchers can also be used to implement vastly more complex
1297	such as triggering an event on each "midnight, local time", or other	2218	timers, such as triggering an event on each "midnight, local time", or
1298	complicated, rules.	2219	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		2220	those cannot react to time jumps.
1299		2221
1300	As with timers, the callback is guarenteed to be invoked only when the	2222	As with timers, the callback is guaranteed to be invoked only when the
1301	time (C<at>) has passed, but if multiple periodic timers become ready	2223	point in time where it is supposed to trigger has passed. If multiple
1302	during the same loop iteration then order of execution is undefined.	2224	timers become ready during the same loop iteration then the ones with
		2225	earlier time-out values are invoked before ones with later time-out values
		2226	(but this is no longer true when a callback calls C<ev_run> recursively).
1303		2227
1304	=head3 Watcher-Specific Functions and Data Members	2228	=head3 Watcher-Specific Functions and Data Members
1305		2229
1306	=over 4	2230	=over 4
1307		2231
1308	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2232	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1309		2233
1310	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2234	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1311		2235
1312	Lots of arguments, lets sort it out... There are basically three modes of	2236	Lots of arguments, let's sort it out... There are basically three modes of
1313	operation, and we will explain them from simplest to complex:	2237	operation, and we will explain them from simplest to most complex:
1314		2238
1315	=over 4	2239	=over 4
1316		2240
1317	=item * absolute timer (at = time, interval = reschedule_cb = 0)	2241	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1318		2242
1319	In this configuration the watcher triggers an event after the wallclock	2243	In this configuration the watcher triggers an event after the wall clock
1320	time C<at> has passed and doesn't repeat. It will not adjust when a time	2244	time C<offset> has passed. It will not repeat and will not adjust when a
1321	jump occurs, that is, if it is to be run at January 1st 2011 then it will	2245	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1322	run when the system time reaches or surpasses this time.	2246	will be stopped and invoked when the system clock reaches or surpasses
		2247	this point in time.
1323		2248
1324	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	2249	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1325		2250
1326	In this mode the watcher will always be scheduled to time out at the next	2251	In this mode the watcher will always be scheduled to time out at the next
1327	C<at + N * interval> time (for some integer N, which can also be negative)	2252	C<offset + N * interval> time (for some integer N, which can also be
1328	and then repeat, regardless of any time jumps.	2253	negative) and then repeat, regardless of any time jumps. The C<offset>
		2254	argument is merely an offset into the C<interval> periods.
1329		2255
1330	This can be used to create timers that do not drift with respect to system	2256	This can be used to create timers that do not drift with respect to the
1331	time, for example, here is a C<ev_periodic> that triggers each hour, on	2257	system clock, for example, here is an C<ev_periodic> that triggers each
1332	the hour:	2258	hour, on the hour (with respect to UTC):
1333		2259
1334	ev_periodic_set (&periodic, 0., 3600., 0);	2260	ev_periodic_set (&periodic, 0., 3600., 0);
1335		2261
1336	This doesn't mean there will always be 3600 seconds in between triggers,	2262	This doesn't mean there will always be 3600 seconds in between triggers,
1337	but only that the the callback will be called when the system time shows a	2263	but only that the callback will be called when the system time shows a
1338	full hour (UTC), or more correctly, when the system time is evenly divisible	2264	full hour (UTC), or more correctly, when the system time is evenly divisible
1339	by 3600.	2265	by 3600.
1340		2266
1341	Another way to think about it (for the mathematically inclined) is that	2267	Another way to think about it (for the mathematically inclined) is that
1342	C<ev_periodic> will try to run the callback in this mode at the next possible	2268	C<ev_periodic> will try to run the callback in this mode at the next possible
1343	time where C<time = at (mod interval)>, regardless of any time jumps.	2269	time where C<time = offset (mod interval)>, regardless of any time jumps.
1344		2270
1345	For numerical stability it is preferable that the C<at> value is near	2271	The C<interval> I<MUST> be positive, and for numerical stability, the
1346	C<ev_now ()> (the current time), but there is no range requirement for	2272	interval value should be higher than C<1/8192> (which is around 100
1347	this value, and in fact is often specified as zero.	2273	microseconds) and C<offset> should be higher than C<0> and should have
		2274	at most a similar magnitude as the current time (say, within a factor of
		2275	ten). Typical values for offset are, in fact, C<0> or something between
		2276	C<0> and C<interval>, which is also the recommended range.
1348		2277
1349	Note also that there is an upper limit to how often a timer can fire (cpu	2278	Note also that there is an upper limit to how often a timer can fire (CPU
1350	speed for example), so if C<interval> is very small then timing stability	2279	speed for example), so if C<interval> is very small then timing stability
1351	will of course detoriate. Libev itself tries to be exact to be about one	2280	will of course deteriorate. Libev itself tries to be exact to be about one
1352	millisecond (if the OS supports it and the machine is fast enough).	2281	millisecond (if the OS supports it and the machine is fast enough).
1353		2282
1354	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	2283	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1355		2284
1356	In this mode the values for C<interval> and C<at> are both being	2285	In this mode the values for C<interval> and C<offset> are both being
1357	ignored. Instead, each time the periodic watcher gets scheduled, the	2286	ignored. Instead, each time the periodic watcher gets scheduled, the
1358	reschedule callback will be called with the watcher as first, and the	2287	reschedule callback will be called with the watcher as first, and the
1359	current time as second argument.	2288	current time as second argument.
1360		2289
1361	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2290	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1362	ever, or make ANY event loop modifications whatsoever>.	2291	or make ANY other event loop modifications whatsoever, unless explicitly
		2292	allowed by documentation here>.
1363		2293
1364	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop	2294	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
1365	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the	2295	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
1366	only event loop modification you are allowed to do).	2296	only event loop modification you are allowed to do).
1367		2297
1368	The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic	2298	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1369	*w, ev_tstamp now)>, e.g.:	2299	*w, ev_tstamp now)>, e.g.:
1370		2300
		2301	static ev_tstamp
1371	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2302	my_rescheduler (ev_periodic *w, ev_tstamp now)
1372	{	2303	{
1373	return now + 60.;	2304	return now + 60.;
1374	}	2305	}
1375		2306
1376	It must return the next time to trigger, based on the passed time value	2307	It must return the next time to trigger, based on the passed time value
…		…
1396	a different time than the last time it was called (e.g. in a crond like	2327	a different time than the last time it was called (e.g. in a crond like
1397	program when the crontabs have changed).	2328	program when the crontabs have changed).
1398		2329
1399	=item ev_tstamp ev_periodic_at (ev_periodic *)	2330	=item ev_tstamp ev_periodic_at (ev_periodic *)
1400		2331
1401	When active, returns the absolute time that the watcher is supposed to	2332	When active, returns the absolute time that the watcher is supposed
1402	trigger next.	2333	to trigger next. This is not the same as the C<offset> argument to
		2334	C<ev_periodic_set>, but indeed works even in interval and manual
		2335	rescheduling modes.
1403		2336
1404	=item ev_tstamp offset [read-write]	2337	=item ev_tstamp offset [read-write]
1405		2338
1406	When repeating, this contains the offset value, otherwise this is the	2339	When repeating, this contains the offset value, otherwise this is the
1407	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2340	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2341	although libev might modify this value for better numerical stability).
1408		2342
1409	Can be modified any time, but changes only take effect when the periodic	2343	Can be modified any time, but changes only take effect when the periodic
1410	timer fires or C<ev_periodic_again> is being called.	2344	timer fires or C<ev_periodic_again> is being called.
1411		2345
1412	=item ev_tstamp interval [read-write]	2346	=item ev_tstamp interval [read-write]
1413		2347
1414	The current interval value. Can be modified any time, but changes only	2348	The current interval value. Can be modified any time, but changes only
1415	take effect when the periodic timer fires or C<ev_periodic_again> is being	2349	take effect when the periodic timer fires or C<ev_periodic_again> is being
1416	called.	2350	called.
1417		2351
1418	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2352	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1419		2353
1420	The current reschedule callback, or C<0>, if this functionality is	2354	The current reschedule callback, or C<0>, if this functionality is
1421	switched off. Can be changed any time, but changes only take effect when	2355	switched off. Can be changed any time, but changes only take effect when
1422	the periodic timer fires or C<ev_periodic_again> is being called.	2356	the periodic timer fires or C<ev_periodic_again> is being called.
1423		2357
1424	=back	2358	=back
1425		2359
1426	=head3 Examples	2360	=head3 Examples
1427		2361
1428	Example: Call a callback every hour, or, more precisely, whenever the	2362	Example: Call a callback every hour, or, more precisely, whenever the
1429	system clock is divisible by 3600. The callback invocation times have	2363	system time is divisible by 3600. The callback invocation times have
1430	potentially a lot of jittering, but good long-term stability.	2364	potentially a lot of jitter, but good long-term stability.
1431		2365
1432	static void	2366	static void
1433	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2367	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1434	{	2368	{
1435	... its now a full hour (UTC, or TAI or whatever your clock follows)	2369	... its now a full hour (UTC, or TAI or whatever your clock follows)
1436	}	2370	}
1437		2371
1438	struct ev_periodic hourly_tick;	2372	ev_periodic hourly_tick;
1439	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2373	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1440	ev_periodic_start (loop, &hourly_tick);	2374	ev_periodic_start (loop, &hourly_tick);
1441		2375
1442	Example: The same as above, but use a reschedule callback to do it:	2376	Example: The same as above, but use a reschedule callback to do it:
1443		2377
1444	#include <math.h>	2378	#include <math.h>
1445		2379
1446	static ev_tstamp	2380	static ev_tstamp
1447	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2381	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1448	{	2382	{
1449	return fmod (now, 3600.) + 3600.;	2383	return now + (3600. - fmod (now, 3600.));
1450	}	2384	}
1451		2385
1452	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2386	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1453		2387
1454	Example: Call a callback every hour, starting now:	2388	Example: Call a callback every hour, starting now:
1455		2389
1456	struct ev_periodic hourly_tick;	2390	ev_periodic hourly_tick;
1457	ev_periodic_init (&hourly_tick, clock_cb,	2391	ev_periodic_init (&hourly_tick, clock_cb,
1458	fmod (ev_now (loop), 3600.), 3600., 0);	2392	fmod (ev_now (loop), 3600.), 3600., 0);
1459	ev_periodic_start (loop, &hourly_tick);	2393	ev_periodic_start (loop, &hourly_tick);
1460		2394
1461		2395
1462	=head2 C<ev_signal> - signal me when a signal gets signalled!	2396	=head2 C<ev_signal> - signal me when a signal gets signalled!
1463		2397
1464	Signal watchers will trigger an event when the process receives a specific	2398	Signal watchers will trigger an event when the process receives a specific
1465	signal one or more times. Even though signals are very asynchronous, libev	2399	signal one or more times. Even though signals are very asynchronous, libev
1466	will try it's best to deliver signals synchronously, i.e. as part of the	2400	will try its best to deliver signals synchronously, i.e. as part of the
1467	normal event processing, like any other event.	2401	normal event processing, like any other event.
1468		2402
		2403	If you want signals to be delivered truly asynchronously, just use
		2404	C<sigaction> as you would do without libev and forget about sharing
		2405	the signal. You can even use C<ev_async> from a signal handler to
		2406	synchronously wake up an event loop.
		2407
1469	You can configure as many watchers as you like per signal. Only when the	2408	You can configure as many watchers as you like for the same signal, but
		2409	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2410	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2411	C<SIGINT> in both the default loop and another loop at the same time. At
		2412	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2413
1470	first watcher gets started will libev actually register a signal watcher	2414	When the first watcher gets started will libev actually register something
1471	with the kernel (thus it coexists with your own signal handlers as long	2415	with the kernel (thus it coexists with your own signal handlers as long as
1472	as you don't register any with libev). Similarly, when the last signal	2416	you don't register any with libev for the same signal).
1473	watcher for a signal is stopped libev will reset the signal handler to
1474	SIG_DFL (regardless of what it was set to before).
1475		2417
1476	If possible and supported, libev will install its handlers with	2418	If possible and supported, libev will install its handlers with
1477	C<SA_RESTART> behaviour enabled, so syscalls should not be unduly	2419	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
1478	interrupted. If you have a problem with syscalls getting interrupted by	2420	not be unduly interrupted. If you have a problem with system calls getting
1479	signals you can block all signals in an C<ev_check> watcher and unblock	2421	interrupted by signals you can block all signals in an C<ev_check> watcher
1480	them in an C<ev_prepare> watcher.	2422	and unblock them in an C<ev_prepare> watcher.
		2423
		2424	=head3 The special problem of inheritance over fork/execve/pthread_create
		2425
		2426	Both the signal mask (C<sigprocmask>) and the signal disposition
		2427	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2428	stopping it again), that is, libev might or might not block the signal,
		2429	and might or might not set or restore the installed signal handler (but
		2430	see C<EVFLAG_NOSIGMASK>).
		2431
		2432	While this does not matter for the signal disposition (libev never
		2433	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2434	C<execve>), this matters for the signal mask: many programs do not expect
		2435	certain signals to be blocked.
		2436
		2437	This means that before calling C<exec> (from the child) you should reset
		2438	the signal mask to whatever "default" you expect (all clear is a good
		2439	choice usually).
		2440
		2441	The simplest way to ensure that the signal mask is reset in the child is
		2442	to install a fork handler with C<pthread_atfork> that resets it. That will
		2443	catch fork calls done by libraries (such as the libc) as well.
		2444
		2445	In current versions of libev, the signal will not be blocked indefinitely
		2446	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2447	the window of opportunity for problems, it will not go away, as libev
		2448	I<has> to modify the signal mask, at least temporarily.
		2449
		2450	So I can't stress this enough: I<If you do not reset your signal mask when
		2451	you expect it to be empty, you have a race condition in your code>. This
		2452	is not a libev-specific thing, this is true for most event libraries.
		2453
		2454	=head3 The special problem of threads signal handling
		2455
		2456	POSIX threads has problematic signal handling semantics, specifically,
		2457	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2458	threads in a process block signals, which is hard to achieve.
		2459
		2460	When you want to use sigwait (or mix libev signal handling with your own
		2461	for the same signals), you can tackle this problem by globally blocking
		2462	all signals before creating any threads (or creating them with a fully set
		2463	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2464	loops. Then designate one thread as "signal receiver thread" which handles
		2465	these signals. You can pass on any signals that libev might be interested
		2466	in by calling C<ev_feed_signal>.
1481		2467
1482	=head3 Watcher-Specific Functions and Data Members	2468	=head3 Watcher-Specific Functions and Data Members
1483		2469
1484	=over 4	2470	=over 4
1485		2471
…		…
1496		2482
1497	=back	2483	=back
1498		2484
1499	=head3 Examples	2485	=head3 Examples
1500		2486
1501	Example: Try to exit cleanly on SIGINT and SIGTERM.	2487	Example: Try to exit cleanly on SIGINT.
1502		2488
1503	static void	2489	static void
1504	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2490	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
1505	{	2491	{
1506	ev_unloop (loop, EVUNLOOP_ALL);	2492	ev_break (loop, EVBREAK_ALL);
1507	}	2493	}
1508		2494
1509	struct ev_signal signal_watcher;	2495	ev_signal signal_watcher;
1510	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2496	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1511	ev_signal_start (loop, &sigint_cb);	2497	ev_signal_start (loop, &signal_watcher);
1512		2498
1513		2499
1514	=head2 C<ev_child> - watch out for process status changes	2500	=head2 C<ev_child> - watch out for process status changes
1515		2501
1516	Child watchers trigger when your process receives a SIGCHLD in response to	2502	Child watchers trigger when your process receives a SIGCHLD in response to
1517	some child status changes (most typically when a child of yours dies). It	2503	some child status changes (most typically when a child of yours dies or
1518	is permissible to install a child watcher I<after> the child has been	2504	exits). It is permissible to install a child watcher I<after> the child
1519	forked (which implies it might have already exited), as long as the event	2505	has been forked (which implies it might have already exited), as long
1520	loop isn't entered (or is continued from a watcher).	2506	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2507	forking and then immediately registering a watcher for the child is fine,
		2508	but forking and registering a watcher a few event loop iterations later or
		2509	in the next callback invocation is not.
1521		2510
1522	Only the default event loop is capable of handling signals, and therefore	2511	Only the default event loop is capable of handling signals, and therefore
1523	you can only rgeister child watchers in the default event loop.	2512	you can only register child watchers in the default event loop.
		2513
		2514	Due to some design glitches inside libev, child watchers will always be
		2515	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2516	libev)
1524		2517
1525	=head3 Process Interaction	2518	=head3 Process Interaction
1526		2519
1527	Libev grabs C<SIGCHLD> as soon as the default event loop is	2520	Libev grabs C<SIGCHLD> as soon as the default event loop is
1528	initialised. This is necessary to guarantee proper behaviour even if	2521	initialised. This is necessary to guarantee proper behaviour even if the
1529	the first child watcher is started after the child exits. The occurance	2522	first child watcher is started after the child exits. The occurrence
1530	of C<SIGCHLD> is recorded asynchronously, but child reaping is done	2523	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
1531	synchronously as part of the event loop processing. Libev always reaps all	2524	synchronously as part of the event loop processing. Libev always reaps all
1532	children, even ones not watched.	2525	children, even ones not watched.
1533		2526
1534	=head3 Overriding the Built-In Processing	2527	=head3 Overriding the Built-In Processing
…		…
1538	handler, you can override it easily by installing your own handler for	2531	handler, you can override it easily by installing your own handler for
1539	C<SIGCHLD> after initialising the default loop, and making sure the	2532	C<SIGCHLD> after initialising the default loop, and making sure the
1540	default loop never gets destroyed. You are encouraged, however, to use an	2533	default loop never gets destroyed. You are encouraged, however, to use an
1541	event-based approach to child reaping and thus use libev's support for	2534	event-based approach to child reaping and thus use libev's support for
1542	that, so other libev users can use C<ev_child> watchers freely.	2535	that, so other libev users can use C<ev_child> watchers freely.
		2536
		2537	=head3 Stopping the Child Watcher
		2538
		2539	Currently, the child watcher never gets stopped, even when the
		2540	child terminates, so normally one needs to stop the watcher in the
		2541	callback. Future versions of libev might stop the watcher automatically
		2542	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2543	problem).
1543		2544
1544	=head3 Watcher-Specific Functions and Data Members	2545	=head3 Watcher-Specific Functions and Data Members
1545		2546
1546	=over 4	2547	=over 4
1547		2548
…		…
1576	=head3 Examples	2577	=head3 Examples
1577		2578
1578	Example: C<fork()> a new process and install a child handler to wait for	2579	Example: C<fork()> a new process and install a child handler to wait for
1579	its completion.	2580	its completion.
1580		2581
1581	ev_child cw;	2582	ev_child cw;
1582		2583
1583	static void	2584	static void
1584	child_cb (EV_P_ struct ev_child *w, int revents)	2585	child_cb (EV_P_ ev_child *w, int revents)
1585	{	2586	{
1586	ev_child_stop (EV_A_ w);	2587	ev_child_stop (EV_A_ w);
1587	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);	2588	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1588	}	2589	}
1589		2590
1590	pid_t pid = fork ();	2591	pid_t pid = fork ();
1591		2592
1592	if (pid < 0)	2593	if (pid < 0)
1593	// error	2594	// error
1594	else if (pid == 0)	2595	else if (pid == 0)
1595	{	2596	{
1596	// the forked child executes here	2597	// the forked child executes here
1597	exit (1);	2598	exit (1);
1598	}	2599	}
1599	else	2600	else
1600	{	2601	{
1601	ev_child_init (&cw, child_cb, pid, 0);	2602	ev_child_init (&cw, child_cb, pid, 0);
1602	ev_child_start (EV_DEFAULT_ &cw);	2603	ev_child_start (EV_DEFAULT_ &cw);
1603	}	2604	}
1604		2605
1605		2606
1606	=head2 C<ev_stat> - did the file attributes just change?	2607	=head2 C<ev_stat> - did the file attributes just change?
1607		2608
1608	This watches a filesystem path for attribute changes. That is, it calls	2609	This watches a file system path for attribute changes. That is, it calls
1609	C<stat> regularly (or when the OS says it changed) and sees if it changed	2610	C<stat> on that path in regular intervals (or when the OS says it changed)
1610	compared to the last time, invoking the callback if it did.	2611	and sees if it changed compared to the last time, invoking the callback if
		2612	it did.
1611		2613
1612	The path does not need to exist: changing from "path exists" to "path does	2614	The path does not need to exist: changing from "path exists" to "path does
1613	not exist" is a status change like any other. The condition "path does	2615	not exist" is a status change like any other. The condition "path does not
1614	not exist" is signified by the C<st_nlink> field being zero (which is	2616	exist" (or more correctly "path cannot be stat'ed") is signified by the
1615	otherwise always forced to be at least one) and all the other fields of	2617	C<st_nlink> field being zero (which is otherwise always forced to be at
1616	the stat buffer having unspecified contents.	2618	least one) and all the other fields of the stat buffer having unspecified
		2619	contents.
1617		2620
1618	The path I<should> be absolute and I<must not> end in a slash. If it is	2621	The path I<must not> end in a slash or contain special components such as
		2622	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1619	relative and your working directory changes, the behaviour is undefined.	2623	your working directory changes, then the behaviour is undefined.
1620		2624
1621	Since there is no standard to do this, the portable implementation simply	2625	Since there is no portable change notification interface available, the
1622	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2626	portable implementation simply calls C<stat(2)> regularly on the path
1623	can specify a recommended polling interval for this case. If you specify	2627	to see if it changed somehow. You can specify a recommended polling
1624	a polling interval of C<0> (highly recommended!) then a I<suitable,	2628	interval for this case. If you specify a polling interval of C<0> (highly
1625	unspecified default> value will be used (which you can expect to be around	2629	recommended!) then a I<suitable, unspecified default> value will be used
1626	five seconds, although this might change dynamically). Libev will also	2630	(which you can expect to be around five seconds, although this might
1627	impose a minimum interval which is currently around C<0.1>, but thats	2631	change dynamically). Libev will also impose a minimum interval which is
1628	usually overkill.	2632	currently around C<0.1>, but that's usually overkill.
1629		2633
1630	This watcher type is not meant for massive numbers of stat watchers,	2634	This watcher type is not meant for massive numbers of stat watchers,
1631	as even with OS-supported change notifications, this can be	2635	as even with OS-supported change notifications, this can be
1632	resource-intensive.	2636	resource-intensive.
1633		2637
1634	At the time of this writing, only the Linux inotify interface is	2638	At the time of this writing, the only OS-specific interface implemented
1635	implemented (implementing kqueue support is left as an exercise for the	2639	is the Linux inotify interface (implementing kqueue support is left as an
1636	reader, note, however, that the author sees no way of implementing ev_stat	2640	exercise for the reader. Note, however, that the author sees no way of
1637	semantics with kqueue). Inotify will be used to give hints only and should	2641	implementing C<ev_stat> semantics with kqueue, except as a hint).
1638	not change the semantics of C<ev_stat> watchers, which means that libev
1639	sometimes needs to fall back to regular polling again even with inotify,
1640	but changes are usually detected immediately, and if the file exists there
1641	will be no polling.
1642		2642
1643	=head3 ABI Issues (Largefile Support)	2643	=head3 ABI Issues (Largefile Support)
1644		2644
1645	Libev by default (unless the user overrides this) uses the default	2645	Libev by default (unless the user overrides this) uses the default
1646	compilation environment, which means that on systems with optionally	2646	compilation environment, which means that on systems with large file
1647	disabled large file support, you get the 32 bit version of the stat	2647	support disabled by default, you get the 32 bit version of the stat
1648	structure. When using the library from programs that change the ABI to	2648	structure. When using the library from programs that change the ABI to
1649	use 64 bit file offsets the programs will fail. In that case you have to	2649	use 64 bit file offsets the programs will fail. In that case you have to
1650	compile libev with the same flags to get binary compatibility. This is	2650	compile libev with the same flags to get binary compatibility. This is
1651	obviously the case with any flags that change the ABI, but the problem is	2651	obviously the case with any flags that change the ABI, but the problem is
1652	most noticably with ev_stat and largefile support.	2652	most noticeably displayed with ev_stat and large file support.
1653		2653
1654	=head3 Inotify	2654	The solution for this is to lobby your distribution maker to make large
		2655	file interfaces available by default (as e.g. FreeBSD does) and not
		2656	optional. Libev cannot simply switch on large file support because it has
		2657	to exchange stat structures with application programs compiled using the
		2658	default compilation environment.
1655		2659
		2660	=head3 Inotify and Kqueue
		2661
1656	When C<inotify (7)> support has been compiled into libev (generally only	2662	When C<inotify (7)> support has been compiled into libev and present at
1657	available on Linux) and present at runtime, it will be used to speed up	2663	runtime, it will be used to speed up change detection where possible. The
1658	change detection where possible. The inotify descriptor will be created lazily	2664	inotify descriptor will be created lazily when the first C<ev_stat>
1659	when the first C<ev_stat> watcher is being started.	2665	watcher is being started.
1660		2666
1661	Inotify presence does not change the semantics of C<ev_stat> watchers	2667	Inotify presence does not change the semantics of C<ev_stat> watchers
1662	except that changes might be detected earlier, and in some cases, to avoid	2668	except that changes might be detected earlier, and in some cases, to avoid
1663	making regular C<stat> calls. Even in the presence of inotify support	2669	making regular C<stat> calls. Even in the presence of inotify support
1664	there are many cases where libev has to resort to regular C<stat> polling.	2670	there are many cases where libev has to resort to regular C<stat> polling,
		2671	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2672	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2673	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2674	xfs are fully working) libev usually gets away without polling.
1665		2675
1666	(There is no support for kqueue, as apparently it cannot be used to	2676	There is no support for kqueue, as apparently it cannot be used to
1667	implement this functionality, due to the requirement of having a file	2677	implement this functionality, due to the requirement of having a file
1668	descriptor open on the object at all times).	2678	descriptor open on the object at all times, and detecting renames, unlinks
		2679	etc. is difficult.
		2680
		2681	=head3 C<stat ()> is a synchronous operation
		2682
		2683	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2684	the process. The exception are C<ev_stat> watchers - those call C<stat
		2685	()>, which is a synchronous operation.
		2686
		2687	For local paths, this usually doesn't matter: unless the system is very
		2688	busy or the intervals between stat's are large, a stat call will be fast,
		2689	as the path data is usually in memory already (except when starting the
		2690	watcher).
		2691
		2692	For networked file systems, calling C<stat ()> can block an indefinite
		2693	time due to network issues, and even under good conditions, a stat call
		2694	often takes multiple milliseconds.
		2695
		2696	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2697	paths, although this is fully supported by libev.
1669		2698
1670	=head3 The special problem of stat time resolution	2699	=head3 The special problem of stat time resolution
1671		2700
1672	The C<stat ()> syscall only supports full-second resolution portably, and	2701	The C<stat ()> system call only supports full-second resolution portably,
1673	even on systems where the resolution is higher, many filesystems still	2702	and even on systems where the resolution is higher, most file systems
1674	only support whole seconds.	2703	still only support whole seconds.
1675		2704
1676	That means that, if the time is the only thing that changes, you can	2705	That means that, if the time is the only thing that changes, you can
1677	easily miss updates: on the first update, C<ev_stat> detects a change and	2706	easily miss updates: on the first update, C<ev_stat> detects a change and
1678	calls your callback, which does something. When there is another update	2707	calls your callback, which does something. When there is another update
1679	within the same second, C<ev_stat> will be unable to detect it as the stat	2708	within the same second, C<ev_stat> will be unable to detect unless the
1680	data does not change.	2709	stat data does change in other ways (e.g. file size).
1681		2710
1682	The solution to this is to delay acting on a change for slightly more	2711	The solution to this is to delay acting on a change for slightly more
1683	than a second (or till slightly after the next full second boundary), using	2712	than a second (or till slightly after the next full second boundary), using
1684	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);	2713	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
1685	ev_timer_again (loop, w)>).	2714	ev_timer_again (loop, w)>).
…		…
1705	C<path>. The C<interval> is a hint on how quickly a change is expected to	2734	C<path>. The C<interval> is a hint on how quickly a change is expected to
1706	be detected and should normally be specified as C<0> to let libev choose	2735	be detected and should normally be specified as C<0> to let libev choose
1707	a suitable value. The memory pointed to by C<path> must point to the same	2736	a suitable value. The memory pointed to by C<path> must point to the same
1708	path for as long as the watcher is active.	2737	path for as long as the watcher is active.
1709		2738
1710	The callback will receive C<EV_STAT> when a change was detected, relative	2739	The callback will receive an C<EV_STAT> event when a change was detected,
1711	to the attributes at the time the watcher was started (or the last change	2740	relative to the attributes at the time the watcher was started (or the
1712	was detected).	2741	last change was detected).
1713		2742
1714	=item ev_stat_stat (loop, ev_stat *)	2743	=item ev_stat_stat (loop, ev_stat *)
1715		2744
1716	Updates the stat buffer immediately with new values. If you change the	2745	Updates the stat buffer immediately with new values. If you change the
1717	watched path in your callback, you could call this function to avoid	2746	watched path in your callback, you could call this function to avoid
…		…
1738		2767
1739	The specified interval.	2768	The specified interval.
1740		2769
1741	=item const char *path [read-only]	2770	=item const char *path [read-only]
1742		2771
1743	The filesystem path that is being watched.	2772	The file system path that is being watched.
1744		2773
1745	=back	2774	=back
1746		2775
1747	=head3 Examples	2776	=head3 Examples
1748		2777
1749	Example: Watch C</etc/passwd> for attribute changes.	2778	Example: Watch C</etc/passwd> for attribute changes.
1750		2779
1751	static void	2780	static void
1752	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2781	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1753	{	2782	{
1754	/* /etc/passwd changed in some way */	2783	/* /etc/passwd changed in some way */
1755	if (w->attr.st_nlink)	2784	if (w->attr.st_nlink)
1756	{	2785	{
1757	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2786	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1758	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2787	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1759	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2788	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1760	}	2789	}
1761	else	2790	else
1762	/* you shalt not abuse printf for puts */	2791	/* you shalt not abuse printf for puts */
1763	puts ("wow, /etc/passwd is not there, expect problems. "	2792	puts ("wow, /etc/passwd is not there, expect problems. "
1764	"if this is windows, they already arrived\n");	2793	"if this is windows, they already arrived\n");
1765	}	2794	}
1766		2795
1767	...	2796	...
1768	ev_stat passwd;	2797	ev_stat passwd;
1769		2798
1770	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);	2799	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1771	ev_stat_start (loop, &passwd);	2800	ev_stat_start (loop, &passwd);
1772		2801
1773	Example: Like above, but additionally use a one-second delay so we do not	2802	Example: Like above, but additionally use a one-second delay so we do not
1774	miss updates (however, frequent updates will delay processing, too, so	2803	miss updates (however, frequent updates will delay processing, too, so
1775	one might do the work both on C<ev_stat> callback invocation I<and> on	2804	one might do the work both on C<ev_stat> callback invocation I<and> on
1776	C<ev_timer> callback invocation).	2805	C<ev_timer> callback invocation).
1777		2806
1778	static ev_stat passwd;	2807	static ev_stat passwd;
1779	static ev_timer timer;	2808	static ev_timer timer;
1780		2809
1781	static void	2810	static void
1782	timer_cb (EV_P_ ev_timer *w, int revents)	2811	timer_cb (EV_P_ ev_timer *w, int revents)
1783	{	2812	{
1784	ev_timer_stop (EV_A_ w);	2813	ev_timer_stop (EV_A_ w);
1785		2814
1786	/* now it's one second after the most recent passwd change */	2815	/* now it's one second after the most recent passwd change */
1787	}	2816	}
1788		2817
1789	static void	2818	static void
1790	stat_cb (EV_P_ ev_stat *w, int revents)	2819	stat_cb (EV_P_ ev_stat *w, int revents)
1791	{	2820	{
1792	/* reset the one-second timer */	2821	/* reset the one-second timer */
1793	ev_timer_again (EV_A_ &timer);	2822	ev_timer_again (EV_A_ &timer);
1794	}	2823	}
1795		2824
1796	...	2825	...
1797	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);	2826	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1798	ev_stat_start (loop, &passwd);	2827	ev_stat_start (loop, &passwd);
1799	ev_timer_init (&timer, timer_cb, 0., 1.02);	2828	ev_timer_init (&timer, timer_cb, 0., 1.02);
1800		2829
1801		2830
1802	=head2 C<ev_idle> - when you've got nothing better to do...	2831	=head2 C<ev_idle> - when you've got nothing better to do...
1803		2832
1804	Idle watchers trigger events when no other events of the same or higher	2833	Idle watchers trigger events when no other events of the same or higher
1805	priority are pending (prepare, check and other idle watchers do not	2834	priority are pending (prepare, check and other idle watchers do not count
1806	count).	2835	as receiving "events").
1807		2836
1808	That is, as long as your process is busy handling sockets or timeouts	2837	That is, as long as your process is busy handling sockets or timeouts
1809	(or even signals, imagine) of the same or higher priority it will not be	2838	(or even signals, imagine) of the same or higher priority it will not be
1810	triggered. But when your process is idle (or only lower-priority watchers	2839	triggered. But when your process is idle (or only lower-priority watchers
1811	are pending), the idle watchers are being called once per event loop	2840	are pending), the idle watchers are being called once per event loop
…		…
1818	Apart from keeping your process non-blocking (which is a useful	2847	Apart from keeping your process non-blocking (which is a useful
1819	effect on its own sometimes), idle watchers are a good place to do	2848	effect on its own sometimes), idle watchers are a good place to do
1820	"pseudo-background processing", or delay processing stuff to after the	2849	"pseudo-background processing", or delay processing stuff to after the
1821	event loop has handled all outstanding events.	2850	event loop has handled all outstanding events.
1822		2851
		2852	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2853
		2854	As long as there is at least one active idle watcher, libev will never
		2855	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2856	For this to work, the idle watcher doesn't need to be invoked at all - the
		2857	lowest priority will do.
		2858
		2859	This mode of operation can be useful together with an C<ev_check> watcher,
		2860	to do something on each event loop iteration - for example to balance load
		2861	between different connections.
		2862
		2863	See L<Abusing an C<ev_check> watcher for its side-effect> for a longer
		2864	example.
		2865
1823	=head3 Watcher-Specific Functions and Data Members	2866	=head3 Watcher-Specific Functions and Data Members
1824		2867
1825	=over 4	2868	=over 4
1826		2869
1827	=item ev_idle_init (ev_signal *, callback)	2870	=item ev_idle_init (ev_idle *, callback)
1828		2871
1829	Initialises and configures the idle watcher - it has no parameters of any	2872	Initialises and configures the idle watcher - it has no parameters of any
1830	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2873	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1831	believe me.	2874	believe me.
1832		2875
…		…
1835	=head3 Examples	2878	=head3 Examples
1836		2879
1837	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2880	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1838	callback, free it. Also, use no error checking, as usual.	2881	callback, free it. Also, use no error checking, as usual.
1839		2882
1840	static void	2883	static void
1841	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2884	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1842	{	2885	{
1843	free (w);	2886	free (w);
1844	// now do something you wanted to do when the program has	2887	// now do something you wanted to do when the program has
1845	// no longer anything immediate to do.	2888	// no longer anything immediate to do.
1846	}	2889	}
1847		2890
1848	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2891	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1849	ev_idle_init (idle_watcher, idle_cb);	2892	ev_idle_init (idle_watcher, idle_cb);
1850	ev_idle_start (loop, idle_cb);	2893	ev_idle_start (loop, idle_watcher);
1851		2894
1852		2895
1853	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2896	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1854		2897
1855	Prepare and check watchers are usually (but not always) used in tandem:	2898	Prepare and check watchers are often (but not always) used in pairs:
1856	prepare watchers get invoked before the process blocks and check watchers	2899	prepare watchers get invoked before the process blocks and check watchers
1857	afterwards.	2900	afterwards.
1858		2901
1859	You I<must not> call C<ev_loop> or similar functions that enter	2902	You I<must not> call C<ev_run> or similar functions that enter
1860	the current event loop from either C<ev_prepare> or C<ev_check>	2903	the current event loop from either C<ev_prepare> or C<ev_check>
1861	watchers. Other loops than the current one are fine, however. The	2904	watchers. Other loops than the current one are fine, however. The
1862	rationale behind this is that you do not need to check for recursion in	2905	rationale behind this is that you do not need to check for recursion in
1863	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2906	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1864	C<ev_check> so if you have one watcher of each kind they will always be	2907	C<ev_check> so if you have one watcher of each kind they will always be
1865	called in pairs bracketing the blocking call.	2908	called in pairs bracketing the blocking call.
1866		2909
1867	Their main purpose is to integrate other event mechanisms into libev and	2910	Their main purpose is to integrate other event mechanisms into libev and
1868	their use is somewhat advanced. This could be used, for example, to track	2911	their use is somewhat advanced. They could be used, for example, to track
1869	variable changes, implement your own watchers, integrate net-snmp or a	2912	variable changes, implement your own watchers, integrate net-snmp or a
1870	coroutine library and lots more. They are also occasionally useful if	2913	coroutine library and lots more. They are also occasionally useful if
1871	you cache some data and want to flush it before blocking (for example,	2914	you cache some data and want to flush it before blocking (for example,
1872	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2915	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1873	watcher).	2916	watcher).
1874		2917
1875	This is done by examining in each prepare call which file descriptors need	2918	This is done by examining in each prepare call which file descriptors
1876	to be watched by the other library, registering C<ev_io> watchers for	2919	need to be watched by the other library, registering C<ev_io> watchers
1877	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2920	for them and starting an C<ev_timer> watcher for any timeouts (many
1878	provide just this functionality). Then, in the check watcher you check for	2921	libraries provide exactly this functionality). Then, in the check watcher,
1879	any events that occured (by checking the pending status of all watchers	2922	you check for any events that occurred (by checking the pending status
1880	and stopping them) and call back into the library. The I/O and timer	2923	of all watchers and stopping them) and call back into the library. The
1881	callbacks will never actually be called (but must be valid nevertheless,	2924	I/O and timer callbacks will never actually be called (but must be valid
1882	because you never know, you know?).	2925	nevertheless, because you never know, you know?).
1883		2926
1884	As another example, the Perl Coro module uses these hooks to integrate	2927	As another example, the Perl Coro module uses these hooks to integrate
1885	coroutines into libev programs, by yielding to other active coroutines	2928	coroutines into libev programs, by yielding to other active coroutines
1886	during each prepare and only letting the process block if no coroutines	2929	during each prepare and only letting the process block if no coroutines
1887	are ready to run (it's actually more complicated: it only runs coroutines	2930	are ready to run (it's actually more complicated: it only runs coroutines
1888	with priority higher than or equal to the event loop and one coroutine	2931	with priority higher than or equal to the event loop and one coroutine
1889	of lower priority, but only once, using idle watchers to keep the event	2932	of lower priority, but only once, using idle watchers to keep the event
1890	loop from blocking if lower-priority coroutines are active, thus mapping	2933	loop from blocking if lower-priority coroutines are active, thus mapping
1891	low-priority coroutines to idle/background tasks).	2934	low-priority coroutines to idle/background tasks).
1892		2935
1893	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2936	When used for this purpose, it is recommended to give C<ev_check> watchers
1894	priority, to ensure that they are being run before any other watchers	2937	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
		2938	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		2939	watchers).
		2940
1895	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2941	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1896	too) should not activate ("feed") events into libev. While libev fully	2942	activate ("feed") events into libev. While libev fully supports this, they
1897	supports this, they might get executed before other C<ev_check> watchers	2943	might get executed before other C<ev_check> watchers did their job. As
1898	did their job. As C<ev_check> watchers are often used to embed other	2944	C<ev_check> watchers are often used to embed other (non-libev) event
1899	(non-libev) event loops those other event loops might be in an unusable	2945	loops those other event loops might be in an unusable state until their
1900	state until their C<ev_check> watcher ran (always remind yourself to	2946	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1901	coexist peacefully with others).	2947	others).
		2948
		2949	=head3 Abusing an C<ev_check> watcher for its side-effect
		2950
		2951	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		2952	useful because they are called once per event loop iteration. For
		2953	example, if you want to handle a large number of connections fairly, you
		2954	normally only do a bit of work for each active connection, and if there
		2955	is more work to do, you wait for the next event loop iteration, so other
		2956	connections have a chance of making progress.
		2957
		2958	Using an C<ev_check> watcher is almost enough: it will be called on the
		2959	next event loop iteration. However, that isn't as soon as possible -
		2960	without external events, your C<ev_check> watcher will not be invoked.
		2961
		2962
		2963	This is where C<ev_idle> watchers come in handy - all you need is a
		2964	single global idle watcher that is active as long as you have one active
		2965	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		2966	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		2967	invoked. Neither watcher alone can do that.
1902		2968
1903	=head3 Watcher-Specific Functions and Data Members	2969	=head3 Watcher-Specific Functions and Data Members
1904		2970
1905	=over 4	2971	=over 4
1906		2972
…		…
1908		2974
1909	=item ev_check_init (ev_check *, callback)	2975	=item ev_check_init (ev_check *, callback)
1910		2976
1911	Initialises and configures the prepare or check watcher - they have no	2977	Initialises and configures the prepare or check watcher - they have no
1912	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2978	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1913	macros, but using them is utterly, utterly and completely pointless.	2979	macros, but using them is utterly, utterly, utterly and completely
		2980	pointless.
1914		2981
1915	=back	2982	=back
1916		2983
1917	=head3 Examples	2984	=head3 Examples
1918		2985
…		…
1927	and in a check watcher, destroy them and call into libadns. What follows	2994	and in a check watcher, destroy them and call into libadns. What follows
1928	is pseudo-code only of course. This requires you to either use a low	2995	is pseudo-code only of course. This requires you to either use a low
1929	priority for the check watcher or use C<ev_clear_pending> explicitly, as	2996	priority for the check watcher or use C<ev_clear_pending> explicitly, as
1930	the callbacks for the IO/timeout watchers might not have been called yet.	2997	the callbacks for the IO/timeout watchers might not have been called yet.
1931		2998
1932	static ev_io iow [nfd];	2999	static ev_io iow [nfd];
1933	static ev_timer tw;	3000	static ev_timer tw;
1934		3001
1935	static void	3002	static void
1936	io_cb (ev_loop *loop, ev_io *w, int revents)	3003	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1937	{	3004	{
1938	}	3005	}
1939		3006
1940	// create io watchers for each fd and a timer before blocking	3007	// create io watchers for each fd and a timer before blocking
1941	static void	3008	static void
1942	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	3009	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1943	{	3010	{
1944	int timeout = 3600000;	3011	int timeout = 3600000;
1945	struct pollfd fds [nfd];	3012	struct pollfd fds [nfd];
1946	// actual code will need to loop here and realloc etc.	3013	// actual code will need to loop here and realloc etc.
1947	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	3014	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1948		3015
1949	/* the callback is illegal, but won't be called as we stop during check */	3016	/* the callback is illegal, but won't be called as we stop during check */
1950	ev_timer_init (&tw, 0, timeout * 1e-3);	3017	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1951	ev_timer_start (loop, &tw);	3018	ev_timer_start (loop, &tw);
1952		3019
1953	// create one ev_io per pollfd	3020	// create one ev_io per pollfd
1954	for (int i = 0; i < nfd; ++i)	3021	for (int i = 0; i < nfd; ++i)
1955	{	3022	{
1956	ev_io_init (iow + i, io_cb, fds [i].fd,	3023	ev_io_init (iow + i, io_cb, fds [i].fd,
1957	((fds [i].events & POLLIN ? EV_READ : 0)	3024	((fds [i].events & POLLIN ? EV_READ : 0)
1958	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	3025	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1959		3026
1960	fds [i].revents = 0;	3027	fds [i].revents = 0;
1961	ev_io_start (loop, iow + i);	3028	ev_io_start (loop, iow + i);
1962	}	3029	}
1963	}	3030	}
1964		3031
1965	// stop all watchers after blocking	3032	// stop all watchers after blocking
1966	static void	3033	static void
1967	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	3034	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1968	{	3035	{
1969	ev_timer_stop (loop, &tw);	3036	ev_timer_stop (loop, &tw);
1970		3037
1971	for (int i = 0; i < nfd; ++i)	3038	for (int i = 0; i < nfd; ++i)
1972	{	3039	{
1973	// set the relevant poll flags	3040	// set the relevant poll flags
1974	// could also call adns_processreadable etc. here	3041	// could also call adns_processreadable etc. here
1975	struct pollfd *fd = fds + i;	3042	struct pollfd *fd = fds + i;
1976	int revents = ev_clear_pending (iow + i);	3043	int revents = ev_clear_pending (iow + i);
1977	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	3044	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1978	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	3045	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1979		3046
1980	// now stop the watcher	3047	// now stop the watcher
1981	ev_io_stop (loop, iow + i);	3048	ev_io_stop (loop, iow + i);
1982	}	3049	}
1983		3050
1984	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	3051	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1985	}	3052	}
1986		3053
1987	Method 2: This would be just like method 1, but you run C<adns_afterpoll>	3054	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
1988	in the prepare watcher and would dispose of the check watcher.	3055	in the prepare watcher and would dispose of the check watcher.
1989		3056
1990	Method 3: If the module to be embedded supports explicit event	3057	Method 3: If the module to be embedded supports explicit event
1991	notification (adns does), you can also make use of the actual watcher	3058	notification (libadns does), you can also make use of the actual watcher
1992	callbacks, and only destroy/create the watchers in the prepare watcher.	3059	callbacks, and only destroy/create the watchers in the prepare watcher.
1993		3060
1994	static void	3061	static void
1995	timer_cb (EV_P_ ev_timer *w, int revents)	3062	timer_cb (EV_P_ ev_timer *w, int revents)
1996	{	3063	{
1997	adns_state ads = (adns_state)w->data;	3064	adns_state ads = (adns_state)w->data;
1998	update_now (EV_A);	3065	update_now (EV_A);
1999		3066
2000	adns_processtimeouts (ads, &tv_now);	3067	adns_processtimeouts (ads, &tv_now);
2001	}	3068	}
2002		3069
2003	static void	3070	static void
2004	io_cb (EV_P_ ev_io *w, int revents)	3071	io_cb (EV_P_ ev_io *w, int revents)
2005	{	3072	{
2006	adns_state ads = (adns_state)w->data;	3073	adns_state ads = (adns_state)w->data;
2007	update_now (EV_A);	3074	update_now (EV_A);
2008		3075
2009	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	3076	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
2010	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	3077	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
2011	}	3078	}
2012		3079
2013	// do not ever call adns_afterpoll	3080	// do not ever call adns_afterpoll
2014		3081
2015	Method 4: Do not use a prepare or check watcher because the module you	3082	Method 4: Do not use a prepare or check watcher because the module you
2016	want to embed is too inflexible to support it. Instead, youc na override	3083	want to embed is not flexible enough to support it. Instead, you can
2017	their poll function. The drawback with this solution is that the main	3084	override their poll function. The drawback with this solution is that the
2018	loop is now no longer controllable by EV. The C<Glib::EV> module does	3085	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
2019	this.	3086	this approach, effectively embedding EV as a client into the horrible
		3087	libglib event loop.
2020		3088
2021	static gint	3089	static gint
2022	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	3090	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
2023	{	3091	{
2024	int got_events = 0;	3092	int got_events = 0;
2025		3093
2026	for (n = 0; n < nfds; ++n)	3094	for (n = 0; n < nfds; ++n)
2027	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events	3095	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
2028		3096
2029	if (timeout >= 0)	3097	if (timeout >= 0)
2030	// create/start timer	3098	// create/start timer
2031		3099
2032	// poll	3100	// poll
2033	ev_loop (EV_A_ 0);	3101	ev_run (EV_A_ 0);
2034		3102
2035	// stop timer again	3103	// stop timer again
2036	if (timeout >= 0)	3104	if (timeout >= 0)
2037	ev_timer_stop (EV_A_ &to);	3105	ev_timer_stop (EV_A_ &to);
2038		3106
2039	// stop io watchers again - their callbacks should have set	3107	// stop io watchers again - their callbacks should have set
2040	for (n = 0; n < nfds; ++n)	3108	for (n = 0; n < nfds; ++n)
2041	ev_io_stop (EV_A_ iow [n]);	3109	ev_io_stop (EV_A_ iow [n]);
2042		3110
2043	return got_events;	3111	return got_events;
2044	}	3112	}
2045		3113
2046		3114
2047	=head2 C<ev_embed> - when one backend isn't enough...	3115	=head2 C<ev_embed> - when one backend isn't enough...
2048		3116
2049	This is a rather advanced watcher type that lets you embed one event loop	3117	This is a rather advanced watcher type that lets you embed one event loop
…		…
2055	prioritise I/O.	3123	prioritise I/O.
2056		3124
2057	As an example for a bug workaround, the kqueue backend might only support	3125	As an example for a bug workaround, the kqueue backend might only support
2058	sockets on some platform, so it is unusable as generic backend, but you	3126	sockets on some platform, so it is unusable as generic backend, but you
2059	still want to make use of it because you have many sockets and it scales	3127	still want to make use of it because you have many sockets and it scales
2060	so nicely. In this case, you would create a kqueue-based loop and embed it	3128	so nicely. In this case, you would create a kqueue-based loop and embed
2061	into your default loop (which might use e.g. poll). Overall operation will	3129	it into your default loop (which might use e.g. poll). Overall operation
2062	be a bit slower because first libev has to poll and then call kevent, but	3130	will be a bit slower because first libev has to call C<poll> and then
2063	at least you can use both at what they are best.	3131	C<kevent>, but at least you can use both mechanisms for what they are
		3132	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
2064		3133
2065	As for prioritising I/O: rarely you have the case where some fds have	3134	As for prioritising I/O: under rare circumstances you have the case where
2066	to be watched and handled very quickly (with low latency), and even	3135	some fds have to be watched and handled very quickly (with low latency),
2067	priorities and idle watchers might have too much overhead. In this case	3136	and even priorities and idle watchers might have too much overhead. In
2068	you would put all the high priority stuff in one loop and all the rest in	3137	this case you would put all the high priority stuff in one loop and all
2069	a second one, and embed the second one in the first.	3138	the rest in a second one, and embed the second one in the first.
2070		3139
2071	As long as the watcher is active, the callback will be invoked every time	3140	As long as the watcher is active, the callback will be invoked every
2072	there might be events pending in the embedded loop. The callback must then	3141	time there might be events pending in the embedded loop. The callback
2073	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	3142	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
2074	their callbacks (you could also start an idle watcher to give the embedded	3143	sweep and invoke their callbacks (the callback doesn't need to invoke the
2075	loop strictly lower priority for example). You can also set the callback	3144	C<ev_embed_sweep> function directly, it could also start an idle watcher
2076	to C<0>, in which case the embed watcher will automatically execute the	3145	to give the embedded loop strictly lower priority for example).
2077	embedded loop sweep.
2078		3146
2079	As long as the watcher is started it will automatically handle events. The	3147	You can also set the callback to C<0>, in which case the embed watcher
2080	callback will be invoked whenever some events have been handled. You can	3148	will automatically execute the embedded loop sweep whenever necessary.
2081	set the callback to C<0> to avoid having to specify one if you are not
2082	interested in that.
2083		3149
2084	Also, there have not currently been made special provisions for forking:	3150	Fork detection will be handled transparently while the C<ev_embed> watcher
2085	when you fork, you not only have to call C<ev_loop_fork> on both loops,	3151	is active, i.e., the embedded loop will automatically be forked when the
2086	but you will also have to stop and restart any C<ev_embed> watchers	3152	embedding loop forks. In other cases, the user is responsible for calling
2087	yourself.	3153	C<ev_loop_fork> on the embedded loop.
2088		3154
2089	Unfortunately, not all backends are embeddable, only the ones returned by	3155	Unfortunately, not all backends are embeddable: only the ones returned by
2090	C<ev_embeddable_backends> are, which, unfortunately, does not include any	3156	C<ev_embeddable_backends> are, which, unfortunately, does not include any
2091	portable one.	3157	portable one.
2092		3158
2093	So when you want to use this feature you will always have to be prepared	3159	So when you want to use this feature you will always have to be prepared
2094	that you cannot get an embeddable loop. The recommended way to get around	3160	that you cannot get an embeddable loop. The recommended way to get around
2095	this is to have a separate variables for your embeddable loop, try to	3161	this is to have a separate variables for your embeddable loop, try to
2096	create it, and if that fails, use the normal loop for everything.	3162	create it, and if that fails, use the normal loop for everything.
2097		3163
		3164	=head3 C<ev_embed> and fork
		3165
		3166	While the C<ev_embed> watcher is running, forks in the embedding loop will
		3167	automatically be applied to the embedded loop as well, so no special
		3168	fork handling is required in that case. When the watcher is not running,
		3169	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		3170	as applicable.
		3171
2098	=head3 Watcher-Specific Functions and Data Members	3172	=head3 Watcher-Specific Functions and Data Members
2099		3173
2100	=over 4	3174	=over 4
2101		3175
2102	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3176	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
…		…
2105		3179
2106	Configures the watcher to embed the given loop, which must be	3180	Configures the watcher to embed the given loop, which must be
2107	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3181	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
2108	invoked automatically, otherwise it is the responsibility of the callback	3182	invoked automatically, otherwise it is the responsibility of the callback
2109	to invoke it (it will continue to be called until the sweep has been done,	3183	to invoke it (it will continue to be called until the sweep has been done,
2110	if you do not want thta, you need to temporarily stop the embed watcher).	3184	if you do not want that, you need to temporarily stop the embed watcher).
2111		3185
2112	=item ev_embed_sweep (loop, ev_embed *)	3186	=item ev_embed_sweep (loop, ev_embed *)
2113		3187
2114	Make a single, non-blocking sweep over the embedded loop. This works	3188	Make a single, non-blocking sweep over the embedded loop. This works
2115	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	3189	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
2116	apropriate way for embedded loops.	3190	appropriate way for embedded loops.
2117		3191
2118	=item struct ev_loop *other [read-only]	3192	=item struct ev_loop *other [read-only]
2119		3193
2120	The embedded event loop.	3194	The embedded event loop.
2121		3195
…		…
2123		3197
2124	=head3 Examples	3198	=head3 Examples
2125		3199
2126	Example: Try to get an embeddable event loop and embed it into the default	3200	Example: Try to get an embeddable event loop and embed it into the default
2127	event loop. If that is not possible, use the default loop. The default	3201	event loop. If that is not possible, use the default loop. The default
2128	loop is stored in C<loop_hi>, while the mebeddable loop is stored in	3202	loop is stored in C<loop_hi>, while the embeddable loop is stored in
2129	C<loop_lo> (which is C<loop_hi> in the acse no embeddable loop can be	3203	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
2130	used).	3204	used).
2131		3205
2132	struct ev_loop *loop_hi = ev_default_init (0);	3206	struct ev_loop *loop_hi = ev_default_init (0);
2133	struct ev_loop *loop_lo = 0;	3207	struct ev_loop *loop_lo = 0;
2134	struct ev_embed embed;	3208	ev_embed embed;
2135		3209
2136	// see if there is a chance of getting one that works	3210	// see if there is a chance of getting one that works
2137	// (remember that a flags value of 0 means autodetection)	3211	// (remember that a flags value of 0 means autodetection)
2138	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3212	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2139	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3213	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
2140	: 0;	3214	: 0;
2141		3215
2142	// if we got one, then embed it, otherwise default to loop_hi	3216	// if we got one, then embed it, otherwise default to loop_hi
2143	if (loop_lo)	3217	if (loop_lo)
2144	{	3218	{
2145	ev_embed_init (&embed, 0, loop_lo);	3219	ev_embed_init (&embed, 0, loop_lo);
2146	ev_embed_start (loop_hi, &embed);	3220	ev_embed_start (loop_hi, &embed);
2147	}	3221	}
2148	else	3222	else
2149	loop_lo = loop_hi;	3223	loop_lo = loop_hi;
2150		3224
2151	Example: Check if kqueue is available but not recommended and create	3225	Example: Check if kqueue is available but not recommended and create
2152	a kqueue backend for use with sockets (which usually work with any	3226	a kqueue backend for use with sockets (which usually work with any
2153	kqueue implementation). Store the kqueue/socket-only event loop in	3227	kqueue implementation). Store the kqueue/socket-only event loop in
2154	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3228	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2155		3229
2156	struct ev_loop *loop = ev_default_init (0);	3230	struct ev_loop *loop = ev_default_init (0);
2157	struct ev_loop *loop_socket = 0;	3231	struct ev_loop *loop_socket = 0;
2158	struct ev_embed embed;	3232	ev_embed embed;
2159		3233
2160	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3234	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2161	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3235	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2162	{	3236	{
2163	ev_embed_init (&embed, 0, loop_socket);	3237	ev_embed_init (&embed, 0, loop_socket);
2164	ev_embed_start (loop, &embed);	3238	ev_embed_start (loop, &embed);
2165	}	3239	}
2166		3240
2167	if (!loop_socket)	3241	if (!loop_socket)
2168	loop_socket = loop;	3242	loop_socket = loop;
2169		3243
2170	// now use loop_socket for all sockets, and loop for everything else	3244	// now use loop_socket for all sockets, and loop for everything else
2171		3245
2172		3246
2173	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3247	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
2174		3248
2175	Fork watchers are called when a C<fork ()> was detected (usually because	3249	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
2178	event loop blocks next and before C<ev_check> watchers are being called,	3252	event loop blocks next and before C<ev_check> watchers are being called,
2179	and only in the child after the fork. If whoever good citizen calling	3253	and only in the child after the fork. If whoever good citizen calling
2180	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3254	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2181	handlers will be invoked, too, of course.	3255	handlers will be invoked, too, of course.
2182		3256
		3257	=head3 The special problem of life after fork - how is it possible?
		3258
		3259	Most uses of C<fork()> consist of forking, then some simple calls to set
		3260	up/change the process environment, followed by a call to C<exec()>. This
		3261	sequence should be handled by libev without any problems.
		3262
		3263	This changes when the application actually wants to do event handling
		3264	in the child, or both parent in child, in effect "continuing" after the
		3265	fork.
		3266
		3267	The default mode of operation (for libev, with application help to detect
		3268	forks) is to duplicate all the state in the child, as would be expected
		3269	when I<either> the parent I<or> the child process continues.
		3270
		3271	When both processes want to continue using libev, then this is usually the
		3272	wrong result. In that case, usually one process (typically the parent) is
		3273	supposed to continue with all watchers in place as before, while the other
		3274	process typically wants to start fresh, i.e. without any active watchers.
		3275
		3276	The cleanest and most efficient way to achieve that with libev is to
		3277	simply create a new event loop, which of course will be "empty", and
		3278	use that for new watchers. This has the advantage of not touching more
		3279	memory than necessary, and thus avoiding the copy-on-write, and the
		3280	disadvantage of having to use multiple event loops (which do not support
		3281	signal watchers).
		3282
		3283	When this is not possible, or you want to use the default loop for
		3284	other reasons, then in the process that wants to start "fresh", call
		3285	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
		3286	Destroying the default loop will "orphan" (not stop) all registered
		3287	watchers, so you have to be careful not to execute code that modifies
		3288	those watchers. Note also that in that case, you have to re-register any
		3289	signal watchers.
		3290
2183	=head3 Watcher-Specific Functions and Data Members	3291	=head3 Watcher-Specific Functions and Data Members
2184		3292
2185	=over 4	3293	=over 4
2186		3294
2187	=item ev_fork_init (ev_signal *, callback)	3295	=item ev_fork_init (ev_fork *, callback)
2188		3296
2189	Initialises and configures the fork watcher - it has no parameters of any	3297	Initialises and configures the fork watcher - it has no parameters of any
2190	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,	3298	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
2191	believe me.	3299	really.
2192		3300
2193	=back	3301	=back
2194		3302
2195		3303
		3304	=head2 C<ev_cleanup> - even the best things end
		3305
		3306	Cleanup watchers are called just before the event loop is being destroyed
		3307	by a call to C<ev_loop_destroy>.
		3308
		3309	While there is no guarantee that the event loop gets destroyed, cleanup
		3310	watchers provide a convenient method to install cleanup hooks for your
		3311	program, worker threads and so on - you just to make sure to destroy the
		3312	loop when you want them to be invoked.
		3313
		3314	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3315	all other watchers, they do not keep a reference to the event loop (which
		3316	makes a lot of sense if you think about it). Like all other watchers, you
		3317	can call libev functions in the callback, except C<ev_cleanup_start>.
		3318
		3319	=head3 Watcher-Specific Functions and Data Members
		3320
		3321	=over 4
		3322
		3323	=item ev_cleanup_init (ev_cleanup *, callback)
		3324
		3325	Initialises and configures the cleanup watcher - it has no parameters of
		3326	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3327	pointless, I assure you.
		3328
		3329	=back
		3330
		3331	Example: Register an atexit handler to destroy the default loop, so any
		3332	cleanup functions are called.
		3333
		3334	static void
		3335	program_exits (void)
		3336	{
		3337	ev_loop_destroy (EV_DEFAULT_UC);
		3338	}
		3339
		3340	...
		3341	atexit (program_exits);
		3342
		3343
2196	=head2 C<ev_async> - how to wake up another event loop	3344	=head2 C<ev_async> - how to wake up an event loop
2197		3345
2198	In general, you cannot use an C<ev_loop> from multiple threads or other	3346	In general, you cannot use an C<ev_loop> from multiple threads or other
2199	asynchronous sources such as signal handlers (as opposed to multiple event	3347	asynchronous sources such as signal handlers (as opposed to multiple event
2200	loops - those are of course safe to use in different threads).	3348	loops - those are of course safe to use in different threads).
2201		3349
2202	Sometimes, however, you need to wake up another event loop you do not	3350	Sometimes, however, you need to wake up an event loop you do not control,
2203	control, for example because it belongs to another thread. This is what	3351	for example because it belongs to another thread. This is what C<ev_async>
2204	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you	3352	watchers do: as long as the C<ev_async> watcher is active, you can signal
2205	can signal it by calling C<ev_async_send>, which is thread- and signal	3353	it by calling C<ev_async_send>, which is thread- and signal safe.
2206	safe.
2207		3354
2208	This functionality is very similar to C<ev_signal> watchers, as signals,	3355	This functionality is very similar to C<ev_signal> watchers, as signals,
2209	too, are asynchronous in nature, and signals, too, will be compressed	3356	too, are asynchronous in nature, and signals, too, will be compressed
2210	(i.e. the number of callback invocations may be less than the number of	3357	(i.e. the number of callback invocations may be less than the number of
2211	C<ev_async_sent> calls).	3358	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
2212		3359	of "global async watchers" by using a watcher on an otherwise unused
2213	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not	3360	signal, and C<ev_feed_signal> to signal this watcher from another thread,
2214	just the default loop.	3361	even without knowing which loop owns the signal.
2215		3362
2216	=head3 Queueing	3363	=head3 Queueing
2217		3364
2218	C<ev_async> does not support queueing of data in any way. The reason	3365	C<ev_async> does not support queueing of data in any way. The reason
2219	is that the author does not know of a simple (or any) algorithm for a	3366	is that the author does not know of a simple (or any) algorithm for a
2220	multiple-writer-single-reader queue that works in all cases and doesn't	3367	multiple-writer-single-reader queue that works in all cases and doesn't
2221	need elaborate support such as pthreads.	3368	need elaborate support such as pthreads or unportable memory access
		3369	semantics.
2222		3370
2223	That means that if you want to queue data, you have to provide your own	3371	That means that if you want to queue data, you have to provide your own
2224	queue. But at least I can tell you would implement locking around your	3372	queue. But at least I can tell you how to implement locking around your
2225	queue:	3373	queue:
2226		3374
2227	=over 4	3375	=over 4
2228		3376
2229	=item queueing from a signal handler context	3377	=item queueing from a signal handler context
2230		3378
2231	To implement race-free queueing, you simply add to the queue in the signal	3379	To implement race-free queueing, you simply add to the queue in the signal
2232	handler but you block the signal handler in the watcher callback. Here is an example that does that for	3380	handler but you block the signal handler in the watcher callback. Here is
2233	some fictitiuous SIGUSR1 handler:	3381	an example that does that for some fictitious SIGUSR1 handler:
2234		3382
2235	static ev_async mysig;	3383	static ev_async mysig;
2236		3384
2237	static void	3385	static void
2238	sigusr1_handler (void)	3386	sigusr1_handler (void)
…		…
2304	=over 4	3452	=over 4
2305		3453
2306	=item ev_async_init (ev_async *, callback)	3454	=item ev_async_init (ev_async *, callback)
2307		3455
2308	Initialises and configures the async watcher - it has no parameters of any	3456	Initialises and configures the async watcher - it has no parameters of any
2309	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,	3457	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
2310	believe me.	3458	trust me.
2311		3459
2312	=item ev_async_send (loop, ev_async *)	3460	=item ev_async_send (loop, ev_async *)
2313		3461
2314	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3462	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
2315	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3463	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3464	returns.
		3465
2316	C<ev_feed_event>, this call is safe to do in other threads, signal or	3466	Unlike C<ev_feed_event>, this call is safe to do from other threads,
2317	similar contexts (see the dicusssion of C<EV_ATOMIC_T> in the embedding	3467	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
2318	section below on what exactly this means).	3468	embedding section below on what exactly this means).
2319		3469
2320	This call incurs the overhead of a syscall only once per loop iteration,	3470	Note that, as with other watchers in libev, multiple events might get
2321	so while the overhead might be noticable, it doesn't apply to repeated	3471	compressed into a single callback invocation (another way to look at
2322	calls to C<ev_async_send>.	3472	this is that C<ev_async> watchers are level-triggered: they are set on
		3473	C<ev_async_send>, reset when the event loop detects that).
		3474
		3475	This call incurs the overhead of at most one extra system call per event
		3476	loop iteration, if the event loop is blocked, and no syscall at all if
		3477	the event loop (or your program) is processing events. That means that
		3478	repeated calls are basically free (there is no need to avoid calls for
		3479	performance reasons) and that the overhead becomes smaller (typically
		3480	zero) under load.
2323		3481
2324	=item bool = ev_async_pending (ev_async *)	3482	=item bool = ev_async_pending (ev_async *)
2325		3483
2326	Returns a non-zero value when C<ev_async_send> has been called on the	3484	Returns a non-zero value when C<ev_async_send> has been called on the
2327	watcher but the event has not yet been processed (or even noted) by the	3485	watcher but the event has not yet been processed (or even noted) by the
2328	event loop.	3486	event loop.
2329		3487
2330	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When	3488	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
2331	the loop iterates next and checks for the watcher to have become active,	3489	the loop iterates next and checks for the watcher to have become active,
2332	it will reset the flag again. C<ev_async_pending> can be used to very	3490	it will reset the flag again. C<ev_async_pending> can be used to very
2333	quickly check wether invoking the loop might be a good idea.	3491	quickly check whether invoking the loop might be a good idea.
2334		3492
2335	Not that this does I<not> check wether the watcher itself is pending, only	3493	Not that this does I<not> check whether the watcher itself is pending,
2336	wether it has been requested to make this watcher pending.	3494	only whether it has been requested to make this watcher pending: there
		3495	is a time window between the event loop checking and resetting the async
		3496	notification, and the callback being invoked.
2337		3497
2338	=back	3498	=back
2339		3499
2340		3500
2341	=head1 OTHER FUNCTIONS	3501	=head1 OTHER FUNCTIONS
…		…
2345	=over 4	3505	=over 4
2346		3506
2347	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3507	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
2348		3508
2349	This function combines a simple timer and an I/O watcher, calls your	3509	This function combines a simple timer and an I/O watcher, calls your
2350	callback on whichever event happens first and automatically stop both	3510	callback on whichever event happens first and automatically stops both
2351	watchers. This is useful if you want to wait for a single event on an fd	3511	watchers. This is useful if you want to wait for a single event on an fd
2352	or timeout without having to allocate/configure/start/stop/free one or	3512	or timeout without having to allocate/configure/start/stop/free one or
2353	more watchers yourself.	3513	more watchers yourself.
2354		3514
2355	If C<fd> is less than 0, then no I/O watcher will be started and events	3515	If C<fd> is less than 0, then no I/O watcher will be started and the
2356	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3516	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
2357	C<events> set will be craeted and started.	3517	the given C<fd> and C<events> set will be created and started.
2358		3518
2359	If C<timeout> is less than 0, then no timeout watcher will be	3519	If C<timeout> is less than 0, then no timeout watcher will be
2360	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3520	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
2361	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3521	repeat = 0) will be started. C<0> is a valid timeout.
2362	dubious value.
2363		3522
2364	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3523	The callback has the type C<void (*cb)(int revents, void *arg)> and is
2365	passed an C<revents> set like normal event callbacks (a combination of	3524	passed an C<revents> set like normal event callbacks (a combination of
2366	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3525	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
2367	value passed to C<ev_once>:	3526	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3527	a timeout and an io event at the same time - you probably should give io
		3528	events precedence.
2368		3529
		3530	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3531
2369	static void stdin_ready (int revents, void *arg)	3532	static void stdin_ready (int revents, void *arg)
		3533	{
		3534	if (revents & EV_READ)
		3535	/* stdin might have data for us, joy! */;
		3536	else if (revents & EV_TIMER)
		3537	/* doh, nothing entered */;
		3538	}
		3539
		3540	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
		3541
		3542	=item ev_feed_fd_event (loop, int fd, int revents)
		3543
		3544	Feed an event on the given fd, as if a file descriptor backend detected
		3545	the given events.
		3546
		3547	=item ev_feed_signal_event (loop, int signum)
		3548
		3549	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
		3550	which is async-safe.
		3551
		3552	=back
		3553
		3554
		3555	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3556
		3557	This section explains some common idioms that are not immediately
		3558	obvious. Note that examples are sprinkled over the whole manual, and this
		3559	section only contains stuff that wouldn't fit anywhere else.
		3560
		3561	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3562
		3563	Each watcher has, by default, a C<void *data> member that you can read
		3564	or modify at any time: libev will completely ignore it. This can be used
		3565	to associate arbitrary data with your watcher. If you need more data and
		3566	don't want to allocate memory separately and store a pointer to it in that
		3567	data member, you can also "subclass" the watcher type and provide your own
		3568	data:
		3569
		3570	struct my_io
		3571	{
		3572	ev_io io;
		3573	int otherfd;
		3574	void *somedata;
		3575	struct whatever *mostinteresting;
		3576	};
		3577
		3578	...
		3579	struct my_io w;
		3580	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3581
		3582	And since your callback will be called with a pointer to the watcher, you
		3583	can cast it back to your own type:
		3584
		3585	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3586	{
		3587	struct my_io *w = (struct my_io *)w_;
		3588	...
		3589	}
		3590
		3591	More interesting and less C-conformant ways of casting your callback
		3592	function type instead have been omitted.
		3593
		3594	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3595
		3596	Another common scenario is to use some data structure with multiple
		3597	embedded watchers, in effect creating your own watcher that combines
		3598	multiple libev event sources into one "super-watcher":
		3599
		3600	struct my_biggy
		3601	{
		3602	int some_data;
		3603	ev_timer t1;
		3604	ev_timer t2;
		3605	}
		3606
		3607	In this case getting the pointer to C<my_biggy> is a bit more
		3608	complicated: Either you store the address of your C<my_biggy> struct in
		3609	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3610	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3611	real programmers):
		3612
		3613	#include <stddef.h>
		3614
		3615	static void
		3616	t1_cb (EV_P_ ev_timer *w, int revents)
		3617	{
		3618	struct my_biggy big = (struct my_biggy *)
		3619	(((char *)w) - offsetof (struct my_biggy, t1));
		3620	}
		3621
		3622	static void
		3623	t2_cb (EV_P_ ev_timer *w, int revents)
		3624	{
		3625	struct my_biggy big = (struct my_biggy *)
		3626	(((char *)w) - offsetof (struct my_biggy, t2));
		3627	}
		3628
		3629	=head2 AVOIDING FINISHING BEFORE RETURNING
		3630
		3631	Often you have structures like this in event-based programs:
		3632
		3633	callback ()
2370	{	3634	{
2371	if (revents & EV_TIMEOUT)	3635	free (request);
2372	/* doh, nothing entered */;
2373	else if (revents & EV_READ)
2374	/* stdin might have data for us, joy! */;
2375	}	3636	}
2376		3637
2377	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3638	request = start_new_request (..., callback);
2378		3639
2379	=item ev_feed_event (ev_loop *, watcher *, int revents)	3640	The intent is to start some "lengthy" operation. The C<request> could be
		3641	used to cancel the operation, or do other things with it.
2380		3642
2381	Feeds the given event set into the event loop, as if the specified event	3643	It's not uncommon to have code paths in C<start_new_request> that
2382	had happened for the specified watcher (which must be a pointer to an	3644	immediately invoke the callback, for example, to report errors. Or you add
2383	initialised but not necessarily started event watcher).	3645	some caching layer that finds that it can skip the lengthy aspects of the
		3646	operation and simply invoke the callback with the result.
2384		3647
2385	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3648	The problem here is that this will happen I<before> C<start_new_request>
		3649	has returned, so C<request> is not set.
2386		3650
2387	Feed an event on the given fd, as if a file descriptor backend detected	3651	Even if you pass the request by some safer means to the callback, you
2388	the given events it.	3652	might want to do something to the request after starting it, such as
		3653	canceling it, which probably isn't working so well when the callback has
		3654	already been invoked.
2389		3655
2390	=item ev_feed_signal_event (ev_loop *loop, int signum)	3656	A common way around all these issues is to make sure that
		3657	C<start_new_request> I<always> returns before the callback is invoked. If
		3658	C<start_new_request> immediately knows the result, it can artificially
		3659	delay invoking the callback by e.g. using a C<prepare> or C<idle> watcher
		3660	for example, or more sneakily, by reusing an existing (stopped) watcher
		3661	and pushing it into the pending queue:
2391		3662
2392	Feed an event as if the given signal occured (C<loop> must be the default	3663	ev_set_cb (watcher, callback);
2393	loop!).	3664	ev_feed_event (EV_A_ watcher, 0);
2394		3665
2395	=back	3666	This way, C<start_new_request> can safely return before the callback is
		3667	invoked, while not delaying callback invocation too much.
		3668
		3669	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3670
		3671	Often (especially in GUI toolkits) there are places where you have
		3672	I<modal> interaction, which is most easily implemented by recursively
		3673	invoking C<ev_run>.
		3674
		3675	This brings the problem of exiting - a callback might want to finish the
		3676	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3677	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3678	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3679	other combination: In these cases, C<ev_break> will not work alone.
		3680
		3681	The solution is to maintain "break this loop" variable for each C<ev_run>
		3682	invocation, and use a loop around C<ev_run> until the condition is
		3683	triggered, using C<EVRUN_ONCE>:
		3684
		3685	// main loop
		3686	int exit_main_loop = 0;
		3687
		3688	while (!exit_main_loop)
		3689	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3690
		3691	// in a modal watcher
		3692	int exit_nested_loop = 0;
		3693
		3694	while (!exit_nested_loop)
		3695	ev_run (EV_A_ EVRUN_ONCE);
		3696
		3697	To exit from any of these loops, just set the corresponding exit variable:
		3698
		3699	// exit modal loop
		3700	exit_nested_loop = 1;
		3701
		3702	// exit main program, after modal loop is finished
		3703	exit_main_loop = 1;
		3704
		3705	// exit both
		3706	exit_main_loop = exit_nested_loop = 1;
		3707
		3708	=head2 THREAD LOCKING EXAMPLE
		3709
		3710	Here is a fictitious example of how to run an event loop in a different
		3711	thread from where callbacks are being invoked and watchers are
		3712	created/added/removed.
		3713
		3714	For a real-world example, see the C<EV::Loop::Async> perl module,
		3715	which uses exactly this technique (which is suited for many high-level
		3716	languages).
		3717
		3718	The example uses a pthread mutex to protect the loop data, a condition
		3719	variable to wait for callback invocations, an async watcher to notify the
		3720	event loop thread and an unspecified mechanism to wake up the main thread.
		3721
		3722	First, you need to associate some data with the event loop:
		3723
		3724	typedef struct {
		3725	mutex_t lock; /* global loop lock */
		3726	ev_async async_w;
		3727	thread_t tid;
		3728	cond_t invoke_cv;
		3729	} userdata;
		3730
		3731	void prepare_loop (EV_P)
		3732	{
		3733	// for simplicity, we use a static userdata struct.
		3734	static userdata u;
		3735
		3736	ev_async_init (&u->async_w, async_cb);
		3737	ev_async_start (EV_A_ &u->async_w);
		3738
		3739	pthread_mutex_init (&u->lock, 0);
		3740	pthread_cond_init (&u->invoke_cv, 0);
		3741
		3742	// now associate this with the loop
		3743	ev_set_userdata (EV_A_ u);
		3744	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3745	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3746
		3747	// then create the thread running ev_run
		3748	pthread_create (&u->tid, 0, l_run, EV_A);
		3749	}
		3750
		3751	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3752	solely to wake up the event loop so it takes notice of any new watchers
		3753	that might have been added:
		3754
		3755	static void
		3756	async_cb (EV_P_ ev_async *w, int revents)
		3757	{
		3758	// just used for the side effects
		3759	}
		3760
		3761	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3762	protecting the loop data, respectively.
		3763
		3764	static void
		3765	l_release (EV_P)
		3766	{
		3767	userdata *u = ev_userdata (EV_A);
		3768	pthread_mutex_unlock (&u->lock);
		3769	}
		3770
		3771	static void
		3772	l_acquire (EV_P)
		3773	{
		3774	userdata *u = ev_userdata (EV_A);
		3775	pthread_mutex_lock (&u->lock);
		3776	}
		3777
		3778	The event loop thread first acquires the mutex, and then jumps straight
		3779	into C<ev_run>:
		3780
		3781	void *
		3782	l_run (void *thr_arg)
		3783	{
		3784	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3785
		3786	l_acquire (EV_A);
		3787	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3788	ev_run (EV_A_ 0);
		3789	l_release (EV_A);
		3790
		3791	return 0;
		3792	}
		3793
		3794	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3795	signal the main thread via some unspecified mechanism (signals? pipe
		3796	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3797	have been called (in a while loop because a) spurious wakeups are possible
		3798	and b) skipping inter-thread-communication when there are no pending
		3799	watchers is very beneficial):
		3800
		3801	static void
		3802	l_invoke (EV_P)
		3803	{
		3804	userdata *u = ev_userdata (EV_A);
		3805
		3806	while (ev_pending_count (EV_A))
		3807	{
		3808	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3809	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3810	}
		3811	}
		3812
		3813	Now, whenever the main thread gets told to invoke pending watchers, it
		3814	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3815	thread to continue:
		3816
		3817	static void
		3818	real_invoke_pending (EV_P)
		3819	{
		3820	userdata *u = ev_userdata (EV_A);
		3821
		3822	pthread_mutex_lock (&u->lock);
		3823	ev_invoke_pending (EV_A);
		3824	pthread_cond_signal (&u->invoke_cv);
		3825	pthread_mutex_unlock (&u->lock);
		3826	}
		3827
		3828	Whenever you want to start/stop a watcher or do other modifications to an
		3829	event loop, you will now have to lock:
		3830
		3831	ev_timer timeout_watcher;
		3832	userdata *u = ev_userdata (EV_A);
		3833
		3834	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3835
		3836	pthread_mutex_lock (&u->lock);
		3837	ev_timer_start (EV_A_ &timeout_watcher);
		3838	ev_async_send (EV_A_ &u->async_w);
		3839	pthread_mutex_unlock (&u->lock);
		3840
		3841	Note that sending the C<ev_async> watcher is required because otherwise
		3842	an event loop currently blocking in the kernel will have no knowledge
		3843	about the newly added timer. By waking up the loop it will pick up any new
		3844	watchers in the next event loop iteration.
		3845
		3846	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3847
		3848	While the overhead of a callback that e.g. schedules a thread is small, it
		3849	is still an overhead. If you embed libev, and your main usage is with some
		3850	kind of threads or coroutines, you might want to customise libev so that
		3851	doesn't need callbacks anymore.
		3852
		3853	Imagine you have coroutines that you can switch to using a function
		3854	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3855	and that due to some magic, the currently active coroutine is stored in a
		3856	global called C<current_coro>. Then you can build your own "wait for libev
		3857	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3858	the differing C<;> conventions):
		3859
		3860	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3861	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3862
		3863	That means instead of having a C callback function, you store the
		3864	coroutine to switch to in each watcher, and instead of having libev call
		3865	your callback, you instead have it switch to that coroutine.
		3866
		3867	A coroutine might now wait for an event with a function called
		3868	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3869	matter when, or whether the watcher is active or not when this function is
		3870	called):
		3871
		3872	void
		3873	wait_for_event (ev_watcher *w)
		3874	{
		3875	ev_cb_set (w) = current_coro;
		3876	switch_to (libev_coro);
		3877	}
		3878
		3879	That basically suspends the coroutine inside C<wait_for_event> and
		3880	continues the libev coroutine, which, when appropriate, switches back to
		3881	this or any other coroutine.
		3882
		3883	You can do similar tricks if you have, say, threads with an event queue -
		3884	instead of storing a coroutine, you store the queue object and instead of
		3885	switching to a coroutine, you push the watcher onto the queue and notify
		3886	any waiters.
		3887
		3888	To embed libev, see L<EMBEDDING>, but in short, it's easiest to create two
		3889	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3890
		3891	// my_ev.h
		3892	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3893	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
		3894	#include "../libev/ev.h"
		3895
		3896	// my_ev.c
		3897	#define EV_H "my_ev.h"
		3898	#include "../libev/ev.c"
		3899
		3900	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3901	F<my_ev.c> into your project. When properly specifying include paths, you
		3902	can even use F<ev.h> as header file name directly.
2396		3903
2397		3904
2398	=head1 LIBEVENT EMULATION	3905	=head1 LIBEVENT EMULATION
2399		3906
2400	Libev offers a compatibility emulation layer for libevent. It cannot	3907	Libev offers a compatibility emulation layer for libevent. It cannot
2401	emulate the internals of libevent, so here are some usage hints:	3908	emulate the internals of libevent, so here are some usage hints:
2402		3909
2403	=over 4	3910	=over 4
		3911
		3912	=item * Only the libevent-1.4.1-beta API is being emulated.
		3913
		3914	This was the newest libevent version available when libev was implemented,
		3915	and is still mostly unchanged in 2010.
2404		3916
2405	=item * Use it by including <event.h>, as usual.	3917	=item * Use it by including <event.h>, as usual.
2406		3918
2407	=item * The following members are fully supported: ev_base, ev_callback,	3919	=item * The following members are fully supported: ev_base, ev_callback,
2408	ev_arg, ev_fd, ev_res, ev_events.	3920	ev_arg, ev_fd, ev_res, ev_events.
…		…
2414	=item * Priorities are not currently supported. Initialising priorities	3926	=item * Priorities are not currently supported. Initialising priorities
2415	will fail and all watchers will have the same priority, even though there	3927	will fail and all watchers will have the same priority, even though there
2416	is an ev_pri field.	3928	is an ev_pri field.
2417		3929
2418	=item * In libevent, the last base created gets the signals, in libev, the	3930	=item * In libevent, the last base created gets the signals, in libev, the
2419	first base created (== the default loop) gets the signals.	3931	base that registered the signal gets the signals.
2420		3932
2421	=item * Other members are not supported.	3933	=item * Other members are not supported.
2422		3934
2423	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3935	=item * The libev emulation is I<not> ABI compatible to libevent, you need
2424	to use the libev header file and library.	3936	to use the libev header file and library.
2425		3937
2426	=back	3938	=back
2427		3939
2428	=head1 C++ SUPPORT	3940	=head1 C++ SUPPORT
2429		3941
		3942	=head2 C API
		3943
		3944	The normal C API should work fine when used from C++: both ev.h and the
		3945	libev sources can be compiled as C++. Therefore, code that uses the C API
		3946	will work fine.
		3947
		3948	Proper exception specifications might have to be added to callbacks passed
		3949	to libev: exceptions may be thrown only from watcher callbacks, all
		3950	other callbacks (allocator, syserr, loop acquire/release and periodioc
		3951	reschedule callbacks) must not throw exceptions, and might need a C<throw
		3952	()> specification. If you have code that needs to be compiled as both C
		3953	and C++ you can use the C<EV_THROW> macro for this:
		3954
		3955	static void
		3956	fatal_error (const char *msg) EV_THROW
		3957	{
		3958	perror (msg);
		3959	abort ();
		3960	}
		3961
		3962	...
		3963	ev_set_syserr_cb (fatal_error);
		3964
		3965	The only API functions that can currently throw exceptions are C<ev_run>,
		3966	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		3967	because it runs cleanup watchers).
		3968
		3969	Throwing exceptions in watcher callbacks is only supported if libev itself
		3970	is compiled with a C++ compiler or your C and C++ environments allow
		3971	throwing exceptions through C libraries (most do).
		3972
		3973	=head2 C++ API
		3974
2430	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3975	Libev comes with some simplistic wrapper classes for C++ that mainly allow
2431	you to use some convinience methods to start/stop watchers and also change	3976	you to use some convenience methods to start/stop watchers and also change
2432	the callback model to a model using method callbacks on objects.	3977	the callback model to a model using method callbacks on objects.
2433		3978
2434	To use it,	3979	To use it,
2435		3980
2436	#include <ev++.h>	3981	#include <ev++.h>
2437		3982
2438	This automatically includes F<ev.h> and puts all of its definitions (many	3983	This automatically includes F<ev.h> and puts all of its definitions (many
2439	of them macros) into the global namespace. All C++ specific things are	3984	of them macros) into the global namespace. All C++ specific things are
2440	put into the C<ev> namespace. It should support all the same embedding	3985	put into the C<ev> namespace. It should support all the same embedding
2441	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	3986	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
2443	Care has been taken to keep the overhead low. The only data member the C++	3988	Care has been taken to keep the overhead low. The only data member the C++
2444	classes add (compared to plain C-style watchers) is the event loop pointer	3989	classes add (compared to plain C-style watchers) is the event loop pointer
2445	that the watcher is associated with (or no additional members at all if	3990	that the watcher is associated with (or no additional members at all if
2446	you disable C<EV_MULTIPLICITY> when embedding libev).	3991	you disable C<EV_MULTIPLICITY> when embedding libev).
2447		3992
2448	Currently, functions, and static and non-static member functions can be	3993	Currently, functions, static and non-static member functions and classes
2449	used as callbacks. Other types should be easy to add as long as they only	3994	with C<operator ()> can be used as callbacks. Other types should be easy
2450	need one additional pointer for context. If you need support for other	3995	to add as long as they only need one additional pointer for context. If
2451	types of functors please contact the author (preferably after implementing	3996	you need support for other types of functors please contact the author
2452	it).	3997	(preferably after implementing it).
		3998
		3999	For all this to work, your C++ compiler either has to use the same calling
		4000	conventions as your C compiler (for static member functions), or you have
		4001	to embed libev and compile libev itself as C++.
2453		4002
2454	Here is a list of things available in the C<ev> namespace:	4003	Here is a list of things available in the C<ev> namespace:
2455		4004
2456	=over 4	4005	=over 4
2457		4006
…		…
2467	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4016	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
2468		4017
2469	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4018	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
2470	the same name in the C<ev> namespace, with the exception of C<ev_signal>	4019	the same name in the C<ev> namespace, with the exception of C<ev_signal>
2471	which is called C<ev::sig> to avoid clashes with the C<signal> macro	4020	which is called C<ev::sig> to avoid clashes with the C<signal> macro
2472	defines by many implementations.	4021	defined by many implementations.
2473		4022
2474	All of those classes have these methods:	4023	All of those classes have these methods:
2475		4024
2476	=over 4	4025	=over 4
2477		4026
2478	=item ev::TYPE::TYPE ()	4027	=item ev::TYPE::TYPE ()
2479		4028
2480	=item ev::TYPE::TYPE (struct ev_loop *)	4029	=item ev::TYPE::TYPE (loop)
2481		4030
2482	=item ev::TYPE::~TYPE	4031	=item ev::TYPE::~TYPE
2483		4032
2484	The constructor (optionally) takes an event loop to associate the watcher	4033	The constructor (optionally) takes an event loop to associate the watcher
2485	with. If it is omitted, it will use C<EV_DEFAULT>.	4034	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
2508	your compiler is good :), then the method will be fully inlined into the	4057	your compiler is good :), then the method will be fully inlined into the
2509	thunking function, making it as fast as a direct C callback.	4058	thunking function, making it as fast as a direct C callback.
2510		4059
2511	Example: simple class declaration and watcher initialisation	4060	Example: simple class declaration and watcher initialisation
2512		4061
2513	struct myclass	4062	struct myclass
2514	{	4063	{
2515	void io_cb (ev::io &w, int revents) { }	4064	void io_cb (ev::io &w, int revents) { }
2516	}	4065	}
2517		4066
2518	myclass obj;	4067	myclass obj;
2519	ev::io iow;	4068	ev::io iow;
2520	iow.set <myclass, &myclass::io_cb> (&obj);	4069	iow.set <myclass, &myclass::io_cb> (&obj);
		4070
		4071	=item w->set (object *)
		4072
		4073	This is a variation of a method callback - leaving out the method to call
		4074	will default the method to C<operator ()>, which makes it possible to use
		4075	functor objects without having to manually specify the C<operator ()> all
		4076	the time. Incidentally, you can then also leave out the template argument
		4077	list.
		4078
		4079	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		4080	int revents)>.
		4081
		4082	See the method-C<set> above for more details.
		4083
		4084	Example: use a functor object as callback.
		4085
		4086	struct myfunctor
		4087	{
		4088	void operator() (ev::io &w, int revents)
		4089	{
		4090	...
		4091	}
		4092	}
		4093
		4094	myfunctor f;
		4095
		4096	ev::io w;
		4097	w.set (&f);
2521		4098
2522	=item w->set<function> (void *data = 0)	4099	=item w->set<function> (void *data = 0)
2523		4100
2524	Also sets a callback, but uses a static method or plain function as	4101	Also sets a callback, but uses a static method or plain function as
2525	callback. The optional C<data> argument will be stored in the watcher's	4102	callback. The optional C<data> argument will be stored in the watcher's
…		…
2527		4104
2528	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	4105	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2529		4106
2530	See the method-C<set> above for more details.	4107	See the method-C<set> above for more details.
2531		4108
2532	Example:	4109	Example: Use a plain function as callback.
2533		4110
2534	static void io_cb (ev::io &w, int revents) { }	4111	static void io_cb (ev::io &w, int revents) { }
2535	iow.set <io_cb> ();	4112	iow.set <io_cb> ();
2536		4113
2537	=item w->set (struct ev_loop *)	4114	=item w->set (loop)
2538		4115
2539	Associates a different C<struct ev_loop> with this watcher. You can only	4116	Associates a different C<struct ev_loop> with this watcher. You can only
2540	do this when the watcher is inactive (and not pending either).	4117	do this when the watcher is inactive (and not pending either).
2541		4118
2542	=item w->set ([args])	4119	=item w->set ([arguments])
2543		4120
2544	Basically the same as C<ev_TYPE_set>, with the same args. Must be	4121	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this
2545	called at least once. Unlike the C counterpart, an active watcher gets	4122	method or a suitable start method must be called at least once. Unlike the
2546	automatically stopped and restarted when reconfiguring it with this	4123	C counterpart, an active watcher gets automatically stopped and restarted
2547	method.	4124	when reconfiguring it with this method.
2548		4125
2549	=item w->start ()	4126	=item w->start ()
2550		4127
2551	Starts the watcher. Note that there is no C<loop> argument, as the	4128	Starts the watcher. Note that there is no C<loop> argument, as the
2552	constructor already stores the event loop.	4129	constructor already stores the event loop.
2553		4130
		4131	=item w->start ([arguments])
		4132
		4133	Instead of calling C<set> and C<start> methods separately, it is often
		4134	convenient to wrap them in one call. Uses the same type of arguments as
		4135	the configure C<set> method of the watcher.
		4136
2554	=item w->stop ()	4137	=item w->stop ()
2555		4138
2556	Stops the watcher if it is active. Again, no C<loop> argument.	4139	Stops the watcher if it is active. Again, no C<loop> argument.
2557		4140
2558	=item w->again () (C<ev::timer>, C<ev::periodic> only)	4141	=item w->again () (C<ev::timer>, C<ev::periodic> only)
…		…
2570		4153
2571	=back	4154	=back
2572		4155
2573	=back	4156	=back
2574		4157
2575	Example: Define a class with an IO and idle watcher, start one of them in	4158	Example: Define a class with two I/O and idle watchers, start the I/O
2576	the constructor.	4159	watchers in the constructor.
2577		4160
2578	class myclass	4161	class myclass
2579	{	4162	{
2580	ev::io io; void io_cb (ev::io &w, int revents);	4163	ev::io io ; void io_cb (ev::io &w, int revents);
		4164	ev::io io2 ; void io2_cb (ev::io &w, int revents);
2581	ev:idle idle void idle_cb (ev::idle &w, int revents);	4165	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2582		4166
2583	myclass (int fd)	4167	myclass (int fd)
2584	{	4168	{
2585	io .set <myclass, &myclass::io_cb > (this);	4169	io .set <myclass, &myclass::io_cb > (this);
		4170	io2 .set <myclass, &myclass::io2_cb > (this);
2586	idle.set <myclass, &myclass::idle_cb> (this);	4171	idle.set <myclass, &myclass::idle_cb> (this);
2587		4172
2588	io.start (fd, ev::READ);	4173	io.set (fd, ev::WRITE); // configure the watcher
		4174	io.start (); // start it whenever convenient
		4175
		4176	io2.start (fd, ev::READ); // set + start in one call
2589	}	4177	}
2590	};	4178	};
2591		4179
2592		4180
2593	=head1 OTHER LANGUAGE BINDINGS	4181	=head1 OTHER LANGUAGE BINDINGS
2594		4182
2595	Libev does not offer other language bindings itself, but bindings for a	4183	Libev does not offer other language bindings itself, but bindings for a
2596	numbe rof languages exist in the form of third-party packages. If you know	4184	number of languages exist in the form of third-party packages. If you know
2597	any interesting language binding in addition to the ones listed here, drop	4185	any interesting language binding in addition to the ones listed here, drop
2598	me a note.	4186	me a note.
2599		4187
2600	=over 4	4188	=over 4
2601		4189
2602	=item Perl	4190	=item Perl
2603		4191
2604	The EV module implements the full libev API and is actually used to test	4192	The EV module implements the full libev API and is actually used to test
2605	libev. EV is developed together with libev. Apart from the EV core module,	4193	libev. EV is developed together with libev. Apart from the EV core module,
2606	there are additional modules that implement libev-compatible interfaces	4194	there are additional modules that implement libev-compatible interfaces
2607	to C<libadns> (C<EV::ADNS>), C<Net::SNMP> (C<Net::SNMP::EV>) and the	4195	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
2608	C<libglib> event core (C<Glib::EV> and C<EV::Glib>).	4196	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		4197	and C<EV::Glib>).
2609		4198
2610	It can be found and installed via CPAN, its homepage is found at	4199	It can be found and installed via CPAN, its homepage is at
2611	L<http://software.schmorp.de/pkg/EV>.	4200	L<http://software.schmorp.de/pkg/EV>.
2612		4201
		4202	=item Python
		4203
		4204	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		4205	seems to be quite complete and well-documented.
		4206
2613	=item Ruby	4207	=item Ruby
2614		4208
2615	Tony Arcieri has written a ruby extension that offers access to a subset	4209	Tony Arcieri has written a ruby extension that offers access to a subset
2616	of the libev API and adds filehandle abstractions, asynchronous DNS and	4210	of the libev API and adds file handle abstractions, asynchronous DNS and
2617	more on top of it. It can be found via gem servers. Its homepage is at	4211	more on top of it. It can be found via gem servers. Its homepage is at
2618	L<http://rev.rubyforge.org/>.	4212	L<http://rev.rubyforge.org/>.
2619		4213
		4214	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		4215	makes rev work even on mingw.
		4216
		4217	=item Haskell
		4218
		4219	A haskell binding to libev is available at
		4220	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		4221
2620	=item D	4222	=item D
2621		4223
2622	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4224	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
2623	be found at L<http://git.llucax.com.ar/?p=software/ev.d.git;a=summary>.	4225	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
		4226
		4227	=item Ocaml
		4228
		4229	Erkki Seppala has written Ocaml bindings for libev, to be found at
		4230	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		4231
		4232	=item Lua
		4233
		4234	Brian Maher has written a partial interface to libev for lua (at the
		4235	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		4236	L<http://github.com/brimworks/lua-ev>.
2624		4237
2625	=back	4238	=back
2626		4239
2627		4240
2628	=head1 MACRO MAGIC	4241	=head1 MACRO MAGIC
2629		4242
2630	Libev can be compiled with a variety of options, the most fundamantal	4243	Libev can be compiled with a variety of options, the most fundamental
2631	of which is C<EV_MULTIPLICITY>. This option determines whether (most)	4244	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2632	functions and callbacks have an initial C<struct ev_loop *> argument.	4245	functions and callbacks have an initial C<struct ev_loop *> argument.
2633		4246
2634	To make it easier to write programs that cope with either variant, the	4247	To make it easier to write programs that cope with either variant, the
2635	following macros are defined:	4248	following macros are defined:
…		…
2640		4253
2641	This provides the loop I<argument> for functions, if one is required ("ev	4254	This provides the loop I<argument> for functions, if one is required ("ev
2642	loop argument"). The C<EV_A> form is used when this is the sole argument,	4255	loop argument"). The C<EV_A> form is used when this is the sole argument,
2643	C<EV_A_> is used when other arguments are following. Example:	4256	C<EV_A_> is used when other arguments are following. Example:
2644		4257
2645	ev_unref (EV_A);	4258	ev_unref (EV_A);
2646	ev_timer_add (EV_A_ watcher);	4259	ev_timer_add (EV_A_ watcher);
2647	ev_loop (EV_A_ 0);	4260	ev_run (EV_A_ 0);
2648		4261
2649	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	4262	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2650	which is often provided by the following macro.	4263	which is often provided by the following macro.
2651		4264
2652	=item C<EV_P>, C<EV_P_>	4265	=item C<EV_P>, C<EV_P_>
2653		4266
2654	This provides the loop I<parameter> for functions, if one is required ("ev	4267	This provides the loop I<parameter> for functions, if one is required ("ev
2655	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	4268	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
2656	C<EV_P_> is used when other parameters are following. Example:	4269	C<EV_P_> is used when other parameters are following. Example:
2657		4270
2658	// this is how ev_unref is being declared	4271	// this is how ev_unref is being declared
2659	static void ev_unref (EV_P);	4272	static void ev_unref (EV_P);
2660		4273
2661	// this is how you can declare your typical callback	4274	// this is how you can declare your typical callback
2662	static void cb (EV_P_ ev_timer *w, int revents)	4275	static void cb (EV_P_ ev_timer *w, int revents)
2663		4276
2664	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	4277	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
2665	suitable for use with C<EV_A>.	4278	suitable for use with C<EV_A>.
2666		4279
2667	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4280	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2668		4281
2669	Similar to the other two macros, this gives you the value of the default	4282	Similar to the other two macros, this gives you the value of the default
2670	loop, if multiple loops are supported ("ev loop default").	4283	loop, if multiple loops are supported ("ev loop default"). The default loop
		4284	will be initialised if it isn't already initialised.
		4285
		4286	For non-multiplicity builds, these macros do nothing, so you always have
		4287	to initialise the loop somewhere.
2671		4288
2672	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4289	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
2673		4290
2674	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4291	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
2675	default loop has been initialised (C<UC> == unchecked). Their behaviour	4292	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
2683		4300
2684	Example: Declare and initialise a check watcher, utilising the above	4301	Example: Declare and initialise a check watcher, utilising the above
2685	macros so it will work regardless of whether multiple loops are supported	4302	macros so it will work regardless of whether multiple loops are supported
2686	or not.	4303	or not.
2687		4304
2688	static void	4305	static void
2689	check_cb (EV_P_ ev_timer *w, int revents)	4306	check_cb (EV_P_ ev_timer *w, int revents)
2690	{	4307	{
2691	ev_check_stop (EV_A_ w);	4308	ev_check_stop (EV_A_ w);
2692	}	4309	}
2693		4310
2694	ev_check check;	4311	ev_check check;
2695	ev_check_init (&check, check_cb);	4312	ev_check_init (&check, check_cb);
2696	ev_check_start (EV_DEFAULT_ &check);	4313	ev_check_start (EV_DEFAULT_ &check);
2697	ev_loop (EV_DEFAULT_ 0);	4314	ev_run (EV_DEFAULT_ 0);
2698		4315
2699	=head1 EMBEDDING	4316	=head1 EMBEDDING
2700		4317
2701	Libev can (and often is) directly embedded into host	4318	Libev can (and often is) directly embedded into host
2702	applications. Examples of applications that embed it include the Deliantra	4319	applications. Examples of applications that embed it include the Deliantra
…		…
2709	libev somewhere in your source tree).	4326	libev somewhere in your source tree).
2710		4327
2711	=head2 FILESETS	4328	=head2 FILESETS
2712		4329
2713	Depending on what features you need you need to include one or more sets of files	4330	Depending on what features you need you need to include one or more sets of files
2714	in your app.	4331	in your application.
2715		4332
2716	=head3 CORE EVENT LOOP	4333	=head3 CORE EVENT LOOP
2717		4334
2718	To include only the libev core (all the C<ev_*> functions), with manual	4335	To include only the libev core (all the C<ev_*> functions), with manual
2719	configuration (no autoconf):	4336	configuration (no autoconf):
2720		4337
2721	#define EV_STANDALONE 1	4338	#define EV_STANDALONE 1
2722	#include "ev.c"	4339	#include "ev.c"
2723		4340
2724	This will automatically include F<ev.h>, too, and should be done in a	4341	This will automatically include F<ev.h>, too, and should be done in a
2725	single C source file only to provide the function implementations. To use	4342	single C source file only to provide the function implementations. To use
2726	it, do the same for F<ev.h> in all files wishing to use this API (best	4343	it, do the same for F<ev.h> in all files wishing to use this API (best
2727	done by writing a wrapper around F<ev.h> that you can include instead and	4344	done by writing a wrapper around F<ev.h> that you can include instead and
2728	where you can put other configuration options):	4345	where you can put other configuration options):
2729		4346
2730	#define EV_STANDALONE 1	4347	#define EV_STANDALONE 1
2731	#include "ev.h"	4348	#include "ev.h"
2732		4349
2733	Both header files and implementation files can be compiled with a C++	4350	Both header files and implementation files can be compiled with a C++
2734	compiler (at least, thats a stated goal, and breakage will be treated	4351	compiler (at least, that's a stated goal, and breakage will be treated
2735	as a bug).	4352	as a bug).
2736		4353
2737	You need the following files in your source tree, or in a directory	4354	You need the following files in your source tree, or in a directory
2738	in your include path (e.g. in libev/ when using -Ilibev):	4355	in your include path (e.g. in libev/ when using -Ilibev):
2739		4356
2740	ev.h	4357	ev.h
2741	ev.c	4358	ev.c
2742	ev_vars.h	4359	ev_vars.h
2743	ev_wrap.h	4360	ev_wrap.h
2744		4361
2745	ev_win32.c required on win32 platforms only	4362	ev_win32.c required on win32 platforms only
2746		4363
2747	ev_select.c only when select backend is enabled (which is enabled by default)	4364	ev_select.c only when select backend is enabled (which is enabled by default)
2748	ev_poll.c only when poll backend is enabled (disabled by default)	4365	ev_poll.c only when poll backend is enabled (disabled by default)
2749	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4366	ev_epoll.c only when the epoll backend is enabled (disabled by default)
2750	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4367	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2751	ev_port.c only when the solaris port backend is enabled (disabled by default)	4368	ev_port.c only when the solaris port backend is enabled (disabled by default)
2752		4369
2753	F<ev.c> includes the backend files directly when enabled, so you only need	4370	F<ev.c> includes the backend files directly when enabled, so you only need
2754	to compile this single file.	4371	to compile this single file.
2755		4372
2756	=head3 LIBEVENT COMPATIBILITY API	4373	=head3 LIBEVENT COMPATIBILITY API
2757		4374
2758	To include the libevent compatibility API, also include:	4375	To include the libevent compatibility API, also include:
2759		4376
2760	#include "event.c"	4377	#include "event.c"
2761		4378
2762	in the file including F<ev.c>, and:	4379	in the file including F<ev.c>, and:
2763		4380
2764	#include "event.h"	4381	#include "event.h"
2765		4382
2766	in the files that want to use the libevent API. This also includes F<ev.h>.	4383	in the files that want to use the libevent API. This also includes F<ev.h>.
2767		4384
2768	You need the following additional files for this:	4385	You need the following additional files for this:
2769		4386
2770	event.h	4387	event.h
2771	event.c	4388	event.c
2772		4389
2773	=head3 AUTOCONF SUPPORT	4390	=head3 AUTOCONF SUPPORT
2774		4391
2775	Instead of using C<EV_STANDALONE=1> and providing your config in	4392	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2776	whatever way you want, you can also C<m4_include([libev.m4])> in your	4393	whatever way you want, you can also C<m4_include([libev.m4])> in your
2777	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	4394	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2778	include F<config.h> and configure itself accordingly.	4395	include F<config.h> and configure itself accordingly.
2779		4396
2780	For this of course you need the m4 file:	4397	For this of course you need the m4 file:
2781		4398
2782	libev.m4	4399	libev.m4
2783		4400
2784	=head2 PREPROCESSOR SYMBOLS/MACROS	4401	=head2 PREPROCESSOR SYMBOLS/MACROS
2785		4402
2786	Libev can be configured via a variety of preprocessor symbols you have to	4403	Libev can be configured via a variety of preprocessor symbols you have to
2787	define before including any of its files. The default in the absense of	4404	define before including (or compiling) any of its files. The default in
2788	autoconf is noted for every option.	4405	the absence of autoconf is documented for every option.
		4406
		4407	Symbols marked with "(h)" do not change the ABI, and can have different
		4408	values when compiling libev vs. including F<ev.h>, so it is permissible
		4409	to redefine them before including F<ev.h> without breaking compatibility
		4410	to a compiled library. All other symbols change the ABI, which means all
		4411	users of libev and the libev code itself must be compiled with compatible
		4412	settings.
2789		4413
2790	=over 4	4414	=over 4
2791		4415
		4416	=item EV_COMPAT3 (h)
		4417
		4418	Backwards compatibility is a major concern for libev. This is why this
		4419	release of libev comes with wrappers for the functions and symbols that
		4420	have been renamed between libev version 3 and 4.
		4421
		4422	You can disable these wrappers (to test compatibility with future
		4423	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		4424	sources. This has the additional advantage that you can drop the C<struct>
		4425	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		4426	typedef in that case.
		4427
		4428	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		4429	and in some even more future version the compatibility code will be
		4430	removed completely.
		4431
2792	=item EV_STANDALONE	4432	=item EV_STANDALONE (h)
2793		4433
2794	Must always be C<1> if you do not use autoconf configuration, which	4434	Must always be C<1> if you do not use autoconf configuration, which
2795	keeps libev from including F<config.h>, and it also defines dummy	4435	keeps libev from including F<config.h>, and it also defines dummy
2796	implementations for some libevent functions (such as logging, which is not	4436	implementations for some libevent functions (such as logging, which is not
2797	supported). It will also not define any of the structs usually found in	4437	supported). It will also not define any of the structs usually found in
2798	F<event.h> that are not directly supported by the libev core alone.	4438	F<event.h> that are not directly supported by the libev core alone.
2799		4439
		4440	In standalone mode, libev will still try to automatically deduce the
		4441	configuration, but has to be more conservative.
		4442
		4443	=item EV_USE_FLOOR
		4444
		4445	If defined to be C<1>, libev will use the C<floor ()> function for its
		4446	periodic reschedule calculations, otherwise libev will fall back on a
		4447	portable (slower) implementation. If you enable this, you usually have to
		4448	link against libm or something equivalent. Enabling this when the C<floor>
		4449	function is not available will fail, so the safe default is to not enable
		4450	this.
		4451
2800	=item EV_USE_MONOTONIC	4452	=item EV_USE_MONOTONIC
2801		4453
2802	If defined to be C<1>, libev will try to detect the availability of the	4454	If defined to be C<1>, libev will try to detect the availability of the
2803	monotonic clock option at both compiletime and runtime. Otherwise no use	4455	monotonic clock option at both compile time and runtime. Otherwise no
2804	of the monotonic clock option will be attempted. If you enable this, you	4456	use of the monotonic clock option will be attempted. If you enable this,
2805	usually have to link against librt or something similar. Enabling it when	4457	you usually have to link against librt or something similar. Enabling it
2806	the functionality isn't available is safe, though, although you have	4458	when the functionality isn't available is safe, though, although you have
2807	to make sure you link against any libraries where the C<clock_gettime>	4459	to make sure you link against any libraries where the C<clock_gettime>
2808	function is hiding in (often F<-lrt>).	4460	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2809		4461
2810	=item EV_USE_REALTIME	4462	=item EV_USE_REALTIME
2811		4463
2812	If defined to be C<1>, libev will try to detect the availability of the	4464	If defined to be C<1>, libev will try to detect the availability of the
2813	realtime clock option at compiletime (and assume its availability at	4465	real-time clock option at compile time (and assume its availability
2814	runtime if successful). Otherwise no use of the realtime clock option will	4466	at runtime if successful). Otherwise no use of the real-time clock
2815	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	4467	option will be attempted. This effectively replaces C<gettimeofday>
2816	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	4468	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2817	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	4469	correctness. See the note about libraries in the description of
		4470	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		4471	C<EV_USE_CLOCK_SYSCALL>.
		4472
		4473	=item EV_USE_CLOCK_SYSCALL
		4474
		4475	If defined to be C<1>, libev will try to use a direct syscall instead
		4476	of calling the system-provided C<clock_gettime> function. This option
		4477	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		4478	unconditionally pulls in C<libpthread>, slowing down single-threaded
		4479	programs needlessly. Using a direct syscall is slightly slower (in
		4480	theory), because no optimised vdso implementation can be used, but avoids
		4481	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		4482	higher, as it simplifies linking (no need for C<-lrt>).
2818		4483
2819	=item EV_USE_NANOSLEEP	4484	=item EV_USE_NANOSLEEP
2820		4485
2821	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	4486	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2822	and will use it for delays. Otherwise it will use C<select ()>.	4487	and will use it for delays. Otherwise it will use C<select ()>.
…		…
2830	2.7 or newer, otherwise disabled.	4495	2.7 or newer, otherwise disabled.
2831		4496
2832	=item EV_USE_SELECT	4497	=item EV_USE_SELECT
2833		4498
2834	If undefined or defined to be C<1>, libev will compile in support for the	4499	If undefined or defined to be C<1>, libev will compile in support for the
2835	C<select>(2) backend. No attempt at autodetection will be done: if no	4500	C<select>(2) backend. No attempt at auto-detection will be done: if no
2836	other method takes over, select will be it. Otherwise the select backend	4501	other method takes over, select will be it. Otherwise the select backend
2837	will not be compiled in.	4502	will not be compiled in.
2838		4503
2839	=item EV_SELECT_USE_FD_SET	4504	=item EV_SELECT_USE_FD_SET
2840		4505
2841	If defined to C<1>, then the select backend will use the system C<fd_set>	4506	If defined to C<1>, then the select backend will use the system C<fd_set>
2842	structure. This is useful if libev doesn't compile due to a missing	4507	structure. This is useful if libev doesn't compile due to a missing
2843	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	4508	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2844	exotic systems. This usually limits the range of file descriptors to some	4509	on exotic systems. This usually limits the range of file descriptors to
2845	low limit such as 1024 or might have other limitations (winsocket only	4510	some low limit such as 1024 or might have other limitations (winsocket
2846	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	4511	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2847	influence the size of the C<fd_set> used.	4512	configures the maximum size of the C<fd_set>.
2848		4513
2849	=item EV_SELECT_IS_WINSOCKET	4514	=item EV_SELECT_IS_WINSOCKET
2850		4515
2851	When defined to C<1>, the select backend will assume that	4516	When defined to C<1>, the select backend will assume that
2852	select/socket/connect etc. don't understand file descriptors but	4517	select/socket/connect etc. don't understand file descriptors but
…		…
2854	be used is the winsock select). This means that it will call	4519	be used is the winsock select). This means that it will call
2855	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	4520	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2856	it is assumed that all these functions actually work on fds, even	4521	it is assumed that all these functions actually work on fds, even
2857	on win32. Should not be defined on non-win32 platforms.	4522	on win32. Should not be defined on non-win32 platforms.
2858		4523
2859	=item EV_FD_TO_WIN32_HANDLE	4524	=item EV_FD_TO_WIN32_HANDLE(fd)
2860		4525
2861	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map	4526	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
2862	file descriptors to socket handles. When not defining this symbol (the	4527	file descriptors to socket handles. When not defining this symbol (the
2863	default), then libev will call C<_get_osfhandle>, which is usually	4528	default), then libev will call C<_get_osfhandle>, which is usually
2864	correct. In some cases, programs use their own file descriptor management,	4529	correct. In some cases, programs use their own file descriptor management,
2865	in which case they can provide this function to map fds to socket handles.	4530	in which case they can provide this function to map fds to socket handles.
		4531
		4532	=item EV_WIN32_HANDLE_TO_FD(handle)
		4533
		4534	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		4535	using the standard C<_open_osfhandle> function. For programs implementing
		4536	their own fd to handle mapping, overwriting this function makes it easier
		4537	to do so. This can be done by defining this macro to an appropriate value.
		4538
		4539	=item EV_WIN32_CLOSE_FD(fd)
		4540
		4541	If programs implement their own fd to handle mapping on win32, then this
		4542	macro can be used to override the C<close> function, useful to unregister
		4543	file descriptors again. Note that the replacement function has to close
		4544	the underlying OS handle.
2866		4545
2867	=item EV_USE_POLL	4546	=item EV_USE_POLL
2868		4547
2869	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4548	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2870	backend. Otherwise it will be enabled on non-win32 platforms. It	4549	backend. Otherwise it will be enabled on non-win32 platforms. It
…		…
2897	otherwise another method will be used as fallback. This is the preferred	4576	otherwise another method will be used as fallback. This is the preferred
2898	backend for Solaris 10 systems.	4577	backend for Solaris 10 systems.
2899		4578
2900	=item EV_USE_DEVPOLL	4579	=item EV_USE_DEVPOLL
2901		4580
2902	reserved for future expansion, works like the USE symbols above.	4581	Reserved for future expansion, works like the USE symbols above.
2903		4582
2904	=item EV_USE_INOTIFY	4583	=item EV_USE_INOTIFY
2905		4584
2906	If defined to be C<1>, libev will compile in support for the Linux inotify	4585	If defined to be C<1>, libev will compile in support for the Linux inotify
2907	interface to speed up C<ev_stat> watchers. Its actual availability will	4586	interface to speed up C<ev_stat> watchers. Its actual availability will
2908	be detected at runtime. If undefined, it will be enabled if the headers	4587	be detected at runtime. If undefined, it will be enabled if the headers
2909	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4588	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2910		4589
		4590	=item EV_NO_SMP
		4591
		4592	If defined to be C<1>, libev will assume that memory is always coherent
		4593	between threads, that is, threads can be used, but threads never run on
		4594	different cpus (or different cpu cores). This reduces dependencies
		4595	and makes libev faster.
		4596
		4597	=item EV_NO_THREADS
		4598
		4599	If defined to be C<1>, libev will assume that it will never be called
		4600	from different threads, which is a stronger assumption than C<EV_NO_SMP>,
		4601	above. This reduces dependencies and makes libev faster.
		4602
2911	=item EV_ATOMIC_T	4603	=item EV_ATOMIC_T
2912		4604
2913	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4605	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
2914	access is atomic with respect to other threads or signal contexts. No such	4606	access is atomic and serialised with respect to other threads or signal
2915	type is easily found in the C language, so you can provide your own type	4607	contexts. No such type is easily found in the C language, so you can
2916	that you know is safe for your purposes. It is used both for signal handler "locking"	4608	provide your own type that you know is safe for your purposes. It is used
2917	as well as for signal and thread safety in C<ev_async> watchers.	4609	both for signal handler "locking" as well as for signal and thread safety
		4610	in C<ev_async> watchers.
2918		4611
2919	In the absense of this define, libev will use C<sig_atomic_t volatile>	4612	In the absence of this define, libev will use C<sig_atomic_t volatile>
2920	(from F<signal.h>), which is usually good enough on most platforms.	4613	(from F<signal.h>), which is usually good enough on most platforms,
		4614	although strictly speaking using a type that also implies a memory fence
		4615	is required.
2921		4616
2922	=item EV_H	4617	=item EV_H (h)
2923		4618
2924	The name of the F<ev.h> header file used to include it. The default if	4619	The name of the F<ev.h> header file used to include it. The default if
2925	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be	4620	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2926	used to virtually rename the F<ev.h> header file in case of conflicts.	4621	used to virtually rename the F<ev.h> header file in case of conflicts.
2927		4622
2928	=item EV_CONFIG_H	4623	=item EV_CONFIG_H (h)
2929		4624
2930	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	4625	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2931	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	4626	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2932	C<EV_H>, above.	4627	C<EV_H>, above.
2933		4628
2934	=item EV_EVENT_H	4629	=item EV_EVENT_H (h)
2935		4630
2936	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	4631	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2937	of how the F<event.h> header can be found, the default is C<"event.h">.	4632	of how the F<event.h> header can be found, the default is C<"event.h">.
2938		4633
2939	=item EV_PROTOTYPES	4634	=item EV_PROTOTYPES (h)
2940		4635
2941	If defined to be C<0>, then F<ev.h> will not define any function	4636	If defined to be C<0>, then F<ev.h> will not define any function
2942	prototypes, but still define all the structs and other symbols. This is	4637	prototypes, but still define all the structs and other symbols. This is
2943	occasionally useful if you want to provide your own wrapper functions	4638	occasionally useful if you want to provide your own wrapper functions
2944	around libev functions.	4639	around libev functions.
…		…
2949	will have the C<struct ev_loop *> as first argument, and you can create	4644	will have the C<struct ev_loop *> as first argument, and you can create
2950	additional independent event loops. Otherwise there will be no support	4645	additional independent event loops. Otherwise there will be no support
2951	for multiple event loops and there is no first event loop pointer	4646	for multiple event loops and there is no first event loop pointer
2952	argument. Instead, all functions act on the single default loop.	4647	argument. Instead, all functions act on the single default loop.
2953		4648
		4649	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4650	default loop when multiplicity is switched off - you always have to
		4651	initialise the loop manually in this case.
		4652
2954	=item EV_MINPRI	4653	=item EV_MINPRI
2955		4654
2956	=item EV_MAXPRI	4655	=item EV_MAXPRI
2957		4656
2958	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4657	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
2963	When doing priority-based operations, libev usually has to linearly search	4662	When doing priority-based operations, libev usually has to linearly search
2964	all the priorities, so having many of them (hundreds) uses a lot of space	4663	all the priorities, so having many of them (hundreds) uses a lot of space
2965	and time, so using the defaults of five priorities (-2 .. +2) is usually	4664	and time, so using the defaults of five priorities (-2 .. +2) is usually
2966	fine.	4665	fine.
2967		4666
2968	If your embedding app does not need any priorities, defining these both to	4667	If your embedding application does not need any priorities, defining these
2969	C<0> will save some memory and cpu.	4668	both to C<0> will save some memory and CPU.
2970		4669
2971	=item EV_PERIODIC_ENABLE	4670	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		4671	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		4672	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
2972		4673
2973	If undefined or defined to be C<1>, then periodic timers are supported. If	4674	If undefined or defined to be C<1> (and the platform supports it), then
2974	defined to be C<0>, then they are not. Disabling them saves a few kB of	4675	the respective watcher type is supported. If defined to be C<0>, then it
2975	code.	4676	is not. Disabling watcher types mainly saves code size.
2976		4677
2977	=item EV_IDLE_ENABLE	4678	=item EV_FEATURES
2978
2979	If undefined or defined to be C<1>, then idle watchers are supported. If
2980	defined to be C<0>, then they are not. Disabling them saves a few kB of
2981	code.
2982
2983	=item EV_EMBED_ENABLE
2984
2985	If undefined or defined to be C<1>, then embed watchers are supported. If
2986	defined to be C<0>, then they are not.
2987
2988	=item EV_STAT_ENABLE
2989
2990	If undefined or defined to be C<1>, then stat watchers are supported. If
2991	defined to be C<0>, then they are not.
2992
2993	=item EV_FORK_ENABLE
2994
2995	If undefined or defined to be C<1>, then fork watchers are supported. If
2996	defined to be C<0>, then they are not.
2997
2998	=item EV_ASYNC_ENABLE
2999
3000	If undefined or defined to be C<1>, then async watchers are supported. If
3001	defined to be C<0>, then they are not.
3002
3003	=item EV_MINIMAL
3004		4679
3005	If you need to shave off some kilobytes of code at the expense of some	4680	If you need to shave off some kilobytes of code at the expense of some
3006	speed, define this symbol to C<1>. Currently this is used to override some	4681	speed (but with the full API), you can define this symbol to request
3007	inlining decisions, saves roughly 30% codesize of amd64. It also selects a	4682	certain subsets of functionality. The default is to enable all features
3008	much smaller 2-heap for timer management over the default 4-heap.	4683	that can be enabled on the platform.
		4684
		4685	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4686	with some broad features you want) and then selectively re-enable
		4687	additional parts you want, for example if you want everything minimal,
		4688	but multiple event loop support, async and child watchers and the poll
		4689	backend, use this:
		4690
		4691	#define EV_FEATURES 0
		4692	#define EV_MULTIPLICITY 1
		4693	#define EV_USE_POLL 1
		4694	#define EV_CHILD_ENABLE 1
		4695	#define EV_ASYNC_ENABLE 1
		4696
		4697	The actual value is a bitset, it can be a combination of the following
		4698	values (by default, all of these are enabled):
		4699
		4700	=over 4
		4701
		4702	=item C<1> - faster/larger code
		4703
		4704	Use larger code to speed up some operations.
		4705
		4706	Currently this is used to override some inlining decisions (enlarging the
		4707	code size by roughly 30% on amd64).
		4708
		4709	When optimising for size, use of compiler flags such as C<-Os> with
		4710	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4711	assertions.
		4712
		4713	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4714	(e.g. gcc with C<-Os>).
		4715
		4716	=item C<2> - faster/larger data structures
		4717
		4718	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4719	hash table sizes and so on. This will usually further increase code size
		4720	and can additionally have an effect on the size of data structures at
		4721	runtime.
		4722
		4723	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4724	(e.g. gcc with C<-Os>).
		4725
		4726	=item C<4> - full API configuration
		4727
		4728	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4729	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4730
		4731	=item C<8> - full API
		4732
		4733	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4734	details on which parts of the API are still available without this
		4735	feature, and do not complain if this subset changes over time.
		4736
		4737	=item C<16> - enable all optional watcher types
		4738
		4739	Enables all optional watcher types. If you want to selectively enable
		4740	only some watcher types other than I/O and timers (e.g. prepare,
		4741	embed, async, child...) you can enable them manually by defining
		4742	C<EV_watchertype_ENABLE> to C<1> instead.
		4743
		4744	=item C<32> - enable all backends
		4745
		4746	This enables all backends - without this feature, you need to enable at
		4747	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4748
		4749	=item C<64> - enable OS-specific "helper" APIs
		4750
		4751	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4752	default.
		4753
		4754	=back
		4755
		4756	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4757	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4758	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4759	watchers, timers and monotonic clock support.
		4760
		4761	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4762	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4763	your program might be left out as well - a binary starting a timer and an
		4764	I/O watcher then might come out at only 5Kb.
		4765
		4766	=item EV_API_STATIC
		4767
		4768	If this symbol is defined (by default it is not), then all identifiers
		4769	will have static linkage. This means that libev will not export any
		4770	identifiers, and you cannot link against libev anymore. This can be useful
		4771	when you embed libev, only want to use libev functions in a single file,
		4772	and do not want its identifiers to be visible.
		4773
		4774	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4775	wants to use libev.
		4776
		4777	This option only works when libev is compiled with a C compiler, as C++
		4778	doesn't support the required declaration syntax.
		4779
		4780	=item EV_AVOID_STDIO
		4781
		4782	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4783	functions (printf, scanf, perror etc.). This will increase the code size
		4784	somewhat, but if your program doesn't otherwise depend on stdio and your
		4785	libc allows it, this avoids linking in the stdio library which is quite
		4786	big.
		4787
		4788	Note that error messages might become less precise when this option is
		4789	enabled.
		4790
		4791	=item EV_NSIG
		4792
		4793	The highest supported signal number, +1 (or, the number of
		4794	signals): Normally, libev tries to deduce the maximum number of signals
		4795	automatically, but sometimes this fails, in which case it can be
		4796	specified. Also, using a lower number than detected (C<32> should be
		4797	good for about any system in existence) can save some memory, as libev
		4798	statically allocates some 12-24 bytes per signal number.
3009		4799
3010	=item EV_PID_HASHSIZE	4800	=item EV_PID_HASHSIZE
3011		4801
3012	C<ev_child> watchers use a small hash table to distribute workload by	4802	C<ev_child> watchers use a small hash table to distribute workload by
3013	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	4803	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
3014	than enough. If you need to manage thousands of children you might want to	4804	usually more than enough. If you need to manage thousands of children you
3015	increase this value (I<must> be a power of two).	4805	might want to increase this value (I<must> be a power of two).
3016		4806
3017	=item EV_INOTIFY_HASHSIZE	4807	=item EV_INOTIFY_HASHSIZE
3018		4808
3019	C<ev_stat> watchers use a small hash table to distribute workload by	4809	C<ev_stat> watchers use a small hash table to distribute workload by
3020	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	4810	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
3021	usually more than enough. If you need to manage thousands of C<ev_stat>	4811	disabled), usually more than enough. If you need to manage thousands of
3022	watchers you might want to increase this value (I<must> be a power of	4812	C<ev_stat> watchers you might want to increase this value (I<must> be a
3023	two).	4813	power of two).
3024		4814
3025	=item EV_USE_4HEAP	4815	=item EV_USE_4HEAP
3026		4816
3027	Heaps are not very cache-efficient. To improve the cache-efficiency of the	4817	Heaps are not very cache-efficient. To improve the cache-efficiency of the
3028	timer and periodics heap, libev uses a 4-heap when this symbol is defined	4818	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
3029	to C<1>. The 4-heap uses more complicated (longer) code but has	4819	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
3030	noticably faster performance with many (thousands) of watchers.	4820	faster performance with many (thousands) of watchers.
3031		4821
3032	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	4822	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3033	(disabled).	4823	will be C<0>.
3034		4824
3035	=item EV_HEAP_CACHE_AT	4825	=item EV_HEAP_CACHE_AT
3036		4826
3037	Heaps are not very cache-efficient. To improve the cache-efficiency of the	4827	Heaps are not very cache-efficient. To improve the cache-efficiency of the
3038	timer and periodics heap, libev can cache the timestamp (I<at>) within	4828	timer and periodics heaps, libev can cache the timestamp (I<at>) within
3039	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),	4829	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
3040	which uses 8-12 bytes more per watcher and a few hundred bytes more code,	4830	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
3041	but avoids random read accesses on heap changes. This improves performance	4831	but avoids random read accesses on heap changes. This improves performance
3042	noticably with with many (hundreds) of watchers.	4832	noticeably with many (hundreds) of watchers.
3043		4833
3044	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	4834	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3045	(disabled).	4835	will be C<0>.
3046		4836
3047	=item EV_VERIFY	4837	=item EV_VERIFY
3048		4838
3049	Controls how much internal verification (see C<ev_loop_verify ()>) will	4839	Controls how much internal verification (see C<ev_verify ()>) will
3050	be done: If set to C<0>, no internal verification code will be compiled	4840	be done: If set to C<0>, no internal verification code will be compiled
3051	in. If set to C<1>, then verification code will be compiled in, but not	4841	in. If set to C<1>, then verification code will be compiled in, but not
3052	called. If set to C<2>, then the internal verification code will be	4842	called. If set to C<2>, then the internal verification code will be
3053	called once per loop, which can slow down libev. If set to C<3>, then the	4843	called once per loop, which can slow down libev. If set to C<3>, then the
3054	verification code will be called very frequently, which will slow down	4844	verification code will be called very frequently, which will slow down
3055	libev considerably.	4845	libev considerably.
3056		4846
3057	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be	4847	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3058	C<0.>	4848	will be C<0>.
3059		4849
3060	=item EV_COMMON	4850	=item EV_COMMON
3061		4851
3062	By default, all watchers have a C<void *data> member. By redefining	4852	By default, all watchers have a C<void *data> member. By redefining
3063	this macro to a something else you can include more and other types of	4853	this macro to something else you can include more and other types of
3064	members. You have to define it each time you include one of the files,	4854	members. You have to define it each time you include one of the files,
3065	though, and it must be identical each time.	4855	though, and it must be identical each time.
3066		4856
3067	For example, the perl EV module uses something like this:	4857	For example, the perl EV module uses something like this:
3068		4858
3069	#define EV_COMMON \	4859	#define EV_COMMON \
3070	SV *self; /* contains this struct */ \	4860	SV *self; /* contains this struct */ \
3071	SV *cb_sv, *fh /* note no trailing ";" */	4861	SV *cb_sv, *fh /* note no trailing ";" */
3072		4862
3073	=item EV_CB_DECLARE (type)	4863	=item EV_CB_DECLARE (type)
3074		4864
3075	=item EV_CB_INVOKE (watcher, revents)	4865	=item EV_CB_INVOKE (watcher, revents)
3076		4866
…		…
3081	definition and a statement, respectively. See the F<ev.h> header file for	4871	definition and a statement, respectively. See the F<ev.h> header file for
3082	their default definitions. One possible use for overriding these is to	4872	their default definitions. One possible use for overriding these is to
3083	avoid the C<struct ev_loop *> as first argument in all cases, or to use	4873	avoid the C<struct ev_loop *> as first argument in all cases, or to use
3084	method calls instead of plain function calls in C++.	4874	method calls instead of plain function calls in C++.
3085		4875
		4876	=back
		4877
3086	=head2 EXPORTED API SYMBOLS	4878	=head2 EXPORTED API SYMBOLS
3087		4879
3088	If you need to re-export the API (e.g. via a dll) and you need a list of	4880	If you need to re-export the API (e.g. via a DLL) and you need a list of
3089	exported symbols, you can use the provided F<Symbol.*> files which list	4881	exported symbols, you can use the provided F<Symbol.*> files which list
3090	all public symbols, one per line:	4882	all public symbols, one per line:
3091		4883
3092	Symbols.ev for libev proper	4884	Symbols.ev for libev proper
3093	Symbols.event for the libevent emulation	4885	Symbols.event for the libevent emulation
3094		4886
3095	This can also be used to rename all public symbols to avoid clashes with	4887	This can also be used to rename all public symbols to avoid clashes with
3096	multiple versions of libev linked together (which is obviously bad in	4888	multiple versions of libev linked together (which is obviously bad in
3097	itself, but sometimes it is inconvinient to avoid this).	4889	itself, but sometimes it is inconvenient to avoid this).
3098		4890
3099	A sed command like this will create wrapper C<#define>'s that you need to	4891	A sed command like this will create wrapper C<#define>'s that you need to
3100	include before including F<ev.h>:	4892	include before including F<ev.h>:
3101		4893
3102	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h	4894	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
…		…
3119	file.	4911	file.
3120		4912
3121	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	4913	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
3122	that everybody includes and which overrides some configure choices:	4914	that everybody includes and which overrides some configure choices:
3123		4915
3124	#define EV_MINIMAL 1	4916	#define EV_FEATURES 8
3125	#define EV_USE_POLL 0	4917	#define EV_USE_SELECT 1
3126	#define EV_MULTIPLICITY 0
3127	#define EV_PERIODIC_ENABLE 0	4918	#define EV_PREPARE_ENABLE 1
		4919	#define EV_IDLE_ENABLE 1
3128	#define EV_STAT_ENABLE 0	4920	#define EV_SIGNAL_ENABLE 1
3129	#define EV_FORK_ENABLE 0	4921	#define EV_CHILD_ENABLE 1
		4922	#define EV_USE_STDEXCEPT 0
3130	#define EV_CONFIG_H <config.h>	4923	#define EV_CONFIG_H <config.h>
3131	#define EV_MINPRI 0
3132	#define EV_MAXPRI 0
3133		4924
3134	#include "ev++.h"	4925	#include "ev++.h"
3135		4926
3136	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4927	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
3137		4928
3138	#include "ev_cpp.h"	4929	#include "ev_cpp.h"
3139	#include "ev.c"	4930	#include "ev.c"
3140		4931
		4932	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
3141		4933
3142	=head1 THREADS AND COROUTINES	4934	=head2 THREADS AND COROUTINES
3143		4935
3144	=head2 THREADS	4936	=head3 THREADS
3145		4937
3146	Libev itself is completely threadsafe, but it uses no locking. This	4938	All libev functions are reentrant and thread-safe unless explicitly
		4939	documented otherwise, but libev implements no locking itself. This means
3147	means that you can use as many loops as you want in parallel, as long as	4940	that you can use as many loops as you want in parallel, as long as there
3148	only one thread ever calls into one libev function with the same loop	4941	are no concurrent calls into any libev function with the same loop
3149	parameter.	4942	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4943	of course): libev guarantees that different event loops share no data
		4944	structures that need any locking.
3150		4945
3151	Or put differently: calls with different loop parameters can be done in	4946	Or to put it differently: calls with different loop parameters can be done
3152	parallel from multiple threads, calls with the same loop parameter must be	4947	concurrently from multiple threads, calls with the same loop parameter
3153	done serially (but can be done from different threads, as long as only one	4948	must be done serially (but can be done from different threads, as long as
3154	thread ever is inside a call at any point in time, e.g. by using a mutex	4949	only one thread ever is inside a call at any point in time, e.g. by using
3155	per loop).	4950	a mutex per loop).
3156		4951
3157	If you want to know which design is best for your problem, then I cannot	4952	Specifically to support threads (and signal handlers), libev implements
		4953	so-called C<ev_async> watchers, which allow some limited form of
		4954	concurrency on the same event loop, namely waking it up "from the
		4955	outside".
		4956
		4957	If you want to know which design (one loop, locking, or multiple loops
		4958	without or something else still) is best for your problem, then I cannot
3158	help you but by giving some generic advice:	4959	help you, but here is some generic advice:
3159		4960
3160	=over 4	4961	=over 4
3161		4962
3162	=item * most applications have a main thread: use the default libev loop	4963	=item * most applications have a main thread: use the default libev loop
3163	in that thread, or create a seperate thread running only the default loop.	4964	in that thread, or create a separate thread running only the default loop.
3164		4965
3165	This helps integrating other libraries or software modules that use libev	4966	This helps integrating other libraries or software modules that use libev
3166	themselves and don't care/know about threading.	4967	themselves and don't care/know about threading.
3167		4968
3168	=item * one loop per thread is usually a good model.	4969	=item * one loop per thread is usually a good model.
3169		4970
3170	Doing this is almost never wrong, sometimes a better-performance model	4971	Doing this is almost never wrong, sometimes a better-performance model
3171	exists, but it is always a good start.	4972	exists, but it is always a good start.
3172		4973
3173	=item * other models exist, such as the leader/follower pattern, where one	4974	=item * other models exist, such as the leader/follower pattern, where one
3174	loop is handed through multiple threads in a kind of round-robbin fashion.	4975	loop is handed through multiple threads in a kind of round-robin fashion.
3175		4976
3176	Chosing a model is hard - look around, learn, know that usually you cna do	4977	Choosing a model is hard - look around, learn, know that usually you can do
3177	better than you currently do :-)	4978	better than you currently do :-)
3178		4979
3179	=item * often you need to talk to some other thread which blocks in the	4980	=item * often you need to talk to some other thread which blocks in the
		4981	event loop.
		4982
3180	event loop - C<ev_async> watchers can be used to wake them up from other	4983	C<ev_async> watchers can be used to wake them up from other threads safely
3181	threads safely (or from signal contexts...).	4984	(or from signal contexts...).
		4985
		4986	An example use would be to communicate signals or other events that only
		4987	work in the default loop by registering the signal watcher with the
		4988	default loop and triggering an C<ev_async> watcher from the default loop
		4989	watcher callback into the event loop interested in the signal.
3182		4990
3183	=back	4991	=back
3184		4992
		4993	See also L<THREAD LOCKING EXAMPLE>.
		4994
3185	=head2 COROUTINES	4995	=head3 COROUTINES
3186		4996
3187	Libev is much more accomodating to coroutines ("cooperative threads"):	4997	Libev is very accommodating to coroutines ("cooperative threads"):
3188	libev fully supports nesting calls to it's functions from different	4998	libev fully supports nesting calls to its functions from different
3189	coroutines (e.g. you can call C<ev_loop> on the same loop from two	4999	coroutines (e.g. you can call C<ev_run> on the same loop from two
3190	different coroutines and switch freely between both coroutines running the	5000	different coroutines, and switch freely between both coroutines running
3191	loop, as long as you don't confuse yourself). The only exception is that	5001	the loop, as long as you don't confuse yourself). The only exception is
3192	you must not do this from C<ev_periodic> reschedule callbacks.	5002	that you must not do this from C<ev_periodic> reschedule callbacks.
3193		5003
3194	Care has been invested into making sure that libev does not keep local	5004	Care has been taken to ensure that libev does not keep local state inside
3195	state inside C<ev_loop>, and other calls do not usually allow coroutine	5005	C<ev_run>, and other calls do not usually allow for coroutine switches as
3196	switches.	5006	they do not call any callbacks.
3197		5007
		5008	=head2 COMPILER WARNINGS
3198		5009
3199	=head1 COMPLEXITIES	5010	Depending on your compiler and compiler settings, you might get no or a
		5011	lot of warnings when compiling libev code. Some people are apparently
		5012	scared by this.
3200		5013
3201	In this section the complexities of (many of) the algorithms used inside	5014	However, these are unavoidable for many reasons. For one, each compiler
3202	libev will be explained. For complexity discussions about backends see the	5015	has different warnings, and each user has different tastes regarding
3203	documentation for C<ev_default_init>.	5016	warning options. "Warn-free" code therefore cannot be a goal except when
		5017	targeting a specific compiler and compiler-version.
3204		5018
3205	All of the following are about amortised time: If an array needs to be	5019	Another reason is that some compiler warnings require elaborate
3206	extended, libev needs to realloc and move the whole array, but this	5020	workarounds, or other changes to the code that make it less clear and less
3207	happens asymptotically never with higher number of elements, so O(1) might	5021	maintainable.
3208	mean it might do a lengthy realloc operation in rare cases, but on average
3209	it is much faster and asymptotically approaches constant time.
3210		5022
3211	=over 4	5023	And of course, some compiler warnings are just plain stupid, or simply
		5024	wrong (because they don't actually warn about the condition their message
		5025	seems to warn about). For example, certain older gcc versions had some
		5026	warnings that resulted in an extreme number of false positives. These have
		5027	been fixed, but some people still insist on making code warn-free with
		5028	such buggy versions.
3212		5029
3213	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	5030	While libev is written to generate as few warnings as possible,
		5031	"warn-free" code is not a goal, and it is recommended not to build libev
		5032	with any compiler warnings enabled unless you are prepared to cope with
		5033	them (e.g. by ignoring them). Remember that warnings are just that:
		5034	warnings, not errors, or proof of bugs.
3214		5035
3215	This means that, when you have a watcher that triggers in one hour and
3216	there are 100 watchers that would trigger before that then inserting will
3217	have to skip roughly seven (C<ld 100>) of these watchers.
3218		5036
3219	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)	5037	=head2 VALGRIND
3220		5038
3221	That means that changing a timer costs less than removing/adding them	5039	Valgrind has a special section here because it is a popular tool that is
3222	as only the relative motion in the event queue has to be paid for.	5040	highly useful. Unfortunately, valgrind reports are very hard to interpret.
3223		5041
3224	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)	5042	If you think you found a bug (memory leak, uninitialised data access etc.)
		5043	in libev, then check twice: If valgrind reports something like:
3225		5044
3226	These just add the watcher into an array or at the head of a list.	5045	==2274== definitely lost: 0 bytes in 0 blocks.
		5046	==2274== possibly lost: 0 bytes in 0 blocks.
		5047	==2274== still reachable: 256 bytes in 1 blocks.
3227		5048
3228	=item Stopping check/prepare/idle/fork/async watchers: O(1)	5049	Then there is no memory leak, just as memory accounted to global variables
		5050	is not a memleak - the memory is still being referenced, and didn't leak.
3229		5051
3230	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	5052	Similarly, under some circumstances, valgrind might report kernel bugs
		5053	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		5054	although an acceptable workaround has been found here), or it might be
		5055	confused.
3231		5056
3232	These watchers are stored in lists then need to be walked to find the	5057	Keep in mind that valgrind is a very good tool, but only a tool. Don't
3233	correct watcher to remove. The lists are usually short (you don't usually	5058	make it into some kind of religion.
3234	have many watchers waiting for the same fd or signal).
3235		5059
3236	=item Finding the next timer in each loop iteration: O(1)	5060	If you are unsure about something, feel free to contact the mailing list
		5061	with the full valgrind report and an explanation on why you think this
		5062	is a bug in libev (best check the archives, too :). However, don't be
		5063	annoyed when you get a brisk "this is no bug" answer and take the chance
		5064	of learning how to interpret valgrind properly.
3237		5065
3238	By virtue of using a binary or 4-heap, the next timer is always found at a	5066	If you need, for some reason, empty reports from valgrind for your project
3239	fixed position in the storage array.	5067	I suggest using suppression lists.
3240		5068
3241	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
3242		5069
3243	A change means an I/O watcher gets started or stopped, which requires	5070	=head1 PORTABILITY NOTES
3244	libev to recalculate its status (and possibly tell the kernel, depending
3245	on backend and wether C<ev_io_set> was used).
3246		5071
3247	=item Activating one watcher (putting it into the pending state): O(1)	5072	=head2 GNU/LINUX 32 BIT LIMITATIONS
3248		5073
3249	=item Priority handling: O(number_of_priorities)	5074	GNU/Linux is the only common platform that supports 64 bit file/large file
		5075	interfaces but I<disables> them by default.
3250		5076
3251	Priorities are implemented by allocating some space for each	5077	That means that libev compiled in the default environment doesn't support
3252	priority. When doing priority-based operations, libev usually has to	5078	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
3253	linearly search all the priorities, but starting/stopping and activating
3254	watchers becomes O(1) w.r.t. priority handling.
3255		5079
3256	=item Sending an ev_async: O(1)	5080	Unfortunately, many programs try to work around this GNU/Linux issue
		5081	by enabling the large file API, which makes them incompatible with the
		5082	standard libev compiled for their system.
3257		5083
3258	=item Processing ev_async_send: O(number_of_async_watchers)	5084	Likewise, libev cannot enable the large file API itself as this would
		5085	suddenly make it incompatible to the default compile time environment,
		5086	i.e. all programs not using special compile switches.
3259		5087
3260	=item Processing signals: O(max_signal_number)	5088	=head2 OS/X AND DARWIN BUGS
3261		5089
3262	Sending involves a syscall I<iff> there were no other C<ev_async_send>	5090	The whole thing is a bug if you ask me - basically any system interface
3263	calls in the current loop iteration. Checking for async and signal events	5091	you touch is broken, whether it is locales, poll, kqueue or even the
3264	involves iterating over all running async watchers or all signal numbers.	5092	OpenGL drivers.
3265		5093
3266	=back	5094	=head3 C<kqueue> is buggy
3267		5095
		5096	The kqueue syscall is broken in all known versions - most versions support
		5097	only sockets, many support pipes.
3268		5098
3269	=head1 Win32 platform limitations and workarounds	5099	Libev tries to work around this by not using C<kqueue> by default on this
		5100	rotten platform, but of course you can still ask for it when creating a
		5101	loop - embedding a socket-only kqueue loop into a select-based one is
		5102	probably going to work well.
		5103
		5104	=head3 C<poll> is buggy
		5105
		5106	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		5107	implementation by something calling C<kqueue> internally around the 10.5.6
		5108	release, so now C<kqueue> I<and> C<poll> are broken.
		5109
		5110	Libev tries to work around this by not using C<poll> by default on
		5111	this rotten platform, but of course you can still ask for it when creating
		5112	a loop.
		5113
		5114	=head3 C<select> is buggy
		5115
		5116	All that's left is C<select>, and of course Apple found a way to fuck this
		5117	one up as well: On OS/X, C<select> actively limits the number of file
		5118	descriptors you can pass in to 1024 - your program suddenly crashes when
		5119	you use more.
		5120
		5121	There is an undocumented "workaround" for this - defining
		5122	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		5123	work on OS/X.
		5124
		5125	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		5126
		5127	=head3 C<errno> reentrancy
		5128
		5129	The default compile environment on Solaris is unfortunately so
		5130	thread-unsafe that you can't even use components/libraries compiled
		5131	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		5132	defined by default. A valid, if stupid, implementation choice.
		5133
		5134	If you want to use libev in threaded environments you have to make sure
		5135	it's compiled with C<_REENTRANT> defined.
		5136
		5137	=head3 Event port backend
		5138
		5139	The scalable event interface for Solaris is called "event
		5140	ports". Unfortunately, this mechanism is very buggy in all major
		5141	releases. If you run into high CPU usage, your program freezes or you get
		5142	a large number of spurious wakeups, make sure you have all the relevant
		5143	and latest kernel patches applied. No, I don't know which ones, but there
		5144	are multiple ones to apply, and afterwards, event ports actually work
		5145	great.
		5146
		5147	If you can't get it to work, you can try running the program by setting
		5148	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		5149	C<select> backends.
		5150
		5151	=head2 AIX POLL BUG
		5152
		5153	AIX unfortunately has a broken C<poll.h> header. Libev works around
		5154	this by trying to avoid the poll backend altogether (i.e. it's not even
		5155	compiled in), which normally isn't a big problem as C<select> works fine
		5156	with large bitsets on AIX, and AIX is dead anyway.
		5157
		5158	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		5159
		5160	=head3 General issues
3270		5161
3271	Win32 doesn't support any of the standards (e.g. POSIX) that libev	5162	Win32 doesn't support any of the standards (e.g. POSIX) that libev
3272	requires, and its I/O model is fundamentally incompatible with the POSIX	5163	requires, and its I/O model is fundamentally incompatible with the POSIX
3273	model. Libev still offers limited functionality on this platform in	5164	model. Libev still offers limited functionality on this platform in
3274	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5165	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
3275	descriptors. This only applies when using Win32 natively, not when using	5166	descriptors. This only applies when using Win32 natively, not when using
3276	e.g. cygwin.	5167	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		5168	as every compiler comes with a slightly differently broken/incompatible
		5169	environment.
3277		5170
3278	Lifting these limitations would basically require the full	5171	Lifting these limitations would basically require the full
3279	re-implementation of the I/O system. If you are into these kinds of	5172	re-implementation of the I/O system. If you are into this kind of thing,
3280	things, then note that glib does exactly that for you in a very portable	5173	then note that glib does exactly that for you in a very portable way (note
3281	way (note also that glib is the slowest event library known to man).	5174	also that glib is the slowest event library known to man).
3282		5175
3283	There is no supported compilation method available on windows except	5176	There is no supported compilation method available on windows except
3284	embedding it into other applications.	5177	embedding it into other applications.
		5178
		5179	Sensible signal handling is officially unsupported by Microsoft - libev
		5180	tries its best, but under most conditions, signals will simply not work.
		5181
		5182	Not a libev limitation but worth mentioning: windows apparently doesn't
		5183	accept large writes: instead of resulting in a partial write, windows will
		5184	either accept everything or return C<ENOBUFS> if the buffer is too large,
		5185	so make sure you only write small amounts into your sockets (less than a
		5186	megabyte seems safe, but this apparently depends on the amount of memory
		5187	available).
3285		5188
3286	Due to the many, low, and arbitrary limits on the win32 platform and	5189	Due to the many, low, and arbitrary limits on the win32 platform and
3287	the abysmal performance of winsockets, using a large number of sockets	5190	the abysmal performance of winsockets, using a large number of sockets
3288	is not recommended (and not reasonable). If your program needs to use	5191	is not recommended (and not reasonable). If your program needs to use
3289	more than a hundred or so sockets, then likely it needs to use a totally	5192	more than a hundred or so sockets, then likely it needs to use a totally
3290	different implementation for windows, as libev offers the POSIX readiness	5193	different implementation for windows, as libev offers the POSIX readiness
3291	notification model, which cannot be implemented efficiently on windows	5194	notification model, which cannot be implemented efficiently on windows
3292	(microsoft monopoly games).	5195	(due to Microsoft monopoly games).
3293		5196
3294	=over 4	5197	A typical way to use libev under windows is to embed it (see the embedding
		5198	section for details) and use the following F<evwrap.h> header file instead
		5199	of F<ev.h>:
3295		5200
		5201	#define EV_STANDALONE /* keeps ev from requiring config.h */
		5202	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		5203
		5204	#include "ev.h"
		5205
		5206	And compile the following F<evwrap.c> file into your project (make sure
		5207	you do I<not> compile the F<ev.c> or any other embedded source files!):
		5208
		5209	#include "evwrap.h"
		5210	#include "ev.c"
		5211
3296	=item The winsocket select function	5212	=head3 The winsocket C<select> function
3297		5213
3298	The winsocket C<select> function doesn't follow POSIX in that it requires	5214	The winsocket C<select> function doesn't follow POSIX in that it
3299	socket I<handles> and not socket I<file descriptors>. This makes select	5215	requires socket I<handles> and not socket I<file descriptors> (it is
3300	very inefficient, and also requires a mapping from file descriptors	5216	also extremely buggy). This makes select very inefficient, and also
3301	to socket handles. See the discussion of the C<EV_SELECT_USE_FD_SET>,	5217	requires a mapping from file descriptors to socket handles (the Microsoft
3302	C<EV_SELECT_IS_WINSOCKET> and C<EV_FD_TO_WIN32_HANDLE> preprocessor	5218	C runtime provides the function C<_open_osfhandle> for this). See the
3303	symbols for more info.	5219	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		5220	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
3304		5221
3305	The configuration for a "naked" win32 using the microsoft runtime	5222	The configuration for a "naked" win32 using the Microsoft runtime
3306	libraries and raw winsocket select is:	5223	libraries and raw winsocket select is:
3307		5224
3308	#define EV_USE_SELECT 1	5225	#define EV_USE_SELECT 1
3309	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */	5226	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
3310		5227
3311	Note that winsockets handling of fd sets is O(n), so you can easily get a	5228	Note that winsockets handling of fd sets is O(n), so you can easily get a
3312	complexity in the O(n²) range when using win32.	5229	complexity in the O(n²) range when using win32.
3313		5230
3314	=item Limited number of file descriptors	5231	=head3 Limited number of file descriptors
3315		5232
3316	Windows has numerous arbitrary (and low) limits on things.	5233	Windows has numerous arbitrary (and low) limits on things.
3317		5234
3318	Early versions of winsocket's select only supported waiting for a maximum	5235	Early versions of winsocket's select only supported waiting for a maximum
3319	of C<64> handles (probably owning to the fact that all windows kernels	5236	of C<64> handles (probably owning to the fact that all windows kernels
3320	can only wait for C<64> things at the same time internally; microsoft	5237	can only wait for C<64> things at the same time internally; Microsoft
3321	recommends spawning a chain of threads and wait for 63 handles and the	5238	recommends spawning a chain of threads and wait for 63 handles and the
3322	previous thread in each. Great).	5239	previous thread in each. Sounds great!).
3323		5240
3324	Newer versions support more handles, but you need to define C<FD_SETSIZE>	5241	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3325	to some high number (e.g. C<2048>) before compiling the winsocket select	5242	to some high number (e.g. C<2048>) before compiling the winsocket select
3326	call (which might be in libev or elsewhere, for example, perl does its own	5243	call (which might be in libev or elsewhere, for example, perl and many
3327	select emulation on windows).	5244	other interpreters do their own select emulation on windows).
3328		5245
3329	Another limit is the number of file descriptors in the microsoft runtime	5246	Another limit is the number of file descriptors in the Microsoft runtime
3330	libraries, which by default is C<64> (there must be a hidden I<64> fetish	5247	libraries, which by default is C<64> (there must be a hidden I<64>
3331	or something like this inside microsoft). You can increase this by calling	5248	fetish or something like this inside Microsoft). You can increase this
3332	C<_setmaxstdio>, which can increase this limit to C<2048> (another	5249	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
3333	arbitrary limit), but is broken in many versions of the microsoft runtime	5250	(another arbitrary limit), but is broken in many versions of the Microsoft
3334	libraries.
3335
3336	This might get you to about C<512> or C<2048> sockets (depending on	5251	runtime libraries. This might get you to about C<512> or C<2048> sockets
3337	windows version and/or the phase of the moon). To get more, you need to	5252	(depending on windows version and/or the phase of the moon). To get more,
3338	wrap all I/O functions and provide your own fd management, but the cost of	5253	you need to wrap all I/O functions and provide your own fd management, but
3339	calling select (O(n²)) will likely make this unworkable.	5254	the cost of calling select (O(n²)) will likely make this unworkable.
3340		5255
3341	=back
3342
3343
3344	=head1 PORTABILITY REQUIREMENTS	5256	=head2 PORTABILITY REQUIREMENTS
3345		5257
3346	In addition to a working ISO-C implementation, libev relies on a few	5258	In addition to a working ISO-C implementation and of course the
3347	additional extensions:	5259	backend-specific APIs, libev relies on a few additional extensions:
3348		5260
3349	=over 4	5261	=over 4
3350		5262
		5263	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		5264	calling conventions regardless of C<ev_watcher_type *>.
		5265
		5266	Libev assumes not only that all watcher pointers have the same internal
		5267	structure (guaranteed by POSIX but not by ISO C for example), but it also
		5268	assumes that the same (machine) code can be used to call any watcher
		5269	callback: The watcher callbacks have different type signatures, but libev
		5270	calls them using an C<ev_watcher *> internally.
		5271
		5272	=item pointer accesses must be thread-atomic
		5273
		5274	Accessing a pointer value must be atomic, it must both be readable and
		5275	writable in one piece - this is the case on all current architectures.
		5276
3351	=item C<sig_atomic_t volatile> must be thread-atomic as well	5277	=item C<sig_atomic_t volatile> must be thread-atomic as well
3352		5278
3353	The type C<sig_atomic_t volatile> (or whatever is defined as	5279	The type C<sig_atomic_t volatile> (or whatever is defined as
3354	C<EV_ATOMIC_T>) must be atomic w.r.t. accesses from different	5280	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
3355	threads. This is not part of the specification for C<sig_atomic_t>, but is	5281	threads. This is not part of the specification for C<sig_atomic_t>, but is
3356	believed to be sufficiently portable.	5282	believed to be sufficiently portable.
3357		5283
3358	=item C<sigprocmask> must work in a threaded environment	5284	=item C<sigprocmask> must work in a threaded environment
3359		5285
…		…
3368	except the initial one, and run the default loop in the initial thread as	5294	except the initial one, and run the default loop in the initial thread as
3369	well.	5295	well.
3370		5296
3371	=item C<long> must be large enough for common memory allocation sizes	5297	=item C<long> must be large enough for common memory allocation sizes
3372		5298
3373	To improve portability and simplify using libev, libev uses C<long>	5299	To improve portability and simplify its API, libev uses C<long> internally
3374	internally instead of C<size_t> when allocating its data structures. On	5300	instead of C<size_t> when allocating its data structures. On non-POSIX
3375	non-POSIX systems (Microsoft...) this might be unexpectedly low, but	5301	systems (Microsoft...) this might be unexpectedly low, but is still at
3376	is still at least 31 bits everywhere, which is enough for hundreds of	5302	least 31 bits everywhere, which is enough for hundreds of millions of
3377	millions of watchers.	5303	watchers.
3378		5304
3379	=item C<double> must hold a time value in seconds with enough accuracy	5305	=item C<double> must hold a time value in seconds with enough accuracy
3380		5306
3381	The type C<double> is used to represent timestamps. It is required to	5307	The type C<double> is used to represent timestamps. It is required to
3382	have at least 51 bits of mantissa (and 9 bits of exponent), which is good	5308	have at least 51 bits of mantissa (and 9 bits of exponent), which is
3383	enough for at least into the year 4000. This requirement is fulfilled by	5309	good enough for at least into the year 4000 with millisecond accuracy
		5310	(the design goal for libev). This requirement is overfulfilled by
3384	implementations implementing IEEE 754 (basically all existing ones).	5311	implementations using IEEE 754, which is basically all existing ones.
		5312
		5313	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5314	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5315	is either obsolete or somebody patched it to use C<long double> or
		5316	something like that, just kidding).
3385		5317
3386	=back	5318	=back
3387		5319
3388	If you know of other additional requirements drop me a note.	5320	If you know of other additional requirements drop me a note.
3389		5321
3390		5322
3391	=head1 VALGRIND	5323	=head1 ALGORITHMIC COMPLEXITIES
3392		5324
3393	Valgrind has a special section here because it is a popular tool that is	5325	In this section the complexities of (many of) the algorithms used inside
3394	highly useful, but valgrind reports are very hard to interpret.	5326	libev will be documented. For complexity discussions about backends see
		5327	the documentation for C<ev_default_init>.
3395		5328
3396	If you think you found a bug (memory leak, uninitialised data access etc.)	5329	All of the following are about amortised time: If an array needs to be
3397	in libev, then check twice: If valgrind reports something like:	5330	extended, libev needs to realloc and move the whole array, but this
		5331	happens asymptotically rarer with higher number of elements, so O(1) might
		5332	mean that libev does a lengthy realloc operation in rare cases, but on
		5333	average it is much faster and asymptotically approaches constant time.
3398		5334
3399	==2274== definitely lost: 0 bytes in 0 blocks.	5335	=over 4
3400	==2274== possibly lost: 0 bytes in 0 blocks.
3401	==2274== still reachable: 256 bytes in 1 blocks.
3402		5336
3403	then there is no memory leak. Similarly, under some circumstances,	5337	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
3404	valgrind might report kernel bugs as if it were a bug in libev, or it
3405	might be confused (it is a very good tool, but only a tool).
3406		5338
3407	If you are unsure about something, feel free to contact the mailing list	5339	This means that, when you have a watcher that triggers in one hour and
3408	with the full valgrind report and an explanation on why you think this is	5340	there are 100 watchers that would trigger before that, then inserting will
3409	a bug in libev. However, don't be annoyed when you get a brisk "this is	5341	have to skip roughly seven (C<ld 100>) of these watchers.
3410	no bug" answer and take the chance of learning how to interpret valgrind
3411	properly.
3412		5342
3413	If you need, for some reason, empty reports from valgrind for your project	5343	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
3414	I suggest using suppression lists.
3415		5344
		5345	That means that changing a timer costs less than removing/adding them,
		5346	as only the relative motion in the event queue has to be paid for.
		5347
		5348	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		5349
		5350	These just add the watcher into an array or at the head of a list.
		5351
		5352	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		5353
		5354	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		5355
		5356	These watchers are stored in lists, so they need to be walked to find the
		5357	correct watcher to remove. The lists are usually short (you don't usually
		5358	have many watchers waiting for the same fd or signal: one is typical, two
		5359	is rare).
		5360
		5361	=item Finding the next timer in each loop iteration: O(1)
		5362
		5363	By virtue of using a binary or 4-heap, the next timer is always found at a
		5364	fixed position in the storage array.
		5365
		5366	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		5367
		5368	A change means an I/O watcher gets started or stopped, which requires
		5369	libev to recalculate its status (and possibly tell the kernel, depending
		5370	on backend and whether C<ev_io_set> was used).
		5371
		5372	=item Activating one watcher (putting it into the pending state): O(1)
		5373
		5374	=item Priority handling: O(number_of_priorities)
		5375
		5376	Priorities are implemented by allocating some space for each
		5377	priority. When doing priority-based operations, libev usually has to
		5378	linearly search all the priorities, but starting/stopping and activating
		5379	watchers becomes O(1) with respect to priority handling.
		5380
		5381	=item Sending an ev_async: O(1)
		5382
		5383	=item Processing ev_async_send: O(number_of_async_watchers)
		5384
		5385	=item Processing signals: O(max_signal_number)
		5386
		5387	Sending involves a system call I<iff> there were no other C<ev_async_send>
		5388	calls in the current loop iteration and the loop is currently
		5389	blocked. Checking for async and signal events involves iterating over all
		5390	running async watchers or all signal numbers.
		5391
		5392	=back
		5393
		5394
		5395	=head1 PORTING FROM LIBEV 3.X TO 4.X
		5396
		5397	The major version 4 introduced some incompatible changes to the API.
		5398
		5399	At the moment, the C<ev.h> header file provides compatibility definitions
		5400	for all changes, so most programs should still compile. The compatibility
		5401	layer might be removed in later versions of libev, so better update to the
		5402	new API early than late.
		5403
		5404	=over 4
		5405
		5406	=item C<EV_COMPAT3> backwards compatibility mechanism
		5407
		5408	The backward compatibility mechanism can be controlled by
		5409	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
		5410	section.
		5411
		5412	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5413
		5414	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5415
		5416	ev_loop_destroy (EV_DEFAULT_UC);
		5417	ev_loop_fork (EV_DEFAULT);
		5418
		5419	=item function/symbol renames
		5420
		5421	A number of functions and symbols have been renamed:
		5422
		5423	ev_loop => ev_run
		5424	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		5425	EVLOOP_ONESHOT => EVRUN_ONCE
		5426
		5427	ev_unloop => ev_break
		5428	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		5429	EVUNLOOP_ONE => EVBREAK_ONE
		5430	EVUNLOOP_ALL => EVBREAK_ALL
		5431
		5432	EV_TIMEOUT => EV_TIMER
		5433
		5434	ev_loop_count => ev_iteration
		5435	ev_loop_depth => ev_depth
		5436	ev_loop_verify => ev_verify
		5437
		5438	Most functions working on C<struct ev_loop> objects don't have an
		5439	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		5440	associated constants have been renamed to not collide with the C<struct
		5441	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		5442	as all other watcher types. Note that C<ev_loop_fork> is still called
		5443	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		5444	typedef.
		5445
		5446	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		5447
		5448	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		5449	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		5450	and work, but the library code will of course be larger.
		5451
		5452	=back
		5453
		5454
		5455	=head1 GLOSSARY
		5456
		5457	=over 4
		5458
		5459	=item active
		5460
		5461	A watcher is active as long as it has been started and not yet stopped.
		5462	See L<WATCHER STATES> for details.
		5463
		5464	=item application
		5465
		5466	In this document, an application is whatever is using libev.
		5467
		5468	=item backend
		5469
		5470	The part of the code dealing with the operating system interfaces.
		5471
		5472	=item callback
		5473
		5474	The address of a function that is called when some event has been
		5475	detected. Callbacks are being passed the event loop, the watcher that
		5476	received the event, and the actual event bitset.
		5477
		5478	=item callback/watcher invocation
		5479
		5480	The act of calling the callback associated with a watcher.
		5481
		5482	=item event
		5483
		5484	A change of state of some external event, such as data now being available
		5485	for reading on a file descriptor, time having passed or simply not having
		5486	any other events happening anymore.
		5487
		5488	In libev, events are represented as single bits (such as C<EV_READ> or
		5489	C<EV_TIMER>).
		5490
		5491	=item event library
		5492
		5493	A software package implementing an event model and loop.
		5494
		5495	=item event loop
		5496
		5497	An entity that handles and processes external events and converts them
		5498	into callback invocations.
		5499
		5500	=item event model
		5501
		5502	The model used to describe how an event loop handles and processes
		5503	watchers and events.
		5504
		5505	=item pending
		5506
		5507	A watcher is pending as soon as the corresponding event has been
		5508	detected. See L<WATCHER STATES> for details.
		5509
		5510	=item real time
		5511
		5512	The physical time that is observed. It is apparently strictly monotonic :)
		5513
		5514	=item wall-clock time
		5515
		5516	The time and date as shown on clocks. Unlike real time, it can actually
		5517	be wrong and jump forwards and backwards, e.g. when you adjust your
		5518	clock.
		5519
		5520	=item watcher
		5521
		5522	A data structure that describes interest in certain events. Watchers need
		5523	to be started (attached to an event loop) before they can receive events.
		5524
		5525	=back
3416		5526
3417	=head1 AUTHOR	5527	=head1 AUTHOR
3418		5528
3419	Marc Lehmann <libev@schmorp.de>.	5529	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5530	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
3420		5531

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