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Revision 1.136 by root, Thu Mar 13 13:06:16 2008 UTC vs.
Revision 1.357 by root, Tue Jan 11 02:15:58 2011 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	// unloop 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://cvs.schmorp.de/libev/ev.html>.	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_update_now> 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 until
138	either it is interrupted or the given time interval has passed. Basically	184	either it is interrupted or the given time interval has passed. Basically
139	this is a subsecond-resolution C<sleep ()>.	185	this is a sub-second-resolution C<sleep ()>.
140		186
141	=item int ev_version_major ()	187	=item int ev_version_major ()
142		188
143	=item int ev_version_minor ()	189	=item int ev_version_minor ()
144		190
…		…
155	as this indicates an incompatible change. Minor versions are usually	201	as this indicates an incompatible change. Minor versions are usually
156	compatible to older versions, so a larger minor version alone is usually	202	compatible to older versions, so a larger minor version alone is usually
157	not a problem.	203	not a problem.
158		204
159	Example: Make sure we haven't accidentally been linked against the wrong	205	Example: Make sure we haven't accidentally been linked against the wrong
160	version.	206	version (note, however, that this will not detect other ABI mismatches,
		207	such as LFS or reentrancy).
161		208
162	assert (("libev version mismatch",	209	assert (("libev version mismatch",
163	ev_version_major () == EV_VERSION_MAJOR	210	ev_version_major () == EV_VERSION_MAJOR
164	&& ev_version_minor () >= EV_VERSION_MINOR));	211	&& ev_version_minor () >= EV_VERSION_MINOR));
165		212
166	=item unsigned int ev_supported_backends ()	213	=item unsigned int ev_supported_backends ()
167		214
168	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	215	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
169	value) compiled into this binary of libev (independent of their	216	value) compiled into this binary of libev (independent of their
…		…
171	a description of the set values.	218	a description of the set values.
172		219
173	Example: make sure we have the epoll method, because yeah this is cool and	220	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	221	a must have and can we have a torrent of it please!!!11
175		222
176	assert (("sorry, no epoll, no sex",	223	assert (("sorry, no epoll, no sex",
177	ev_supported_backends () & EVBACKEND_EPOLL));	224	ev_supported_backends () & EVBACKEND_EPOLL));
178		225
179	=item unsigned int ev_recommended_backends ()	226	=item unsigned int ev_recommended_backends ()
180		227
181	Return the set of all backends compiled into this binary of libev and also	228	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	229	also recommended for this platform, meaning it will work for most file
		230	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	231	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	232	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	233	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.	234	probe for if you specify no backends explicitly.
187		235
188	=item unsigned int ev_embeddable_backends ()	236	=item unsigned int ev_embeddable_backends ()
189		237
190	Returns the set of backends that are embeddable in other event loops. This	238	Returns the set of backends that are embeddable in other event loops. This
191	is the theoretical, all-platform, value. To find which backends	239	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	240	current system. To find which embeddable backends might be supported on
193	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	241	the current system, you would need to look at C<ev_embeddable_backends ()
194	recommended ones.	242	& ev_supported_backends ()>, likewise for recommended ones.
195		243
196	See the description of C<ev_embed> watchers for more info.	244	See the description of C<ev_embed> watchers for more info.
197		245
198	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	246	=item ev_set_allocator (void *(*cb)(void *ptr, long size))
199		247
200	Sets the allocation function to use (the prototype is similar - the	248	Sets the allocation function to use (the prototype is similar - the
201	semantics is identical - to the realloc C function). It is used to	249	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
202	allocate and free memory (no surprises here). If it returns zero when	250	used to allocate and free memory (no surprises here). If it returns zero
203	memory needs to be allocated, the library might abort or take some	251	when memory needs to be allocated (C<size != 0>), the library might abort
204	potentially destructive action. The default is your system realloc	252	or take some potentially destructive action.
205	function.	253
		254	Since some systems (at least OpenBSD and Darwin) fail to implement
		255	correct C<realloc> semantics, libev will use a wrapper around the system
		256	C<realloc> and C<free> functions by default.
206		257
207	You could override this function in high-availability programs to, say,	258	You could override this function in high-availability programs to, say,
208	free some memory if it cannot allocate memory, to use a special allocator,	259	free some memory if it cannot allocate memory, to use a special allocator,
209	or even to sleep a while and retry until some memory is available.	260	or even to sleep a while and retry until some memory is available.
210		261
211	Example: Replace the libev allocator with one that waits a bit and then	262	Example: Replace the libev allocator with one that waits a bit and then
212	retries).	263	retries (example requires a standards-compliant C<realloc>).
213		264
214	static void *	265	static void *
215	persistent_realloc (void *ptr, size_t size)	266	persistent_realloc (void *ptr, size_t size)
216	{	267	{
217	for (;;)	268	for (;;)
…		…
226	}	277	}
227		278
228	...	279	...
229	ev_set_allocator (persistent_realloc);	280	ev_set_allocator (persistent_realloc);
230		281
231	=item ev_set_syserr_cb (void (*cb)(const char *msg));	282	=item ev_set_syserr_cb (void (*cb)(const char *msg))
232		283
233	Set the callback function to call on a retryable syscall error (such	284	Set the callback function to call on a retryable system call error (such
234	as failed select, poll, epoll_wait). The message is a printable string	285	as failed select, poll, epoll_wait). The message is a printable string
235	indicating the system call or subsystem causing the problem. If this	286	indicating the system call or subsystem causing the problem. If this
236	callback is set, then libev will expect it to remedy the sitution, no	287	callback is set, then libev will expect it to remedy the situation, no
237	matter what, when it returns. That is, libev will generally retry the	288	matter what, when it returns. That is, libev will generally retry the
238	requested operation, or, if the condition doesn't go away, do bad stuff	289	requested operation, or, if the condition doesn't go away, do bad stuff
239	(such as abort).	290	(such as abort).
240		291
241	Example: This is basically the same thing that libev does internally, too.	292	Example: This is basically the same thing that libev does internally, too.
…		…
248	}	299	}
249		300
250	...	301	...
251	ev_set_syserr_cb (fatal_error);	302	ev_set_syserr_cb (fatal_error);
252		303
		304	=item ev_feed_signal (int signum)
		305
		306	This function can be used to "simulate" a signal receive. It is completely
		307	safe to call this function at any time, from any context, including signal
		308	handlers or random threads.
		309
		310	Its main use is to customise signal handling in your process, especially
		311	in the presence of threads. For example, you could block signals
		312	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		313	creating any loops), and in one thread, use C<sigwait> or any other
		314	mechanism to wait for signals, then "deliver" them to libev by calling
		315	C<ev_feed_signal>.
		316
253	=back	317	=back
254		318
255	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	319	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
256		320
257	An event loop is described by a C<struct ev_loop *>. The library knows two	321	An event loop is described by a C<struct ev_loop *> (the C<struct> is
258	types of such loops, the I<default> loop, which supports signals and child	322	I<not> optional in this case unless libev 3 compatibility is disabled, as
259	events, and dynamically created loops which do not.	323	libev 3 had an C<ev_loop> function colliding with the struct name).
260		324
261	If you use threads, a common model is to run the default event loop	325	The library knows two types of such loops, the I<default> loop, which
262	in your main thread (or in a separate thread) and for each thread you	326	supports child process events, and dynamically created event loops which
263	create, you also create another event loop. Libev itself does no locking	327	do not.
264	whatsoever, so if you mix calls to the same event loop in different
265	threads, make sure you lock (this is usually a bad idea, though, even if
266	done correctly, because it's hideous and inefficient).
267		328
268	=over 4	329	=over 4
269		330
270	=item struct ev_loop *ev_default_loop (unsigned int flags)	331	=item struct ev_loop *ev_default_loop (unsigned int flags)
271		332
272	This will initialise the default event loop if it hasn't been initialised	333	This returns the "default" event loop object, which is what you should
273	yet and return it. If the default loop could not be initialised, returns	334	normally use when you just need "the event loop". Event loop objects and
274	false. If it already was initialised it simply returns it (and ignores the	335	the C<flags> parameter are described in more detail in the entry for
275	flags. If that is troubling you, check C<ev_backend ()> afterwards).	336	C<ev_loop_new>.
		337
		338	If the default loop is already initialised then this function simply
		339	returns it (and ignores the flags. If that is troubling you, check
		340	C<ev_backend ()> afterwards). Otherwise it will create it with the given
		341	flags, which should almost always be C<0>, unless the caller is also the
		342	one calling C<ev_run> or otherwise qualifies as "the main program".
276		343
277	If you don't know what event loop to use, use the one returned from this	344	If you don't know what event loop to use, use the one returned from this
278	function.	345	function (or via the C<EV_DEFAULT> macro).
279		346
		347	Note that this function is I<not> thread-safe, so if you want to use it
		348	from multiple threads, you have to employ some kind of mutex (note also
		349	that this case is unlikely, as loops cannot be shared easily between
		350	threads anyway).
		351
280	The default loop is the only loop that can handle C<ev_signal> and	352	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	353	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	354	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	355	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	356	C<SIGCHLD> signal handler I<after> calling C<ev_default_init>.
285	C<ev_default_init>.	357
		358	Example: This is the most typical usage.
		359
		360	if (!ev_default_loop (0))
		361	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		362
		363	Example: Restrict libev to the select and poll backends, and do not allow
		364	environment settings to be taken into account:
		365
		366	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		367
		368	=item struct ev_loop *ev_loop_new (unsigned int flags)
		369
		370	This will create and initialise a new event loop object. If the loop
		371	could not be initialised, returns false.
		372
		373	This function is thread-safe, and one common way to use libev with
		374	threads is indeed to create one loop per thread, and using the default
		375	loop in the "main" or "initial" thread.
286		376
287	The flags argument can be used to specify special behaviour or specific	377	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>).	378	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
289		379
290	The following flags are supported:	380	The following flags are supported:
…		…
296	The default flags value. Use this if you have no clue (it's the right	386	The default flags value. Use this if you have no clue (it's the right
297	thing, believe me).	387	thing, believe me).
298		388
299	=item C<EVFLAG_NOENV>	389	=item C<EVFLAG_NOENV>
300		390
301	If this flag bit is ored into the flag value (or the program runs setuid	391	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	392	or setgid) then libev will I<not> look at the environment variable
303	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	393	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
304	override the flags completely if it is found in the environment. This is	394	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	395	useful to try out specific backends to test their performance, or to work
306	around bugs.	396	around bugs.
307		397
308	=item C<EVFLAG_FORKCHECK>	398	=item C<EVFLAG_FORKCHECK>
309		399
310	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after	400	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	401	make libev check for a fork in each iteration by enabling this flag.
312	enabling this flag.
313		402
314	This works by calling C<getpid ()> on every iteration of the loop,	403	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	404	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	405	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	406	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	407	without a system call and thus I<very> fast, but my GNU/Linux system also has
319	C<pthread_atfork> which is even faster).	408	C<pthread_atfork> which is even faster).
320		409
321	The big advantage of this flag is that you can forget about fork (and	410	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	411	forget about forgetting to tell libev about forking) when you use this
323	flag.	412	flag.
324		413
325	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>	414	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
326	environment variable.	415	environment variable.
		416
		417	=item C<EVFLAG_NOINOTIFY>
		418
		419	When this flag is specified, then libev will not attempt to use the
		420	I<inotify> API for its C<ev_stat> watchers. Apart from debugging and
		421	testing, this flag can be useful to conserve inotify file descriptors, as
		422	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		423
		424	=item C<EVFLAG_SIGNALFD>
		425
		426	When this flag is specified, then libev will attempt to use the
		427	I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API
		428	delivers signals synchronously, which makes it both faster and might make
		429	it possible to get the queued signal data. It can also simplify signal
		430	handling with threads, as long as you properly block signals in your
		431	threads that are not interested in handling them.
		432
		433	Signalfd will not be used by default as this changes your signal mask, and
		434	there are a lot of shoddy libraries and programs (glib's threadpool for
		435	example) that can't properly initialise their signal masks.
		436
		437	=item C<EVFLAG_NOSIGMASK>
		438
		439	When this flag is specified, then libev will avoid to modify the signal
		440	mask. Specifically, this means you ahve to make sure signals are unblocked
		441	when you want to receive them.
		442
		443	This behaviour is useful when you want to do your own signal handling, or
		444	want to handle signals only in specific threads and want to avoid libev
		445	unblocking the signals.
		446
		447	This flag's behaviour will become the default in future versions of libev.
327		448
328	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	449	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
329		450
330	This is your standard select(2) backend. Not I<completely> standard, as	451	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,	452	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	453	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	454	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.	455	usually the fastest backend for a low number of (low-numbered :) fds.
335		456
336	To get good performance out of this backend you need a high amount of	457	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	458	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	459	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	460	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	461	a look at C<ev_set_io_collect_interval ()> to increase the amount of
341	readyness notifications you get per iteration.	462	readiness notifications you get per iteration.
		463
		464	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		465	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		466	C<exceptfds> set on that platform).
342		467
343	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	468	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
344		469
345	And this is your standard poll(2) backend. It's more complicated	470	And this is your standard poll(2) backend. It's more complicated
346	than select, but handles sparse fds better and has no artificial	471	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	472	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,	473	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	474	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
350	performance tips.	475	performance tips.
351		476
		477	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		478	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
		479
352	=item C<EVBACKEND_EPOLL> (value 4, Linux)	480	=item C<EVBACKEND_EPOLL> (value 4, Linux)
		481
		482	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		483	kernels).
353		484
354	For few fds, this backend is a bit little slower than poll and select,	485	For few fds, this backend is a bit little slower than poll and select,
355	but it scales phenomenally better. While poll and select usually scale	486	but it scales phenomenally better. While poll and select usually scale
356	like O(total_fds) where n is the total number of fds (or the highest fd),	487	like O(total_fds) where n is the total number of fds (or the highest fd),
357	epoll scales either O(1) or O(active_fds). The epoll design has a number	488	epoll scales either O(1) or O(active_fds).
358	of shortcomings, such as silently dropping events in some hard-to-detect	489
359	cases and rewiring a syscall per fd change, no fork support and bad	490	The epoll mechanism deserves honorable mention as the most misdesigned
360	support for dup.	491	of the more advanced event mechanisms: mere annoyances include silently
		492	dropping file descriptors, requiring a system call per change per file
		493	descriptor (and unnecessary guessing of parameters), problems with dup,
		494	returning before the timeout value, resulting in additional iterations
		495	(and only giving 5ms accuracy while select on the same platform gives
		496	0.1ms) and so on. The biggest issue is fork races, however - if a program
		497	forks then I<both> parent and child process have to recreate the epoll
		498	set, which can take considerable time (one syscall per file descriptor)
		499	and is of course hard to detect.
		500
		501	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		502	of course I<doesn't>, and epoll just loves to report events for totally
		503	I<different> file descriptors (even already closed ones, so one cannot
		504	even remove them from the set) than registered in the set (especially
		505	on SMP systems). Libev tries to counter these spurious notifications by
		506	employing an additional generation counter and comparing that against the
		507	events to filter out spurious ones, recreating the set when required. Last
		508	not least, it also refuses to work with some file descriptors which work
		509	perfectly fine with C<select> (files, many character devices...).
		510
		511	Epoll is truly the train wreck analog among event poll mechanisms,
		512	a frankenpoll, cobbled together in a hurry, no thought to design or
		513	interaction with others.
361		514
362	While stopping, setting and starting an I/O watcher in the same iteration	515	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	516	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	517	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	518	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
366	very well if you register events for both fds.	519	file descriptors might not work very well if you register events for both
367		520	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		521
372	Best performance from this backend is achieved by not unregistering all	522	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.	523	watchers for a file descriptor until it has been closed, if possible,
374	keep at least one watcher active per fd at all times.	524	i.e. keep at least one watcher active per fd at all times. Stopping and
		525	starting a watcher (without re-setting it) also usually doesn't cause
		526	extra overhead. A fork can both result in spurious notifications as well
		527	as in libev having to destroy and recreate the epoll object, which can
		528	take considerable time and thus should be avoided.
375		529
		530	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		531	faster than epoll for maybe up to a hundred file descriptors, depending on
		532	the usage. So sad.
		533
376	While nominally embeddeble in other event loops, this feature is broken in	534	While nominally embeddable in other event loops, this feature is broken in
377	all kernel versions tested so far.	535	all kernel versions tested so far.
		536
		537	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		538	C<EVBACKEND_POLL>.
378		539
379	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	540	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
380		541
381	Kqueue deserves special mention, as at the time of this writing, it	542	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	543	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	544	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"	545	it's completely useless). Unlike epoll, however, whose brokenness
		546	is by design, these kqueue bugs can (and eventually will) be fixed
		547	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	548	"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)	549	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
387	system like NetBSD.	550	system like NetBSD.
388		551
389	You still can embed kqueue into a normal poll or select backend and use it	552	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	553	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.	554	the target platform). See C<ev_embed> watchers for more info.
392		555
393	It scales in the same way as the epoll backend, but the interface to the	556	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	557	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	558	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	559	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	560	two event changes per incident. Support for C<fork ()> is very bad (but
398	drops fds silently in similarly hard-to-detect cases.	561	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		562	cases
399		563
400	This backend usually performs well under most conditions.	564	This backend usually performs well under most conditions.
401		565
402	While nominally embeddable in other event loops, this doesn't work	566	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	567	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	568	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	569	(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	570	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
407	sockets.	571	also broken on OS X)) and, did I mention it, using it only for sockets.
		572
		573	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		574	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		575	C<NOTE_EOF>.
408		576
409	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	577	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
410		578
411	This is not implemented yet (and might never be, unless you send me an	579	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	580	implementation). According to reports, C</dev/poll> only supports sockets
…		…
416	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	584	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
417		585
418	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	586	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)).	587	it's really slow, but it still scales very well (O(active_fds)).
420		588
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	589	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	590	file descriptor per loop iteration. For small and medium numbers of file
427	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	591	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
428	might perform better.	592	might perform better.
429		593
430	On the positive side, ignoring the spurious readyness notifications, this	594	On the positive side, this backend actually performed fully to
431	backend actually performed to specification in all tests and is fully	595	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.	596	among the OS-specific backends (I vastly prefer correctness over speed
		597	hacks).
		598
		599	On the negative side, the interface is I<bizarre> - so bizarre that
		600	even sun itself gets it wrong in their code examples: The event polling
		601	function sometimes returning events to the caller even though an error
		602	occurred, but with no indication whether it has done so or not (yes, it's
		603	even documented that way) - deadly for edge-triggered interfaces where
		604	you absolutely have to know whether an event occurred or not because you
		605	have to re-arm the watcher.
		606
		607	Fortunately libev seems to be able to work around these idiocies.
		608
		609	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		610	C<EVBACKEND_POLL>.
433		611
434	=item C<EVBACKEND_ALL>	612	=item C<EVBACKEND_ALL>
435		613
436	Try all backends (even potentially broken ones that wouldn't be tried	614	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	615	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
438	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	616	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
439		617
440	It is definitely not recommended to use this flag.	618	It is definitely not recommended to use this flag, use whatever
		619	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		620	at all.
		621
		622	=item C<EVBACKEND_MASK>
		623
		624	Not a backend at all, but a mask to select all backend bits from a
		625	C<flags> value, in case you want to mask out any backends from a flags
		626	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
441		627
442	=back	628	=back
443		629
444	If one or more of these are ored into the flags value, then only these	630	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	631	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.	632	here). If none are specified, all backends in C<ev_recommended_backends
447		633	()> 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		634
471	Example: Try to create a event loop that uses epoll and nothing else.	635	Example: Try to create a event loop that uses epoll and nothing else.
472		636
473	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	637	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
474	if (!epoller)	638	if (!epoller)
475	fatal ("no epoll found here, maybe it hides under your chair");	639	fatal ("no epoll found here, maybe it hides under your chair");
476		640
		641	Example: Use whatever libev has to offer, but make sure that kqueue is
		642	used if available.
		643
		644	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		645
477	=item ev_default_destroy ()	646	=item ev_loop_destroy (loop)
478		647
479	Destroys the default loop again (frees all memory and kernel state	648	Destroys an event loop object (frees all memory and kernel state
480	etc.). None of the active event watchers will be stopped in the normal	649	etc.). None of the active event watchers will be stopped in the normal
481	sense, so e.g. C<ev_is_active> might still return true. It is your	650	sense, so e.g. C<ev_is_active> might still return true. It is your
482	responsibility to either stop all watchers cleanly yoursef I<before>	651	responsibility to either stop all watchers cleanly yourself I<before>
483	calling this function, or cope with the fact afterwards (which is usually	652	calling this function, or cope with the fact afterwards (which is usually
484	the easiest thing, you can just ignore the watchers and/or C<free ()> them	653	the easiest thing, you can just ignore the watchers and/or C<free ()> them
485	for example).	654	for example).
486		655
487	Note that certain global state, such as signal state, will not be freed by	656	Note that certain global state, such as signal state (and installed signal
488	this function, and related watchers (such as signal and child watchers)	657	handlers), will not be freed by this function, and related watchers (such
489	would need to be stopped manually.	658	as signal and child watchers) would need to be stopped manually.
490		659
491	In general it is not advisable to call this function except in the	660	This function is normally used on loop objects allocated by
492	rare occasion where you really need to free e.g. the signal handling	661	C<ev_loop_new>, but it can also be used on the default loop returned by
		662	C<ev_default_loop>, in which case it is not thread-safe.
		663
		664	Note that it is not advisable to call this function on the default loop
		665	except in the rare occasion where you really need to free its resources.
493	pipe fds. If you need dynamically allocated loops it is better to use	666	If you need dynamically allocated loops it is better to use C<ev_loop_new>
494	C<ev_loop_new> and C<ev_loop_destroy>).	667	and C<ev_loop_destroy>.
495		668
496	=item ev_loop_destroy (loop)	669	=item ev_loop_fork (loop)
497		670
498	Like C<ev_default_destroy>, but destroys an event loop created by an
499	earlier call to C<ev_loop_new>.
500
501	=item ev_default_fork ()
502
503	This function sets a flag that causes subsequent C<ev_loop> iterations	671	This function sets a flag that causes subsequent C<ev_run> iterations to
504	to reinitialise the kernel state for backends that have one. Despite the	672	reinitialise the kernel state for backends that have one. Despite the
505	name, you can call it anytime, but it makes most sense after forking, in	673	name, you can call it anytime, but it makes most sense after forking, in
506	the child process (or both child and parent, but that again makes little	674	the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the
507	sense). You I<must> call it in the child before using any of the libev	675	child before resuming or calling C<ev_run>.
508	functions, and it will only take effect at the next C<ev_loop> iteration.	676
		677	Again, you I<have> to call it on I<any> loop that you want to re-use after
		678	a fork, I<even if you do not plan to use the loop in the parent>. This is
		679	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		680	during fork.
509		681
510	On the other hand, you only need to call this function in the child	682	On the other hand, you only need to call this function in the child
511	process if and only if you want to use the event library in the child. If	683	process if and only if you want to use the event loop in the child. If
512	you just fork+exec, you don't have to call it at all.	684	you just fork+exec or create a new loop in the child, you don't have to
		685	call it at all (in fact, C<epoll> is so badly broken that it makes a
		686	difference, but libev will usually detect this case on its own and do a
		687	costly reset of the backend).
513		688
514	The function itself is quite fast and it's usually not a problem to call	689	The function itself is quite fast and it's usually not a problem to call
515	it just in case after a fork. To make this easy, the function will fit in	690	it just in case after a fork.
516	quite nicely into a call to C<pthread_atfork>:
517		691
		692	Example: Automate calling C<ev_loop_fork> on the default loop when
		693	using pthreads.
		694
		695	static void
		696	post_fork_child (void)
		697	{
		698	ev_loop_fork (EV_DEFAULT);
		699	}
		700
		701	...
518	pthread_atfork (0, 0, ev_default_fork);	702	pthread_atfork (0, 0, post_fork_child);
519
520	=item ev_loop_fork (loop)
521
522	Like C<ev_default_fork>, but acts on an event loop created by
523	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
524	after fork, and how you do this is entirely your own problem.
525		703
526	=item int ev_is_default_loop (loop)	704	=item int ev_is_default_loop (loop)
527		705
528	Returns true when the given loop actually is the default loop, false otherwise.	706	Returns true when the given loop is, in fact, the default loop, and false
		707	otherwise.
529		708
530	=item unsigned int ev_loop_count (loop)	709	=item unsigned int ev_iteration (loop)
531		710
532	Returns the count of loop iterations for the loop, which is identical to	711	Returns the current iteration count for the event loop, which is identical
533	the number of times libev did poll for new events. It starts at C<0> and	712	to the number of times libev did poll for new events. It starts at C<0>
534	happily wraps around with enough iterations.	713	and happily wraps around with enough iterations.
535		714
536	This value can sometimes be useful as a generation counter of sorts (it	715	This value can sometimes be useful as a generation counter of sorts (it
537	"ticks" the number of loop iterations), as it roughly corresponds with	716	"ticks" the number of loop iterations), as it roughly corresponds with
538	C<ev_prepare> and C<ev_check> calls.	717	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		718	prepare and check phases.
		719
		720	=item unsigned int ev_depth (loop)
		721
		722	Returns the number of times C<ev_run> was entered minus the number of
		723	times C<ev_run> was exited normally, in other words, the recursion depth.
		724
		725	Outside C<ev_run>, this number is zero. In a callback, this number is
		726	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
		727	in which case it is higher.
		728
		729	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
		730	throwing an exception etc.), doesn't count as "exit" - consider this
		731	as a hint to avoid such ungentleman-like behaviour unless it's really
		732	convenient, in which case it is fully supported.
539		733
540	=item unsigned int ev_backend (loop)	734	=item unsigned int ev_backend (loop)
541		735
542	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	736	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
543	use.	737	use.
…		…
548	received events and started processing them. This timestamp does not	742	received events and started processing them. This timestamp does not
549	change as long as callbacks are being processed, and this is also the base	743	change as long as callbacks are being processed, and this is also the base
550	time used for relative timers. You can treat it as the timestamp of the	744	time used for relative timers. You can treat it as the timestamp of the
551	event occurring (or more correctly, libev finding out about it).	745	event occurring (or more correctly, libev finding out about it).
552		746
		747	=item ev_now_update (loop)
		748
		749	Establishes the current time by querying the kernel, updating the time
		750	returned by C<ev_now ()> in the progress. This is a costly operation and
		751	is usually done automatically within C<ev_run ()>.
		752
		753	This function is rarely useful, but when some event callback runs for a
		754	very long time without entering the event loop, updating libev's idea of
		755	the current time is a good idea.
		756
		757	See also L<The special problem of time updates> in the C<ev_timer> section.
		758
		759	=item ev_suspend (loop)
		760
		761	=item ev_resume (loop)
		762
		763	These two functions suspend and resume an event loop, for use when the
		764	loop is not used for a while and timeouts should not be processed.
		765
		766	A typical use case would be an interactive program such as a game: When
		767	the user presses C<^Z> to suspend the game and resumes it an hour later it
		768	would be best to handle timeouts as if no time had actually passed while
		769	the program was suspended. This can be achieved by calling C<ev_suspend>
		770	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		771	C<ev_resume> directly afterwards to resume timer processing.
		772
		773	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		774	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		775	will be rescheduled (that is, they will lose any events that would have
		776	occurred while suspended).
		777
		778	After calling C<ev_suspend> you B<must not> call I<any> function on the
		779	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		780	without a previous call to C<ev_suspend>.
		781
		782	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		783	event loop time (see C<ev_now_update>).
		784
553	=item ev_loop (loop, int flags)	785	=item ev_run (loop, int flags)
554		786
555	Finally, this is it, the event handler. This function usually is called	787	Finally, this is it, the event handler. This function usually is called
556	after you initialised all your watchers and you want to start handling	788	after you have initialised all your watchers and you want to start
557	events.	789	handling events. It will ask the operating system for any new events, call
		790	the watcher callbacks, an then repeat the whole process indefinitely: This
		791	is why event loops are called I<loops>.
558		792
559	If the flags argument is specified as C<0>, it will not return until	793	If the flags argument is specified as C<0>, it will keep handling events
560	either no event watchers are active anymore or C<ev_unloop> was called.	794	until either no event watchers are active anymore or C<ev_break> was
		795	called.
561		796
562	Please note that an explicit C<ev_unloop> is usually better than	797	Please note that an explicit C<ev_break> is usually better than
563	relying on all watchers to be stopped when deciding when a program has	798	relying on all watchers to be stopped when deciding when a program has
564	finished (especially in interactive programs), but having a program that	799	finished (especially in interactive programs), but having a program
565	automatically loops as long as it has to and no longer by virtue of	800	that automatically loops as long as it has to and no longer by virtue
566	relying on its watchers stopping correctly is a thing of beauty.	801	of relying on its watchers stopping correctly, that is truly a thing of
		802	beauty.
567		803
		804	This function is also I<mostly> exception-safe - you can break out of
		805	a C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		806	exception and so on. This does not decrement the C<ev_depth> value, nor
		807	will it clear any outstanding C<EVBREAK_ONE> breaks.
		808
568	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	809	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
569	those events and any outstanding ones, but will not block your process in	810	those events and any already outstanding ones, but will not wait and
570	case there are no events and will return after one iteration of the loop.	811	block your process in case there are no events and will return after one
		812	iteration of the loop. This is sometimes useful to poll and handle new
		813	events while doing lengthy calculations, to keep the program responsive.
571		814
572	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	815	A flags value of C<EVRUN_ONCE> will look for new events (waiting if
573	neccessary) and will handle those and any outstanding ones. It will block	816	necessary) and will handle those and any already outstanding ones. It
574	your process until at least one new event arrives, and will return after	817	will block your process until at least one new event arrives (which could
575	one iteration of the loop. This is useful if you are waiting for some	818	be an event internal to libev itself, so there is no guarantee that a
576	external event in conjunction with something not expressible using other	819	user-registered callback will be called), and will return after one
		820	iteration of the loop.
		821
		822	This is useful if you are waiting for some external event in conjunction
		823	with something not expressible using other libev watchers (i.e. "roll your
577	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	824	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
578	usually a better approach for this kind of thing.	825	usually a better approach for this kind of thing.
579		826
580	Here are the gory details of what C<ev_loop> does:	827	Here are the gory details of what C<ev_run> does:
581		828
		829	- Increment loop depth.
		830	- Reset the ev_break status.
582	- Before the first iteration, call any pending watchers.	831	- Before the first iteration, call any pending watchers.
		832	LOOP:
583	* If EVFLAG_FORKCHECK was used, check for a fork.	833	- If EVFLAG_FORKCHECK was used, check for a fork.
584	- If a fork was detected, queue and call all fork watchers.	834	- If a fork was detected (by any means), queue and call all fork watchers.
585	- Queue and call all prepare watchers.	835	- Queue and call all prepare watchers.
		836	- If ev_break was called, goto FINISH.
586	- If we have been forked, recreate the kernel state.	837	- If we have been forked, detach and recreate the kernel state
		838	as to not disturb the other process.
587	- Update the kernel state with all outstanding changes.	839	- Update the kernel state with all outstanding changes.
588	- Update the "event loop time".	840	- Update the "event loop time" (ev_now ()).
589	- Calculate for how long to sleep or block, if at all	841	- Calculate for how long to sleep or block, if at all
590	(active idle watchers, EVLOOP_NONBLOCK or not having	842	(active idle watchers, EVRUN_NOWAIT or not having
591	any active watchers at all will result in not sleeping).	843	any active watchers at all will result in not sleeping).
592	- Sleep if the I/O and timer collect interval say so.	844	- Sleep if the I/O and timer collect interval say so.
		845	- Increment loop iteration counter.
593	- Block the process, waiting for any events.	846	- Block the process, waiting for any events.
594	- Queue all outstanding I/O (fd) events.	847	- Queue all outstanding I/O (fd) events.
595	- Update the "event loop time" and do time jump handling.	848	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
596	- Queue all outstanding timers.	849	- Queue all expired timers.
597	- Queue all outstanding periodics.	850	- Queue all expired periodics.
598	- If no events are pending now, queue all idle watchers.	851	- Queue all idle watchers with priority higher than that of pending events.
599	- Queue all check watchers.	852	- Queue all check watchers.
600	- Call all queued watchers in reverse order (i.e. check watchers first).	853	- Call all queued watchers in reverse order (i.e. check watchers first).
601	Signals and child watchers are implemented as I/O watchers, and will	854	Signals and child watchers are implemented as I/O watchers, and will
602	be handled here by queueing them when their watcher gets executed.	855	be handled here by queueing them when their watcher gets executed.
603	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	856	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
604	were used, or there are no active watchers, return, otherwise	857	were used, or there are no active watchers, goto FINISH, otherwise
605	continue with step *.	858	continue with step LOOP.
		859	FINISH:
		860	- Reset the ev_break status iff it was EVBREAK_ONE.
		861	- Decrement the loop depth.
		862	- Return.
606		863
607	Example: Queue some jobs and then loop until no events are outstanding	864	Example: Queue some jobs and then loop until no events are outstanding
608	anymore.	865	anymore.
609		866
610	... queue jobs here, make sure they register event watchers as long	867	... queue jobs here, make sure they register event watchers as long
611	... as they still have work to do (even an idle watcher will do..)	868	... as they still have work to do (even an idle watcher will do..)
612	ev_loop (my_loop, 0);	869	ev_run (my_loop, 0);
613	... jobs done. yeah!	870	... jobs done or somebody called unloop. yeah!
614		871
615	=item ev_unloop (loop, how)	872	=item ev_break (loop, how)
616		873
617	Can be used to make a call to C<ev_loop> return early (but only after it	874	Can be used to make a call to C<ev_run> return early (but only after it
618	has processed all outstanding events). The C<how> argument must be either	875	has processed all outstanding events). The C<how> argument must be either
619	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	876	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
620	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	877	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
621		878
622	This "unloop state" will be cleared when entering C<ev_loop> again.	879	This "break state" will be cleared on the next call to C<ev_run>.
		880
		881	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		882	which case it will have no effect.
623		883
624	=item ev_ref (loop)	884	=item ev_ref (loop)
625		885
626	=item ev_unref (loop)	886	=item ev_unref (loop)
627		887
628	Ref/unref can be used to add or remove a reference count on the event	888	Ref/unref can be used to add or remove a reference count on the event
629	loop: Every watcher keeps one reference, and as long as the reference	889	loop: Every watcher keeps one reference, and as long as the reference
630	count is nonzero, C<ev_loop> will not return on its own. If you have	890	count is nonzero, C<ev_run> will not return on its own.
631	a watcher you never unregister that should not keep C<ev_loop> from	891
632	returning, ev_unref() after starting, and ev_ref() before stopping it. For	892	This is useful when you have a watcher that you never intend to
		893	unregister, but that nevertheless should not keep C<ev_run> from
		894	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		895	before stopping it.
		896
633	example, libev itself uses this for its internal signal pipe: It is not	897	As an example, libev itself uses this for its internal signal pipe: It
634	visible to the libev user and should not keep C<ev_loop> from exiting if	898	is not visible to the libev user and should not keep C<ev_run> from
635	no event watchers registered by it are active. It is also an excellent	899	exiting if no event watchers registered by it are active. It is also an
636	way to do this for generic recurring timers or from within third-party	900	excellent way to do this for generic recurring timers or from within
637	libraries. Just remember to I<unref after start> and I<ref before stop>	901	third-party libraries. Just remember to I<unref after start> and I<ref
638	(but only if the watcher wasn't active before, or was active before,	902	before stop> (but only if the watcher wasn't active before, or was active
639	respectively).	903	before, respectively. Note also that libev might stop watchers itself
		904	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		905	in the callback).
640		906
641	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	907	Example: Create a signal watcher, but keep it from keeping C<ev_run>
642	running when nothing else is active.	908	running when nothing else is active.
643		909
644	struct ev_signal exitsig;	910	ev_signal exitsig;
645	ev_signal_init (&exitsig, sig_cb, SIGINT);	911	ev_signal_init (&exitsig, sig_cb, SIGINT);
646	ev_signal_start (loop, &exitsig);	912	ev_signal_start (loop, &exitsig);
647	evf_unref (loop);	913	ev_unref (loop);
648		914
649	Example: For some weird reason, unregister the above signal handler again.	915	Example: For some weird reason, unregister the above signal handler again.
650		916
651	ev_ref (loop);	917	ev_ref (loop);
652	ev_signal_stop (loop, &exitsig);	918	ev_signal_stop (loop, &exitsig);
653		919
654	=item ev_set_io_collect_interval (loop, ev_tstamp interval)	920	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
655		921
656	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)	922	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
657		923
658	These advanced functions influence the time that libev will spend waiting	924	These advanced functions influence the time that libev will spend waiting
659	for events. Both are by default C<0>, meaning that libev will try to	925	for events. Both time intervals are by default C<0>, meaning that libev
660	invoke timer/periodic callbacks and I/O callbacks with minimum latency.	926	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		927	latency.
661		928
662	Setting these to a higher value (the C<interval> I<must> be >= C<0>)	929	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
663	allows libev to delay invocation of I/O and timer/periodic callbacks to	930	allows libev to delay invocation of I/O and timer/periodic callbacks
664	increase efficiency of loop iterations.	931	to increase efficiency of loop iterations (or to increase power-saving
		932	opportunities).
665		933
666	The background is that sometimes your program runs just fast enough to	934	The idea is that sometimes your program runs just fast enough to handle
667	handle one (or very few) event(s) per loop iteration. While this makes	935	one (or very few) event(s) per loop iteration. While this makes the
668	the program responsive, it also wastes a lot of CPU time to poll for new	936	program responsive, it also wastes a lot of CPU time to poll for new
669	events, especially with backends like C<select ()> which have a high	937	events, especially with backends like C<select ()> which have a high
670	overhead for the actual polling but can deliver many events at once.	938	overhead for the actual polling but can deliver many events at once.
671		939
672	By setting a higher I<io collect interval> you allow libev to spend more	940	By setting a higher I<io collect interval> you allow libev to spend more
673	time collecting I/O events, so you can handle more events per iteration,	941	time collecting I/O events, so you can handle more events per iteration,
674	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	942	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
675	C<ev_timer>) will be not affected. Setting this to a non-null value will	943	C<ev_timer>) will be not affected. Setting this to a non-null value will
676	introduce an additional C<ev_sleep ()> call into most loop iterations.	944	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		945	sleep time ensures that libev will not poll for I/O events more often then
		946	once per this interval, on average.
677		947
678	Likewise, by setting a higher I<timeout collect interval> you allow libev	948	Likewise, by setting a higher I<timeout collect interval> you allow libev
679	to spend more time collecting timeouts, at the expense of increased	949	to spend more time collecting timeouts, at the expense of increased
680	latency (the watcher callback will be called later). C<ev_io> watchers	950	latency/jitter/inexactness (the watcher callback will be called
681	will not be affected. Setting this to a non-null value will not introduce	951	later). C<ev_io> watchers will not be affected. Setting this to a non-null
682	any overhead in libev.	952	value will not introduce any overhead in libev.
683		953
684	Many (busy) programs can usually benefit by setting the io collect	954	Many (busy) programs can usually benefit by setting the I/O collect
685	interval to a value near C<0.1> or so, which is often enough for	955	interval to a value near C<0.1> or so, which is often enough for
686	interactive servers (of course not for games), likewise for timeouts. It	956	interactive servers (of course not for games), likewise for timeouts. It
687	usually doesn't make much sense to set it to a lower value than C<0.01>,	957	usually doesn't make much sense to set it to a lower value than C<0.01>,
688	as this approsaches the timing granularity of most systems.	958	as this approaches the timing granularity of most systems. Note that if
		959	you do transactions with the outside world and you can't increase the
		960	parallelity, then this setting will limit your transaction rate (if you
		961	need to poll once per transaction and the I/O collect interval is 0.01,
		962	then you can't do more than 100 transactions per second).
		963
		964	Setting the I<timeout collect interval> can improve the opportunity for
		965	saving power, as the program will "bundle" timer callback invocations that
		966	are "near" in time together, by delaying some, thus reducing the number of
		967	times the process sleeps and wakes up again. Another useful technique to
		968	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		969	they fire on, say, one-second boundaries only.
		970
		971	Example: we only need 0.1s timeout granularity, and we wish not to poll
		972	more often than 100 times per second:
		973
		974	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		975	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		976
		977	=item ev_invoke_pending (loop)
		978
		979	This call will simply invoke all pending watchers while resetting their
		980	pending state. Normally, C<ev_run> does this automatically when required,
		981	but when overriding the invoke callback this call comes handy. This
		982	function can be invoked from a watcher - this can be useful for example
		983	when you want to do some lengthy calculation and want to pass further
		984	event handling to another thread (you still have to make sure only one
		985	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
		986
		987	=item int ev_pending_count (loop)
		988
		989	Returns the number of pending watchers - zero indicates that no watchers
		990	are pending.
		991
		992	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		993
		994	This overrides the invoke pending functionality of the loop: Instead of
		995	invoking all pending watchers when there are any, C<ev_run> will call
		996	this callback instead. This is useful, for example, when you want to
		997	invoke the actual watchers inside another context (another thread etc.).
		998
		999	If you want to reset the callback, use C<ev_invoke_pending> as new
		1000	callback.
		1001
		1002	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		1003
		1004	Sometimes you want to share the same loop between multiple threads. This
		1005	can be done relatively simply by putting mutex_lock/unlock calls around
		1006	each call to a libev function.
		1007
		1008	However, C<ev_run> can run an indefinite time, so it is not feasible
		1009	to wait for it to return. One way around this is to wake up the event
		1010	loop via C<ev_break> and C<av_async_send>, another way is to set these
		1011	I<release> and I<acquire> callbacks on the loop.
		1012
		1013	When set, then C<release> will be called just before the thread is
		1014	suspended waiting for new events, and C<acquire> is called just
		1015	afterwards.
		1016
		1017	Ideally, C<release> will just call your mutex_unlock function, and
		1018	C<acquire> will just call the mutex_lock function again.
		1019
		1020	While event loop modifications are allowed between invocations of
		1021	C<release> and C<acquire> (that's their only purpose after all), no
		1022	modifications done will affect the event loop, i.e. adding watchers will
		1023	have no effect on the set of file descriptors being watched, or the time
		1024	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		1025	to take note of any changes you made.
		1026
		1027	In theory, threads executing C<ev_run> will be async-cancel safe between
		1028	invocations of C<release> and C<acquire>.
		1029
		1030	See also the locking example in the C<THREADS> section later in this
		1031	document.
		1032
		1033	=item ev_set_userdata (loop, void *data)
		1034
		1035	=item void *ev_userdata (loop)
		1036
		1037	Set and retrieve a single C<void *> associated with a loop. When
		1038	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		1039	C<0>.
		1040
		1041	These two functions can be used to associate arbitrary data with a loop,
		1042	and are intended solely for the C<invoke_pending_cb>, C<release> and
		1043	C<acquire> callbacks described above, but of course can be (ab-)used for
		1044	any other purpose as well.
		1045
		1046	=item ev_verify (loop)
		1047
		1048	This function only does something when C<EV_VERIFY> support has been
		1049	compiled in, which is the default for non-minimal builds. It tries to go
		1050	through all internal structures and checks them for validity. If anything
		1051	is found to be inconsistent, it will print an error message to standard
		1052	error and call C<abort ()>.
		1053
		1054	This can be used to catch bugs inside libev itself: under normal
		1055	circumstances, this function will never abort as of course libev keeps its
		1056	data structures consistent.
689		1057
690	=back	1058	=back
691		1059
692		1060
693	=head1 ANATOMY OF A WATCHER	1061	=head1 ANATOMY OF A WATCHER
694		1062
		1063	In the following description, uppercase C<TYPE> in names stands for the
		1064	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		1065	watchers and C<ev_io_start> for I/O watchers.
		1066
695	A watcher is a structure that you create and register to record your	1067	A watcher is an opaque structure that you allocate and register to record
696	interest in some event. For instance, if you want to wait for STDIN to	1068	your interest in some event. To make a concrete example, imagine you want
697	become readable, you would create an C<ev_io> watcher for that:	1069	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1070	for that:
698		1071
699	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1072	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
700	{	1073	{
701	ev_io_stop (w);	1074	ev_io_stop (w);
702	ev_unloop (loop, EVUNLOOP_ALL);	1075	ev_break (loop, EVBREAK_ALL);
703	}	1076	}
704		1077
705	struct ev_loop *loop = ev_default_loop (0);	1078	struct ev_loop *loop = ev_default_loop (0);
		1079
706	struct ev_io stdin_watcher;	1080	ev_io stdin_watcher;
		1081
707	ev_init (&stdin_watcher, my_cb);	1082	ev_init (&stdin_watcher, my_cb);
708	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1083	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
709	ev_io_start (loop, &stdin_watcher);	1084	ev_io_start (loop, &stdin_watcher);
		1085
710	ev_loop (loop, 0);	1086	ev_run (loop, 0);
711		1087
712	As you can see, you are responsible for allocating the memory for your	1088	As you can see, you are responsible for allocating the memory for your
713	watcher structures (and it is usually a bad idea to do this on the stack,	1089	watcher structures (and it is I<usually> a bad idea to do this on the
714	although this can sometimes be quite valid).	1090	stack).
715		1091
		1092	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1093	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1094
716	Each watcher structure must be initialised by a call to C<ev_init	1095	Each watcher structure must be initialised by a call to C<ev_init (watcher
717	(watcher *, callback)>, which expects a callback to be provided. This	1096	*, callback)>, which expects a callback to be provided. This callback is
718	callback gets invoked each time the event occurs (or, in the case of io	1097	invoked each time the event occurs (or, in the case of I/O watchers, each
719	watchers, each time the event loop detects that the file descriptor given	1098	time the event loop detects that the file descriptor given is readable
720	is readable and/or writable).	1099	and/or writable).
721		1100
722	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1101	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
723	with arguments specific to this watcher type. There is also a macro	1102	macro to configure it, with arguments specific to the watcher type. There
724	to combine initialisation and setting in one call: C<< ev_<type>_init	1103	is also a macro to combine initialisation and setting in one call: C<<
725	(watcher *, callback, ...) >>.	1104	ev_TYPE_init (watcher *, callback, ...) >>.
726		1105
727	To make the watcher actually watch out for events, you have to start it	1106	To make the watcher actually watch out for events, you have to start it
728	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1107	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
729	*) >>), and you can stop watching for events at any time by calling the	1108	*) >>), and you can stop watching for events at any time by calling the
730	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1109	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
731		1110
732	As long as your watcher is active (has been started but not stopped) you	1111	As long as your watcher is active (has been started but not stopped) you
733	must not touch the values stored in it. Most specifically you must never	1112	must not touch the values stored in it. Most specifically you must never
734	reinitialise it or call its C<set> macro.	1113	reinitialise it or call its C<ev_TYPE_set> macro.
735		1114
736	Each and every callback receives the event loop pointer as first, the	1115	Each and every callback receives the event loop pointer as first, the
737	registered watcher structure as second, and a bitset of received events as	1116	registered watcher structure as second, and a bitset of received events as
738	third argument.	1117	third argument.
739		1118
…		…
748	=item C<EV_WRITE>	1127	=item C<EV_WRITE>
749		1128
750	The file descriptor in the C<ev_io> watcher has become readable and/or	1129	The file descriptor in the C<ev_io> watcher has become readable and/or
751	writable.	1130	writable.
752		1131
753	=item C<EV_TIMEOUT>	1132	=item C<EV_TIMER>
754		1133
755	The C<ev_timer> watcher has timed out.	1134	The C<ev_timer> watcher has timed out.
756		1135
757	=item C<EV_PERIODIC>	1136	=item C<EV_PERIODIC>
758		1137
…		…
776		1155
777	=item C<EV_PREPARE>	1156	=item C<EV_PREPARE>
778		1157
779	=item C<EV_CHECK>	1158	=item C<EV_CHECK>
780		1159
781	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts	1160	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts
782	to gather new events, and all C<ev_check> watchers are invoked just after	1161	to gather new events, and all C<ev_check> watchers are invoked just after
783	C<ev_loop> has gathered them, but before it invokes any callbacks for any	1162	C<ev_run> has gathered them, but before it invokes any callbacks for any
784	received events. Callbacks of both watcher types can start and stop as	1163	received events. Callbacks of both watcher types can start and stop as
785	many watchers as they want, and all of them will be taken into account	1164	many watchers as they want, and all of them will be taken into account
786	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1165	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
787	C<ev_loop> from blocking).	1166	C<ev_run> from blocking).
788		1167
789	=item C<EV_EMBED>	1168	=item C<EV_EMBED>
790		1169
791	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1170	The embedded event loop specified in the C<ev_embed> watcher needs attention.
792		1171
793	=item C<EV_FORK>	1172	=item C<EV_FORK>
794		1173
795	The event loop has been resumed in the child process after fork (see	1174	The event loop has been resumed in the child process after fork (see
796	C<ev_fork>).	1175	C<ev_fork>).
797		1176
		1177	=item C<EV_CLEANUP>
		1178
		1179	The event loop is about to be destroyed (see C<ev_cleanup>).
		1180
798	=item C<EV_ASYNC>	1181	=item C<EV_ASYNC>
799		1182
800	The given async watcher has been asynchronously notified (see C<ev_async>).	1183	The given async watcher has been asynchronously notified (see C<ev_async>).
801		1184
		1185	=item C<EV_CUSTOM>
		1186
		1187	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1188	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1189
802	=item C<EV_ERROR>	1190	=item C<EV_ERROR>
803		1191
804	An unspecified error has occured, the watcher has been stopped. This might	1192	An unspecified error has occurred, the watcher has been stopped. This might
805	happen because the watcher could not be properly started because libev	1193	happen because the watcher could not be properly started because libev
806	ran out of memory, a file descriptor was found to be closed or any other	1194	ran out of memory, a file descriptor was found to be closed or any other
		1195	problem. Libev considers these application bugs.
		1196
807	problem. You best act on it by reporting the problem and somehow coping	1197	You best act on it by reporting the problem and somehow coping with the
808	with the watcher being stopped.	1198	watcher being stopped. Note that well-written programs should not receive
		1199	an error ever, so when your watcher receives it, this usually indicates a
		1200	bug in your program.
809		1201
810	Libev will usually signal a few "dummy" events together with an error,	1202	Libev will usually signal a few "dummy" events together with an error, for
811	for example it might indicate that a fd is readable or writable, and if	1203	example it might indicate that a fd is readable or writable, and if your
812	your callbacks is well-written it can just attempt the operation and cope	1204	callbacks is well-written it can just attempt the operation and cope with
813	with the error from read() or write(). This will not work in multithreaded	1205	the error from read() or write(). This will not work in multi-threaded
814	programs, though, so beware.	1206	programs, though, as the fd could already be closed and reused for another
		1207	thing, so beware.
815		1208
816	=back	1209	=back
817		1210
818	=head2 GENERIC WATCHER FUNCTIONS	1211	=head2 GENERIC WATCHER FUNCTIONS
819
820	In the following description, C<TYPE> stands for the watcher type,
821	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
822		1212
823	=over 4	1213	=over 4
824		1214
825	=item C<ev_init> (ev_TYPE *watcher, callback)	1215	=item C<ev_init> (ev_TYPE *watcher, callback)
826		1216
…		…
832	which rolls both calls into one.	1222	which rolls both calls into one.
833		1223
834	You can reinitialise a watcher at any time as long as it has been stopped	1224	You can reinitialise a watcher at any time as long as it has been stopped
835	(or never started) and there are no pending events outstanding.	1225	(or never started) and there are no pending events outstanding.
836		1226
837	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1227	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
838	int revents)>.	1228	int revents)>.
839		1229
		1230	Example: Initialise an C<ev_io> watcher in two steps.
		1231
		1232	ev_io w;
		1233	ev_init (&w, my_cb);
		1234	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1235
840	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1236	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
841		1237
842	This macro initialises the type-specific parts of a watcher. You need to	1238	This macro initialises the type-specific parts of a watcher. You need to
843	call C<ev_init> at least once before you call this macro, but you can	1239	call C<ev_init> at least once before you call this macro, but you can
844	call C<ev_TYPE_set> any number of times. You must not, however, call this	1240	call C<ev_TYPE_set> any number of times. You must not, however, call this
845	macro on a watcher that is active (it can be pending, however, which is a	1241	macro on a watcher that is active (it can be pending, however, which is a
846	difference to the C<ev_init> macro).	1242	difference to the C<ev_init> macro).
847		1243
848	Although some watcher types do not have type-specific arguments	1244	Although some watcher types do not have type-specific arguments
849	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1245	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
850		1246
		1247	See C<ev_init>, above, for an example.
		1248
851	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1249	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
852		1250
853	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1251	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
854	calls into a single call. This is the most convinient method to initialise	1252	calls into a single call. This is the most convenient method to initialise
855	a watcher. The same limitations apply, of course.	1253	a watcher. The same limitations apply, of course.
856		1254
		1255	Example: Initialise and set an C<ev_io> watcher in one step.
		1256
		1257	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1258
857	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1259	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
858		1260
859	Starts (activates) the given watcher. Only active watchers will receive	1261	Starts (activates) the given watcher. Only active watchers will receive
860	events. If the watcher is already active nothing will happen.	1262	events. If the watcher is already active nothing will happen.
861		1263
		1264	Example: Start the C<ev_io> watcher that is being abused as example in this
		1265	whole section.
		1266
		1267	ev_io_start (EV_DEFAULT_UC, &w);
		1268
862	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1269	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
863		1270
864	Stops the given watcher again (if active) and clears the pending	1271	Stops the given watcher if active, and clears the pending status (whether
		1272	the watcher was active or not).
		1273
865	status. It is possible that stopped watchers are pending (for example,	1274	It is possible that stopped watchers are pending - for example,
866	non-repeating timers are being stopped when they become pending), but	1275	non-repeating timers are being stopped when they become pending - but
867	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1276	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
868	you want to free or reuse the memory used by the watcher it is therefore a	1277	pending. If you want to free or reuse the memory used by the watcher it is
869	good idea to always call its C<ev_TYPE_stop> function.	1278	therefore a good idea to always call its C<ev_TYPE_stop> function.
870		1279
871	=item bool ev_is_active (ev_TYPE *watcher)	1280	=item bool ev_is_active (ev_TYPE *watcher)
872		1281
873	Returns a true value iff the watcher is active (i.e. it has been started	1282	Returns a true value iff the watcher is active (i.e. it has been started
874	and not yet been stopped). As long as a watcher is active you must not modify	1283	and not yet been stopped). As long as a watcher is active you must not modify
…		…
890	=item ev_cb_set (ev_TYPE *watcher, callback)	1299	=item ev_cb_set (ev_TYPE *watcher, callback)
891		1300
892	Change the callback. You can change the callback at virtually any time	1301	Change the callback. You can change the callback at virtually any time
893	(modulo threads).	1302	(modulo threads).
894		1303
895	=item ev_set_priority (ev_TYPE *watcher, priority)	1304	=item ev_set_priority (ev_TYPE *watcher, int priority)
896		1305
897	=item int ev_priority (ev_TYPE *watcher)	1306	=item int ev_priority (ev_TYPE *watcher)
898		1307
899	Set and query the priority of the watcher. The priority is a small	1308	Set and query the priority of the watcher. The priority is a small
900	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1309	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
901	(default: C<-2>). Pending watchers with higher priority will be invoked	1310	(default: C<-2>). Pending watchers with higher priority will be invoked
902	before watchers with lower priority, but priority will not keep watchers	1311	before watchers with lower priority, but priority will not keep watchers
903	from being executed (except for C<ev_idle> watchers).	1312	from being executed (except for C<ev_idle> watchers).
904		1313
905	This means that priorities are I<only> used for ordering callback
906	invocation after new events have been received. This is useful, for
907	example, to reduce latency after idling, or more often, to bind two
908	watchers on the same event and make sure one is called first.
909
910	If you need to suppress invocation when higher priority events are pending	1314	If you need to suppress invocation when higher priority events are pending
911	you need to look at C<ev_idle> watchers, which provide this functionality.	1315	you need to look at C<ev_idle> watchers, which provide this functionality.
912		1316
913	You I<must not> change the priority of a watcher as long as it is active or	1317	You I<must not> change the priority of a watcher as long as it is active or
914	pending.	1318	pending.
915		1319
		1320	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1321	fine, as long as you do not mind that the priority value you query might
		1322	or might not have been clamped to the valid range.
		1323
916	The default priority used by watchers when no priority has been set is	1324	The default priority used by watchers when no priority has been set is
917	always C<0>, which is supposed to not be too high and not be too low :).	1325	always C<0>, which is supposed to not be too high and not be too low :).
918		1326
919	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1327	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
920	fine, as long as you do not mind that the priority value you query might	1328	priorities.
921	or might not have been adjusted to be within valid range.
922		1329
923	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1330	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
924		1331
925	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1332	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
926	C<loop> nor C<revents> need to be valid as long as the watcher callback	1333	C<loop> nor C<revents> need to be valid as long as the watcher callback
927	can deal with that fact.	1334	can deal with that fact, as both are simply passed through to the
		1335	callback.
928		1336
929	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1337	=item int ev_clear_pending (loop, ev_TYPE *watcher)
930		1338
931	If the watcher is pending, this function returns clears its pending status	1339	If the watcher is pending, this function clears its pending status and
932	and returns its C<revents> bitset (as if its callback was invoked). If the	1340	returns its C<revents> bitset (as if its callback was invoked). If the
933	watcher isn't pending it does nothing and returns C<0>.	1341	watcher isn't pending it does nothing and returns C<0>.
934		1342
		1343	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1344	callback to be invoked, which can be accomplished with this function.
		1345
		1346	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1347
		1348	Feeds the given event set into the event loop, as if the specified event
		1349	had happened for the specified watcher (which must be a pointer to an
		1350	initialised but not necessarily started event watcher). Obviously you must
		1351	not free the watcher as long as it has pending events.
		1352
		1353	Stopping the watcher, letting libev invoke it, or calling
		1354	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1355	not started in the first place.
		1356
		1357	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1358	functions that do not need a watcher.
		1359
935	=back	1360	=back
936		1361
		1362	See also the L<ASSOCIATING CUSTOM DATA WITH A WATCHER> and L<BUILDING YOUR
		1363	OWN COMPOSITE WATCHERS> idioms.
937		1364
938	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1365	=head2 WATCHER STATES
939		1366
940	Each watcher has, by default, a member C<void *data> that you can change	1367	There are various watcher states mentioned throughout this manual -
941	and read at any time, libev will completely ignore it. This can be used	1368	active, pending and so on. In this section these states and the rules to
942	to associate arbitrary data with your watcher. If you need more data and	1369	transition between them will be described in more detail - and while these
943	don't want to allocate memory and store a pointer to it in that data	1370	rules might look complicated, they usually do "the right thing".
944	member, you can also "subclass" the watcher type and provide your own
945	data:
946		1371
947	struct my_io	1372	=over 4
948	{
949	struct ev_io io;
950	int otherfd;
951	void *somedata;
952	struct whatever *mostinteresting;
953	}
954		1373
955	And since your callback will be called with a pointer to the watcher, you	1374	=item initialiased
956	can cast it back to your own type:
957		1375
958	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1376	Before a watcher can be registered with the event looop it has to be
959	{	1377	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
960	struct my_io *w = (struct my_io *)w_;	1378	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
961	...
962	}
963		1379
964	More interesting and less C-conformant ways of casting your callback type	1380	In this state it is simply some block of memory that is suitable for use
965	instead have been omitted.	1381	in an event loop. It can be moved around, freed, reused etc. at will.
966		1382
967	Another common scenario is having some data structure with multiple	1383	=item started/running/active
968	watchers:
969		1384
970	struct my_biggy	1385	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
971	{	1386	property of the event loop, and is actively waiting for events. While in
972	int some_data;	1387	this state it cannot be accessed (except in a few documented ways), moved,
973	ev_timer t1;	1388	freed or anything else - the only legal thing is to keep a pointer to it,
974	ev_timer t2;	1389	and call libev functions on it that are documented to work on active watchers.
975	}
976		1390
977	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1391	=item pending
978	you need to use C<offsetof>:
979		1392
980	#include <stddef.h>	1393	If a watcher is active and libev determines that an event it is interested
		1394	in has occurred (such as a timer expiring), it will become pending. It will
		1395	stay in this pending state until either it is stopped or its callback is
		1396	about to be invoked, so it is not normally pending inside the watcher
		1397	callback.
981		1398
		1399	The watcher might or might not be active while it is pending (for example,
		1400	an expired non-repeating timer can be pending but no longer active). If it
		1401	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1402	but it is still property of the event loop at this time, so cannot be
		1403	moved, freed or reused. And if it is active the rules described in the
		1404	previous item still apply.
		1405
		1406	It is also possible to feed an event on a watcher that is not active (e.g.
		1407	via C<ev_feed_event>), in which case it becomes pending without being
		1408	active.
		1409
		1410	=item stopped
		1411
		1412	A watcher can be stopped implicitly by libev (in which case it might still
		1413	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1414	latter will clear any pending state the watcher might be in, regardless
		1415	of whether it was active or not, so stopping a watcher explicitly before
		1416	freeing it is often a good idea.
		1417
		1418	While stopped (and not pending) the watcher is essentially in the
		1419	initialised state, that is it can be reused, moved, modified in any way
		1420	you wish.
		1421
		1422	=back
		1423
		1424	=head2 WATCHER PRIORITY MODELS
		1425
		1426	Many event loops support I<watcher priorities>, which are usually small
		1427	integers that influence the ordering of event callback invocation
		1428	between watchers in some way, all else being equal.
		1429
		1430	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1431	description for the more technical details such as the actual priority
		1432	range.
		1433
		1434	There are two common ways how these these priorities are being interpreted
		1435	by event loops:
		1436
		1437	In the more common lock-out model, higher priorities "lock out" invocation
		1438	of lower priority watchers, which means as long as higher priority
		1439	watchers receive events, lower priority watchers are not being invoked.
		1440
		1441	The less common only-for-ordering model uses priorities solely to order
		1442	callback invocation within a single event loop iteration: Higher priority
		1443	watchers are invoked before lower priority ones, but they all get invoked
		1444	before polling for new events.
		1445
		1446	Libev uses the second (only-for-ordering) model for all its watchers
		1447	except for idle watchers (which use the lock-out model).
		1448
		1449	The rationale behind this is that implementing the lock-out model for
		1450	watchers is not well supported by most kernel interfaces, and most event
		1451	libraries will just poll for the same events again and again as long as
		1452	their callbacks have not been executed, which is very inefficient in the
		1453	common case of one high-priority watcher locking out a mass of lower
		1454	priority ones.
		1455
		1456	Static (ordering) priorities are most useful when you have two or more
		1457	watchers handling the same resource: a typical usage example is having an
		1458	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1459	timeouts. Under load, data might be received while the program handles
		1460	other jobs, but since timers normally get invoked first, the timeout
		1461	handler will be executed before checking for data. In that case, giving
		1462	the timer a lower priority than the I/O watcher ensures that I/O will be
		1463	handled first even under adverse conditions (which is usually, but not
		1464	always, what you want).
		1465
		1466	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1467	will only be executed when no same or higher priority watchers have
		1468	received events, they can be used to implement the "lock-out" model when
		1469	required.
		1470
		1471	For example, to emulate how many other event libraries handle priorities,
		1472	you can associate an C<ev_idle> watcher to each such watcher, and in
		1473	the normal watcher callback, you just start the idle watcher. The real
		1474	processing is done in the idle watcher callback. This causes libev to
		1475	continuously poll and process kernel event data for the watcher, but when
		1476	the lock-out case is known to be rare (which in turn is rare :), this is
		1477	workable.
		1478
		1479	Usually, however, the lock-out model implemented that way will perform
		1480	miserably under the type of load it was designed to handle. In that case,
		1481	it might be preferable to stop the real watcher before starting the
		1482	idle watcher, so the kernel will not have to process the event in case
		1483	the actual processing will be delayed for considerable time.
		1484
		1485	Here is an example of an I/O watcher that should run at a strictly lower
		1486	priority than the default, and which should only process data when no
		1487	other events are pending:
		1488
		1489	ev_idle idle; // actual processing watcher
		1490	ev_io io; // actual event watcher
		1491
982	static void	1492	static void
983	t1_cb (EV_P_ struct ev_timer *w, int revents)	1493	io_cb (EV_P_ ev_io *w, int revents)
984	{	1494	{
985	struct my_biggy big = (struct my_biggy *	1495	// stop the I/O watcher, we received the event, but
986	(((char *)w) - offsetof (struct my_biggy, t1));	1496	// are not yet ready to handle it.
		1497	ev_io_stop (EV_A_ w);
		1498
		1499	// start the idle watcher to handle the actual event.
		1500	// it will not be executed as long as other watchers
		1501	// with the default priority are receiving events.
		1502	ev_idle_start (EV_A_ &idle);
987	}	1503	}
988		1504
989	static void	1505	static void
990	t2_cb (EV_P_ struct ev_timer *w, int revents)	1506	idle_cb (EV_P_ ev_idle *w, int revents)
991	{	1507	{
992	struct my_biggy big = (struct my_biggy *	1508	// actual processing
993	(((char *)w) - offsetof (struct my_biggy, t2));	1509	read (STDIN_FILENO, ...);
		1510
		1511	// have to start the I/O watcher again, as
		1512	// we have handled the event
		1513	ev_io_start (EV_P_ &io);
994	}	1514	}
		1515
		1516	// initialisation
		1517	ev_idle_init (&idle, idle_cb);
		1518	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1519	ev_io_start (EV_DEFAULT_ &io);
		1520
		1521	In the "real" world, it might also be beneficial to start a timer, so that
		1522	low-priority connections can not be locked out forever under load. This
		1523	enables your program to keep a lower latency for important connections
		1524	during short periods of high load, while not completely locking out less
		1525	important ones.
995		1526
996		1527
997	=head1 WATCHER TYPES	1528	=head1 WATCHER TYPES
998		1529
999	This section describes each watcher in detail, but will not repeat	1530	This section describes each watcher in detail, but will not repeat
…		…
1023	In general you can register as many read and/or write event watchers per	1554	In general you can register as many read and/or write event watchers per
1024	fd as you want (as long as you don't confuse yourself). Setting all file	1555	fd as you want (as long as you don't confuse yourself). Setting all file
1025	descriptors to non-blocking mode is also usually a good idea (but not	1556	descriptors to non-blocking mode is also usually a good idea (but not
1026	required if you know what you are doing).	1557	required if you know what you are doing).
1027		1558
1028	If you must do this, then force the use of a known-to-be-good backend
1029	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
1030	C<EVBACKEND_POLL>).
1031
1032	Another thing you have to watch out for is that it is quite easy to	1559	Another thing you have to watch out for is that it is quite easy to
1033	receive "spurious" readyness notifications, that is your callback might	1560	receive "spurious" readiness notifications, that is, your callback might
1034	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1561	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1035	because there is no data. Not only are some backends known to create a	1562	because there is no data. It is very easy to get into this situation even
1036	lot of those (for example solaris ports), it is very easy to get into	1563	with a relatively standard program structure. Thus it is best to always
1037	this situation even with a relatively standard program structure. Thus	1564	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1038	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1039	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1565	preferable to a program hanging until some data arrives.
1040		1566
1041	If you cannot run the fd in non-blocking mode (for example you should not	1567	If you cannot run the fd in non-blocking mode (for example you should
1042	play around with an Xlib connection), then you have to seperately re-test	1568	not play around with an Xlib connection), then you have to separately
1043	whether a file descriptor is really ready with a known-to-be good interface	1569	re-test whether a file descriptor is really ready with a known-to-be good
1044	such as poll (fortunately in our Xlib example, Xlib already does this on	1570	interface such as poll (fortunately in the case of Xlib, it already does
1045	its own, so its quite safe to use).	1571	this on its own, so its quite safe to use). Some people additionally
		1572	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1573	indefinitely.
		1574
		1575	But really, best use non-blocking mode.
1046		1576
1047	=head3 The special problem of disappearing file descriptors	1577	=head3 The special problem of disappearing file descriptors
1048		1578
1049	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1579	Some backends (e.g. kqueue, epoll) need to be told about closing a file
1050	descriptor (either by calling C<close> explicitly or by any other means,	1580	descriptor (either due to calling C<close> explicitly or any other means,
1051	such as C<dup>). The reason is that you register interest in some file	1581	such as C<dup2>). The reason is that you register interest in some file
1052	descriptor, but when it goes away, the operating system will silently drop	1582	descriptor, but when it goes away, the operating system will silently drop
1053	this interest. If another file descriptor with the same number then is	1583	this interest. If another file descriptor with the same number then is
1054	registered with libev, there is no efficient way to see that this is, in	1584	registered with libev, there is no efficient way to see that this is, in
1055	fact, a different file descriptor.	1585	fact, a different file descriptor.
1056		1586
…		…
1074		1604
1075	There is no workaround possible except not registering events	1605	There is no workaround possible except not registering events
1076	for potentially C<dup ()>'ed file descriptors, or to resort to	1606	for potentially C<dup ()>'ed file descriptors, or to resort to
1077	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1607	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1078		1608
		1609	=head3 The special problem of files
		1610
		1611	Many people try to use C<select> (or libev) on file descriptors
		1612	representing files, and expect it to become ready when their program
		1613	doesn't block on disk accesses (which can take a long time on their own).
		1614
		1615	However, this cannot ever work in the "expected" way - you get a readiness
		1616	notification as soon as the kernel knows whether and how much data is
		1617	there, and in the case of open files, that's always the case, so you
		1618	always get a readiness notification instantly, and your read (or possibly
		1619	write) will still block on the disk I/O.
		1620
		1621	Another way to view it is that in the case of sockets, pipes, character
		1622	devices and so on, there is another party (the sender) that delivers data
		1623	on it's own, but in the case of files, there is no such thing: the disk
		1624	will not send data on it's own, simply because it doesn't know what you
		1625	wish to read - you would first have to request some data.
		1626
		1627	Since files are typically not-so-well supported by advanced notification
		1628	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1629	to files, even though you should not use it. The reason for this is
		1630	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1631	usually a tty, often a pipe, but also sometimes files or special devices
		1632	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1633	F</dev/urandom>), and even though the file might better be served with
		1634	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1635	it "just works" instead of freezing.
		1636
		1637	So avoid file descriptors pointing to files when you know it (e.g. use
		1638	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1639	when you rarely read from a file instead of from a socket, and want to
		1640	reuse the same code path.
		1641
1079	=head3 The special problem of fork	1642	=head3 The special problem of fork
1080		1643
1081	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1644	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
1082	useless behaviour. Libev fully supports fork, but needs to be told about	1645	useless behaviour. Libev fully supports fork, but needs to be told about
1083	it in the child.	1646	it in the child if you want to continue to use it in the child.
1084		1647
1085	To support fork in your programs, you either have to call	1648	To support fork in your child processes, you have to call C<ev_loop_fork
1086	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1649	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1087	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1650	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1088	C<EVBACKEND_POLL>.
1089		1651
		1652	=head3 The special problem of SIGPIPE
		1653
		1654	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1655	when writing to a pipe whose other end has been closed, your program gets
		1656	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1657	this is sensible behaviour, for daemons, this is usually undesirable.
		1658
		1659	So when you encounter spurious, unexplained daemon exits, make sure you
		1660	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1661	somewhere, as that would have given you a big clue).
		1662
		1663	=head3 The special problem of accept()ing when you can't
		1664
		1665	Many implementations of the POSIX C<accept> function (for example,
		1666	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1667	connection from the pending queue in all error cases.
		1668
		1669	For example, larger servers often run out of file descriptors (because
		1670	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1671	rejecting the connection, leading to libev signalling readiness on
		1672	the next iteration again (the connection still exists after all), and
		1673	typically causing the program to loop at 100% CPU usage.
		1674
		1675	Unfortunately, the set of errors that cause this issue differs between
		1676	operating systems, there is usually little the app can do to remedy the
		1677	situation, and no known thread-safe method of removing the connection to
		1678	cope with overload is known (to me).
		1679
		1680	One of the easiest ways to handle this situation is to just ignore it
		1681	- when the program encounters an overload, it will just loop until the
		1682	situation is over. While this is a form of busy waiting, no OS offers an
		1683	event-based way to handle this situation, so it's the best one can do.
		1684
		1685	A better way to handle the situation is to log any errors other than
		1686	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1687	messages, and continue as usual, which at least gives the user an idea of
		1688	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1689	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1690	usage.
		1691
		1692	If your program is single-threaded, then you could also keep a dummy file
		1693	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1694	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1695	close that fd, and create a new dummy fd. This will gracefully refuse
		1696	clients under typical overload conditions.
		1697
		1698	The last way to handle it is to simply log the error and C<exit>, as
		1699	is often done with C<malloc> failures, but this results in an easy
		1700	opportunity for a DoS attack.
1090		1701
1091	=head3 Watcher-Specific Functions	1702	=head3 Watcher-Specific Functions
1092		1703
1093	=over 4	1704	=over 4
1094		1705
1095	=item ev_io_init (ev_io *, callback, int fd, int events)	1706	=item ev_io_init (ev_io *, callback, int fd, int events)
1096		1707
1097	=item ev_io_set (ev_io *, int fd, int events)	1708	=item ev_io_set (ev_io *, int fd, int events)
1098		1709
1099	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1710	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1100	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1711	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
1101	C<EV_READ | EV_WRITE> to receive the given events.	1712	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1102		1713
1103	=item int fd [read-only]	1714	=item int fd [read-only]
1104		1715
1105	The file descriptor being watched.	1716	The file descriptor being watched.
1106		1717
…		…
1114		1725
1115	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1726	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1116	readable, but only once. Since it is likely line-buffered, you could	1727	readable, but only once. Since it is likely line-buffered, you could
1117	attempt to read a whole line in the callback.	1728	attempt to read a whole line in the callback.
1118		1729
1119	static void	1730	static void
1120	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1731	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1121	{	1732	{
1122	ev_io_stop (loop, w);	1733	ev_io_stop (loop, w);
1123	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1734	.. read from stdin here (or from w->fd) and handle any I/O errors
1124	}	1735	}
1125		1736
1126	...	1737	...
1127	struct ev_loop *loop = ev_default_init (0);	1738	struct ev_loop *loop = ev_default_init (0);
1128	struct ev_io stdin_readable;	1739	ev_io stdin_readable;
1129	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1740	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1130	ev_io_start (loop, &stdin_readable);	1741	ev_io_start (loop, &stdin_readable);
1131	ev_loop (loop, 0);	1742	ev_run (loop, 0);
1132		1743
1133		1744
1134	=head2 C<ev_timer> - relative and optionally repeating timeouts	1745	=head2 C<ev_timer> - relative and optionally repeating timeouts
1135		1746
1136	Timer watchers are simple relative timers that generate an event after a	1747	Timer watchers are simple relative timers that generate an event after a
1137	given time, and optionally repeating in regular intervals after that.	1748	given time, and optionally repeating in regular intervals after that.
1138		1749
1139	The timers are based on real time, that is, if you register an event that	1750	The timers are based on real time, that is, if you register an event that
1140	times out after an hour and you reset your system clock to last years	1751	times out after an hour and you reset your system clock to January last
1141	time, it will still time out after (roughly) and hour. "Roughly" because	1752	year, it will still time out after (roughly) one hour. "Roughly" because
1142	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1753	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1143	monotonic clock option helps a lot here).	1754	monotonic clock option helps a lot here).
		1755
		1756	The callback is guaranteed to be invoked only I<after> its timeout has
		1757	passed (not I<at>, so on systems with very low-resolution clocks this
		1758	might introduce a small delay). If multiple timers become ready during the
		1759	same loop iteration then the ones with earlier time-out values are invoked
		1760	before ones of the same priority with later time-out values (but this is
		1761	no longer true when a callback calls C<ev_run> recursively).
		1762
		1763	=head3 Be smart about timeouts
		1764
		1765	Many real-world problems involve some kind of timeout, usually for error
		1766	recovery. A typical example is an HTTP request - if the other side hangs,
		1767	you want to raise some error after a while.
		1768
		1769	What follows are some ways to handle this problem, from obvious and
		1770	inefficient to smart and efficient.
		1771
		1772	In the following, a 60 second activity timeout is assumed - a timeout that
		1773	gets reset to 60 seconds each time there is activity (e.g. each time some
		1774	data or other life sign was received).
		1775
		1776	=over 4
		1777
		1778	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1779
		1780	This is the most obvious, but not the most simple way: In the beginning,
		1781	start the watcher:
		1782
		1783	ev_timer_init (timer, callback, 60., 0.);
		1784	ev_timer_start (loop, timer);
		1785
		1786	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1787	and start it again:
		1788
		1789	ev_timer_stop (loop, timer);
		1790	ev_timer_set (timer, 60., 0.);
		1791	ev_timer_start (loop, timer);
		1792
		1793	This is relatively simple to implement, but means that each time there is
		1794	some activity, libev will first have to remove the timer from its internal
		1795	data structure and then add it again. Libev tries to be fast, but it's
		1796	still not a constant-time operation.
		1797
		1798	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1799
		1800	This is the easiest way, and involves using C<ev_timer_again> instead of
		1801	C<ev_timer_start>.
		1802
		1803	To implement this, configure an C<ev_timer> with a C<repeat> value
		1804	of C<60> and then call C<ev_timer_again> at start and each time you
		1805	successfully read or write some data. If you go into an idle state where
		1806	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1807	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1808
		1809	That means you can ignore both the C<ev_timer_start> function and the
		1810	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1811	member and C<ev_timer_again>.
		1812
		1813	At start:
		1814
		1815	ev_init (timer, callback);
		1816	timer->repeat = 60.;
		1817	ev_timer_again (loop, timer);
		1818
		1819	Each time there is some activity:
		1820
		1821	ev_timer_again (loop, timer);
		1822
		1823	It is even possible to change the time-out on the fly, regardless of
		1824	whether the watcher is active or not:
		1825
		1826	timer->repeat = 30.;
		1827	ev_timer_again (loop, timer);
		1828
		1829	This is slightly more efficient then stopping/starting the timer each time
		1830	you want to modify its timeout value, as libev does not have to completely
		1831	remove and re-insert the timer from/into its internal data structure.
		1832
		1833	It is, however, even simpler than the "obvious" way to do it.
		1834
		1835	=item 3. Let the timer time out, but then re-arm it as required.
		1836
		1837	This method is more tricky, but usually most efficient: Most timeouts are
		1838	relatively long compared to the intervals between other activity - in
		1839	our example, within 60 seconds, there are usually many I/O events with
		1840	associated activity resets.
		1841
		1842	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1843	but remember the time of last activity, and check for a real timeout only
		1844	within the callback:
		1845
		1846	ev_tstamp last_activity; // time of last activity
		1847
		1848	static void
		1849	callback (EV_P_ ev_timer *w, int revents)
		1850	{
		1851	ev_tstamp now = ev_now (EV_A);
		1852	ev_tstamp timeout = last_activity + 60.;
		1853
		1854	// if last_activity + 60. is older than now, we did time out
		1855	if (timeout < now)
		1856	{
		1857	// timeout occurred, take action
		1858	}
		1859	else
		1860	{
		1861	// callback was invoked, but there was some activity, re-arm
		1862	// the watcher to fire in last_activity + 60, which is
		1863	// guaranteed to be in the future, so "again" is positive:
		1864	w->repeat = timeout - now;
		1865	ev_timer_again (EV_A_ w);
		1866	}
		1867	}
		1868
		1869	To summarise the callback: first calculate the real timeout (defined
		1870	as "60 seconds after the last activity"), then check if that time has
		1871	been reached, which means something I<did>, in fact, time out. Otherwise
		1872	the callback was invoked too early (C<timeout> is in the future), so
		1873	re-schedule the timer to fire at that future time, to see if maybe we have
		1874	a timeout then.
		1875
		1876	Note how C<ev_timer_again> is used, taking advantage of the
		1877	C<ev_timer_again> optimisation when the timer is already running.
		1878
		1879	This scheme causes more callback invocations (about one every 60 seconds
		1880	minus half the average time between activity), but virtually no calls to
		1881	libev to change the timeout.
		1882
		1883	To start the timer, simply initialise the watcher and set C<last_activity>
		1884	to the current time (meaning we just have some activity :), then call the
		1885	callback, which will "do the right thing" and start the timer:
		1886
		1887	ev_init (timer, callback);
		1888	last_activity = ev_now (loop);
		1889	callback (loop, timer, EV_TIMER);
		1890
		1891	And when there is some activity, simply store the current time in
		1892	C<last_activity>, no libev calls at all:
		1893
		1894	last_activity = ev_now (loop);
		1895
		1896	This technique is slightly more complex, but in most cases where the
		1897	time-out is unlikely to be triggered, much more efficient.
		1898
		1899	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1900	callback :) - just change the timeout and invoke the callback, which will
		1901	fix things for you.
		1902
		1903	=item 4. Wee, just use a double-linked list for your timeouts.
		1904
		1905	If there is not one request, but many thousands (millions...), all
		1906	employing some kind of timeout with the same timeout value, then one can
		1907	do even better:
		1908
		1909	When starting the timeout, calculate the timeout value and put the timeout
		1910	at the I<end> of the list.
		1911
		1912	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1913	the list is expected to fire (for example, using the technique #3).
		1914
		1915	When there is some activity, remove the timer from the list, recalculate
		1916	the timeout, append it to the end of the list again, and make sure to
		1917	update the C<ev_timer> if it was taken from the beginning of the list.
		1918
		1919	This way, one can manage an unlimited number of timeouts in O(1) time for
		1920	starting, stopping and updating the timers, at the expense of a major
		1921	complication, and having to use a constant timeout. The constant timeout
		1922	ensures that the list stays sorted.
		1923
		1924	=back
		1925
		1926	So which method the best?
		1927
		1928	Method #2 is a simple no-brain-required solution that is adequate in most
		1929	situations. Method #3 requires a bit more thinking, but handles many cases
		1930	better, and isn't very complicated either. In most case, choosing either
		1931	one is fine, with #3 being better in typical situations.
		1932
		1933	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1934	rather complicated, but extremely efficient, something that really pays
		1935	off after the first million or so of active timers, i.e. it's usually
		1936	overkill :)
		1937
		1938	=head3 The special problem of time updates
		1939
		1940	Establishing the current time is a costly operation (it usually takes at
		1941	least two system calls): EV therefore updates its idea of the current
		1942	time only before and after C<ev_run> collects new events, which causes a
		1943	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1944	lots of events in one iteration.
1144		1945
1145	The relative timeouts are calculated relative to the C<ev_now ()>	1946	The relative timeouts are calculated relative to the C<ev_now ()>
1146	time. This is usually the right thing as this timestamp refers to the time	1947	time. This is usually the right thing as this timestamp refers to the time
1147	of the event triggering whatever timeout you are modifying/starting. If	1948	of the event triggering whatever timeout you are modifying/starting. If
1148	you suspect event processing to be delayed and you I<need> to base the timeout	1949	you suspect event processing to be delayed and you I<need> to base the
1149	on the current time, use something like this to adjust for this:	1950	timeout on the current time, use something like this to adjust for this:
1150		1951
1151	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1952	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1152		1953
1153	The callback is guarenteed to be invoked only when its timeout has passed,	1954	If the event loop is suspended for a long time, you can also force an
1154	but if multiple timers become ready during the same loop iteration then	1955	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1155	order of execution is undefined.	1956	()>.
		1957
		1958	=head3 The special problems of suspended animation
		1959
		1960	When you leave the server world it is quite customary to hit machines that
		1961	can suspend/hibernate - what happens to the clocks during such a suspend?
		1962
		1963	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1964	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1965	to run until the system is suspended, but they will not advance while the
		1966	system is suspended. That means, on resume, it will be as if the program
		1967	was frozen for a few seconds, but the suspend time will not be counted
		1968	towards C<ev_timer> when a monotonic clock source is used. The real time
		1969	clock advanced as expected, but if it is used as sole clocksource, then a
		1970	long suspend would be detected as a time jump by libev, and timers would
		1971	be adjusted accordingly.
		1972
		1973	I would not be surprised to see different behaviour in different between
		1974	operating systems, OS versions or even different hardware.
		1975
		1976	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1977	time jump in the monotonic clocks and the realtime clock. If the program
		1978	is suspended for a very long time, and monotonic clock sources are in use,
		1979	then you can expect C<ev_timer>s to expire as the full suspension time
		1980	will be counted towards the timers. When no monotonic clock source is in
		1981	use, then libev will again assume a timejump and adjust accordingly.
		1982
		1983	It might be beneficial for this latter case to call C<ev_suspend>
		1984	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1985	deterministic behaviour in this case (you can do nothing against
		1986	C<SIGSTOP>).
1156		1987
1157	=head3 Watcher-Specific Functions and Data Members	1988	=head3 Watcher-Specific Functions and Data Members
1158		1989
1159	=over 4	1990	=over 4
1160		1991
1161	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1992	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1162		1993
1163	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1994	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1164		1995
1165	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1996	Configure the timer to trigger after C<after> seconds. If C<repeat>
1166	C<0.>, then it will automatically be stopped. If it is positive, then the	1997	is C<0.>, then it will automatically be stopped once the timeout is
1167	timer will automatically be configured to trigger again C<repeat> seconds	1998	reached. If it is positive, then the timer will automatically be
1168	later, again, and again, until stopped manually.	1999	configured to trigger again C<repeat> seconds later, again, and again,
		2000	until stopped manually.
1169		2001
1170	The timer itself will do a best-effort at avoiding drift, that is, if you	2002	The timer itself will do a best-effort at avoiding drift, that is, if
1171	configure a timer to trigger every 10 seconds, then it will trigger at	2003	you configure a timer to trigger every 10 seconds, then it will normally
1172	exactly 10 second intervals. If, however, your program cannot keep up with	2004	trigger at exactly 10 second intervals. If, however, your program cannot
1173	the timer (because it takes longer than those 10 seconds to do stuff) the	2005	keep up with the timer (because it takes longer than those 10 seconds to
1174	timer will not fire more than once per event loop iteration.	2006	do stuff) the timer will not fire more than once per event loop iteration.
1175		2007
1176	=item ev_timer_again (loop, ev_timer *)	2008	=item ev_timer_again (loop, ev_timer *)
1177		2009
1178	This will act as if the timer timed out and restart it again if it is	2010	This will act as if the timer timed out and restart it again if it is
1179	repeating. The exact semantics are:	2011	repeating. The exact semantics are:
1180		2012
1181	If the timer is pending, its pending status is cleared.	2013	If the timer is pending, its pending status is cleared.
1182		2014
1183	If the timer is started but nonrepeating, stop it (as if it timed out).	2015	If the timer is started but non-repeating, stop it (as if it timed out).
1184		2016
1185	If the timer is repeating, either start it if necessary (with the	2017	If the timer is repeating, either start it if necessary (with the
1186	C<repeat> value), or reset the running timer to the C<repeat> value.	2018	C<repeat> value), or reset the running timer to the C<repeat> value.
1187		2019
1188	This sounds a bit complicated, but here is a useful and typical	2020	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1189	example: Imagine you have a tcp connection and you want a so-called idle	2021	usage example.
1190	timeout, that is, you want to be called when there have been, say, 60
1191	seconds of inactivity on the socket. The easiest way to do this is to
1192	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1193	C<ev_timer_again> each time you successfully read or write some data. If
1194	you go into an idle state where you do not expect data to travel on the
1195	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1196	automatically restart it if need be.
1197		2022
1198	That means you can ignore the C<after> value and C<ev_timer_start>	2023	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1199	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1200		2024
1201	ev_timer_init (timer, callback, 0., 5.);	2025	Returns the remaining time until a timer fires. If the timer is active,
1202	ev_timer_again (loop, timer);	2026	then this time is relative to the current event loop time, otherwise it's
1203	...	2027	the timeout value currently configured.
1204	timer->again = 17.;
1205	ev_timer_again (loop, timer);
1206	...
1207	timer->again = 10.;
1208	ev_timer_again (loop, timer);
1209		2028
1210	This is more slightly efficient then stopping/starting the timer each time	2029	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
1211	you want to modify its timeout value.	2030	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		2031	will return C<4>. When the timer expires and is restarted, it will return
		2032	roughly C<7> (likely slightly less as callback invocation takes some time,
		2033	too), and so on.
1212		2034
1213	=item ev_tstamp repeat [read-write]	2035	=item ev_tstamp repeat [read-write]
1214		2036
1215	The current C<repeat> value. Will be used each time the watcher times out	2037	The current C<repeat> value. Will be used each time the watcher times out
1216	or C<ev_timer_again> is called and determines the next timeout (if any),	2038	or C<ev_timer_again> is called, and determines the next timeout (if any),
1217	which is also when any modifications are taken into account.	2039	which is also when any modifications are taken into account.
1218		2040
1219	=back	2041	=back
1220		2042
1221	=head3 Examples	2043	=head3 Examples
1222		2044
1223	Example: Create a timer that fires after 60 seconds.	2045	Example: Create a timer that fires after 60 seconds.
1224		2046
1225	static void	2047	static void
1226	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2048	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1227	{	2049	{
1228	.. one minute over, w is actually stopped right here	2050	.. one minute over, w is actually stopped right here
1229	}	2051	}
1230		2052
1231	struct ev_timer mytimer;	2053	ev_timer mytimer;
1232	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	2054	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1233	ev_timer_start (loop, &mytimer);	2055	ev_timer_start (loop, &mytimer);
1234		2056
1235	Example: Create a timeout timer that times out after 10 seconds of	2057	Example: Create a timeout timer that times out after 10 seconds of
1236	inactivity.	2058	inactivity.
1237		2059
1238	static void	2060	static void
1239	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2061	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1240	{	2062	{
1241	.. ten seconds without any activity	2063	.. ten seconds without any activity
1242	}	2064	}
1243		2065
1244	struct ev_timer mytimer;	2066	ev_timer mytimer;
1245	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	2067	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1246	ev_timer_again (&mytimer); /* start timer */	2068	ev_timer_again (&mytimer); /* start timer */
1247	ev_loop (loop, 0);	2069	ev_run (loop, 0);
1248		2070
1249	// and in some piece of code that gets executed on any "activity":	2071	// and in some piece of code that gets executed on any "activity":
1250	// reset the timeout to start ticking again at 10 seconds	2072	// reset the timeout to start ticking again at 10 seconds
1251	ev_timer_again (&mytimer);	2073	ev_timer_again (&mytimer);
1252		2074
1253		2075
1254	=head2 C<ev_periodic> - to cron or not to cron?	2076	=head2 C<ev_periodic> - to cron or not to cron?
1255		2077
1256	Periodic watchers are also timers of a kind, but they are very versatile	2078	Periodic watchers are also timers of a kind, but they are very versatile
1257	(and unfortunately a bit complex).	2079	(and unfortunately a bit complex).
1258		2080
1259	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2081	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1260	but on wallclock time (absolute time). You can tell a periodic watcher	2082	relative time, the physical time that passes) but on wall clock time
1261	to trigger "at" some specific point in time. For example, if you tell a	2083	(absolute time, the thing you can read on your calender or clock). The
1262	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	2084	difference is that wall clock time can run faster or slower than real
1263	+ 10.>) and then reset your system clock to the last year, then it will	2085	time, and time jumps are not uncommon (e.g. when you adjust your
1264	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	2086	wrist-watch).
1265	roughly 10 seconds later).
1266		2087
1267	They can also be used to implement vastly more complex timers, such as	2088	You can tell a periodic watcher to trigger after some specific point
1268	triggering an event on each midnight, local time or other, complicated,	2089	in time: for example, if you tell a periodic watcher to trigger "in 10
1269	rules.	2090	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2091	not a delay) and then reset your system clock to January of the previous
		2092	year, then it will take a year or more to trigger the event (unlike an
		2093	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2094	it, as it uses a relative timeout).
1270		2095
		2096	C<ev_periodic> watchers can also be used to implement vastly more complex
		2097	timers, such as triggering an event on each "midnight, local time", or
		2098	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		2099	those cannot react to time jumps.
		2100
1271	As with timers, the callback is guarenteed to be invoked only when the	2101	As with timers, the callback is guaranteed to be invoked only when the
1272	time (C<at>) has been passed, but if multiple periodic timers become ready	2102	point in time where it is supposed to trigger has passed. If multiple
1273	during the same loop iteration then order of execution is undefined.	2103	timers become ready during the same loop iteration then the ones with
		2104	earlier time-out values are invoked before ones with later time-out values
		2105	(but this is no longer true when a callback calls C<ev_run> recursively).
1274		2106
1275	=head3 Watcher-Specific Functions and Data Members	2107	=head3 Watcher-Specific Functions and Data Members
1276		2108
1277	=over 4	2109	=over 4
1278		2110
1279	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2111	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1280		2112
1281	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2113	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1282		2114
1283	Lots of arguments, lets sort it out... There are basically three modes of	2115	Lots of arguments, let's sort it out... There are basically three modes of
1284	operation, and we will explain them from simplest to complex:	2116	operation, and we will explain them from simplest to most complex:
1285		2117
1286	=over 4	2118	=over 4
1287		2119
1288	=item * absolute timer (at = time, interval = reschedule_cb = 0)	2120	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1289		2121
1290	In this configuration the watcher triggers an event at the wallclock time	2122	In this configuration the watcher triggers an event after the wall clock
1291	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	2123	time C<offset> has passed. It will not repeat and will not adjust when a
1292	that is, if it is to be run at January 1st 2011 then it will run when the	2124	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1293	system time reaches or surpasses this time.	2125	will be stopped and invoked when the system clock reaches or surpasses
		2126	this point in time.
1294		2127
1295	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	2128	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1296		2129
1297	In this mode the watcher will always be scheduled to time out at the next	2130	In this mode the watcher will always be scheduled to time out at the next
1298	C<at + N * interval> time (for some integer N, which can also be negative)	2131	C<offset + N * interval> time (for some integer N, which can also be
1299	and then repeat, regardless of any time jumps.	2132	negative) and then repeat, regardless of any time jumps. The C<offset>
		2133	argument is merely an offset into the C<interval> periods.
1300		2134
1301	This can be used to create timers that do not drift with respect to system	2135	This can be used to create timers that do not drift with respect to the
1302	time:	2136	system clock, for example, here is an C<ev_periodic> that triggers each
		2137	hour, on the hour (with respect to UTC):
1303		2138
1304	ev_periodic_set (&periodic, 0., 3600., 0);	2139	ev_periodic_set (&periodic, 0., 3600., 0);
1305		2140
1306	This doesn't mean there will always be 3600 seconds in between triggers,	2141	This doesn't mean there will always be 3600 seconds in between triggers,
1307	but only that the the callback will be called when the system time shows a	2142	but only that the callback will be called when the system time shows a
1308	full hour (UTC), or more correctly, when the system time is evenly divisible	2143	full hour (UTC), or more correctly, when the system time is evenly divisible
1309	by 3600.	2144	by 3600.
1310		2145
1311	Another way to think about it (for the mathematically inclined) is that	2146	Another way to think about it (for the mathematically inclined) is that
1312	C<ev_periodic> will try to run the callback in this mode at the next possible	2147	C<ev_periodic> will try to run the callback in this mode at the next possible
1313	time where C<time = at (mod interval)>, regardless of any time jumps.	2148	time where C<time = offset (mod interval)>, regardless of any time jumps.
1314		2149
1315	For numerical stability it is preferable that the C<at> value is near	2150	For numerical stability it is preferable that the C<offset> value is near
1316	C<ev_now ()> (the current time), but there is no range requirement for	2151	C<ev_now ()> (the current time), but there is no range requirement for
1317	this value.	2152	this value, and in fact is often specified as zero.
1318		2153
		2154	Note also that there is an upper limit to how often a timer can fire (CPU
		2155	speed for example), so if C<interval> is very small then timing stability
		2156	will of course deteriorate. Libev itself tries to be exact to be about one
		2157	millisecond (if the OS supports it and the machine is fast enough).
		2158
1319	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	2159	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1320		2160
1321	In this mode the values for C<interval> and C<at> are both being	2161	In this mode the values for C<interval> and C<offset> are both being
1322	ignored. Instead, each time the periodic watcher gets scheduled, the	2162	ignored. Instead, each time the periodic watcher gets scheduled, the
1323	reschedule callback will be called with the watcher as first, and the	2163	reschedule callback will be called with the watcher as first, and the
1324	current time as second argument.	2164	current time as second argument.
1325		2165
1326	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2166	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1327	ever, or make any event loop modifications>. If you need to stop it,	2167	or make ANY other event loop modifications whatsoever, unless explicitly
1328	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	2168	allowed by documentation here>.
1329	starting an C<ev_prepare> watcher, which is legal).
1330		2169
		2170	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2171	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2172	only event loop modification you are allowed to do).
		2173
1331	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2174	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1332	ev_tstamp now)>, e.g.:	2175	*w, ev_tstamp now)>, e.g.:
1333		2176
		2177	static ev_tstamp
1334	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2178	my_rescheduler (ev_periodic *w, ev_tstamp now)
1335	{	2179	{
1336	return now + 60.;	2180	return now + 60.;
1337	}	2181	}
1338		2182
1339	It must return the next time to trigger, based on the passed time value	2183	It must return the next time to trigger, based on the passed time value
1340	(that is, the lowest time value larger than to the second argument). It	2184	(that is, the lowest time value larger than to the second argument). It
1341	will usually be called just before the callback will be triggered, but	2185	will usually be called just before the callback will be triggered, but
1342	might be called at other times, too.	2186	might be called at other times, too.
1343		2187
1344	NOTE: I<< This callback must always return a time that is later than the	2188	NOTE: I<< This callback must always return a time that is higher than or
1345	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2189	equal to the passed C<now> value >>.
1346		2190
1347	This can be used to create very complex timers, such as a timer that	2191	This can be used to create very complex timers, such as a timer that
1348	triggers on each midnight, local time. To do this, you would calculate the	2192	triggers on "next midnight, local time". To do this, you would calculate the
1349	next midnight after C<now> and return the timestamp value for this. How	2193	next midnight after C<now> and return the timestamp value for this. How
1350	you do this is, again, up to you (but it is not trivial, which is the main	2194	you do this is, again, up to you (but it is not trivial, which is the main
1351	reason I omitted it as an example).	2195	reason I omitted it as an example).
1352		2196
1353	=back	2197	=back
…		…
1357	Simply stops and restarts the periodic watcher again. This is only useful	2201	Simply stops and restarts the periodic watcher again. This is only useful
1358	when you changed some parameters or the reschedule callback would return	2202	when you changed some parameters or the reschedule callback would return
1359	a different time than the last time it was called (e.g. in a crond like	2203	a different time than the last time it was called (e.g. in a crond like
1360	program when the crontabs have changed).	2204	program when the crontabs have changed).
1361		2205
		2206	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2207
		2208	When active, returns the absolute time that the watcher is supposed
		2209	to trigger next. This is not the same as the C<offset> argument to
		2210	C<ev_periodic_set>, but indeed works even in interval and manual
		2211	rescheduling modes.
		2212
1362	=item ev_tstamp offset [read-write]	2213	=item ev_tstamp offset [read-write]
1363		2214
1364	When repeating, this contains the offset value, otherwise this is the	2215	When repeating, this contains the offset value, otherwise this is the
1365	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2216	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2217	although libev might modify this value for better numerical stability).
1366		2218
1367	Can be modified any time, but changes only take effect when the periodic	2219	Can be modified any time, but changes only take effect when the periodic
1368	timer fires or C<ev_periodic_again> is being called.	2220	timer fires or C<ev_periodic_again> is being called.
1369		2221
1370	=item ev_tstamp interval [read-write]	2222	=item ev_tstamp interval [read-write]
1371		2223
1372	The current interval value. Can be modified any time, but changes only	2224	The current interval value. Can be modified any time, but changes only
1373	take effect when the periodic timer fires or C<ev_periodic_again> is being	2225	take effect when the periodic timer fires or C<ev_periodic_again> is being
1374	called.	2226	called.
1375		2227
1376	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2228	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1377		2229
1378	The current reschedule callback, or C<0>, if this functionality is	2230	The current reschedule callback, or C<0>, if this functionality is
1379	switched off. Can be changed any time, but changes only take effect when	2231	switched off. Can be changed any time, but changes only take effect when
1380	the periodic timer fires or C<ev_periodic_again> is being called.	2232	the periodic timer fires or C<ev_periodic_again> is being called.
1381		2233
1382	=item ev_tstamp at [read-only]
1383
1384	When active, contains the absolute time that the watcher is supposed to
1385	trigger next.
1386
1387	=back	2234	=back
1388		2235
1389	=head3 Examples	2236	=head3 Examples
1390		2237
1391	Example: Call a callback every hour, or, more precisely, whenever the	2238	Example: Call a callback every hour, or, more precisely, whenever the
1392	system clock is divisible by 3600. The callback invocation times have	2239	system time is divisible by 3600. The callback invocation times have
1393	potentially a lot of jittering, but good long-term stability.	2240	potentially a lot of jitter, but good long-term stability.
1394		2241
1395	static void	2242	static void
1396	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2243	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1397	{	2244	{
1398	... its now a full hour (UTC, or TAI or whatever your clock follows)	2245	... its now a full hour (UTC, or TAI or whatever your clock follows)
1399	}	2246	}
1400		2247
1401	struct ev_periodic hourly_tick;	2248	ev_periodic hourly_tick;
1402	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2249	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1403	ev_periodic_start (loop, &hourly_tick);	2250	ev_periodic_start (loop, &hourly_tick);
1404		2251
1405	Example: The same as above, but use a reschedule callback to do it:	2252	Example: The same as above, but use a reschedule callback to do it:
1406		2253
1407	#include <math.h>	2254	#include <math.h>
1408		2255
1409	static ev_tstamp	2256	static ev_tstamp
1410	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2257	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1411	{	2258	{
1412	return fmod (now, 3600.) + 3600.;	2259	return now + (3600. - fmod (now, 3600.));
1413	}	2260	}
1414		2261
1415	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2262	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1416		2263
1417	Example: Call a callback every hour, starting now:	2264	Example: Call a callback every hour, starting now:
1418		2265
1419	struct ev_periodic hourly_tick;	2266	ev_periodic hourly_tick;
1420	ev_periodic_init (&hourly_tick, clock_cb,	2267	ev_periodic_init (&hourly_tick, clock_cb,
1421	fmod (ev_now (loop), 3600.), 3600., 0);	2268	fmod (ev_now (loop), 3600.), 3600., 0);
1422	ev_periodic_start (loop, &hourly_tick);	2269	ev_periodic_start (loop, &hourly_tick);
1423		2270
1424		2271
1425	=head2 C<ev_signal> - signal me when a signal gets signalled!	2272	=head2 C<ev_signal> - signal me when a signal gets signalled!
1426		2273
1427	Signal watchers will trigger an event when the process receives a specific	2274	Signal watchers will trigger an event when the process receives a specific
1428	signal one or more times. Even though signals are very asynchronous, libev	2275	signal one or more times. Even though signals are very asynchronous, libev
1429	will try it's best to deliver signals synchronously, i.e. as part of the	2276	will try its best to deliver signals synchronously, i.e. as part of the
1430	normal event processing, like any other event.	2277	normal event processing, like any other event.
1431		2278
		2279	If you want signals to be delivered truly asynchronously, just use
		2280	C<sigaction> as you would do without libev and forget about sharing
		2281	the signal. You can even use C<ev_async> from a signal handler to
		2282	synchronously wake up an event loop.
		2283
1432	You can configure as many watchers as you like per signal. Only when the	2284	You can configure as many watchers as you like for the same signal, but
		2285	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2286	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2287	C<SIGINT> in both the default loop and another loop at the same time. At
		2288	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2289
1433	first watcher gets started will libev actually register a signal watcher	2290	When the first watcher gets started will libev actually register something
1434	with the kernel (thus it coexists with your own signal handlers as long	2291	with the kernel (thus it coexists with your own signal handlers as long as
1435	as you don't register any with libev). Similarly, when the last signal	2292	you don't register any with libev for the same signal).
1436	watcher for a signal is stopped libev will reset the signal handler to
1437	SIG_DFL (regardless of what it was set to before).
1438		2293
1439	If possible and supported, libev will install its handlers with	2294	If possible and supported, libev will install its handlers with
1440	C<SA_RESTART> behaviour enabled, so syscalls should not be unduly	2295	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
1441	interrupted. If you have a problem with syscalls getting interrupted by	2296	not be unduly interrupted. If you have a problem with system calls getting
1442	signals you can block all signals in an C<ev_check> watcher and unblock	2297	interrupted by signals you can block all signals in an C<ev_check> watcher
1443	them in an C<ev_prepare> watcher.	2298	and unblock them in an C<ev_prepare> watcher.
		2299
		2300	=head3 The special problem of inheritance over fork/execve/pthread_create
		2301
		2302	Both the signal mask (C<sigprocmask>) and the signal disposition
		2303	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2304	stopping it again), that is, libev might or might not block the signal,
		2305	and might or might not set or restore the installed signal handler.
		2306
		2307	While this does not matter for the signal disposition (libev never
		2308	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2309	C<execve>), this matters for the signal mask: many programs do not expect
		2310	certain signals to be blocked.
		2311
		2312	This means that before calling C<exec> (from the child) you should reset
		2313	the signal mask to whatever "default" you expect (all clear is a good
		2314	choice usually).
		2315
		2316	The simplest way to ensure that the signal mask is reset in the child is
		2317	to install a fork handler with C<pthread_atfork> that resets it. That will
		2318	catch fork calls done by libraries (such as the libc) as well.
		2319
		2320	In current versions of libev, the signal will not be blocked indefinitely
		2321	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2322	the window of opportunity for problems, it will not go away, as libev
		2323	I<has> to modify the signal mask, at least temporarily.
		2324
		2325	So I can't stress this enough: I<If you do not reset your signal mask when
		2326	you expect it to be empty, you have a race condition in your code>. This
		2327	is not a libev-specific thing, this is true for most event libraries.
		2328
		2329	=head3 The special problem of threads signal handling
		2330
		2331	POSIX threads has problematic signal handling semantics, specifically,
		2332	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2333	threads in a process block signals, which is hard to achieve.
		2334
		2335	When you want to use sigwait (or mix libev signal handling with your own
		2336	for the same signals), you can tackle this problem by globally blocking
		2337	all signals before creating any threads (or creating them with a fully set
		2338	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2339	loops. Then designate one thread as "signal receiver thread" which handles
		2340	these signals. You can pass on any signals that libev might be interested
		2341	in by calling C<ev_feed_signal>.
1444		2342
1445	=head3 Watcher-Specific Functions and Data Members	2343	=head3 Watcher-Specific Functions and Data Members
1446		2344
1447	=over 4	2345	=over 4
1448		2346
…		…
1459		2357
1460	=back	2358	=back
1461		2359
1462	=head3 Examples	2360	=head3 Examples
1463		2361
1464	Example: Try to exit cleanly on SIGINT and SIGTERM.	2362	Example: Try to exit cleanly on SIGINT.
1465		2363
1466	static void	2364	static void
1467	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2365	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
1468	{	2366	{
1469	ev_unloop (loop, EVUNLOOP_ALL);	2367	ev_break (loop, EVBREAK_ALL);
1470	}	2368	}
1471		2369
1472	struct ev_signal signal_watcher;	2370	ev_signal signal_watcher;
1473	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2371	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1474	ev_signal_start (loop, &sigint_cb);	2372	ev_signal_start (loop, &signal_watcher);
1475		2373
1476		2374
1477	=head2 C<ev_child> - watch out for process status changes	2375	=head2 C<ev_child> - watch out for process status changes
1478		2376
1479	Child watchers trigger when your process receives a SIGCHLD in response to	2377	Child watchers trigger when your process receives a SIGCHLD in response to
1480	some child status changes (most typically when a child of yours dies). It	2378	some child status changes (most typically when a child of yours dies or
1481	is permissible to install a child watcher I<after> the child has been	2379	exits). It is permissible to install a child watcher I<after> the child
1482	forked (which implies it might have already exited), as long as the event	2380	has been forked (which implies it might have already exited), as long
1483	loop isn't entered (or is continued from a watcher).	2381	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2382	forking and then immediately registering a watcher for the child is fine,
		2383	but forking and registering a watcher a few event loop iterations later or
		2384	in the next callback invocation is not.
1484		2385
1485	Only the default event loop is capable of handling signals, and therefore	2386	Only the default event loop is capable of handling signals, and therefore
1486	you can only rgeister child watchers in the default event loop.	2387	you can only register child watchers in the default event loop.
		2388
		2389	Due to some design glitches inside libev, child watchers will always be
		2390	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2391	libev)
1487		2392
1488	=head3 Process Interaction	2393	=head3 Process Interaction
1489		2394
1490	Libev grabs C<SIGCHLD> as soon as the default event loop is	2395	Libev grabs C<SIGCHLD> as soon as the default event loop is
1491	initialised. This is necessary to guarantee proper behaviour even if	2396	initialised. This is necessary to guarantee proper behaviour even if the
1492	the first child watcher is started after the child exits. The occurance	2397	first child watcher is started after the child exits. The occurrence
1493	of C<SIGCHLD> is recorded asynchronously, but child reaping is done	2398	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
1494	synchronously as part of the event loop processing. Libev always reaps all	2399	synchronously as part of the event loop processing. Libev always reaps all
1495	children, even ones not watched.	2400	children, even ones not watched.
1496		2401
1497	=head3 Overriding the Built-In Processing	2402	=head3 Overriding the Built-In Processing
…		…
1501	handler, you can override it easily by installing your own handler for	2406	handler, you can override it easily by installing your own handler for
1502	C<SIGCHLD> after initialising the default loop, and making sure the	2407	C<SIGCHLD> after initialising the default loop, and making sure the
1503	default loop never gets destroyed. You are encouraged, however, to use an	2408	default loop never gets destroyed. You are encouraged, however, to use an
1504	event-based approach to child reaping and thus use libev's support for	2409	event-based approach to child reaping and thus use libev's support for
1505	that, so other libev users can use C<ev_child> watchers freely.	2410	that, so other libev users can use C<ev_child> watchers freely.
		2411
		2412	=head3 Stopping the Child Watcher
		2413
		2414	Currently, the child watcher never gets stopped, even when the
		2415	child terminates, so normally one needs to stop the watcher in the
		2416	callback. Future versions of libev might stop the watcher automatically
		2417	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2418	problem).
1506		2419
1507	=head3 Watcher-Specific Functions and Data Members	2420	=head3 Watcher-Specific Functions and Data Members
1508		2421
1509	=over 4	2422	=over 4
1510		2423
…		…
1539	=head3 Examples	2452	=head3 Examples
1540		2453
1541	Example: C<fork()> a new process and install a child handler to wait for	2454	Example: C<fork()> a new process and install a child handler to wait for
1542	its completion.	2455	its completion.
1543		2456
1544	ev_child cw;	2457	ev_child cw;
1545		2458
1546	static void	2459	static void
1547	child_cb (EV_P_ struct ev_child *w, int revents)	2460	child_cb (EV_P_ ev_child *w, int revents)
1548	{	2461	{
1549	ev_child_stop (EV_A_ w);	2462	ev_child_stop (EV_A_ w);
1550	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);	2463	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1551	}	2464	}
1552		2465
1553	pid_t pid = fork ();	2466	pid_t pid = fork ();
1554		2467
1555	if (pid < 0)	2468	if (pid < 0)
1556	// error	2469	// error
1557	else if (pid == 0)	2470	else if (pid == 0)
1558	{	2471	{
1559	// the forked child executes here	2472	// the forked child executes here
1560	exit (1);	2473	exit (1);
1561	}	2474	}
1562	else	2475	else
1563	{	2476	{
1564	ev_child_init (&cw, child_cb, pid, 0);	2477	ev_child_init (&cw, child_cb, pid, 0);
1565	ev_child_start (EV_DEFAULT_ &cw);	2478	ev_child_start (EV_DEFAULT_ &cw);
1566	}	2479	}
1567		2480
1568		2481
1569	=head2 C<ev_stat> - did the file attributes just change?	2482	=head2 C<ev_stat> - did the file attributes just change?
1570		2483
1571	This watches a filesystem path for attribute changes. That is, it calls	2484	This watches a file system path for attribute changes. That is, it calls
1572	C<stat> regularly (or when the OS says it changed) and sees if it changed	2485	C<stat> on that path in regular intervals (or when the OS says it changed)
1573	compared to the last time, invoking the callback if it did.	2486	and sees if it changed compared to the last time, invoking the callback if
		2487	it did.
1574		2488
1575	The path does not need to exist: changing from "path exists" to "path does	2489	The path does not need to exist: changing from "path exists" to "path does
1576	not exist" is a status change like any other. The condition "path does	2490	not exist" is a status change like any other. The condition "path does not
1577	not exist" is signified by the C<st_nlink> field being zero (which is	2491	exist" (or more correctly "path cannot be stat'ed") is signified by the
1578	otherwise always forced to be at least one) and all the other fields of	2492	C<st_nlink> field being zero (which is otherwise always forced to be at
1579	the stat buffer having unspecified contents.	2493	least one) and all the other fields of the stat buffer having unspecified
		2494	contents.
1580		2495
1581	The path I<should> be absolute and I<must not> end in a slash. If it is	2496	The path I<must not> end in a slash or contain special components such as
		2497	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1582	relative and your working directory changes, the behaviour is undefined.	2498	your working directory changes, then the behaviour is undefined.
1583		2499
1584	Since there is no standard to do this, the portable implementation simply	2500	Since there is no portable change notification interface available, the
1585	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2501	portable implementation simply calls C<stat(2)> regularly on the path
1586	can specify a recommended polling interval for this case. If you specify	2502	to see if it changed somehow. You can specify a recommended polling
1587	a polling interval of C<0> (highly recommended!) then a I<suitable,	2503	interval for this case. If you specify a polling interval of C<0> (highly
1588	unspecified default> value will be used (which you can expect to be around	2504	recommended!) then a I<suitable, unspecified default> value will be used
1589	five seconds, although this might change dynamically). Libev will also	2505	(which you can expect to be around five seconds, although this might
1590	impose a minimum interval which is currently around C<0.1>, but thats	2506	change dynamically). Libev will also impose a minimum interval which is
1591	usually overkill.	2507	currently around C<0.1>, but that's usually overkill.
1592		2508
1593	This watcher type is not meant for massive numbers of stat watchers,	2509	This watcher type is not meant for massive numbers of stat watchers,
1594	as even with OS-supported change notifications, this can be	2510	as even with OS-supported change notifications, this can be
1595	resource-intensive.	2511	resource-intensive.
1596		2512
1597	At the time of this writing, only the Linux inotify interface is	2513	At the time of this writing, the only OS-specific interface implemented
1598	implemented (implementing kqueue support is left as an exercise for the	2514	is the Linux inotify interface (implementing kqueue support is left as an
1599	reader). Inotify will be used to give hints only and should not change the	2515	exercise for the reader. Note, however, that the author sees no way of
1600	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2516	implementing C<ev_stat> semantics with kqueue, except as a hint).
1601	to fall back to regular polling again even with inotify, but changes are
1602	usually detected immediately, and if the file exists there will be no
1603	polling.
1604		2517
1605	=head3 Inotify	2518	=head3 ABI Issues (Largefile Support)
1606		2519
		2520	Libev by default (unless the user overrides this) uses the default
		2521	compilation environment, which means that on systems with large file
		2522	support disabled by default, you get the 32 bit version of the stat
		2523	structure. When using the library from programs that change the ABI to
		2524	use 64 bit file offsets the programs will fail. In that case you have to
		2525	compile libev with the same flags to get binary compatibility. This is
		2526	obviously the case with any flags that change the ABI, but the problem is
		2527	most noticeably displayed with ev_stat and large file support.
		2528
		2529	The solution for this is to lobby your distribution maker to make large
		2530	file interfaces available by default (as e.g. FreeBSD does) and not
		2531	optional. Libev cannot simply switch on large file support because it has
		2532	to exchange stat structures with application programs compiled using the
		2533	default compilation environment.
		2534
		2535	=head3 Inotify and Kqueue
		2536
1607	When C<inotify (7)> support has been compiled into libev (generally only	2537	When C<inotify (7)> support has been compiled into libev and present at
1608	available on Linux) and present at runtime, it will be used to speed up	2538	runtime, it will be used to speed up change detection where possible. The
1609	change detection where possible. The inotify descriptor will be created lazily	2539	inotify descriptor will be created lazily when the first C<ev_stat>
1610	when the first C<ev_stat> watcher is being started.	2540	watcher is being started.
1611		2541
1612	Inotify presense does not change the semantics of C<ev_stat> watchers	2542	Inotify presence does not change the semantics of C<ev_stat> watchers
1613	except that changes might be detected earlier, and in some cases, to avoid	2543	except that changes might be detected earlier, and in some cases, to avoid
1614	making regular C<stat> calls. Even in the presense of inotify support	2544	making regular C<stat> calls. Even in the presence of inotify support
1615	there are many cases where libev has to resort to regular C<stat> polling.	2545	there are many cases where libev has to resort to regular C<stat> polling,
		2546	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2547	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2548	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2549	xfs are fully working) libev usually gets away without polling.
1616		2550
1617	(There is no support for kqueue, as apparently it cannot be used to	2551	There is no support for kqueue, as apparently it cannot be used to
1618	implement this functionality, due to the requirement of having a file	2552	implement this functionality, due to the requirement of having a file
1619	descriptor open on the object at all times).	2553	descriptor open on the object at all times, and detecting renames, unlinks
		2554	etc. is difficult.
		2555
		2556	=head3 C<stat ()> is a synchronous operation
		2557
		2558	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2559	the process. The exception are C<ev_stat> watchers - those call C<stat
		2560	()>, which is a synchronous operation.
		2561
		2562	For local paths, this usually doesn't matter: unless the system is very
		2563	busy or the intervals between stat's are large, a stat call will be fast,
		2564	as the path data is usually in memory already (except when starting the
		2565	watcher).
		2566
		2567	For networked file systems, calling C<stat ()> can block an indefinite
		2568	time due to network issues, and even under good conditions, a stat call
		2569	often takes multiple milliseconds.
		2570
		2571	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2572	paths, although this is fully supported by libev.
1620		2573
1621	=head3 The special problem of stat time resolution	2574	=head3 The special problem of stat time resolution
1622		2575
1623	The C<stat ()> syscall only supports full-second resolution portably, and	2576	The C<stat ()> system call only supports full-second resolution portably,
1624	even on systems where the resolution is higher, many filesystems still	2577	and even on systems where the resolution is higher, most file systems
1625	only support whole seconds.	2578	still only support whole seconds.
1626		2579
1627	That means that, if the time is the only thing that changes, you might	2580	That means that, if the time is the only thing that changes, you can
1628	miss updates: on the first update, C<ev_stat> detects a change and calls	2581	easily miss updates: on the first update, C<ev_stat> detects a change and
1629	your callback, which does something. When there is another update within	2582	calls your callback, which does something. When there is another update
1630	the same second, C<ev_stat> will be unable to detect it.	2583	within the same second, C<ev_stat> will be unable to detect unless the
		2584	stat data does change in other ways (e.g. file size).
1631		2585
1632	The solution to this is to delay acting on a change for a second (or till	2586	The solution to this is to delay acting on a change for slightly more
1633	the next second boundary), using a roughly one-second delay C<ev_timer>	2587	than a second (or till slightly after the next full second boundary), using
1634	(C<ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)>). The C<.01>	2588	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
1635	is added to work around small timing inconsistencies of some operating	2589	ev_timer_again (loop, w)>).
1636	systems.	2590
		2591	The C<.02> offset is added to work around small timing inconsistencies
		2592	of some operating systems (where the second counter of the current time
		2593	might be be delayed. One such system is the Linux kernel, where a call to
		2594	C<gettimeofday> might return a timestamp with a full second later than
		2595	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2596	update file times then there will be a small window where the kernel uses
		2597	the previous second to update file times but libev might already execute
		2598	the timer callback).
1637		2599
1638	=head3 Watcher-Specific Functions and Data Members	2600	=head3 Watcher-Specific Functions and Data Members
1639		2601
1640	=over 4	2602	=over 4
1641		2603
…		…
1647	C<path>. The C<interval> is a hint on how quickly a change is expected to	2609	C<path>. The C<interval> is a hint on how quickly a change is expected to
1648	be detected and should normally be specified as C<0> to let libev choose	2610	be detected and should normally be specified as C<0> to let libev choose
1649	a suitable value. The memory pointed to by C<path> must point to the same	2611	a suitable value. The memory pointed to by C<path> must point to the same
1650	path for as long as the watcher is active.	2612	path for as long as the watcher is active.
1651		2613
1652	The callback will be receive C<EV_STAT> when a change was detected,	2614	The callback will receive an C<EV_STAT> event when a change was detected,
1653	relative to the attributes at the time the watcher was started (or the	2615	relative to the attributes at the time the watcher was started (or the
1654	last change was detected).	2616	last change was detected).
1655		2617
1656	=item ev_stat_stat (loop, ev_stat *)	2618	=item ev_stat_stat (loop, ev_stat *)
1657		2619
1658	Updates the stat buffer immediately with new values. If you change the	2620	Updates the stat buffer immediately with new values. If you change the
1659	watched path in your callback, you could call this fucntion to avoid	2621	watched path in your callback, you could call this function to avoid
1660	detecting this change (while introducing a race condition). Can also be	2622	detecting this change (while introducing a race condition if you are not
1661	useful simply to find out the new values.	2623	the only one changing the path). Can also be useful simply to find out the
		2624	new values.
1662		2625
1663	=item ev_statdata attr [read-only]	2626	=item ev_statdata attr [read-only]
1664		2627
1665	The most-recently detected attributes of the file. Although the type is of	2628	The most-recently detected attributes of the file. Although the type is
1666	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2629	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1667	suitable for your system. If the C<st_nlink> member is C<0>, then there	2630	suitable for your system, but you can only rely on the POSIX-standardised
		2631	members to be present. If the C<st_nlink> member is C<0>, then there was
1668	was some error while C<stat>ing the file.	2632	some error while C<stat>ing the file.
1669		2633
1670	=item ev_statdata prev [read-only]	2634	=item ev_statdata prev [read-only]
1671		2635
1672	The previous attributes of the file. The callback gets invoked whenever	2636	The previous attributes of the file. The callback gets invoked whenever
1673	C<prev> != C<attr>.	2637	C<prev> != C<attr>, or, more precisely, one or more of these members
		2638	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2639	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1674		2640
1675	=item ev_tstamp interval [read-only]	2641	=item ev_tstamp interval [read-only]
1676		2642
1677	The specified interval.	2643	The specified interval.
1678		2644
1679	=item const char *path [read-only]	2645	=item const char *path [read-only]
1680		2646
1681	The filesystem path that is being watched.	2647	The file system path that is being watched.
1682		2648
1683	=back	2649	=back
1684		2650
1685	=head3 Examples	2651	=head3 Examples
1686		2652
1687	Example: Watch C</etc/passwd> for attribute changes.	2653	Example: Watch C</etc/passwd> for attribute changes.
1688		2654
1689	static void	2655	static void
1690	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2656	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1691	{	2657	{
1692	/* /etc/passwd changed in some way */	2658	/* /etc/passwd changed in some way */
1693	if (w->attr.st_nlink)	2659	if (w->attr.st_nlink)
1694	{	2660	{
1695	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2661	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1696	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2662	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1697	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2663	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1698	}	2664	}
1699	else	2665	else
1700	/* you shalt not abuse printf for puts */	2666	/* you shalt not abuse printf for puts */
1701	puts ("wow, /etc/passwd is not there, expect problems. "	2667	puts ("wow, /etc/passwd is not there, expect problems. "
1702	"if this is windows, they already arrived\n");	2668	"if this is windows, they already arrived\n");
1703	}	2669	}
1704		2670
1705	...	2671	...
1706	ev_stat passwd;	2672	ev_stat passwd;
1707		2673
1708	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);	2674	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1709	ev_stat_start (loop, &passwd);	2675	ev_stat_start (loop, &passwd);
1710		2676
1711	Example: Like above, but additionally use a one-second delay so we do not	2677	Example: Like above, but additionally use a one-second delay so we do not
1712	miss updates (however, frequent updates will delay processing, too, so	2678	miss updates (however, frequent updates will delay processing, too, so
1713	one might do the work both on C<ev_stat> callback invocation I<and> on	2679	one might do the work both on C<ev_stat> callback invocation I<and> on
1714	C<ev_timer> callback invocation).	2680	C<ev_timer> callback invocation).
1715		2681
1716	static ev_stat passwd;	2682	static ev_stat passwd;
1717	static ev_timer timer;	2683	static ev_timer timer;
1718		2684
1719	static void	2685	static void
1720	timer_cb (EV_P_ ev_timer *w, int revents)	2686	timer_cb (EV_P_ ev_timer *w, int revents)
1721	{	2687	{
1722	ev_timer_stop (EV_A_ w);	2688	ev_timer_stop (EV_A_ w);
1723		2689
1724	/* now it's one second after the most recent passwd change */	2690	/* now it's one second after the most recent passwd change */
1725	}	2691	}
1726		2692
1727	static void	2693	static void
1728	stat_cb (EV_P_ ev_stat *w, int revents)	2694	stat_cb (EV_P_ ev_stat *w, int revents)
1729	{	2695	{
1730	/* reset the one-second timer */	2696	/* reset the one-second timer */
1731	ev_timer_again (EV_A_ &timer);	2697	ev_timer_again (EV_A_ &timer);
1732	}	2698	}
1733		2699
1734	...	2700	...
1735	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);	2701	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1736	ev_stat_start (loop, &passwd);	2702	ev_stat_start (loop, &passwd);
1737	ev_timer_init (&timer, timer_cb, 0., 1.01);	2703	ev_timer_init (&timer, timer_cb, 0., 1.02);
1738		2704
1739		2705
1740	=head2 C<ev_idle> - when you've got nothing better to do...	2706	=head2 C<ev_idle> - when you've got nothing better to do...
1741		2707
1742	Idle watchers trigger events when no other events of the same or higher	2708	Idle watchers trigger events when no other events of the same or higher
1743	priority are pending (prepare, check and other idle watchers do not	2709	priority are pending (prepare, check and other idle watchers do not count
1744	count).	2710	as receiving "events").
1745		2711
1746	That is, as long as your process is busy handling sockets or timeouts	2712	That is, as long as your process is busy handling sockets or timeouts
1747	(or even signals, imagine) of the same or higher priority it will not be	2713	(or even signals, imagine) of the same or higher priority it will not be
1748	triggered. But when your process is idle (or only lower-priority watchers	2714	triggered. But when your process is idle (or only lower-priority watchers
1749	are pending), the idle watchers are being called once per event loop	2715	are pending), the idle watchers are being called once per event loop
…		…
1760		2726
1761	=head3 Watcher-Specific Functions and Data Members	2727	=head3 Watcher-Specific Functions and Data Members
1762		2728
1763	=over 4	2729	=over 4
1764		2730
1765	=item ev_idle_init (ev_signal *, callback)	2731	=item ev_idle_init (ev_idle *, callback)
1766		2732
1767	Initialises and configures the idle watcher - it has no parameters of any	2733	Initialises and configures the idle watcher - it has no parameters of any
1768	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2734	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1769	believe me.	2735	believe me.
1770		2736
…		…
1773	=head3 Examples	2739	=head3 Examples
1774		2740
1775	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2741	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1776	callback, free it. Also, use no error checking, as usual.	2742	callback, free it. Also, use no error checking, as usual.
1777		2743
1778	static void	2744	static void
1779	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2745	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1780	{	2746	{
1781	free (w);	2747	free (w);
1782	// now do something you wanted to do when the program has	2748	// now do something you wanted to do when the program has
1783	// no longer anything immediate to do.	2749	// no longer anything immediate to do.
1784	}	2750	}
1785		2751
1786	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2752	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1787	ev_idle_init (idle_watcher, idle_cb);	2753	ev_idle_init (idle_watcher, idle_cb);
1788	ev_idle_start (loop, idle_cb);	2754	ev_idle_start (loop, idle_watcher);
1789		2755
1790		2756
1791	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2757	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1792		2758
1793	Prepare and check watchers are usually (but not always) used in tandem:	2759	Prepare and check watchers are usually (but not always) used in pairs:
1794	prepare watchers get invoked before the process blocks and check watchers	2760	prepare watchers get invoked before the process blocks and check watchers
1795	afterwards.	2761	afterwards.
1796		2762
1797	You I<must not> call C<ev_loop> or similar functions that enter	2763	You I<must not> call C<ev_run> or similar functions that enter
1798	the current event loop from either C<ev_prepare> or C<ev_check>	2764	the current event loop from either C<ev_prepare> or C<ev_check>
1799	watchers. Other loops than the current one are fine, however. The	2765	watchers. Other loops than the current one are fine, however. The
1800	rationale behind this is that you do not need to check for recursion in	2766	rationale behind this is that you do not need to check for recursion in
1801	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2767	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1802	C<ev_check> so if you have one watcher of each kind they will always be	2768	C<ev_check> so if you have one watcher of each kind they will always be
1803	called in pairs bracketing the blocking call.	2769	called in pairs bracketing the blocking call.
1804		2770
1805	Their main purpose is to integrate other event mechanisms into libev and	2771	Their main purpose is to integrate other event mechanisms into libev and
1806	their use is somewhat advanced. This could be used, for example, to track	2772	their use is somewhat advanced. They could be used, for example, to track
1807	variable changes, implement your own watchers, integrate net-snmp or a	2773	variable changes, implement your own watchers, integrate net-snmp or a
1808	coroutine library and lots more. They are also occasionally useful if	2774	coroutine library and lots more. They are also occasionally useful if
1809	you cache some data and want to flush it before blocking (for example,	2775	you cache some data and want to flush it before blocking (for example,
1810	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2776	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1811	watcher).	2777	watcher).
1812		2778
1813	This is done by examining in each prepare call which file descriptors need	2779	This is done by examining in each prepare call which file descriptors
1814	to be watched by the other library, registering C<ev_io> watchers for	2780	need to be watched by the other library, registering C<ev_io> watchers
1815	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2781	for them and starting an C<ev_timer> watcher for any timeouts (many
1816	provide just this functionality). Then, in the check watcher you check for	2782	libraries provide exactly this functionality). Then, in the check watcher,
1817	any events that occured (by checking the pending status of all watchers	2783	you check for any events that occurred (by checking the pending status
1818	and stopping them) and call back into the library. The I/O and timer	2784	of all watchers and stopping them) and call back into the library. The
1819	callbacks will never actually be called (but must be valid nevertheless,	2785	I/O and timer callbacks will never actually be called (but must be valid
1820	because you never know, you know?).	2786	nevertheless, because you never know, you know?).
1821		2787
1822	As another example, the Perl Coro module uses these hooks to integrate	2788	As another example, the Perl Coro module uses these hooks to integrate
1823	coroutines into libev programs, by yielding to other active coroutines	2789	coroutines into libev programs, by yielding to other active coroutines
1824	during each prepare and only letting the process block if no coroutines	2790	during each prepare and only letting the process block if no coroutines
1825	are ready to run (it's actually more complicated: it only runs coroutines	2791	are ready to run (it's actually more complicated: it only runs coroutines
…		…
1828	loop from blocking if lower-priority coroutines are active, thus mapping	2794	loop from blocking if lower-priority coroutines are active, thus mapping
1829	low-priority coroutines to idle/background tasks).	2795	low-priority coroutines to idle/background tasks).
1830		2796
1831	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2797	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1832	priority, to ensure that they are being run before any other watchers	2798	priority, to ensure that they are being run before any other watchers
		2799	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2800
1833	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2801	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1834	too) should not activate ("feed") events into libev. While libev fully	2802	activate ("feed") events into libev. While libev fully supports this, they
1835	supports this, they will be called before other C<ev_check> watchers	2803	might get executed before other C<ev_check> watchers did their job. As
1836	did their job. As C<ev_check> watchers are often used to embed other	2804	C<ev_check> watchers are often used to embed other (non-libev) event
1837	(non-libev) event loops those other event loops might be in an unusable	2805	loops those other event loops might be in an unusable state until their
1838	state until their C<ev_check> watcher ran (always remind yourself to	2806	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1839	coexist peacefully with others).	2807	others).
1840		2808
1841	=head3 Watcher-Specific Functions and Data Members	2809	=head3 Watcher-Specific Functions and Data Members
1842		2810
1843	=over 4	2811	=over 4
1844		2812
…		…
1846		2814
1847	=item ev_check_init (ev_check *, callback)	2815	=item ev_check_init (ev_check *, callback)
1848		2816
1849	Initialises and configures the prepare or check watcher - they have no	2817	Initialises and configures the prepare or check watcher - they have no
1850	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2818	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1851	macros, but using them is utterly, utterly and completely pointless.	2819	macros, but using them is utterly, utterly, utterly and completely
		2820	pointless.
1852		2821
1853	=back	2822	=back
1854		2823
1855	=head3 Examples	2824	=head3 Examples
1856		2825
1857	There are a number of principal ways to embed other event loops or modules	2826	There are a number of principal ways to embed other event loops or modules
1858	into libev. Here are some ideas on how to include libadns into libev	2827	into libev. Here are some ideas on how to include libadns into libev
1859	(there is a Perl module named C<EV::ADNS> that does this, which you could	2828	(there is a Perl module named C<EV::ADNS> that does this, which you could
1860	use for an actually working example. Another Perl module named C<EV::Glib>	2829	use as a working example. Another Perl module named C<EV::Glib> embeds a
1861	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV	2830	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1862	into the Glib event loop).	2831	Glib event loop).
1863		2832
1864	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	2833	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1865	and in a check watcher, destroy them and call into libadns. What follows	2834	and in a check watcher, destroy them and call into libadns. What follows
1866	is pseudo-code only of course. This requires you to either use a low	2835	is pseudo-code only of course. This requires you to either use a low
1867	priority for the check watcher or use C<ev_clear_pending> explicitly, as	2836	priority for the check watcher or use C<ev_clear_pending> explicitly, as
1868	the callbacks for the IO/timeout watchers might not have been called yet.	2837	the callbacks for the IO/timeout watchers might not have been called yet.
1869		2838
1870	static ev_io iow [nfd];	2839	static ev_io iow [nfd];
1871	static ev_timer tw;	2840	static ev_timer tw;
1872		2841
1873	static void	2842	static void
1874	io_cb (ev_loop *loop, ev_io *w, int revents)	2843	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1875	{	2844	{
1876	}	2845	}
1877		2846
1878	// create io watchers for each fd and a timer before blocking	2847	// create io watchers for each fd and a timer before blocking
1879	static void	2848	static void
1880	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2849	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1881	{	2850	{
1882	int timeout = 3600000;	2851	int timeout = 3600000;
1883	struct pollfd fds [nfd];	2852	struct pollfd fds [nfd];
1884	// actual code will need to loop here and realloc etc.	2853	// actual code will need to loop here and realloc etc.
1885	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2854	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1886		2855
1887	/* the callback is illegal, but won't be called as we stop during check */	2856	/* the callback is illegal, but won't be called as we stop during check */
1888	ev_timer_init (&tw, 0, timeout * 1e-3);	2857	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1889	ev_timer_start (loop, &tw);	2858	ev_timer_start (loop, &tw);
1890		2859
1891	// create one ev_io per pollfd	2860	// create one ev_io per pollfd
1892	for (int i = 0; i < nfd; ++i)	2861	for (int i = 0; i < nfd; ++i)
1893	{	2862	{
1894	ev_io_init (iow + i, io_cb, fds [i].fd,	2863	ev_io_init (iow + i, io_cb, fds [i].fd,
1895	((fds [i].events & POLLIN ? EV_READ : 0)	2864	((fds [i].events & POLLIN ? EV_READ : 0)
1896	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2865	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1897		2866
1898	fds [i].revents = 0;	2867	fds [i].revents = 0;
1899	ev_io_start (loop, iow + i);	2868	ev_io_start (loop, iow + i);
1900	}	2869	}
1901	}	2870	}
1902		2871
1903	// stop all watchers after blocking	2872	// stop all watchers after blocking
1904	static void	2873	static void
1905	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2874	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1906	{	2875	{
1907	ev_timer_stop (loop, &tw);	2876	ev_timer_stop (loop, &tw);
1908		2877
1909	for (int i = 0; i < nfd; ++i)	2878	for (int i = 0; i < nfd; ++i)
1910	{	2879	{
1911	// set the relevant poll flags	2880	// set the relevant poll flags
1912	// could also call adns_processreadable etc. here	2881	// could also call adns_processreadable etc. here
1913	struct pollfd *fd = fds + i;	2882	struct pollfd *fd = fds + i;
1914	int revents = ev_clear_pending (iow + i);	2883	int revents = ev_clear_pending (iow + i);
1915	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	2884	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1916	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	2885	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1917		2886
1918	// now stop the watcher	2887	// now stop the watcher
1919	ev_io_stop (loop, iow + i);	2888	ev_io_stop (loop, iow + i);
1920	}	2889	}
1921		2890
1922	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2891	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1923	}	2892	}
1924		2893
1925	Method 2: This would be just like method 1, but you run C<adns_afterpoll>	2894	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
1926	in the prepare watcher and would dispose of the check watcher.	2895	in the prepare watcher and would dispose of the check watcher.
1927		2896
1928	Method 3: If the module to be embedded supports explicit event	2897	Method 3: If the module to be embedded supports explicit event
1929	notification (adns does), you can also make use of the actual watcher	2898	notification (libadns does), you can also make use of the actual watcher
1930	callbacks, and only destroy/create the watchers in the prepare watcher.	2899	callbacks, and only destroy/create the watchers in the prepare watcher.
1931		2900
1932	static void	2901	static void
1933	timer_cb (EV_P_ ev_timer *w, int revents)	2902	timer_cb (EV_P_ ev_timer *w, int revents)
1934	{	2903	{
1935	adns_state ads = (adns_state)w->data;	2904	adns_state ads = (adns_state)w->data;
1936	update_now (EV_A);	2905	update_now (EV_A);
1937		2906
1938	adns_processtimeouts (ads, &tv_now);	2907	adns_processtimeouts (ads, &tv_now);
1939	}	2908	}
1940		2909
1941	static void	2910	static void
1942	io_cb (EV_P_ ev_io *w, int revents)	2911	io_cb (EV_P_ ev_io *w, int revents)
1943	{	2912	{
1944	adns_state ads = (adns_state)w->data;	2913	adns_state ads = (adns_state)w->data;
1945	update_now (EV_A);	2914	update_now (EV_A);
1946		2915
1947	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	2916	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1948	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	2917	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1949	}	2918	}
1950		2919
1951	// do not ever call adns_afterpoll	2920	// do not ever call adns_afterpoll
1952		2921
1953	Method 4: Do not use a prepare or check watcher because the module you	2922	Method 4: Do not use a prepare or check watcher because the module you
1954	want to embed is too inflexible to support it. Instead, youc na override	2923	want to embed is not flexible enough to support it. Instead, you can
1955	their poll function. The drawback with this solution is that the main	2924	override their poll function. The drawback with this solution is that the
1956	loop is now no longer controllable by EV. The C<Glib::EV> module does	2925	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
1957	this.	2926	this approach, effectively embedding EV as a client into the horrible
		2927	libglib event loop.
1958		2928
1959	static gint	2929	static gint
1960	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	2930	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1961	{	2931	{
1962	int got_events = 0;	2932	int got_events = 0;
1963		2933
1964	for (n = 0; n < nfds; ++n)	2934	for (n = 0; n < nfds; ++n)
1965	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events	2935	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1966		2936
1967	if (timeout >= 0)	2937	if (timeout >= 0)
1968	// create/start timer	2938	// create/start timer
1969		2939
1970	// poll	2940	// poll
1971	ev_loop (EV_A_ 0);	2941	ev_run (EV_A_ 0);
1972		2942
1973	// stop timer again	2943	// stop timer again
1974	if (timeout >= 0)	2944	if (timeout >= 0)
1975	ev_timer_stop (EV_A_ &to);	2945	ev_timer_stop (EV_A_ &to);
1976		2946
1977	// stop io watchers again - their callbacks should have set	2947	// stop io watchers again - their callbacks should have set
1978	for (n = 0; n < nfds; ++n)	2948	for (n = 0; n < nfds; ++n)
1979	ev_io_stop (EV_A_ iow [n]);	2949	ev_io_stop (EV_A_ iow [n]);
1980		2950
1981	return got_events;	2951	return got_events;
1982	}	2952	}
1983		2953
1984		2954
1985	=head2 C<ev_embed> - when one backend isn't enough...	2955	=head2 C<ev_embed> - when one backend isn't enough...
1986		2956
1987	This is a rather advanced watcher type that lets you embed one event loop	2957	This is a rather advanced watcher type that lets you embed one event loop
…		…
1993	prioritise I/O.	2963	prioritise I/O.
1994		2964
1995	As an example for a bug workaround, the kqueue backend might only support	2965	As an example for a bug workaround, the kqueue backend might only support
1996	sockets on some platform, so it is unusable as generic backend, but you	2966	sockets on some platform, so it is unusable as generic backend, but you
1997	still want to make use of it because you have many sockets and it scales	2967	still want to make use of it because you have many sockets and it scales
1998	so nicely. In this case, you would create a kqueue-based loop and embed it	2968	so nicely. In this case, you would create a kqueue-based loop and embed
1999	into your default loop (which might use e.g. poll). Overall operation will	2969	it into your default loop (which might use e.g. poll). Overall operation
2000	be a bit slower because first libev has to poll and then call kevent, but	2970	will be a bit slower because first libev has to call C<poll> and then
2001	at least you can use both at what they are best.	2971	C<kevent>, but at least you can use both mechanisms for what they are
		2972	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
2002		2973
2003	As for prioritising I/O: rarely you have the case where some fds have	2974	As for prioritising I/O: under rare circumstances you have the case where
2004	to be watched and handled very quickly (with low latency), and even	2975	some fds have to be watched and handled very quickly (with low latency),
2005	priorities and idle watchers might have too much overhead. In this case	2976	and even priorities and idle watchers might have too much overhead. In
2006	you would put all the high priority stuff in one loop and all the rest in	2977	this case you would put all the high priority stuff in one loop and all
2007	a second one, and embed the second one in the first.	2978	the rest in a second one, and embed the second one in the first.
2008		2979
2009	As long as the watcher is active, the callback will be invoked every time	2980	As long as the watcher is active, the callback will be invoked every
2010	there might be events pending in the embedded loop. The callback must then	2981	time there might be events pending in the embedded loop. The callback
2011	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2982	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
2012	their callbacks (you could also start an idle watcher to give the embedded	2983	sweep and invoke their callbacks (the callback doesn't need to invoke the
2013	loop strictly lower priority for example). You can also set the callback	2984	C<ev_embed_sweep> function directly, it could also start an idle watcher
2014	to C<0>, in which case the embed watcher will automatically execute the	2985	to give the embedded loop strictly lower priority for example).
2015	embedded loop sweep.
2016		2986
2017	As long as the watcher is started it will automatically handle events. The	2987	You can also set the callback to C<0>, in which case the embed watcher
2018	callback will be invoked whenever some events have been handled. You can	2988	will automatically execute the embedded loop sweep whenever necessary.
2019	set the callback to C<0> to avoid having to specify one if you are not
2020	interested in that.
2021		2989
2022	Also, there have not currently been made special provisions for forking:	2990	Fork detection will be handled transparently while the C<ev_embed> watcher
2023	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2991	is active, i.e., the embedded loop will automatically be forked when the
2024	but you will also have to stop and restart any C<ev_embed> watchers	2992	embedding loop forks. In other cases, the user is responsible for calling
2025	yourself.	2993	C<ev_loop_fork> on the embedded loop.
2026		2994
2027	Unfortunately, not all backends are embeddable, only the ones returned by	2995	Unfortunately, not all backends are embeddable: only the ones returned by
2028	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2996	C<ev_embeddable_backends> are, which, unfortunately, does not include any
2029	portable one.	2997	portable one.
2030		2998
2031	So when you want to use this feature you will always have to be prepared	2999	So when you want to use this feature you will always have to be prepared
2032	that you cannot get an embeddable loop. The recommended way to get around	3000	that you cannot get an embeddable loop. The recommended way to get around
2033	this is to have a separate variables for your embeddable loop, try to	3001	this is to have a separate variables for your embeddable loop, try to
2034	create it, and if that fails, use the normal loop for everything.	3002	create it, and if that fails, use the normal loop for everything.
2035		3003
		3004	=head3 C<ev_embed> and fork
		3005
		3006	While the C<ev_embed> watcher is running, forks in the embedding loop will
		3007	automatically be applied to the embedded loop as well, so no special
		3008	fork handling is required in that case. When the watcher is not running,
		3009	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		3010	as applicable.
		3011
2036	=head3 Watcher-Specific Functions and Data Members	3012	=head3 Watcher-Specific Functions and Data Members
2037		3013
2038	=over 4	3014	=over 4
2039		3015
2040	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3016	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
…		…
2043		3019
2044	Configures the watcher to embed the given loop, which must be	3020	Configures the watcher to embed the given loop, which must be
2045	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3021	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
2046	invoked automatically, otherwise it is the responsibility of the callback	3022	invoked automatically, otherwise it is the responsibility of the callback
2047	to invoke it (it will continue to be called until the sweep has been done,	3023	to invoke it (it will continue to be called until the sweep has been done,
2048	if you do not want thta, you need to temporarily stop the embed watcher).	3024	if you do not want that, you need to temporarily stop the embed watcher).
2049		3025
2050	=item ev_embed_sweep (loop, ev_embed *)	3026	=item ev_embed_sweep (loop, ev_embed *)
2051		3027
2052	Make a single, non-blocking sweep over the embedded loop. This works	3028	Make a single, non-blocking sweep over the embedded loop. This works
2053	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	3029	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
2054	apropriate way for embedded loops.	3030	appropriate way for embedded loops.
2055		3031
2056	=item struct ev_loop *other [read-only]	3032	=item struct ev_loop *other [read-only]
2057		3033
2058	The embedded event loop.	3034	The embedded event loop.
2059		3035
…		…
2061		3037
2062	=head3 Examples	3038	=head3 Examples
2063		3039
2064	Example: Try to get an embeddable event loop and embed it into the default	3040	Example: Try to get an embeddable event loop and embed it into the default
2065	event loop. If that is not possible, use the default loop. The default	3041	event loop. If that is not possible, use the default loop. The default
2066	loop is stored in C<loop_hi>, while the mebeddable loop is stored in	3042	loop is stored in C<loop_hi>, while the embeddable loop is stored in
2067	C<loop_lo> (which is C<loop_hi> in the acse no embeddable loop can be	3043	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
2068	used).	3044	used).
2069		3045
2070	struct ev_loop *loop_hi = ev_default_init (0);	3046	struct ev_loop *loop_hi = ev_default_init (0);
2071	struct ev_loop *loop_lo = 0;	3047	struct ev_loop *loop_lo = 0;
2072	struct ev_embed embed;	3048	ev_embed embed;
2073		3049
2074	// see if there is a chance of getting one that works	3050	// see if there is a chance of getting one that works
2075	// (remember that a flags value of 0 means autodetection)	3051	// (remember that a flags value of 0 means autodetection)
2076	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3052	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2077	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3053	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
2078	: 0;	3054	: 0;
2079		3055
2080	// if we got one, then embed it, otherwise default to loop_hi	3056	// if we got one, then embed it, otherwise default to loop_hi
2081	if (loop_lo)	3057	if (loop_lo)
2082	{	3058	{
2083	ev_embed_init (&embed, 0, loop_lo);	3059	ev_embed_init (&embed, 0, loop_lo);
2084	ev_embed_start (loop_hi, &embed);	3060	ev_embed_start (loop_hi, &embed);
2085	}	3061	}
2086	else	3062	else
2087	loop_lo = loop_hi;	3063	loop_lo = loop_hi;
2088		3064
2089	Example: Check if kqueue is available but not recommended and create	3065	Example: Check if kqueue is available but not recommended and create
2090	a kqueue backend for use with sockets (which usually work with any	3066	a kqueue backend for use with sockets (which usually work with any
2091	kqueue implementation). Store the kqueue/socket-only event loop in	3067	kqueue implementation). Store the kqueue/socket-only event loop in
2092	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3068	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2093		3069
2094	struct ev_loop *loop = ev_default_init (0);	3070	struct ev_loop *loop = ev_default_init (0);
2095	struct ev_loop *loop_socket = 0;	3071	struct ev_loop *loop_socket = 0;
2096	struct ev_embed embed;	3072	ev_embed embed;
2097		3073
2098	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3074	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2099	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3075	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2100	{	3076	{
2101	ev_embed_init (&embed, 0, loop_socket);	3077	ev_embed_init (&embed, 0, loop_socket);
2102	ev_embed_start (loop, &embed);	3078	ev_embed_start (loop, &embed);
2103	}	3079	}
2104		3080
2105	if (!loop_socket)	3081	if (!loop_socket)
2106	loop_socket = loop;	3082	loop_socket = loop;
2107		3083
2108	// now use loop_socket for all sockets, and loop for everything else	3084	// now use loop_socket for all sockets, and loop for everything else
2109		3085
2110		3086
2111	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3087	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
2112		3088
2113	Fork watchers are called when a C<fork ()> was detected (usually because	3089	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
2116	event loop blocks next and before C<ev_check> watchers are being called,	3092	event loop blocks next and before C<ev_check> watchers are being called,
2117	and only in the child after the fork. If whoever good citizen calling	3093	and only in the child after the fork. If whoever good citizen calling
2118	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3094	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2119	handlers will be invoked, too, of course.	3095	handlers will be invoked, too, of course.
2120		3096
		3097	=head3 The special problem of life after fork - how is it possible?
		3098
		3099	Most uses of C<fork()> consist of forking, then some simple calls to set
		3100	up/change the process environment, followed by a call to C<exec()>. This
		3101	sequence should be handled by libev without any problems.
		3102
		3103	This changes when the application actually wants to do event handling
		3104	in the child, or both parent in child, in effect "continuing" after the
		3105	fork.
		3106
		3107	The default mode of operation (for libev, with application help to detect
		3108	forks) is to duplicate all the state in the child, as would be expected
		3109	when I<either> the parent I<or> the child process continues.
		3110
		3111	When both processes want to continue using libev, then this is usually the
		3112	wrong result. In that case, usually one process (typically the parent) is
		3113	supposed to continue with all watchers in place as before, while the other
		3114	process typically wants to start fresh, i.e. without any active watchers.
		3115
		3116	The cleanest and most efficient way to achieve that with libev is to
		3117	simply create a new event loop, which of course will be "empty", and
		3118	use that for new watchers. This has the advantage of not touching more
		3119	memory than necessary, and thus avoiding the copy-on-write, and the
		3120	disadvantage of having to use multiple event loops (which do not support
		3121	signal watchers).
		3122
		3123	When this is not possible, or you want to use the default loop for
		3124	other reasons, then in the process that wants to start "fresh", call
		3125	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
		3126	Destroying the default loop will "orphan" (not stop) all registered
		3127	watchers, so you have to be careful not to execute code that modifies
		3128	those watchers. Note also that in that case, you have to re-register any
		3129	signal watchers.
		3130
2121	=head3 Watcher-Specific Functions and Data Members	3131	=head3 Watcher-Specific Functions and Data Members
2122		3132
2123	=over 4	3133	=over 4
2124		3134
2125	=item ev_fork_init (ev_signal *, callback)	3135	=item ev_fork_init (ev_fork *, callback)
2126		3136
2127	Initialises and configures the fork watcher - it has no parameters of any	3137	Initialises and configures the fork watcher - it has no parameters of any
2128	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,	3138	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
2129	believe me.	3139	really.
2130		3140
2131	=back	3141	=back
2132		3142
2133		3143
		3144	=head2 C<ev_cleanup> - even the best things end
		3145
		3146	Cleanup watchers are called just before the event loop is being destroyed
		3147	by a call to C<ev_loop_destroy>.
		3148
		3149	While there is no guarantee that the event loop gets destroyed, cleanup
		3150	watchers provide a convenient method to install cleanup hooks for your
		3151	program, worker threads and so on - you just to make sure to destroy the
		3152	loop when you want them to be invoked.
		3153
		3154	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3155	all other watchers, they do not keep a reference to the event loop (which
		3156	makes a lot of sense if you think about it). Like all other watchers, you
		3157	can call libev functions in the callback, except C<ev_cleanup_start>.
		3158
		3159	=head3 Watcher-Specific Functions and Data Members
		3160
		3161	=over 4
		3162
		3163	=item ev_cleanup_init (ev_cleanup *, callback)
		3164
		3165	Initialises and configures the cleanup watcher - it has no parameters of
		3166	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3167	pointless, I assure you.
		3168
		3169	=back
		3170
		3171	Example: Register an atexit handler to destroy the default loop, so any
		3172	cleanup functions are called.
		3173
		3174	static void
		3175	program_exits (void)
		3176	{
		3177	ev_loop_destroy (EV_DEFAULT_UC);
		3178	}
		3179
		3180	...
		3181	atexit (program_exits);
		3182
		3183
2134	=head2 C<ev_async> - how to wake up another event loop	3184	=head2 C<ev_async> - how to wake up an event loop
2135		3185
2136	In general, you cannot use an C<ev_loop> from multiple threads or other	3186	In general, you cannot use an C<ev_run> from multiple threads or other
2137	asynchronous sources such as signal handlers (as opposed to multiple event	3187	asynchronous sources such as signal handlers (as opposed to multiple event
2138	loops - those are of course safe to use in different threads).	3188	loops - those are of course safe to use in different threads).
2139		3189
2140	Sometimes, however, you need to wake up another event loop you do not	3190	Sometimes, however, you need to wake up an event loop you do not control,
2141	control, for example because it belongs to another thread. This is what	3191	for example because it belongs to another thread. This is what C<ev_async>
2142	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you	3192	watchers do: as long as the C<ev_async> watcher is active, you can signal
2143	can signal it by calling C<ev_async_send>, which is thread- and signal	3193	it by calling C<ev_async_send>, which is thread- and signal safe.
2144	safe.
2145		3194
2146	This functionality is very similar to C<ev_signal> watchers, as signals,	3195	This functionality is very similar to C<ev_signal> watchers, as signals,
2147	too, are asynchronous in nature, and signals, too, will be compressed	3196	too, are asynchronous in nature, and signals, too, will be compressed
2148	(i.e. the number of callback invocations may be less than the number of	3197	(i.e. the number of callback invocations may be less than the number of
2149	C<ev_async_sent> calls).	3198	C<ev_async_sent> calls). In fact, you could use signal watchers as a kind
		3199	of "global async watchers" by using a watcher on an otherwise unused
		3200	signal, and C<ev_feed_signal> to signal this watcher from another thread,
		3201	even without knowing which loop owns the signal.
2150		3202
2151	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not	3203	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
2152	just the default loop.	3204	just the default loop.
2153		3205
2154	=head3 Queueing	3206	=head3 Queueing
2155		3207
2156	C<ev_async> does not support queueing of data in any way. The reason	3208	C<ev_async> does not support queueing of data in any way. The reason
2157	is that the author does not know of a simple (or any) algorithm for a	3209	is that the author does not know of a simple (or any) algorithm for a
2158	multiple-writer-single-reader queue that works in all cases and doesn't	3210	multiple-writer-single-reader queue that works in all cases and doesn't
2159	need elaborate support such as pthreads.	3211	need elaborate support such as pthreads or unportable memory access
		3212	semantics.
2160		3213
2161	That means that if you want to queue data, you have to provide your own	3214	That means that if you want to queue data, you have to provide your own
2162	queue. But at least I can tell you would implement locking around your	3215	queue. But at least I can tell you how to implement locking around your
2163	queue:	3216	queue:
2164		3217
2165	=over 4	3218	=over 4
2166		3219
2167	=item queueing from a signal handler context	3220	=item queueing from a signal handler context
2168		3221
2169	To implement race-free queueing, you simply add to the queue in the signal	3222	To implement race-free queueing, you simply add to the queue in the signal
2170	handler but you block the signal handler in the watcher callback. Here is an example that does that for	3223	handler but you block the signal handler in the watcher callback. Here is
2171	some fictitiuous SIGUSR1 handler:	3224	an example that does that for some fictitious SIGUSR1 handler:
2172		3225
2173	static ev_async mysig;	3226	static ev_async mysig;
2174		3227
2175	static void	3228	static void
2176	sigusr1_handler (void)	3229	sigusr1_handler (void)
…		…
2242	=over 4	3295	=over 4
2243		3296
2244	=item ev_async_init (ev_async *, callback)	3297	=item ev_async_init (ev_async *, callback)
2245		3298
2246	Initialises and configures the async watcher - it has no parameters of any	3299	Initialises and configures the async watcher - it has no parameters of any
2247	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,	3300	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
2248	believe me.	3301	trust me.
2249		3302
2250	=item ev_async_send (loop, ev_async *)	3303	=item ev_async_send (loop, ev_async *)
2251		3304
2252	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3305	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
2253	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3306	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
2254	C<ev_feed_event>, this call is safe to do in other threads, signal or	3307	C<ev_feed_event>, this call is safe to do from other threads, signal or
2255	similar contexts (see the dicusssion of C<EV_ATOMIC_T> in the embedding	3308	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
2256	section below on what exactly this means).	3309	section below on what exactly this means).
2257		3310
		3311	Note that, as with other watchers in libev, multiple events might get
		3312	compressed into a single callback invocation (another way to look at this
		3313	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3314	reset when the event loop detects that).
		3315
2258	This call incurs the overhead of a syscall only once per loop iteration,	3316	This call incurs the overhead of a system call only once per event loop
2259	so while the overhead might be noticable, it doesn't apply to repeated	3317	iteration, so while the overhead might be noticeable, it doesn't apply to
2260	calls to C<ev_async_send>.	3318	repeated calls to C<ev_async_send> for the same event loop.
		3319
		3320	=item bool = ev_async_pending (ev_async *)
		3321
		3322	Returns a non-zero value when C<ev_async_send> has been called on the
		3323	watcher but the event has not yet been processed (or even noted) by the
		3324	event loop.
		3325
		3326	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3327	the loop iterates next and checks for the watcher to have become active,
		3328	it will reset the flag again. C<ev_async_pending> can be used to very
		3329	quickly check whether invoking the loop might be a good idea.
		3330
		3331	Not that this does I<not> check whether the watcher itself is pending,
		3332	only whether it has been requested to make this watcher pending: there
		3333	is a time window between the event loop checking and resetting the async
		3334	notification, and the callback being invoked.
2261		3335
2262	=back	3336	=back
2263		3337
2264		3338
2265	=head1 OTHER FUNCTIONS	3339	=head1 OTHER FUNCTIONS
…		…
2269	=over 4	3343	=over 4
2270		3344
2271	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3345	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
2272		3346
2273	This function combines a simple timer and an I/O watcher, calls your	3347	This function combines a simple timer and an I/O watcher, calls your
2274	callback on whichever event happens first and automatically stop both	3348	callback on whichever event happens first and automatically stops both
2275	watchers. This is useful if you want to wait for a single event on an fd	3349	watchers. This is useful if you want to wait for a single event on an fd
2276	or timeout without having to allocate/configure/start/stop/free one or	3350	or timeout without having to allocate/configure/start/stop/free one or
2277	more watchers yourself.	3351	more watchers yourself.
2278		3352
2279	If C<fd> is less than 0, then no I/O watcher will be started and events	3353	If C<fd> is less than 0, then no I/O watcher will be started and the
2280	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3354	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
2281	C<events> set will be craeted and started.	3355	the given C<fd> and C<events> set will be created and started.
2282		3356
2283	If C<timeout> is less than 0, then no timeout watcher will be	3357	If C<timeout> is less than 0, then no timeout watcher will be
2284	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3358	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
2285	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3359	repeat = 0) will be started. C<0> is a valid timeout.
2286	dubious value.
2287		3360
2288	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3361	The callback has the type C<void (*cb)(int revents, void *arg)> and is
2289	passed an C<revents> set like normal event callbacks (a combination of	3362	passed an C<revents> set like normal event callbacks (a combination of
2290	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3363	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
2291	value passed to C<ev_once>:	3364	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3365	a timeout and an io event at the same time - you probably should give io
		3366	events precedence.
2292		3367
		3368	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3369
2293	static void stdin_ready (int revents, void *arg)	3370	static void stdin_ready (int revents, void *arg)
2294	{	3371	{
2295	if (revents & EV_TIMEOUT)
2296	/* doh, nothing entered */;
2297	else if (revents & EV_READ)	3372	if (revents & EV_READ)
2298	/* stdin might have data for us, joy! */;	3373	/* stdin might have data for us, joy! */;
		3374	else if (revents & EV_TIMER)
		3375	/* doh, nothing entered */;
2299	}	3376	}
2300		3377
2301	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3378	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2302		3379
2303	=item ev_feed_event (ev_loop *, watcher *, int revents)
2304
2305	Feeds the given event set into the event loop, as if the specified event
2306	had happened for the specified watcher (which must be a pointer to an
2307	initialised but not necessarily started event watcher).
2308
2309	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3380	=item ev_feed_fd_event (loop, int fd, int revents)
2310		3381
2311	Feed an event on the given fd, as if a file descriptor backend detected	3382	Feed an event on the given fd, as if a file descriptor backend detected
2312	the given events it.	3383	the given events it.
2313		3384
2314	=item ev_feed_signal_event (ev_loop *loop, int signum)	3385	=item ev_feed_signal_event (loop, int signum)
2315		3386
2316	Feed an event as if the given signal occured (C<loop> must be the default	3387	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
2317	loop!).	3388	which is async-safe.
2318		3389
2319	=back	3390	=back
		3391
		3392
		3393	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3394
		3395	This section explains some common idioms that are not immediately
		3396	obvious. Note that examples are sprinkled over the whole manual, and this
		3397	section only contains stuff that wouldn't fit anywhere else.
		3398
		3399	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3400
		3401	Each watcher has, by default, a C<void *data> member that you can read
		3402	or modify at any time: libev will completely ignore it. This can be used
		3403	to associate arbitrary data with your watcher. If you need more data and
		3404	don't want to allocate memory separately and store a pointer to it in that
		3405	data member, you can also "subclass" the watcher type and provide your own
		3406	data:
		3407
		3408	struct my_io
		3409	{
		3410	ev_io io;
		3411	int otherfd;
		3412	void *somedata;
		3413	struct whatever *mostinteresting;
		3414	};
		3415
		3416	...
		3417	struct my_io w;
		3418	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3419
		3420	And since your callback will be called with a pointer to the watcher, you
		3421	can cast it back to your own type:
		3422
		3423	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3424	{
		3425	struct my_io *w = (struct my_io *)w_;
		3426	...
		3427	}
		3428
		3429	More interesting and less C-conformant ways of casting your callback
		3430	function type instead have been omitted.
		3431
		3432	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3433
		3434	Another common scenario is to use some data structure with multiple
		3435	embedded watchers, in effect creating your own watcher that combines
		3436	multiple libev event sources into one "super-watcher":
		3437
		3438	struct my_biggy
		3439	{
		3440	int some_data;
		3441	ev_timer t1;
		3442	ev_timer t2;
		3443	}
		3444
		3445	In this case getting the pointer to C<my_biggy> is a bit more
		3446	complicated: Either you store the address of your C<my_biggy> struct in
		3447	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3448	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3449	real programmers):
		3450
		3451	#include <stddef.h>
		3452
		3453	static void
		3454	t1_cb (EV_P_ ev_timer *w, int revents)
		3455	{
		3456	struct my_biggy big = (struct my_biggy *)
		3457	(((char *)w) - offsetof (struct my_biggy, t1));
		3458	}
		3459
		3460	static void
		3461	t2_cb (EV_P_ ev_timer *w, int revents)
		3462	{
		3463	struct my_biggy big = (struct my_biggy *)
		3464	(((char *)w) - offsetof (struct my_biggy, t2));
		3465	}
		3466
		3467	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3468
		3469	Often (especially in GUI toolkits) there are places where you have
		3470	I<modal> interaction, which is most easily implemented by recursively
		3471	invoking C<ev_run>.
		3472
		3473	This brings the problem of exiting - a callback might want to finish the
		3474	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3475	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3476	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3477	other combination: In these cases, C<ev_break> will not work alone.
		3478
		3479	The solution is to maintain "break this loop" variable for each C<ev_run>
		3480	invocation, and use a loop around C<ev_run> until the condition is
		3481	triggered, using C<EVRUN_ONCE>:
		3482
		3483	// main loop
		3484	int exit_main_loop = 0;
		3485
		3486	while (!exit_main_loop)
		3487	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3488
		3489	// in a model watcher
		3490	int exit_nested_loop = 0;
		3491
		3492	while (!exit_nested_loop)
		3493	ev_run (EV_A_ EVRUN_ONCE);
		3494
		3495	To exit from any of these loops, just set the corresponding exit variable:
		3496
		3497	// exit modal loop
		3498	exit_nested_loop = 1;
		3499
		3500	// exit main program, after modal loop is finished
		3501	exit_main_loop = 1;
		3502
		3503	// exit both
		3504	exit_main_loop = exit_nested_loop = 1;
		3505
		3506	=head2 THREAD LOCKING EXAMPLE
		3507
		3508	Here is a fictitious example of how to run an event loop in a different
		3509	thread than where callbacks are being invoked and watchers are
		3510	created/added/removed.
		3511
		3512	For a real-world example, see the C<EV::Loop::Async> perl module,
		3513	which uses exactly this technique (which is suited for many high-level
		3514	languages).
		3515
		3516	The example uses a pthread mutex to protect the loop data, a condition
		3517	variable to wait for callback invocations, an async watcher to notify the
		3518	event loop thread and an unspecified mechanism to wake up the main thread.
		3519
		3520	First, you need to associate some data with the event loop:
		3521
		3522	typedef struct {
		3523	mutex_t lock; /* global loop lock */
		3524	ev_async async_w;
		3525	thread_t tid;
		3526	cond_t invoke_cv;
		3527	} userdata;
		3528
		3529	void prepare_loop (EV_P)
		3530	{
		3531	// for simplicity, we use a static userdata struct.
		3532	static userdata u;
		3533
		3534	ev_async_init (&u->async_w, async_cb);
		3535	ev_async_start (EV_A_ &u->async_w);
		3536
		3537	pthread_mutex_init (&u->lock, 0);
		3538	pthread_cond_init (&u->invoke_cv, 0);
		3539
		3540	// now associate this with the loop
		3541	ev_set_userdata (EV_A_ u);
		3542	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3543	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3544
		3545	// then create the thread running ev_loop
		3546	pthread_create (&u->tid, 0, l_run, EV_A);
		3547	}
		3548
		3549	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3550	solely to wake up the event loop so it takes notice of any new watchers
		3551	that might have been added:
		3552
		3553	static void
		3554	async_cb (EV_P_ ev_async *w, int revents)
		3555	{
		3556	// just used for the side effects
		3557	}
		3558
		3559	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3560	protecting the loop data, respectively.
		3561
		3562	static void
		3563	l_release (EV_P)
		3564	{
		3565	userdata *u = ev_userdata (EV_A);
		3566	pthread_mutex_unlock (&u->lock);
		3567	}
		3568
		3569	static void
		3570	l_acquire (EV_P)
		3571	{
		3572	userdata *u = ev_userdata (EV_A);
		3573	pthread_mutex_lock (&u->lock);
		3574	}
		3575
		3576	The event loop thread first acquires the mutex, and then jumps straight
		3577	into C<ev_run>:
		3578
		3579	void *
		3580	l_run (void *thr_arg)
		3581	{
		3582	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3583
		3584	l_acquire (EV_A);
		3585	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3586	ev_run (EV_A_ 0);
		3587	l_release (EV_A);
		3588
		3589	return 0;
		3590	}
		3591
		3592	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3593	signal the main thread via some unspecified mechanism (signals? pipe
		3594	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3595	have been called (in a while loop because a) spurious wakeups are possible
		3596	and b) skipping inter-thread-communication when there are no pending
		3597	watchers is very beneficial):
		3598
		3599	static void
		3600	l_invoke (EV_P)
		3601	{
		3602	userdata *u = ev_userdata (EV_A);
		3603
		3604	while (ev_pending_count (EV_A))
		3605	{
		3606	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3607	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3608	}
		3609	}
		3610
		3611	Now, whenever the main thread gets told to invoke pending watchers, it
		3612	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3613	thread to continue:
		3614
		3615	static void
		3616	real_invoke_pending (EV_P)
		3617	{
		3618	userdata *u = ev_userdata (EV_A);
		3619
		3620	pthread_mutex_lock (&u->lock);
		3621	ev_invoke_pending (EV_A);
		3622	pthread_cond_signal (&u->invoke_cv);
		3623	pthread_mutex_unlock (&u->lock);
		3624	}
		3625
		3626	Whenever you want to start/stop a watcher or do other modifications to an
		3627	event loop, you will now have to lock:
		3628
		3629	ev_timer timeout_watcher;
		3630	userdata *u = ev_userdata (EV_A);
		3631
		3632	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3633
		3634	pthread_mutex_lock (&u->lock);
		3635	ev_timer_start (EV_A_ &timeout_watcher);
		3636	ev_async_send (EV_A_ &u->async_w);
		3637	pthread_mutex_unlock (&u->lock);
		3638
		3639	Note that sending the C<ev_async> watcher is required because otherwise
		3640	an event loop currently blocking in the kernel will have no knowledge
		3641	about the newly added timer. By waking up the loop it will pick up any new
		3642	watchers in the next event loop iteration.
		3643
		3644	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3645
		3646	While the overhead of a callback that e.g. schedules a thread is small, it
		3647	is still an overhead. If you embed libev, and your main usage is with some
		3648	kind of threads or coroutines, you might want to customise libev so that
		3649	doesn't need callbacks anymore.
		3650
		3651	Imagine you have coroutines that you can switch to using a function
		3652	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3653	and that due to some magic, the currently active coroutine is stored in a
		3654	global called C<current_coro>. Then you can build your own "wait for libev
		3655	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3656	the differing C<;> conventions):
		3657
		3658	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3659	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3660
		3661	That means instead of having a C callback function, you store the
		3662	coroutine to switch to in each watcher, and instead of having libev call
		3663	your callback, you instead have it switch to that coroutine.
		3664
		3665	A coroutine might now wait for an event with a function called
		3666	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3667	matter when, or whether the watcher is active or not when this function is
		3668	called):
		3669
		3670	void
		3671	wait_for_event (ev_watcher *w)
		3672	{
		3673	ev_cb_set (w) = current_coro;
		3674	switch_to (libev_coro);
		3675	}
		3676
		3677	That basically suspends the coroutine inside C<wait_for_event> and
		3678	continues the libev coroutine, which, when appropriate, switches back to
		3679	this or any other coroutine. I am sure if you sue this your own :)
		3680
		3681	You can do similar tricks if you have, say, threads with an event queue -
		3682	instead of storing a coroutine, you store the queue object and instead of
		3683	switching to a coroutine, you push the watcher onto the queue and notify
		3684	any waiters.
		3685
		3686	To embed libev, see L<EMBEDDING>, but in short, it's easiest to create two
		3687	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3688
		3689	// my_ev.h
		3690	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3691	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
		3692	#include "../libev/ev.h"
		3693
		3694	// my_ev.c
		3695	#define EV_H "my_ev.h"
		3696	#include "../libev/ev.c"
		3697
		3698	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3699	F<my_ev.c> into your project. When properly specifying include paths, you
		3700	can even use F<ev.h> as header file name directly.
2320		3701
2321		3702
2322	=head1 LIBEVENT EMULATION	3703	=head1 LIBEVENT EMULATION
2323		3704
2324	Libev offers a compatibility emulation layer for libevent. It cannot	3705	Libev offers a compatibility emulation layer for libevent. It cannot
2325	emulate the internals of libevent, so here are some usage hints:	3706	emulate the internals of libevent, so here are some usage hints:
2326		3707
2327	=over 4	3708	=over 4
		3709
		3710	=item * Only the libevent-1.4.1-beta API is being emulated.
		3711
		3712	This was the newest libevent version available when libev was implemented,
		3713	and is still mostly unchanged in 2010.
2328		3714
2329	=item * Use it by including <event.h>, as usual.	3715	=item * Use it by including <event.h>, as usual.
2330		3716
2331	=item * The following members are fully supported: ev_base, ev_callback,	3717	=item * The following members are fully supported: ev_base, ev_callback,
2332	ev_arg, ev_fd, ev_res, ev_events.	3718	ev_arg, ev_fd, ev_res, ev_events.
…		…
2337		3723
2338	=item * Priorities are not currently supported. Initialising priorities	3724	=item * Priorities are not currently supported. Initialising priorities
2339	will fail and all watchers will have the same priority, even though there	3725	will fail and all watchers will have the same priority, even though there
2340	is an ev_pri field.	3726	is an ev_pri field.
2341		3727
		3728	=item * In libevent, the last base created gets the signals, in libev, the
		3729	base that registered the signal gets the signals.
		3730
2342	=item * Other members are not supported.	3731	=item * Other members are not supported.
2343		3732
2344	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3733	=item * The libev emulation is I<not> ABI compatible to libevent, you need
2345	to use the libev header file and library.	3734	to use the libev header file and library.
2346		3735
2347	=back	3736	=back
2348		3737
2349	=head1 C++ SUPPORT	3738	=head1 C++ SUPPORT
2350		3739
2351	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3740	Libev comes with some simplistic wrapper classes for C++ that mainly allow
2352	you to use some convinience methods to start/stop watchers and also change	3741	you to use some convenience methods to start/stop watchers and also change
2353	the callback model to a model using method callbacks on objects.	3742	the callback model to a model using method callbacks on objects.
2354		3743
2355	To use it,	3744	To use it,
2356		3745
2357	#include <ev++.h>	3746	#include <ev++.h>
2358		3747
2359	This automatically includes F<ev.h> and puts all of its definitions (many	3748	This automatically includes F<ev.h> and puts all of its definitions (many
2360	of them macros) into the global namespace. All C++ specific things are	3749	of them macros) into the global namespace. All C++ specific things are
2361	put into the C<ev> namespace. It should support all the same embedding	3750	put into the C<ev> namespace. It should support all the same embedding
2362	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	3751	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
2364	Care has been taken to keep the overhead low. The only data member the C++	3753	Care has been taken to keep the overhead low. The only data member the C++
2365	classes add (compared to plain C-style watchers) is the event loop pointer	3754	classes add (compared to plain C-style watchers) is the event loop pointer
2366	that the watcher is associated with (or no additional members at all if	3755	that the watcher is associated with (or no additional members at all if
2367	you disable C<EV_MULTIPLICITY> when embedding libev).	3756	you disable C<EV_MULTIPLICITY> when embedding libev).
2368		3757
2369	Currently, functions, and static and non-static member functions can be	3758	Currently, functions, static and non-static member functions and classes
2370	used as callbacks. Other types should be easy to add as long as they only	3759	with C<operator ()> can be used as callbacks. Other types should be easy
2371	need one additional pointer for context. If you need support for other	3760	to add as long as they only need one additional pointer for context. If
2372	types of functors please contact the author (preferably after implementing	3761	you need support for other types of functors please contact the author
2373	it).	3762	(preferably after implementing it).
2374		3763
2375	Here is a list of things available in the C<ev> namespace:	3764	Here is a list of things available in the C<ev> namespace:
2376		3765
2377	=over 4	3766	=over 4
2378		3767
…		…
2396		3785
2397	=over 4	3786	=over 4
2398		3787
2399	=item ev::TYPE::TYPE ()	3788	=item ev::TYPE::TYPE ()
2400		3789
2401	=item ev::TYPE::TYPE (struct ev_loop *)	3790	=item ev::TYPE::TYPE (loop)
2402		3791
2403	=item ev::TYPE::~TYPE	3792	=item ev::TYPE::~TYPE
2404		3793
2405	The constructor (optionally) takes an event loop to associate the watcher	3794	The constructor (optionally) takes an event loop to associate the watcher
2406	with. If it is omitted, it will use C<EV_DEFAULT>.	3795	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
2429	your compiler is good :), then the method will be fully inlined into the	3818	your compiler is good :), then the method will be fully inlined into the
2430	thunking function, making it as fast as a direct C callback.	3819	thunking function, making it as fast as a direct C callback.
2431		3820
2432	Example: simple class declaration and watcher initialisation	3821	Example: simple class declaration and watcher initialisation
2433		3822
2434	struct myclass	3823	struct myclass
2435	{	3824	{
2436	void io_cb (ev::io &w, int revents) { }	3825	void io_cb (ev::io &w, int revents) { }
2437	}	3826	}
2438		3827
2439	myclass obj;	3828	myclass obj;
2440	ev::io iow;	3829	ev::io iow;
2441	iow.set <myclass, &myclass::io_cb> (&obj);	3830	iow.set <myclass, &myclass::io_cb> (&obj);
		3831
		3832	=item w->set (object *)
		3833
		3834	This is a variation of a method callback - leaving out the method to call
		3835	will default the method to C<operator ()>, which makes it possible to use
		3836	functor objects without having to manually specify the C<operator ()> all
		3837	the time. Incidentally, you can then also leave out the template argument
		3838	list.
		3839
		3840	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3841	int revents)>.
		3842
		3843	See the method-C<set> above for more details.
		3844
		3845	Example: use a functor object as callback.
		3846
		3847	struct myfunctor
		3848	{
		3849	void operator() (ev::io &w, int revents)
		3850	{
		3851	...
		3852	}
		3853	}
		3854
		3855	myfunctor f;
		3856
		3857	ev::io w;
		3858	w.set (&f);
2442		3859
2443	=item w->set<function> (void *data = 0)	3860	=item w->set<function> (void *data = 0)
2444		3861
2445	Also sets a callback, but uses a static method or plain function as	3862	Also sets a callback, but uses a static method or plain function as
2446	callback. The optional C<data> argument will be stored in the watcher's	3863	callback. The optional C<data> argument will be stored in the watcher's
…		…
2448		3865
2449	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	3866	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2450		3867
2451	See the method-C<set> above for more details.	3868	See the method-C<set> above for more details.
2452		3869
2453	Example:	3870	Example: Use a plain function as callback.
2454		3871
2455	static void io_cb (ev::io &w, int revents) { }	3872	static void io_cb (ev::io &w, int revents) { }
2456	iow.set <io_cb> ();	3873	iow.set <io_cb> ();
2457		3874
2458	=item w->set (struct ev_loop *)	3875	=item w->set (loop)
2459		3876
2460	Associates a different C<struct ev_loop> with this watcher. You can only	3877	Associates a different C<struct ev_loop> with this watcher. You can only
2461	do this when the watcher is inactive (and not pending either).	3878	do this when the watcher is inactive (and not pending either).
2462		3879
2463	=item w->set ([args])	3880	=item w->set ([arguments])
2464		3881
2465	Basically the same as C<ev_TYPE_set>, with the same args. Must be	3882	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this
2466	called at least once. Unlike the C counterpart, an active watcher gets	3883	method or a suitable start method must be called at least once. Unlike the
2467	automatically stopped and restarted when reconfiguring it with this	3884	C counterpart, an active watcher gets automatically stopped and restarted
2468	method.	3885	when reconfiguring it with this method.
2469		3886
2470	=item w->start ()	3887	=item w->start ()
2471		3888
2472	Starts the watcher. Note that there is no C<loop> argument, as the	3889	Starts the watcher. Note that there is no C<loop> argument, as the
2473	constructor already stores the event loop.	3890	constructor already stores the event loop.
2474		3891
		3892	=item w->start ([arguments])
		3893
		3894	Instead of calling C<set> and C<start> methods separately, it is often
		3895	convenient to wrap them in one call. Uses the same type of arguments as
		3896	the configure C<set> method of the watcher.
		3897
2475	=item w->stop ()	3898	=item w->stop ()
2476		3899
2477	Stops the watcher if it is active. Again, no C<loop> argument.	3900	Stops the watcher if it is active. Again, no C<loop> argument.
2478		3901
2479	=item w->again () (C<ev::timer>, C<ev::periodic> only)	3902	=item w->again () (C<ev::timer>, C<ev::periodic> only)
…		…
2491		3914
2492	=back	3915	=back
2493		3916
2494	=back	3917	=back
2495		3918
2496	Example: Define a class with an IO and idle watcher, start one of them in	3919	Example: Define a class with two I/O and idle watchers, start the I/O
2497	the constructor.	3920	watchers in the constructor.
2498		3921
2499	class myclass	3922	class myclass
2500	{	3923	{
2501	ev::io io; void io_cb (ev::io &w, int revents);	3924	ev::io io ; void io_cb (ev::io &w, int revents);
		3925	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);
2502	ev:idle idle void idle_cb (ev::idle &w, int revents);	3926	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2503		3927
2504	myclass (int fd)	3928	myclass (int fd)
2505	{	3929	{
2506	io .set <myclass, &myclass::io_cb > (this);	3930	io .set <myclass, &myclass::io_cb > (this);
		3931	io2 .set <myclass, &myclass::io2_cb > (this);
2507	idle.set <myclass, &myclass::idle_cb> (this);	3932	idle.set <myclass, &myclass::idle_cb> (this);
2508		3933
2509	io.start (fd, ev::READ);	3934	io.set (fd, ev::WRITE); // configure the watcher
		3935	io.start (); // start it whenever convenient
		3936
		3937	io2.start (fd, ev::READ); // set + start in one call
2510	}	3938	}
2511	};	3939	};
2512		3940
2513		3941
2514	=head1 OTHER LANGUAGE BINDINGS	3942	=head1 OTHER LANGUAGE BINDINGS
2515		3943
2516	Libev does not offer other language bindings itself, but bindings for a	3944	Libev does not offer other language bindings itself, but bindings for a
2517	numbe rof languages exist in the form of third-party packages. If you know	3945	number of languages exist in the form of third-party packages. If you know
2518	any interesting language binding in addition to the ones listed here, drop	3946	any interesting language binding in addition to the ones listed here, drop
2519	me a note.	3947	me a note.
2520		3948
2521	=over 4	3949	=over 4
2522		3950
2523	=item Perl	3951	=item Perl
2524		3952
2525	The EV module implements the full libev API and is actually used to test	3953	The EV module implements the full libev API and is actually used to test
2526	libev. EV is developed together with libev. Apart from the EV core module,	3954	libev. EV is developed together with libev. Apart from the EV core module,
2527	there are additional modules that implement libev-compatible interfaces	3955	there are additional modules that implement libev-compatible interfaces
2528	to C<libadns> (C<EV::ADNS>), C<Net::SNMP> (C<Net::SNMP::EV>) and the	3956	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
2529	C<libglib> event core (C<Glib::EV> and C<EV::Glib>).	3957	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3958	and C<EV::Glib>).
2530		3959
2531	It can be found and installed via CPAN, its homepage is found at	3960	It can be found and installed via CPAN, its homepage is at
2532	L<http://software.schmorp.de/pkg/EV>.	3961	L<http://software.schmorp.de/pkg/EV>.
2533		3962
		3963	=item Python
		3964
		3965	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3966	seems to be quite complete and well-documented.
		3967
2534	=item Ruby	3968	=item Ruby
2535		3969
2536	Tony Arcieri has written a ruby extension that offers access to a subset	3970	Tony Arcieri has written a ruby extension that offers access to a subset
2537	of the libev API and adds filehandle abstractions, asynchronous DNS and	3971	of the libev API and adds file handle abstractions, asynchronous DNS and
2538	more on top of it. It can be found via gem servers. Its homepage is at	3972	more on top of it. It can be found via gem servers. Its homepage is at
2539	L<http://rev.rubyforge.org/>.	3973	L<http://rev.rubyforge.org/>.
2540		3974
		3975	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3976	makes rev work even on mingw.
		3977
		3978	=item Haskell
		3979
		3980	A haskell binding to libev is available at
		3981	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3982
2541	=item D	3983	=item D
2542		3984
2543	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	3985	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
2544	be found at L<http://git.llucax.com.ar/?p=software/ev.d.git;a=summary>.	3986	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3987
		3988	=item Ocaml
		3989
		3990	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3991	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3992
		3993	=item Lua
		3994
		3995	Brian Maher has written a partial interface to libev for lua (at the
		3996	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		3997	L<http://github.com/brimworks/lua-ev>.
2545		3998
2546	=back	3999	=back
2547		4000
2548		4001
2549	=head1 MACRO MAGIC	4002	=head1 MACRO MAGIC
2550		4003
2551	Libev can be compiled with a variety of options, the most fundamantal	4004	Libev can be compiled with a variety of options, the most fundamental
2552	of which is C<EV_MULTIPLICITY>. This option determines whether (most)	4005	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2553	functions and callbacks have an initial C<struct ev_loop *> argument.	4006	functions and callbacks have an initial C<struct ev_loop *> argument.
2554		4007
2555	To make it easier to write programs that cope with either variant, the	4008	To make it easier to write programs that cope with either variant, the
2556	following macros are defined:	4009	following macros are defined:
…		…
2561		4014
2562	This provides the loop I<argument> for functions, if one is required ("ev	4015	This provides the loop I<argument> for functions, if one is required ("ev
2563	loop argument"). The C<EV_A> form is used when this is the sole argument,	4016	loop argument"). The C<EV_A> form is used when this is the sole argument,
2564	C<EV_A_> is used when other arguments are following. Example:	4017	C<EV_A_> is used when other arguments are following. Example:
2565		4018
2566	ev_unref (EV_A);	4019	ev_unref (EV_A);
2567	ev_timer_add (EV_A_ watcher);	4020	ev_timer_add (EV_A_ watcher);
2568	ev_loop (EV_A_ 0);	4021	ev_run (EV_A_ 0);
2569		4022
2570	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	4023	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2571	which is often provided by the following macro.	4024	which is often provided by the following macro.
2572		4025
2573	=item C<EV_P>, C<EV_P_>	4026	=item C<EV_P>, C<EV_P_>
2574		4027
2575	This provides the loop I<parameter> for functions, if one is required ("ev	4028	This provides the loop I<parameter> for functions, if one is required ("ev
2576	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	4029	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
2577	C<EV_P_> is used when other parameters are following. Example:	4030	C<EV_P_> is used when other parameters are following. Example:
2578		4031
2579	// this is how ev_unref is being declared	4032	// this is how ev_unref is being declared
2580	static void ev_unref (EV_P);	4033	static void ev_unref (EV_P);
2581		4034
2582	// this is how you can declare your typical callback	4035	// this is how you can declare your typical callback
2583	static void cb (EV_P_ ev_timer *w, int revents)	4036	static void cb (EV_P_ ev_timer *w, int revents)
2584		4037
2585	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	4038	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
2586	suitable for use with C<EV_A>.	4039	suitable for use with C<EV_A>.
2587		4040
2588	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4041	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2589		4042
2590	Similar to the other two macros, this gives you the value of the default	4043	Similar to the other two macros, this gives you the value of the default
2591	loop, if multiple loops are supported ("ev loop default").	4044	loop, if multiple loops are supported ("ev loop default").
		4045
		4046	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		4047
		4048	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		4049	default loop has been initialised (C<UC> == unchecked). Their behaviour
		4050	is undefined when the default loop has not been initialised by a previous
		4051	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		4052
		4053	It is often prudent to use C<EV_DEFAULT> when initialising the first
		4054	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
2592		4055
2593	=back	4056	=back
2594		4057
2595	Example: Declare and initialise a check watcher, utilising the above	4058	Example: Declare and initialise a check watcher, utilising the above
2596	macros so it will work regardless of whether multiple loops are supported	4059	macros so it will work regardless of whether multiple loops are supported
2597	or not.	4060	or not.
2598		4061
2599	static void	4062	static void
2600	check_cb (EV_P_ ev_timer *w, int revents)	4063	check_cb (EV_P_ ev_timer *w, int revents)
2601	{	4064	{
2602	ev_check_stop (EV_A_ w);	4065	ev_check_stop (EV_A_ w);
2603	}	4066	}
2604		4067
2605	ev_check check;	4068	ev_check check;
2606	ev_check_init (&check, check_cb);	4069	ev_check_init (&check, check_cb);
2607	ev_check_start (EV_DEFAULT_ &check);	4070	ev_check_start (EV_DEFAULT_ &check);
2608	ev_loop (EV_DEFAULT_ 0);	4071	ev_run (EV_DEFAULT_ 0);
2609		4072
2610	=head1 EMBEDDING	4073	=head1 EMBEDDING
2611		4074
2612	Libev can (and often is) directly embedded into host	4075	Libev can (and often is) directly embedded into host
2613	applications. Examples of applications that embed it include the Deliantra	4076	applications. Examples of applications that embed it include the Deliantra
…		…
2620	libev somewhere in your source tree).	4083	libev somewhere in your source tree).
2621		4084
2622	=head2 FILESETS	4085	=head2 FILESETS
2623		4086
2624	Depending on what features you need you need to include one or more sets of files	4087	Depending on what features you need you need to include one or more sets of files
2625	in your app.	4088	in your application.
2626		4089
2627	=head3 CORE EVENT LOOP	4090	=head3 CORE EVENT LOOP
2628		4091
2629	To include only the libev core (all the C<ev_*> functions), with manual	4092	To include only the libev core (all the C<ev_*> functions), with manual
2630	configuration (no autoconf):	4093	configuration (no autoconf):
2631		4094
2632	#define EV_STANDALONE 1	4095	#define EV_STANDALONE 1
2633	#include "ev.c"	4096	#include "ev.c"
2634		4097
2635	This will automatically include F<ev.h>, too, and should be done in a	4098	This will automatically include F<ev.h>, too, and should be done in a
2636	single C source file only to provide the function implementations. To use	4099	single C source file only to provide the function implementations. To use
2637	it, do the same for F<ev.h> in all files wishing to use this API (best	4100	it, do the same for F<ev.h> in all files wishing to use this API (best
2638	done by writing a wrapper around F<ev.h> that you can include instead and	4101	done by writing a wrapper around F<ev.h> that you can include instead and
2639	where you can put other configuration options):	4102	where you can put other configuration options):
2640		4103
2641	#define EV_STANDALONE 1	4104	#define EV_STANDALONE 1
2642	#include "ev.h"	4105	#include "ev.h"
2643		4106
2644	Both header files and implementation files can be compiled with a C++	4107	Both header files and implementation files can be compiled with a C++
2645	compiler (at least, thats a stated goal, and breakage will be treated	4108	compiler (at least, that's a stated goal, and breakage will be treated
2646	as a bug).	4109	as a bug).
2647		4110
2648	You need the following files in your source tree, or in a directory	4111	You need the following files in your source tree, or in a directory
2649	in your include path (e.g. in libev/ when using -Ilibev):	4112	in your include path (e.g. in libev/ when using -Ilibev):
2650		4113
2651	ev.h	4114	ev.h
2652	ev.c	4115	ev.c
2653	ev_vars.h	4116	ev_vars.h
2654	ev_wrap.h	4117	ev_wrap.h
2655		4118
2656	ev_win32.c required on win32 platforms only	4119	ev_win32.c required on win32 platforms only
2657		4120
2658	ev_select.c only when select backend is enabled (which is enabled by default)	4121	ev_select.c only when select backend is enabled (which is enabled by default)
2659	ev_poll.c only when poll backend is enabled (disabled by default)	4122	ev_poll.c only when poll backend is enabled (disabled by default)
2660	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4123	ev_epoll.c only when the epoll backend is enabled (disabled by default)
2661	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4124	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2662	ev_port.c only when the solaris port backend is enabled (disabled by default)	4125	ev_port.c only when the solaris port backend is enabled (disabled by default)
2663		4126
2664	F<ev.c> includes the backend files directly when enabled, so you only need	4127	F<ev.c> includes the backend files directly when enabled, so you only need
2665	to compile this single file.	4128	to compile this single file.
2666		4129
2667	=head3 LIBEVENT COMPATIBILITY API	4130	=head3 LIBEVENT COMPATIBILITY API
2668		4131
2669	To include the libevent compatibility API, also include:	4132	To include the libevent compatibility API, also include:
2670		4133
2671	#include "event.c"	4134	#include "event.c"
2672		4135
2673	in the file including F<ev.c>, and:	4136	in the file including F<ev.c>, and:
2674		4137
2675	#include "event.h"	4138	#include "event.h"
2676		4139
2677	in the files that want to use the libevent API. This also includes F<ev.h>.	4140	in the files that want to use the libevent API. This also includes F<ev.h>.
2678		4141
2679	You need the following additional files for this:	4142	You need the following additional files for this:
2680		4143
2681	event.h	4144	event.h
2682	event.c	4145	event.c
2683		4146
2684	=head3 AUTOCONF SUPPORT	4147	=head3 AUTOCONF SUPPORT
2685		4148
2686	Instead of using C<EV_STANDALONE=1> and providing your config in	4149	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2687	whatever way you want, you can also C<m4_include([libev.m4])> in your	4150	whatever way you want, you can also C<m4_include([libev.m4])> in your
2688	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	4151	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2689	include F<config.h> and configure itself accordingly.	4152	include F<config.h> and configure itself accordingly.
2690		4153
2691	For this of course you need the m4 file:	4154	For this of course you need the m4 file:
2692		4155
2693	libev.m4	4156	libev.m4
2694		4157
2695	=head2 PREPROCESSOR SYMBOLS/MACROS	4158	=head2 PREPROCESSOR SYMBOLS/MACROS
2696		4159
2697	Libev can be configured via a variety of preprocessor symbols you have to define	4160	Libev can be configured via a variety of preprocessor symbols you have to
2698	before including any of its files. The default is not to build for multiplicity	4161	define before including (or compiling) any of its files. The default in
2699	and only include the select backend.	4162	the absence of autoconf is documented for every option.
		4163
		4164	Symbols marked with "(h)" do not change the ABI, and can have different
		4165	values when compiling libev vs. including F<ev.h>, so it is permissible
		4166	to redefine them before including F<ev.h> without breaking compatibility
		4167	to a compiled library. All other symbols change the ABI, which means all
		4168	users of libev and the libev code itself must be compiled with compatible
		4169	settings.
2700		4170
2701	=over 4	4171	=over 4
2702		4172
		4173	=item EV_COMPAT3 (h)
		4174
		4175	Backwards compatibility is a major concern for libev. This is why this
		4176	release of libev comes with wrappers for the functions and symbols that
		4177	have been renamed between libev version 3 and 4.
		4178
		4179	You can disable these wrappers (to test compatibility with future
		4180	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		4181	sources. This has the additional advantage that you can drop the C<struct>
		4182	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		4183	typedef in that case.
		4184
		4185	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		4186	and in some even more future version the compatibility code will be
		4187	removed completely.
		4188
2703	=item EV_STANDALONE	4189	=item EV_STANDALONE (h)
2704		4190
2705	Must always be C<1> if you do not use autoconf configuration, which	4191	Must always be C<1> if you do not use autoconf configuration, which
2706	keeps libev from including F<config.h>, and it also defines dummy	4192	keeps libev from including F<config.h>, and it also defines dummy
2707	implementations for some libevent functions (such as logging, which is not	4193	implementations for some libevent functions (such as logging, which is not
2708	supported). It will also not define any of the structs usually found in	4194	supported). It will also not define any of the structs usually found in
2709	F<event.h> that are not directly supported by the libev core alone.	4195	F<event.h> that are not directly supported by the libev core alone.
2710		4196
		4197	In standalone mode, libev will still try to automatically deduce the
		4198	configuration, but has to be more conservative.
		4199
2711	=item EV_USE_MONOTONIC	4200	=item EV_USE_MONOTONIC
2712		4201
2713	If defined to be C<1>, libev will try to detect the availability of the	4202	If defined to be C<1>, libev will try to detect the availability of the
2714	monotonic clock option at both compiletime and runtime. Otherwise no use	4203	monotonic clock option at both compile time and runtime. Otherwise no
2715	of the monotonic clock option will be attempted. If you enable this, you	4204	use of the monotonic clock option will be attempted. If you enable this,
2716	usually have to link against librt or something similar. Enabling it when	4205	you usually have to link against librt or something similar. Enabling it
2717	the functionality isn't available is safe, though, although you have	4206	when the functionality isn't available is safe, though, although you have
2718	to make sure you link against any libraries where the C<clock_gettime>	4207	to make sure you link against any libraries where the C<clock_gettime>
2719	function is hiding in (often F<-lrt>).	4208	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2720		4209
2721	=item EV_USE_REALTIME	4210	=item EV_USE_REALTIME
2722		4211
2723	If defined to be C<1>, libev will try to detect the availability of the	4212	If defined to be C<1>, libev will try to detect the availability of the
2724	realtime clock option at compiletime (and assume its availability at	4213	real-time clock option at compile time (and assume its availability
2725	runtime if successful). Otherwise no use of the realtime clock option will	4214	at runtime if successful). Otherwise no use of the real-time clock
2726	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	4215	option will be attempted. This effectively replaces C<gettimeofday>
2727	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	4216	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2728	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	4217	correctness. See the note about libraries in the description of
		4218	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		4219	C<EV_USE_CLOCK_SYSCALL>.
		4220
		4221	=item EV_USE_CLOCK_SYSCALL
		4222
		4223	If defined to be C<1>, libev will try to use a direct syscall instead
		4224	of calling the system-provided C<clock_gettime> function. This option
		4225	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		4226	unconditionally pulls in C<libpthread>, slowing down single-threaded
		4227	programs needlessly. Using a direct syscall is slightly slower (in
		4228	theory), because no optimised vdso implementation can be used, but avoids
		4229	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		4230	higher, as it simplifies linking (no need for C<-lrt>).
2729		4231
2730	=item EV_USE_NANOSLEEP	4232	=item EV_USE_NANOSLEEP
2731		4233
2732	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	4234	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2733	and will use it for delays. Otherwise it will use C<select ()>.	4235	and will use it for delays. Otherwise it will use C<select ()>.
2734		4236
		4237	=item EV_USE_EVENTFD
		4238
		4239	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		4240	available and will probe for kernel support at runtime. This will improve
		4241	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		4242	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4243	2.7 or newer, otherwise disabled.
		4244
2735	=item EV_USE_SELECT	4245	=item EV_USE_SELECT
2736		4246
2737	If undefined or defined to be C<1>, libev will compile in support for the	4247	If undefined or defined to be C<1>, libev will compile in support for the
2738	C<select>(2) backend. No attempt at autodetection will be done: if no	4248	C<select>(2) backend. No attempt at auto-detection will be done: if no
2739	other method takes over, select will be it. Otherwise the select backend	4249	other method takes over, select will be it. Otherwise the select backend
2740	will not be compiled in.	4250	will not be compiled in.
2741		4251
2742	=item EV_SELECT_USE_FD_SET	4252	=item EV_SELECT_USE_FD_SET
2743		4253
2744	If defined to C<1>, then the select backend will use the system C<fd_set>	4254	If defined to C<1>, then the select backend will use the system C<fd_set>
2745	structure. This is useful if libev doesn't compile due to a missing	4255	structure. This is useful if libev doesn't compile due to a missing
2746	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	4256	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2747	exotic systems. This usually limits the range of file descriptors to some	4257	on exotic systems. This usually limits the range of file descriptors to
2748	low limit such as 1024 or might have other limitations (winsocket only	4258	some low limit such as 1024 or might have other limitations (winsocket
2749	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	4259	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2750	influence the size of the C<fd_set> used.	4260	configures the maximum size of the C<fd_set>.
2751		4261
2752	=item EV_SELECT_IS_WINSOCKET	4262	=item EV_SELECT_IS_WINSOCKET
2753		4263
2754	When defined to C<1>, the select backend will assume that	4264	When defined to C<1>, the select backend will assume that
2755	select/socket/connect etc. don't understand file descriptors but	4265	select/socket/connect etc. don't understand file descriptors but
…		…
2757	be used is the winsock select). This means that it will call	4267	be used is the winsock select). This means that it will call
2758	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	4268	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2759	it is assumed that all these functions actually work on fds, even	4269	it is assumed that all these functions actually work on fds, even
2760	on win32. Should not be defined on non-win32 platforms.	4270	on win32. Should not be defined on non-win32 platforms.
2761		4271
2762	=item EV_FD_TO_WIN32_HANDLE	4272	=item EV_FD_TO_WIN32_HANDLE(fd)
2763		4273
2764	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map	4274	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
2765	file descriptors to socket handles. When not defining this symbol (the	4275	file descriptors to socket handles. When not defining this symbol (the
2766	default), then libev will call C<_get_osfhandle>, which is usually	4276	default), then libev will call C<_get_osfhandle>, which is usually
2767	correct. In some cases, programs use their own file descriptor management,	4277	correct. In some cases, programs use their own file descriptor management,
2768	in which case they can provide this function to map fds to socket handles.	4278	in which case they can provide this function to map fds to socket handles.
2769		4279
		4280	=item EV_WIN32_HANDLE_TO_FD(handle)
		4281
		4282	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		4283	using the standard C<_open_osfhandle> function. For programs implementing
		4284	their own fd to handle mapping, overwriting this function makes it easier
		4285	to do so. This can be done by defining this macro to an appropriate value.
		4286
		4287	=item EV_WIN32_CLOSE_FD(fd)
		4288
		4289	If programs implement their own fd to handle mapping on win32, then this
		4290	macro can be used to override the C<close> function, useful to unregister
		4291	file descriptors again. Note that the replacement function has to close
		4292	the underlying OS handle.
		4293
2770	=item EV_USE_POLL	4294	=item EV_USE_POLL
2771		4295
2772	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4296	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2773	backend. Otherwise it will be enabled on non-win32 platforms. It	4297	backend. Otherwise it will be enabled on non-win32 platforms. It
2774	takes precedence over select.	4298	takes precedence over select.
2775		4299
2776	=item EV_USE_EPOLL	4300	=item EV_USE_EPOLL
2777		4301
2778	If defined to be C<1>, libev will compile in support for the Linux	4302	If defined to be C<1>, libev will compile in support for the Linux
2779	C<epoll>(7) backend. Its availability will be detected at runtime,	4303	C<epoll>(7) backend. Its availability will be detected at runtime,
2780	otherwise another method will be used as fallback. This is the	4304	otherwise another method will be used as fallback. This is the preferred
2781	preferred backend for GNU/Linux systems.	4305	backend for GNU/Linux systems. If undefined, it will be enabled if the
		4306	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2782		4307
2783	=item EV_USE_KQUEUE	4308	=item EV_USE_KQUEUE
2784		4309
2785	If defined to be C<1>, libev will compile in support for the BSD style	4310	If defined to be C<1>, libev will compile in support for the BSD style
2786	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	4311	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2799	otherwise another method will be used as fallback. This is the preferred	4324	otherwise another method will be used as fallback. This is the preferred
2800	backend for Solaris 10 systems.	4325	backend for Solaris 10 systems.
2801		4326
2802	=item EV_USE_DEVPOLL	4327	=item EV_USE_DEVPOLL
2803		4328
2804	reserved for future expansion, works like the USE symbols above.	4329	Reserved for future expansion, works like the USE symbols above.
2805		4330
2806	=item EV_USE_INOTIFY	4331	=item EV_USE_INOTIFY
2807		4332
2808	If defined to be C<1>, libev will compile in support for the Linux inotify	4333	If defined to be C<1>, libev will compile in support for the Linux inotify
2809	interface to speed up C<ev_stat> watchers. Its actual availability will	4334	interface to speed up C<ev_stat> watchers. Its actual availability will
2810	be detected at runtime.	4335	be detected at runtime. If undefined, it will be enabled if the headers
		4336	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2811		4337
2812	=item EV_ATOMIC_T	4338	=item EV_ATOMIC_T
2813		4339
2814	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4340	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
2815	access is atomic with respect to other threads or signal contexts. No such	4341	access is atomic with respect to other threads or signal contexts. No such
2816	type is easily found in the C language, so you can provide your own type	4342	type is easily found in the C language, so you can provide your own type
2817	that you know is safe for your purposes. It is used both for signal handler "locking"	4343	that you know is safe for your purposes. It is used both for signal handler "locking"
2818	as well as for signal and thread safety in C<ev_async> watchers.	4344	as well as for signal and thread safety in C<ev_async> watchers.
2819		4345
2820	In the absense of this define, libev will use C<sig_atomic_t volatile>	4346	In the absence of this define, libev will use C<sig_atomic_t volatile>
2821	(from F<signal.h>), which is usually good enough on most platforms.	4347	(from F<signal.h>), which is usually good enough on most platforms.
2822		4348
2823	=item EV_H	4349	=item EV_H (h)
2824		4350
2825	The name of the F<ev.h> header file used to include it. The default if	4351	The name of the F<ev.h> header file used to include it. The default if
2826	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be	4352	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2827	used to virtually rename the F<ev.h> header file in case of conflicts.	4353	used to virtually rename the F<ev.h> header file in case of conflicts.
2828		4354
2829	=item EV_CONFIG_H	4355	=item EV_CONFIG_H (h)
2830		4356
2831	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	4357	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2832	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	4358	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2833	C<EV_H>, above.	4359	C<EV_H>, above.
2834		4360
2835	=item EV_EVENT_H	4361	=item EV_EVENT_H (h)
2836		4362
2837	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	4363	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2838	of how the F<event.h> header can be found, the default is C<"event.h">.	4364	of how the F<event.h> header can be found, the default is C<"event.h">.
2839		4365
2840	=item EV_PROTOTYPES	4366	=item EV_PROTOTYPES (h)
2841		4367
2842	If defined to be C<0>, then F<ev.h> will not define any function	4368	If defined to be C<0>, then F<ev.h> will not define any function
2843	prototypes, but still define all the structs and other symbols. This is	4369	prototypes, but still define all the structs and other symbols. This is
2844	occasionally useful if you want to provide your own wrapper functions	4370	occasionally useful if you want to provide your own wrapper functions
2845	around libev functions.	4371	around libev functions.
…		…
2864	When doing priority-based operations, libev usually has to linearly search	4390	When doing priority-based operations, libev usually has to linearly search
2865	all the priorities, so having many of them (hundreds) uses a lot of space	4391	all the priorities, so having many of them (hundreds) uses a lot of space
2866	and time, so using the defaults of five priorities (-2 .. +2) is usually	4392	and time, so using the defaults of five priorities (-2 .. +2) is usually
2867	fine.	4393	fine.
2868		4394
2869	If your embedding app does not need any priorities, defining these both to	4395	If your embedding application does not need any priorities, defining these
2870	C<0> will save some memory and cpu.	4396	both to C<0> will save some memory and CPU.
2871		4397
2872	=item EV_PERIODIC_ENABLE	4398	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		4399	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		4400	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
2873		4401
2874	If undefined or defined to be C<1>, then periodic timers are supported. If	4402	If undefined or defined to be C<1> (and the platform supports it), then
2875	defined to be C<0>, then they are not. Disabling them saves a few kB of	4403	the respective watcher type is supported. If defined to be C<0>, then it
2876	code.	4404	is not. Disabling watcher types mainly saves code size.
2877		4405
2878	=item EV_IDLE_ENABLE	4406	=item EV_FEATURES
2879
2880	If undefined or defined to be C<1>, then idle watchers are supported. If
2881	defined to be C<0>, then they are not. Disabling them saves a few kB of
2882	code.
2883
2884	=item EV_EMBED_ENABLE
2885
2886	If undefined or defined to be C<1>, then embed watchers are supported. If
2887	defined to be C<0>, then they are not.
2888
2889	=item EV_STAT_ENABLE
2890
2891	If undefined or defined to be C<1>, then stat watchers are supported. If
2892	defined to be C<0>, then they are not.
2893
2894	=item EV_FORK_ENABLE
2895
2896	If undefined or defined to be C<1>, then fork watchers are supported. If
2897	defined to be C<0>, then they are not.
2898
2899	=item EV_ASYNC_ENABLE
2900
2901	If undefined or defined to be C<1>, then async watchers are supported. If
2902	defined to be C<0>, then they are not.
2903
2904	=item EV_MINIMAL
2905		4407
2906	If you need to shave off some kilobytes of code at the expense of some	4408	If you need to shave off some kilobytes of code at the expense of some
2907	speed, define this symbol to C<1>. Currently only used for gcc to override	4409	speed (but with the full API), you can define this symbol to request
2908	some inlining decisions, saves roughly 30% codesize of amd64.	4410	certain subsets of functionality. The default is to enable all features
		4411	that can be enabled on the platform.
		4412
		4413	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4414	with some broad features you want) and then selectively re-enable
		4415	additional parts you want, for example if you want everything minimal,
		4416	but multiple event loop support, async and child watchers and the poll
		4417	backend, use this:
		4418
		4419	#define EV_FEATURES 0
		4420	#define EV_MULTIPLICITY 1
		4421	#define EV_USE_POLL 1
		4422	#define EV_CHILD_ENABLE 1
		4423	#define EV_ASYNC_ENABLE 1
		4424
		4425	The actual value is a bitset, it can be a combination of the following
		4426	values:
		4427
		4428	=over 4
		4429
		4430	=item C<1> - faster/larger code
		4431
		4432	Use larger code to speed up some operations.
		4433
		4434	Currently this is used to override some inlining decisions (enlarging the
		4435	code size by roughly 30% on amd64).
		4436
		4437	When optimising for size, use of compiler flags such as C<-Os> with
		4438	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4439	assertions.
		4440
		4441	=item C<2> - faster/larger data structures
		4442
		4443	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4444	hash table sizes and so on. This will usually further increase code size
		4445	and can additionally have an effect on the size of data structures at
		4446	runtime.
		4447
		4448	=item C<4> - full API configuration
		4449
		4450	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4451	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4452
		4453	=item C<8> - full API
		4454
		4455	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4456	details on which parts of the API are still available without this
		4457	feature, and do not complain if this subset changes over time.
		4458
		4459	=item C<16> - enable all optional watcher types
		4460
		4461	Enables all optional watcher types. If you want to selectively enable
		4462	only some watcher types other than I/O and timers (e.g. prepare,
		4463	embed, async, child...) you can enable them manually by defining
		4464	C<EV_watchertype_ENABLE> to C<1> instead.
		4465
		4466	=item C<32> - enable all backends
		4467
		4468	This enables all backends - without this feature, you need to enable at
		4469	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4470
		4471	=item C<64> - enable OS-specific "helper" APIs
		4472
		4473	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4474	default.
		4475
		4476	=back
		4477
		4478	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4479	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4480	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4481	watchers, timers and monotonic clock support.
		4482
		4483	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4484	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4485	your program might be left out as well - a binary starting a timer and an
		4486	I/O watcher then might come out at only 5Kb.
		4487
		4488	=item EV_AVOID_STDIO
		4489
		4490	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4491	functions (printf, scanf, perror etc.). This will increase the code size
		4492	somewhat, but if your program doesn't otherwise depend on stdio and your
		4493	libc allows it, this avoids linking in the stdio library which is quite
		4494	big.
		4495
		4496	Note that error messages might become less precise when this option is
		4497	enabled.
		4498
		4499	=item EV_NSIG
		4500
		4501	The highest supported signal number, +1 (or, the number of
		4502	signals): Normally, libev tries to deduce the maximum number of signals
		4503	automatically, but sometimes this fails, in which case it can be
		4504	specified. Also, using a lower number than detected (C<32> should be
		4505	good for about any system in existence) can save some memory, as libev
		4506	statically allocates some 12-24 bytes per signal number.
2909		4507
2910	=item EV_PID_HASHSIZE	4508	=item EV_PID_HASHSIZE
2911		4509
2912	C<ev_child> watchers use a small hash table to distribute workload by	4510	C<ev_child> watchers use a small hash table to distribute workload by
2913	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	4511	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
2914	than enough. If you need to manage thousands of children you might want to	4512	usually more than enough. If you need to manage thousands of children you
2915	increase this value (I<must> be a power of two).	4513	might want to increase this value (I<must> be a power of two).
2916		4514
2917	=item EV_INOTIFY_HASHSIZE	4515	=item EV_INOTIFY_HASHSIZE
2918		4516
2919	C<ev_stat> watchers use a small hash table to distribute workload by	4517	C<ev_stat> watchers use a small hash table to distribute workload by
2920	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	4518	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
2921	usually more than enough. If you need to manage thousands of C<ev_stat>	4519	disabled), usually more than enough. If you need to manage thousands of
2922	watchers you might want to increase this value (I<must> be a power of	4520	C<ev_stat> watchers you might want to increase this value (I<must> be a
2923	two).	4521	power of two).
		4522
		4523	=item EV_USE_4HEAP
		4524
		4525	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4526	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		4527	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		4528	faster performance with many (thousands) of watchers.
		4529
		4530	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4531	will be C<0>.
		4532
		4533	=item EV_HEAP_CACHE_AT
		4534
		4535	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4536	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		4537	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		4538	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		4539	but avoids random read accesses on heap changes. This improves performance
		4540	noticeably with many (hundreds) of watchers.
		4541
		4542	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4543	will be C<0>.
		4544
		4545	=item EV_VERIFY
		4546
		4547	Controls how much internal verification (see C<ev_verify ()>) will
		4548	be done: If set to C<0>, no internal verification code will be compiled
		4549	in. If set to C<1>, then verification code will be compiled in, but not
		4550	called. If set to C<2>, then the internal verification code will be
		4551	called once per loop, which can slow down libev. If set to C<3>, then the
		4552	verification code will be called very frequently, which will slow down
		4553	libev considerably.
		4554
		4555	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4556	will be C<0>.
2924		4557
2925	=item EV_COMMON	4558	=item EV_COMMON
2926		4559
2927	By default, all watchers have a C<void *data> member. By redefining	4560	By default, all watchers have a C<void *data> member. By redefining
2928	this macro to a something else you can include more and other types of	4561	this macro to something else you can include more and other types of
2929	members. You have to define it each time you include one of the files,	4562	members. You have to define it each time you include one of the files,
2930	though, and it must be identical each time.	4563	though, and it must be identical each time.
2931		4564
2932	For example, the perl EV module uses something like this:	4565	For example, the perl EV module uses something like this:
2933		4566
2934	#define EV_COMMON \	4567	#define EV_COMMON \
2935	SV *self; /* contains this struct */ \	4568	SV *self; /* contains this struct */ \
2936	SV *cb_sv, *fh /* note no trailing ";" */	4569	SV *cb_sv, *fh /* note no trailing ";" */
2937		4570
2938	=item EV_CB_DECLARE (type)	4571	=item EV_CB_DECLARE (type)
2939		4572
2940	=item EV_CB_INVOKE (watcher, revents)	4573	=item EV_CB_INVOKE (watcher, revents)
2941		4574
…		…
2946	definition and a statement, respectively. See the F<ev.h> header file for	4579	definition and a statement, respectively. See the F<ev.h> header file for
2947	their default definitions. One possible use for overriding these is to	4580	their default definitions. One possible use for overriding these is to
2948	avoid the C<struct ev_loop *> as first argument in all cases, or to use	4581	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2949	method calls instead of plain function calls in C++.	4582	method calls instead of plain function calls in C++.
2950		4583
		4584	=back
		4585
2951	=head2 EXPORTED API SYMBOLS	4586	=head2 EXPORTED API SYMBOLS
2952		4587
2953	If you need to re-export the API (e.g. via a dll) and you need a list of	4588	If you need to re-export the API (e.g. via a DLL) and you need a list of
2954	exported symbols, you can use the provided F<Symbol.*> files which list	4589	exported symbols, you can use the provided F<Symbol.*> files which list
2955	all public symbols, one per line:	4590	all public symbols, one per line:
2956		4591
2957	Symbols.ev for libev proper	4592	Symbols.ev for libev proper
2958	Symbols.event for the libevent emulation	4593	Symbols.event for the libevent emulation
2959		4594
2960	This can also be used to rename all public symbols to avoid clashes with	4595	This can also be used to rename all public symbols to avoid clashes with
2961	multiple versions of libev linked together (which is obviously bad in	4596	multiple versions of libev linked together (which is obviously bad in
2962	itself, but sometimes it is inconvinient to avoid this).	4597	itself, but sometimes it is inconvenient to avoid this).
2963		4598
2964	A sed command like this will create wrapper C<#define>'s that you need to	4599	A sed command like this will create wrapper C<#define>'s that you need to
2965	include before including F<ev.h>:	4600	include before including F<ev.h>:
2966		4601
2967	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h	4602	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
…		…
2984	file.	4619	file.
2985		4620
2986	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	4621	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2987	that everybody includes and which overrides some configure choices:	4622	that everybody includes and which overrides some configure choices:
2988		4623
2989	#define EV_MINIMAL 1	4624	#define EV_FEATURES 8
2990	#define EV_USE_POLL 0	4625	#define EV_USE_SELECT 1
2991	#define EV_MULTIPLICITY 0
2992	#define EV_PERIODIC_ENABLE 0	4626	#define EV_PREPARE_ENABLE 1
		4627	#define EV_IDLE_ENABLE 1
2993	#define EV_STAT_ENABLE 0	4628	#define EV_SIGNAL_ENABLE 1
2994	#define EV_FORK_ENABLE 0	4629	#define EV_CHILD_ENABLE 1
		4630	#define EV_USE_STDEXCEPT 0
2995	#define EV_CONFIG_H <config.h>	4631	#define EV_CONFIG_H <config.h>
2996	#define EV_MINPRI 0
2997	#define EV_MAXPRI 0
2998		4632
2999	#include "ev++.h"	4633	#include "ev++.h"
3000		4634
3001	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4635	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
3002		4636
3003	#include "ev_cpp.h"	4637	#include "ev_cpp.h"
3004	#include "ev.c"	4638	#include "ev.c"
3005		4639
		4640	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
3006		4641
3007	=head1 COMPLEXITIES	4642	=head2 THREADS AND COROUTINES
3008		4643
3009	In this section the complexities of (many of) the algorithms used inside	4644	=head3 THREADS
3010	libev will be explained. For complexity discussions about backends see the
3011	documentation for C<ev_default_init>.
3012		4645
3013	All of the following are about amortised time: If an array needs to be	4646	All libev functions are reentrant and thread-safe unless explicitly
3014	extended, libev needs to realloc and move the whole array, but this	4647	documented otherwise, but libev implements no locking itself. This means
3015	happens asymptotically never with higher number of elements, so O(1) might	4648	that you can use as many loops as you want in parallel, as long as there
3016	mean it might do a lengthy realloc operation in rare cases, but on average	4649	are no concurrent calls into any libev function with the same loop
3017	it is much faster and asymptotically approaches constant time.	4650	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4651	of course): libev guarantees that different event loops share no data
		4652	structures that need any locking.
		4653
		4654	Or to put it differently: calls with different loop parameters can be done
		4655	concurrently from multiple threads, calls with the same loop parameter
		4656	must be done serially (but can be done from different threads, as long as
		4657	only one thread ever is inside a call at any point in time, e.g. by using
		4658	a mutex per loop).
		4659
		4660	Specifically to support threads (and signal handlers), libev implements
		4661	so-called C<ev_async> watchers, which allow some limited form of
		4662	concurrency on the same event loop, namely waking it up "from the
		4663	outside".
		4664
		4665	If you want to know which design (one loop, locking, or multiple loops
		4666	without or something else still) is best for your problem, then I cannot
		4667	help you, but here is some generic advice:
3018		4668
3019	=over 4	4669	=over 4
3020		4670
3021	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4671	=item * most applications have a main thread: use the default libev loop
		4672	in that thread, or create a separate thread running only the default loop.
3022		4673
3023	This means that, when you have a watcher that triggers in one hour and	4674	This helps integrating other libraries or software modules that use libev
3024	there are 100 watchers that would trigger before that then inserting will	4675	themselves and don't care/know about threading.
3025	have to skip roughly seven (C<ld 100>) of these watchers.
3026		4676
3027	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)	4677	=item * one loop per thread is usually a good model.
3028		4678
3029	That means that changing a timer costs less than removing/adding them	4679	Doing this is almost never wrong, sometimes a better-performance model
3030	as only the relative motion in the event queue has to be paid for.	4680	exists, but it is always a good start.
3031		4681
3032	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)	4682	=item * other models exist, such as the leader/follower pattern, where one
		4683	loop is handed through multiple threads in a kind of round-robin fashion.
3033		4684
3034	These just add the watcher into an array or at the head of a list.	4685	Choosing a model is hard - look around, learn, know that usually you can do
		4686	better than you currently do :-)
3035		4687
3036	=item Stopping check/prepare/idle/fork/async watchers: O(1)	4688	=item * often you need to talk to some other thread which blocks in the
		4689	event loop.
3037		4690
3038	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	4691	C<ev_async> watchers can be used to wake them up from other threads safely
		4692	(or from signal contexts...).
3039		4693
3040	These watchers are stored in lists then need to be walked to find the	4694	An example use would be to communicate signals or other events that only
3041	correct watcher to remove. The lists are usually short (you don't usually	4695	work in the default loop by registering the signal watcher with the
3042	have many watchers waiting for the same fd or signal).	4696	default loop and triggering an C<ev_async> watcher from the default loop
3043		4697	watcher callback into the event loop interested in the signal.
3044	=item Finding the next timer in each loop iteration: O(1)
3045
3046	By virtue of using a binary heap, the next timer is always found at the
3047	beginning of the storage array.
3048
3049	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
3050
3051	A change means an I/O watcher gets started or stopped, which requires
3052	libev to recalculate its status (and possibly tell the kernel, depending
3053	on backend and wether C<ev_io_set> was used).
3054
3055	=item Activating one watcher (putting it into the pending state): O(1)
3056
3057	=item Priority handling: O(number_of_priorities)
3058
3059	Priorities are implemented by allocating some space for each
3060	priority. When doing priority-based operations, libev usually has to
3061	linearly search all the priorities, but starting/stopping and activating
3062	watchers becomes O(1) w.r.t. priority handling.
3063
3064	=item Sending an ev_async: O(1)
3065
3066	=item Processing ev_async_send: O(number_of_async_watchers)
3067
3068	=item Processing signals: O(max_signal_number)
3069
3070	Sending involves a syscall I<iff> there were no other C<ev_async_send>
3071	calls in the current loop iteration. Checking for async and signal events
3072	involves iterating over all running async watchers or all signal numbers.
3073		4698
3074	=back	4699	=back
3075		4700
		4701	See also L<THREAD LOCKING EXAMPLE>.
3076		4702
3077	=head1 Win32 platform limitations and workarounds	4703	=head3 COROUTINES
		4704
		4705	Libev is very accommodating to coroutines ("cooperative threads"):
		4706	libev fully supports nesting calls to its functions from different
		4707	coroutines (e.g. you can call C<ev_run> on the same loop from two
		4708	different coroutines, and switch freely between both coroutines running
		4709	the loop, as long as you don't confuse yourself). The only exception is
		4710	that you must not do this from C<ev_periodic> reschedule callbacks.
		4711
		4712	Care has been taken to ensure that libev does not keep local state inside
		4713	C<ev_run>, and other calls do not usually allow for coroutine switches as
		4714	they do not call any callbacks.
		4715
		4716	=head2 COMPILER WARNINGS
		4717
		4718	Depending on your compiler and compiler settings, you might get no or a
		4719	lot of warnings when compiling libev code. Some people are apparently
		4720	scared by this.
		4721
		4722	However, these are unavoidable for many reasons. For one, each compiler
		4723	has different warnings, and each user has different tastes regarding
		4724	warning options. "Warn-free" code therefore cannot be a goal except when
		4725	targeting a specific compiler and compiler-version.
		4726
		4727	Another reason is that some compiler warnings require elaborate
		4728	workarounds, or other changes to the code that make it less clear and less
		4729	maintainable.
		4730
		4731	And of course, some compiler warnings are just plain stupid, or simply
		4732	wrong (because they don't actually warn about the condition their message
		4733	seems to warn about). For example, certain older gcc versions had some
		4734	warnings that resulted in an extreme number of false positives. These have
		4735	been fixed, but some people still insist on making code warn-free with
		4736	such buggy versions.
		4737
		4738	While libev is written to generate as few warnings as possible,
		4739	"warn-free" code is not a goal, and it is recommended not to build libev
		4740	with any compiler warnings enabled unless you are prepared to cope with
		4741	them (e.g. by ignoring them). Remember that warnings are just that:
		4742	warnings, not errors, or proof of bugs.
		4743
		4744
		4745	=head2 VALGRIND
		4746
		4747	Valgrind has a special section here because it is a popular tool that is
		4748	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		4749
		4750	If you think you found a bug (memory leak, uninitialised data access etc.)
		4751	in libev, then check twice: If valgrind reports something like:
		4752
		4753	==2274== definitely lost: 0 bytes in 0 blocks.
		4754	==2274== possibly lost: 0 bytes in 0 blocks.
		4755	==2274== still reachable: 256 bytes in 1 blocks.
		4756
		4757	Then there is no memory leak, just as memory accounted to global variables
		4758	is not a memleak - the memory is still being referenced, and didn't leak.
		4759
		4760	Similarly, under some circumstances, valgrind might report kernel bugs
		4761	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4762	although an acceptable workaround has been found here), or it might be
		4763	confused.
		4764
		4765	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		4766	make it into some kind of religion.
		4767
		4768	If you are unsure about something, feel free to contact the mailing list
		4769	with the full valgrind report and an explanation on why you think this
		4770	is a bug in libev (best check the archives, too :). However, don't be
		4771	annoyed when you get a brisk "this is no bug" answer and take the chance
		4772	of learning how to interpret valgrind properly.
		4773
		4774	If you need, for some reason, empty reports from valgrind for your project
		4775	I suggest using suppression lists.
		4776
		4777
		4778	=head1 PORTABILITY NOTES
		4779
		4780	=head2 GNU/LINUX 32 BIT LIMITATIONS
		4781
		4782	GNU/Linux is the only common platform that supports 64 bit file/large file
		4783	interfaces but I<disables> them by default.
		4784
		4785	That means that libev compiled in the default environment doesn't support
		4786	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
		4787
		4788	Unfortunately, many programs try to work around this GNU/Linux issue
		4789	by enabling the large file API, which makes them incompatible with the
		4790	standard libev compiled for their system.
		4791
		4792	Likewise, libev cannot enable the large file API itself as this would
		4793	suddenly make it incompatible to the default compile time environment,
		4794	i.e. all programs not using special compile switches.
		4795
		4796	=head2 OS/X AND DARWIN BUGS
		4797
		4798	The whole thing is a bug if you ask me - basically any system interface
		4799	you touch is broken, whether it is locales, poll, kqueue or even the
		4800	OpenGL drivers.
		4801
		4802	=head3 C<kqueue> is buggy
		4803
		4804	The kqueue syscall is broken in all known versions - most versions support
		4805	only sockets, many support pipes.
		4806
		4807	Libev tries to work around this by not using C<kqueue> by default on this
		4808	rotten platform, but of course you can still ask for it when creating a
		4809	loop - embedding a socket-only kqueue loop into a select-based one is
		4810	probably going to work well.
		4811
		4812	=head3 C<poll> is buggy
		4813
		4814	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		4815	implementation by something calling C<kqueue> internally around the 10.5.6
		4816	release, so now C<kqueue> I<and> C<poll> are broken.
		4817
		4818	Libev tries to work around this by not using C<poll> by default on
		4819	this rotten platform, but of course you can still ask for it when creating
		4820	a loop.
		4821
		4822	=head3 C<select> is buggy
		4823
		4824	All that's left is C<select>, and of course Apple found a way to fuck this
		4825	one up as well: On OS/X, C<select> actively limits the number of file
		4826	descriptors you can pass in to 1024 - your program suddenly crashes when
		4827	you use more.
		4828
		4829	There is an undocumented "workaround" for this - defining
		4830	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		4831	work on OS/X.
		4832
		4833	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		4834
		4835	=head3 C<errno> reentrancy
		4836
		4837	The default compile environment on Solaris is unfortunately so
		4838	thread-unsafe that you can't even use components/libraries compiled
		4839	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		4840	defined by default. A valid, if stupid, implementation choice.
		4841
		4842	If you want to use libev in threaded environments you have to make sure
		4843	it's compiled with C<_REENTRANT> defined.
		4844
		4845	=head3 Event port backend
		4846
		4847	The scalable event interface for Solaris is called "event
		4848	ports". Unfortunately, this mechanism is very buggy in all major
		4849	releases. If you run into high CPU usage, your program freezes or you get
		4850	a large number of spurious wakeups, make sure you have all the relevant
		4851	and latest kernel patches applied. No, I don't know which ones, but there
		4852	are multiple ones to apply, and afterwards, event ports actually work
		4853	great.
		4854
		4855	If you can't get it to work, you can try running the program by setting
		4856	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		4857	C<select> backends.
		4858
		4859	=head2 AIX POLL BUG
		4860
		4861	AIX unfortunately has a broken C<poll.h> header. Libev works around
		4862	this by trying to avoid the poll backend altogether (i.e. it's not even
		4863	compiled in), which normally isn't a big problem as C<select> works fine
		4864	with large bitsets on AIX, and AIX is dead anyway.
		4865
		4866	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		4867
		4868	=head3 General issues
3078		4869
3079	Win32 doesn't support any of the standards (e.g. POSIX) that libev	4870	Win32 doesn't support any of the standards (e.g. POSIX) that libev
3080	requires, and its I/O model is fundamentally incompatible with the POSIX	4871	requires, and its I/O model is fundamentally incompatible with the POSIX
3081	model. Libev still offers limited functionality on this platform in	4872	model. Libev still offers limited functionality on this platform in
3082	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	4873	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
3083	descriptors. This only applies when using Win32 natively, not when using	4874	descriptors. This only applies when using Win32 natively, not when using
3084	e.g. cygwin.	4875	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		4876	as every compielr comes with a slightly differently broken/incompatible
		4877	environment.
		4878
		4879	Lifting these limitations would basically require the full
		4880	re-implementation of the I/O system. If you are into this kind of thing,
		4881	then note that glib does exactly that for you in a very portable way (note
		4882	also that glib is the slowest event library known to man).
3085		4883
3086	There is no supported compilation method available on windows except	4884	There is no supported compilation method available on windows except
3087	embedding it into other applications.	4885	embedding it into other applications.
3088		4886
		4887	Sensible signal handling is officially unsupported by Microsoft - libev
		4888	tries its best, but under most conditions, signals will simply not work.
		4889
		4890	Not a libev limitation but worth mentioning: windows apparently doesn't
		4891	accept large writes: instead of resulting in a partial write, windows will
		4892	either accept everything or return C<ENOBUFS> if the buffer is too large,
		4893	so make sure you only write small amounts into your sockets (less than a
		4894	megabyte seems safe, but this apparently depends on the amount of memory
		4895	available).
		4896
3089	Due to the many, low, and arbitrary limits on the win32 platform and the	4897	Due to the many, low, and arbitrary limits on the win32 platform and
3090	abysmal performance of winsockets, using a large number of sockets is not	4898	the abysmal performance of winsockets, using a large number of sockets
3091	recommended (and not reasonable). If your program needs to use more than	4899	is not recommended (and not reasonable). If your program needs to use
3092	a hundred or so sockets, then likely it needs to use a totally different	4900	more than a hundred or so sockets, then likely it needs to use a totally
3093	implementation for windows, as libev offers the POSIX model, which cannot	4901	different implementation for windows, as libev offers the POSIX readiness
3094	be implemented efficiently on windows (microsoft monopoly games).	4902	notification model, which cannot be implemented efficiently on windows
		4903	(due to Microsoft monopoly games).
3095		4904
3096	=over 4	4905	A typical way to use libev under windows is to embed it (see the embedding
		4906	section for details) and use the following F<evwrap.h> header file instead
		4907	of F<ev.h>:
3097		4908
		4909	#define EV_STANDALONE /* keeps ev from requiring config.h */
		4910	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		4911
		4912	#include "ev.h"
		4913
		4914	And compile the following F<evwrap.c> file into your project (make sure
		4915	you do I<not> compile the F<ev.c> or any other embedded source files!):
		4916
		4917	#include "evwrap.h"
		4918	#include "ev.c"
		4919
3098	=item The winsocket select function	4920	=head3 The winsocket C<select> function
3099		4921
3100	The winsocket C<select> function doesn't follow POSIX in that it requires	4922	The winsocket C<select> function doesn't follow POSIX in that it
3101	socket I<handles> and not socket I<file descriptors>. This makes select	4923	requires socket I<handles> and not socket I<file descriptors> (it is
3102	very inefficient, and also requires a mapping from file descriptors	4924	also extremely buggy). This makes select very inefficient, and also
3103	to socket handles. See the discussion of the C<EV_SELECT_USE_FD_SET>,	4925	requires a mapping from file descriptors to socket handles (the Microsoft
3104	C<EV_SELECT_IS_WINSOCKET> and C<EV_FD_TO_WIN32_HANDLE> preprocessor	4926	C runtime provides the function C<_open_osfhandle> for this). See the
3105	symbols for more info.	4927	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		4928	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
3106		4929
3107	The configuration for a "naked" win32 using the microsoft runtime	4930	The configuration for a "naked" win32 using the Microsoft runtime
3108	libraries and raw winsocket select is:	4931	libraries and raw winsocket select is:
3109		4932
3110	#define EV_USE_SELECT 1	4933	#define EV_USE_SELECT 1
3111	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */	4934	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
3112		4935
3113	Note that winsockets handling of fd sets is O(n), so you can easily get a	4936	Note that winsockets handling of fd sets is O(n), so you can easily get a
3114	complexity in the O(n²) range when using win32.	4937	complexity in the O(n²) range when using win32.
3115		4938
3116	=item Limited number of file descriptors	4939	=head3 Limited number of file descriptors
3117		4940
3118	Windows has numerous arbitrary (and low) limits on things. Early versions	4941	Windows has numerous arbitrary (and low) limits on things.
3119	of winsocket's select only supported waiting for a max. of C<64> handles	4942
		4943	Early versions of winsocket's select only supported waiting for a maximum
3120	(probably owning to the fact that all windows kernels can only wait for	4944	of C<64> handles (probably owning to the fact that all windows kernels
3121	C<64> things at the same time internally; microsoft recommends spawning a	4945	can only wait for C<64> things at the same time internally; Microsoft
3122	chain of threads and wait for 63 handles and the previous thread in each).	4946	recommends spawning a chain of threads and wait for 63 handles and the
		4947	previous thread in each. Sounds great!).
3123		4948
3124	Newer versions support more handles, but you need to define C<FD_SETSIZE>	4949	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3125	to some high number (e.g. C<2048>) before compiling the winsocket select	4950	to some high number (e.g. C<2048>) before compiling the winsocket select
3126	call (which might be in libev or elsewhere, for example, perl does its own	4951	call (which might be in libev or elsewhere, for example, perl and many
3127	select emulation on windows).	4952	other interpreters do their own select emulation on windows).
3128		4953
3129	Another limit is the number of file descriptors in the microsoft runtime	4954	Another limit is the number of file descriptors in the Microsoft runtime
3130	libraries, which by default is C<64> (there must be a hidden I<64> fetish	4955	libraries, which by default is C<64> (there must be a hidden I<64>
3131	or something like this inside microsoft). You can increase this by calling	4956	fetish or something like this inside Microsoft). You can increase this
3132	C<_setmaxstdio>, which can increase this limit to C<2048> (another	4957	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
3133	arbitrary limit), but is broken in many versions of the microsoft runtime	4958	(another arbitrary limit), but is broken in many versions of the Microsoft
3134	libraries.
3135
3136	This might get you to about C<512> or C<2048> sockets (depending on	4959	runtime libraries. This might get you to about C<512> or C<2048> sockets
3137	windows version and/or the phase of the moon). To get more, you need to	4960	(depending on windows version and/or the phase of the moon). To get more,
3138	wrap all I/O functions and provide your own fd management, but the cost of	4961	you need to wrap all I/O functions and provide your own fd management, but
3139	calling select (O(n²)) will likely make this unworkable.	4962	the cost of calling select (O(n²)) will likely make this unworkable.
		4963
		4964	=head2 PORTABILITY REQUIREMENTS
		4965
		4966	In addition to a working ISO-C implementation and of course the
		4967	backend-specific APIs, libev relies on a few additional extensions:
		4968
		4969	=over 4
		4970
		4971	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4972	calling conventions regardless of C<ev_watcher_type *>.
		4973
		4974	Libev assumes not only that all watcher pointers have the same internal
		4975	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4976	assumes that the same (machine) code can be used to call any watcher
		4977	callback: The watcher callbacks have different type signatures, but libev
		4978	calls them using an C<ev_watcher *> internally.
		4979
		4980	=item pointer accesses must be thread-atomic
		4981
		4982	Accessing a pointer value must be atomic, it must both be readable and
		4983	writable in one piece - this is the case on all current architectures.
		4984
		4985	=item C<sig_atomic_t volatile> must be thread-atomic as well
		4986
		4987	The type C<sig_atomic_t volatile> (or whatever is defined as
		4988	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		4989	threads. This is not part of the specification for C<sig_atomic_t>, but is
		4990	believed to be sufficiently portable.
		4991
		4992	=item C<sigprocmask> must work in a threaded environment
		4993
		4994	Libev uses C<sigprocmask> to temporarily block signals. This is not
		4995	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		4996	pthread implementations will either allow C<sigprocmask> in the "main
		4997	thread" or will block signals process-wide, both behaviours would
		4998	be compatible with libev. Interaction between C<sigprocmask> and
		4999	C<pthread_sigmask> could complicate things, however.
		5000
		5001	The most portable way to handle signals is to block signals in all threads
		5002	except the initial one, and run the default loop in the initial thread as
		5003	well.
		5004
		5005	=item C<long> must be large enough for common memory allocation sizes
		5006
		5007	To improve portability and simplify its API, libev uses C<long> internally
		5008	instead of C<size_t> when allocating its data structures. On non-POSIX
		5009	systems (Microsoft...) this might be unexpectedly low, but is still at
		5010	least 31 bits everywhere, which is enough for hundreds of millions of
		5011	watchers.
		5012
		5013	=item C<double> must hold a time value in seconds with enough accuracy
		5014
		5015	The type C<double> is used to represent timestamps. It is required to
		5016	have at least 51 bits of mantissa (and 9 bits of exponent), which is
		5017	good enough for at least into the year 4000 with millisecond accuracy
		5018	(the design goal for libev). This requirement is overfulfilled by
		5019	implementations using IEEE 754, which is basically all existing ones. With
		5020	IEEE 754 doubles, you get microsecond accuracy until at least 2200.
3140		5021
3141	=back	5022	=back
3142		5023
		5024	If you know of other additional requirements drop me a note.
		5025
		5026
		5027	=head1 ALGORITHMIC COMPLEXITIES
		5028
		5029	In this section the complexities of (many of) the algorithms used inside
		5030	libev will be documented. For complexity discussions about backends see
		5031	the documentation for C<ev_default_init>.
		5032
		5033	All of the following are about amortised time: If an array needs to be
		5034	extended, libev needs to realloc and move the whole array, but this
		5035	happens asymptotically rarer with higher number of elements, so O(1) might
		5036	mean that libev does a lengthy realloc operation in rare cases, but on
		5037	average it is much faster and asymptotically approaches constant time.
		5038
		5039	=over 4
		5040
		5041	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		5042
		5043	This means that, when you have a watcher that triggers in one hour and
		5044	there are 100 watchers that would trigger before that, then inserting will
		5045	have to skip roughly seven (C<ld 100>) of these watchers.
		5046
		5047	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		5048
		5049	That means that changing a timer costs less than removing/adding them,
		5050	as only the relative motion in the event queue has to be paid for.
		5051
		5052	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		5053
		5054	These just add the watcher into an array or at the head of a list.
		5055
		5056	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		5057
		5058	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		5059
		5060	These watchers are stored in lists, so they need to be walked to find the
		5061	correct watcher to remove. The lists are usually short (you don't usually
		5062	have many watchers waiting for the same fd or signal: one is typical, two
		5063	is rare).
		5064
		5065	=item Finding the next timer in each loop iteration: O(1)
		5066
		5067	By virtue of using a binary or 4-heap, the next timer is always found at a
		5068	fixed position in the storage array.
		5069
		5070	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		5071
		5072	A change means an I/O watcher gets started or stopped, which requires
		5073	libev to recalculate its status (and possibly tell the kernel, depending
		5074	on backend and whether C<ev_io_set> was used).
		5075
		5076	=item Activating one watcher (putting it into the pending state): O(1)
		5077
		5078	=item Priority handling: O(number_of_priorities)
		5079
		5080	Priorities are implemented by allocating some space for each
		5081	priority. When doing priority-based operations, libev usually has to
		5082	linearly search all the priorities, but starting/stopping and activating
		5083	watchers becomes O(1) with respect to priority handling.
		5084
		5085	=item Sending an ev_async: O(1)
		5086
		5087	=item Processing ev_async_send: O(number_of_async_watchers)
		5088
		5089	=item Processing signals: O(max_signal_number)
		5090
		5091	Sending involves a system call I<iff> there were no other C<ev_async_send>
		5092	calls in the current loop iteration. Checking for async and signal events
		5093	involves iterating over all running async watchers or all signal numbers.
		5094
		5095	=back
		5096
		5097
		5098	=head1 PORTING FROM LIBEV 3.X TO 4.X
		5099
		5100	The major version 4 introduced some incompatible changes to the API.
		5101
		5102	At the moment, the C<ev.h> header file provides compatibility definitions
		5103	for all changes, so most programs should still compile. The compatibility
		5104	layer might be removed in later versions of libev, so better update to the
		5105	new API early than late.
		5106
		5107	=over 4
		5108
		5109	=item C<EV_COMPAT3> backwards compatibility mechanism
		5110
		5111	The backward compatibility mechanism can be controlled by
		5112	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
		5113	section.
		5114
		5115	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5116
		5117	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5118
		5119	ev_loop_destroy (EV_DEFAULT_UC);
		5120	ev_loop_fork (EV_DEFAULT);
		5121
		5122	=item function/symbol renames
		5123
		5124	A number of functions and symbols have been renamed:
		5125
		5126	ev_loop => ev_run
		5127	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		5128	EVLOOP_ONESHOT => EVRUN_ONCE
		5129
		5130	ev_unloop => ev_break
		5131	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		5132	EVUNLOOP_ONE => EVBREAK_ONE
		5133	EVUNLOOP_ALL => EVBREAK_ALL
		5134
		5135	EV_TIMEOUT => EV_TIMER
		5136
		5137	ev_loop_count => ev_iteration
		5138	ev_loop_depth => ev_depth
		5139	ev_loop_verify => ev_verify
		5140
		5141	Most functions working on C<struct ev_loop> objects don't have an
		5142	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		5143	associated constants have been renamed to not collide with the C<struct
		5144	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		5145	as all other watcher types. Note that C<ev_loop_fork> is still called
		5146	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		5147	typedef.
		5148
		5149	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		5150
		5151	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		5152	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		5153	and work, but the library code will of course be larger.
		5154
		5155	=back
		5156
		5157
		5158	=head1 GLOSSARY
		5159
		5160	=over 4
		5161
		5162	=item active
		5163
		5164	A watcher is active as long as it has been started and not yet stopped.
		5165	See L<WATCHER STATES> for details.
		5166
		5167	=item application
		5168
		5169	In this document, an application is whatever is using libev.
		5170
		5171	=item backend
		5172
		5173	The part of the code dealing with the operating system interfaces.
		5174
		5175	=item callback
		5176
		5177	The address of a function that is called when some event has been
		5178	detected. Callbacks are being passed the event loop, the watcher that
		5179	received the event, and the actual event bitset.
		5180
		5181	=item callback/watcher invocation
		5182
		5183	The act of calling the callback associated with a watcher.
		5184
		5185	=item event
		5186
		5187	A change of state of some external event, such as data now being available
		5188	for reading on a file descriptor, time having passed or simply not having
		5189	any other events happening anymore.
		5190
		5191	In libev, events are represented as single bits (such as C<EV_READ> or
		5192	C<EV_TIMER>).
		5193
		5194	=item event library
		5195
		5196	A software package implementing an event model and loop.
		5197
		5198	=item event loop
		5199
		5200	An entity that handles and processes external events and converts them
		5201	into callback invocations.
		5202
		5203	=item event model
		5204
		5205	The model used to describe how an event loop handles and processes
		5206	watchers and events.
		5207
		5208	=item pending
		5209
		5210	A watcher is pending as soon as the corresponding event has been
		5211	detected. See L<WATCHER STATES> for details.
		5212
		5213	=item real time
		5214
		5215	The physical time that is observed. It is apparently strictly monotonic :)
		5216
		5217	=item wall-clock time
		5218
		5219	The time and date as shown on clocks. Unlike real time, it can actually
		5220	be wrong and jump forwards and backwards, e.g. when the you adjust your
		5221	clock.
		5222
		5223	=item watcher
		5224
		5225	A data structure that describes interest in certain events. Watchers need
		5226	to be started (attached to an event loop) before they can receive events.
		5227
		5228	=back
3143		5229
3144	=head1 AUTHOR	5230	=head1 AUTHOR
3145		5231
3146	Marc Lehmann <libev@schmorp.de>.	5232	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5233	Magnusson and Emanuele Giaquinta.
3147		5234

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