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		1	=encoding utf-8
		2
1	=head1 NAME	3	=head1 NAME
2		4
3	libev - a high performance full-featured event loop written in C	5	libev - a high performance full-featured event loop written in C
4		6
5	=head1 SYNOPSIS	7	=head1 SYNOPSIS
6		8
7	#include <ev.h>	9	#include <ev.h>
8		10
9	=head2 EXAMPLE PROGRAM	11	=head2 EXAMPLE PROGRAM
10		12
11	// a single header file is required	13	// a single header file is required
12	#include <ev.h>	14	#include <ev.h>
13		15
		16	#include <stdio.h> // for puts
		17
14	// every watcher type has its own typedef'd struct	18	// every watcher type has its own typedef'd struct
15	// with the name ev_<type>	19	// with the name ev_TYPE
16	ev_io stdin_watcher;	20	ev_io stdin_watcher;
17	ev_timer timeout_watcher;	21	ev_timer timeout_watcher;
18		22
19	// all watcher callbacks have a similar signature	23	// all watcher callbacks have a similar signature
20	// this callback is called when data is readable on stdin	24	// this callback is called when data is readable on stdin
21	static void	25	static void
22	stdin_cb (EV_P_ struct ev_io *w, int revents)	26	stdin_cb (EV_P_ ev_io *w, int revents)
23	{	27	{
24	puts ("stdin ready");	28	puts ("stdin ready");
25	// for one-shot events, one must manually stop the watcher	29	// for one-shot events, one must manually stop the watcher
26	// with its corresponding stop function.	30	// with its corresponding stop function.
27	ev_io_stop (EV_A_ w);	31	ev_io_stop (EV_A_ w);
28		32
29	// this causes all nested ev_loop's to stop iterating	33	// this causes all nested ev_run's to stop iterating
30	ev_unloop (EV_A_ EVUNLOOP_ALL);	34	ev_break (EV_A_ EVBREAK_ALL);
31	}	35	}
32		36
33	// another callback, this time for a time-out	37	// another callback, this time for a time-out
34	static void	38	static void
35	timeout_cb (EV_P_ struct ev_timer *w, int revents)	39	timeout_cb (EV_P_ ev_timer *w, int revents)
36	{	40	{
37	puts ("timeout");	41	puts ("timeout");
38	// this causes the innermost ev_loop to stop iterating	42	// this causes the innermost ev_run to stop iterating
39	ev_unloop (EV_A_ EVUNLOOP_ONE);	43	ev_break (EV_A_ EVBREAK_ONE);
40	}	44	}
41		45
42	int	46	int
43	main (void)	47	main (void)
44	{	48	{
45	// use the default event loop unless you have special needs	49	// use the default event loop unless you have special needs
46	struct ev_loop *loop = ev_default_loop (0);	50	struct ev_loop *loop = EV_DEFAULT;
47		51
48	// initialise an io watcher, then start it	52	// initialise an io watcher, then start it
49	// this one will watch for stdin to become readable	53	// this one will watch for stdin to become readable
50	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	54	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
51	ev_io_start (loop, &stdin_watcher);	55	ev_io_start (loop, &stdin_watcher);
52		56
53	// initialise a timer watcher, then start it	57	// initialise a timer watcher, then start it
54	// simple non-repeating 5.5 second timeout	58	// simple non-repeating 5.5 second timeout
55	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);	59	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
56	ev_timer_start (loop, &timeout_watcher);	60	ev_timer_start (loop, &timeout_watcher);
57		61
58	// now wait for events to arrive	62	// now wait for events to arrive
59	ev_loop (loop, 0);	63	ev_run (loop, 0);
60		64
61	// unloop was called, so exit	65	// break was called, so exit
62	return 0;	66	return 0;
63	}	67	}
64		68
65	=head1 DESCRIPTION	69	=head1 ABOUT THIS DOCUMENT
		70
		71	This document documents the libev software package.
66		72
67	The newest version of this document is also available as an html-formatted	73	The newest version of this document is also available as an html-formatted
68	web page you might find easier to navigate when reading it for the first	74	web page you might find easier to navigate when reading it for the first
69	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.	75	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		76
		77	While this document tries to be as complete as possible in documenting
		78	libev, its usage and the rationale behind its design, it is not a tutorial
		79	on event-based programming, nor will it introduce event-based programming
		80	with libev.
		81
		82	Familiarity with event based programming techniques in general is assumed
		83	throughout this document.
		84
		85	=head1 WHAT TO READ WHEN IN A HURRY
		86
		87	This manual tries to be very detailed, but unfortunately, this also makes
		88	it very long. If you just want to know the basics of libev, I suggest
		89	reading L</ANATOMY OF A WATCHER>, then the L</EXAMPLE PROGRAM> above and
		90	look up the missing functions in L</GLOBAL FUNCTIONS> and the C<ev_io> and
		91	C<ev_timer> sections in L</WATCHER TYPES>.
		92
		93	=head1 ABOUT LIBEV
70		94
71	Libev is an event loop: you register interest in certain events (such as a	95	Libev is an event loop: you register interest in certain events (such as a
72	file descriptor being readable or a timeout occurring), and it will manage	96	file descriptor being readable or a timeout occurring), and it will manage
73	these event sources and provide your program with events.	97	these event sources and provide your program with events.
74		98
…		…
81	details of the event, and then hand it over to libev by I<starting> the	105	details of the event, and then hand it over to libev by I<starting> the
82	watcher.	106	watcher.
83		107
84	=head2 FEATURES	108	=head2 FEATURES
85		109
86	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	110	Libev supports C<select>, C<poll>, the Linux-specific aio and C<epoll>
87	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	111	interfaces, the BSD-specific C<kqueue> and the Solaris-specific event port
88	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	112	mechanisms for file descriptor events (C<ev_io>), the Linux C<inotify>
89	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	113	interface (for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
90	with customised rescheduling (C<ev_periodic>), synchronous signals	114	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
91	(C<ev_signal>), process status change events (C<ev_child>), and event	115	timers (C<ev_timer>), absolute timers with customised rescheduling
92	watchers dealing with the event loop mechanism itself (C<ev_idle>,	116	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
93	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as	117	change events (C<ev_child>), and event watchers dealing with the event
94	file watchers (C<ev_stat>) and even limited support for fork events	118	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
95	(C<ev_fork>).	119	C<ev_check> watchers) as well as file watchers (C<ev_stat>) and even
		120	limited support for fork events (C<ev_fork>).
96		121
97	It also is quite fast (see this	122	It also is quite fast (see this
98	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent	123	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
99	for example).	124	for example).
100		125
…		…
108	name C<loop> (which is always of type C<struct ev_loop *>) will not have	133	name C<loop> (which is always of type C<struct ev_loop *>) will not have
109	this argument.	134	this argument.
110		135
111	=head2 TIME REPRESENTATION	136	=head2 TIME REPRESENTATION
112		137
113	Libev represents time as a single floating point number, representing the	138	Libev represents time as a single floating point number, representing
114	(fractional) number of seconds since the (POSIX) epoch (somewhere near	139	the (fractional) number of seconds since the (POSIX) epoch (in practice
115	the beginning of 1970, details are complicated, don't ask). This type is	140	somewhere near the beginning of 1970, details are complicated, don't
116	called C<ev_tstamp>, which is what you should use too. It usually aliases	141	ask). This type is called C<ev_tstamp>, which is what you should use
117	to the C<double> type in C, and when you need to do any calculations on	142	too. It usually aliases to the C<double> type in C. When you need to do
118	it, you should treat it as some floatingpoint value. Unlike the name	143	any calculations on it, you should treat it as some floating point value.
		144
119	component C<stamp> might indicate, it is also used for time differences	145	Unlike the name component C<stamp> might indicate, it is also used for
120	throughout libev.	146	time differences (e.g. delays) throughout libev.
		147
		148	=head1 ERROR HANDLING
		149
		150	Libev knows three classes of errors: operating system errors, usage errors
		151	and internal errors (bugs).
		152
		153	When libev catches an operating system error it cannot handle (for example
		154	a system call indicating a condition libev cannot fix), it calls the callback
		155	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		156	abort. The default is to print a diagnostic message and to call C<abort
		157	()>.
		158
		159	When libev detects a usage error such as a negative timer interval, then
		160	it will print a diagnostic message and abort (via the C<assert> mechanism,
		161	so C<NDEBUG> will disable this checking): these are programming errors in
		162	the libev caller and need to be fixed there.
		163
		164	Libev also has a few internal error-checking C<assert>ions, and also has
		165	extensive consistency checking code. These do not trigger under normal
		166	circumstances, as they indicate either a bug in libev or worse.
		167
121		168
122	=head1 GLOBAL FUNCTIONS	169	=head1 GLOBAL FUNCTIONS
123		170
124	These functions can be called anytime, even before initialising the	171	These functions can be called anytime, even before initialising the
125	library in any way.	172	library in any way.
…		…
128		175
129	=item ev_tstamp ev_time ()	176	=item ev_tstamp ev_time ()
130		177
131	Returns the current time as libev would use it. Please note that the	178	Returns the current time as libev would use it. Please note that the
132	C<ev_now> function is usually faster and also often returns the timestamp	179	C<ev_now> function is usually faster and also often returns the timestamp
133	you actually want to know.	180	you actually want to know. Also interesting is the combination of
		181	C<ev_now_update> and C<ev_now>.
134		182
135	=item ev_sleep (ev_tstamp interval)	183	=item ev_sleep (ev_tstamp interval)
136		184
137	Sleep for the given interval: The current thread will be blocked until	185	Sleep for the given interval: The current thread will be blocked
138	either it is interrupted or the given time interval has passed. Basically	186	until either it is interrupted or the given time interval has
		187	passed (approximately - it might return a bit earlier even if not
		188	interrupted). Returns immediately if C<< interval <= 0 >>.
		189
139	this is a subsecond-resolution C<sleep ()>.	190	Basically this is a sub-second-resolution C<sleep ()>.
		191
		192	The range of the C<interval> is limited - libev only guarantees to work
		193	with sleep times of up to one day (C<< interval <= 86400 >>).
140		194
141	=item int ev_version_major ()	195	=item int ev_version_major ()
142		196
143	=item int ev_version_minor ()	197	=item int ev_version_minor ()
144		198
…		…
155	as this indicates an incompatible change. Minor versions are usually	209	as this indicates an incompatible change. Minor versions are usually
156	compatible to older versions, so a larger minor version alone is usually	210	compatible to older versions, so a larger minor version alone is usually
157	not a problem.	211	not a problem.
158		212
159	Example: Make sure we haven't accidentally been linked against the wrong	213	Example: Make sure we haven't accidentally been linked against the wrong
160	version.	214	version (note, however, that this will not detect other ABI mismatches,
		215	such as LFS or reentrancy).
161		216
162	assert (("libev version mismatch",	217	assert (("libev version mismatch",
163	ev_version_major () == EV_VERSION_MAJOR	218	ev_version_major () == EV_VERSION_MAJOR
164	&& ev_version_minor () >= EV_VERSION_MINOR));	219	&& ev_version_minor () >= EV_VERSION_MINOR));
165		220
166	=item unsigned int ev_supported_backends ()	221	=item unsigned int ev_supported_backends ()
167		222
168	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	223	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
169	value) compiled into this binary of libev (independent of their	224	value) compiled into this binary of libev (independent of their
…		…
171	a description of the set values.	226	a description of the set values.
172		227
173	Example: make sure we have the epoll method, because yeah this is cool and	228	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	229	a must have and can we have a torrent of it please!!!11
175		230
176	assert (("sorry, no epoll, no sex",	231	assert (("sorry, no epoll, no sex",
177	ev_supported_backends () & EVBACKEND_EPOLL));	232	ev_supported_backends () & EVBACKEND_EPOLL));
178		233
179	=item unsigned int ev_recommended_backends ()	234	=item unsigned int ev_recommended_backends ()
180		235
181	Return the set of all backends compiled into this binary of libev and also	236	Return the set of all backends compiled into this binary of libev and
182	recommended for this platform. This set is often smaller than the one	237	also recommended for this platform, meaning it will work for most file
		238	descriptor types. This set is often smaller than the one returned by
183	returned by C<ev_supported_backends>, as for example kqueue is broken on	239	C<ev_supported_backends>, as for example kqueue is broken on most BSDs
184	most BSDs and will not be autodetected unless you explicitly request it	240	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	241	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.	242	probe for if you specify no backends explicitly.
187		243
188	=item unsigned int ev_embeddable_backends ()	244	=item unsigned int ev_embeddable_backends ()
189		245
190	Returns the set of backends that are embeddable in other event loops. This	246	Returns the set of backends that are embeddable in other event loops. This
191	is the theoretical, all-platform, value. To find which backends	247	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	248	current system. To find which embeddable backends might be supported on
193	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	249	the current system, you would need to look at C<ev_embeddable_backends ()
194	recommended ones.	250	& ev_supported_backends ()>, likewise for recommended ones.
195		251
196	See the description of C<ev_embed> watchers for more info.	252	See the description of C<ev_embed> watchers for more info.
197		253
198	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	254	=item ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())
199		255
200	Sets the allocation function to use (the prototype is similar - the	256	Sets the allocation function to use (the prototype is similar - the
201	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is	257	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
202	used to allocate and free memory (no surprises here). If it returns zero	258	used to allocate and free memory (no surprises here). If it returns zero
203	when memory needs to be allocated (C<size != 0>), the library might abort	259	when memory needs to be allocated (C<size != 0>), the library might abort
…		…
209		265
210	You could override this function in high-availability programs to, say,	266	You could override this function in high-availability programs to, say,
211	free some memory if it cannot allocate memory, to use a special allocator,	267	free some memory if it cannot allocate memory, to use a special allocator,
212	or even to sleep a while and retry until some memory is available.	268	or even to sleep a while and retry until some memory is available.
213		269
		270	Example: The following is the C<realloc> function that libev itself uses
		271	which should work with C<realloc> and C<free> functions of all kinds and
		272	is probably a good basis for your own implementation.
		273
		274	static void *
		275	ev_realloc_emul (void *ptr, long size) EV_NOEXCEPT
		276	{
		277	if (size)
		278	return realloc (ptr, size);
		279
		280	free (ptr);
		281	return 0;
		282	}
		283
214	Example: Replace the libev allocator with one that waits a bit and then	284	Example: Replace the libev allocator with one that waits a bit and then
215	retries (example requires a standards-compliant C<realloc>).	285	retries.
216		286
217	static void *	287	static void *
218	persistent_realloc (void *ptr, size_t size)	288	persistent_realloc (void *ptr, size_t size)
219	{	289	{
		290	if (!size)
		291	{
		292	free (ptr);
		293	return 0;
		294	}
		295
220	for (;;)	296	for (;;)
221	{	297	{
222	void *newptr = realloc (ptr, size);	298	void *newptr = realloc (ptr, size);
223		299
224	if (newptr)	300	if (newptr)
…		…
229	}	305	}
230		306
231	...	307	...
232	ev_set_allocator (persistent_realloc);	308	ev_set_allocator (persistent_realloc);
233		309
234	=item ev_set_syserr_cb (void (*cb)(const char *msg));	310	=item ev_set_syserr_cb (void (*cb)(const char *msg) throw ())
235		311
236	Set the callback function to call on a retryable syscall error (such	312	Set the callback function to call on a retryable system call error (such
237	as failed select, poll, epoll_wait). The message is a printable string	313	as failed select, poll, epoll_wait). The message is a printable string
238	indicating the system call or subsystem causing the problem. If this	314	indicating the system call or subsystem causing the problem. If this
239	callback is set, then libev will expect it to remedy the sitution, no	315	callback is set, then libev will expect it to remedy the situation, no
240	matter what, when it returns. That is, libev will generally retry the	316	matter what, when it returns. That is, libev will generally retry the
241	requested operation, or, if the condition doesn't go away, do bad stuff	317	requested operation, or, if the condition doesn't go away, do bad stuff
242	(such as abort).	318	(such as abort).
243		319
244	Example: This is basically the same thing that libev does internally, too.	320	Example: This is basically the same thing that libev does internally, too.
…		…
251	}	327	}
252		328
253	...	329	...
254	ev_set_syserr_cb (fatal_error);	330	ev_set_syserr_cb (fatal_error);
255		331
		332	=item ev_feed_signal (int signum)
		333
		334	This function can be used to "simulate" a signal receive. It is completely
		335	safe to call this function at any time, from any context, including signal
		336	handlers or random threads.
		337
		338	Its main use is to customise signal handling in your process, especially
		339	in the presence of threads. For example, you could block signals
		340	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		341	creating any loops), and in one thread, use C<sigwait> or any other
		342	mechanism to wait for signals, then "deliver" them to libev by calling
		343	C<ev_feed_signal>.
		344
256	=back	345	=back
257		346
258	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	347	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
259		348
260	An event loop is described by a C<struct ev_loop *>. The library knows two	349	An event loop is described by a C<struct ev_loop *> (the C<struct> is
261	types of such loops, the I<default> loop, which supports signals and child	350	I<not> optional in this case unless libev 3 compatibility is disabled, as
262	events, and dynamically created loops which do not.	351	libev 3 had an C<ev_loop> function colliding with the struct name).
		352
		353	The library knows two types of such loops, the I<default> loop, which
		354	supports child process events, and dynamically created event loops which
		355	do not.
263		356
264	=over 4	357	=over 4
265		358
266	=item struct ev_loop *ev_default_loop (unsigned int flags)	359	=item struct ev_loop *ev_default_loop (unsigned int flags)
267		360
268	This will initialise the default event loop if it hasn't been initialised	361	This returns the "default" event loop object, which is what you should
269	yet and return it. If the default loop could not be initialised, returns	362	normally use when you just need "the event loop". Event loop objects and
270	false. If it already was initialised it simply returns it (and ignores the	363	the C<flags> parameter are described in more detail in the entry for
271	flags. If that is troubling you, check C<ev_backend ()> afterwards).	364	C<ev_loop_new>.
		365
		366	If the default loop is already initialised then this function simply
		367	returns it (and ignores the flags. If that is troubling you, check
		368	C<ev_backend ()> afterwards). Otherwise it will create it with the given
		369	flags, which should almost always be C<0>, unless the caller is also the
		370	one calling C<ev_run> or otherwise qualifies as "the main program".
272		371
273	If you don't know what event loop to use, use the one returned from this	372	If you don't know what event loop to use, use the one returned from this
274	function.	373	function (or via the C<EV_DEFAULT> macro).
275		374
276	Note that this function is I<not> thread-safe, so if you want to use it	375	Note that this function is I<not> thread-safe, so if you want to use it
277	from multiple threads, you have to lock (note also that this is unlikely,	376	from multiple threads, you have to employ some kind of mutex (note also
278	as loops cannot bes hared easily between threads anyway).	377	that this case is unlikely, as loops cannot be shared easily between
		378	threads anyway).
279		379
280	The default loop is the only loop that can handle C<ev_signal> and	380	The default loop is the only loop that can handle C<ev_child> watchers,
281	C<ev_child> watchers, and to do this, it always registers a handler	381	and to do this, it always registers a handler for C<SIGCHLD>. If this is
282	for C<SIGCHLD>. If this is a problem for your app you can either	382	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	383	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	384	C<SIGCHLD> signal handler I<after> calling C<ev_default_init>.
285	C<ev_default_init>.	385
		386	Example: This is the most typical usage.
		387
		388	if (!ev_default_loop (0))
		389	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		390
		391	Example: Restrict libev to the select and poll backends, and do not allow
		392	environment settings to be taken into account:
		393
		394	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		395
		396	=item struct ev_loop *ev_loop_new (unsigned int flags)
		397
		398	This will create and initialise a new event loop object. If the loop
		399	could not be initialised, returns false.
		400
		401	This function is thread-safe, and one common way to use libev with
		402	threads is indeed to create one loop per thread, and using the default
		403	loop in the "main" or "initial" thread.
286		404
287	The flags argument can be used to specify special behaviour or specific	405	The flags argument can be used to specify special behaviour or specific
288	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	406	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
289		407
290	The following flags are supported:	408	The following flags are supported:
…		…
296	The default flags value. Use this if you have no clue (it's the right	414	The default flags value. Use this if you have no clue (it's the right
297	thing, believe me).	415	thing, believe me).
298		416
299	=item C<EVFLAG_NOENV>	417	=item C<EVFLAG_NOENV>
300		418
301	If this flag bit is ored into the flag value (or the program runs setuid	419	If this flag bit is or'ed into the flag value (or the program runs setuid
302	or setgid) then libev will I<not> look at the environment variable	420	or setgid) then libev will I<not> look at the environment variable
303	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	421	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
304	override the flags completely if it is found in the environment. This is	422	override the flags completely if it is found in the environment. This is
305	useful to try out specific backends to test their performance, or to work	423	useful to try out specific backends to test their performance, to work
306	around bugs.	424	around bugs, or to make libev threadsafe (accessing environment variables
		425	cannot be done in a threadsafe way, but usually it works if no other
		426	thread modifies them).
307		427
308	=item C<EVFLAG_FORKCHECK>	428	=item C<EVFLAG_FORKCHECK>
309		429
310	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after	430	Instead of calling C<ev_loop_fork> manually after a fork, you can also
311	a fork, you can also make libev check for a fork in each iteration by	431	make libev check for a fork in each iteration by enabling this flag.
312	enabling this flag.
313		432
314	This works by calling C<getpid ()> on every iteration of the loop,	433	This works by calling C<getpid ()> on every iteration of the loop,
315	and thus this might slow down your event loop if you do a lot of loop	434	and thus this might slow down your event loop if you do a lot of loop
316	iterations and little real work, but is usually not noticeable (on my	435	iterations and little real work, but is usually not noticeable (on my
317	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence	436	GNU/Linux system for example, C<getpid> is actually a simple 5-insn
318	without a syscall and thus I<very> fast, but my GNU/Linux system also has	437	sequence without a system call and thus I<very> fast, but my GNU/Linux
319	C<pthread_atfork> which is even faster).	438	system also has C<pthread_atfork> which is even faster). (Update: glibc
		439	versions 2.25 apparently removed the C<getpid> optimisation again).
320		440
321	The big advantage of this flag is that you can forget about fork (and	441	The big advantage of this flag is that you can forget about fork (and
322	forget about forgetting to tell libev about forking) when you use this	442	forget about forgetting to tell libev about forking, although you still
323	flag.	443	have to ignore C<SIGPIPE>) when you use this flag.
324		444
325	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>	445	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
326	environment variable.	446	environment variable.
		447
		448	=item C<EVFLAG_NOINOTIFY>
		449
		450	When this flag is specified, then libev will not attempt to use the
		451	I<inotify> API for its C<ev_stat> watchers. Apart from debugging and
		452	testing, this flag can be useful to conserve inotify file descriptors, as
		453	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		454
		455	=item C<EVFLAG_SIGNALFD>
		456
		457	When this flag is specified, then libev will attempt to use the
		458	I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API
		459	delivers signals synchronously, which makes it both faster and might make
		460	it possible to get the queued signal data. It can also simplify signal
		461	handling with threads, as long as you properly block signals in your
		462	threads that are not interested in handling them.
		463
		464	Signalfd will not be used by default as this changes your signal mask, and
		465	there are a lot of shoddy libraries and programs (glib's threadpool for
		466	example) that can't properly initialise their signal masks.
		467
		468	=item C<EVFLAG_NOSIGMASK>
		469
		470	When this flag is specified, then libev will avoid to modify the signal
		471	mask. Specifically, this means you have to make sure signals are unblocked
		472	when you want to receive them.
		473
		474	This behaviour is useful when you want to do your own signal handling, or
		475	want to handle signals only in specific threads and want to avoid libev
		476	unblocking the signals.
		477
		478	It's also required by POSIX in a threaded program, as libev calls
		479	C<sigprocmask>, whose behaviour is officially unspecified.
		480
		481	This flag's behaviour will become the default in future versions of libev.
327		482
328	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	483	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
329		484
330	This is your standard select(2) backend. Not I<completely> standard, as	485	This is your standard select(2) backend. Not I<completely> standard, as
331	libev tries to roll its own fd_set with no limits on the number of fds,	486	libev tries to roll its own fd_set with no limits on the number of fds,
332	but if that fails, expect a fairly low limit on the number of fds when	487	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	488	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.	489	usually the fastest backend for a low number of (low-numbered :) fds.
335		490
336	To get good performance out of this backend you need a high amount of	491	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	492	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	493	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	494	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	495	a look at C<ev_set_io_collect_interval ()> to increase the amount of
341	readiness notifications you get per iteration.	496	readiness notifications you get per iteration.
		497
		498	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		499	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		500	C<exceptfds> set on that platform).
342		501
343	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	502	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
344		503
345	And this is your standard poll(2) backend. It's more complicated	504	And this is your standard poll(2) backend. It's more complicated
346	than select, but handles sparse fds better and has no artificial	505	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	506	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,	507	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	508	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
350	performance tips.	509	performance tips.
351		510
		511	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		512	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
		513
352	=item C<EVBACKEND_EPOLL> (value 4, Linux)	514	=item C<EVBACKEND_EPOLL> (value 4, Linux)
353		515
		516	Use the Linux-specific epoll(7) interface (for both pre- and post-2.6.9
		517	kernels).
		518
354	For few fds, this backend is a bit little slower than poll and select,	519	For few fds, this backend is a bit little slower than poll and select, but
355	but it scales phenomenally better. While poll and select usually scale	520	it scales phenomenally better. While poll and select usually scale like
356	like O(total_fds) where n is the total number of fds (or the highest fd),	521	O(total_fds) where total_fds is the total number of fds (or the highest
357	epoll scales either O(1) or O(active_fds). The epoll design has a number	522	fd), epoll scales either O(1) or O(active_fds).
358	of shortcomings, such as silently dropping events in some hard-to-detect	523
359	cases and requiring a syscall per fd change, no fork support and bad	524	The epoll mechanism deserves honorable mention as the most misdesigned
360	support for dup.	525	of the more advanced event mechanisms: mere annoyances include silently
		526	dropping file descriptors, requiring a system call per change per file
		527	descriptor (and unnecessary guessing of parameters), problems with dup,
		528	returning before the timeout value, resulting in additional iterations
		529	(and only giving 5ms accuracy while select on the same platform gives
		530	0.1ms) and so on. The biggest issue is fork races, however - if a program
		531	forks then I<both> parent and child process have to recreate the epoll
		532	set, which can take considerable time (one syscall per file descriptor)
		533	and is of course hard to detect.
		534
		535	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
		536	but of course I<doesn't>, and epoll just loves to report events for
		537	totally I<different> file descriptors (even already closed ones, so
		538	one cannot even remove them from the set) than registered in the set
		539	(especially on SMP systems). Libev tries to counter these spurious
		540	notifications by employing an additional generation counter and comparing
		541	that against the events to filter out spurious ones, recreating the set
		542	when required. Epoll also erroneously rounds down timeouts, but gives you
		543	no way to know when and by how much, so sometimes you have to busy-wait
		544	because epoll returns immediately despite a nonzero timeout. And last
		545	not least, it also refuses to work with some file descriptors which work
		546	perfectly fine with C<select> (files, many character devices...).
		547
		548	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		549	cobbled together in a hurry, no thought to design or interaction with
		550	others. Oh, the pain, will it ever stop...
361		551
362	While stopping, setting and starting an I/O watcher in the same iteration	552	While stopping, setting and starting an I/O watcher in the same iteration
363	will result in some caching, there is still a syscall per such incident	553	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	554	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	555	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
366	very well if you register events for both fds.	556	file descriptors might not work very well if you register events for both
367		557	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		558
372	Best performance from this backend is achieved by not unregistering all	559	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.	560	watchers for a file descriptor until it has been closed, if possible,
374	keep at least one watcher active per fd at all times.	561	i.e. keep at least one watcher active per fd at all times. Stopping and
		562	starting a watcher (without re-setting it) also usually doesn't cause
		563	extra overhead. A fork can both result in spurious notifications as well
		564	as in libev having to destroy and recreate the epoll object, which can
		565	take considerable time and thus should be avoided.
375		566
		567	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		568	faster than epoll for maybe up to a hundred file descriptors, depending on
		569	the usage. So sad.
		570
376	While nominally embeddeble in other event loops, this feature is broken in	571	While nominally embeddable in other event loops, this feature is broken in
377	all kernel versions tested so far.	572	a lot of kernel revisions, but probably(!) works in current versions.
		573
		574	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		575	C<EVBACKEND_POLL>.
		576
		577	=item C<EVBACKEND_LINUXAIO> (value 64, Linux)
		578
		579	Use the Linux-specific Linux AIO (I<not> C<< aio(7) >> but C<<
		580	io_submit(2) >>) event interface available in post-4.18 kernels (but libev
		581	only tries to use it in 4.19+).
		582
		583	This is another Linux train wreck of an event interface.
		584
		585	If this backend works for you (as of this writing, it was very
		586	experimental), it is the best event interface available on Linux and might
		587	be well worth enabling it - if it isn't available in your kernel this will
		588	be detected and this backend will be skipped.
		589
		590	This backend can batch oneshot requests and supports a user-space ring
		591	buffer to receive events. It also doesn't suffer from most of the design
		592	problems of epoll (such as not being able to remove event sources from
		593	the epoll set), and generally sounds too good to be true. Because, this
		594	being the Linux kernel, of course it suffers from a whole new set of
		595	limitations, forcing you to fall back to epoll, inheriting all its design
		596	issues.
		597
		598	For one, it is not easily embeddable (but probably could be done using
		599	an event fd at some extra overhead). It also is subject to a system wide
		600	limit that can be configured in F</proc/sys/fs/aio-max-nr>. If no AIO
		601	requests are left, this backend will be skipped during initialisation, and
		602	will switch to epoll when the loop is active.
		603
		604	Most problematic in practice, however, is that not all file descriptors
		605	work with it. For example, in Linux 5.1, TCP sockets, pipes, event fds,
		606	files, F</dev/null> and many others are supported, but ttys do not work
		607	properly (a known bug that the kernel developers don't care about, see
		608	L<https://lore.kernel.org/patchwork/patch/1047453/>), so this is not
		609	(yet?) a generic event polling interface.
		610
		611	Overall, it seems the Linux developers just don't want it to have a
		612	generic event handling mechanism other than C<select> or C<poll>.
		613
		614	To work around all these problem, the current version of libev uses its
		615	epoll backend as a fallback for file descriptor types that do not work. Or
		616	falls back completely to epoll if the kernel acts up.
		617
		618	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		619	C<EVBACKEND_POLL>.
378		620
379	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	621	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
380		622
381	Kqueue deserves special mention, as at the time of this writing, it	623	Kqueue deserves special mention, as at the time this backend was
382	was broken on all BSDs except NetBSD (usually it doesn't work reliably	624	implemented, it was broken on all BSDs except NetBSD (usually it doesn't
383	with anything but sockets and pipes, except on Darwin, where of course	625	work reliably with anything but sockets and pipes, except on Darwin,
384	it's completely useless). For this reason it's not being "autodetected"	626	where of course it's completely useless). Unlike epoll, however, whose
385	unless you explicitly specify it explicitly in the flags (i.e. using	627	brokenness is by design, these kqueue bugs can be (and mostly have been)
386	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)	628	fixed without API changes to existing programs. For this reason it's not
387	system like NetBSD.	629	being "auto-detected" on all platforms unless you explicitly specify it
		630	in the flags (i.e. using C<EVBACKEND_KQUEUE>) or libev was compiled on a
		631	known-to-be-good (-enough) system like NetBSD.
388		632
389	You still can embed kqueue into a normal poll or select backend and use it	633	You still can embed kqueue into a normal poll or select backend and use it
390	only for sockets (after having made sure that sockets work with kqueue on	634	only for sockets (after having made sure that sockets work with kqueue on
391	the target platform). See C<ev_embed> watchers for more info.	635	the target platform). See C<ev_embed> watchers for more info.
392		636
393	It scales in the same way as the epoll backend, but the interface to the	637	It scales in the same way as the epoll backend, but the interface to the
394	kernel is more efficient (which says nothing about its actual speed, of	638	kernel is more efficient (which says nothing about its actual speed, of
395	course). While stopping, setting and starting an I/O watcher does never	639	course). While stopping, setting and starting an I/O watcher does never
396	cause an extra syscall as with C<EVBACKEND_EPOLL>, it still adds up to	640	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
397	two event changes per incident, support for C<fork ()> is very bad and it	641	two event changes per incident. Support for C<fork ()> is very bad (you
		642	might have to leak fds on fork, but it's more sane than epoll) and it
398	drops fds silently in similarly hard-to-detect cases.	643	drops fds silently in similarly hard-to-detect cases.
399		644
400	This backend usually performs well under most conditions.	645	This backend usually performs well under most conditions.
401		646
402	While nominally embeddable in other event loops, this doesn't work	647	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	648	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	649	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	650	(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	651	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
407	sockets.	652	also broken on OS X)) and, did I mention it, using it only for sockets.
		653
		654	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		655	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		656	C<NOTE_EOF>.
408		657
409	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	658	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
410		659
411	This is not implemented yet (and might never be, unless you send me an	660	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	661	implementation). According to reports, C</dev/poll> only supports sockets
…		…
416	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	665	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
417		666
418	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	667	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
419	it's really slow, but it still scales very well (O(active_fds)).	668	it's really slow, but it still scales very well (O(active_fds)).
420		669
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	670	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	671	file descriptor per loop iteration. For small and medium numbers of file
427	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	672	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
428	might perform better.	673	might perform better.
429		674
430	On the positive side, ignoring the spurious readiness notifications, this	675	On the positive side, this backend actually performed fully to
431	backend actually performed to specification in all tests and is fully	676	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.	677	among the OS-specific backends (I vastly prefer correctness over speed
		678	hacks).
		679
		680	On the negative side, the interface is I<bizarre> - so bizarre that
		681	even sun itself gets it wrong in their code examples: The event polling
		682	function sometimes returns events to the caller even though an error
		683	occurred, but with no indication whether it has done so or not (yes, it's
		684	even documented that way) - deadly for edge-triggered interfaces where you
		685	absolutely have to know whether an event occurred or not because you have
		686	to re-arm the watcher.
		687
		688	Fortunately libev seems to be able to work around these idiocies.
		689
		690	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		691	C<EVBACKEND_POLL>.
433		692
434	=item C<EVBACKEND_ALL>	693	=item C<EVBACKEND_ALL>
435		694
436	Try all backends (even potentially broken ones that wouldn't be tried	695	Try all backends (even potentially broken ones that wouldn't be tried
437	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	696	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
438	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	697	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
439		698
440	It is definitely not recommended to use this flag.	699	It is definitely not recommended to use this flag, use whatever
		700	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		701	at all.
		702
		703	=item C<EVBACKEND_MASK>
		704
		705	Not a backend at all, but a mask to select all backend bits from a
		706	C<flags> value, in case you want to mask out any backends from a flags
		707	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
441		708
442	=back	709	=back
443		710
444	If one or more of these are ored into the flags value, then only these	711	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	712	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.	713	here). If none are specified, all backends in C<ev_recommended_backends
447		714	()> will be tried.
448	The most typical usage is like this:
449
450	if (!ev_default_loop (0))
451	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
452
453	Restrict libev to the select and poll backends, and do not allow
454	environment settings to be taken into account:
455
456	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
457
458	Use whatever libev has to offer, but make sure that kqueue is used if
459	available (warning, breaks stuff, best use only with your own private
460	event loop and only if you know the OS supports your types of fds):
461
462	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
463
464	=item struct ev_loop *ev_loop_new (unsigned int flags)
465
466	Similar to C<ev_default_loop>, but always creates a new event loop that is
467	always distinct from the default loop. Unlike the default loop, it cannot
468	handle signal and child watchers, and attempts to do so will be greeted by
469	undefined behaviour (or a failed assertion if assertions are enabled).
470
471	Note that this function I<is> thread-safe, and the recommended way to use
472	libev with threads is indeed to create one loop per thread, and using the
473	default loop in the "main" or "initial" thread.
474		715
475	Example: Try to create a event loop that uses epoll and nothing else.	716	Example: Try to create a event loop that uses epoll and nothing else.
476		717
477	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	718	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
478	if (!epoller)	719	if (!epoller)
479	fatal ("no epoll found here, maybe it hides under your chair");	720	fatal ("no epoll found here, maybe it hides under your chair");
480		721
		722	Example: Use whatever libev has to offer, but make sure that kqueue is
		723	used if available.
		724
		725	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		726
		727	Example: Similarly, on linux, you mgiht want to take advantage of the
		728	linux aio backend if possible, but fall back to something else if that
		729	isn't available.
		730
		731	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_LINUXAIO);
		732
481	=item ev_default_destroy ()	733	=item ev_loop_destroy (loop)
482		734
483	Destroys the default loop again (frees all memory and kernel state	735	Destroys an event loop object (frees all memory and kernel state
484	etc.). None of the active event watchers will be stopped in the normal	736	etc.). None of the active event watchers will be stopped in the normal
485	sense, so e.g. C<ev_is_active> might still return true. It is your	737	sense, so e.g. C<ev_is_active> might still return true. It is your
486	responsibility to either stop all watchers cleanly yoursef I<before>	738	responsibility to either stop all watchers cleanly yourself I<before>
487	calling this function, or cope with the fact afterwards (which is usually	739	calling this function, or cope with the fact afterwards (which is usually
488	the easiest thing, you can just ignore the watchers and/or C<free ()> them	740	the easiest thing, you can just ignore the watchers and/or C<free ()> them
489	for example).	741	for example).
490		742
491	Note that certain global state, such as signal state, will not be freed by	743	Note that certain global state, such as signal state (and installed signal
492	this function, and related watchers (such as signal and child watchers)	744	handlers), will not be freed by this function, and related watchers (such
493	would need to be stopped manually.	745	as signal and child watchers) would need to be stopped manually.
494		746
495	In general it is not advisable to call this function except in the	747	This function is normally used on loop objects allocated by
496	rare occasion where you really need to free e.g. the signal handling	748	C<ev_loop_new>, but it can also be used on the default loop returned by
		749	C<ev_default_loop>, in which case it is not thread-safe.
		750
		751	Note that it is not advisable to call this function on the default loop
		752	except in the rare occasion where you really need to free its resources.
497	pipe fds. If you need dynamically allocated loops it is better to use	753	If you need dynamically allocated loops it is better to use C<ev_loop_new>
498	C<ev_loop_new> and C<ev_loop_destroy>).	754	and C<ev_loop_destroy>.
499		755
500	=item ev_loop_destroy (loop)	756	=item ev_loop_fork (loop)
501		757
502	Like C<ev_default_destroy>, but destroys an event loop created by an
503	earlier call to C<ev_loop_new>.
504
505	=item ev_default_fork ()
506
507	This function sets a flag that causes subsequent C<ev_loop> iterations	758	This function sets a flag that causes subsequent C<ev_run> iterations
508	to reinitialise the kernel state for backends that have one. Despite the	759	to reinitialise the kernel state for backends that have one. Despite
509	name, you can call it anytime, but it makes most sense after forking, in	760	the name, you can call it anytime you are allowed to start or stop
510	the child process (or both child and parent, but that again makes little	761	watchers (except inside an C<ev_prepare> callback), but it makes most
511	sense). You I<must> call it in the child before using any of the libev	762	sense after forking, in the child process. You I<must> call it (or use
512	functions, and it will only take effect at the next C<ev_loop> iteration.	763	C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.
		764
		765	In addition, if you want to reuse a loop (via this function or
		766	C<EVFLAG_FORKCHECK>), you I<also> have to ignore C<SIGPIPE>.
		767
		768	Again, you I<have> to call it on I<any> loop that you want to re-use after
		769	a fork, I<even if you do not plan to use the loop in the parent>. This is
		770	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		771	during fork.
513		772
514	On the other hand, you only need to call this function in the child	773	On the other hand, you only need to call this function in the child
515	process if and only if you want to use the event library in the child. If	774	process if and only if you want to use the event loop in the child. If
516	you just fork+exec, you don't have to call it at all.	775	you just fork+exec or create a new loop in the child, you don't have to
		776	call it at all (in fact, C<epoll> is so badly broken that it makes a
		777	difference, but libev will usually detect this case on its own and do a
		778	costly reset of the backend).
517		779
518	The function itself is quite fast and it's usually not a problem to call	780	The function itself is quite fast and it's usually not a problem to call
519	it just in case after a fork. To make this easy, the function will fit in	781	it just in case after a fork.
520	quite nicely into a call to C<pthread_atfork>:
521		782
		783	Example: Automate calling C<ev_loop_fork> on the default loop when
		784	using pthreads.
		785
		786	static void
		787	post_fork_child (void)
		788	{
		789	ev_loop_fork (EV_DEFAULT);
		790	}
		791
		792	...
522	pthread_atfork (0, 0, ev_default_fork);	793	pthread_atfork (0, 0, post_fork_child);
523
524	=item ev_loop_fork (loop)
525
526	Like C<ev_default_fork>, but acts on an event loop created by
527	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
528	after fork, and how you do this is entirely your own problem.
529		794
530	=item int ev_is_default_loop (loop)	795	=item int ev_is_default_loop (loop)
531		796
532	Returns true when the given loop actually is the default loop, false otherwise.	797	Returns true when the given loop is, in fact, the default loop, and false
		798	otherwise.
533		799
534	=item unsigned int ev_loop_count (loop)	800	=item unsigned int ev_iteration (loop)
535		801
536	Returns the count of loop iterations for the loop, which is identical to	802	Returns the current iteration count for the event loop, which is identical
537	the number of times libev did poll for new events. It starts at C<0> and	803	to the number of times libev did poll for new events. It starts at C<0>
538	happily wraps around with enough iterations.	804	and happily wraps around with enough iterations.
539		805
540	This value can sometimes be useful as a generation counter of sorts (it	806	This value can sometimes be useful as a generation counter of sorts (it
541	"ticks" the number of loop iterations), as it roughly corresponds with	807	"ticks" the number of loop iterations), as it roughly corresponds with
542	C<ev_prepare> and C<ev_check> calls.	808	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		809	prepare and check phases.
		810
		811	=item unsigned int ev_depth (loop)
		812
		813	Returns the number of times C<ev_run> was entered minus the number of
		814	times C<ev_run> was exited normally, in other words, the recursion depth.
		815
		816	Outside C<ev_run>, this number is zero. In a callback, this number is
		817	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
		818	in which case it is higher.
		819
		820	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
		821	throwing an exception etc.), doesn't count as "exit" - consider this
		822	as a hint to avoid such ungentleman-like behaviour unless it's really
		823	convenient, in which case it is fully supported.
543		824
544	=item unsigned int ev_backend (loop)	825	=item unsigned int ev_backend (loop)
545		826
546	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	827	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
547	use.	828	use.
…		…
552	received events and started processing them. This timestamp does not	833	received events and started processing them. This timestamp does not
553	change as long as callbacks are being processed, and this is also the base	834	change as long as callbacks are being processed, and this is also the base
554	time used for relative timers. You can treat it as the timestamp of the	835	time used for relative timers. You can treat it as the timestamp of the
555	event occurring (or more correctly, libev finding out about it).	836	event occurring (or more correctly, libev finding out about it).
556		837
		838	=item ev_now_update (loop)
		839
		840	Establishes the current time by querying the kernel, updating the time
		841	returned by C<ev_now ()> in the progress. This is a costly operation and
		842	is usually done automatically within C<ev_run ()>.
		843
		844	This function is rarely useful, but when some event callback runs for a
		845	very long time without entering the event loop, updating libev's idea of
		846	the current time is a good idea.
		847
		848	See also L</The special problem of time updates> in the C<ev_timer> section.
		849
		850	=item ev_suspend (loop)
		851
		852	=item ev_resume (loop)
		853
		854	These two functions suspend and resume an event loop, for use when the
		855	loop is not used for a while and timeouts should not be processed.
		856
		857	A typical use case would be an interactive program such as a game: When
		858	the user presses C<^Z> to suspend the game and resumes it an hour later it
		859	would be best to handle timeouts as if no time had actually passed while
		860	the program was suspended. This can be achieved by calling C<ev_suspend>
		861	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		862	C<ev_resume> directly afterwards to resume timer processing.
		863
		864	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		865	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		866	will be rescheduled (that is, they will lose any events that would have
		867	occurred while suspended).
		868
		869	After calling C<ev_suspend> you B<must not> call I<any> function on the
		870	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		871	without a previous call to C<ev_suspend>.
		872
		873	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		874	event loop time (see C<ev_now_update>).
		875
557	=item ev_loop (loop, int flags)	876	=item bool ev_run (loop, int flags)
558		877
559	Finally, this is it, the event handler. This function usually is called	878	Finally, this is it, the event handler. This function usually is called
560	after you initialised all your watchers and you want to start handling	879	after you have initialised all your watchers and you want to start
561	events.	880	handling events. It will ask the operating system for any new events, call
		881	the watcher callbacks, and then repeat the whole process indefinitely: This
		882	is why event loops are called I<loops>.
562		883
563	If the flags argument is specified as C<0>, it will not return until	884	If the flags argument is specified as C<0>, it will keep handling events
564	either no event watchers are active anymore or C<ev_unloop> was called.	885	until either no event watchers are active anymore or C<ev_break> was
		886	called.
565		887
		888	The return value is false if there are no more active watchers (which
		889	usually means "all jobs done" or "deadlock"), and true in all other cases
		890	(which usually means " you should call C<ev_run> again").
		891
566	Please note that an explicit C<ev_unloop> is usually better than	892	Please note that an explicit C<ev_break> is usually better than
567	relying on all watchers to be stopped when deciding when a program has	893	relying on all watchers to be stopped when deciding when a program has
568	finished (especially in interactive programs), but having a program that	894	finished (especially in interactive programs), but having a program
569	automatically loops as long as it has to and no longer by virtue of	895	that automatically loops as long as it has to and no longer by virtue
570	relying on its watchers stopping correctly is a thing of beauty.	896	of relying on its watchers stopping correctly, that is truly a thing of
		897	beauty.
571		898
		899	This function is I<mostly> exception-safe - you can break out of a
		900	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		901	exception and so on. This does not decrement the C<ev_depth> value, nor
		902	will it clear any outstanding C<EVBREAK_ONE> breaks.
		903
572	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	904	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
573	those events and any outstanding ones, but will not block your process in	905	those events and any already outstanding ones, but will not wait and
574	case there are no events and will return after one iteration of the loop.	906	block your process in case there are no events and will return after one
		907	iteration of the loop. This is sometimes useful to poll and handle new
		908	events while doing lengthy calculations, to keep the program responsive.
575		909
576	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	910	A flags value of C<EVRUN_ONCE> will look for new events (waiting if
577	neccessary) and will handle those and any outstanding ones. It will block	911	necessary) and will handle those and any already outstanding ones. It
578	your process until at least one new event arrives, and will return after	912	will block your process until at least one new event arrives (which could
579	one iteration of the loop. This is useful if you are waiting for some	913	be an event internal to libev itself, so there is no guarantee that a
580	external event in conjunction with something not expressible using other	914	user-registered callback will be called), and will return after one
		915	iteration of the loop.
		916
		917	This is useful if you are waiting for some external event in conjunction
		918	with something not expressible using other libev watchers (i.e. "roll your
581	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	919	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
582	usually a better approach for this kind of thing.	920	usually a better approach for this kind of thing.
583		921
584	Here are the gory details of what C<ev_loop> does:	922	Here are the gory details of what C<ev_run> does (this is for your
		923	understanding, not a guarantee that things will work exactly like this in
		924	future versions):
585		925
		926	- Increment loop depth.
		927	- Reset the ev_break status.
586	- Before the first iteration, call any pending watchers.	928	- Before the first iteration, call any pending watchers.
		929	LOOP:
587	* If EVFLAG_FORKCHECK was used, check for a fork.	930	- If EVFLAG_FORKCHECK was used, check for a fork.
588	- If a fork was detected, queue and call all fork watchers.	931	- If a fork was detected (by any means), queue and call all fork watchers.
589	- Queue and call all prepare watchers.	932	- Queue and call all prepare watchers.
		933	- If ev_break was called, goto FINISH.
590	- If we have been forked, recreate the kernel state.	934	- If we have been forked, detach and recreate the kernel state
		935	as to not disturb the other process.
591	- Update the kernel state with all outstanding changes.	936	- Update the kernel state with all outstanding changes.
592	- Update the "event loop time".	937	- Update the "event loop time" (ev_now ()).
593	- Calculate for how long to sleep or block, if at all	938	- Calculate for how long to sleep or block, if at all
594	(active idle watchers, EVLOOP_NONBLOCK or not having	939	(active idle watchers, EVRUN_NOWAIT or not having
595	any active watchers at all will result in not sleeping).	940	any active watchers at all will result in not sleeping).
596	- Sleep if the I/O and timer collect interval say so.	941	- Sleep if the I/O and timer collect interval say so.
		942	- Increment loop iteration counter.
597	- Block the process, waiting for any events.	943	- Block the process, waiting for any events.
598	- Queue all outstanding I/O (fd) events.	944	- Queue all outstanding I/O (fd) events.
599	- Update the "event loop time" and do time jump handling.	945	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
600	- Queue all outstanding timers.	946	- Queue all expired timers.
601	- Queue all outstanding periodics.	947	- Queue all expired periodics.
602	- If no events are pending now, queue all idle watchers.	948	- Queue all idle watchers with priority higher than that of pending events.
603	- Queue all check watchers.	949	- Queue all check watchers.
604	- Call all queued watchers in reverse order (i.e. check watchers first).	950	- Call all queued watchers in reverse order (i.e. check watchers first).
605	Signals and child watchers are implemented as I/O watchers, and will	951	Signals and child watchers are implemented as I/O watchers, and will
606	be handled here by queueing them when their watcher gets executed.	952	be handled here by queueing them when their watcher gets executed.
607	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	953	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
608	were used, or there are no active watchers, return, otherwise	954	were used, or there are no active watchers, goto FINISH, otherwise
609	continue with step *.	955	continue with step LOOP.
		956	FINISH:
		957	- Reset the ev_break status iff it was EVBREAK_ONE.
		958	- Decrement the loop depth.
		959	- Return.
610		960
611	Example: Queue some jobs and then loop until no events are outstanding	961	Example: Queue some jobs and then loop until no events are outstanding
612	anymore.	962	anymore.
613		963
614	... queue jobs here, make sure they register event watchers as long	964	... queue jobs here, make sure they register event watchers as long
615	... as they still have work to do (even an idle watcher will do..)	965	... as they still have work to do (even an idle watcher will do..)
616	ev_loop (my_loop, 0);	966	ev_run (my_loop, 0);
617	... jobs done. yeah!	967	... jobs done or somebody called break. yeah!
618		968
619	=item ev_unloop (loop, how)	969	=item ev_break (loop, how)
620		970
621	Can be used to make a call to C<ev_loop> return early (but only after it	971	Can be used to make a call to C<ev_run> return early (but only after it
622	has processed all outstanding events). The C<how> argument must be either	972	has processed all outstanding events). The C<how> argument must be either
623	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	973	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
624	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	974	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
625		975
626	This "unloop state" will be cleared when entering C<ev_loop> again.	976	This "break state" will be cleared on the next call to C<ev_run>.
		977
		978	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		979	which case it will have no effect.
627		980
628	=item ev_ref (loop)	981	=item ev_ref (loop)
629		982
630	=item ev_unref (loop)	983	=item ev_unref (loop)
631		984
632	Ref/unref can be used to add or remove a reference count on the event	985	Ref/unref can be used to add or remove a reference count on the event
633	loop: Every watcher keeps one reference, and as long as the reference	986	loop: Every watcher keeps one reference, and as long as the reference
634	count is nonzero, C<ev_loop> will not return on its own. If you have	987	count is nonzero, C<ev_run> will not return on its own.
635	a watcher you never unregister that should not keep C<ev_loop> from	988
636	returning, ev_unref() after starting, and ev_ref() before stopping it. For	989	This is useful when you have a watcher that you never intend to
		990	unregister, but that nevertheless should not keep C<ev_run> from
		991	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		992	before stopping it.
		993
637	example, libev itself uses this for its internal signal pipe: It is not	994	As an example, libev itself uses this for its internal signal pipe: It
638	visible to the libev user and should not keep C<ev_loop> from exiting if	995	is not visible to the libev user and should not keep C<ev_run> from
639	no event watchers registered by it are active. It is also an excellent	996	exiting if no event watchers registered by it are active. It is also an
640	way to do this for generic recurring timers or from within third-party	997	excellent way to do this for generic recurring timers or from within
641	libraries. Just remember to I<unref after start> and I<ref before stop>	998	third-party libraries. Just remember to I<unref after start> and I<ref
642	(but only if the watcher wasn't active before, or was active before,	999	before stop> (but only if the watcher wasn't active before, or was active
643	respectively).	1000	before, respectively. Note also that libev might stop watchers itself
		1001	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		1002	in the callback).
644		1003
645	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	1004	Example: Create a signal watcher, but keep it from keeping C<ev_run>
646	running when nothing else is active.	1005	running when nothing else is active.
647		1006
648	struct ev_signal exitsig;	1007	ev_signal exitsig;
649	ev_signal_init (&exitsig, sig_cb, SIGINT);	1008	ev_signal_init (&exitsig, sig_cb, SIGINT);
650	ev_signal_start (loop, &exitsig);	1009	ev_signal_start (loop, &exitsig);
651	evf_unref (loop);	1010	ev_unref (loop);
652		1011
653	Example: For some weird reason, unregister the above signal handler again.	1012	Example: For some weird reason, unregister the above signal handler again.
654		1013
655	ev_ref (loop);	1014	ev_ref (loop);
656	ev_signal_stop (loop, &exitsig);	1015	ev_signal_stop (loop, &exitsig);
657		1016
658	=item ev_set_io_collect_interval (loop, ev_tstamp interval)	1017	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
659		1018
660	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)	1019	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
661		1020
662	These advanced functions influence the time that libev will spend waiting	1021	These advanced functions influence the time that libev will spend waiting
663	for events. Both are by default C<0>, meaning that libev will try to	1022	for events. Both time intervals are by default C<0>, meaning that libev
664	invoke timer/periodic callbacks and I/O callbacks with minimum latency.	1023	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		1024	latency.
665		1025
666	Setting these to a higher value (the C<interval> I<must> be >= C<0>)	1026	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
667	allows libev to delay invocation of I/O and timer/periodic callbacks to	1027	allows libev to delay invocation of I/O and timer/periodic callbacks
668	increase efficiency of loop iterations.	1028	to increase efficiency of loop iterations (or to increase power-saving
		1029	opportunities).
669		1030
670	The background is that sometimes your program runs just fast enough to	1031	The idea is that sometimes your program runs just fast enough to handle
671	handle one (or very few) event(s) per loop iteration. While this makes	1032	one (or very few) event(s) per loop iteration. While this makes the
672	the program responsive, it also wastes a lot of CPU time to poll for new	1033	program responsive, it also wastes a lot of CPU time to poll for new
673	events, especially with backends like C<select ()> which have a high	1034	events, especially with backends like C<select ()> which have a high
674	overhead for the actual polling but can deliver many events at once.	1035	overhead for the actual polling but can deliver many events at once.
675		1036
676	By setting a higher I<io collect interval> you allow libev to spend more	1037	By setting a higher I<io collect interval> you allow libev to spend more
677	time collecting I/O events, so you can handle more events per iteration,	1038	time collecting I/O events, so you can handle more events per iteration,
678	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	1039	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
679	C<ev_timer>) will be not affected. Setting this to a non-null value will	1040	C<ev_timer>) will not be affected. Setting this to a non-null value will
680	introduce an additional C<ev_sleep ()> call into most loop iterations.	1041	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		1042	sleep time ensures that libev will not poll for I/O events more often then
		1043	once per this interval, on average (as long as the host time resolution is
		1044	good enough).
681		1045
682	Likewise, by setting a higher I<timeout collect interval> you allow libev	1046	Likewise, by setting a higher I<timeout collect interval> you allow libev
683	to spend more time collecting timeouts, at the expense of increased	1047	to spend more time collecting timeouts, at the expense of increased
684	latency (the watcher callback will be called later). C<ev_io> watchers	1048	latency/jitter/inexactness (the watcher callback will be called
685	will not be affected. Setting this to a non-null value will not introduce	1049	later). C<ev_io> watchers will not be affected. Setting this to a non-null
686	any overhead in libev.	1050	value will not introduce any overhead in libev.
687		1051
688	Many (busy) programs can usually benefit by setting the io collect	1052	Many (busy) programs can usually benefit by setting the I/O collect
689	interval to a value near C<0.1> or so, which is often enough for	1053	interval to a value near C<0.1> or so, which is often enough for
690	interactive servers (of course not for games), likewise for timeouts. It	1054	interactive servers (of course not for games), likewise for timeouts. It
691	usually doesn't make much sense to set it to a lower value than C<0.01>,	1055	usually doesn't make much sense to set it to a lower value than C<0.01>,
692	as this approsaches the timing granularity of most systems.	1056	as this approaches the timing granularity of most systems. Note that if
		1057	you do transactions with the outside world and you can't increase the
		1058	parallelity, then this setting will limit your transaction rate (if you
		1059	need to poll once per transaction and the I/O collect interval is 0.01,
		1060	then you can't do more than 100 transactions per second).
		1061
		1062	Setting the I<timeout collect interval> can improve the opportunity for
		1063	saving power, as the program will "bundle" timer callback invocations that
		1064	are "near" in time together, by delaying some, thus reducing the number of
		1065	times the process sleeps and wakes up again. Another useful technique to
		1066	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		1067	they fire on, say, one-second boundaries only.
		1068
		1069	Example: we only need 0.1s timeout granularity, and we wish not to poll
		1070	more often than 100 times per second:
		1071
		1072	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		1073	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		1074
		1075	=item ev_invoke_pending (loop)
		1076
		1077	This call will simply invoke all pending watchers while resetting their
		1078	pending state. Normally, C<ev_run> does this automatically when required,
		1079	but when overriding the invoke callback this call comes handy. This
		1080	function can be invoked from a watcher - this can be useful for example
		1081	when you want to do some lengthy calculation and want to pass further
		1082	event handling to another thread (you still have to make sure only one
		1083	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
		1084
		1085	=item int ev_pending_count (loop)
		1086
		1087	Returns the number of pending watchers - zero indicates that no watchers
		1088	are pending.
		1089
		1090	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		1091
		1092	This overrides the invoke pending functionality of the loop: Instead of
		1093	invoking all pending watchers when there are any, C<ev_run> will call
		1094	this callback instead. This is useful, for example, when you want to
		1095	invoke the actual watchers inside another context (another thread etc.).
		1096
		1097	If you want to reset the callback, use C<ev_invoke_pending> as new
		1098	callback.
		1099
		1100	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
		1101
		1102	Sometimes you want to share the same loop between multiple threads. This
		1103	can be done relatively simply by putting mutex_lock/unlock calls around
		1104	each call to a libev function.
		1105
		1106	However, C<ev_run> can run an indefinite time, so it is not feasible
		1107	to wait for it to return. One way around this is to wake up the event
		1108	loop via C<ev_break> and C<ev_async_send>, another way is to set these
		1109	I<release> and I<acquire> callbacks on the loop.
		1110
		1111	When set, then C<release> will be called just before the thread is
		1112	suspended waiting for new events, and C<acquire> is called just
		1113	afterwards.
		1114
		1115	Ideally, C<release> will just call your mutex_unlock function, and
		1116	C<acquire> will just call the mutex_lock function again.
		1117
		1118	While event loop modifications are allowed between invocations of
		1119	C<release> and C<acquire> (that's their only purpose after all), no
		1120	modifications done will affect the event loop, i.e. adding watchers will
		1121	have no effect on the set of file descriptors being watched, or the time
		1122	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		1123	to take note of any changes you made.
		1124
		1125	In theory, threads executing C<ev_run> will be async-cancel safe between
		1126	invocations of C<release> and C<acquire>.
		1127
		1128	See also the locking example in the C<THREADS> section later in this
		1129	document.
		1130
		1131	=item ev_set_userdata (loop, void *data)
		1132
		1133	=item void *ev_userdata (loop)
		1134
		1135	Set and retrieve a single C<void *> associated with a loop. When
		1136	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		1137	C<0>.
		1138
		1139	These two functions can be used to associate arbitrary data with a loop,
		1140	and are intended solely for the C<invoke_pending_cb>, C<release> and
		1141	C<acquire> callbacks described above, but of course can be (ab-)used for
		1142	any other purpose as well.
		1143
		1144	=item ev_verify (loop)
		1145
		1146	This function only does something when C<EV_VERIFY> support has been
		1147	compiled in, which is the default for non-minimal builds. It tries to go
		1148	through all internal structures and checks them for validity. If anything
		1149	is found to be inconsistent, it will print an error message to standard
		1150	error and call C<abort ()>.
		1151
		1152	This can be used to catch bugs inside libev itself: under normal
		1153	circumstances, this function will never abort as of course libev keeps its
		1154	data structures consistent.
693		1155
694	=back	1156	=back
695		1157
696		1158
697	=head1 ANATOMY OF A WATCHER	1159	=head1 ANATOMY OF A WATCHER
698		1160
		1161	In the following description, uppercase C<TYPE> in names stands for the
		1162	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		1163	watchers and C<ev_io_start> for I/O watchers.
		1164
699	A watcher is a structure that you create and register to record your	1165	A watcher is an opaque structure that you allocate and register to record
700	interest in some event. For instance, if you want to wait for STDIN to	1166	your interest in some event. To make a concrete example, imagine you want
701	become readable, you would create an C<ev_io> watcher for that:	1167	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1168	for that:
702		1169
703	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1170	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
704	{	1171	{
705	ev_io_stop (w);	1172	ev_io_stop (w);
706	ev_unloop (loop, EVUNLOOP_ALL);	1173	ev_break (loop, EVBREAK_ALL);
707	}	1174	}
708		1175
709	struct ev_loop *loop = ev_default_loop (0);	1176	struct ev_loop *loop = ev_default_loop (0);
		1177
710	struct ev_io stdin_watcher;	1178	ev_io stdin_watcher;
		1179
711	ev_init (&stdin_watcher, my_cb);	1180	ev_init (&stdin_watcher, my_cb);
712	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1181	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
713	ev_io_start (loop, &stdin_watcher);	1182	ev_io_start (loop, &stdin_watcher);
		1183
714	ev_loop (loop, 0);	1184	ev_run (loop, 0);
715		1185
716	As you can see, you are responsible for allocating the memory for your	1186	As you can see, you are responsible for allocating the memory for your
717	watcher structures (and it is usually a bad idea to do this on the stack,	1187	watcher structures (and it is I<usually> a bad idea to do this on the
718	although this can sometimes be quite valid).	1188	stack).
719		1189
		1190	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1191	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1192
720	Each watcher structure must be initialised by a call to C<ev_init	1193	Each watcher structure must be initialised by a call to C<ev_init (watcher
721	(watcher *, callback)>, which expects a callback to be provided. This	1194	*, callback)>, which expects a callback to be provided. This callback is
722	callback gets invoked each time the event occurs (or, in the case of io	1195	invoked each time the event occurs (or, in the case of I/O watchers, each
723	watchers, each time the event loop detects that the file descriptor given	1196	time the event loop detects that the file descriptor given is readable
724	is readable and/or writable).	1197	and/or writable).
725		1198
726	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1199	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
727	with arguments specific to this watcher type. There is also a macro	1200	macro to configure it, with arguments specific to the watcher type. There
728	to combine initialisation and setting in one call: C<< ev_<type>_init	1201	is also a macro to combine initialisation and setting in one call: C<<
729	(watcher *, callback, ...) >>.	1202	ev_TYPE_init (watcher *, callback, ...) >>.
730		1203
731	To make the watcher actually watch out for events, you have to start it	1204	To make the watcher actually watch out for events, you have to start it
732	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1205	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
733	*) >>), and you can stop watching for events at any time by calling the	1206	*) >>), and you can stop watching for events at any time by calling the
734	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1207	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
735		1208
736	As long as your watcher is active (has been started but not stopped) you	1209	As long as your watcher is active (has been started but not stopped) you
737	must not touch the values stored in it. Most specifically you must never	1210	must not touch the values stored in it. Most specifically you must never
738	reinitialise it or call its C<set> macro.	1211	reinitialise it or call its C<ev_TYPE_set> macro.
739		1212
740	Each and every callback receives the event loop pointer as first, the	1213	Each and every callback receives the event loop pointer as first, the
741	registered watcher structure as second, and a bitset of received events as	1214	registered watcher structure as second, and a bitset of received events as
742	third argument.	1215	third argument.
743		1216
…		…
752	=item C<EV_WRITE>	1225	=item C<EV_WRITE>
753		1226
754	The file descriptor in the C<ev_io> watcher has become readable and/or	1227	The file descriptor in the C<ev_io> watcher has become readable and/or
755	writable.	1228	writable.
756		1229
757	=item C<EV_TIMEOUT>	1230	=item C<EV_TIMER>
758		1231
759	The C<ev_timer> watcher has timed out.	1232	The C<ev_timer> watcher has timed out.
760		1233
761	=item C<EV_PERIODIC>	1234	=item C<EV_PERIODIC>
762		1235
…		…
780		1253
781	=item C<EV_PREPARE>	1254	=item C<EV_PREPARE>
782		1255
783	=item C<EV_CHECK>	1256	=item C<EV_CHECK>
784		1257
785	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts	1258	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts to
786	to gather new events, and all C<ev_check> watchers are invoked just after	1259	gather new events, and all C<ev_check> watchers are queued (not invoked)
787	C<ev_loop> has gathered them, but before it invokes any callbacks for any	1260	just after C<ev_run> has gathered them, but before it queues any callbacks
		1261	for any received events. That means C<ev_prepare> watchers are the last
		1262	watchers invoked before the event loop sleeps or polls for new events, and
		1263	C<ev_check> watchers will be invoked before any other watchers of the same
		1264	or lower priority within an event loop iteration.
		1265
788	received events. Callbacks of both watcher types can start and stop as	1266	Callbacks of both watcher types can start and stop as many watchers as
789	many watchers as they want, and all of them will be taken into account	1267	they want, and all of them will be taken into account (for example, a
790	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1268	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
791	C<ev_loop> from blocking).	1269	blocking).
792		1270
793	=item C<EV_EMBED>	1271	=item C<EV_EMBED>
794		1272
795	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1273	The embedded event loop specified in the C<ev_embed> watcher needs attention.
796		1274
797	=item C<EV_FORK>	1275	=item C<EV_FORK>
798		1276
799	The event loop has been resumed in the child process after fork (see	1277	The event loop has been resumed in the child process after fork (see
800	C<ev_fork>).	1278	C<ev_fork>).
801		1279
		1280	=item C<EV_CLEANUP>
		1281
		1282	The event loop is about to be destroyed (see C<ev_cleanup>).
		1283
802	=item C<EV_ASYNC>	1284	=item C<EV_ASYNC>
803		1285
804	The given async watcher has been asynchronously notified (see C<ev_async>).	1286	The given async watcher has been asynchronously notified (see C<ev_async>).
805		1287
		1288	=item C<EV_CUSTOM>
		1289
		1290	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1291	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1292
806	=item C<EV_ERROR>	1293	=item C<EV_ERROR>
807		1294
808	An unspecified error has occured, the watcher has been stopped. This might	1295	An unspecified error has occurred, the watcher has been stopped. This might
809	happen because the watcher could not be properly started because libev	1296	happen because the watcher could not be properly started because libev
810	ran out of memory, a file descriptor was found to be closed or any other	1297	ran out of memory, a file descriptor was found to be closed or any other
		1298	problem. Libev considers these application bugs.
		1299
811	problem. You best act on it by reporting the problem and somehow coping	1300	You best act on it by reporting the problem and somehow coping with the
812	with the watcher being stopped.	1301	watcher being stopped. Note that well-written programs should not receive
		1302	an error ever, so when your watcher receives it, this usually indicates a
		1303	bug in your program.
813		1304
814	Libev will usually signal a few "dummy" events together with an error,	1305	Libev will usually signal a few "dummy" events together with an error, for
815	for example it might indicate that a fd is readable or writable, and if	1306	example it might indicate that a fd is readable or writable, and if your
816	your callbacks is well-written it can just attempt the operation and cope	1307	callbacks is well-written it can just attempt the operation and cope with
817	with the error from read() or write(). This will not work in multithreaded	1308	the error from read() or write(). This will not work in multi-threaded
818	programs, though, so beware.	1309	programs, though, as the fd could already be closed and reused for another
		1310	thing, so beware.
819		1311
820	=back	1312	=back
821		1313
822	=head2 GENERIC WATCHER FUNCTIONS	1314	=head2 GENERIC WATCHER FUNCTIONS
823
824	In the following description, C<TYPE> stands for the watcher type,
825	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
826		1315
827	=over 4	1316	=over 4
828		1317
829	=item C<ev_init> (ev_TYPE *watcher, callback)	1318	=item C<ev_init> (ev_TYPE *watcher, callback)
830		1319
…		…
836	which rolls both calls into one.	1325	which rolls both calls into one.
837		1326
838	You can reinitialise a watcher at any time as long as it has been stopped	1327	You can reinitialise a watcher at any time as long as it has been stopped
839	(or never started) and there are no pending events outstanding.	1328	(or never started) and there are no pending events outstanding.
840		1329
841	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1330	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
842	int revents)>.	1331	int revents)>.
843		1332
		1333	Example: Initialise an C<ev_io> watcher in two steps.
		1334
		1335	ev_io w;
		1336	ev_init (&w, my_cb);
		1337	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1338
844	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1339	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
845		1340
846	This macro initialises the type-specific parts of a watcher. You need to	1341	This macro initialises the type-specific parts of a watcher. You need to
847	call C<ev_init> at least once before you call this macro, but you can	1342	call C<ev_init> at least once before you call this macro, but you can
848	call C<ev_TYPE_set> any number of times. You must not, however, call this	1343	call C<ev_TYPE_set> any number of times. You must not, however, call this
849	macro on a watcher that is active (it can be pending, however, which is a	1344	macro on a watcher that is active (it can be pending, however, which is a
850	difference to the C<ev_init> macro).	1345	difference to the C<ev_init> macro).
851		1346
852	Although some watcher types do not have type-specific arguments	1347	Although some watcher types do not have type-specific arguments
853	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1348	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
854		1349
		1350	See C<ev_init>, above, for an example.
		1351
855	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1352	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
856		1353
857	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1354	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
858	calls into a single call. This is the most convinient method to initialise	1355	calls into a single call. This is the most convenient method to initialise
859	a watcher. The same limitations apply, of course.	1356	a watcher. The same limitations apply, of course.
860		1357
		1358	Example: Initialise and set an C<ev_io> watcher in one step.
		1359
		1360	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1361
861	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1362	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
862		1363
863	Starts (activates) the given watcher. Only active watchers will receive	1364	Starts (activates) the given watcher. Only active watchers will receive
864	events. If the watcher is already active nothing will happen.	1365	events. If the watcher is already active nothing will happen.
865		1366
		1367	Example: Start the C<ev_io> watcher that is being abused as example in this
		1368	whole section.
		1369
		1370	ev_io_start (EV_DEFAULT_UC, &w);
		1371
866	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1372	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
867		1373
868	Stops the given watcher again (if active) and clears the pending	1374	Stops the given watcher if active, and clears the pending status (whether
		1375	the watcher was active or not).
		1376
869	status. It is possible that stopped watchers are pending (for example,	1377	It is possible that stopped watchers are pending - for example,
870	non-repeating timers are being stopped when they become pending), but	1378	non-repeating timers are being stopped when they become pending - but
871	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1379	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
872	you want to free or reuse the memory used by the watcher it is therefore a	1380	pending. If you want to free or reuse the memory used by the watcher it is
873	good idea to always call its C<ev_TYPE_stop> function.	1381	therefore a good idea to always call its C<ev_TYPE_stop> function.
874		1382
875	=item bool ev_is_active (ev_TYPE *watcher)	1383	=item bool ev_is_active (ev_TYPE *watcher)
876		1384
877	Returns a true value iff the watcher is active (i.e. it has been started	1385	Returns a true value iff the watcher is active (i.e. it has been started
878	and not yet been stopped). As long as a watcher is active you must not modify	1386	and not yet been stopped). As long as a watcher is active you must not modify
…		…
889		1397
890	=item callback ev_cb (ev_TYPE *watcher)	1398	=item callback ev_cb (ev_TYPE *watcher)
891		1399
892	Returns the callback currently set on the watcher.	1400	Returns the callback currently set on the watcher.
893		1401
894	=item ev_cb_set (ev_TYPE *watcher, callback)	1402	=item ev_set_cb (ev_TYPE *watcher, callback)
895		1403
896	Change the callback. You can change the callback at virtually any time	1404	Change the callback. You can change the callback at virtually any time
897	(modulo threads).	1405	(modulo threads).
898		1406
899	=item ev_set_priority (ev_TYPE *watcher, priority)	1407	=item ev_set_priority (ev_TYPE *watcher, int priority)
900		1408
901	=item int ev_priority (ev_TYPE *watcher)	1409	=item int ev_priority (ev_TYPE *watcher)
902		1410
903	Set and query the priority of the watcher. The priority is a small	1411	Set and query the priority of the watcher. The priority is a small
904	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1412	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
905	(default: C<-2>). Pending watchers with higher priority will be invoked	1413	(default: C<-2>). Pending watchers with higher priority will be invoked
906	before watchers with lower priority, but priority will not keep watchers	1414	before watchers with lower priority, but priority will not keep watchers
907	from being executed (except for C<ev_idle> watchers).	1415	from being executed (except for C<ev_idle> watchers).
908		1416
909	This means that priorities are I<only> used for ordering callback
910	invocation after new events have been received. This is useful, for
911	example, to reduce latency after idling, or more often, to bind two
912	watchers on the same event and make sure one is called first.
913
914	If you need to suppress invocation when higher priority events are pending	1417	If you need to suppress invocation when higher priority events are pending
915	you need to look at C<ev_idle> watchers, which provide this functionality.	1418	you need to look at C<ev_idle> watchers, which provide this functionality.
916		1419
917	You I<must not> change the priority of a watcher as long as it is active or	1420	You I<must not> change the priority of a watcher as long as it is active or
918	pending.	1421	pending.
919		1422
		1423	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1424	fine, as long as you do not mind that the priority value you query might
		1425	or might not have been clamped to the valid range.
		1426
920	The default priority used by watchers when no priority has been set is	1427	The default priority used by watchers when no priority has been set is
921	always C<0>, which is supposed to not be too high and not be too low :).	1428	always C<0>, which is supposed to not be too high and not be too low :).
922		1429
923	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1430	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
924	fine, as long as you do not mind that the priority value you query might	1431	priorities.
925	or might not have been adjusted to be within valid range.
926		1432
927	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1433	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
928		1434
929	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1435	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
930	C<loop> nor C<revents> need to be valid as long as the watcher callback	1436	C<loop> nor C<revents> need to be valid as long as the watcher callback
931	can deal with that fact.	1437	can deal with that fact, as both are simply passed through to the
		1438	callback.
932		1439
933	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1440	=item int ev_clear_pending (loop, ev_TYPE *watcher)
934		1441
935	If the watcher is pending, this function returns clears its pending status	1442	If the watcher is pending, this function clears its pending status and
936	and returns its C<revents> bitset (as if its callback was invoked). If the	1443	returns its C<revents> bitset (as if its callback was invoked). If the
937	watcher isn't pending it does nothing and returns C<0>.	1444	watcher isn't pending it does nothing and returns C<0>.
938		1445
		1446	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1447	callback to be invoked, which can be accomplished with this function.
		1448
		1449	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1450
		1451	Feeds the given event set into the event loop, as if the specified event
		1452	had happened for the specified watcher (which must be a pointer to an
		1453	initialised but not necessarily started event watcher). Obviously you must
		1454	not free the watcher as long as it has pending events.
		1455
		1456	Stopping the watcher, letting libev invoke it, or calling
		1457	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1458	not started in the first place.
		1459
		1460	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1461	functions that do not need a watcher.
		1462
939	=back	1463	=back
940		1464
		1465	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
		1466	OWN COMPOSITE WATCHERS> idioms.
941		1467
942	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1468	=head2 WATCHER STATES
943		1469
944	Each watcher has, by default, a member C<void *data> that you can change	1470	There are various watcher states mentioned throughout this manual -
945	and read at any time, libev will completely ignore it. This can be used	1471	active, pending and so on. In this section these states and the rules to
946	to associate arbitrary data with your watcher. If you need more data and	1472	transition between them will be described in more detail - and while these
947	don't want to allocate memory and store a pointer to it in that data	1473	rules might look complicated, they usually do "the right thing".
948	member, you can also "subclass" the watcher type and provide your own
949	data:
950		1474
951	struct my_io	1475	=over 4
952	{
953	struct ev_io io;
954	int otherfd;
955	void *somedata;
956	struct whatever *mostinteresting;
957	}
958		1476
959	And since your callback will be called with a pointer to the watcher, you	1477	=item initialised
960	can cast it back to your own type:
961		1478
962	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1479	Before a watcher can be registered with the event loop it has to be
963	{	1480	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
964	struct my_io *w = (struct my_io *)w_;	1481	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
965	...
966	}
967		1482
968	More interesting and less C-conformant ways of casting your callback type	1483	In this state it is simply some block of memory that is suitable for
969	instead have been omitted.	1484	use in an event loop. It can be moved around, freed, reused etc. at
		1485	will - as long as you either keep the memory contents intact, or call
		1486	C<ev_TYPE_init> again.
970		1487
971	Another common scenario is having some data structure with multiple	1488	=item started/running/active
972	watchers:
973		1489
974	struct my_biggy	1490	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
975	{	1491	property of the event loop, and is actively waiting for events. While in
976	int some_data;	1492	this state it cannot be accessed (except in a few documented ways), moved,
977	ev_timer t1;	1493	freed or anything else - the only legal thing is to keep a pointer to it,
978	ev_timer t2;	1494	and call libev functions on it that are documented to work on active watchers.
979	}
980		1495
981	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1496	=item pending
982	you need to use C<offsetof>:
983		1497
984	#include <stddef.h>	1498	If a watcher is active and libev determines that an event it is interested
		1499	in has occurred (such as a timer expiring), it will become pending. It will
		1500	stay in this pending state until either it is stopped or its callback is
		1501	about to be invoked, so it is not normally pending inside the watcher
		1502	callback.
985		1503
		1504	The watcher might or might not be active while it is pending (for example,
		1505	an expired non-repeating timer can be pending but no longer active). If it
		1506	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1507	but it is still property of the event loop at this time, so cannot be
		1508	moved, freed or reused. And if it is active the rules described in the
		1509	previous item still apply.
		1510
		1511	It is also possible to feed an event on a watcher that is not active (e.g.
		1512	via C<ev_feed_event>), in which case it becomes pending without being
		1513	active.
		1514
		1515	=item stopped
		1516
		1517	A watcher can be stopped implicitly by libev (in which case it might still
		1518	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1519	latter will clear any pending state the watcher might be in, regardless
		1520	of whether it was active or not, so stopping a watcher explicitly before
		1521	freeing it is often a good idea.
		1522
		1523	While stopped (and not pending) the watcher is essentially in the
		1524	initialised state, that is, it can be reused, moved, modified in any way
		1525	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1526	it again).
		1527
		1528	=back
		1529
		1530	=head2 WATCHER PRIORITY MODELS
		1531
		1532	Many event loops support I<watcher priorities>, which are usually small
		1533	integers that influence the ordering of event callback invocation
		1534	between watchers in some way, all else being equal.
		1535
		1536	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1537	description for the more technical details such as the actual priority
		1538	range.
		1539
		1540	There are two common ways how these these priorities are being interpreted
		1541	by event loops:
		1542
		1543	In the more common lock-out model, higher priorities "lock out" invocation
		1544	of lower priority watchers, which means as long as higher priority
		1545	watchers receive events, lower priority watchers are not being invoked.
		1546
		1547	The less common only-for-ordering model uses priorities solely to order
		1548	callback invocation within a single event loop iteration: Higher priority
		1549	watchers are invoked before lower priority ones, but they all get invoked
		1550	before polling for new events.
		1551
		1552	Libev uses the second (only-for-ordering) model for all its watchers
		1553	except for idle watchers (which use the lock-out model).
		1554
		1555	The rationale behind this is that implementing the lock-out model for
		1556	watchers is not well supported by most kernel interfaces, and most event
		1557	libraries will just poll for the same events again and again as long as
		1558	their callbacks have not been executed, which is very inefficient in the
		1559	common case of one high-priority watcher locking out a mass of lower
		1560	priority ones.
		1561
		1562	Static (ordering) priorities are most useful when you have two or more
		1563	watchers handling the same resource: a typical usage example is having an
		1564	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1565	timeouts. Under load, data might be received while the program handles
		1566	other jobs, but since timers normally get invoked first, the timeout
		1567	handler will be executed before checking for data. In that case, giving
		1568	the timer a lower priority than the I/O watcher ensures that I/O will be
		1569	handled first even under adverse conditions (which is usually, but not
		1570	always, what you want).
		1571
		1572	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1573	will only be executed when no same or higher priority watchers have
		1574	received events, they can be used to implement the "lock-out" model when
		1575	required.
		1576
		1577	For example, to emulate how many other event libraries handle priorities,
		1578	you can associate an C<ev_idle> watcher to each such watcher, and in
		1579	the normal watcher callback, you just start the idle watcher. The real
		1580	processing is done in the idle watcher callback. This causes libev to
		1581	continuously poll and process kernel event data for the watcher, but when
		1582	the lock-out case is known to be rare (which in turn is rare :), this is
		1583	workable.
		1584
		1585	Usually, however, the lock-out model implemented that way will perform
		1586	miserably under the type of load it was designed to handle. In that case,
		1587	it might be preferable to stop the real watcher before starting the
		1588	idle watcher, so the kernel will not have to process the event in case
		1589	the actual processing will be delayed for considerable time.
		1590
		1591	Here is an example of an I/O watcher that should run at a strictly lower
		1592	priority than the default, and which should only process data when no
		1593	other events are pending:
		1594
		1595	ev_idle idle; // actual processing watcher
		1596	ev_io io; // actual event watcher
		1597
986	static void	1598	static void
987	t1_cb (EV_P_ struct ev_timer *w, int revents)	1599	io_cb (EV_P_ ev_io *w, int revents)
988	{	1600	{
989	struct my_biggy big = (struct my_biggy *	1601	// stop the I/O watcher, we received the event, but
990	(((char *)w) - offsetof (struct my_biggy, t1));	1602	// are not yet ready to handle it.
		1603	ev_io_stop (EV_A_ w);
		1604
		1605	// start the idle watcher to handle the actual event.
		1606	// it will not be executed as long as other watchers
		1607	// with the default priority are receiving events.
		1608	ev_idle_start (EV_A_ &idle);
991	}	1609	}
992		1610
993	static void	1611	static void
994	t2_cb (EV_P_ struct ev_timer *w, int revents)	1612	idle_cb (EV_P_ ev_idle *w, int revents)
995	{	1613	{
996	struct my_biggy big = (struct my_biggy *	1614	// actual processing
997	(((char *)w) - offsetof (struct my_biggy, t2));	1615	read (STDIN_FILENO, ...);
		1616
		1617	// have to start the I/O watcher again, as
		1618	// we have handled the event
		1619	ev_io_start (EV_P_ &io);
998	}	1620	}
		1621
		1622	// initialisation
		1623	ev_idle_init (&idle, idle_cb);
		1624	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1625	ev_io_start (EV_DEFAULT_ &io);
		1626
		1627	In the "real" world, it might also be beneficial to start a timer, so that
		1628	low-priority connections can not be locked out forever under load. This
		1629	enables your program to keep a lower latency for important connections
		1630	during short periods of high load, while not completely locking out less
		1631	important ones.
999		1632
1000		1633
1001	=head1 WATCHER TYPES	1634	=head1 WATCHER TYPES
1002		1635
1003	This section describes each watcher in detail, but will not repeat	1636	This section describes each watcher in detail, but will not repeat
…		…
1027	In general you can register as many read and/or write event watchers per	1660	In general you can register as many read and/or write event watchers per
1028	fd as you want (as long as you don't confuse yourself). Setting all file	1661	fd as you want (as long as you don't confuse yourself). Setting all file
1029	descriptors to non-blocking mode is also usually a good idea (but not	1662	descriptors to non-blocking mode is also usually a good idea (but not
1030	required if you know what you are doing).	1663	required if you know what you are doing).
1031		1664
1032	If you must do this, then force the use of a known-to-be-good backend
1033	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
1034	C<EVBACKEND_POLL>).
1035
1036	Another thing you have to watch out for is that it is quite easy to	1665	Another thing you have to watch out for is that it is quite easy to
1037	receive "spurious" readiness notifications, that is your callback might	1666	receive "spurious" readiness notifications, that is, your callback might
1038	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1667	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1039	because there is no data. Not only are some backends known to create a	1668	because there is no data. It is very easy to get into this situation even
1040	lot of those (for example solaris ports), it is very easy to get into	1669	with a relatively standard program structure. Thus it is best to always
1041	this situation even with a relatively standard program structure. Thus	1670	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1042	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1043	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1671	preferable to a program hanging until some data arrives.
1044		1672
1045	If you cannot run the fd in non-blocking mode (for example you should not	1673	If you cannot run the fd in non-blocking mode (for example you should
1046	play around with an Xlib connection), then you have to seperately re-test	1674	not play around with an Xlib connection), then you have to separately
1047	whether a file descriptor is really ready with a known-to-be good interface	1675	re-test whether a file descriptor is really ready with a known-to-be good
1048	such as poll (fortunately in our Xlib example, Xlib already does this on	1676	interface such as poll (fortunately in the case of Xlib, it already does
1049	its own, so its quite safe to use).	1677	this on its own, so its quite safe to use). Some people additionally
		1678	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1679	indefinitely.
		1680
		1681	But really, best use non-blocking mode.
1050		1682
1051	=head3 The special problem of disappearing file descriptors	1683	=head3 The special problem of disappearing file descriptors
1052		1684
1053	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1685	Some backends (e.g. kqueue, epoll, linuxaio) need to be told about closing
1054	descriptor (either by calling C<close> explicitly or by any other means,	1686	a file descriptor (either due to calling C<close> explicitly or any other
1055	such as C<dup>). The reason is that you register interest in some file	1687	means, such as C<dup2>). The reason is that you register interest in some
1056	descriptor, but when it goes away, the operating system will silently drop	1688	file descriptor, but when it goes away, the operating system will silently
1057	this interest. If another file descriptor with the same number then is	1689	drop this interest. If another file descriptor with the same number then
1058	registered with libev, there is no efficient way to see that this is, in	1690	is registered with libev, there is no efficient way to see that this is,
1059	fact, a different file descriptor.	1691	in fact, a different file descriptor.
1060		1692
1061	To avoid having to explicitly tell libev about such cases, libev follows	1693	To avoid having to explicitly tell libev about such cases, libev follows
1062	the following policy: Each time C<ev_io_set> is being called, libev	1694	the following policy: Each time C<ev_io_set> is being called, libev
1063	will assume that this is potentially a new file descriptor, otherwise	1695	will assume that this is potentially a new file descriptor, otherwise
1064	it is assumed that the file descriptor stays the same. That means that	1696	it is assumed that the file descriptor stays the same. That means that
…		…
1078		1710
1079	There is no workaround possible except not registering events	1711	There is no workaround possible except not registering events
1080	for potentially C<dup ()>'ed file descriptors, or to resort to	1712	for potentially C<dup ()>'ed file descriptors, or to resort to
1081	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1713	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1082		1714
		1715	=head3 The special problem of files
		1716
		1717	Many people try to use C<select> (or libev) on file descriptors
		1718	representing files, and expect it to become ready when their program
		1719	doesn't block on disk accesses (which can take a long time on their own).
		1720
		1721	However, this cannot ever work in the "expected" way - you get a readiness
		1722	notification as soon as the kernel knows whether and how much data is
		1723	there, and in the case of open files, that's always the case, so you
		1724	always get a readiness notification instantly, and your read (or possibly
		1725	write) will still block on the disk I/O.
		1726
		1727	Another way to view it is that in the case of sockets, pipes, character
		1728	devices and so on, there is another party (the sender) that delivers data
		1729	on its own, but in the case of files, there is no such thing: the disk
		1730	will not send data on its own, simply because it doesn't know what you
		1731	wish to read - you would first have to request some data.
		1732
		1733	Since files are typically not-so-well supported by advanced notification
		1734	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1735	to files, even though you should not use it. The reason for this is
		1736	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1737	usually a tty, often a pipe, but also sometimes files or special devices
		1738	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1739	F</dev/urandom>), and even though the file might better be served with
		1740	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1741	it "just works" instead of freezing.
		1742
		1743	So avoid file descriptors pointing to files when you know it (e.g. use
		1744	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1745	when you rarely read from a file instead of from a socket, and want to
		1746	reuse the same code path.
		1747
1083	=head3 The special problem of fork	1748	=head3 The special problem of fork
1084		1749
1085	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1750	Some backends (epoll, kqueue, probably linuxaio) do not support C<fork ()>
1086	useless behaviour. Libev fully supports fork, but needs to be told about	1751	at all or exhibit useless behaviour. Libev fully supports fork, but needs
1087	it in the child.	1752	to be told about it in the child if you want to continue to use it in the
		1753	child.
1088		1754
1089	To support fork in your programs, you either have to call	1755	To support fork in your child processes, you have to call C<ev_loop_fork
1090	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1756	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1091	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1757	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1092	C<EVBACKEND_POLL>.
1093		1758
1094	=head3 The special problem of SIGPIPE	1759	=head3 The special problem of SIGPIPE
1095		1760
1096	While not really specific to libev, it is easy to forget about SIGPIPE:	1761	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1097	when reading from a pipe whose other end has been closed, your program	1762	when writing to a pipe whose other end has been closed, your program gets
1098	gets send a SIGPIPE, which, by default, aborts your program. For most	1763	sent a SIGPIPE, which, by default, aborts your program. For most programs
1099	programs this is sensible behaviour, for daemons, this is usually	1764	this is sensible behaviour, for daemons, this is usually undesirable.
1100	undesirable.
1101		1765
1102	So when you encounter spurious, unexplained daemon exits, make sure you	1766	So when you encounter spurious, unexplained daemon exits, make sure you
1103	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon	1767	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
1104	somewhere, as that would have given you a big clue).	1768	somewhere, as that would have given you a big clue).
1105		1769
		1770	=head3 The special problem of accept()ing when you can't
		1771
		1772	Many implementations of the POSIX C<accept> function (for example,
		1773	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1774	connection from the pending queue in all error cases.
		1775
		1776	For example, larger servers often run out of file descriptors (because
		1777	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1778	rejecting the connection, leading to libev signalling readiness on
		1779	the next iteration again (the connection still exists after all), and
		1780	typically causing the program to loop at 100% CPU usage.
		1781
		1782	Unfortunately, the set of errors that cause this issue differs between
		1783	operating systems, there is usually little the app can do to remedy the
		1784	situation, and no known thread-safe method of removing the connection to
		1785	cope with overload is known (to me).
		1786
		1787	One of the easiest ways to handle this situation is to just ignore it
		1788	- when the program encounters an overload, it will just loop until the
		1789	situation is over. While this is a form of busy waiting, no OS offers an
		1790	event-based way to handle this situation, so it's the best one can do.
		1791
		1792	A better way to handle the situation is to log any errors other than
		1793	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1794	messages, and continue as usual, which at least gives the user an idea of
		1795	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1796	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1797	usage.
		1798
		1799	If your program is single-threaded, then you could also keep a dummy file
		1800	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1801	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1802	close that fd, and create a new dummy fd. This will gracefully refuse
		1803	clients under typical overload conditions.
		1804
		1805	The last way to handle it is to simply log the error and C<exit>, as
		1806	is often done with C<malloc> failures, but this results in an easy
		1807	opportunity for a DoS attack.
1106		1808
1107	=head3 Watcher-Specific Functions	1809	=head3 Watcher-Specific Functions
1108		1810
1109	=over 4	1811	=over 4
1110		1812
1111	=item ev_io_init (ev_io *, callback, int fd, int events)	1813	=item ev_io_init (ev_io *, callback, int fd, int events)
1112		1814
1113	=item ev_io_set (ev_io *, int fd, int events)	1815	=item ev_io_set (ev_io *, int fd, int events)
1114		1816
1115	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1817	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1116	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1818	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
1117	C<EV_READ | EV_WRITE> to receive the given events.	1819	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1118		1820
1119	=item int fd [read-only]	1821	=item int fd [read-only]
1120		1822
1121	The file descriptor being watched.	1823	The file descriptor being watched.
1122		1824
…		…
1130		1832
1131	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1833	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1132	readable, but only once. Since it is likely line-buffered, you could	1834	readable, but only once. Since it is likely line-buffered, you could
1133	attempt to read a whole line in the callback.	1835	attempt to read a whole line in the callback.
1134		1836
1135	static void	1837	static void
1136	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1838	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1137	{	1839	{
1138	ev_io_stop (loop, w);	1840	ev_io_stop (loop, w);
1139	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1841	.. read from stdin here (or from w->fd) and handle any I/O errors
1140	}	1842	}
1141		1843
1142	...	1844	...
1143	struct ev_loop *loop = ev_default_init (0);	1845	struct ev_loop *loop = ev_default_init (0);
1144	struct ev_io stdin_readable;	1846	ev_io stdin_readable;
1145	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1847	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1146	ev_io_start (loop, &stdin_readable);	1848	ev_io_start (loop, &stdin_readable);
1147	ev_loop (loop, 0);	1849	ev_run (loop, 0);
1148		1850
1149		1851
1150	=head2 C<ev_timer> - relative and optionally repeating timeouts	1852	=head2 C<ev_timer> - relative and optionally repeating timeouts
1151		1853
1152	Timer watchers are simple relative timers that generate an event after a	1854	Timer watchers are simple relative timers that generate an event after a
1153	given time, and optionally repeating in regular intervals after that.	1855	given time, and optionally repeating in regular intervals after that.
1154		1856
1155	The timers are based on real time, that is, if you register an event that	1857	The timers are based on real time, that is, if you register an event that
1156	times out after an hour and you reset your system clock to january last	1858	times out after an hour and you reset your system clock to January last
1157	year, it will still time out after (roughly) and hour. "Roughly" because	1859	year, it will still time out after (roughly) one hour. "Roughly" because
1158	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1860	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1159	monotonic clock option helps a lot here).	1861	monotonic clock option helps a lot here).
		1862
		1863	The callback is guaranteed to be invoked only I<after> its timeout has
		1864	passed (not I<at>, so on systems with very low-resolution clocks this
		1865	might introduce a small delay, see "the special problem of being too
		1866	early", below). If multiple timers become ready during the same loop
		1867	iteration then the ones with earlier time-out values are invoked before
		1868	ones of the same priority with later time-out values (but this is no
		1869	longer true when a callback calls C<ev_run> recursively).
		1870
		1871	=head3 Be smart about timeouts
		1872
		1873	Many real-world problems involve some kind of timeout, usually for error
		1874	recovery. A typical example is an HTTP request - if the other side hangs,
		1875	you want to raise some error after a while.
		1876
		1877	What follows are some ways to handle this problem, from obvious and
		1878	inefficient to smart and efficient.
		1879
		1880	In the following, a 60 second activity timeout is assumed - a timeout that
		1881	gets reset to 60 seconds each time there is activity (e.g. each time some
		1882	data or other life sign was received).
		1883
		1884	=over 4
		1885
		1886	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1887
		1888	This is the most obvious, but not the most simple way: In the beginning,
		1889	start the watcher:
		1890
		1891	ev_timer_init (timer, callback, 60., 0.);
		1892	ev_timer_start (loop, timer);
		1893
		1894	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1895	and start it again:
		1896
		1897	ev_timer_stop (loop, timer);
		1898	ev_timer_set (timer, 60., 0.);
		1899	ev_timer_start (loop, timer);
		1900
		1901	This is relatively simple to implement, but means that each time there is
		1902	some activity, libev will first have to remove the timer from its internal
		1903	data structure and then add it again. Libev tries to be fast, but it's
		1904	still not a constant-time operation.
		1905
		1906	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1907
		1908	This is the easiest way, and involves using C<ev_timer_again> instead of
		1909	C<ev_timer_start>.
		1910
		1911	To implement this, configure an C<ev_timer> with a C<repeat> value
		1912	of C<60> and then call C<ev_timer_again> at start and each time you
		1913	successfully read or write some data. If you go into an idle state where
		1914	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1915	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1916
		1917	That means you can ignore both the C<ev_timer_start> function and the
		1918	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1919	member and C<ev_timer_again>.
		1920
		1921	At start:
		1922
		1923	ev_init (timer, callback);
		1924	timer->repeat = 60.;
		1925	ev_timer_again (loop, timer);
		1926
		1927	Each time there is some activity:
		1928
		1929	ev_timer_again (loop, timer);
		1930
		1931	It is even possible to change the time-out on the fly, regardless of
		1932	whether the watcher is active or not:
		1933
		1934	timer->repeat = 30.;
		1935	ev_timer_again (loop, timer);
		1936
		1937	This is slightly more efficient then stopping/starting the timer each time
		1938	you want to modify its timeout value, as libev does not have to completely
		1939	remove and re-insert the timer from/into its internal data structure.
		1940
		1941	It is, however, even simpler than the "obvious" way to do it.
		1942
		1943	=item 3. Let the timer time out, but then re-arm it as required.
		1944
		1945	This method is more tricky, but usually most efficient: Most timeouts are
		1946	relatively long compared to the intervals between other activity - in
		1947	our example, within 60 seconds, there are usually many I/O events with
		1948	associated activity resets.
		1949
		1950	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1951	but remember the time of last activity, and check for a real timeout only
		1952	within the callback:
		1953
		1954	ev_tstamp timeout = 60.;
		1955	ev_tstamp last_activity; // time of last activity
		1956	ev_timer timer;
		1957
		1958	static void
		1959	callback (EV_P_ ev_timer *w, int revents)
		1960	{
		1961	// calculate when the timeout would happen
		1962	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
		1963
		1964	// if negative, it means we the timeout already occurred
		1965	if (after < 0.)
		1966	{
		1967	// timeout occurred, take action
		1968	}
		1969	else
		1970	{
		1971	// callback was invoked, but there was some recent
		1972	// activity. simply restart the timer to time out
		1973	// after "after" seconds, which is the earliest time
		1974	// the timeout can occur.
		1975	ev_timer_set (w, after, 0.);
		1976	ev_timer_start (EV_A_ w);
		1977	}
		1978	}
		1979
		1980	To summarise the callback: first calculate in how many seconds the
		1981	timeout will occur (by calculating the absolute time when it would occur,
		1982	C<last_activity + timeout>, and subtracting the current time, C<ev_now
		1983	(EV_A)> from that).
		1984
		1985	If this value is negative, then we are already past the timeout, i.e. we
		1986	timed out, and need to do whatever is needed in this case.
		1987
		1988	Otherwise, we now the earliest time at which the timeout would trigger,
		1989	and simply start the timer with this timeout value.
		1990
		1991	In other words, each time the callback is invoked it will check whether
		1992	the timeout occurred. If not, it will simply reschedule itself to check
		1993	again at the earliest time it could time out. Rinse. Repeat.
		1994
		1995	This scheme causes more callback invocations (about one every 60 seconds
		1996	minus half the average time between activity), but virtually no calls to
		1997	libev to change the timeout.
		1998
		1999	To start the machinery, simply initialise the watcher and set
		2000	C<last_activity> to the current time (meaning there was some activity just
		2001	now), then call the callback, which will "do the right thing" and start
		2002	the timer:
		2003
		2004	last_activity = ev_now (EV_A);
		2005	ev_init (&timer, callback);
		2006	callback (EV_A_ &timer, 0);
		2007
		2008	When there is some activity, simply store the current time in
		2009	C<last_activity>, no libev calls at all:
		2010
		2011	if (activity detected)
		2012	last_activity = ev_now (EV_A);
		2013
		2014	When your timeout value changes, then the timeout can be changed by simply
		2015	providing a new value, stopping the timer and calling the callback, which
		2016	will again do the right thing (for example, time out immediately :).
		2017
		2018	timeout = new_value;
		2019	ev_timer_stop (EV_A_ &timer);
		2020	callback (EV_A_ &timer, 0);
		2021
		2022	This technique is slightly more complex, but in most cases where the
		2023	time-out is unlikely to be triggered, much more efficient.
		2024
		2025	=item 4. Wee, just use a double-linked list for your timeouts.
		2026
		2027	If there is not one request, but many thousands (millions...), all
		2028	employing some kind of timeout with the same timeout value, then one can
		2029	do even better:
		2030
		2031	When starting the timeout, calculate the timeout value and put the timeout
		2032	at the I<end> of the list.
		2033
		2034	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		2035	the list is expected to fire (for example, using the technique #3).
		2036
		2037	When there is some activity, remove the timer from the list, recalculate
		2038	the timeout, append it to the end of the list again, and make sure to
		2039	update the C<ev_timer> if it was taken from the beginning of the list.
		2040
		2041	This way, one can manage an unlimited number of timeouts in O(1) time for
		2042	starting, stopping and updating the timers, at the expense of a major
		2043	complication, and having to use a constant timeout. The constant timeout
		2044	ensures that the list stays sorted.
		2045
		2046	=back
		2047
		2048	So which method the best?
		2049
		2050	Method #2 is a simple no-brain-required solution that is adequate in most
		2051	situations. Method #3 requires a bit more thinking, but handles many cases
		2052	better, and isn't very complicated either. In most case, choosing either
		2053	one is fine, with #3 being better in typical situations.
		2054
		2055	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		2056	rather complicated, but extremely efficient, something that really pays
		2057	off after the first million or so of active timers, i.e. it's usually
		2058	overkill :)
		2059
		2060	=head3 The special problem of being too early
		2061
		2062	If you ask a timer to call your callback after three seconds, then
		2063	you expect it to be invoked after three seconds - but of course, this
		2064	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		2065	guaranteed to any precision by libev - imagine somebody suspending the
		2066	process with a STOP signal for a few hours for example.
		2067
		2068	So, libev tries to invoke your callback as soon as possible I<after> the
		2069	delay has occurred, but cannot guarantee this.
		2070
		2071	A less obvious failure mode is calling your callback too early: many event
		2072	loops compare timestamps with a "elapsed delay >= requested delay", but
		2073	this can cause your callback to be invoked much earlier than you would
		2074	expect.
		2075
		2076	To see why, imagine a system with a clock that only offers full second
		2077	resolution (think windows if you can't come up with a broken enough OS
		2078	yourself). If you schedule a one-second timer at the time 500.9, then the
		2079	event loop will schedule your timeout to elapse at a system time of 500
		2080	(500.9 truncated to the resolution) + 1, or 501.
		2081
		2082	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2083	501" and invoke the callback 0.1s after it was started, even though a
		2084	one-second delay was requested - this is being "too early", despite best
		2085	intentions.
		2086
		2087	This is the reason why libev will never invoke the callback if the elapsed
		2088	delay equals the requested delay, but only when the elapsed delay is
		2089	larger than the requested delay. In the example above, libev would only invoke
		2090	the callback at system time 502, or 1.1s after the timer was started.
		2091
		2092	So, while libev cannot guarantee that your callback will be invoked
		2093	exactly when requested, it I<can> and I<does> guarantee that the requested
		2094	delay has actually elapsed, or in other words, it always errs on the "too
		2095	late" side of things.
		2096
		2097	=head3 The special problem of time updates
		2098
		2099	Establishing the current time is a costly operation (it usually takes
		2100	at least one system call): EV therefore updates its idea of the current
		2101	time only before and after C<ev_run> collects new events, which causes a
		2102	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		2103	lots of events in one iteration.
1160		2104
1161	The relative timeouts are calculated relative to the C<ev_now ()>	2105	The relative timeouts are calculated relative to the C<ev_now ()>
1162	time. This is usually the right thing as this timestamp refers to the time	2106	time. This is usually the right thing as this timestamp refers to the time
1163	of the event triggering whatever timeout you are modifying/starting. If	2107	of the event triggering whatever timeout you are modifying/starting. If
1164	you suspect event processing to be delayed and you I<need> to base the timeout	2108	you suspect event processing to be delayed and you I<need> to base the
1165	on the current time, use something like this to adjust for this:	2109	timeout on the current time, use something like the following to adjust
		2110	for it:
1166		2111
1167	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2112	ev_timer_set (&timer, after + (ev_time () - ev_now ()), 0.);
1168		2113
1169	The callback is guarenteed to be invoked only after its timeout has passed,	2114	If the event loop is suspended for a long time, you can also force an
1170	but if multiple timers become ready during the same loop iteration then	2115	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1171	order of execution is undefined.	2116	()>, although that will push the event time of all outstanding events
		2117	further into the future.
		2118
		2119	=head3 The special problem of unsynchronised clocks
		2120
		2121	Modern systems have a variety of clocks - libev itself uses the normal
		2122	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2123	jumps).
		2124
		2125	Neither of these clocks is synchronised with each other or any other clock
		2126	on the system, so C<ev_time ()> might return a considerably different time
		2127	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2128	a call to C<gettimeofday> might return a second count that is one higher
		2129	than a directly following call to C<time>.
		2130
		2131	The moral of this is to only compare libev-related timestamps with
		2132	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2133	a second or so.
		2134
		2135	One more problem arises due to this lack of synchronisation: if libev uses
		2136	the system monotonic clock and you compare timestamps from C<ev_time>
		2137	or C<ev_now> from when you started your timer and when your callback is
		2138	invoked, you will find that sometimes the callback is a bit "early".
		2139
		2140	This is because C<ev_timer>s work in real time, not wall clock time, so
		2141	libev makes sure your callback is not invoked before the delay happened,
		2142	I<measured according to the real time>, not the system clock.
		2143
		2144	If your timeouts are based on a physical timescale (e.g. "time out this
		2145	connection after 100 seconds") then this shouldn't bother you as it is
		2146	exactly the right behaviour.
		2147
		2148	If you want to compare wall clock/system timestamps to your timers, then
		2149	you need to use C<ev_periodic>s, as these are based on the wall clock
		2150	time, where your comparisons will always generate correct results.
		2151
		2152	=head3 The special problems of suspended animation
		2153
		2154	When you leave the server world it is quite customary to hit machines that
		2155	can suspend/hibernate - what happens to the clocks during such a suspend?
		2156
		2157	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		2158	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		2159	to run until the system is suspended, but they will not advance while the
		2160	system is suspended. That means, on resume, it will be as if the program
		2161	was frozen for a few seconds, but the suspend time will not be counted
		2162	towards C<ev_timer> when a monotonic clock source is used. The real time
		2163	clock advanced as expected, but if it is used as sole clocksource, then a
		2164	long suspend would be detected as a time jump by libev, and timers would
		2165	be adjusted accordingly.
		2166
		2167	I would not be surprised to see different behaviour in different between
		2168	operating systems, OS versions or even different hardware.
		2169
		2170	The other form of suspend (job control, or sending a SIGSTOP) will see a
		2171	time jump in the monotonic clocks and the realtime clock. If the program
		2172	is suspended for a very long time, and monotonic clock sources are in use,
		2173	then you can expect C<ev_timer>s to expire as the full suspension time
		2174	will be counted towards the timers. When no monotonic clock source is in
		2175	use, then libev will again assume a timejump and adjust accordingly.
		2176
		2177	It might be beneficial for this latter case to call C<ev_suspend>
		2178	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		2179	deterministic behaviour in this case (you can do nothing against
		2180	C<SIGSTOP>).
1172		2181
1173	=head3 Watcher-Specific Functions and Data Members	2182	=head3 Watcher-Specific Functions and Data Members
1174		2183
1175	=over 4	2184	=over 4
1176		2185
1177	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2186	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1178		2187
1179	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2188	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1180		2189
1181	Configure the timer to trigger after C<after> seconds. If C<repeat>	2190	Configure the timer to trigger after C<after> seconds (fractional and
1182	is C<0.>, then it will automatically be stopped once the timeout is	2191	negative values are supported). If C<repeat> is C<0.>, then it will
1183	reached. If it is positive, then the timer will automatically be	2192	automatically be stopped once the timeout is reached. If it is positive,
1184	configured to trigger again C<repeat> seconds later, again, and again,	2193	then the timer will automatically be configured to trigger again C<repeat>
1185	until stopped manually.	2194	seconds later, again, and again, until stopped manually.
1186		2195
1187	The timer itself will do a best-effort at avoiding drift, that is, if	2196	The timer itself will do a best-effort at avoiding drift, that is, if
1188	you configure a timer to trigger every 10 seconds, then it will normally	2197	you configure a timer to trigger every 10 seconds, then it will normally
1189	trigger at exactly 10 second intervals. If, however, your program cannot	2198	trigger at exactly 10 second intervals. If, however, your program cannot
1190	keep up with the timer (because it takes longer than those 10 seconds to	2199	keep up with the timer (because it takes longer than those 10 seconds to
1191	do stuff) the timer will not fire more than once per event loop iteration.	2200	do stuff) the timer will not fire more than once per event loop iteration.
1192		2201
1193	=item ev_timer_again (loop, ev_timer *)	2202	=item ev_timer_again (loop, ev_timer *)
1194		2203
1195	This will act as if the timer timed out and restart it again if it is	2204	This will act as if the timer timed out, and restarts it again if it is
1196	repeating. The exact semantics are:	2205	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2206	timeout to the C<repeat> value and calling C<ev_timer_start>.
1197		2207
		2208	The exact semantics are as in the following rules, all of which will be
		2209	applied to the watcher:
		2210
		2211	=over 4
		2212
1198	If the timer is pending, its pending status is cleared.	2213	=item If the timer is pending, the pending status is always cleared.
1199		2214
1200	If the timer is started but nonrepeating, stop it (as if it timed out).	2215	=item If the timer is started but non-repeating, stop it (as if it timed
		2216	out, without invoking it).
1201		2217
1202	If the timer is repeating, either start it if necessary (with the	2218	=item If the timer is repeating, make the C<repeat> value the new timeout
1203	C<repeat> value), or reset the running timer to the C<repeat> value.	2219	and start the timer, if necessary.
1204		2220
1205	This sounds a bit complicated, but here is a useful and typical	2221	=back
1206	example: Imagine you have a tcp connection and you want a so-called idle
1207	timeout, that is, you want to be called when there have been, say, 60
1208	seconds of inactivity on the socket. The easiest way to do this is to
1209	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1210	C<ev_timer_again> each time you successfully read or write some data. If
1211	you go into an idle state where you do not expect data to travel on the
1212	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1213	automatically restart it if need be.
1214		2222
1215	That means you can ignore the C<after> value and C<ev_timer_start>	2223	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
1216	altogether and only ever use the C<repeat> value and C<ev_timer_again>:	2224	usage example.
1217		2225
1218	ev_timer_init (timer, callback, 0., 5.);	2226	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1219	ev_timer_again (loop, timer);
1220	...
1221	timer->again = 17.;
1222	ev_timer_again (loop, timer);
1223	...
1224	timer->again = 10.;
1225	ev_timer_again (loop, timer);
1226		2227
1227	This is more slightly efficient then stopping/starting the timer each time	2228	Returns the remaining time until a timer fires. If the timer is active,
1228	you want to modify its timeout value.	2229	then this time is relative to the current event loop time, otherwise it's
		2230	the timeout value currently configured.
		2231
		2232	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
		2233	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		2234	will return C<4>. When the timer expires and is restarted, it will return
		2235	roughly C<7> (likely slightly less as callback invocation takes some time,
		2236	too), and so on.
1229		2237
1230	=item ev_tstamp repeat [read-write]	2238	=item ev_tstamp repeat [read-write]
1231		2239
1232	The current C<repeat> value. Will be used each time the watcher times out	2240	The current C<repeat> value. Will be used each time the watcher times out
1233	or C<ev_timer_again> is called and determines the next timeout (if any),	2241	or C<ev_timer_again> is called, and determines the next timeout (if any),
1234	which is also when any modifications are taken into account.	2242	which is also when any modifications are taken into account.
1235		2243
1236	=back	2244	=back
1237		2245
1238	=head3 Examples	2246	=head3 Examples
1239		2247
1240	Example: Create a timer that fires after 60 seconds.	2248	Example: Create a timer that fires after 60 seconds.
1241		2249
1242	static void	2250	static void
1243	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2251	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1244	{	2252	{
1245	.. one minute over, w is actually stopped right here	2253	.. one minute over, w is actually stopped right here
1246	}	2254	}
1247		2255
1248	struct ev_timer mytimer;	2256	ev_timer mytimer;
1249	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	2257	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1250	ev_timer_start (loop, &mytimer);	2258	ev_timer_start (loop, &mytimer);
1251		2259
1252	Example: Create a timeout timer that times out after 10 seconds of	2260	Example: Create a timeout timer that times out after 10 seconds of
1253	inactivity.	2261	inactivity.
1254		2262
1255	static void	2263	static void
1256	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2264	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1257	{	2265	{
1258	.. ten seconds without any activity	2266	.. ten seconds without any activity
1259	}	2267	}
1260		2268
1261	struct ev_timer mytimer;	2269	ev_timer mytimer;
1262	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	2270	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1263	ev_timer_again (&mytimer); /* start timer */	2271	ev_timer_again (&mytimer); /* start timer */
1264	ev_loop (loop, 0);	2272	ev_run (loop, 0);
1265		2273
1266	// and in some piece of code that gets executed on any "activity":	2274	// and in some piece of code that gets executed on any "activity":
1267	// reset the timeout to start ticking again at 10 seconds	2275	// reset the timeout to start ticking again at 10 seconds
1268	ev_timer_again (&mytimer);	2276	ev_timer_again (&mytimer);
1269		2277
1270		2278
1271	=head2 C<ev_periodic> - to cron or not to cron?	2279	=head2 C<ev_periodic> - to cron or not to cron?
1272		2280
1273	Periodic watchers are also timers of a kind, but they are very versatile	2281	Periodic watchers are also timers of a kind, but they are very versatile
1274	(and unfortunately a bit complex).	2282	(and unfortunately a bit complex).
1275		2283
1276	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2284	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1277	but on wallclock time (absolute time). You can tell a periodic watcher	2285	relative time, the physical time that passes) but on wall clock time
1278	to trigger after some specific point in time. For example, if you tell a	2286	(absolute time, the thing you can read on your calendar or clock). The
1279	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	2287	difference is that wall clock time can run faster or slower than real
1280	+ 10.>, that is, an absolute time not a delay) and then reset your system	2288	time, and time jumps are not uncommon (e.g. when you adjust your
1281	clock to january of the previous year, then it will take more than year	2289	wrist-watch).
1282	to trigger the event (unlike an C<ev_timer>, which would still trigger
1283	roughly 10 seconds later as it uses a relative timeout).
1284		2290
		2291	You can tell a periodic watcher to trigger after some specific point
		2292	in time: for example, if you tell a periodic watcher to trigger "in 10
		2293	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2294	not a delay) and then reset your system clock to January of the previous
		2295	year, then it will take a year or more to trigger the event (unlike an
		2296	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2297	it, as it uses a relative timeout).
		2298
1285	C<ev_periodic>s can also be used to implement vastly more complex timers,	2299	C<ev_periodic> watchers can also be used to implement vastly more complex
1286	such as triggering an event on each "midnight, local time", or other	2300	timers, such as triggering an event on each "midnight, local time", or
1287	complicated, rules.	2301	other complicated rules. This cannot easily be done with C<ev_timer>
		2302	watchers, as those cannot react to time jumps.
1288		2303
1289	As with timers, the callback is guarenteed to be invoked only when the	2304	As with timers, the callback is guaranteed to be invoked only when the
1290	time (C<at>) has passed, but if multiple periodic timers become ready	2305	point in time where it is supposed to trigger has passed. If multiple
1291	during the same loop iteration then order of execution is undefined.	2306	timers become ready during the same loop iteration then the ones with
		2307	earlier time-out values are invoked before ones with later time-out values
		2308	(but this is no longer true when a callback calls C<ev_run> recursively).
1292		2309
1293	=head3 Watcher-Specific Functions and Data Members	2310	=head3 Watcher-Specific Functions and Data Members
1294		2311
1295	=over 4	2312	=over 4
1296		2313
1297	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2314	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1298		2315
1299	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2316	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1300		2317
1301	Lots of arguments, lets sort it out... There are basically three modes of	2318	Lots of arguments, let's sort it out... There are basically three modes of
1302	operation, and we will explain them from simplest to complex:	2319	operation, and we will explain them from simplest to most complex:
1303		2320
1304	=over 4	2321	=over 4
1305		2322
1306	=item * absolute timer (at = time, interval = reschedule_cb = 0)	2323	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1307		2324
1308	In this configuration the watcher triggers an event after the wallclock	2325	In this configuration the watcher triggers an event after the wall clock
1309	time C<at> has passed and doesn't repeat. It will not adjust when a time	2326	time C<offset> has passed. It will not repeat and will not adjust when a
1310	jump occurs, that is, if it is to be run at January 1st 2011 then it will	2327	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1311	run when the system time reaches or surpasses this time.	2328	will be stopped and invoked when the system clock reaches or surpasses
		2329	this point in time.
1312		2330
1313	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	2331	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1314		2332
1315	In this mode the watcher will always be scheduled to time out at the next	2333	In this mode the watcher will always be scheduled to time out at the next
1316	C<at + N * interval> time (for some integer N, which can also be negative)	2334	C<offset + N * interval> time (for some integer N, which can also be
1317	and then repeat, regardless of any time jumps.	2335	negative) and then repeat, regardless of any time jumps. The C<offset>
		2336	argument is merely an offset into the C<interval> periods.
1318		2337
1319	This can be used to create timers that do not drift with respect to system	2338	This can be used to create timers that do not drift with respect to the
1320	time, for example, here is a C<ev_periodic> that triggers each hour, on	2339	system clock, for example, here is an C<ev_periodic> that triggers each
1321	the hour:	2340	hour, on the hour (with respect to UTC):
1322		2341
1323	ev_periodic_set (&periodic, 0., 3600., 0);	2342	ev_periodic_set (&periodic, 0., 3600., 0);
1324		2343
1325	This doesn't mean there will always be 3600 seconds in between triggers,	2344	This doesn't mean there will always be 3600 seconds in between triggers,
1326	but only that the the callback will be called when the system time shows a	2345	but only that the callback will be called when the system time shows a
1327	full hour (UTC), or more correctly, when the system time is evenly divisible	2346	full hour (UTC), or more correctly, when the system time is evenly divisible
1328	by 3600.	2347	by 3600.
1329		2348
1330	Another way to think about it (for the mathematically inclined) is that	2349	Another way to think about it (for the mathematically inclined) is that
1331	C<ev_periodic> will try to run the callback in this mode at the next possible	2350	C<ev_periodic> will try to run the callback in this mode at the next possible
1332	time where C<time = at (mod interval)>, regardless of any time jumps.	2351	time where C<time = offset (mod interval)>, regardless of any time jumps.
1333		2352
1334	For numerical stability it is preferable that the C<at> value is near	2353	The C<interval> I<MUST> be positive, and for numerical stability, the
1335	C<ev_now ()> (the current time), but there is no range requirement for	2354	interval value should be higher than C<1/8192> (which is around 100
1336	this value, and in fact is often specified as zero.	2355	microseconds) and C<offset> should be higher than C<0> and should have
		2356	at most a similar magnitude as the current time (say, within a factor of
		2357	ten). Typical values for offset are, in fact, C<0> or something between
		2358	C<0> and C<interval>, which is also the recommended range.
1337		2359
1338	Note also that there is an upper limit to how often a timer can fire (cpu	2360	Note also that there is an upper limit to how often a timer can fire (CPU
1339	speed for example), so if C<interval> is very small then timing stability	2361	speed for example), so if C<interval> is very small then timing stability
1340	will of course detoriate. Libev itself tries to be exact to be about one	2362	will of course deteriorate. Libev itself tries to be exact to be about one
1341	millisecond (if the OS supports it and the machine is fast enough).	2363	millisecond (if the OS supports it and the machine is fast enough).
1342		2364
1343	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	2365	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1344		2366
1345	In this mode the values for C<interval> and C<at> are both being	2367	In this mode the values for C<interval> and C<offset> are both being
1346	ignored. Instead, each time the periodic watcher gets scheduled, the	2368	ignored. Instead, each time the periodic watcher gets scheduled, the
1347	reschedule callback will be called with the watcher as first, and the	2369	reschedule callback will be called with the watcher as first, and the
1348	current time as second argument.	2370	current time as second argument.
1349		2371
1350	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2372	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1351	ever, or make ANY event loop modifications whatsoever>.	2373	or make ANY other event loop modifications whatsoever, unless explicitly
		2374	allowed by documentation here>.
1352		2375
1353	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop	2376	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
1354	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the	2377	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
1355	only event loop modification you are allowed to do).	2378	only event loop modification you are allowed to do).
1356		2379
1357	The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic	2380	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1358	*w, ev_tstamp now)>, e.g.:	2381	*w, ev_tstamp now)>, e.g.:
1359		2382
		2383	static ev_tstamp
1360	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2384	my_rescheduler (ev_periodic *w, ev_tstamp now)
1361	{	2385	{
1362	return now + 60.;	2386	return now + 60.;
1363	}	2387	}
1364		2388
1365	It must return the next time to trigger, based on the passed time value	2389	It must return the next time to trigger, based on the passed time value
…		…
1369		2393
1370	NOTE: I<< This callback must always return a time that is higher than or	2394	NOTE: I<< This callback must always return a time that is higher than or
1371	equal to the passed C<now> value >>.	2395	equal to the passed C<now> value >>.
1372		2396
1373	This can be used to create very complex timers, such as a timer that	2397	This can be used to create very complex timers, such as a timer that
1374	triggers on "next midnight, local time". To do this, you would calculate the	2398	triggers on "next midnight, local time". To do this, you would calculate
1375	next midnight after C<now> and return the timestamp value for this. How	2399	the next midnight after C<now> and return the timestamp value for
1376	you do this is, again, up to you (but it is not trivial, which is the main	2400	this. Here is a (completely untested, no error checking) example on how to
1377	reason I omitted it as an example).	2401	do this:
		2402
		2403	#include <time.h>
		2404
		2405	static ev_tstamp
		2406	my_rescheduler (ev_periodic *w, ev_tstamp now)
		2407	{
		2408	time_t tnow = (time_t)now;
		2409	struct tm tm;
		2410	localtime_r (&tnow, &tm);
		2411
		2412	tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
		2413	++tm.tm_mday; // midnight next day
		2414
		2415	return mktime (&tm);
		2416	}
		2417
		2418	Note: this code might run into trouble on days that have more then two
		2419	midnights (beginning and end).
1378		2420
1379	=back	2421	=back
1380		2422
1381	=item ev_periodic_again (loop, ev_periodic *)	2423	=item ev_periodic_again (loop, ev_periodic *)
1382		2424
…		…
1385	a different time than the last time it was called (e.g. in a crond like	2427	a different time than the last time it was called (e.g. in a crond like
1386	program when the crontabs have changed).	2428	program when the crontabs have changed).
1387		2429
1388	=item ev_tstamp ev_periodic_at (ev_periodic *)	2430	=item ev_tstamp ev_periodic_at (ev_periodic *)
1389		2431
1390	When active, returns the absolute time that the watcher is supposed to	2432	When active, returns the absolute time that the watcher is supposed
1391	trigger next.	2433	to trigger next. This is not the same as the C<offset> argument to
		2434	C<ev_periodic_set>, but indeed works even in interval and manual
		2435	rescheduling modes.
1392		2436
1393	=item ev_tstamp offset [read-write]	2437	=item ev_tstamp offset [read-write]
1394		2438
1395	When repeating, this contains the offset value, otherwise this is the	2439	When repeating, this contains the offset value, otherwise this is the
1396	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2440	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2441	although libev might modify this value for better numerical stability).
1397		2442
1398	Can be modified any time, but changes only take effect when the periodic	2443	Can be modified any time, but changes only take effect when the periodic
1399	timer fires or C<ev_periodic_again> is being called.	2444	timer fires or C<ev_periodic_again> is being called.
1400		2445
1401	=item ev_tstamp interval [read-write]	2446	=item ev_tstamp interval [read-write]
1402		2447
1403	The current interval value. Can be modified any time, but changes only	2448	The current interval value. Can be modified any time, but changes only
1404	take effect when the periodic timer fires or C<ev_periodic_again> is being	2449	take effect when the periodic timer fires or C<ev_periodic_again> is being
1405	called.	2450	called.
1406		2451
1407	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2452	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1408		2453
1409	The current reschedule callback, or C<0>, if this functionality is	2454	The current reschedule callback, or C<0>, if this functionality is
1410	switched off. Can be changed any time, but changes only take effect when	2455	switched off. Can be changed any time, but changes only take effect when
1411	the periodic timer fires or C<ev_periodic_again> is being called.	2456	the periodic timer fires or C<ev_periodic_again> is being called.
1412		2457
1413	=back	2458	=back
1414		2459
1415	=head3 Examples	2460	=head3 Examples
1416		2461
1417	Example: Call a callback every hour, or, more precisely, whenever the	2462	Example: Call a callback every hour, or, more precisely, whenever the
1418	system clock is divisible by 3600. The callback invocation times have	2463	system time is divisible by 3600. The callback invocation times have
1419	potentially a lot of jittering, but good long-term stability.	2464	potentially a lot of jitter, but good long-term stability.
1420		2465
1421	static void	2466	static void
1422	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2467	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1423	{	2468	{
1424	... its now a full hour (UTC, or TAI or whatever your clock follows)	2469	... its now a full hour (UTC, or TAI or whatever your clock follows)
1425	}	2470	}
1426		2471
1427	struct ev_periodic hourly_tick;	2472	ev_periodic hourly_tick;
1428	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2473	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1429	ev_periodic_start (loop, &hourly_tick);	2474	ev_periodic_start (loop, &hourly_tick);
1430		2475
1431	Example: The same as above, but use a reschedule callback to do it:	2476	Example: The same as above, but use a reschedule callback to do it:
1432		2477
1433	#include <math.h>	2478	#include <math.h>
1434		2479
1435	static ev_tstamp	2480	static ev_tstamp
1436	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2481	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1437	{	2482	{
1438	return fmod (now, 3600.) + 3600.;	2483	return now + (3600. - fmod (now, 3600.));
1439	}	2484	}
1440		2485
1441	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2486	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1442		2487
1443	Example: Call a callback every hour, starting now:	2488	Example: Call a callback every hour, starting now:
1444		2489
1445	struct ev_periodic hourly_tick;	2490	ev_periodic hourly_tick;
1446	ev_periodic_init (&hourly_tick, clock_cb,	2491	ev_periodic_init (&hourly_tick, clock_cb,
1447	fmod (ev_now (loop), 3600.), 3600., 0);	2492	fmod (ev_now (loop), 3600.), 3600., 0);
1448	ev_periodic_start (loop, &hourly_tick);	2493	ev_periodic_start (loop, &hourly_tick);
1449		2494
1450		2495
1451	=head2 C<ev_signal> - signal me when a signal gets signalled!	2496	=head2 C<ev_signal> - signal me when a signal gets signalled!
1452		2497
1453	Signal watchers will trigger an event when the process receives a specific	2498	Signal watchers will trigger an event when the process receives a specific
1454	signal one or more times. Even though signals are very asynchronous, libev	2499	signal one or more times. Even though signals are very asynchronous, libev
1455	will try it's best to deliver signals synchronously, i.e. as part of the	2500	will try its best to deliver signals synchronously, i.e. as part of the
1456	normal event processing, like any other event.	2501	normal event processing, like any other event.
1457		2502
		2503	If you want signals to be delivered truly asynchronously, just use
		2504	C<sigaction> as you would do without libev and forget about sharing
		2505	the signal. You can even use C<ev_async> from a signal handler to
		2506	synchronously wake up an event loop.
		2507
1458	You can configure as many watchers as you like per signal. Only when the	2508	You can configure as many watchers as you like for the same signal, but
1459	first watcher gets started will libev actually register a signal watcher	2509	only within the same loop, i.e. you can watch for C<SIGINT> in your
1460	with the kernel (thus it coexists with your own signal handlers as long	2510	default loop and for C<SIGIO> in another loop, but you cannot watch for
1461	as you don't register any with libev). Similarly, when the last signal	2511	C<SIGINT> in both the default loop and another loop at the same time. At
1462	watcher for a signal is stopped libev will reset the signal handler to	2512	the moment, C<SIGCHLD> is permanently tied to the default loop.
1463	SIG_DFL (regardless of what it was set to before).	2513
		2514	Only after the first watcher for a signal is started will libev actually
		2515	register something with the kernel. It thus coexists with your own signal
		2516	handlers as long as you don't register any with libev for the same signal.
1464		2517
1465	If possible and supported, libev will install its handlers with	2518	If possible and supported, libev will install its handlers with
1466	C<SA_RESTART> behaviour enabled, so syscalls should not be unduly	2519	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
1467	interrupted. If you have a problem with syscalls getting interrupted by	2520	not be unduly interrupted. If you have a problem with system calls getting
1468	signals you can block all signals in an C<ev_check> watcher and unblock	2521	interrupted by signals you can block all signals in an C<ev_check> watcher
1469	them in an C<ev_prepare> watcher.	2522	and unblock them in an C<ev_prepare> watcher.
		2523
		2524	=head3 The special problem of inheritance over fork/execve/pthread_create
		2525
		2526	Both the signal mask (C<sigprocmask>) and the signal disposition
		2527	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2528	stopping it again), that is, libev might or might not block the signal,
		2529	and might or might not set or restore the installed signal handler (but
		2530	see C<EVFLAG_NOSIGMASK>).
		2531
		2532	While this does not matter for the signal disposition (libev never
		2533	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2534	C<execve>), this matters for the signal mask: many programs do not expect
		2535	certain signals to be blocked.
		2536
		2537	This means that before calling C<exec> (from the child) you should reset
		2538	the signal mask to whatever "default" you expect (all clear is a good
		2539	choice usually).
		2540
		2541	The simplest way to ensure that the signal mask is reset in the child is
		2542	to install a fork handler with C<pthread_atfork> that resets it. That will
		2543	catch fork calls done by libraries (such as the libc) as well.
		2544
		2545	In current versions of libev, the signal will not be blocked indefinitely
		2546	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2547	the window of opportunity for problems, it will not go away, as libev
		2548	I<has> to modify the signal mask, at least temporarily.
		2549
		2550	So I can't stress this enough: I<If you do not reset your signal mask when
		2551	you expect it to be empty, you have a race condition in your code>. This
		2552	is not a libev-specific thing, this is true for most event libraries.
		2553
		2554	=head3 The special problem of threads signal handling
		2555
		2556	POSIX threads has problematic signal handling semantics, specifically,
		2557	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2558	threads in a process block signals, which is hard to achieve.
		2559
		2560	When you want to use sigwait (or mix libev signal handling with your own
		2561	for the same signals), you can tackle this problem by globally blocking
		2562	all signals before creating any threads (or creating them with a fully set
		2563	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2564	loops. Then designate one thread as "signal receiver thread" which handles
		2565	these signals. You can pass on any signals that libev might be interested
		2566	in by calling C<ev_feed_signal>.
1470		2567
1471	=head3 Watcher-Specific Functions and Data Members	2568	=head3 Watcher-Specific Functions and Data Members
1472		2569
1473	=over 4	2570	=over 4
1474		2571
…		…
1485		2582
1486	=back	2583	=back
1487		2584
1488	=head3 Examples	2585	=head3 Examples
1489		2586
1490	Example: Try to exit cleanly on SIGINT and SIGTERM.	2587	Example: Try to exit cleanly on SIGINT.
1491		2588
1492	static void	2589	static void
1493	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2590	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
1494	{	2591	{
1495	ev_unloop (loop, EVUNLOOP_ALL);	2592	ev_break (loop, EVBREAK_ALL);
1496	}	2593	}
1497		2594
1498	struct ev_signal signal_watcher;	2595	ev_signal signal_watcher;
1499	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2596	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1500	ev_signal_start (loop, &sigint_cb);	2597	ev_signal_start (loop, &signal_watcher);
1501		2598
1502		2599
1503	=head2 C<ev_child> - watch out for process status changes	2600	=head2 C<ev_child> - watch out for process status changes
1504		2601
1505	Child watchers trigger when your process receives a SIGCHLD in response to	2602	Child watchers trigger when your process receives a SIGCHLD in response to
1506	some child status changes (most typically when a child of yours dies). It	2603	some child status changes (most typically when a child of yours dies or
1507	is permissible to install a child watcher I<after> the child has been	2604	exits). It is permissible to install a child watcher I<after> the child
1508	forked (which implies it might have already exited), as long as the event	2605	has been forked (which implies it might have already exited), as long
1509	loop isn't entered (or is continued from a watcher).	2606	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2607	forking and then immediately registering a watcher for the child is fine,
		2608	but forking and registering a watcher a few event loop iterations later or
		2609	in the next callback invocation is not.
1510		2610
1511	Only the default event loop is capable of handling signals, and therefore	2611	Only the default event loop is capable of handling signals, and therefore
1512	you can only rgeister child watchers in the default event loop.	2612	you can only register child watchers in the default event loop.
		2613
		2614	Due to some design glitches inside libev, child watchers will always be
		2615	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2616	libev)
1513		2617
1514	=head3 Process Interaction	2618	=head3 Process Interaction
1515		2619
1516	Libev grabs C<SIGCHLD> as soon as the default event loop is	2620	Libev grabs C<SIGCHLD> as soon as the default event loop is
1517	initialised. This is necessary to guarantee proper behaviour even if	2621	initialised. This is necessary to guarantee proper behaviour even if the
1518	the first child watcher is started after the child exits. The occurance	2622	first child watcher is started after the child exits. The occurrence
1519	of C<SIGCHLD> is recorded asynchronously, but child reaping is done	2623	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
1520	synchronously as part of the event loop processing. Libev always reaps all	2624	synchronously as part of the event loop processing. Libev always reaps all
1521	children, even ones not watched.	2625	children, even ones not watched.
1522		2626
1523	=head3 Overriding the Built-In Processing	2627	=head3 Overriding the Built-In Processing
…		…
1527	handler, you can override it easily by installing your own handler for	2631	handler, you can override it easily by installing your own handler for
1528	C<SIGCHLD> after initialising the default loop, and making sure the	2632	C<SIGCHLD> after initialising the default loop, and making sure the
1529	default loop never gets destroyed. You are encouraged, however, to use an	2633	default loop never gets destroyed. You are encouraged, however, to use an
1530	event-based approach to child reaping and thus use libev's support for	2634	event-based approach to child reaping and thus use libev's support for
1531	that, so other libev users can use C<ev_child> watchers freely.	2635	that, so other libev users can use C<ev_child> watchers freely.
		2636
		2637	=head3 Stopping the Child Watcher
		2638
		2639	Currently, the child watcher never gets stopped, even when the
		2640	child terminates, so normally one needs to stop the watcher in the
		2641	callback. Future versions of libev might stop the watcher automatically
		2642	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2643	problem).
1532		2644
1533	=head3 Watcher-Specific Functions and Data Members	2645	=head3 Watcher-Specific Functions and Data Members
1534		2646
1535	=over 4	2647	=over 4
1536		2648
…		…
1565	=head3 Examples	2677	=head3 Examples
1566		2678
1567	Example: C<fork()> a new process and install a child handler to wait for	2679	Example: C<fork()> a new process and install a child handler to wait for
1568	its completion.	2680	its completion.
1569		2681
1570	ev_child cw;	2682	ev_child cw;
1571		2683
1572	static void	2684	static void
1573	child_cb (EV_P_ struct ev_child *w, int revents)	2685	child_cb (EV_P_ ev_child *w, int revents)
1574	{	2686	{
1575	ev_child_stop (EV_A_ w);	2687	ev_child_stop (EV_A_ w);
1576	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);	2688	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1577	}	2689	}
1578		2690
1579	pid_t pid = fork ();	2691	pid_t pid = fork ();
1580		2692
1581	if (pid < 0)	2693	if (pid < 0)
1582	// error	2694	// error
1583	else if (pid == 0)	2695	else if (pid == 0)
1584	{	2696	{
1585	// the forked child executes here	2697	// the forked child executes here
1586	exit (1);	2698	exit (1);
1587	}	2699	}
1588	else	2700	else
1589	{	2701	{
1590	ev_child_init (&cw, child_cb, pid, 0);	2702	ev_child_init (&cw, child_cb, pid, 0);
1591	ev_child_start (EV_DEFAULT_ &cw);	2703	ev_child_start (EV_DEFAULT_ &cw);
1592	}	2704	}
1593		2705
1594		2706
1595	=head2 C<ev_stat> - did the file attributes just change?	2707	=head2 C<ev_stat> - did the file attributes just change?
1596		2708
1597	This watches a filesystem path for attribute changes. That is, it calls	2709	This watches a file system path for attribute changes. That is, it calls
1598	C<stat> regularly (or when the OS says it changed) and sees if it changed	2710	C<stat> on that path in regular intervals (or when the OS says it changed)
1599	compared to the last time, invoking the callback if it did.	2711	and sees if it changed compared to the last time, invoking the callback
		2712	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2713	happen after the watcher has been started will be reported.
1600		2714
1601	The path does not need to exist: changing from "path exists" to "path does	2715	The path does not need to exist: changing from "path exists" to "path does
1602	not exist" is a status change like any other. The condition "path does	2716	not exist" is a status change like any other. The condition "path does not
1603	not exist" is signified by the C<st_nlink> field being zero (which is	2717	exist" (or more correctly "path cannot be stat'ed") is signified by the
1604	otherwise always forced to be at least one) and all the other fields of	2718	C<st_nlink> field being zero (which is otherwise always forced to be at
1605	the stat buffer having unspecified contents.	2719	least one) and all the other fields of the stat buffer having unspecified
		2720	contents.
1606		2721
1607	The path I<should> be absolute and I<must not> end in a slash. If it is	2722	The path I<must not> end in a slash or contain special components such as
		2723	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1608	relative and your working directory changes, the behaviour is undefined.	2724	your working directory changes, then the behaviour is undefined.
1609		2725
1610	Since there is no standard to do this, the portable implementation simply	2726	Since there is no portable change notification interface available, the
1611	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2727	portable implementation simply calls C<stat(2)> regularly on the path
1612	can specify a recommended polling interval for this case. If you specify	2728	to see if it changed somehow. You can specify a recommended polling
1613	a polling interval of C<0> (highly recommended!) then a I<suitable,	2729	interval for this case. If you specify a polling interval of C<0> (highly
1614	unspecified default> value will be used (which you can expect to be around	2730	recommended!) then a I<suitable, unspecified default> value will be used
1615	five seconds, although this might change dynamically). Libev will also	2731	(which you can expect to be around five seconds, although this might
1616	impose a minimum interval which is currently around C<0.1>, but thats	2732	change dynamically). Libev will also impose a minimum interval which is
1617	usually overkill.	2733	currently around C<0.1>, but that's usually overkill.
1618		2734
1619	This watcher type is not meant for massive numbers of stat watchers,	2735	This watcher type is not meant for massive numbers of stat watchers,
1620	as even with OS-supported change notifications, this can be	2736	as even with OS-supported change notifications, this can be
1621	resource-intensive.	2737	resource-intensive.
1622		2738
1623	At the time of this writing, only the Linux inotify interface is	2739	At the time of this writing, the only OS-specific interface implemented
1624	implemented (implementing kqueue support is left as an exercise for the	2740	is the Linux inotify interface (implementing kqueue support is left as an
1625	reader, note, however, that the author sees no way of implementing ev_stat	2741	exercise for the reader. Note, however, that the author sees no way of
1626	semantics with kqueue). Inotify will be used to give hints only and should	2742	implementing C<ev_stat> semantics with kqueue, except as a hint).
1627	not change the semantics of C<ev_stat> watchers, which means that libev
1628	sometimes needs to fall back to regular polling again even with inotify,
1629	but changes are usually detected immediately, and if the file exists there
1630	will be no polling.
1631		2743
1632	=head3 ABI Issues (Largefile Support)	2744	=head3 ABI Issues (Largefile Support)
1633		2745
1634	Libev by default (unless the user overrides this) uses the default	2746	Libev by default (unless the user overrides this) uses the default
1635	compilation environment, which means that on systems with optionally	2747	compilation environment, which means that on systems with large file
1636	disabled large file support, you get the 32 bit version of the stat	2748	support disabled by default, you get the 32 bit version of the stat
1637	structure. When using the library from programs that change the ABI to	2749	structure. When using the library from programs that change the ABI to
1638	use 64 bit file offsets the programs will fail. In that case you have to	2750	use 64 bit file offsets the programs will fail. In that case you have to
1639	compile libev with the same flags to get binary compatibility. This is	2751	compile libev with the same flags to get binary compatibility. This is
1640	obviously the case with any flags that change the ABI, but the problem is	2752	obviously the case with any flags that change the ABI, but the problem is
1641	most noticably with ev_stat and largefile support.	2753	most noticeably displayed with ev_stat and large file support.
1642		2754
1643	=head3 Inotify	2755	The solution for this is to lobby your distribution maker to make large
		2756	file interfaces available by default (as e.g. FreeBSD does) and not
		2757	optional. Libev cannot simply switch on large file support because it has
		2758	to exchange stat structures with application programs compiled using the
		2759	default compilation environment.
1644		2760
		2761	=head3 Inotify and Kqueue
		2762
1645	When C<inotify (7)> support has been compiled into libev (generally only	2763	When C<inotify (7)> support has been compiled into libev and present at
1646	available on Linux) and present at runtime, it will be used to speed up	2764	runtime, it will be used to speed up change detection where possible. The
1647	change detection where possible. The inotify descriptor will be created lazily	2765	inotify descriptor will be created lazily when the first C<ev_stat>
1648	when the first C<ev_stat> watcher is being started.	2766	watcher is being started.
1649		2767
1650	Inotify presence does not change the semantics of C<ev_stat> watchers	2768	Inotify presence does not change the semantics of C<ev_stat> watchers
1651	except that changes might be detected earlier, and in some cases, to avoid	2769	except that changes might be detected earlier, and in some cases, to avoid
1652	making regular C<stat> calls. Even in the presence of inotify support	2770	making regular C<stat> calls. Even in the presence of inotify support
1653	there are many cases where libev has to resort to regular C<stat> polling.	2771	there are many cases where libev has to resort to regular C<stat> polling,
		2772	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2773	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2774	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2775	xfs are fully working) libev usually gets away without polling.
1654		2776
1655	(There is no support for kqueue, as apparently it cannot be used to	2777	There is no support for kqueue, as apparently it cannot be used to
1656	implement this functionality, due to the requirement of having a file	2778	implement this functionality, due to the requirement of having a file
1657	descriptor open on the object at all times).	2779	descriptor open on the object at all times, and detecting renames, unlinks
		2780	etc. is difficult.
		2781
		2782	=head3 C<stat ()> is a synchronous operation
		2783
		2784	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2785	the process. The exception are C<ev_stat> watchers - those call C<stat
		2786	()>, which is a synchronous operation.
		2787
		2788	For local paths, this usually doesn't matter: unless the system is very
		2789	busy or the intervals between stat's are large, a stat call will be fast,
		2790	as the path data is usually in memory already (except when starting the
		2791	watcher).
		2792
		2793	For networked file systems, calling C<stat ()> can block an indefinite
		2794	time due to network issues, and even under good conditions, a stat call
		2795	often takes multiple milliseconds.
		2796
		2797	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2798	paths, although this is fully supported by libev.
1658		2799
1659	=head3 The special problem of stat time resolution	2800	=head3 The special problem of stat time resolution
1660		2801
1661	The C<stat ()> syscall only supports full-second resolution portably, and	2802	The C<stat ()> system call only supports full-second resolution portably,
1662	even on systems where the resolution is higher, many filesystems still	2803	and even on systems where the resolution is higher, most file systems
1663	only support whole seconds.	2804	still only support whole seconds.
1664		2805
1665	That means that, if the time is the only thing that changes, you can	2806	That means that, if the time is the only thing that changes, you can
1666	easily miss updates: on the first update, C<ev_stat> detects a change and	2807	easily miss updates: on the first update, C<ev_stat> detects a change and
1667	calls your callback, which does something. When there is another update	2808	calls your callback, which does something. When there is another update
1668	within the same second, C<ev_stat> will be unable to detect it as the stat	2809	within the same second, C<ev_stat> will be unable to detect unless the
1669	data does not change.	2810	stat data does change in other ways (e.g. file size).
1670		2811
1671	The solution to this is to delay acting on a change for slightly more	2812	The solution to this is to delay acting on a change for slightly more
1672	than a second (or till slightly after the next full second boundary), using	2813	than a second (or till slightly after the next full second boundary), using
1673	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);	2814	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
1674	ev_timer_again (loop, w)>).	2815	ev_timer_again (loop, w)>).
…		…
1694	C<path>. The C<interval> is a hint on how quickly a change is expected to	2835	C<path>. The C<interval> is a hint on how quickly a change is expected to
1695	be detected and should normally be specified as C<0> to let libev choose	2836	be detected and should normally be specified as C<0> to let libev choose
1696	a suitable value. The memory pointed to by C<path> must point to the same	2837	a suitable value. The memory pointed to by C<path> must point to the same
1697	path for as long as the watcher is active.	2838	path for as long as the watcher is active.
1698		2839
1699	The callback will receive C<EV_STAT> when a change was detected, relative	2840	The callback will receive an C<EV_STAT> event when a change was detected,
1700	to the attributes at the time the watcher was started (or the last change	2841	relative to the attributes at the time the watcher was started (or the
1701	was detected).	2842	last change was detected).
1702		2843
1703	=item ev_stat_stat (loop, ev_stat *)	2844	=item ev_stat_stat (loop, ev_stat *)
1704		2845
1705	Updates the stat buffer immediately with new values. If you change the	2846	Updates the stat buffer immediately with new values. If you change the
1706	watched path in your callback, you could call this function to avoid	2847	watched path in your callback, you could call this function to avoid
…		…
1727		2868
1728	The specified interval.	2869	The specified interval.
1729		2870
1730	=item const char *path [read-only]	2871	=item const char *path [read-only]
1731		2872
1732	The filesystem path that is being watched.	2873	The file system path that is being watched.
1733		2874
1734	=back	2875	=back
1735		2876
1736	=head3 Examples	2877	=head3 Examples
1737		2878
1738	Example: Watch C</etc/passwd> for attribute changes.	2879	Example: Watch C</etc/passwd> for attribute changes.
1739		2880
1740	static void	2881	static void
1741	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2882	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1742	{	2883	{
1743	/* /etc/passwd changed in some way */	2884	/* /etc/passwd changed in some way */
1744	if (w->attr.st_nlink)	2885	if (w->attr.st_nlink)
1745	{	2886	{
1746	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2887	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1747	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2888	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1748	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2889	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1749	}	2890	}
1750	else	2891	else
1751	/* you shalt not abuse printf for puts */	2892	/* you shalt not abuse printf for puts */
1752	puts ("wow, /etc/passwd is not there, expect problems. "	2893	puts ("wow, /etc/passwd is not there, expect problems. "
1753	"if this is windows, they already arrived\n");	2894	"if this is windows, they already arrived\n");
1754	}	2895	}
1755		2896
1756	...	2897	...
1757	ev_stat passwd;	2898	ev_stat passwd;
1758		2899
1759	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);	2900	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1760	ev_stat_start (loop, &passwd);	2901	ev_stat_start (loop, &passwd);
1761		2902
1762	Example: Like above, but additionally use a one-second delay so we do not	2903	Example: Like above, but additionally use a one-second delay so we do not
1763	miss updates (however, frequent updates will delay processing, too, so	2904	miss updates (however, frequent updates will delay processing, too, so
1764	one might do the work both on C<ev_stat> callback invocation I<and> on	2905	one might do the work both on C<ev_stat> callback invocation I<and> on
1765	C<ev_timer> callback invocation).	2906	C<ev_timer> callback invocation).
1766		2907
1767	static ev_stat passwd;	2908	static ev_stat passwd;
1768	static ev_timer timer;	2909	static ev_timer timer;
1769		2910
1770	static void	2911	static void
1771	timer_cb (EV_P_ ev_timer *w, int revents)	2912	timer_cb (EV_P_ ev_timer *w, int revents)
1772	{	2913	{
1773	ev_timer_stop (EV_A_ w);	2914	ev_timer_stop (EV_A_ w);
1774		2915
1775	/* now it's one second after the most recent passwd change */	2916	/* now it's one second after the most recent passwd change */
1776	}	2917	}
1777		2918
1778	static void	2919	static void
1779	stat_cb (EV_P_ ev_stat *w, int revents)	2920	stat_cb (EV_P_ ev_stat *w, int revents)
1780	{	2921	{
1781	/* reset the one-second timer */	2922	/* reset the one-second timer */
1782	ev_timer_again (EV_A_ &timer);	2923	ev_timer_again (EV_A_ &timer);
1783	}	2924	}
1784		2925
1785	...	2926	...
1786	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);	2927	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1787	ev_stat_start (loop, &passwd);	2928	ev_stat_start (loop, &passwd);
1788	ev_timer_init (&timer, timer_cb, 0., 1.02);	2929	ev_timer_init (&timer, timer_cb, 0., 1.02);
1789		2930
1790		2931
1791	=head2 C<ev_idle> - when you've got nothing better to do...	2932	=head2 C<ev_idle> - when you've got nothing better to do...
1792		2933
1793	Idle watchers trigger events when no other events of the same or higher	2934	Idle watchers trigger events when no other events of the same or higher
1794	priority are pending (prepare, check and other idle watchers do not	2935	priority are pending (prepare, check and other idle watchers do not count
1795	count).	2936	as receiving "events").
1796		2937
1797	That is, as long as your process is busy handling sockets or timeouts	2938	That is, as long as your process is busy handling sockets or timeouts
1798	(or even signals, imagine) of the same or higher priority it will not be	2939	(or even signals, imagine) of the same or higher priority it will not be
1799	triggered. But when your process is idle (or only lower-priority watchers	2940	triggered. But when your process is idle (or only lower-priority watchers
1800	are pending), the idle watchers are being called once per event loop	2941	are pending), the idle watchers are being called once per event loop
…		…
1807	Apart from keeping your process non-blocking (which is a useful	2948	Apart from keeping your process non-blocking (which is a useful
1808	effect on its own sometimes), idle watchers are a good place to do	2949	effect on its own sometimes), idle watchers are a good place to do
1809	"pseudo-background processing", or delay processing stuff to after the	2950	"pseudo-background processing", or delay processing stuff to after the
1810	event loop has handled all outstanding events.	2951	event loop has handled all outstanding events.
1811		2952
		2953	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2954
		2955	As long as there is at least one active idle watcher, libev will never
		2956	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2957	For this to work, the idle watcher doesn't need to be invoked at all - the
		2958	lowest priority will do.
		2959
		2960	This mode of operation can be useful together with an C<ev_check> watcher,
		2961	to do something on each event loop iteration - for example to balance load
		2962	between different connections.
		2963
		2964	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2965	example.
		2966
1812	=head3 Watcher-Specific Functions and Data Members	2967	=head3 Watcher-Specific Functions and Data Members
1813		2968
1814	=over 4	2969	=over 4
1815		2970
1816	=item ev_idle_init (ev_signal *, callback)	2971	=item ev_idle_init (ev_idle *, callback)
1817		2972
1818	Initialises and configures the idle watcher - it has no parameters of any	2973	Initialises and configures the idle watcher - it has no parameters of any
1819	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2974	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1820	believe me.	2975	believe me.
1821		2976
…		…
1824	=head3 Examples	2979	=head3 Examples
1825		2980
1826	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2981	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1827	callback, free it. Also, use no error checking, as usual.	2982	callback, free it. Also, use no error checking, as usual.
1828		2983
1829	static void	2984	static void
1830	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2985	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1831	{	2986	{
		2987	// stop the watcher
		2988	ev_idle_stop (loop, w);
		2989
		2990	// now we can free it
1832	free (w);	2991	free (w);
		2992
1833	// now do something you wanted to do when the program has	2993	// now do something you wanted to do when the program has
1834	// no longer anything immediate to do.	2994	// no longer anything immediate to do.
1835	}	2995	}
1836		2996
1837	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2997	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1838	ev_idle_init (idle_watcher, idle_cb);	2998	ev_idle_init (idle_watcher, idle_cb);
1839	ev_idle_start (loop, idle_cb);	2999	ev_idle_start (loop, idle_watcher);
1840		3000
1841		3001
1842	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	3002	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1843		3003
1844	Prepare and check watchers are usually (but not always) used in tandem:	3004	Prepare and check watchers are often (but not always) used in pairs:
1845	prepare watchers get invoked before the process blocks and check watchers	3005	prepare watchers get invoked before the process blocks and check watchers
1846	afterwards.	3006	afterwards.
1847		3007
1848	You I<must not> call C<ev_loop> or similar functions that enter	3008	You I<must not> call C<ev_run> (or similar functions that enter the
1849	the current event loop from either C<ev_prepare> or C<ev_check>	3009	current event loop) or C<ev_loop_fork> from either C<ev_prepare> or
1850	watchers. Other loops than the current one are fine, however. The	3010	C<ev_check> watchers. Other loops than the current one are fine,
1851	rationale behind this is that you do not need to check for recursion in	3011	however. The rationale behind this is that you do not need to check
1852	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	3012	for recursion in those watchers, i.e. the sequence will always be
1853	C<ev_check> so if you have one watcher of each kind they will always be	3013	C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
1854	called in pairs bracketing the blocking call.	3014	kind they will always be called in pairs bracketing the blocking call.
1855		3015
1856	Their main purpose is to integrate other event mechanisms into libev and	3016	Their main purpose is to integrate other event mechanisms into libev and
1857	their use is somewhat advanced. This could be used, for example, to track	3017	their use is somewhat advanced. They could be used, for example, to track
1858	variable changes, implement your own watchers, integrate net-snmp or a	3018	variable changes, implement your own watchers, integrate net-snmp or a
1859	coroutine library and lots more. They are also occasionally useful if	3019	coroutine library and lots more. They are also occasionally useful if
1860	you cache some data and want to flush it before blocking (for example,	3020	you cache some data and want to flush it before blocking (for example,
1861	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	3021	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1862	watcher).	3022	watcher).
1863		3023
1864	This is done by examining in each prepare call which file descriptors need	3024	This is done by examining in each prepare call which file descriptors
1865	to be watched by the other library, registering C<ev_io> watchers for	3025	need to be watched by the other library, registering C<ev_io> watchers
1866	them and starting an C<ev_timer> watcher for any timeouts (many libraries	3026	for them and starting an C<ev_timer> watcher for any timeouts (many
1867	provide just this functionality). Then, in the check watcher you check for	3027	libraries provide exactly this functionality). Then, in the check watcher,
1868	any events that occured (by checking the pending status of all watchers	3028	you check for any events that occurred (by checking the pending status
1869	and stopping them) and call back into the library. The I/O and timer	3029	of all watchers and stopping them) and call back into the library. The
1870	callbacks will never actually be called (but must be valid nevertheless,	3030	I/O and timer callbacks will never actually be called (but must be valid
1871	because you never know, you know?).	3031	nevertheless, because you never know, you know?).
1872		3032
1873	As another example, the Perl Coro module uses these hooks to integrate	3033	As another example, the Perl Coro module uses these hooks to integrate
1874	coroutines into libev programs, by yielding to other active coroutines	3034	coroutines into libev programs, by yielding to other active coroutines
1875	during each prepare and only letting the process block if no coroutines	3035	during each prepare and only letting the process block if no coroutines
1876	are ready to run (it's actually more complicated: it only runs coroutines	3036	are ready to run (it's actually more complicated: it only runs coroutines
1877	with priority higher than or equal to the event loop and one coroutine	3037	with priority higher than or equal to the event loop and one coroutine
1878	of lower priority, but only once, using idle watchers to keep the event	3038	of lower priority, but only once, using idle watchers to keep the event
1879	loop from blocking if lower-priority coroutines are active, thus mapping	3039	loop from blocking if lower-priority coroutines are active, thus mapping
1880	low-priority coroutines to idle/background tasks).	3040	low-priority coroutines to idle/background tasks).
1881		3041
1882	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	3042	When used for this purpose, it is recommended to give C<ev_check> watchers
1883	priority, to ensure that they are being run before any other watchers	3043	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
		3044	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		3045	watchers).
		3046
1884	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	3047	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1885	too) should not activate ("feed") events into libev. While libev fully	3048	activate ("feed") events into libev. While libev fully supports this, they
1886	supports this, they might get executed before other C<ev_check> watchers	3049	might get executed before other C<ev_check> watchers did their job. As
1887	did their job. As C<ev_check> watchers are often used to embed other	3050	C<ev_check> watchers are often used to embed other (non-libev) event
1888	(non-libev) event loops those other event loops might be in an unusable	3051	loops those other event loops might be in an unusable state until their
1889	state until their C<ev_check> watcher ran (always remind yourself to	3052	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1890	coexist peacefully with others).	3053	others).
		3054
		3055	=head3 Abusing an C<ev_check> watcher for its side-effect
		3056
		3057	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		3058	useful because they are called once per event loop iteration. For
		3059	example, if you want to handle a large number of connections fairly, you
		3060	normally only do a bit of work for each active connection, and if there
		3061	is more work to do, you wait for the next event loop iteration, so other
		3062	connections have a chance of making progress.
		3063
		3064	Using an C<ev_check> watcher is almost enough: it will be called on the
		3065	next event loop iteration. However, that isn't as soon as possible -
		3066	without external events, your C<ev_check> watcher will not be invoked.
		3067
		3068	This is where C<ev_idle> watchers come in handy - all you need is a
		3069	single global idle watcher that is active as long as you have one active
		3070	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		3071	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		3072	invoked. Neither watcher alone can do that.
1891		3073
1892	=head3 Watcher-Specific Functions and Data Members	3074	=head3 Watcher-Specific Functions and Data Members
1893		3075
1894	=over 4	3076	=over 4
1895		3077
…		…
1897		3079
1898	=item ev_check_init (ev_check *, callback)	3080	=item ev_check_init (ev_check *, callback)
1899		3081
1900	Initialises and configures the prepare or check watcher - they have no	3082	Initialises and configures the prepare or check watcher - they have no
1901	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	3083	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1902	macros, but using them is utterly, utterly and completely pointless.	3084	macros, but using them is utterly, utterly, utterly and completely
		3085	pointless.
1903		3086
1904	=back	3087	=back
1905		3088
1906	=head3 Examples	3089	=head3 Examples
1907		3090
…		…
1916	and in a check watcher, destroy them and call into libadns. What follows	3099	and in a check watcher, destroy them and call into libadns. What follows
1917	is pseudo-code only of course. This requires you to either use a low	3100	is pseudo-code only of course. This requires you to either use a low
1918	priority for the check watcher or use C<ev_clear_pending> explicitly, as	3101	priority for the check watcher or use C<ev_clear_pending> explicitly, as
1919	the callbacks for the IO/timeout watchers might not have been called yet.	3102	the callbacks for the IO/timeout watchers might not have been called yet.
1920		3103
1921	static ev_io iow [nfd];	3104	static ev_io iow [nfd];
1922	static ev_timer tw;	3105	static ev_timer tw;
1923		3106
1924	static void	3107	static void
1925	io_cb (ev_loop *loop, ev_io *w, int revents)	3108	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1926	{	3109	{
1927	}	3110	}
1928		3111
1929	// create io watchers for each fd and a timer before blocking	3112	// create io watchers for each fd and a timer before blocking
1930	static void	3113	static void
1931	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	3114	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1932	{	3115	{
1933	int timeout = 3600000;	3116	int timeout = 3600000;
1934	struct pollfd fds [nfd];	3117	struct pollfd fds [nfd];
1935	// actual code will need to loop here and realloc etc.	3118	// actual code will need to loop here and realloc etc.
1936	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	3119	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1937		3120
1938	/* the callback is illegal, but won't be called as we stop during check */	3121	/* the callback is illegal, but won't be called as we stop during check */
1939	ev_timer_init (&tw, 0, timeout * 1e-3);	3122	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1940	ev_timer_start (loop, &tw);	3123	ev_timer_start (loop, &tw);
1941		3124
1942	// create one ev_io per pollfd	3125	// create one ev_io per pollfd
1943	for (int i = 0; i < nfd; ++i)	3126	for (int i = 0; i < nfd; ++i)
1944	{	3127	{
1945	ev_io_init (iow + i, io_cb, fds [i].fd,	3128	ev_io_init (iow + i, io_cb, fds [i].fd,
1946	((fds [i].events & POLLIN ? EV_READ : 0)	3129	((fds [i].events & POLLIN ? EV_READ : 0)
1947	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	3130	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1948		3131
1949	fds [i].revents = 0;	3132	fds [i].revents = 0;
1950	ev_io_start (loop, iow + i);	3133	ev_io_start (loop, iow + i);
1951	}	3134	}
1952	}	3135	}
1953		3136
1954	// stop all watchers after blocking	3137	// stop all watchers after blocking
1955	static void	3138	static void
1956	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	3139	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1957	{	3140	{
1958	ev_timer_stop (loop, &tw);	3141	ev_timer_stop (loop, &tw);
1959		3142
1960	for (int i = 0; i < nfd; ++i)	3143	for (int i = 0; i < nfd; ++i)
1961	{	3144	{
1962	// set the relevant poll flags	3145	// set the relevant poll flags
1963	// could also call adns_processreadable etc. here	3146	// could also call adns_processreadable etc. here
1964	struct pollfd *fd = fds + i;	3147	struct pollfd *fd = fds + i;
1965	int revents = ev_clear_pending (iow + i);	3148	int revents = ev_clear_pending (iow + i);
1966	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	3149	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1967	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	3150	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1968		3151
1969	// now stop the watcher	3152	// now stop the watcher
1970	ev_io_stop (loop, iow + i);	3153	ev_io_stop (loop, iow + i);
1971	}	3154	}
1972		3155
1973	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	3156	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1974	}	3157	}
1975		3158
1976	Method 2: This would be just like method 1, but you run C<adns_afterpoll>	3159	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
1977	in the prepare watcher and would dispose of the check watcher.	3160	in the prepare watcher and would dispose of the check watcher.
1978		3161
1979	Method 3: If the module to be embedded supports explicit event	3162	Method 3: If the module to be embedded supports explicit event
1980	notification (adns does), you can also make use of the actual watcher	3163	notification (libadns does), you can also make use of the actual watcher
1981	callbacks, and only destroy/create the watchers in the prepare watcher.	3164	callbacks, and only destroy/create the watchers in the prepare watcher.
1982		3165
1983	static void	3166	static void
1984	timer_cb (EV_P_ ev_timer *w, int revents)	3167	timer_cb (EV_P_ ev_timer *w, int revents)
1985	{	3168	{
1986	adns_state ads = (adns_state)w->data;	3169	adns_state ads = (adns_state)w->data;
1987	update_now (EV_A);	3170	update_now (EV_A);
1988		3171
1989	adns_processtimeouts (ads, &tv_now);	3172	adns_processtimeouts (ads, &tv_now);
1990	}	3173	}
1991		3174
1992	static void	3175	static void
1993	io_cb (EV_P_ ev_io *w, int revents)	3176	io_cb (EV_P_ ev_io *w, int revents)
1994	{	3177	{
1995	adns_state ads = (adns_state)w->data;	3178	adns_state ads = (adns_state)w->data;
1996	update_now (EV_A);	3179	update_now (EV_A);
1997		3180
1998	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	3181	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1999	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	3182	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
2000	}	3183	}
2001		3184
2002	// do not ever call adns_afterpoll	3185	// do not ever call adns_afterpoll
2003		3186
2004	Method 4: Do not use a prepare or check watcher because the module you	3187	Method 4: Do not use a prepare or check watcher because the module you
2005	want to embed is too inflexible to support it. Instead, youc na override	3188	want to embed is not flexible enough to support it. Instead, you can
2006	their poll function. The drawback with this solution is that the main	3189	override their poll function. The drawback with this solution is that the
2007	loop is now no longer controllable by EV. The C<Glib::EV> module does	3190	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
2008	this.	3191	this approach, effectively embedding EV as a client into the horrible
		3192	libglib event loop.
2009		3193
2010	static gint	3194	static gint
2011	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	3195	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
2012	{	3196	{
2013	int got_events = 0;	3197	int got_events = 0;
2014		3198
2015	for (n = 0; n < nfds; ++n)	3199	for (n = 0; n < nfds; ++n)
2016	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events	3200	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
2017		3201
2018	if (timeout >= 0)	3202	if (timeout >= 0)
2019	// create/start timer	3203	// create/start timer
2020		3204
2021	// poll	3205	// poll
2022	ev_loop (EV_A_ 0);	3206	ev_run (EV_A_ 0);
2023		3207
2024	// stop timer again	3208	// stop timer again
2025	if (timeout >= 0)	3209	if (timeout >= 0)
2026	ev_timer_stop (EV_A_ &to);	3210	ev_timer_stop (EV_A_ &to);
2027		3211
2028	// stop io watchers again - their callbacks should have set	3212	// stop io watchers again - their callbacks should have set
2029	for (n = 0; n < nfds; ++n)	3213	for (n = 0; n < nfds; ++n)
2030	ev_io_stop (EV_A_ iow [n]);	3214	ev_io_stop (EV_A_ iow [n]);
2031		3215
2032	return got_events;	3216	return got_events;
2033	}	3217	}
2034		3218
2035		3219
2036	=head2 C<ev_embed> - when one backend isn't enough...	3220	=head2 C<ev_embed> - when one backend isn't enough...
2037		3221
2038	This is a rather advanced watcher type that lets you embed one event loop	3222	This is a rather advanced watcher type that lets you embed one event loop
…		…
2044	prioritise I/O.	3228	prioritise I/O.
2045		3229
2046	As an example for a bug workaround, the kqueue backend might only support	3230	As an example for a bug workaround, the kqueue backend might only support
2047	sockets on some platform, so it is unusable as generic backend, but you	3231	sockets on some platform, so it is unusable as generic backend, but you
2048	still want to make use of it because you have many sockets and it scales	3232	still want to make use of it because you have many sockets and it scales
2049	so nicely. In this case, you would create a kqueue-based loop and embed it	3233	so nicely. In this case, you would create a kqueue-based loop and embed
2050	into your default loop (which might use e.g. poll). Overall operation will	3234	it into your default loop (which might use e.g. poll). Overall operation
2051	be a bit slower because first libev has to poll and then call kevent, but	3235	will be a bit slower because first libev has to call C<poll> and then
2052	at least you can use both at what they are best.	3236	C<kevent>, but at least you can use both mechanisms for what they are
		3237	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
2053		3238
2054	As for prioritising I/O: rarely you have the case where some fds have	3239	As for prioritising I/O: under rare circumstances you have the case where
2055	to be watched and handled very quickly (with low latency), and even	3240	some fds have to be watched and handled very quickly (with low latency),
2056	priorities and idle watchers might have too much overhead. In this case	3241	and even priorities and idle watchers might have too much overhead. In
2057	you would put all the high priority stuff in one loop and all the rest in	3242	this case you would put all the high priority stuff in one loop and all
2058	a second one, and embed the second one in the first.	3243	the rest in a second one, and embed the second one in the first.
2059		3244
2060	As long as the watcher is active, the callback will be invoked every time	3245	As long as the watcher is active, the callback will be invoked every
2061	there might be events pending in the embedded loop. The callback must then	3246	time there might be events pending in the embedded loop. The callback
2062	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	3247	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
2063	their callbacks (you could also start an idle watcher to give the embedded	3248	sweep and invoke their callbacks (the callback doesn't need to invoke the
2064	loop strictly lower priority for example). You can also set the callback	3249	C<ev_embed_sweep> function directly, it could also start an idle watcher
2065	to C<0>, in which case the embed watcher will automatically execute the	3250	to give the embedded loop strictly lower priority for example).
2066	embedded loop sweep.
2067		3251
2068	As long as the watcher is started it will automatically handle events. The	3252	You can also set the callback to C<0>, in which case the embed watcher
2069	callback will be invoked whenever some events have been handled. You can	3253	will automatically execute the embedded loop sweep whenever necessary.
2070	set the callback to C<0> to avoid having to specify one if you are not
2071	interested in that.
2072		3254
2073	Also, there have not currently been made special provisions for forking:	3255	Fork detection will be handled transparently while the C<ev_embed> watcher
2074	when you fork, you not only have to call C<ev_loop_fork> on both loops,	3256	is active, i.e., the embedded loop will automatically be forked when the
2075	but you will also have to stop and restart any C<ev_embed> watchers	3257	embedding loop forks. In other cases, the user is responsible for calling
2076	yourself.	3258	C<ev_loop_fork> on the embedded loop.
2077		3259
2078	Unfortunately, not all backends are embeddable, only the ones returned by	3260	Unfortunately, not all backends are embeddable: only the ones returned by
2079	C<ev_embeddable_backends> are, which, unfortunately, does not include any	3261	C<ev_embeddable_backends> are, which, unfortunately, does not include any
2080	portable one.	3262	portable one.
2081		3263
2082	So when you want to use this feature you will always have to be prepared	3264	So when you want to use this feature you will always have to be prepared
2083	that you cannot get an embeddable loop. The recommended way to get around	3265	that you cannot get an embeddable loop. The recommended way to get around
2084	this is to have a separate variables for your embeddable loop, try to	3266	this is to have a separate variables for your embeddable loop, try to
2085	create it, and if that fails, use the normal loop for everything.	3267	create it, and if that fails, use the normal loop for everything.
2086		3268
		3269	=head3 C<ev_embed> and fork
		3270
		3271	While the C<ev_embed> watcher is running, forks in the embedding loop will
		3272	automatically be applied to the embedded loop as well, so no special
		3273	fork handling is required in that case. When the watcher is not running,
		3274	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		3275	as applicable.
		3276
2087	=head3 Watcher-Specific Functions and Data Members	3277	=head3 Watcher-Specific Functions and Data Members
2088		3278
2089	=over 4	3279	=over 4
2090		3280
2091	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3281	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
2092		3282
2093	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3283	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
2094		3284
2095	Configures the watcher to embed the given loop, which must be	3285	Configures the watcher to embed the given loop, which must be
2096	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3286	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
2097	invoked automatically, otherwise it is the responsibility of the callback	3287	invoked automatically, otherwise it is the responsibility of the callback
2098	to invoke it (it will continue to be called until the sweep has been done,	3288	to invoke it (it will continue to be called until the sweep has been done,
2099	if you do not want thta, you need to temporarily stop the embed watcher).	3289	if you do not want that, you need to temporarily stop the embed watcher).
2100		3290
2101	=item ev_embed_sweep (loop, ev_embed *)	3291	=item ev_embed_sweep (loop, ev_embed *)
2102		3292
2103	Make a single, non-blocking sweep over the embedded loop. This works	3293	Make a single, non-blocking sweep over the embedded loop. This works
2104	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	3294	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
2105	apropriate way for embedded loops.	3295	appropriate way for embedded loops.
2106		3296
2107	=item struct ev_loop *other [read-only]	3297	=item struct ev_loop *other [read-only]
2108		3298
2109	The embedded event loop.	3299	The embedded event loop.
2110		3300
…		…
2112		3302
2113	=head3 Examples	3303	=head3 Examples
2114		3304
2115	Example: Try to get an embeddable event loop and embed it into the default	3305	Example: Try to get an embeddable event loop and embed it into the default
2116	event loop. If that is not possible, use the default loop. The default	3306	event loop. If that is not possible, use the default loop. The default
2117	loop is stored in C<loop_hi>, while the mebeddable loop is stored in	3307	loop is stored in C<loop_hi>, while the embeddable loop is stored in
2118	C<loop_lo> (which is C<loop_hi> in the acse no embeddable loop can be	3308	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
2119	used).	3309	used).
2120		3310
2121	struct ev_loop *loop_hi = ev_default_init (0);	3311	struct ev_loop *loop_hi = ev_default_init (0);
2122	struct ev_loop *loop_lo = 0;	3312	struct ev_loop *loop_lo = 0;
2123	struct ev_embed embed;	3313	ev_embed embed;
2124		3314
2125	// see if there is a chance of getting one that works	3315	// see if there is a chance of getting one that works
2126	// (remember that a flags value of 0 means autodetection)	3316	// (remember that a flags value of 0 means autodetection)
2127	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3317	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2128	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3318	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
2129	: 0;	3319	: 0;
2130		3320
2131	// if we got one, then embed it, otherwise default to loop_hi	3321	// if we got one, then embed it, otherwise default to loop_hi
2132	if (loop_lo)	3322	if (loop_lo)
2133	{	3323	{
2134	ev_embed_init (&embed, 0, loop_lo);	3324	ev_embed_init (&embed, 0, loop_lo);
2135	ev_embed_start (loop_hi, &embed);	3325	ev_embed_start (loop_hi, &embed);
2136	}	3326	}
2137	else	3327	else
2138	loop_lo = loop_hi;	3328	loop_lo = loop_hi;
2139		3329
2140	Example: Check if kqueue is available but not recommended and create	3330	Example: Check if kqueue is available but not recommended and create
2141	a kqueue backend for use with sockets (which usually work with any	3331	a kqueue backend for use with sockets (which usually work with any
2142	kqueue implementation). Store the kqueue/socket-only event loop in	3332	kqueue implementation). Store the kqueue/socket-only event loop in
2143	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3333	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2144		3334
2145	struct ev_loop *loop = ev_default_init (0);	3335	struct ev_loop *loop = ev_default_init (0);
2146	struct ev_loop *loop_socket = 0;	3336	struct ev_loop *loop_socket = 0;
2147	struct ev_embed embed;	3337	ev_embed embed;
2148		3338
2149	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3339	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2150	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3340	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2151	{	3341	{
2152	ev_embed_init (&embed, 0, loop_socket);	3342	ev_embed_init (&embed, 0, loop_socket);
2153	ev_embed_start (loop, &embed);	3343	ev_embed_start (loop, &embed);
2154	}	3344	}
2155		3345
2156	if (!loop_socket)	3346	if (!loop_socket)
2157	loop_socket = loop;	3347	loop_socket = loop;
2158		3348
2159	// now use loop_socket for all sockets, and loop for everything else	3349	// now use loop_socket for all sockets, and loop for everything else
2160		3350
2161		3351
2162	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3352	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
2163		3353
2164	Fork watchers are called when a C<fork ()> was detected (usually because	3354	Fork watchers are called when a C<fork ()> was detected (usually because
2165	whoever is a good citizen cared to tell libev about it by calling	3355	whoever is a good citizen cared to tell libev about it by calling
2166	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the	3356	C<ev_loop_fork>). The invocation is done before the event loop blocks next
2167	event loop blocks next and before C<ev_check> watchers are being called,	3357	and before C<ev_check> watchers are being called, and only in the child
2168	and only in the child after the fork. If whoever good citizen calling	3358	after the fork. If whoever good citizen calling C<ev_default_fork> cheats
2169	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3359	and calls it in the wrong process, the fork handlers will be invoked, too,
2170	handlers will be invoked, too, of course.	3360	of course.
		3361
		3362	=head3 The special problem of life after fork - how is it possible?
		3363
		3364	Most uses of C<fork ()> consist of forking, then some simple calls to set
		3365	up/change the process environment, followed by a call to C<exec()>. This
		3366	sequence should be handled by libev without any problems.
		3367
		3368	This changes when the application actually wants to do event handling
		3369	in the child, or both parent in child, in effect "continuing" after the
		3370	fork.
		3371
		3372	The default mode of operation (for libev, with application help to detect
		3373	forks) is to duplicate all the state in the child, as would be expected
		3374	when I<either> the parent I<or> the child process continues.
		3375
		3376	When both processes want to continue using libev, then this is usually the
		3377	wrong result. In that case, usually one process (typically the parent) is
		3378	supposed to continue with all watchers in place as before, while the other
		3379	process typically wants to start fresh, i.e. without any active watchers.
		3380
		3381	The cleanest and most efficient way to achieve that with libev is to
		3382	simply create a new event loop, which of course will be "empty", and
		3383	use that for new watchers. This has the advantage of not touching more
		3384	memory than necessary, and thus avoiding the copy-on-write, and the
		3385	disadvantage of having to use multiple event loops (which do not support
		3386	signal watchers).
		3387
		3388	When this is not possible, or you want to use the default loop for
		3389	other reasons, then in the process that wants to start "fresh", call
		3390	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
		3391	Destroying the default loop will "orphan" (not stop) all registered
		3392	watchers, so you have to be careful not to execute code that modifies
		3393	those watchers. Note also that in that case, you have to re-register any
		3394	signal watchers.
2171		3395
2172	=head3 Watcher-Specific Functions and Data Members	3396	=head3 Watcher-Specific Functions and Data Members
2173		3397
2174	=over 4	3398	=over 4
2175		3399
2176	=item ev_fork_init (ev_signal *, callback)	3400	=item ev_fork_init (ev_fork *, callback)
2177		3401
2178	Initialises and configures the fork watcher - it has no parameters of any	3402	Initialises and configures the fork watcher - it has no parameters of any
2179	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,	3403	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
2180	believe me.	3404	really.
2181		3405
2182	=back	3406	=back
2183		3407
2184		3408
		3409	=head2 C<ev_cleanup> - even the best things end
		3410
		3411	Cleanup watchers are called just before the event loop is being destroyed
		3412	by a call to C<ev_loop_destroy>.
		3413
		3414	While there is no guarantee that the event loop gets destroyed, cleanup
		3415	watchers provide a convenient method to install cleanup hooks for your
		3416	program, worker threads and so on - you just to make sure to destroy the
		3417	loop when you want them to be invoked.
		3418
		3419	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3420	all other watchers, they do not keep a reference to the event loop (which
		3421	makes a lot of sense if you think about it). Like all other watchers, you
		3422	can call libev functions in the callback, except C<ev_cleanup_start>.
		3423
		3424	=head3 Watcher-Specific Functions and Data Members
		3425
		3426	=over 4
		3427
		3428	=item ev_cleanup_init (ev_cleanup *, callback)
		3429
		3430	Initialises and configures the cleanup watcher - it has no parameters of
		3431	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3432	pointless, I assure you.
		3433
		3434	=back
		3435
		3436	Example: Register an atexit handler to destroy the default loop, so any
		3437	cleanup functions are called.
		3438
		3439	static void
		3440	program_exits (void)
		3441	{
		3442	ev_loop_destroy (EV_DEFAULT_UC);
		3443	}
		3444
		3445	...
		3446	atexit (program_exits);
		3447
		3448
2185	=head2 C<ev_async> - how to wake up another event loop	3449	=head2 C<ev_async> - how to wake up an event loop
2186		3450
2187	In general, you cannot use an C<ev_loop> from multiple threads or other	3451	In general, you cannot use an C<ev_loop> from multiple threads or other
2188	asynchronous sources such as signal handlers (as opposed to multiple event	3452	asynchronous sources such as signal handlers (as opposed to multiple event
2189	loops - those are of course safe to use in different threads).	3453	loops - those are of course safe to use in different threads).
2190		3454
2191	Sometimes, however, you need to wake up another event loop you do not	3455	Sometimes, however, you need to wake up an event loop you do not control,
2192	control, for example because it belongs to another thread. This is what	3456	for example because it belongs to another thread. This is what C<ev_async>
2193	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you	3457	watchers do: as long as the C<ev_async> watcher is active, you can signal
2194	can signal it by calling C<ev_async_send>, which is thread- and signal	3458	it by calling C<ev_async_send>, which is thread- and signal safe.
2195	safe.
2196		3459
2197	This functionality is very similar to C<ev_signal> watchers, as signals,	3460	This functionality is very similar to C<ev_signal> watchers, as signals,
2198	too, are asynchronous in nature, and signals, too, will be compressed	3461	too, are asynchronous in nature, and signals, too, will be compressed
2199	(i.e. the number of callback invocations may be less than the number of	3462	(i.e. the number of callback invocations may be less than the number of
2200	C<ev_async_sent> calls).	3463	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
2201		3464	of "global async watchers" by using a watcher on an otherwise unused
2202	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not	3465	signal, and C<ev_feed_signal> to signal this watcher from another thread,
2203	just the default loop.	3466	even without knowing which loop owns the signal.
2204		3467
2205	=head3 Queueing	3468	=head3 Queueing
2206		3469
2207	C<ev_async> does not support queueing of data in any way. The reason	3470	C<ev_async> does not support queueing of data in any way. The reason
2208	is that the author does not know of a simple (or any) algorithm for a	3471	is that the author does not know of a simple (or any) algorithm for a
2209	multiple-writer-single-reader queue that works in all cases and doesn't	3472	multiple-writer-single-reader queue that works in all cases and doesn't
2210	need elaborate support such as pthreads.	3473	need elaborate support such as pthreads or unportable memory access
		3474	semantics.
2211		3475
2212	That means that if you want to queue data, you have to provide your own	3476	That means that if you want to queue data, you have to provide your own
2213	queue. But at least I can tell you would implement locking around your	3477	queue. But at least I can tell you how to implement locking around your
2214	queue:	3478	queue:
2215		3479
2216	=over 4	3480	=over 4
2217		3481
2218	=item queueing from a signal handler context	3482	=item queueing from a signal handler context
2219		3483
2220	To implement race-free queueing, you simply add to the queue in the signal	3484	To implement race-free queueing, you simply add to the queue in the signal
2221	handler but you block the signal handler in the watcher callback. Here is an example that does that for	3485	handler but you block the signal handler in the watcher callback. Here is
2222	some fictitiuous SIGUSR1 handler:	3486	an example that does that for some fictitious SIGUSR1 handler:
2223		3487
2224	static ev_async mysig;	3488	static ev_async mysig;
2225		3489
2226	static void	3490	static void
2227	sigusr1_handler (void)	3491	sigusr1_handler (void)
…		…
2293	=over 4	3557	=over 4
2294		3558
2295	=item ev_async_init (ev_async *, callback)	3559	=item ev_async_init (ev_async *, callback)
2296		3560
2297	Initialises and configures the async watcher - it has no parameters of any	3561	Initialises and configures the async watcher - it has no parameters of any
2298	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,	3562	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
2299	believe me.	3563	trust me.
2300		3564
2301	=item ev_async_send (loop, ev_async *)	3565	=item ev_async_send (loop, ev_async *)
2302		3566
2303	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3567	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
2304	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3568	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3569	returns.
		3570
2305	C<ev_feed_event>, this call is safe to do in other threads, signal or	3571	Unlike C<ev_feed_event>, this call is safe to do from other threads,
2306	similar contexts (see the dicusssion of C<EV_ATOMIC_T> in the embedding	3572	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
2307	section below on what exactly this means).	3573	embedding section below on what exactly this means).
2308		3574
2309	This call incurs the overhead of a syscall only once per loop iteration,	3575	Note that, as with other watchers in libev, multiple events might get
2310	so while the overhead might be noticable, it doesn't apply to repeated	3576	compressed into a single callback invocation (another way to look at
2311	calls to C<ev_async_send>.	3577	this is that C<ev_async> watchers are level-triggered: they are set on
		3578	C<ev_async_send>, reset when the event loop detects that).
		3579
		3580	This call incurs the overhead of at most one extra system call per event
		3581	loop iteration, if the event loop is blocked, and no syscall at all if
		3582	the event loop (or your program) is processing events. That means that
		3583	repeated calls are basically free (there is no need to avoid calls for
		3584	performance reasons) and that the overhead becomes smaller (typically
		3585	zero) under load.
2312		3586
2313	=item bool = ev_async_pending (ev_async *)	3587	=item bool = ev_async_pending (ev_async *)
2314		3588
2315	Returns a non-zero value when C<ev_async_send> has been called on the	3589	Returns a non-zero value when C<ev_async_send> has been called on the
2316	watcher but the event has not yet been processed (or even noted) by the	3590	watcher but the event has not yet been processed (or even noted) by the
2317	event loop.	3591	event loop.
2318		3592
2319	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When	3593	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
2320	the loop iterates next and checks for the watcher to have become active,	3594	the loop iterates next and checks for the watcher to have become active,
2321	it will reset the flag again. C<ev_async_pending> can be used to very	3595	it will reset the flag again. C<ev_async_pending> can be used to very
2322	quickly check wether invoking the loop might be a good idea.	3596	quickly check whether invoking the loop might be a good idea.
2323		3597
2324	Not that this does I<not> check wether the watcher itself is pending, only	3598	Not that this does I<not> check whether the watcher itself is pending,
2325	wether it has been requested to make this watcher pending.	3599	only whether it has been requested to make this watcher pending: there
		3600	is a time window between the event loop checking and resetting the async
		3601	notification, and the callback being invoked.
2326		3602
2327	=back	3603	=back
2328		3604
2329		3605
2330	=head1 OTHER FUNCTIONS	3606	=head1 OTHER FUNCTIONS
2331		3607
2332	There are some other functions of possible interest. Described. Here. Now.	3608	There are some other functions of possible interest. Described. Here. Now.
2333		3609
2334	=over 4	3610	=over 4
2335		3611
2336	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3612	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)
2337		3613
2338	This function combines a simple timer and an I/O watcher, calls your	3614	This function combines a simple timer and an I/O watcher, calls your
2339	callback on whichever event happens first and automatically stop both	3615	callback on whichever event happens first and automatically stops both
2340	watchers. This is useful if you want to wait for a single event on an fd	3616	watchers. This is useful if you want to wait for a single event on an fd
2341	or timeout without having to allocate/configure/start/stop/free one or	3617	or timeout without having to allocate/configure/start/stop/free one or
2342	more watchers yourself.	3618	more watchers yourself.
2343		3619
2344	If C<fd> is less than 0, then no I/O watcher will be started and events	3620	If C<fd> is less than 0, then no I/O watcher will be started and the
2345	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3621	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
2346	C<events> set will be craeted and started.	3622	the given C<fd> and C<events> set will be created and started.
2347		3623
2348	If C<timeout> is less than 0, then no timeout watcher will be	3624	If C<timeout> is less than 0, then no timeout watcher will be
2349	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3625	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
2350	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3626	repeat = 0) will be started. C<0> is a valid timeout.
2351	dubious value.
2352		3627
2353	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3628	The callback has the type C<void (*cb)(int revents, void *arg)> and is
2354	passed an C<revents> set like normal event callbacks (a combination of	3629	passed an C<revents> set like normal event callbacks (a combination of
2355	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3630	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
2356	value passed to C<ev_once>:	3631	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3632	a timeout and an io event at the same time - you probably should give io
		3633	events precedence.
2357		3634
		3635	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3636
2358	static void stdin_ready (int revents, void *arg)	3637	static void stdin_ready (int revents, void *arg)
		3638	{
		3639	if (revents & EV_READ)
		3640	/* stdin might have data for us, joy! */;
		3641	else if (revents & EV_TIMER)
		3642	/* doh, nothing entered */;
		3643	}
		3644
		3645	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
		3646
		3647	=item ev_feed_fd_event (loop, int fd, int revents)
		3648
		3649	Feed an event on the given fd, as if a file descriptor backend detected
		3650	the given events.
		3651
		3652	=item ev_feed_signal_event (loop, int signum)
		3653
		3654	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
		3655	which is async-safe.
		3656
		3657	=back
		3658
		3659
		3660	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3661
		3662	This section explains some common idioms that are not immediately
		3663	obvious. Note that examples are sprinkled over the whole manual, and this
		3664	section only contains stuff that wouldn't fit anywhere else.
		3665
		3666	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3667
		3668	Each watcher has, by default, a C<void *data> member that you can read
		3669	or modify at any time: libev will completely ignore it. This can be used
		3670	to associate arbitrary data with your watcher. If you need more data and
		3671	don't want to allocate memory separately and store a pointer to it in that
		3672	data member, you can also "subclass" the watcher type and provide your own
		3673	data:
		3674
		3675	struct my_io
		3676	{
		3677	ev_io io;
		3678	int otherfd;
		3679	void *somedata;
		3680	struct whatever *mostinteresting;
		3681	};
		3682
		3683	...
		3684	struct my_io w;
		3685	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3686
		3687	And since your callback will be called with a pointer to the watcher, you
		3688	can cast it back to your own type:
		3689
		3690	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3691	{
		3692	struct my_io *w = (struct my_io *)w_;
		3693	...
		3694	}
		3695
		3696	More interesting and less C-conformant ways of casting your callback
		3697	function type instead have been omitted.
		3698
		3699	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3700
		3701	Another common scenario is to use some data structure with multiple
		3702	embedded watchers, in effect creating your own watcher that combines
		3703	multiple libev event sources into one "super-watcher":
		3704
		3705	struct my_biggy
		3706	{
		3707	int some_data;
		3708	ev_timer t1;
		3709	ev_timer t2;
		3710	}
		3711
		3712	In this case getting the pointer to C<my_biggy> is a bit more
		3713	complicated: Either you store the address of your C<my_biggy> struct in
		3714	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3715	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3716	real programmers):
		3717
		3718	#include <stddef.h>
		3719
		3720	static void
		3721	t1_cb (EV_P_ ev_timer *w, int revents)
		3722	{
		3723	struct my_biggy big = (struct my_biggy *)
		3724	(((char *)w) - offsetof (struct my_biggy, t1));
		3725	}
		3726
		3727	static void
		3728	t2_cb (EV_P_ ev_timer *w, int revents)
		3729	{
		3730	struct my_biggy big = (struct my_biggy *)
		3731	(((char *)w) - offsetof (struct my_biggy, t2));
		3732	}
		3733
		3734	=head2 AVOIDING FINISHING BEFORE RETURNING
		3735
		3736	Often you have structures like this in event-based programs:
		3737
		3738	callback ()
2359	{	3739	{
2360	if (revents & EV_TIMEOUT)	3740	free (request);
2361	/* doh, nothing entered */;
2362	else if (revents & EV_READ)
2363	/* stdin might have data for us, joy! */;
2364	}	3741	}
2365		3742
2366	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3743	request = start_new_request (..., callback);
2367		3744
2368	=item ev_feed_event (ev_loop *, watcher *, int revents)	3745	The intent is to start some "lengthy" operation. The C<request> could be
		3746	used to cancel the operation, or do other things with it.
2369		3747
2370	Feeds the given event set into the event loop, as if the specified event	3748	It's not uncommon to have code paths in C<start_new_request> that
2371	had happened for the specified watcher (which must be a pointer to an	3749	immediately invoke the callback, for example, to report errors. Or you add
2372	initialised but not necessarily started event watcher).	3750	some caching layer that finds that it can skip the lengthy aspects of the
		3751	operation and simply invoke the callback with the result.
2373		3752
2374	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3753	The problem here is that this will happen I<before> C<start_new_request>
		3754	has returned, so C<request> is not set.
2375		3755
2376	Feed an event on the given fd, as if a file descriptor backend detected	3756	Even if you pass the request by some safer means to the callback, you
2377	the given events it.	3757	might want to do something to the request after starting it, such as
		3758	canceling it, which probably isn't working so well when the callback has
		3759	already been invoked.
2378		3760
2379	=item ev_feed_signal_event (ev_loop *loop, int signum)	3761	A common way around all these issues is to make sure that
		3762	C<start_new_request> I<always> returns before the callback is invoked. If
		3763	C<start_new_request> immediately knows the result, it can artificially
		3764	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3765	example, or more sneakily, by reusing an existing (stopped) watcher and
		3766	pushing it into the pending queue:
2380		3767
2381	Feed an event as if the given signal occured (C<loop> must be the default	3768	ev_set_cb (watcher, callback);
2382	loop!).	3769	ev_feed_event (EV_A_ watcher, 0);
2383		3770
2384	=back	3771	This way, C<start_new_request> can safely return before the callback is
		3772	invoked, while not delaying callback invocation too much.
		3773
		3774	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3775
		3776	Often (especially in GUI toolkits) there are places where you have
		3777	I<modal> interaction, which is most easily implemented by recursively
		3778	invoking C<ev_run>.
		3779
		3780	This brings the problem of exiting - a callback might want to finish the
		3781	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3782	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3783	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3784	other combination: In these cases, a simple C<ev_break> will not work.
		3785
		3786	The solution is to maintain "break this loop" variable for each C<ev_run>
		3787	invocation, and use a loop around C<ev_run> until the condition is
		3788	triggered, using C<EVRUN_ONCE>:
		3789
		3790	// main loop
		3791	int exit_main_loop = 0;
		3792
		3793	while (!exit_main_loop)
		3794	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3795
		3796	// in a modal watcher
		3797	int exit_nested_loop = 0;
		3798
		3799	while (!exit_nested_loop)
		3800	ev_run (EV_A_ EVRUN_ONCE);
		3801
		3802	To exit from any of these loops, just set the corresponding exit variable:
		3803
		3804	// exit modal loop
		3805	exit_nested_loop = 1;
		3806
		3807	// exit main program, after modal loop is finished
		3808	exit_main_loop = 1;
		3809
		3810	// exit both
		3811	exit_main_loop = exit_nested_loop = 1;
		3812
		3813	=head2 THREAD LOCKING EXAMPLE
		3814
		3815	Here is a fictitious example of how to run an event loop in a different
		3816	thread from where callbacks are being invoked and watchers are
		3817	created/added/removed.
		3818
		3819	For a real-world example, see the C<EV::Loop::Async> perl module,
		3820	which uses exactly this technique (which is suited for many high-level
		3821	languages).
		3822
		3823	The example uses a pthread mutex to protect the loop data, a condition
		3824	variable to wait for callback invocations, an async watcher to notify the
		3825	event loop thread and an unspecified mechanism to wake up the main thread.
		3826
		3827	First, you need to associate some data with the event loop:
		3828
		3829	typedef struct {
		3830	mutex_t lock; /* global loop lock */
		3831	ev_async async_w;
		3832	thread_t tid;
		3833	cond_t invoke_cv;
		3834	} userdata;
		3835
		3836	void prepare_loop (EV_P)
		3837	{
		3838	// for simplicity, we use a static userdata struct.
		3839	static userdata u;
		3840
		3841	ev_async_init (&u->async_w, async_cb);
		3842	ev_async_start (EV_A_ &u->async_w);
		3843
		3844	pthread_mutex_init (&u->lock, 0);
		3845	pthread_cond_init (&u->invoke_cv, 0);
		3846
		3847	// now associate this with the loop
		3848	ev_set_userdata (EV_A_ u);
		3849	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3850	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3851
		3852	// then create the thread running ev_run
		3853	pthread_create (&u->tid, 0, l_run, EV_A);
		3854	}
		3855
		3856	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3857	solely to wake up the event loop so it takes notice of any new watchers
		3858	that might have been added:
		3859
		3860	static void
		3861	async_cb (EV_P_ ev_async *w, int revents)
		3862	{
		3863	// just used for the side effects
		3864	}
		3865
		3866	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3867	protecting the loop data, respectively.
		3868
		3869	static void
		3870	l_release (EV_P)
		3871	{
		3872	userdata *u = ev_userdata (EV_A);
		3873	pthread_mutex_unlock (&u->lock);
		3874	}
		3875
		3876	static void
		3877	l_acquire (EV_P)
		3878	{
		3879	userdata *u = ev_userdata (EV_A);
		3880	pthread_mutex_lock (&u->lock);
		3881	}
		3882
		3883	The event loop thread first acquires the mutex, and then jumps straight
		3884	into C<ev_run>:
		3885
		3886	void *
		3887	l_run (void *thr_arg)
		3888	{
		3889	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3890
		3891	l_acquire (EV_A);
		3892	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3893	ev_run (EV_A_ 0);
		3894	l_release (EV_A);
		3895
		3896	return 0;
		3897	}
		3898
		3899	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3900	signal the main thread via some unspecified mechanism (signals? pipe
		3901	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3902	have been called (in a while loop because a) spurious wakeups are possible
		3903	and b) skipping inter-thread-communication when there are no pending
		3904	watchers is very beneficial):
		3905
		3906	static void
		3907	l_invoke (EV_P)
		3908	{
		3909	userdata *u = ev_userdata (EV_A);
		3910
		3911	while (ev_pending_count (EV_A))
		3912	{
		3913	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3914	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3915	}
		3916	}
		3917
		3918	Now, whenever the main thread gets told to invoke pending watchers, it
		3919	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3920	thread to continue:
		3921
		3922	static void
		3923	real_invoke_pending (EV_P)
		3924	{
		3925	userdata *u = ev_userdata (EV_A);
		3926
		3927	pthread_mutex_lock (&u->lock);
		3928	ev_invoke_pending (EV_A);
		3929	pthread_cond_signal (&u->invoke_cv);
		3930	pthread_mutex_unlock (&u->lock);
		3931	}
		3932
		3933	Whenever you want to start/stop a watcher or do other modifications to an
		3934	event loop, you will now have to lock:
		3935
		3936	ev_timer timeout_watcher;
		3937	userdata *u = ev_userdata (EV_A);
		3938
		3939	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3940
		3941	pthread_mutex_lock (&u->lock);
		3942	ev_timer_start (EV_A_ &timeout_watcher);
		3943	ev_async_send (EV_A_ &u->async_w);
		3944	pthread_mutex_unlock (&u->lock);
		3945
		3946	Note that sending the C<ev_async> watcher is required because otherwise
		3947	an event loop currently blocking in the kernel will have no knowledge
		3948	about the newly added timer. By waking up the loop it will pick up any new
		3949	watchers in the next event loop iteration.
		3950
		3951	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3952
		3953	While the overhead of a callback that e.g. schedules a thread is small, it
		3954	is still an overhead. If you embed libev, and your main usage is with some
		3955	kind of threads or coroutines, you might want to customise libev so that
		3956	doesn't need callbacks anymore.
		3957
		3958	Imagine you have coroutines that you can switch to using a function
		3959	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3960	and that due to some magic, the currently active coroutine is stored in a
		3961	global called C<current_coro>. Then you can build your own "wait for libev
		3962	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3963	the differing C<;> conventions):
		3964
		3965	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3966	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3967
		3968	That means instead of having a C callback function, you store the
		3969	coroutine to switch to in each watcher, and instead of having libev call
		3970	your callback, you instead have it switch to that coroutine.
		3971
		3972	A coroutine might now wait for an event with a function called
		3973	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3974	matter when, or whether the watcher is active or not when this function is
		3975	called):
		3976
		3977	void
		3978	wait_for_event (ev_watcher *w)
		3979	{
		3980	ev_set_cb (w, current_coro);
		3981	switch_to (libev_coro);
		3982	}
		3983
		3984	That basically suspends the coroutine inside C<wait_for_event> and
		3985	continues the libev coroutine, which, when appropriate, switches back to
		3986	this or any other coroutine.
		3987
		3988	You can do similar tricks if you have, say, threads with an event queue -
		3989	instead of storing a coroutine, you store the queue object and instead of
		3990	switching to a coroutine, you push the watcher onto the queue and notify
		3991	any waiters.
		3992
		3993	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		3994	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3995
		3996	// my_ev.h
		3997	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3998	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3999	#include "../libev/ev.h"
		4000
		4001	// my_ev.c
		4002	#define EV_H "my_ev.h"
		4003	#include "../libev/ev.c"
		4004
		4005	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		4006	F<my_ev.c> into your project. When properly specifying include paths, you
		4007	can even use F<ev.h> as header file name directly.
2385		4008
2386		4009
2387	=head1 LIBEVENT EMULATION	4010	=head1 LIBEVENT EMULATION
2388		4011
2389	Libev offers a compatibility emulation layer for libevent. It cannot	4012	Libev offers a compatibility emulation layer for libevent. It cannot
2390	emulate the internals of libevent, so here are some usage hints:	4013	emulate the internals of libevent, so here are some usage hints:
2391		4014
2392	=over 4	4015	=over 4
		4016
		4017	=item * Only the libevent-1.4.1-beta API is being emulated.
		4018
		4019	This was the newest libevent version available when libev was implemented,
		4020	and is still mostly unchanged in 2010.
2393		4021
2394	=item * Use it by including <event.h>, as usual.	4022	=item * Use it by including <event.h>, as usual.
2395		4023
2396	=item * The following members are fully supported: ev_base, ev_callback,	4024	=item * The following members are fully supported: ev_base, ev_callback,
2397	ev_arg, ev_fd, ev_res, ev_events.	4025	ev_arg, ev_fd, ev_res, ev_events.
…		…
2403	=item * Priorities are not currently supported. Initialising priorities	4031	=item * Priorities are not currently supported. Initialising priorities
2404	will fail and all watchers will have the same priority, even though there	4032	will fail and all watchers will have the same priority, even though there
2405	is an ev_pri field.	4033	is an ev_pri field.
2406		4034
2407	=item * In libevent, the last base created gets the signals, in libev, the	4035	=item * In libevent, the last base created gets the signals, in libev, the
2408	first base created (== the default loop) gets the signals.	4036	base that registered the signal gets the signals.
2409		4037
2410	=item * Other members are not supported.	4038	=item * Other members are not supported.
2411		4039
2412	=item * The libev emulation is I<not> ABI compatible to libevent, you need	4040	=item * The libev emulation is I<not> ABI compatible to libevent, you need
2413	to use the libev header file and library.	4041	to use the libev header file and library.
2414		4042
2415	=back	4043	=back
2416		4044
2417	=head1 C++ SUPPORT	4045	=head1 C++ SUPPORT
2418		4046
		4047	=head2 C API
		4048
		4049	The normal C API should work fine when used from C++: both ev.h and the
		4050	libev sources can be compiled as C++. Therefore, code that uses the C API
		4051	will work fine.
		4052
		4053	Proper exception specifications might have to be added to callbacks passed
		4054	to libev: exceptions may be thrown only from watcher callbacks, all other
		4055	callbacks (allocator, syserr, loop acquire/release and periodic reschedule
		4056	callbacks) must not throw exceptions, and might need a C<noexcept>
		4057	specification. If you have code that needs to be compiled as both C and
		4058	C++ you can use the C<EV_NOEXCEPT> macro for this:
		4059
		4060	static void
		4061	fatal_error (const char *msg) EV_NOEXCEPT
		4062	{
		4063	perror (msg);
		4064	abort ();
		4065	}
		4066
		4067	...
		4068	ev_set_syserr_cb (fatal_error);
		4069
		4070	The only API functions that can currently throw exceptions are C<ev_run>,
		4071	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		4072	because it runs cleanup watchers).
		4073
		4074	Throwing exceptions in watcher callbacks is only supported if libev itself
		4075	is compiled with a C++ compiler or your C and C++ environments allow
		4076	throwing exceptions through C libraries (most do).
		4077
		4078	=head2 C++ API
		4079
2419	Libev comes with some simplistic wrapper classes for C++ that mainly allow	4080	Libev comes with some simplistic wrapper classes for C++ that mainly allow
2420	you to use some convinience methods to start/stop watchers and also change	4081	you to use some convenience methods to start/stop watchers and also change
2421	the callback model to a model using method callbacks on objects.	4082	the callback model to a model using method callbacks on objects.
2422		4083
2423	To use it,	4084	To use it,
2424		4085
2425	#include <ev++.h>	4086	#include <ev++.h>
2426		4087
2427	This automatically includes F<ev.h> and puts all of its definitions (many	4088	This automatically includes F<ev.h> and puts all of its definitions (many
2428	of them macros) into the global namespace. All C++ specific things are	4089	of them macros) into the global namespace. All C++ specific things are
2429	put into the C<ev> namespace. It should support all the same embedding	4090	put into the C<ev> namespace. It should support all the same embedding
2430	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	4091	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
2432	Care has been taken to keep the overhead low. The only data member the C++	4093	Care has been taken to keep the overhead low. The only data member the C++
2433	classes add (compared to plain C-style watchers) is the event loop pointer	4094	classes add (compared to plain C-style watchers) is the event loop pointer
2434	that the watcher is associated with (or no additional members at all if	4095	that the watcher is associated with (or no additional members at all if
2435	you disable C<EV_MULTIPLICITY> when embedding libev).	4096	you disable C<EV_MULTIPLICITY> when embedding libev).
2436		4097
2437	Currently, functions, and static and non-static member functions can be	4098	Currently, functions, static and non-static member functions and classes
2438	used as callbacks. Other types should be easy to add as long as they only	4099	with C<operator ()> can be used as callbacks. Other types should be easy
2439	need one additional pointer for context. If you need support for other	4100	to add as long as they only need one additional pointer for context. If
2440	types of functors please contact the author (preferably after implementing	4101	you need support for other types of functors please contact the author
2441	it).	4102	(preferably after implementing it).
		4103
		4104	For all this to work, your C++ compiler either has to use the same calling
		4105	conventions as your C compiler (for static member functions), or you have
		4106	to embed libev and compile libev itself as C++.
2442		4107
2443	Here is a list of things available in the C<ev> namespace:	4108	Here is a list of things available in the C<ev> namespace:
2444		4109
2445	=over 4	4110	=over 4
2446		4111
…		…
2456	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4121	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
2457		4122
2458	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4123	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
2459	the same name in the C<ev> namespace, with the exception of C<ev_signal>	4124	the same name in the C<ev> namespace, with the exception of C<ev_signal>
2460	which is called C<ev::sig> to avoid clashes with the C<signal> macro	4125	which is called C<ev::sig> to avoid clashes with the C<signal> macro
2461	defines by many implementations.	4126	defined by many implementations.
2462		4127
2463	All of those classes have these methods:	4128	All of those classes have these methods:
2464		4129
2465	=over 4	4130	=over 4
2466		4131
2467	=item ev::TYPE::TYPE ()	4132	=item ev::TYPE::TYPE ()
2468		4133
2469	=item ev::TYPE::TYPE (struct ev_loop *)	4134	=item ev::TYPE::TYPE (loop)
2470		4135
2471	=item ev::TYPE::~TYPE	4136	=item ev::TYPE::~TYPE
2472		4137
2473	The constructor (optionally) takes an event loop to associate the watcher	4138	The constructor (optionally) takes an event loop to associate the watcher
2474	with. If it is omitted, it will use C<EV_DEFAULT>.	4139	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
2497	your compiler is good :), then the method will be fully inlined into the	4162	your compiler is good :), then the method will be fully inlined into the
2498	thunking function, making it as fast as a direct C callback.	4163	thunking function, making it as fast as a direct C callback.
2499		4164
2500	Example: simple class declaration and watcher initialisation	4165	Example: simple class declaration and watcher initialisation
2501		4166
2502	struct myclass	4167	struct myclass
2503	{	4168	{
2504	void io_cb (ev::io &w, int revents) { }	4169	void io_cb (ev::io &w, int revents) { }
2505	}	4170	}
2506		4171
2507	myclass obj;	4172	myclass obj;
2508	ev::io iow;	4173	ev::io iow;
2509	iow.set <myclass, &myclass::io_cb> (&obj);	4174	iow.set <myclass, &myclass::io_cb> (&obj);
		4175
		4176	=item w->set (object *)
		4177
		4178	This is a variation of a method callback - leaving out the method to call
		4179	will default the method to C<operator ()>, which makes it possible to use
		4180	functor objects without having to manually specify the C<operator ()> all
		4181	the time. Incidentally, you can then also leave out the template argument
		4182	list.
		4183
		4184	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		4185	int revents)>.
		4186
		4187	See the method-C<set> above for more details.
		4188
		4189	Example: use a functor object as callback.
		4190
		4191	struct myfunctor
		4192	{
		4193	void operator() (ev::io &w, int revents)
		4194	{
		4195	...
		4196	}
		4197	}
		4198
		4199	myfunctor f;
		4200
		4201	ev::io w;
		4202	w.set (&f);
2510		4203
2511	=item w->set<function> (void *data = 0)	4204	=item w->set<function> (void *data = 0)
2512		4205
2513	Also sets a callback, but uses a static method or plain function as	4206	Also sets a callback, but uses a static method or plain function as
2514	callback. The optional C<data> argument will be stored in the watcher's	4207	callback. The optional C<data> argument will be stored in the watcher's
…		…
2516		4209
2517	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	4210	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2518		4211
2519	See the method-C<set> above for more details.	4212	See the method-C<set> above for more details.
2520		4213
2521	Example:	4214	Example: Use a plain function as callback.
2522		4215
2523	static void io_cb (ev::io &w, int revents) { }	4216	static void io_cb (ev::io &w, int revents) { }
2524	iow.set <io_cb> ();	4217	iow.set <io_cb> ();
2525		4218
2526	=item w->set (struct ev_loop *)	4219	=item w->set (loop)
2527		4220
2528	Associates a different C<struct ev_loop> with this watcher. You can only	4221	Associates a different C<struct ev_loop> with this watcher. You can only
2529	do this when the watcher is inactive (and not pending either).	4222	do this when the watcher is inactive (and not pending either).
2530		4223
2531	=item w->set ([args])	4224	=item w->set ([arguments])
2532		4225
2533	Basically the same as C<ev_TYPE_set>, with the same args. Must be	4226	Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
		4227	with the same arguments. Either this method or a suitable start method
2534	called at least once. Unlike the C counterpart, an active watcher gets	4228	must be called at least once. Unlike the C counterpart, an active watcher
2535	automatically stopped and restarted when reconfiguring it with this	4229	gets automatically stopped and restarted when reconfiguring it with this
2536	method.	4230	method.
		4231
		4232	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4233	clashing with the C<set (loop)> method.
2537		4234
2538	=item w->start ()	4235	=item w->start ()
2539		4236
2540	Starts the watcher. Note that there is no C<loop> argument, as the	4237	Starts the watcher. Note that there is no C<loop> argument, as the
2541	constructor already stores the event loop.	4238	constructor already stores the event loop.
2542		4239
		4240	=item w->start ([arguments])
		4241
		4242	Instead of calling C<set> and C<start> methods separately, it is often
		4243	convenient to wrap them in one call. Uses the same type of arguments as
		4244	the configure C<set> method of the watcher.
		4245
2543	=item w->stop ()	4246	=item w->stop ()
2544		4247
2545	Stops the watcher if it is active. Again, no C<loop> argument.	4248	Stops the watcher if it is active. Again, no C<loop> argument.
2546		4249
2547	=item w->again () (C<ev::timer>, C<ev::periodic> only)	4250	=item w->again () (C<ev::timer>, C<ev::periodic> only)
…		…
2559		4262
2560	=back	4263	=back
2561		4264
2562	=back	4265	=back
2563		4266
2564	Example: Define a class with an IO and idle watcher, start one of them in	4267	Example: Define a class with two I/O and idle watchers, start the I/O
2565	the constructor.	4268	watchers in the constructor.
2566		4269
2567	class myclass	4270	class myclass
2568	{	4271	{
2569	ev::io io; void io_cb (ev::io &w, int revents);	4272	ev::io io ; void io_cb (ev::io &w, int revents);
		4273	ev::io io2 ; void io2_cb (ev::io &w, int revents);
2570	ev:idle idle void idle_cb (ev::idle &w, int revents);	4274	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2571		4275
2572	myclass (int fd)	4276	myclass (int fd)
2573	{	4277	{
2574	io .set <myclass, &myclass::io_cb > (this);	4278	io .set <myclass, &myclass::io_cb > (this);
		4279	io2 .set <myclass, &myclass::io2_cb > (this);
2575	idle.set <myclass, &myclass::idle_cb> (this);	4280	idle.set <myclass, &myclass::idle_cb> (this);
2576		4281
2577	io.start (fd, ev::READ);	4282	io.set (fd, ev::WRITE); // configure the watcher
		4283	io.start (); // start it whenever convenient
		4284
		4285	io2.start (fd, ev::READ); // set + start in one call
2578	}	4286	}
2579	};	4287	};
2580		4288
2581		4289
2582	=head1 OTHER LANGUAGE BINDINGS	4290	=head1 OTHER LANGUAGE BINDINGS
2583		4291
2584	Libev does not offer other language bindings itself, but bindings for a	4292	Libev does not offer other language bindings itself, but bindings for a
2585	numbe rof languages exist in the form of third-party packages. If you know	4293	number of languages exist in the form of third-party packages. If you know
2586	any interesting language binding in addition to the ones listed here, drop	4294	any interesting language binding in addition to the ones listed here, drop
2587	me a note.	4295	me a note.
2588		4296
2589	=over 4	4297	=over 4
2590		4298
2591	=item Perl	4299	=item Perl
2592		4300
2593	The EV module implements the full libev API and is actually used to test	4301	The EV module implements the full libev API and is actually used to test
2594	libev. EV is developed together with libev. Apart from the EV core module,	4302	libev. EV is developed together with libev. Apart from the EV core module,
2595	there are additional modules that implement libev-compatible interfaces	4303	there are additional modules that implement libev-compatible interfaces
2596	to C<libadns> (C<EV::ADNS>), C<Net::SNMP> (C<Net::SNMP::EV>) and the	4304	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
2597	C<libglib> event core (C<Glib::EV> and C<EV::Glib>).	4305	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		4306	and C<EV::Glib>).
2598		4307
2599	It can be found and installed via CPAN, its homepage is found at	4308	It can be found and installed via CPAN, its homepage is at
2600	L<http://software.schmorp.de/pkg/EV>.	4309	L<http://software.schmorp.de/pkg/EV>.
2601		4310
		4311	=item Python
		4312
		4313	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		4314	seems to be quite complete and well-documented.
		4315
2602	=item Ruby	4316	=item Ruby
2603		4317
2604	Tony Arcieri has written a ruby extension that offers access to a subset	4318	Tony Arcieri has written a ruby extension that offers access to a subset
2605	of the libev API and adds filehandle abstractions, asynchronous DNS and	4319	of the libev API and adds file handle abstractions, asynchronous DNS and
2606	more on top of it. It can be found via gem servers. Its homepage is at	4320	more on top of it. It can be found via gem servers. Its homepage is at
2607	L<http://rev.rubyforge.org/>.	4321	L<http://rev.rubyforge.org/>.
2608		4322
		4323	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		4324	makes rev work even on mingw.
		4325
		4326	=item Haskell
		4327
		4328	A haskell binding to libev is available at
		4329	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		4330
2609	=item D	4331	=item D
2610		4332
2611	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4333	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
2612	be found at L<http://git.llucax.com.ar/?p=software/ev.d.git;a=summary>.	4334	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
		4335
		4336	=item Ocaml
		4337
		4338	Erkki Seppala has written Ocaml bindings for libev, to be found at
		4339	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		4340
		4341	=item Lua
		4342
		4343	Brian Maher has written a partial interface to libev for lua (at the
		4344	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		4345	L<http://github.com/brimworks/lua-ev>.
		4346
		4347	=item Javascript
		4348
		4349	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4350
		4351	=item Others
		4352
		4353	There are others, and I stopped counting.
2613		4354
2614	=back	4355	=back
2615		4356
2616		4357
2617	=head1 MACRO MAGIC	4358	=head1 MACRO MAGIC
2618		4359
2619	Libev can be compiled with a variety of options, the most fundamantal	4360	Libev can be compiled with a variety of options, the most fundamental
2620	of which is C<EV_MULTIPLICITY>. This option determines whether (most)	4361	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2621	functions and callbacks have an initial C<struct ev_loop *> argument.	4362	functions and callbacks have an initial C<struct ev_loop *> argument.
2622		4363
2623	To make it easier to write programs that cope with either variant, the	4364	To make it easier to write programs that cope with either variant, the
2624	following macros are defined:	4365	following macros are defined:
…		…
2629		4370
2630	This provides the loop I<argument> for functions, if one is required ("ev	4371	This provides the loop I<argument> for functions, if one is required ("ev
2631	loop argument"). The C<EV_A> form is used when this is the sole argument,	4372	loop argument"). The C<EV_A> form is used when this is the sole argument,
2632	C<EV_A_> is used when other arguments are following. Example:	4373	C<EV_A_> is used when other arguments are following. Example:
2633		4374
2634	ev_unref (EV_A);	4375	ev_unref (EV_A);
2635	ev_timer_add (EV_A_ watcher);	4376	ev_timer_add (EV_A_ watcher);
2636	ev_loop (EV_A_ 0);	4377	ev_run (EV_A_ 0);
2637		4378
2638	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	4379	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2639	which is often provided by the following macro.	4380	which is often provided by the following macro.
2640		4381
2641	=item C<EV_P>, C<EV_P_>	4382	=item C<EV_P>, C<EV_P_>
2642		4383
2643	This provides the loop I<parameter> for functions, if one is required ("ev	4384	This provides the loop I<parameter> for functions, if one is required ("ev
2644	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	4385	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
2645	C<EV_P_> is used when other parameters are following. Example:	4386	C<EV_P_> is used when other parameters are following. Example:
2646		4387
2647	// this is how ev_unref is being declared	4388	// this is how ev_unref is being declared
2648	static void ev_unref (EV_P);	4389	static void ev_unref (EV_P);
2649		4390
2650	// this is how you can declare your typical callback	4391	// this is how you can declare your typical callback
2651	static void cb (EV_P_ ev_timer *w, int revents)	4392	static void cb (EV_P_ ev_timer *w, int revents)
2652		4393
2653	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	4394	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
2654	suitable for use with C<EV_A>.	4395	suitable for use with C<EV_A>.
2655		4396
2656	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4397	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2657		4398
2658	Similar to the other two macros, this gives you the value of the default	4399	Similar to the other two macros, this gives you the value of the default
2659	loop, if multiple loops are supported ("ev loop default").	4400	loop, if multiple loops are supported ("ev loop default"). The default loop
		4401	will be initialised if it isn't already initialised.
		4402
		4403	For non-multiplicity builds, these macros do nothing, so you always have
		4404	to initialise the loop somewhere.
2660		4405
2661	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4406	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
2662		4407
2663	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4408	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
2664	default loop has been initialised (C<UC> == unchecked). Their behaviour	4409	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
2672		4417
2673	Example: Declare and initialise a check watcher, utilising the above	4418	Example: Declare and initialise a check watcher, utilising the above
2674	macros so it will work regardless of whether multiple loops are supported	4419	macros so it will work regardless of whether multiple loops are supported
2675	or not.	4420	or not.
2676		4421
2677	static void	4422	static void
2678	check_cb (EV_P_ ev_timer *w, int revents)	4423	check_cb (EV_P_ ev_timer *w, int revents)
2679	{	4424	{
2680	ev_check_stop (EV_A_ w);	4425	ev_check_stop (EV_A_ w);
2681	}	4426	}
2682		4427
2683	ev_check check;	4428	ev_check check;
2684	ev_check_init (&check, check_cb);	4429	ev_check_init (&check, check_cb);
2685	ev_check_start (EV_DEFAULT_ &check);	4430	ev_check_start (EV_DEFAULT_ &check);
2686	ev_loop (EV_DEFAULT_ 0);	4431	ev_run (EV_DEFAULT_ 0);
2687		4432
2688	=head1 EMBEDDING	4433	=head1 EMBEDDING
2689		4434
2690	Libev can (and often is) directly embedded into host	4435	Libev can (and often is) directly embedded into host
2691	applications. Examples of applications that embed it include the Deliantra	4436	applications. Examples of applications that embed it include the Deliantra
…		…
2698	libev somewhere in your source tree).	4443	libev somewhere in your source tree).
2699		4444
2700	=head2 FILESETS	4445	=head2 FILESETS
2701		4446
2702	Depending on what features you need you need to include one or more sets of files	4447	Depending on what features you need you need to include one or more sets of files
2703	in your app.	4448	in your application.
2704		4449
2705	=head3 CORE EVENT LOOP	4450	=head3 CORE EVENT LOOP
2706		4451
2707	To include only the libev core (all the C<ev_*> functions), with manual	4452	To include only the libev core (all the C<ev_*> functions), with manual
2708	configuration (no autoconf):	4453	configuration (no autoconf):
2709		4454
2710	#define EV_STANDALONE 1	4455	#define EV_STANDALONE 1
2711	#include "ev.c"	4456	#include "ev.c"
2712		4457
2713	This will automatically include F<ev.h>, too, and should be done in a	4458	This will automatically include F<ev.h>, too, and should be done in a
2714	single C source file only to provide the function implementations. To use	4459	single C source file only to provide the function implementations. To use
2715	it, do the same for F<ev.h> in all files wishing to use this API (best	4460	it, do the same for F<ev.h> in all files wishing to use this API (best
2716	done by writing a wrapper around F<ev.h> that you can include instead and	4461	done by writing a wrapper around F<ev.h> that you can include instead and
2717	where you can put other configuration options):	4462	where you can put other configuration options):
2718		4463
2719	#define EV_STANDALONE 1	4464	#define EV_STANDALONE 1
2720	#include "ev.h"	4465	#include "ev.h"
2721		4466
2722	Both header files and implementation files can be compiled with a C++	4467	Both header files and implementation files can be compiled with a C++
2723	compiler (at least, thats a stated goal, and breakage will be treated	4468	compiler (at least, that's a stated goal, and breakage will be treated
2724	as a bug).	4469	as a bug).
2725		4470
2726	You need the following files in your source tree, or in a directory	4471	You need the following files in your source tree, or in a directory
2727	in your include path (e.g. in libev/ when using -Ilibev):	4472	in your include path (e.g. in libev/ when using -Ilibev):
2728		4473
2729	ev.h	4474	ev.h
2730	ev.c	4475	ev.c
2731	ev_vars.h	4476	ev_vars.h
2732	ev_wrap.h	4477	ev_wrap.h
2733		4478
2734	ev_win32.c required on win32 platforms only	4479	ev_win32.c required on win32 platforms only
2735		4480
2736	ev_select.c only when select backend is enabled (which is enabled by default)	4481	ev_select.c only when select backend is enabled
2737	ev_poll.c only when poll backend is enabled (disabled by default)	4482	ev_poll.c only when poll backend is enabled
2738	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4483	ev_epoll.c only when the epoll backend is enabled
		4484	ev_linuxaio.c only when the linux aio backend is enabled
2739	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4485	ev_kqueue.c only when the kqueue backend is enabled
2740	ev_port.c only when the solaris port backend is enabled (disabled by default)	4486	ev_port.c only when the solaris port backend is enabled
2741		4487
2742	F<ev.c> includes the backend files directly when enabled, so you only need	4488	F<ev.c> includes the backend files directly when enabled, so you only need
2743	to compile this single file.	4489	to compile this single file.
2744		4490
2745	=head3 LIBEVENT COMPATIBILITY API	4491	=head3 LIBEVENT COMPATIBILITY API
2746		4492
2747	To include the libevent compatibility API, also include:	4493	To include the libevent compatibility API, also include:
2748		4494
2749	#include "event.c"	4495	#include "event.c"
2750		4496
2751	in the file including F<ev.c>, and:	4497	in the file including F<ev.c>, and:
2752		4498
2753	#include "event.h"	4499	#include "event.h"
2754		4500
2755	in the files that want to use the libevent API. This also includes F<ev.h>.	4501	in the files that want to use the libevent API. This also includes F<ev.h>.
2756		4502
2757	You need the following additional files for this:	4503	You need the following additional files for this:
2758		4504
2759	event.h	4505	event.h
2760	event.c	4506	event.c
2761		4507
2762	=head3 AUTOCONF SUPPORT	4508	=head3 AUTOCONF SUPPORT
2763		4509
2764	Instead of using C<EV_STANDALONE=1> and providing your config in	4510	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2765	whatever way you want, you can also C<m4_include([libev.m4])> in your	4511	whatever way you want, you can also C<m4_include([libev.m4])> in your
2766	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	4512	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2767	include F<config.h> and configure itself accordingly.	4513	include F<config.h> and configure itself accordingly.
2768		4514
2769	For this of course you need the m4 file:	4515	For this of course you need the m4 file:
2770		4516
2771	libev.m4	4517	libev.m4
2772		4518
2773	=head2 PREPROCESSOR SYMBOLS/MACROS	4519	=head2 PREPROCESSOR SYMBOLS/MACROS
2774		4520
2775	Libev can be configured via a variety of preprocessor symbols you have to	4521	Libev can be configured via a variety of preprocessor symbols you have to
2776	define before including any of its files. The default in the absense of	4522	define before including (or compiling) any of its files. The default in
2777	autoconf is noted for every option.	4523	the absence of autoconf is documented for every option.
		4524
		4525	Symbols marked with "(h)" do not change the ABI, and can have different
		4526	values when compiling libev vs. including F<ev.h>, so it is permissible
		4527	to redefine them before including F<ev.h> without breaking compatibility
		4528	to a compiled library. All other symbols change the ABI, which means all
		4529	users of libev and the libev code itself must be compiled with compatible
		4530	settings.
2778		4531
2779	=over 4	4532	=over 4
2780		4533
		4534	=item EV_COMPAT3 (h)
		4535
		4536	Backwards compatibility is a major concern for libev. This is why this
		4537	release of libev comes with wrappers for the functions and symbols that
		4538	have been renamed between libev version 3 and 4.
		4539
		4540	You can disable these wrappers (to test compatibility with future
		4541	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		4542	sources. This has the additional advantage that you can drop the C<struct>
		4543	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		4544	typedef in that case.
		4545
		4546	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		4547	and in some even more future version the compatibility code will be
		4548	removed completely.
		4549
2781	=item EV_STANDALONE	4550	=item EV_STANDALONE (h)
2782		4551
2783	Must always be C<1> if you do not use autoconf configuration, which	4552	Must always be C<1> if you do not use autoconf configuration, which
2784	keeps libev from including F<config.h>, and it also defines dummy	4553	keeps libev from including F<config.h>, and it also defines dummy
2785	implementations for some libevent functions (such as logging, which is not	4554	implementations for some libevent functions (such as logging, which is not
2786	supported). It will also not define any of the structs usually found in	4555	supported). It will also not define any of the structs usually found in
2787	F<event.h> that are not directly supported by the libev core alone.	4556	F<event.h> that are not directly supported by the libev core alone.
2788		4557
		4558	In standalone mode, libev will still try to automatically deduce the
		4559	configuration, but has to be more conservative.
		4560
		4561	=item EV_USE_FLOOR
		4562
		4563	If defined to be C<1>, libev will use the C<floor ()> function for its
		4564	periodic reschedule calculations, otherwise libev will fall back on a
		4565	portable (slower) implementation. If you enable this, you usually have to
		4566	link against libm or something equivalent. Enabling this when the C<floor>
		4567	function is not available will fail, so the safe default is to not enable
		4568	this.
		4569
2789	=item EV_USE_MONOTONIC	4570	=item EV_USE_MONOTONIC
2790		4571
2791	If defined to be C<1>, libev will try to detect the availability of the	4572	If defined to be C<1>, libev will try to detect the availability of the
2792	monotonic clock option at both compiletime and runtime. Otherwise no use	4573	monotonic clock option at both compile time and runtime. Otherwise no
2793	of the monotonic clock option will be attempted. If you enable this, you	4574	use of the monotonic clock option will be attempted. If you enable this,
2794	usually have to link against librt or something similar. Enabling it when	4575	you usually have to link against librt or something similar. Enabling it
2795	the functionality isn't available is safe, though, although you have	4576	when the functionality isn't available is safe, though, although you have
2796	to make sure you link against any libraries where the C<clock_gettime>	4577	to make sure you link against any libraries where the C<clock_gettime>
2797	function is hiding in (often F<-lrt>).	4578	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2798		4579
2799	=item EV_USE_REALTIME	4580	=item EV_USE_REALTIME
2800		4581
2801	If defined to be C<1>, libev will try to detect the availability of the	4582	If defined to be C<1>, libev will try to detect the availability of the
2802	realtime clock option at compiletime (and assume its availability at	4583	real-time clock option at compile time (and assume its availability
2803	runtime if successful). Otherwise no use of the realtime clock option will	4584	at runtime if successful). Otherwise no use of the real-time clock
2804	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	4585	option will be attempted. This effectively replaces C<gettimeofday>
2805	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	4586	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2806	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	4587	correctness. See the note about libraries in the description of
		4588	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		4589	C<EV_USE_CLOCK_SYSCALL>.
		4590
		4591	=item EV_USE_CLOCK_SYSCALL
		4592
		4593	If defined to be C<1>, libev will try to use a direct syscall instead
		4594	of calling the system-provided C<clock_gettime> function. This option
		4595	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		4596	unconditionally pulls in C<libpthread>, slowing down single-threaded
		4597	programs needlessly. Using a direct syscall is slightly slower (in
		4598	theory), because no optimised vdso implementation can be used, but avoids
		4599	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		4600	higher, as it simplifies linking (no need for C<-lrt>).
2807		4601
2808	=item EV_USE_NANOSLEEP	4602	=item EV_USE_NANOSLEEP
2809		4603
2810	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	4604	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2811	and will use it for delays. Otherwise it will use C<select ()>.	4605	and will use it for delays. Otherwise it will use C<select ()>.
…		…
2819	2.7 or newer, otherwise disabled.	4613	2.7 or newer, otherwise disabled.
2820		4614
2821	=item EV_USE_SELECT	4615	=item EV_USE_SELECT
2822		4616
2823	If undefined or defined to be C<1>, libev will compile in support for the	4617	If undefined or defined to be C<1>, libev will compile in support for the
2824	C<select>(2) backend. No attempt at autodetection will be done: if no	4618	C<select>(2) backend. No attempt at auto-detection will be done: if no
2825	other method takes over, select will be it. Otherwise the select backend	4619	other method takes over, select will be it. Otherwise the select backend
2826	will not be compiled in.	4620	will not be compiled in.
2827		4621
2828	=item EV_SELECT_USE_FD_SET	4622	=item EV_SELECT_USE_FD_SET
2829		4623
2830	If defined to C<1>, then the select backend will use the system C<fd_set>	4624	If defined to C<1>, then the select backend will use the system C<fd_set>
2831	structure. This is useful if libev doesn't compile due to a missing	4625	structure. This is useful if libev doesn't compile due to a missing
2832	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	4626	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2833	exotic systems. This usually limits the range of file descriptors to some	4627	on exotic systems. This usually limits the range of file descriptors to
2834	low limit such as 1024 or might have other limitations (winsocket only	4628	some low limit such as 1024 or might have other limitations (winsocket
2835	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	4629	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2836	influence the size of the C<fd_set> used.	4630	configures the maximum size of the C<fd_set>.
2837		4631
2838	=item EV_SELECT_IS_WINSOCKET	4632	=item EV_SELECT_IS_WINSOCKET
2839		4633
2840	When defined to C<1>, the select backend will assume that	4634	When defined to C<1>, the select backend will assume that
2841	select/socket/connect etc. don't understand file descriptors but	4635	select/socket/connect etc. don't understand file descriptors but
…		…
2843	be used is the winsock select). This means that it will call	4637	be used is the winsock select). This means that it will call
2844	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	4638	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2845	it is assumed that all these functions actually work on fds, even	4639	it is assumed that all these functions actually work on fds, even
2846	on win32. Should not be defined on non-win32 platforms.	4640	on win32. Should not be defined on non-win32 platforms.
2847		4641
2848	=item EV_FD_TO_WIN32_HANDLE	4642	=item EV_FD_TO_WIN32_HANDLE(fd)
2849		4643
2850	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map	4644	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
2851	file descriptors to socket handles. When not defining this symbol (the	4645	file descriptors to socket handles. When not defining this symbol (the
2852	default), then libev will call C<_get_osfhandle>, which is usually	4646	default), then libev will call C<_get_osfhandle>, which is usually
2853	correct. In some cases, programs use their own file descriptor management,	4647	correct. In some cases, programs use their own file descriptor management,
2854	in which case they can provide this function to map fds to socket handles.	4648	in which case they can provide this function to map fds to socket handles.
2855		4649
		4650	=item EV_WIN32_HANDLE_TO_FD(handle)
		4651
		4652	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		4653	using the standard C<_open_osfhandle> function. For programs implementing
		4654	their own fd to handle mapping, overwriting this function makes it easier
		4655	to do so. This can be done by defining this macro to an appropriate value.
		4656
		4657	=item EV_WIN32_CLOSE_FD(fd)
		4658
		4659	If programs implement their own fd to handle mapping on win32, then this
		4660	macro can be used to override the C<close> function, useful to unregister
		4661	file descriptors again. Note that the replacement function has to close
		4662	the underlying OS handle.
		4663
		4664	=item EV_USE_WSASOCKET
		4665
		4666	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4667	communication socket, which works better in some environments. Otherwise,
		4668	the normal C<socket> function will be used, which works better in other
		4669	environments.
		4670
2856	=item EV_USE_POLL	4671	=item EV_USE_POLL
2857		4672
2858	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4673	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2859	backend. Otherwise it will be enabled on non-win32 platforms. It	4674	backend. Otherwise it will be enabled on non-win32 platforms. It
2860	takes precedence over select.	4675	takes precedence over select.
…		…
2864	If defined to be C<1>, libev will compile in support for the Linux	4679	If defined to be C<1>, libev will compile in support for the Linux
2865	C<epoll>(7) backend. Its availability will be detected at runtime,	4680	C<epoll>(7) backend. Its availability will be detected at runtime,
2866	otherwise another method will be used as fallback. This is the preferred	4681	otherwise another method will be used as fallback. This is the preferred
2867	backend for GNU/Linux systems. If undefined, it will be enabled if the	4682	backend for GNU/Linux systems. If undefined, it will be enabled if the
2868	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4683	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4684
		4685	=item EV_USE_LINUXAIO
		4686
		4687	If defined to be C<1>, libev will compile in support for the Linux
		4688	aio backend. Due to it's currenbt limitations it has to be requested
		4689	explicitly. If undefined, it will be enabled on linux, otherwise
		4690	disabled.
2869		4691
2870	=item EV_USE_KQUEUE	4692	=item EV_USE_KQUEUE
2871		4693
2872	If defined to be C<1>, libev will compile in support for the BSD style	4694	If defined to be C<1>, libev will compile in support for the BSD style
2873	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	4695	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2886	otherwise another method will be used as fallback. This is the preferred	4708	otherwise another method will be used as fallback. This is the preferred
2887	backend for Solaris 10 systems.	4709	backend for Solaris 10 systems.
2888		4710
2889	=item EV_USE_DEVPOLL	4711	=item EV_USE_DEVPOLL
2890		4712
2891	reserved for future expansion, works like the USE symbols above.	4713	Reserved for future expansion, works like the USE symbols above.
2892		4714
2893	=item EV_USE_INOTIFY	4715	=item EV_USE_INOTIFY
2894		4716
2895	If defined to be C<1>, libev will compile in support for the Linux inotify	4717	If defined to be C<1>, libev will compile in support for the Linux inotify
2896	interface to speed up C<ev_stat> watchers. Its actual availability will	4718	interface to speed up C<ev_stat> watchers. Its actual availability will
2897	be detected at runtime. If undefined, it will be enabled if the headers	4719	be detected at runtime. If undefined, it will be enabled if the headers
2898	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4720	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2899		4721
		4722	=item EV_NO_SMP
		4723
		4724	If defined to be C<1>, libev will assume that memory is always coherent
		4725	between threads, that is, threads can be used, but threads never run on
		4726	different cpus (or different cpu cores). This reduces dependencies
		4727	and makes libev faster.
		4728
		4729	=item EV_NO_THREADS
		4730
		4731	If defined to be C<1>, libev will assume that it will never be called from
		4732	different threads (that includes signal handlers), which is a stronger
		4733	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4734	libev faster.
		4735
2900	=item EV_ATOMIC_T	4736	=item EV_ATOMIC_T
2901		4737
2902	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4738	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
2903	access is atomic with respect to other threads or signal contexts. No such	4739	access is atomic with respect to other threads or signal contexts. No
2904	type is easily found in the C language, so you can provide your own type	4740	such type is easily found in the C language, so you can provide your own
2905	that you know is safe for your purposes. It is used both for signal handler "locking"	4741	type that you know is safe for your purposes. It is used both for signal
2906	as well as for signal and thread safety in C<ev_async> watchers.	4742	handler "locking" as well as for signal and thread safety in C<ev_async>
		4743	watchers.
2907		4744
2908	In the absense of this define, libev will use C<sig_atomic_t volatile>	4745	In the absence of this define, libev will use C<sig_atomic_t volatile>
2909	(from F<signal.h>), which is usually good enough on most platforms.	4746	(from F<signal.h>), which is usually good enough on most platforms.
2910		4747
2911	=item EV_H	4748	=item EV_H (h)
2912		4749
2913	The name of the F<ev.h> header file used to include it. The default if	4750	The name of the F<ev.h> header file used to include it. The default if
2914	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be	4751	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2915	used to virtually rename the F<ev.h> header file in case of conflicts.	4752	used to virtually rename the F<ev.h> header file in case of conflicts.
2916		4753
2917	=item EV_CONFIG_H	4754	=item EV_CONFIG_H (h)
2918		4755
2919	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	4756	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2920	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	4757	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2921	C<EV_H>, above.	4758	C<EV_H>, above.
2922		4759
2923	=item EV_EVENT_H	4760	=item EV_EVENT_H (h)
2924		4761
2925	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	4762	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2926	of how the F<event.h> header can be found, the default is C<"event.h">.	4763	of how the F<event.h> header can be found, the default is C<"event.h">.
2927		4764
2928	=item EV_PROTOTYPES	4765	=item EV_PROTOTYPES (h)
2929		4766
2930	If defined to be C<0>, then F<ev.h> will not define any function	4767	If defined to be C<0>, then F<ev.h> will not define any function
2931	prototypes, but still define all the structs and other symbols. This is	4768	prototypes, but still define all the structs and other symbols. This is
2932	occasionally useful if you want to provide your own wrapper functions	4769	occasionally useful if you want to provide your own wrapper functions
2933	around libev functions.	4770	around libev functions.
…		…
2938	will have the C<struct ev_loop *> as first argument, and you can create	4775	will have the C<struct ev_loop *> as first argument, and you can create
2939	additional independent event loops. Otherwise there will be no support	4776	additional independent event loops. Otherwise there will be no support
2940	for multiple event loops and there is no first event loop pointer	4777	for multiple event loops and there is no first event loop pointer
2941	argument. Instead, all functions act on the single default loop.	4778	argument. Instead, all functions act on the single default loop.
2942		4779
		4780	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4781	default loop when multiplicity is switched off - you always have to
		4782	initialise the loop manually in this case.
		4783
2943	=item EV_MINPRI	4784	=item EV_MINPRI
2944		4785
2945	=item EV_MAXPRI	4786	=item EV_MAXPRI
2946		4787
2947	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4788	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
2952	When doing priority-based operations, libev usually has to linearly search	4793	When doing priority-based operations, libev usually has to linearly search
2953	all the priorities, so having many of them (hundreds) uses a lot of space	4794	all the priorities, so having many of them (hundreds) uses a lot of space
2954	and time, so using the defaults of five priorities (-2 .. +2) is usually	4795	and time, so using the defaults of five priorities (-2 .. +2) is usually
2955	fine.	4796	fine.
2956		4797
2957	If your embedding app does not need any priorities, defining these both to	4798	If your embedding application does not need any priorities, defining these
2958	C<0> will save some memory and cpu.	4799	both to C<0> will save some memory and CPU.
2959		4800
2960	=item EV_PERIODIC_ENABLE	4801	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		4802	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		4803	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
2961		4804
2962	If undefined or defined to be C<1>, then periodic timers are supported. If	4805	If undefined or defined to be C<1> (and the platform supports it), then
2963	defined to be C<0>, then they are not. Disabling them saves a few kB of	4806	the respective watcher type is supported. If defined to be C<0>, then it
2964	code.	4807	is not. Disabling watcher types mainly saves code size.
2965		4808
2966	=item EV_IDLE_ENABLE	4809	=item EV_FEATURES
2967
2968	If undefined or defined to be C<1>, then idle watchers are supported. If
2969	defined to be C<0>, then they are not. Disabling them saves a few kB of
2970	code.
2971
2972	=item EV_EMBED_ENABLE
2973
2974	If undefined or defined to be C<1>, then embed watchers are supported. If
2975	defined to be C<0>, then they are not.
2976
2977	=item EV_STAT_ENABLE
2978
2979	If undefined or defined to be C<1>, then stat watchers are supported. If
2980	defined to be C<0>, then they are not.
2981
2982	=item EV_FORK_ENABLE
2983
2984	If undefined or defined to be C<1>, then fork watchers are supported. If
2985	defined to be C<0>, then they are not.
2986
2987	=item EV_ASYNC_ENABLE
2988
2989	If undefined or defined to be C<1>, then async watchers are supported. If
2990	defined to be C<0>, then they are not.
2991
2992	=item EV_MINIMAL
2993		4810
2994	If you need to shave off some kilobytes of code at the expense of some	4811	If you need to shave off some kilobytes of code at the expense of some
2995	speed, define this symbol to C<1>. Currently this is used to override some	4812	speed (but with the full API), you can define this symbol to request
2996	inlining decisions, saves roughly 30% codesize of amd64. It also selects a	4813	certain subsets of functionality. The default is to enable all features
2997	much smaller 2-heap for timer management over the default 4-heap.	4814	that can be enabled on the platform.
		4815
		4816	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4817	with some broad features you want) and then selectively re-enable
		4818	additional parts you want, for example if you want everything minimal,
		4819	but multiple event loop support, async and child watchers and the poll
		4820	backend, use this:
		4821
		4822	#define EV_FEATURES 0
		4823	#define EV_MULTIPLICITY 1
		4824	#define EV_USE_POLL 1
		4825	#define EV_CHILD_ENABLE 1
		4826	#define EV_ASYNC_ENABLE 1
		4827
		4828	The actual value is a bitset, it can be a combination of the following
		4829	values (by default, all of these are enabled):
		4830
		4831	=over 4
		4832
		4833	=item C<1> - faster/larger code
		4834
		4835	Use larger code to speed up some operations.
		4836
		4837	Currently this is used to override some inlining decisions (enlarging the
		4838	code size by roughly 30% on amd64).
		4839
		4840	When optimising for size, use of compiler flags such as C<-Os> with
		4841	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4842	assertions.
		4843
		4844	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4845	(e.g. gcc with C<-Os>).
		4846
		4847	=item C<2> - faster/larger data structures
		4848
		4849	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4850	hash table sizes and so on. This will usually further increase code size
		4851	and can additionally have an effect on the size of data structures at
		4852	runtime.
		4853
		4854	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4855	(e.g. gcc with C<-Os>).
		4856
		4857	=item C<4> - full API configuration
		4858
		4859	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4860	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4861
		4862	=item C<8> - full API
		4863
		4864	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4865	details on which parts of the API are still available without this
		4866	feature, and do not complain if this subset changes over time.
		4867
		4868	=item C<16> - enable all optional watcher types
		4869
		4870	Enables all optional watcher types. If you want to selectively enable
		4871	only some watcher types other than I/O and timers (e.g. prepare,
		4872	embed, async, child...) you can enable them manually by defining
		4873	C<EV_watchertype_ENABLE> to C<1> instead.
		4874
		4875	=item C<32> - enable all backends
		4876
		4877	This enables all backends - without this feature, you need to enable at
		4878	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4879
		4880	=item C<64> - enable OS-specific "helper" APIs
		4881
		4882	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4883	default.
		4884
		4885	=back
		4886
		4887	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4888	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4889	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4890	watchers, timers and monotonic clock support.
		4891
		4892	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4893	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4894	your program might be left out as well - a binary starting a timer and an
		4895	I/O watcher then might come out at only 5Kb.
		4896
		4897	=item EV_API_STATIC
		4898
		4899	If this symbol is defined (by default it is not), then all identifiers
		4900	will have static linkage. This means that libev will not export any
		4901	identifiers, and you cannot link against libev anymore. This can be useful
		4902	when you embed libev, only want to use libev functions in a single file,
		4903	and do not want its identifiers to be visible.
		4904
		4905	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4906	wants to use libev.
		4907
		4908	This option only works when libev is compiled with a C compiler, as C++
		4909	doesn't support the required declaration syntax.
		4910
		4911	=item EV_AVOID_STDIO
		4912
		4913	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4914	functions (printf, scanf, perror etc.). This will increase the code size
		4915	somewhat, but if your program doesn't otherwise depend on stdio and your
		4916	libc allows it, this avoids linking in the stdio library which is quite
		4917	big.
		4918
		4919	Note that error messages might become less precise when this option is
		4920	enabled.
		4921
		4922	=item EV_NSIG
		4923
		4924	The highest supported signal number, +1 (or, the number of
		4925	signals): Normally, libev tries to deduce the maximum number of signals
		4926	automatically, but sometimes this fails, in which case it can be
		4927	specified. Also, using a lower number than detected (C<32> should be
		4928	good for about any system in existence) can save some memory, as libev
		4929	statically allocates some 12-24 bytes per signal number.
2998		4930
2999	=item EV_PID_HASHSIZE	4931	=item EV_PID_HASHSIZE
3000		4932
3001	C<ev_child> watchers use a small hash table to distribute workload by	4933	C<ev_child> watchers use a small hash table to distribute workload by
3002	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	4934	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
3003	than enough. If you need to manage thousands of children you might want to	4935	usually more than enough. If you need to manage thousands of children you
3004	increase this value (I<must> be a power of two).	4936	might want to increase this value (I<must> be a power of two).
3005		4937
3006	=item EV_INOTIFY_HASHSIZE	4938	=item EV_INOTIFY_HASHSIZE
3007		4939
3008	C<ev_stat> watchers use a small hash table to distribute workload by	4940	C<ev_stat> watchers use a small hash table to distribute workload by
3009	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	4941	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
3010	usually more than enough. If you need to manage thousands of C<ev_stat>	4942	disabled), usually more than enough. If you need to manage thousands of
3011	watchers you might want to increase this value (I<must> be a power of	4943	C<ev_stat> watchers you might want to increase this value (I<must> be a
3012	two).	4944	power of two).
3013		4945
3014	=item EV_USE_4HEAP	4946	=item EV_USE_4HEAP
3015		4947
3016	Heaps are not very cache-efficient. To improve the cache-efficiency of the	4948	Heaps are not very cache-efficient. To improve the cache-efficiency of the
3017	timer and periodics heap, libev uses a 4-heap when this symbol is defined	4949	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
3018	to C<1>. The 4-heap uses more complicated (longer) code but has	4950	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
3019	noticably faster performance with many (thousands) of watchers.	4951	faster performance with many (thousands) of watchers.
3020		4952
3021	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	4953	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3022	(disabled).	4954	will be C<0>.
3023		4955
3024	=item EV_HEAP_CACHE_AT	4956	=item EV_HEAP_CACHE_AT
3025		4957
3026	Heaps are not very cache-efficient. To improve the cache-efficiency of the	4958	Heaps are not very cache-efficient. To improve the cache-efficiency of the
3027	timer and periodics heap, libev can cache the timestamp (I<at>) within	4959	timer and periodics heaps, libev can cache the timestamp (I<at>) within
3028	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),	4960	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
3029	which uses 8-12 bytes more per watcher and a few hundred bytes more code,	4961	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
3030	but avoids random read accesses on heap changes. This improves performance	4962	but avoids random read accesses on heap changes. This improves performance
3031	noticably with with many (hundreds) of watchers.	4963	noticeably with many (hundreds) of watchers.
3032		4964
3033	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	4965	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3034	(disabled).	4966	will be C<0>.
		4967
		4968	=item EV_VERIFY
		4969
		4970	Controls how much internal verification (see C<ev_verify ()>) will
		4971	be done: If set to C<0>, no internal verification code will be compiled
		4972	in. If set to C<1>, then verification code will be compiled in, but not
		4973	called. If set to C<2>, then the internal verification code will be
		4974	called once per loop, which can slow down libev. If set to C<3>, then the
		4975	verification code will be called very frequently, which will slow down
		4976	libev considerably.
		4977
		4978	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4979	will be C<0>.
3035		4980
3036	=item EV_COMMON	4981	=item EV_COMMON
3037		4982
3038	By default, all watchers have a C<void *data> member. By redefining	4983	By default, all watchers have a C<void *data> member. By redefining
3039	this macro to a something else you can include more and other types of	4984	this macro to something else you can include more and other types of
3040	members. You have to define it each time you include one of the files,	4985	members. You have to define it each time you include one of the files,
3041	though, and it must be identical each time.	4986	though, and it must be identical each time.
3042		4987
3043	For example, the perl EV module uses something like this:	4988	For example, the perl EV module uses something like this:
3044		4989
3045	#define EV_COMMON \	4990	#define EV_COMMON \
3046	SV *self; /* contains this struct */ \	4991	SV *self; /* contains this struct */ \
3047	SV *cb_sv, *fh /* note no trailing ";" */	4992	SV *cb_sv, *fh /* note no trailing ";" */
3048		4993
3049	=item EV_CB_DECLARE (type)	4994	=item EV_CB_DECLARE (type)
3050		4995
3051	=item EV_CB_INVOKE (watcher, revents)	4996	=item EV_CB_INVOKE (watcher, revents)
3052		4997
…		…
3057	definition and a statement, respectively. See the F<ev.h> header file for	5002	definition and a statement, respectively. See the F<ev.h> header file for
3058	their default definitions. One possible use for overriding these is to	5003	their default definitions. One possible use for overriding these is to
3059	avoid the C<struct ev_loop *> as first argument in all cases, or to use	5004	avoid the C<struct ev_loop *> as first argument in all cases, or to use
3060	method calls instead of plain function calls in C++.	5005	method calls instead of plain function calls in C++.
3061		5006
		5007	=back
		5008
3062	=head2 EXPORTED API SYMBOLS	5009	=head2 EXPORTED API SYMBOLS
3063		5010
3064	If you need to re-export the API (e.g. via a dll) and you need a list of	5011	If you need to re-export the API (e.g. via a DLL) and you need a list of
3065	exported symbols, you can use the provided F<Symbol.*> files which list	5012	exported symbols, you can use the provided F<Symbol.*> files which list
3066	all public symbols, one per line:	5013	all public symbols, one per line:
3067		5014
3068	Symbols.ev for libev proper	5015	Symbols.ev for libev proper
3069	Symbols.event for the libevent emulation	5016	Symbols.event for the libevent emulation
3070		5017
3071	This can also be used to rename all public symbols to avoid clashes with	5018	This can also be used to rename all public symbols to avoid clashes with
3072	multiple versions of libev linked together (which is obviously bad in	5019	multiple versions of libev linked together (which is obviously bad in
3073	itself, but sometimes it is inconvinient to avoid this).	5020	itself, but sometimes it is inconvenient to avoid this).
3074		5021
3075	A sed command like this will create wrapper C<#define>'s that you need to	5022	A sed command like this will create wrapper C<#define>'s that you need to
3076	include before including F<ev.h>:	5023	include before including F<ev.h>:
3077		5024
3078	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h	5025	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
…		…
3095	file.	5042	file.
3096		5043
3097	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	5044	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
3098	that everybody includes and which overrides some configure choices:	5045	that everybody includes and which overrides some configure choices:
3099		5046
3100	#define EV_MINIMAL 1	5047	#define EV_FEATURES 8
3101	#define EV_USE_POLL 0	5048	#define EV_USE_SELECT 1
3102	#define EV_MULTIPLICITY 0
3103	#define EV_PERIODIC_ENABLE 0	5049	#define EV_PREPARE_ENABLE 1
		5050	#define EV_IDLE_ENABLE 1
3104	#define EV_STAT_ENABLE 0	5051	#define EV_SIGNAL_ENABLE 1
3105	#define EV_FORK_ENABLE 0	5052	#define EV_CHILD_ENABLE 1
		5053	#define EV_USE_STDEXCEPT 0
3106	#define EV_CONFIG_H <config.h>	5054	#define EV_CONFIG_H <config.h>
3107	#define EV_MINPRI 0
3108	#define EV_MAXPRI 0
3109		5055
3110	#include "ev++.h"	5056	#include "ev++.h"
3111		5057
3112	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	5058	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
3113		5059
3114	#include "ev_cpp.h"	5060	#include "ev_cpp.h"
3115	#include "ev.c"	5061	#include "ev.c"
3116		5062
		5063	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
3117		5064
3118	=head1 THREADS AND COROUTINES	5065	=head2 THREADS AND COROUTINES
3119		5066
3120	=head2 THREADS	5067	=head3 THREADS
3121		5068
3122	Libev itself is completely threadsafe, but it uses no locking. This	5069	All libev functions are reentrant and thread-safe unless explicitly
		5070	documented otherwise, but libev implements no locking itself. This means
3123	means that you can use as many loops as you want in parallel, as long as	5071	that you can use as many loops as you want in parallel, as long as there
3124	only one thread ever calls into one libev function with the same loop	5072	are no concurrent calls into any libev function with the same loop
3125	parameter.	5073	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		5074	of course): libev guarantees that different event loops share no data
		5075	structures that need any locking.
3126		5076
3127	Or put differently: calls with different loop parameters can be done in	5077	Or to put it differently: calls with different loop parameters can be done
3128	parallel from multiple threads, calls with the same loop parameter must be	5078	concurrently from multiple threads, calls with the same loop parameter
3129	done serially (but can be done from different threads, as long as only one	5079	must be done serially (but can be done from different threads, as long as
3130	thread ever is inside a call at any point in time, e.g. by using a mutex	5080	only one thread ever is inside a call at any point in time, e.g. by using
3131	per loop).	5081	a mutex per loop).
3132		5082
3133	If you want to know which design is best for your problem, then I cannot	5083	Specifically to support threads (and signal handlers), libev implements
		5084	so-called C<ev_async> watchers, which allow some limited form of
		5085	concurrency on the same event loop, namely waking it up "from the
		5086	outside".
		5087
		5088	If you want to know which design (one loop, locking, or multiple loops
		5089	without or something else still) is best for your problem, then I cannot
3134	help you but by giving some generic advice:	5090	help you, but here is some generic advice:
3135		5091
3136	=over 4	5092	=over 4
3137		5093
3138	=item * most applications have a main thread: use the default libev loop	5094	=item * most applications have a main thread: use the default libev loop
3139	in that thread, or create a seperate thread running only the default loop.	5095	in that thread, or create a separate thread running only the default loop.
3140		5096
3141	This helps integrating other libraries or software modules that use libev	5097	This helps integrating other libraries or software modules that use libev
3142	themselves and don't care/know about threading.	5098	themselves and don't care/know about threading.
3143		5099
3144	=item * one loop per thread is usually a good model.	5100	=item * one loop per thread is usually a good model.
3145		5101
3146	Doing this is almost never wrong, sometimes a better-performance model	5102	Doing this is almost never wrong, sometimes a better-performance model
3147	exists, but it is always a good start.	5103	exists, but it is always a good start.
3148		5104
3149	=item * other models exist, such as the leader/follower pattern, where one	5105	=item * other models exist, such as the leader/follower pattern, where one
3150	loop is handed through multiple threads in a kind of round-robbin fashion.	5106	loop is handed through multiple threads in a kind of round-robin fashion.
3151		5107
3152	Chosing a model is hard - look around, learn, know that usually you cna do	5108	Choosing a model is hard - look around, learn, know that usually you can do
3153	better than you currently do :-)	5109	better than you currently do :-)
3154		5110
3155	=item * often you need to talk to some other thread which blocks in the	5111	=item * often you need to talk to some other thread which blocks in the
		5112	event loop.
		5113
3156	event loop - C<ev_async> watchers can be used to wake them up from other	5114	C<ev_async> watchers can be used to wake them up from other threads safely
3157	threads safely (or from signal contexts...).	5115	(or from signal contexts...).
		5116
		5117	An example use would be to communicate signals or other events that only
		5118	work in the default loop by registering the signal watcher with the
		5119	default loop and triggering an C<ev_async> watcher from the default loop
		5120	watcher callback into the event loop interested in the signal.
3158		5121
3159	=back	5122	=back
3160		5123
		5124	See also L</THREAD LOCKING EXAMPLE>.
		5125
3161	=head2 COROUTINES	5126	=head3 COROUTINES
3162		5127
3163	Libev is much more accomodating to coroutines ("cooperative threads"):	5128	Libev is very accommodating to coroutines ("cooperative threads"):
3164	libev fully supports nesting calls to it's functions from different	5129	libev fully supports nesting calls to its functions from different
3165	coroutines (e.g. you can call C<ev_loop> on the same loop from two	5130	coroutines (e.g. you can call C<ev_run> on the same loop from two
3166	different coroutines and switch freely between both coroutines running the	5131	different coroutines, and switch freely between both coroutines running
3167	loop, as long as you don't confuse yourself). The only exception is that	5132	the loop, as long as you don't confuse yourself). The only exception is
3168	you must not do this from C<ev_periodic> reschedule callbacks.	5133	that you must not do this from C<ev_periodic> reschedule callbacks.
3169		5134
3170	Care has been invested into making sure that libev does not keep local	5135	Care has been taken to ensure that libev does not keep local state inside
3171	state inside C<ev_loop>, and other calls do not usually allow coroutine	5136	C<ev_run>, and other calls do not usually allow for coroutine switches as
3172	switches.	5137	they do not call any callbacks.
3173		5138
		5139	=head2 COMPILER WARNINGS
3174		5140
3175	=head1 COMPLEXITIES	5141	Depending on your compiler and compiler settings, you might get no or a
		5142	lot of warnings when compiling libev code. Some people are apparently
		5143	scared by this.
3176		5144
3177	In this section the complexities of (many of) the algorithms used inside	5145	However, these are unavoidable for many reasons. For one, each compiler
3178	libev will be explained. For complexity discussions about backends see the	5146	has different warnings, and each user has different tastes regarding
3179	documentation for C<ev_default_init>.	5147	warning options. "Warn-free" code therefore cannot be a goal except when
		5148	targeting a specific compiler and compiler-version.
3180		5149
3181	All of the following are about amortised time: If an array needs to be	5150	Another reason is that some compiler warnings require elaborate
3182	extended, libev needs to realloc and move the whole array, but this	5151	workarounds, or other changes to the code that make it less clear and less
3183	happens asymptotically never with higher number of elements, so O(1) might	5152	maintainable.
3184	mean it might do a lengthy realloc operation in rare cases, but on average
3185	it is much faster and asymptotically approaches constant time.
3186		5153
3187	=over 4	5154	And of course, some compiler warnings are just plain stupid, or simply
		5155	wrong (because they don't actually warn about the condition their message
		5156	seems to warn about). For example, certain older gcc versions had some
		5157	warnings that resulted in an extreme number of false positives. These have
		5158	been fixed, but some people still insist on making code warn-free with
		5159	such buggy versions.
3188		5160
3189	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	5161	While libev is written to generate as few warnings as possible,
		5162	"warn-free" code is not a goal, and it is recommended not to build libev
		5163	with any compiler warnings enabled unless you are prepared to cope with
		5164	them (e.g. by ignoring them). Remember that warnings are just that:
		5165	warnings, not errors, or proof of bugs.
3190		5166
3191	This means that, when you have a watcher that triggers in one hour and
3192	there are 100 watchers that would trigger before that then inserting will
3193	have to skip roughly seven (C<ld 100>) of these watchers.
3194		5167
3195	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)	5168	=head2 VALGRIND
3196		5169
3197	That means that changing a timer costs less than removing/adding them	5170	Valgrind has a special section here because it is a popular tool that is
3198	as only the relative motion in the event queue has to be paid for.	5171	highly useful. Unfortunately, valgrind reports are very hard to interpret.
3199		5172
3200	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)	5173	If you think you found a bug (memory leak, uninitialised data access etc.)
		5174	in libev, then check twice: If valgrind reports something like:
3201		5175
3202	These just add the watcher into an array or at the head of a list.	5176	==2274== definitely lost: 0 bytes in 0 blocks.
		5177	==2274== possibly lost: 0 bytes in 0 blocks.
		5178	==2274== still reachable: 256 bytes in 1 blocks.
3203		5179
3204	=item Stopping check/prepare/idle/fork/async watchers: O(1)	5180	Then there is no memory leak, just as memory accounted to global variables
		5181	is not a memleak - the memory is still being referenced, and didn't leak.
3205		5182
3206	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	5183	Similarly, under some circumstances, valgrind might report kernel bugs
		5184	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		5185	although an acceptable workaround has been found here), or it might be
		5186	confused.
3207		5187
3208	These watchers are stored in lists then need to be walked to find the	5188	Keep in mind that valgrind is a very good tool, but only a tool. Don't
3209	correct watcher to remove. The lists are usually short (you don't usually	5189	make it into some kind of religion.
3210	have many watchers waiting for the same fd or signal).
3211		5190
3212	=item Finding the next timer in each loop iteration: O(1)	5191	If you are unsure about something, feel free to contact the mailing list
		5192	with the full valgrind report and an explanation on why you think this
		5193	is a bug in libev (best check the archives, too :). However, don't be
		5194	annoyed when you get a brisk "this is no bug" answer and take the chance
		5195	of learning how to interpret valgrind properly.
3213		5196
3214	By virtue of using a binary or 4-heap, the next timer is always found at a	5197	If you need, for some reason, empty reports from valgrind for your project
3215	fixed position in the storage array.	5198	I suggest using suppression lists.
3216		5199
3217	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
3218		5200
3219	A change means an I/O watcher gets started or stopped, which requires	5201	=head1 PORTABILITY NOTES
3220	libev to recalculate its status (and possibly tell the kernel, depending
3221	on backend and wether C<ev_io_set> was used).
3222		5202
3223	=item Activating one watcher (putting it into the pending state): O(1)	5203	=head2 GNU/LINUX 32 BIT LIMITATIONS
3224		5204
3225	=item Priority handling: O(number_of_priorities)	5205	GNU/Linux is the only common platform that supports 64 bit file/large file
		5206	interfaces but I<disables> them by default.
3226		5207
3227	Priorities are implemented by allocating some space for each	5208	That means that libev compiled in the default environment doesn't support
3228	priority. When doing priority-based operations, libev usually has to	5209	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
3229	linearly search all the priorities, but starting/stopping and activating
3230	watchers becomes O(1) w.r.t. priority handling.
3231		5210
3232	=item Sending an ev_async: O(1)	5211	Unfortunately, many programs try to work around this GNU/Linux issue
		5212	by enabling the large file API, which makes them incompatible with the
		5213	standard libev compiled for their system.
3233		5214
3234	=item Processing ev_async_send: O(number_of_async_watchers)	5215	Likewise, libev cannot enable the large file API itself as this would
		5216	suddenly make it incompatible to the default compile time environment,
		5217	i.e. all programs not using special compile switches.
3235		5218
3236	=item Processing signals: O(max_signal_number)	5219	=head2 OS/X AND DARWIN BUGS
3237		5220
3238	Sending involves a syscall I<iff> there were no other C<ev_async_send>	5221	The whole thing is a bug if you ask me - basically any system interface
3239	calls in the current loop iteration. Checking for async and signal events	5222	you touch is broken, whether it is locales, poll, kqueue or even the
3240	involves iterating over all running async watchers or all signal numbers.	5223	OpenGL drivers.
3241		5224
3242	=back	5225	=head3 C<kqueue> is buggy
3243		5226
		5227	The kqueue syscall is broken in all known versions - most versions support
		5228	only sockets, many support pipes.
3244		5229
3245	=head1 Win32 platform limitations and workarounds	5230	Libev tries to work around this by not using C<kqueue> by default on this
		5231	rotten platform, but of course you can still ask for it when creating a
		5232	loop - embedding a socket-only kqueue loop into a select-based one is
		5233	probably going to work well.
		5234
		5235	=head3 C<poll> is buggy
		5236
		5237	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		5238	implementation by something calling C<kqueue> internally around the 10.5.6
		5239	release, so now C<kqueue> I<and> C<poll> are broken.
		5240
		5241	Libev tries to work around this by not using C<poll> by default on
		5242	this rotten platform, but of course you can still ask for it when creating
		5243	a loop.
		5244
		5245	=head3 C<select> is buggy
		5246
		5247	All that's left is C<select>, and of course Apple found a way to fuck this
		5248	one up as well: On OS/X, C<select> actively limits the number of file
		5249	descriptors you can pass in to 1024 - your program suddenly crashes when
		5250	you use more.
		5251
		5252	There is an undocumented "workaround" for this - defining
		5253	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		5254	work on OS/X.
		5255
		5256	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		5257
		5258	=head3 C<errno> reentrancy
		5259
		5260	The default compile environment on Solaris is unfortunately so
		5261	thread-unsafe that you can't even use components/libraries compiled
		5262	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		5263	defined by default. A valid, if stupid, implementation choice.
		5264
		5265	If you want to use libev in threaded environments you have to make sure
		5266	it's compiled with C<_REENTRANT> defined.
		5267
		5268	=head3 Event port backend
		5269
		5270	The scalable event interface for Solaris is called "event
		5271	ports". Unfortunately, this mechanism is very buggy in all major
		5272	releases. If you run into high CPU usage, your program freezes or you get
		5273	a large number of spurious wakeups, make sure you have all the relevant
		5274	and latest kernel patches applied. No, I don't know which ones, but there
		5275	are multiple ones to apply, and afterwards, event ports actually work
		5276	great.
		5277
		5278	If you can't get it to work, you can try running the program by setting
		5279	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		5280	C<select> backends.
		5281
		5282	=head2 AIX POLL BUG
		5283
		5284	AIX unfortunately has a broken C<poll.h> header. Libev works around
		5285	this by trying to avoid the poll backend altogether (i.e. it's not even
		5286	compiled in), which normally isn't a big problem as C<select> works fine
		5287	with large bitsets on AIX, and AIX is dead anyway.
		5288
		5289	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		5290
		5291	=head3 General issues
3246		5292
3247	Win32 doesn't support any of the standards (e.g. POSIX) that libev	5293	Win32 doesn't support any of the standards (e.g. POSIX) that libev
3248	requires, and its I/O model is fundamentally incompatible with the POSIX	5294	requires, and its I/O model is fundamentally incompatible with the POSIX
3249	model. Libev still offers limited functionality on this platform in	5295	model. Libev still offers limited functionality on this platform in
3250	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5296	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
3251	descriptors. This only applies when using Win32 natively, not when using	5297	descriptors. This only applies when using Win32 natively, not when using
3252	e.g. cygwin.	5298	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		5299	as every compiler comes with a slightly differently broken/incompatible
		5300	environment.
3253		5301
3254	Lifting these limitations would basically require the full	5302	Lifting these limitations would basically require the full
3255	re-implementation of the I/O system. If you are into these kinds of	5303	re-implementation of the I/O system. If you are into this kind of thing,
3256	things, then note that glib does exactly that for you in a very portable	5304	then note that glib does exactly that for you in a very portable way (note
3257	way (note also that glib is the slowest event library known to man).	5305	also that glib is the slowest event library known to man).
3258		5306
3259	There is no supported compilation method available on windows except	5307	There is no supported compilation method available on windows except
3260	embedding it into other applications.	5308	embedding it into other applications.
		5309
		5310	Sensible signal handling is officially unsupported by Microsoft - libev
		5311	tries its best, but under most conditions, signals will simply not work.
		5312
		5313	Not a libev limitation but worth mentioning: windows apparently doesn't
		5314	accept large writes: instead of resulting in a partial write, windows will
		5315	either accept everything or return C<ENOBUFS> if the buffer is too large,
		5316	so make sure you only write small amounts into your sockets (less than a
		5317	megabyte seems safe, but this apparently depends on the amount of memory
		5318	available).
3261		5319
3262	Due to the many, low, and arbitrary limits on the win32 platform and	5320	Due to the many, low, and arbitrary limits on the win32 platform and
3263	the abysmal performance of winsockets, using a large number of sockets	5321	the abysmal performance of winsockets, using a large number of sockets
3264	is not recommended (and not reasonable). If your program needs to use	5322	is not recommended (and not reasonable). If your program needs to use
3265	more than a hundred or so sockets, then likely it needs to use a totally	5323	more than a hundred or so sockets, then likely it needs to use a totally
3266	different implementation for windows, as libev offers the POSIX readiness	5324	different implementation for windows, as libev offers the POSIX readiness
3267	notification model, which cannot be implemented efficiently on windows	5325	notification model, which cannot be implemented efficiently on windows
3268	(microsoft monopoly games).	5326	(due to Microsoft monopoly games).
3269		5327
3270	=over 4	5328	A typical way to use libev under windows is to embed it (see the embedding
		5329	section for details) and use the following F<evwrap.h> header file instead
		5330	of F<ev.h>:
3271		5331
		5332	#define EV_STANDALONE /* keeps ev from requiring config.h */
		5333	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		5334
		5335	#include "ev.h"
		5336
		5337	And compile the following F<evwrap.c> file into your project (make sure
		5338	you do I<not> compile the F<ev.c> or any other embedded source files!):
		5339
		5340	#include "evwrap.h"
		5341	#include "ev.c"
		5342
3272	=item The winsocket select function	5343	=head3 The winsocket C<select> function
3273		5344
3274	The winsocket C<select> function doesn't follow POSIX in that it requires	5345	The winsocket C<select> function doesn't follow POSIX in that it
3275	socket I<handles> and not socket I<file descriptors>. This makes select	5346	requires socket I<handles> and not socket I<file descriptors> (it is
3276	very inefficient, and also requires a mapping from file descriptors	5347	also extremely buggy). This makes select very inefficient, and also
3277	to socket handles. See the discussion of the C<EV_SELECT_USE_FD_SET>,	5348	requires a mapping from file descriptors to socket handles (the Microsoft
3278	C<EV_SELECT_IS_WINSOCKET> and C<EV_FD_TO_WIN32_HANDLE> preprocessor	5349	C runtime provides the function C<_open_osfhandle> for this). See the
3279	symbols for more info.	5350	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		5351	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
3280		5352
3281	The configuration for a "naked" win32 using the microsoft runtime	5353	The configuration for a "naked" win32 using the Microsoft runtime
3282	libraries and raw winsocket select is:	5354	libraries and raw winsocket select is:
3283		5355
3284	#define EV_USE_SELECT 1	5356	#define EV_USE_SELECT 1
3285	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */	5357	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
3286		5358
3287	Note that winsockets handling of fd sets is O(n), so you can easily get a	5359	Note that winsockets handling of fd sets is O(n), so you can easily get a
3288	complexity in the O(n²) range when using win32.	5360	complexity in the O(n²) range when using win32.
3289		5361
3290	=item Limited number of file descriptors	5362	=head3 Limited number of file descriptors
3291		5363
3292	Windows has numerous arbitrary (and low) limits on things.	5364	Windows has numerous arbitrary (and low) limits on things.
3293		5365
3294	Early versions of winsocket's select only supported waiting for a maximum	5366	Early versions of winsocket's select only supported waiting for a maximum
3295	of C<64> handles (probably owning to the fact that all windows kernels	5367	of C<64> handles (probably owning to the fact that all windows kernels
3296	can only wait for C<64> things at the same time internally; microsoft	5368	can only wait for C<64> things at the same time internally; Microsoft
3297	recommends spawning a chain of threads and wait for 63 handles and the	5369	recommends spawning a chain of threads and wait for 63 handles and the
3298	previous thread in each. Great).	5370	previous thread in each. Sounds great!).
3299		5371
3300	Newer versions support more handles, but you need to define C<FD_SETSIZE>	5372	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3301	to some high number (e.g. C<2048>) before compiling the winsocket select	5373	to some high number (e.g. C<2048>) before compiling the winsocket select
3302	call (which might be in libev or elsewhere, for example, perl does its own	5374	call (which might be in libev or elsewhere, for example, perl and many
3303	select emulation on windows).	5375	other interpreters do their own select emulation on windows).
3304		5376
3305	Another limit is the number of file descriptors in the microsoft runtime	5377	Another limit is the number of file descriptors in the Microsoft runtime
3306	libraries, which by default is C<64> (there must be a hidden I<64> fetish	5378	libraries, which by default is C<64> (there must be a hidden I<64>
3307	or something like this inside microsoft). You can increase this by calling	5379	fetish or something like this inside Microsoft). You can increase this
3308	C<_setmaxstdio>, which can increase this limit to C<2048> (another	5380	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
3309	arbitrary limit), but is broken in many versions of the microsoft runtime	5381	(another arbitrary limit), but is broken in many versions of the Microsoft
3310	libraries.
3311
3312	This might get you to about C<512> or C<2048> sockets (depending on	5382	runtime libraries. This might get you to about C<512> or C<2048> sockets
3313	windows version and/or the phase of the moon). To get more, you need to	5383	(depending on windows version and/or the phase of the moon). To get more,
3314	wrap all I/O functions and provide your own fd management, but the cost of	5384	you need to wrap all I/O functions and provide your own fd management, but
3315	calling select (O(n²)) will likely make this unworkable.	5385	the cost of calling select (O(n²)) will likely make this unworkable.
3316		5386
3317	=back
3318
3319
3320	=head1 PORTABILITY REQUIREMENTS	5387	=head2 PORTABILITY REQUIREMENTS
3321		5388
3322	In addition to a working ISO-C implementation, libev relies on a few	5389	In addition to a working ISO-C implementation and of course the
3323	additional extensions:	5390	backend-specific APIs, libev relies on a few additional extensions:
3324		5391
3325	=over 4	5392	=over 4
3326		5393
		5394	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		5395	calling conventions regardless of C<ev_watcher_type *>.
		5396
		5397	Libev assumes not only that all watcher pointers have the same internal
		5398	structure (guaranteed by POSIX but not by ISO C for example), but it also
		5399	assumes that the same (machine) code can be used to call any watcher
		5400	callback: The watcher callbacks have different type signatures, but libev
		5401	calls them using an C<ev_watcher *> internally.
		5402
		5403	=item null pointers and integer zero are represented by 0 bytes
		5404
		5405	Libev uses C<memset> to initialise structs and arrays to C<0> bytes, and
		5406	relies on this setting pointers and integers to null.
		5407
		5408	=item pointer accesses must be thread-atomic
		5409
		5410	Accessing a pointer value must be atomic, it must both be readable and
		5411	writable in one piece - this is the case on all current architectures.
		5412
3327	=item C<sig_atomic_t volatile> must be thread-atomic as well	5413	=item C<sig_atomic_t volatile> must be thread-atomic as well
3328		5414
3329	The type C<sig_atomic_t volatile> (or whatever is defined as	5415	The type C<sig_atomic_t volatile> (or whatever is defined as
3330	C<EV_ATOMIC_T>) must be atomic w.r.t. accesses from different	5416	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
3331	threads. This is not part of the specification for C<sig_atomic_t>, but is	5417	threads. This is not part of the specification for C<sig_atomic_t>, but is
3332	believed to be sufficiently portable.	5418	believed to be sufficiently portable.
3333		5419
3334	=item C<sigprocmask> must work in a threaded environment	5420	=item C<sigprocmask> must work in a threaded environment
3335		5421
…		…
3339	thread" or will block signals process-wide, both behaviours would	5425	thread" or will block signals process-wide, both behaviours would
3340	be compatible with libev. Interaction between C<sigprocmask> and	5426	be compatible with libev. Interaction between C<sigprocmask> and
3341	C<pthread_sigmask> could complicate things, however.	5427	C<pthread_sigmask> could complicate things, however.
3342		5428
3343	The most portable way to handle signals is to block signals in all threads	5429	The most portable way to handle signals is to block signals in all threads
3344	except the initial one, and run the default loop in the initial thread as	5430	except the initial one, and run the signal handling loop in the initial
3345	well.	5431	thread as well.
3346		5432
3347	=item C<long> must be large enough for common memory allocation sizes	5433	=item C<long> must be large enough for common memory allocation sizes
3348		5434
3349	To improve portability and simplify using libev, libev uses C<long>	5435	To improve portability and simplify its API, libev uses C<long> internally
3350	internally instead of C<size_t> when allocating its data structures. On	5436	instead of C<size_t> when allocating its data structures. On non-POSIX
3351	non-POSIX systems (Microsoft...) this might be unexpectedly low, but	5437	systems (Microsoft...) this might be unexpectedly low, but is still at
3352	is still at least 31 bits everywhere, which is enough for hundreds of	5438	least 31 bits everywhere, which is enough for hundreds of millions of
3353	millions of watchers.	5439	watchers.
3354		5440
3355	=item C<double> must hold a time value in seconds with enough accuracy	5441	=item C<double> must hold a time value in seconds with enough accuracy
3356		5442
3357	The type C<double> is used to represent timestamps. It is required to	5443	The type C<double> is used to represent timestamps. It is required to
3358	have at least 51 bits of mantissa (and 9 bits of exponent), which is good	5444	have at least 51 bits of mantissa (and 9 bits of exponent), which is
3359	enough for at least into the year 4000. This requirement is fulfilled by	5445	good enough for at least into the year 4000 with millisecond accuracy
		5446	(the design goal for libev). This requirement is overfulfilled by
3360	implementations implementing IEEE 754 (basically all existing ones).	5447	implementations using IEEE 754, which is basically all existing ones.
		5448
		5449	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5450	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5451	is either obsolete or somebody patched it to use C<long double> or
		5452	something like that, just kidding).
3361		5453
3362	=back	5454	=back
3363		5455
3364	If you know of other additional requirements drop me a note.	5456	If you know of other additional requirements drop me a note.
3365		5457
3366		5458
3367	=head1 VALGRIND	5459	=head1 ALGORITHMIC COMPLEXITIES
3368		5460
3369	Valgrind has a special section here because it is a popular tool that is	5461	In this section the complexities of (many of) the algorithms used inside
3370	highly useful, but valgrind reports are very hard to interpret.	5462	libev will be documented. For complexity discussions about backends see
		5463	the documentation for C<ev_default_init>.
3371		5464
3372	If you think you found a bug (memory leak, uninitialised data access etc.)	5465	All of the following are about amortised time: If an array needs to be
3373	in libev, then check twice: If valgrind reports something like:	5466	extended, libev needs to realloc and move the whole array, but this
		5467	happens asymptotically rarer with higher number of elements, so O(1) might
		5468	mean that libev does a lengthy realloc operation in rare cases, but on
		5469	average it is much faster and asymptotically approaches constant time.
3374		5470
3375	==2274== definitely lost: 0 bytes in 0 blocks.	5471	=over 4
3376	==2274== possibly lost: 0 bytes in 0 blocks.
3377	==2274== still reachable: 256 bytes in 1 blocks.
3378		5472
3379	then there is no memory leak. Similarly, under some circumstances,	5473	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
3380	valgrind might report kernel bugs as if it were a bug in libev, or it
3381	might be confused (it is a very good tool, but only a tool).
3382		5474
3383	If you are unsure about something, feel free to contact the mailing list	5475	This means that, when you have a watcher that triggers in one hour and
3384	with the full valgrind report and an explanation on why you think this is	5476	there are 100 watchers that would trigger before that, then inserting will
3385	a bug in libev. However, don't be annoyed when you get a brisk "this is	5477	have to skip roughly seven (C<ld 100>) of these watchers.
3386	no bug" answer and take the chance of learning how to interpret valgrind
3387	properly.
3388		5478
3389	If you need, for some reason, empty reports from valgrind for your project	5479	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
3390	I suggest using suppression lists.
3391		5480
		5481	That means that changing a timer costs less than removing/adding them,
		5482	as only the relative motion in the event queue has to be paid for.
		5483
		5484	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		5485
		5486	These just add the watcher into an array or at the head of a list.
		5487
		5488	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		5489
		5490	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		5491
		5492	These watchers are stored in lists, so they need to be walked to find the
		5493	correct watcher to remove. The lists are usually short (you don't usually
		5494	have many watchers waiting for the same fd or signal: one is typical, two
		5495	is rare).
		5496
		5497	=item Finding the next timer in each loop iteration: O(1)
		5498
		5499	By virtue of using a binary or 4-heap, the next timer is always found at a
		5500	fixed position in the storage array.
		5501
		5502	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		5503
		5504	A change means an I/O watcher gets started or stopped, which requires
		5505	libev to recalculate its status (and possibly tell the kernel, depending
		5506	on backend and whether C<ev_io_set> was used).
		5507
		5508	=item Activating one watcher (putting it into the pending state): O(1)
		5509
		5510	=item Priority handling: O(number_of_priorities)
		5511
		5512	Priorities are implemented by allocating some space for each
		5513	priority. When doing priority-based operations, libev usually has to
		5514	linearly search all the priorities, but starting/stopping and activating
		5515	watchers becomes O(1) with respect to priority handling.
		5516
		5517	=item Sending an ev_async: O(1)
		5518
		5519	=item Processing ev_async_send: O(number_of_async_watchers)
		5520
		5521	=item Processing signals: O(max_signal_number)
		5522
		5523	Sending involves a system call I<iff> there were no other C<ev_async_send>
		5524	calls in the current loop iteration and the loop is currently
		5525	blocked. Checking for async and signal events involves iterating over all
		5526	running async watchers or all signal numbers.
		5527
		5528	=back
		5529
		5530
		5531	=head1 PORTING FROM LIBEV 3.X TO 4.X
		5532
		5533	The major version 4 introduced some incompatible changes to the API.
		5534
		5535	At the moment, the C<ev.h> header file provides compatibility definitions
		5536	for all changes, so most programs should still compile. The compatibility
		5537	layer might be removed in later versions of libev, so better update to the
		5538	new API early than late.
		5539
		5540	=over 4
		5541
		5542	=item C<EV_COMPAT3> backwards compatibility mechanism
		5543
		5544	The backward compatibility mechanism can be controlled by
		5545	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
		5546	section.
		5547
		5548	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5549
		5550	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5551
		5552	ev_loop_destroy (EV_DEFAULT_UC);
		5553	ev_loop_fork (EV_DEFAULT);
		5554
		5555	=item function/symbol renames
		5556
		5557	A number of functions and symbols have been renamed:
		5558
		5559	ev_loop => ev_run
		5560	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		5561	EVLOOP_ONESHOT => EVRUN_ONCE
		5562
		5563	ev_unloop => ev_break
		5564	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		5565	EVUNLOOP_ONE => EVBREAK_ONE
		5566	EVUNLOOP_ALL => EVBREAK_ALL
		5567
		5568	EV_TIMEOUT => EV_TIMER
		5569
		5570	ev_loop_count => ev_iteration
		5571	ev_loop_depth => ev_depth
		5572	ev_loop_verify => ev_verify
		5573
		5574	Most functions working on C<struct ev_loop> objects don't have an
		5575	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		5576	associated constants have been renamed to not collide with the C<struct
		5577	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		5578	as all other watcher types. Note that C<ev_loop_fork> is still called
		5579	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		5580	typedef.
		5581
		5582	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		5583
		5584	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		5585	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		5586	and work, but the library code will of course be larger.
		5587
		5588	=back
		5589
		5590
		5591	=head1 GLOSSARY
		5592
		5593	=over 4
		5594
		5595	=item active
		5596
		5597	A watcher is active as long as it has been started and not yet stopped.
		5598	See L</WATCHER STATES> for details.
		5599
		5600	=item application
		5601
		5602	In this document, an application is whatever is using libev.
		5603
		5604	=item backend
		5605
		5606	The part of the code dealing with the operating system interfaces.
		5607
		5608	=item callback
		5609
		5610	The address of a function that is called when some event has been
		5611	detected. Callbacks are being passed the event loop, the watcher that
		5612	received the event, and the actual event bitset.
		5613
		5614	=item callback/watcher invocation
		5615
		5616	The act of calling the callback associated with a watcher.
		5617
		5618	=item event
		5619
		5620	A change of state of some external event, such as data now being available
		5621	for reading on a file descriptor, time having passed or simply not having
		5622	any other events happening anymore.
		5623
		5624	In libev, events are represented as single bits (such as C<EV_READ> or
		5625	C<EV_TIMER>).
		5626
		5627	=item event library
		5628
		5629	A software package implementing an event model and loop.
		5630
		5631	=item event loop
		5632
		5633	An entity that handles and processes external events and converts them
		5634	into callback invocations.
		5635
		5636	=item event model
		5637
		5638	The model used to describe how an event loop handles and processes
		5639	watchers and events.
		5640
		5641	=item pending
		5642
		5643	A watcher is pending as soon as the corresponding event has been
		5644	detected. See L</WATCHER STATES> for details.
		5645
		5646	=item real time
		5647
		5648	The physical time that is observed. It is apparently strictly monotonic :)
		5649
		5650	=item wall-clock time
		5651
		5652	The time and date as shown on clocks. Unlike real time, it can actually
		5653	be wrong and jump forwards and backwards, e.g. when you adjust your
		5654	clock.
		5655
		5656	=item watcher
		5657
		5658	A data structure that describes interest in certain events. Watchers need
		5659	to be started (attached to an event loop) before they can receive events.
		5660
		5661	=back
3392		5662
3393	=head1 AUTHOR	5663	=head1 AUTHOR
3394		5664
3395	Marc Lehmann <libev@schmorp.de>.	5665	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5666	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
3396		5667

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