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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://cvs.schmorp.de/libev/ev.html>.	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 is identical - to the realloc C function). It is used to	257	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
202	allocate and free memory (no surprises here). If it returns zero when	258	used to allocate and free memory (no surprises here). If it returns zero
203	memory needs to be allocated, the library might abort or take some	259	when memory needs to be allocated (C<size != 0>), the library might abort
204	potentially destructive action. The default is your system realloc	260	or take some potentially destructive action.
205	function.	261
		262	Since some systems (at least OpenBSD and Darwin) fail to implement
		263	correct C<realloc> semantics, libev will use a wrapper around the system
		264	C<realloc> and C<free> functions by default.
206		265
207	You could override this function in high-availability programs to, say,	266	You could override this function in high-availability programs to, say,
208	free some memory if it cannot allocate memory, to use a special allocator,	267	free some memory if it cannot allocate memory, to use a special allocator,
209	or even to sleep a while and retry until some memory is available.	268	or even to sleep a while and retry until some memory is available.
210		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
211	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
212	retries).	285	retries.
213		286
214	static void *	287	static void *
215	persistent_realloc (void *ptr, size_t size)	288	persistent_realloc (void *ptr, size_t size)
216	{	289	{
		290	if (!size)
		291	{
		292	free (ptr);
		293	return 0;
		294	}
		295
217	for (;;)	296	for (;;)
218	{	297	{
219	void *newptr = realloc (ptr, size);	298	void *newptr = realloc (ptr, size);
220		299
221	if (newptr)	300	if (newptr)
…		…
226	}	305	}
227		306
228	...	307	...
229	ev_set_allocator (persistent_realloc);	308	ev_set_allocator (persistent_realloc);
230		309
231	=item ev_set_syserr_cb (void (*cb)(const char *msg));	310	=item ev_set_syserr_cb (void (*cb)(const char *msg) throw ())
232		311
233	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
234	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
235	indicating the system call or subsystem causing the problem. If this	314	indicating the system call or subsystem causing the problem. If this
236	callback is set, then libev will expect it to remedy the sitution, no	315	callback is set, then libev will expect it to remedy the situation, no
237	matter what, when it returns. That is, libev will generally retry the	316	matter what, when it returns. That is, libev will generally retry the
238	requested operation, or, if the condition doesn't go away, do bad stuff	317	requested operation, or, if the condition doesn't go away, do bad stuff
239	(such as abort).	318	(such as abort).
240		319
241	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.
…		…
248	}	327	}
249		328
250	...	329	...
251	ev_set_syserr_cb (fatal_error);	330	ev_set_syserr_cb (fatal_error);
252		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
253	=back	345	=back
254		346
255	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	347	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
256		348
257	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
258	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
259	events, and dynamically created loops which do not.	351	libev 3 had an C<ev_loop> function colliding with the struct name).
260		352
261	If you use threads, a common model is to run the default event loop	353	The library knows two types of such loops, the I<default> loop, which
262	in your main thread (or in a separate thread) and for each thread you	354	supports child process events, and dynamically created event loops which
263	create, you also create another event loop. Libev itself does no locking	355	do not.
264	whatsoever, so if you mix calls to the same event loop in different
265	threads, make sure you lock (this is usually a bad idea, though, even if
266	done correctly, because it's hideous and inefficient).
267		356
268	=over 4	357	=over 4
269		358
270	=item struct ev_loop *ev_default_loop (unsigned int flags)	359	=item struct ev_loop *ev_default_loop (unsigned int flags)
271		360
272	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
273	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
274	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
275	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".
276		371
277	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
278	function.	373	function (or via the C<EV_DEFAULT> macro).
279		374
		375	Note that this function is I<not> thread-safe, so if you want to use it
		376	from multiple threads, you have to employ some kind of mutex (note also
		377	that this case is unlikely, as loops cannot be shared easily between
		378	threads anyway).
		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	readyness 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 rewiring 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 readyness 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		715
471	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.
472		717
473	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	718	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
474	if (!epoller)	719	if (!epoller)
475	fatal ("no epoll found here, maybe it hides under your chair");	720	fatal ("no epoll found here, maybe it hides under your chair");
476		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
477	=item ev_default_destroy ()	733	=item ev_loop_destroy (loop)
478		734
479	Destroys the default loop again (frees all memory and kernel state	735	Destroys an event loop object (frees all memory and kernel state
480	etc.). None of the active event watchers will be stopped in the normal	736	etc.). None of the active event watchers will be stopped in the normal
481	sense, so e.g. C<ev_is_active> might still return true. It is your	737	sense, so e.g. C<ev_is_active> might still return true. It is your
482	responsibility to either stop all watchers cleanly yoursef I<before>	738	responsibility to either stop all watchers cleanly yourself I<before>
483	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
484	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
485	for example).	741	for example).
486		742
487	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
488	this function, and related watchers (such as signal and child watchers)	744	handlers), will not be freed by this function, and related watchers (such
489	would need to be stopped manually.	745	as signal and child watchers) would need to be stopped manually.
490		746
491	In general it is not advisable to call this function except in the	747	This function is normally used on loop objects allocated by
492	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.
493	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>
494	C<ev_loop_new> and C<ev_loop_destroy>).	754	and C<ev_loop_destroy>.
495		755
496	=item ev_loop_destroy (loop)	756	=item ev_loop_fork (loop)
497		757
498	Like C<ev_default_destroy>, but destroys an event loop created by an
499	earlier call to C<ev_loop_new>.
500
501	=item ev_default_fork ()
502
503	This function sets a flag that causes subsequent C<ev_loop> iterations	758	This function sets a flag that causes subsequent C<ev_run> iterations
504	to reinitialise the kernel state for backends that have one. Despite the	759	to reinitialise the kernel state for backends that have one. Despite
505	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
506	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
507	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
508	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.
509		772
510	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
511	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
512	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).
513		779
514	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
515	it just in case after a fork. To make this easy, the function will fit in	781	it just in case after a fork.
516	quite nicely into a call to C<pthread_atfork>:
517		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	...
518	pthread_atfork (0, 0, ev_default_fork);	793	pthread_atfork (0, 0, post_fork_child);
519
520	=item ev_loop_fork (loop)
521
522	Like C<ev_default_fork>, but acts on an event loop created by
523	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
524	after fork, and how you do this is entirely your own problem.
525		794
526	=item int ev_is_default_loop (loop)	795	=item int ev_is_default_loop (loop)
527		796
528	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.
529		799
530	=item unsigned int ev_loop_count (loop)	800	=item unsigned int ev_iteration (loop)
531		801
532	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
533	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>
534	happily wraps around with enough iterations.	804	and happily wraps around with enough iterations.
535		805
536	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
537	"ticks" the number of loop iterations), as it roughly corresponds with	807	"ticks" the number of loop iterations), as it roughly corresponds with
538	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.
539		824
540	=item unsigned int ev_backend (loop)	825	=item unsigned int ev_backend (loop)
541		826
542	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
543	use.	828	use.
…		…
548	received events and started processing them. This timestamp does not	833	received events and started processing them. This timestamp does not
549	change as long as callbacks are being processed, and this is also the base	834	change as long as callbacks are being processed, and this is also the base
550	time used for relative timers. You can treat it as the timestamp of the	835	time used for relative timers. You can treat it as the timestamp of the
551	event occurring (or more correctly, libev finding out about it).	836	event occurring (or more correctly, libev finding out about it).
552		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
553	=item ev_loop (loop, int flags)	876	=item bool ev_run (loop, int flags)
554		877
555	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
556	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
557	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>.
558		883
559	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
560	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.
561		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
562	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
563	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
564	finished (especially in interactive programs), but having a program that	894	finished (especially in interactive programs), but having a program
565	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
566	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.
567		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
568	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
569	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
570	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.
571		909
572	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
573	neccessary) and will handle those and any outstanding ones. It will block	911	necessary) and will handle those and any already outstanding ones. It
574	your process until at least one new event arrives, and will return after	912	will block your process until at least one new event arrives (which could
575	one iteration of the loop. This is useful if you are waiting for some	913	be an event internal to libev itself, so there is no guarantee that a
576	external event in conjunction with something not expressible using other	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
577	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
578	usually a better approach for this kind of thing.	920	usually a better approach for this kind of thing.
579		921
580	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):
581		925
		926	- Increment loop depth.
		927	- Reset the ev_break status.
582	- Before the first iteration, call any pending watchers.	928	- Before the first iteration, call any pending watchers.
		929	LOOP:
583	* If EVFLAG_FORKCHECK was used, check for a fork.	930	- If EVFLAG_FORKCHECK was used, check for a fork.
584	- 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.
585	- Queue and call all prepare watchers.	932	- Queue and call all prepare watchers.
		933	- If ev_break was called, goto FINISH.
586	- 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.
587	- Update the kernel state with all outstanding changes.	936	- Update the kernel state with all outstanding changes.
588	- Update the "event loop time".	937	- Update the "event loop time" (ev_now ()).
589	- Calculate for how long to sleep or block, if at all	938	- Calculate for how long to sleep or block, if at all
590	(active idle watchers, EVLOOP_NONBLOCK or not having	939	(active idle watchers, EVRUN_NOWAIT or not having
591	any active watchers at all will result in not sleeping).	940	any active watchers at all will result in not sleeping).
592	- 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.
593	- Block the process, waiting for any events.	943	- Block the process, waiting for any events.
594	- Queue all outstanding I/O (fd) events.	944	- Queue all outstanding I/O (fd) events.
595	- Update the "event loop time" and do time jump handling.	945	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
596	- Queue all outstanding timers.	946	- Queue all expired timers.
597	- Queue all outstanding periodics.	947	- Queue all expired periodics.
598	- If no events are pending now, queue all idle watchers.	948	- Queue all idle watchers with priority higher than that of pending events.
599	- Queue all check watchers.	949	- Queue all check watchers.
600	- 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).
601	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
602	be handled here by queueing them when their watcher gets executed.	952	be handled here by queueing them when their watcher gets executed.
603	- 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
604	were used, or there are no active watchers, return, otherwise	954	were used, or there are no active watchers, goto FINISH, otherwise
605	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.
606		960
607	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
608	anymore.	962	anymore.
609		963
610	... queue jobs here, make sure they register event watchers as long	964	... queue jobs here, make sure they register event watchers as long
611	... as they still have work to do (even an idle watcher will do..)	965	... as they still have work to do (even an idle watcher will do..)
612	ev_loop (my_loop, 0);	966	ev_run (my_loop, 0);
613	... jobs done. yeah!	967	... jobs done or somebody called break. yeah!
614		968
615	=item ev_unloop (loop, how)	969	=item ev_break (loop, how)
616		970
617	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
618	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
619	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
620	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.
621		975
622	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.
623		980
624	=item ev_ref (loop)	981	=item ev_ref (loop)
625		982
626	=item ev_unref (loop)	983	=item ev_unref (loop)
627		984
628	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
629	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
630	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.
631	a watcher you never unregister that should not keep C<ev_loop> from	988
632	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
633	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
634	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
635	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
636	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
637	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
638	(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
639	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).
640		1003
641	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>
642	running when nothing else is active.	1005	running when nothing else is active.
643		1006
644	struct ev_signal exitsig;	1007	ev_signal exitsig;
645	ev_signal_init (&exitsig, sig_cb, SIGINT);	1008	ev_signal_init (&exitsig, sig_cb, SIGINT);
646	ev_signal_start (loop, &exitsig);	1009	ev_signal_start (loop, &exitsig);
647	evf_unref (loop);	1010	ev_unref (loop);
648		1011
649	Example: For some weird reason, unregister the above signal handler again.	1012	Example: For some weird reason, unregister the above signal handler again.
650		1013
651	ev_ref (loop);	1014	ev_ref (loop);
652	ev_signal_stop (loop, &exitsig);	1015	ev_signal_stop (loop, &exitsig);
653		1016
654	=item ev_set_io_collect_interval (loop, ev_tstamp interval)	1017	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
655		1018
656	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)	1019	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
657		1020
658	These advanced functions influence the time that libev will spend waiting	1021	These advanced functions influence the time that libev will spend waiting
659	for events. Both are by default C<0>, meaning that libev will try to	1022	for events. Both time intervals are by default C<0>, meaning that libev
660	invoke timer/periodic callbacks and I/O callbacks with minimum latency.	1023	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		1024	latency.
661		1025
662	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>)
663	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
664	increase efficiency of loop iterations.	1028	to increase efficiency of loop iterations (or to increase power-saving
		1029	opportunities).
665		1030
666	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
667	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
668	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
669	events, especially with backends like C<select ()> which have a high	1034	events, especially with backends like C<select ()> which have a high
670	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.
671		1036
672	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
673	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,
674	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
675	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
676	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).
677		1045
678	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
679	to spend more time collecting timeouts, at the expense of increased	1047	to spend more time collecting timeouts, at the expense of increased
680	latency (the watcher callback will be called later). C<ev_io> watchers	1048	latency/jitter/inexactness (the watcher callback will be called
681	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
682	any overhead in libev.	1050	value will not introduce any overhead in libev.
683		1051
684	Many (busy) programs can usually benefit by setting the io collect	1052	Many (busy) programs can usually benefit by setting the I/O collect
685	interval to a value near C<0.1> or so, which is often enough for	1053	interval to a value near C<0.1> or so, which is often enough for
686	interactive servers (of course not for games), likewise for timeouts. It	1054	interactive servers (of course not for games), likewise for timeouts. It
687	usually doesn't make much sense to set it to a lower value than C<0.01>,	1055	usually doesn't make much sense to set it to a lower value than C<0.01>,
688	as this approsaches the timing granularity of most systems.	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.
689		1155
690	=back	1156	=back
691		1157
692		1158
693	=head1 ANATOMY OF A WATCHER	1159	=head1 ANATOMY OF A WATCHER
694		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
695	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
696	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
697	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:
698		1169
699	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)
700	{	1171	{
701	ev_io_stop (w);	1172	ev_io_stop (w);
702	ev_unloop (loop, EVUNLOOP_ALL);	1173	ev_break (loop, EVBREAK_ALL);
703	}	1174	}
704		1175
705	struct ev_loop *loop = ev_default_loop (0);	1176	struct ev_loop *loop = ev_default_loop (0);
		1177
706	struct ev_io stdin_watcher;	1178	ev_io stdin_watcher;
		1179
707	ev_init (&stdin_watcher, my_cb);	1180	ev_init (&stdin_watcher, my_cb);
708	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1181	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
709	ev_io_start (loop, &stdin_watcher);	1182	ev_io_start (loop, &stdin_watcher);
		1183
710	ev_loop (loop, 0);	1184	ev_run (loop, 0);
711		1185
712	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
713	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
714	although this can sometimes be quite valid).	1188	stack).
715		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
716	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
717	(watcher *, callback)>, which expects a callback to be provided. This	1194	*, callback)>, which expects a callback to be provided. This callback is
718	callback gets invoked each time the event occurs (or, in the case of io	1195	invoked each time the event occurs (or, in the case of I/O watchers, each
719	watchers, each time the event loop detects that the file descriptor given	1196	time the event loop detects that the file descriptor given is readable
720	is readable and/or writable).	1197	and/or writable).
721		1198
722	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 *, ...) >>
723	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
724	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<<
725	(watcher *, callback, ...) >>.	1202	ev_TYPE_init (watcher *, callback, ...) >>.
726		1203
727	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
728	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
729	*) >>), 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
730	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1207	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
731		1208
732	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
733	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
734	reinitialise it or call its C<set> macro.	1211	reinitialise it or call its C<ev_TYPE_set> macro.
735		1212
736	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
737	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
738	third argument.	1215	third argument.
739		1216
…		…
748	=item C<EV_WRITE>	1225	=item C<EV_WRITE>
749		1226
750	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
751	writable.	1228	writable.
752		1229
753	=item C<EV_TIMEOUT>	1230	=item C<EV_TIMER>
754		1231
755	The C<ev_timer> watcher has timed out.	1232	The C<ev_timer> watcher has timed out.
756		1233
757	=item C<EV_PERIODIC>	1234	=item C<EV_PERIODIC>
758		1235
…		…
776		1253
777	=item C<EV_PREPARE>	1254	=item C<EV_PREPARE>
778		1255
779	=item C<EV_CHECK>	1256	=item C<EV_CHECK>
780		1257
781	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
782	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)
783	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
784	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
785	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
786	(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
787	C<ev_loop> from blocking).	1269	blocking).
788		1270
789	=item C<EV_EMBED>	1271	=item C<EV_EMBED>
790		1272
791	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.
792		1274
793	=item C<EV_FORK>	1275	=item C<EV_FORK>
794		1276
795	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
796	C<ev_fork>).	1278	C<ev_fork>).
797		1279
		1280	=item C<EV_CLEANUP>
		1281
		1282	The event loop is about to be destroyed (see C<ev_cleanup>).
		1283
798	=item C<EV_ASYNC>	1284	=item C<EV_ASYNC>
799		1285
800	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>).
801		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
802	=item C<EV_ERROR>	1293	=item C<EV_ERROR>
803		1294
804	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
805	happen because the watcher could not be properly started because libev	1296	happen because the watcher could not be properly started because libev
806	ran out of memory, a file descriptor was found to be closed or any other	1297	ran out of memory, a file descriptor was found to be closed or any other
		1298	problem. Libev considers these application bugs.
		1299
807	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
808	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.
809		1304
810	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
811	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
812	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
813	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
814	programs, though, so beware.	1309	programs, though, as the fd could already be closed and reused for another
		1310	thing, so beware.
815		1311
816	=back	1312	=back
817		1313
818	=head2 GENERIC WATCHER FUNCTIONS	1314	=head2 GENERIC WATCHER FUNCTIONS
819
820	In the following description, C<TYPE> stands for the watcher type,
821	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
822		1315
823	=over 4	1316	=over 4
824		1317
825	=item C<ev_init> (ev_TYPE *watcher, callback)	1318	=item C<ev_init> (ev_TYPE *watcher, callback)
826		1319
…		…
832	which rolls both calls into one.	1325	which rolls both calls into one.
833		1326
834	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
835	(or never started) and there are no pending events outstanding.	1328	(or never started) and there are no pending events outstanding.
836		1329
837	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,
838	int revents)>.	1331	int revents)>.
839		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
840	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1339	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
841		1340
842	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
843	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
844	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
845	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
846	difference to the C<ev_init> macro).	1345	difference to the C<ev_init> macro).
847		1346
848	Although some watcher types do not have type-specific arguments	1347	Although some watcher types do not have type-specific arguments
849	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1348	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
850		1349
		1350	See C<ev_init>, above, for an example.
		1351
851	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1352	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
852		1353
853	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
854	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
855	a watcher. The same limitations apply, of course.	1356	a watcher. The same limitations apply, of course.
856		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
857	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1362	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
858		1363
859	Starts (activates) the given watcher. Only active watchers will receive	1364	Starts (activates) the given watcher. Only active watchers will receive
860	events. If the watcher is already active nothing will happen.	1365	events. If the watcher is already active nothing will happen.
861		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
862	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1372	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
863		1373
864	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
865	status. It is possible that stopped watchers are pending (for example,	1377	It is possible that stopped watchers are pending - for example,
866	non-repeating timers are being stopped when they become pending), but	1378	non-repeating timers are being stopped when they become pending - but
867	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1379	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
868	you want to free or reuse the memory used by the watcher it is therefore a	1380	pending. If you want to free or reuse the memory used by the watcher it is
869	good idea to always call its C<ev_TYPE_stop> function.	1381	therefore a good idea to always call its C<ev_TYPE_stop> function.
870		1382
871	=item bool ev_is_active (ev_TYPE *watcher)	1383	=item bool ev_is_active (ev_TYPE *watcher)
872		1384
873	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
874	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
…		…
885		1397
886	=item callback ev_cb (ev_TYPE *watcher)	1398	=item callback ev_cb (ev_TYPE *watcher)
887		1399
888	Returns the callback currently set on the watcher.	1400	Returns the callback currently set on the watcher.
889		1401
890	=item ev_cb_set (ev_TYPE *watcher, callback)	1402	=item ev_set_cb (ev_TYPE *watcher, callback)
891		1403
892	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
893	(modulo threads).	1405	(modulo threads).
894		1406
895	=item ev_set_priority (ev_TYPE *watcher, priority)	1407	=item ev_set_priority (ev_TYPE *watcher, int priority)
896		1408
897	=item int ev_priority (ev_TYPE *watcher)	1409	=item int ev_priority (ev_TYPE *watcher)
898		1410
899	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
900	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>
901	(default: C<-2>). Pending watchers with higher priority will be invoked	1413	(default: C<-2>). Pending watchers with higher priority will be invoked
902	before watchers with lower priority, but priority will not keep watchers	1414	before watchers with lower priority, but priority will not keep watchers
903	from being executed (except for C<ev_idle> watchers).	1415	from being executed (except for C<ev_idle> watchers).
904		1416
905	This means that priorities are I<only> used for ordering callback
906	invocation after new events have been received. This is useful, for
907	example, to reduce latency after idling, or more often, to bind two
908	watchers on the same event and make sure one is called first.
909
910	If you need to suppress invocation when higher priority events are pending	1417	If you need to suppress invocation when higher priority events are pending
911	you need to look at C<ev_idle> watchers, which provide this functionality.	1418	you need to look at C<ev_idle> watchers, which provide this functionality.
912		1419
913	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
914	pending.	1421	pending.
915		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
916	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
917	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 :).
918		1429
919	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
920	fine, as long as you do not mind that the priority value you query might	1431	priorities.
921	or might not have been adjusted to be within valid range.
922		1432
923	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1433	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
924		1434
925	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
926	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
927	can deal with that fact.	1437	can deal with that fact, as both are simply passed through to the
		1438	callback.
928		1439
929	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1440	=item int ev_clear_pending (loop, ev_TYPE *watcher)
930		1441
931	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
932	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
933	watcher isn't pending it does nothing and returns C<0>.	1444	watcher isn't pending it does nothing and returns C<0>.
934		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
935	=back	1463	=back
936		1464
		1465	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
		1466	OWN COMPOSITE WATCHERS> idioms.
937		1467
938	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1468	=head2 WATCHER STATES
939		1469
940	Each watcher has, by default, a member C<void *data> that you can change	1470	There are various watcher states mentioned throughout this manual -
941	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
942	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
943	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".
944	member, you can also "subclass" the watcher type and provide your own
945	data:
946		1474
947	struct my_io	1475	=over 4
948	{
949	struct ev_io io;
950	int otherfd;
951	void *somedata;
952	struct whatever *mostinteresting;
953	}
954		1476
955	And since your callback will be called with a pointer to the watcher, you	1477	=item initialised
956	can cast it back to your own type:
957		1478
958	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
959	{	1480	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
960	struct my_io *w = (struct my_io *)w_;	1481	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
961	...
962	}
963		1482
964	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
965	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.
966		1487
967	Another common scenario is having some data structure with multiple	1488	=item started/running/active
968	watchers:
969		1489
970	struct my_biggy	1490	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
971	{	1491	property of the event loop, and is actively waiting for events. While in
972	int some_data;	1492	this state it cannot be accessed (except in a few documented ways), moved,
973	ev_timer t1;	1493	freed or anything else - the only legal thing is to keep a pointer to it,
974	ev_timer t2;	1494	and call libev functions on it that are documented to work on active watchers.
975	}
976		1495
977	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1496	=item pending
978	you need to use C<offsetof>:
979		1497
980	#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.
981		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
982	static void	1598	static void
983	t1_cb (EV_P_ struct ev_timer *w, int revents)	1599	io_cb (EV_P_ ev_io *w, int revents)
984	{	1600	{
985	struct my_biggy big = (struct my_biggy *	1601	// stop the I/O watcher, we received the event, but
986	(((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);
987	}	1609	}
988		1610
989	static void	1611	static void
990	t2_cb (EV_P_ struct ev_timer *w, int revents)	1612	idle_cb (EV_P_ ev_idle *w, int revents)
991	{	1613	{
992	struct my_biggy big = (struct my_biggy *	1614	// actual processing
993	(((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);
994	}	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.
995		1632
996		1633
997	=head1 WATCHER TYPES	1634	=head1 WATCHER TYPES
998		1635
999	This section describes each watcher in detail, but will not repeat	1636	This section describes each watcher in detail, but will not repeat
…		…
1023	In general you can register as many read and/or write event watchers per	1660	In general you can register as many read and/or write event watchers per
1024	fd as you want (as long as you don't confuse yourself). Setting all file	1661	fd as you want (as long as you don't confuse yourself). Setting all file
1025	descriptors to non-blocking mode is also usually a good idea (but not	1662	descriptors to non-blocking mode is also usually a good idea (but not
1026	required if you know what you are doing).	1663	required if you know what you are doing).
1027		1664
1028	If you must do this, then force the use of a known-to-be-good backend
1029	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
1030	C<EVBACKEND_POLL>).
1031
1032	Another thing you have to watch out for is that it is quite easy to	1665	Another thing you have to watch out for is that it is quite easy to
1033	receive "spurious" readyness notifications, that is your callback might	1666	receive "spurious" readiness notifications, that is, your callback might
1034	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1667	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1035	because there is no data. Not only are some backends known to create a	1668	because there is no data. It is very easy to get into this situation even
1036	lot of those (for example solaris ports), it is very easy to get into	1669	with a relatively standard program structure. Thus it is best to always
1037	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
1038	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1039	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1671	preferable to a program hanging until some data arrives.
1040		1672
1041	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
1042	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
1043	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
1044	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
1045	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.
1046		1682
1047	=head3 The special problem of disappearing file descriptors	1683	=head3 The special problem of disappearing file descriptors
1048		1684
1049	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
1050	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
1051	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
1052	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
1053	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
1054	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,
1055	fact, a different file descriptor.	1691	in fact, a different file descriptor.
1056		1692
1057	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
1058	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
1059	will assume that this is potentially a new file descriptor, otherwise	1695	will assume that this is potentially a new file descriptor, otherwise
1060	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
…		…
1074		1710
1075	There is no workaround possible except not registering events	1711	There is no workaround possible except not registering events
1076	for potentially C<dup ()>'ed file descriptors, or to resort to	1712	for potentially C<dup ()>'ed file descriptors, or to resort to
1077	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1713	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1078		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
1079	=head3 The special problem of fork	1748	=head3 The special problem of fork
1080		1749
1081	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 ()>
1082	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
1083	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.
1084		1754
1085	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
1086	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
1087	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1757	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1088	C<EVBACKEND_POLL>.
1089		1758
1090	=head3 The special problem of SIGPIPE	1759	=head3 The special problem of SIGPIPE
1091		1760
1092	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>:
1093	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
1094	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
1095	programs this is sensible behaviour, for daemons, this is usually	1764	this is sensible behaviour, for daemons, this is usually undesirable.
1096	undesirable.
1097		1765
1098	So when you encounter spurious, unexplained daemon exits, make sure you	1766	So when you encounter spurious, unexplained daemon exits, make sure you
1099	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
1100	somewhere, as that would have given you a big clue).	1768	somewhere, as that would have given you a big clue).
1101		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.
1102		1808
1103	=head3 Watcher-Specific Functions	1809	=head3 Watcher-Specific Functions
1104		1810
1105	=over 4	1811	=over 4
1106		1812
1107	=item ev_io_init (ev_io *, callback, int fd, int events)	1813	=item ev_io_init (ev_io *, callback, int fd, int events)
1108		1814
1109	=item ev_io_set (ev_io *, int fd, int events)	1815	=item ev_io_set (ev_io *, int fd, int events)
1110		1816
1111	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
1112	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
1113	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.
1114		1820
1115	=item int fd [read-only]	1821	=item int fd [read-only]
1116		1822
1117	The file descriptor being watched.	1823	The file descriptor being watched.
1118		1824
…		…
1126		1832
1127	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
1128	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
1129	attempt to read a whole line in the callback.	1835	attempt to read a whole line in the callback.
1130		1836
1131	static void	1837	static void
1132	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)
1133	{	1839	{
1134	ev_io_stop (loop, w);	1840	ev_io_stop (loop, w);
1135	.. 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
1136	}	1842	}
1137		1843
1138	...	1844	...
1139	struct ev_loop *loop = ev_default_init (0);	1845	struct ev_loop *loop = ev_default_init (0);
1140	struct ev_io stdin_readable;	1846	ev_io stdin_readable;
1141	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);
1142	ev_io_start (loop, &stdin_readable);	1848	ev_io_start (loop, &stdin_readable);
1143	ev_loop (loop, 0);	1849	ev_run (loop, 0);
1144		1850
1145		1851
1146	=head2 C<ev_timer> - relative and optionally repeating timeouts	1852	=head2 C<ev_timer> - relative and optionally repeating timeouts
1147		1853
1148	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
1149	given time, and optionally repeating in regular intervals after that.	1855	given time, and optionally repeating in regular intervals after that.
1150		1856
1151	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
1152	times out after an hour and you reset your system clock to last years	1858	times out after an hour and you reset your system clock to January last
1153	time, it will still time out after (roughly) and hour. "Roughly" because	1859	year, it will still time out after (roughly) one hour. "Roughly" because
1154	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1860	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1155	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.
1156		2104
1157	The relative timeouts are calculated relative to the C<ev_now ()>	2105	The relative timeouts are calculated relative to the C<ev_now ()>
1158	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
1159	of the event triggering whatever timeout you are modifying/starting. If	2107	of the event triggering whatever timeout you are modifying/starting. If
1160	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
1161	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:
1162		2111
1163	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2112	ev_timer_set (&timer, after + (ev_time () - ev_now ()), 0.);
1164		2113
1165	The callback is guarenteed to be invoked only when its timeout has passed,	2114	If the event loop is suspended for a long time, you can also force an
1166	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
1167	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>).
1168		2181
1169	=head3 Watcher-Specific Functions and Data Members	2182	=head3 Watcher-Specific Functions and Data Members
1170		2183
1171	=over 4	2184	=over 4
1172		2185
1173	=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)
1174		2187
1175	=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)
1176		2189
1177	Configure the timer to trigger after C<after> seconds. If C<repeat> is	2190	Configure the timer to trigger after C<after> seconds (fractional and
1178	C<0.>, then it will automatically be stopped. If it is positive, then the	2191	negative values are supported). If C<repeat> is C<0.>, then it will
		2192	automatically be stopped once the timeout is reached. If it is positive,
1179	timer will automatically be configured to trigger again C<repeat> seconds	2193	then the timer will automatically be configured to trigger again C<repeat>
1180	later, again, and again, until stopped manually.	2194	seconds later, again, and again, until stopped manually.
1181		2195
1182	The timer itself will do a best-effort at avoiding drift, that is, if you	2196	The timer itself will do a best-effort at avoiding drift, that is, if
1183	configure a timer to trigger every 10 seconds, then it will trigger at	2197	you configure a timer to trigger every 10 seconds, then it will normally
1184	exactly 10 second intervals. If, however, your program cannot keep up with	2198	trigger at exactly 10 second intervals. If, however, your program cannot
1185	the timer (because it takes longer than those 10 seconds to do stuff) the	2199	keep up with the timer (because it takes longer than those 10 seconds to
1186	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.
1187		2201
1188	=item ev_timer_again (loop, ev_timer *)	2202	=item ev_timer_again (loop, ev_timer *)
1189		2203
1190	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
1191	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>.
1192		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
1193	If the timer is pending, its pending status is cleared.	2213	=item If the timer is pending, the pending status is always cleared.
1194		2214
1195	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).
1196		2217
1197	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
1198	C<repeat> value), or reset the running timer to the C<repeat> value.	2219	and start the timer, if necessary.
1199		2220
1200	This sounds a bit complicated, but here is a useful and typical	2221	=back
1201	example: Imagine you have a tcp connection and you want a so-called idle
1202	timeout, that is, you want to be called when there have been, say, 60
1203	seconds of inactivity on the socket. The easiest way to do this is to
1204	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1205	C<ev_timer_again> each time you successfully read or write some data. If
1206	you go into an idle state where you do not expect data to travel on the
1207	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1208	automatically restart it if need be.
1209		2222
1210	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
1211	altogether and only ever use the C<repeat> value and C<ev_timer_again>:	2224	usage example.
1212		2225
1213	ev_timer_init (timer, callback, 0., 5.);	2226	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1214	ev_timer_again (loop, timer);
1215	...
1216	timer->again = 17.;
1217	ev_timer_again (loop, timer);
1218	...
1219	timer->again = 10.;
1220	ev_timer_again (loop, timer);
1221		2227
1222	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,
1223	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.
1224		2237
1225	=item ev_tstamp repeat [read-write]	2238	=item ev_tstamp repeat [read-write]
1226		2239
1227	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
1228	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),
1229	which is also when any modifications are taken into account.	2242	which is also when any modifications are taken into account.
1230		2243
1231	=back	2244	=back
1232		2245
1233	=head3 Examples	2246	=head3 Examples
1234		2247
1235	Example: Create a timer that fires after 60 seconds.	2248	Example: Create a timer that fires after 60 seconds.
1236		2249
1237	static void	2250	static void
1238	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)
1239	{	2252	{
1240	.. one minute over, w is actually stopped right here	2253	.. one minute over, w is actually stopped right here
1241	}	2254	}
1242		2255
1243	struct ev_timer mytimer;	2256	ev_timer mytimer;
1244	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	2257	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1245	ev_timer_start (loop, &mytimer);	2258	ev_timer_start (loop, &mytimer);
1246		2259
1247	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
1248	inactivity.	2261	inactivity.
1249		2262
1250	static void	2263	static void
1251	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2264	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1252	{	2265	{
1253	.. ten seconds without any activity	2266	.. ten seconds without any activity
1254	}	2267	}
1255		2268
1256	struct ev_timer mytimer;	2269	ev_timer mytimer;
1257	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 */
1258	ev_timer_again (&mytimer); /* start timer */	2271	ev_timer_again (&mytimer); /* start timer */
1259	ev_loop (loop, 0);	2272	ev_run (loop, 0);
1260		2273
1261	// 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":
1262	// reset the timeout to start ticking again at 10 seconds	2275	// reset the timeout to start ticking again at 10 seconds
1263	ev_timer_again (&mytimer);	2276	ev_timer_again (&mytimer);
1264		2277
1265		2278
1266	=head2 C<ev_periodic> - to cron or not to cron?	2279	=head2 C<ev_periodic> - to cron or not to cron?
1267		2280
1268	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
1269	(and unfortunately a bit complex).	2282	(and unfortunately a bit complex).
1270		2283
1271	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
1272	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
1273	to trigger "at" 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
1274	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
1275	+ 10.>) and then reset your system clock to the last year, then it will	2288	time, and time jumps are not uncommon (e.g. when you adjust your
1276	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	2289	wrist-watch).
1277	roughly 10 seconds later).
1278		2290
1279	They can also be used to implement vastly more complex timers, such as	2291	You can tell a periodic watcher to trigger after some specific point
1280	triggering an event on each midnight, local time or other, complicated,	2292	in time: for example, if you tell a periodic watcher to trigger "in 10
1281	rules.	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).
1282		2298
		2299	C<ev_periodic> watchers can also be used to implement vastly more complex
		2300	timers, such as triggering an event on each "midnight, local time", or
		2301	other complicated rules. This cannot easily be done with C<ev_timer>
		2302	watchers, as those cannot react to time jumps.
		2303
1283	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
1284	time (C<at>) has been passed, but if multiple periodic timers become ready	2305	point in time where it is supposed to trigger has passed. If multiple
1285	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).
1286		2309
1287	=head3 Watcher-Specific Functions and Data Members	2310	=head3 Watcher-Specific Functions and Data Members
1288		2311
1289	=over 4	2312	=over 4
1290		2313
1291	=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)
1292		2315
1293	=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)
1294		2317
1295	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
1296	operation, and we will explain them from simplest to complex:	2319	operation, and we will explain them from simplest to most complex:
1297		2320
1298	=over 4	2321	=over 4
1299		2322
1300	=item * absolute timer (at = time, interval = reschedule_cb = 0)	2323	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1301		2324
1302	In this configuration the watcher triggers an event at the wallclock time	2325	In this configuration the watcher triggers an event after the wall clock
1303	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	2326	time C<offset> has passed. It will not repeat and will not adjust when a
1304	that is, if it is to be run at January 1st 2011 then it will run when the	2327	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1305	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.
1306		2330
1307	=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)
1308		2332
1309	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
1310	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
1311	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.
1312		2337
1313	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
1314	time:	2339	system clock, for example, here is an C<ev_periodic> that triggers each
		2340	hour, on the hour (with respect to UTC):
1315		2341
1316	ev_periodic_set (&periodic, 0., 3600., 0);	2342	ev_periodic_set (&periodic, 0., 3600., 0);
1317		2343
1318	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,
1319	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
1320	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
1321	by 3600.	2347	by 3600.
1322		2348
1323	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
1324	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
1325	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.
1326		2352
1327	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
1328	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
1329	this value.	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.
1330		2359
		2360	Note also that there is an upper limit to how often a timer can fire (CPU
		2361	speed for example), so if C<interval> is very small then timing stability
		2362	will of course deteriorate. Libev itself tries to be exact to be about one
		2363	millisecond (if the OS supports it and the machine is fast enough).
		2364
1331	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	2365	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1332		2366
1333	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
1334	ignored. Instead, each time the periodic watcher gets scheduled, the	2368	ignored. Instead, each time the periodic watcher gets scheduled, the
1335	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
1336	current time as second argument.	2370	current time as second argument.
1337		2371
1338	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,
1339	ever, or make any event loop modifications>. If you need to stop it,	2373	or make ANY other event loop modifications whatsoever, unless explicitly
1340	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	2374	allowed by documentation here>.
1341	starting an C<ev_prepare> watcher, which is legal).
1342		2375
		2376	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2377	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2378	only event loop modification you are allowed to do).
		2379
1343	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2380	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1344	ev_tstamp now)>, e.g.:	2381	*w, ev_tstamp now)>, e.g.:
1345		2382
		2383	static ev_tstamp
1346	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2384	my_rescheduler (ev_periodic *w, ev_tstamp now)
1347	{	2385	{
1348	return now + 60.;	2386	return now + 60.;
1349	}	2387	}
1350		2388
1351	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
1352	(that is, the lowest time value larger than to the second argument). It	2390	(that is, the lowest time value larger than to the second argument). It
1353	will usually be called just before the callback will be triggered, but	2391	will usually be called just before the callback will be triggered, but
1354	might be called at other times, too.	2392	might be called at other times, too.
1355		2393
1356	NOTE: I<< This callback must always return a time that is later than the	2394	NOTE: I<< This callback must always return a time that is higher than or
1357	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2395	equal to the passed C<now> value >>.
1358		2396
1359	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
1360	triggers on each midnight, local time. To do this, you would calculate the	2398	triggers on "next midnight, local time". To do this, you would calculate
1361	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
1362	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
1363	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).
1364		2420
1365	=back	2421	=back
1366		2422
1367	=item ev_periodic_again (loop, ev_periodic *)	2423	=item ev_periodic_again (loop, ev_periodic *)
1368		2424
1369	Simply stops and restarts the periodic watcher again. This is only useful	2425	Simply stops and restarts the periodic watcher again. This is only useful
1370	when you changed some parameters or the reschedule callback would return	2426	when you changed some parameters or the reschedule callback would return
1371	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
1372	program when the crontabs have changed).	2428	program when the crontabs have changed).
1373		2429
		2430	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2431
		2432	When active, returns the absolute time that the watcher is supposed
		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.
		2436
1374	=item ev_tstamp offset [read-write]	2437	=item ev_tstamp offset [read-write]
1375		2438
1376	When repeating, this contains the offset value, otherwise this is the	2439	When repeating, this contains the offset value, otherwise this is the
1377	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).
1378		2442
1379	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
1380	timer fires or C<ev_periodic_again> is being called.	2444	timer fires or C<ev_periodic_again> is being called.
1381		2445
1382	=item ev_tstamp interval [read-write]	2446	=item ev_tstamp interval [read-write]
1383		2447
1384	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
1385	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
1386	called.	2450	called.
1387		2451
1388	=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]
1389		2453
1390	The current reschedule callback, or C<0>, if this functionality is	2454	The current reschedule callback, or C<0>, if this functionality is
1391	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
1392	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.
1393		2457
1394	=item ev_tstamp at [read-only]
1395
1396	When active, contains the absolute time that the watcher is supposed to
1397	trigger next.
1398
1399	=back	2458	=back
1400		2459
1401	=head3 Examples	2460	=head3 Examples
1402		2461
1403	Example: Call a callback every hour, or, more precisely, whenever the	2462	Example: Call a callback every hour, or, more precisely, whenever the
1404	system clock is divisible by 3600. The callback invocation times have	2463	system time is divisible by 3600. The callback invocation times have
1405	potentially a lot of jittering, but good long-term stability.	2464	potentially a lot of jitter, but good long-term stability.
1406		2465
1407	static void	2466	static void
1408	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2467	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1409	{	2468	{
1410	... 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)
1411	}	2470	}
1412		2471
1413	struct ev_periodic hourly_tick;	2472	ev_periodic hourly_tick;
1414	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2473	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1415	ev_periodic_start (loop, &hourly_tick);	2474	ev_periodic_start (loop, &hourly_tick);
1416		2475
1417	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:
1418		2477
1419	#include <math.h>	2478	#include <math.h>
1420		2479
1421	static ev_tstamp	2480	static ev_tstamp
1422	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2481	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1423	{	2482	{
1424	return fmod (now, 3600.) + 3600.;	2483	return now + (3600. - fmod (now, 3600.));
1425	}	2484	}
1426		2485
1427	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);
1428		2487
1429	Example: Call a callback every hour, starting now:	2488	Example: Call a callback every hour, starting now:
1430		2489
1431	struct ev_periodic hourly_tick;	2490	ev_periodic hourly_tick;
1432	ev_periodic_init (&hourly_tick, clock_cb,	2491	ev_periodic_init (&hourly_tick, clock_cb,
1433	fmod (ev_now (loop), 3600.), 3600., 0);	2492	fmod (ev_now (loop), 3600.), 3600., 0);
1434	ev_periodic_start (loop, &hourly_tick);	2493	ev_periodic_start (loop, &hourly_tick);
1435		2494
1436		2495
1437	=head2 C<ev_signal> - signal me when a signal gets signalled!	2496	=head2 C<ev_signal> - signal me when a signal gets signalled!
1438		2497
1439	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
1440	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
1441	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
1442	normal event processing, like any other event.	2501	normal event processing, like any other event.
1443		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
1444	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
1445	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
1446	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
1447	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
1448	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.
1449	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.
1450		2517
1451	If possible and supported, libev will install its handlers with	2518	If possible and supported, libev will install its handlers with
1452	C<SA_RESTART> behaviour enabled, so syscalls should not be unduly	2519	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
1453	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
1454	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
1455	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>.
1456		2567
1457	=head3 Watcher-Specific Functions and Data Members	2568	=head3 Watcher-Specific Functions and Data Members
1458		2569
1459	=over 4	2570	=over 4
1460		2571
…		…
1471		2582
1472	=back	2583	=back
1473		2584
1474	=head3 Examples	2585	=head3 Examples
1475		2586
1476	Example: Try to exit cleanly on SIGINT and SIGTERM.	2587	Example: Try to exit cleanly on SIGINT.
1477		2588
1478	static void	2589	static void
1479	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2590	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
1480	{	2591	{
1481	ev_unloop (loop, EVUNLOOP_ALL);	2592	ev_break (loop, EVBREAK_ALL);
1482	}	2593	}
1483		2594
1484	struct ev_signal signal_watcher;	2595	ev_signal signal_watcher;
1485	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2596	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1486	ev_signal_start (loop, &sigint_cb);	2597	ev_signal_start (loop, &signal_watcher);
1487		2598
1488		2599
1489	=head2 C<ev_child> - watch out for process status changes	2600	=head2 C<ev_child> - watch out for process status changes
1490		2601
1491	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
1492	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
1493	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
1494	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
1495	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.
1496		2610
1497	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
1498	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)
1499		2617
1500	=head3 Process Interaction	2618	=head3 Process Interaction
1501		2619
1502	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
1503	initialised. This is necessary to guarantee proper behaviour even if	2621	initialised. This is necessary to guarantee proper behaviour even if the
1504	the first child watcher is started after the child exits. The occurance	2622	first child watcher is started after the child exits. The occurrence
1505	of C<SIGCHLD> is recorded asynchronously, but child reaping is done	2623	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
1506	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
1507	children, even ones not watched.	2625	children, even ones not watched.
1508		2626
1509	=head3 Overriding the Built-In Processing	2627	=head3 Overriding the Built-In Processing
…		…
1513	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
1514	C<SIGCHLD> after initialising the default loop, and making sure the	2632	C<SIGCHLD> after initialising the default loop, and making sure the
1515	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
1516	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
1517	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).
1518		2644
1519	=head3 Watcher-Specific Functions and Data Members	2645	=head3 Watcher-Specific Functions and Data Members
1520		2646
1521	=over 4	2647	=over 4
1522		2648
…		…
1551	=head3 Examples	2677	=head3 Examples
1552		2678
1553	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
1554	its completion.	2680	its completion.
1555		2681
1556	ev_child cw;	2682	ev_child cw;
1557		2683
1558	static void	2684	static void
1559	child_cb (EV_P_ struct ev_child *w, int revents)	2685	child_cb (EV_P_ ev_child *w, int revents)
1560	{	2686	{
1561	ev_child_stop (EV_A_ w);	2687	ev_child_stop (EV_A_ w);
1562	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);
1563	}	2689	}
1564		2690
1565	pid_t pid = fork ();	2691	pid_t pid = fork ();
1566		2692
1567	if (pid < 0)	2693	if (pid < 0)
1568	// error	2694	// error
1569	else if (pid == 0)	2695	else if (pid == 0)
1570	{	2696	{
1571	// the forked child executes here	2697	// the forked child executes here
1572	exit (1);	2698	exit (1);
1573	}	2699	}
1574	else	2700	else
1575	{	2701	{
1576	ev_child_init (&cw, child_cb, pid, 0);	2702	ev_child_init (&cw, child_cb, pid, 0);
1577	ev_child_start (EV_DEFAULT_ &cw);	2703	ev_child_start (EV_DEFAULT_ &cw);
1578	}	2704	}
1579		2705
1580		2706
1581	=head2 C<ev_stat> - did the file attributes just change?	2707	=head2 C<ev_stat> - did the file attributes just change?
1582		2708
1583	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
1584	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)
1585	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.
1586		2714
1587	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
1588	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
1589	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
1590	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
1591	the stat buffer having unspecified contents.	2719	least one) and all the other fields of the stat buffer having unspecified
		2720	contents.
1592		2721
1593	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
1594	relative and your working directory changes, the behaviour is undefined.	2724	your working directory changes, then the behaviour is undefined.
1595		2725
1596	Since there is no standard to do this, the portable implementation simply	2726	Since there is no portable change notification interface available, the
1597	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
1598	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
1599	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
1600	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
1601	five seconds, although this might change dynamically). Libev will also	2731	(which you can expect to be around five seconds, although this might
1602	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
1603	usually overkill.	2733	currently around C<0.1>, but that's usually overkill.
1604		2734
1605	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,
1606	as even with OS-supported change notifications, this can be	2736	as even with OS-supported change notifications, this can be
1607	resource-intensive.	2737	resource-intensive.
1608		2738
1609	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
1610	implemented (implementing kqueue support is left as an exercise for the	2740	is the Linux inotify interface (implementing kqueue support is left as an
1611	reader). Inotify will be used to give hints only and should not change the	2741	exercise for the reader. Note, however, that the author sees no way of
1612	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2742	implementing C<ev_stat> semantics with kqueue, except as a hint).
1613	to fall back to regular polling again even with inotify, but changes are
1614	usually detected immediately, and if the file exists there will be no
1615	polling.
1616		2743
1617	=head3 ABI Issues (Largefile Support)	2744	=head3 ABI Issues (Largefile Support)
1618		2745
1619	Libev by default (unless the user overrides this) uses the default	2746	Libev by default (unless the user overrides this) uses the default
1620	compilation environment, which means that on systems with optionally	2747	compilation environment, which means that on systems with large file
1621	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
1622	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
1623	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
1624	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
1625	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
1626	most noticably with ev_stat and largefile support.	2753	most noticeably displayed with ev_stat and large file support.
1627		2754
1628	=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.
1629		2760
		2761	=head3 Inotify and Kqueue
		2762
1630	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
1631	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
1632	change detection where possible. The inotify descriptor will be created lazily	2765	inotify descriptor will be created lazily when the first C<ev_stat>
1633	when the first C<ev_stat> watcher is being started.	2766	watcher is being started.
1634		2767
1635	Inotify presense does not change the semantics of C<ev_stat> watchers	2768	Inotify presence does not change the semantics of C<ev_stat> watchers
1636	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
1637	making regular C<stat> calls. Even in the presense of inotify support	2770	making regular C<stat> calls. Even in the presence of inotify support
1638	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.
1639		2776
1640	(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
1641	implement this functionality, due to the requirement of having a file	2778	implement this functionality, due to the requirement of having a file
1642	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.
1643		2799
1644	=head3 The special problem of stat time resolution	2800	=head3 The special problem of stat time resolution
1645		2801
1646	The C<stat ()> syscall only supports full-second resolution portably, and	2802	The C<stat ()> system call only supports full-second resolution portably,
1647	even on systems where the resolution is higher, many filesystems still	2803	and even on systems where the resolution is higher, most file systems
1648	only support whole seconds.	2804	still only support whole seconds.
1649		2805
1650	That means that, if the time is the only thing that changes, you might	2806	That means that, if the time is the only thing that changes, you can
1651	miss updates: on the first update, C<ev_stat> detects a change and calls	2807	easily miss updates: on the first update, C<ev_stat> detects a change and
1652	your callback, which does something. When there is another update within	2808	calls your callback, which does something. When there is another update
1653	the same second, C<ev_stat> will be unable to detect it.	2809	within the same second, C<ev_stat> will be unable to detect unless the
		2810	stat data does change in other ways (e.g. file size).
1654		2811
1655	The solution to this is to delay acting on a change for a second (or till	2812	The solution to this is to delay acting on a change for slightly more
1656	the next second boundary), using a roughly one-second delay C<ev_timer>	2813	than a second (or till slightly after the next full second boundary), using
1657	(C<ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)>). The C<.01>	2814	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
1658	is added to work around small timing inconsistencies of some operating	2815	ev_timer_again (loop, w)>).
1659	systems.	2816
		2817	The C<.02> offset is added to work around small timing inconsistencies
		2818	of some operating systems (where the second counter of the current time
		2819	might be be delayed. One such system is the Linux kernel, where a call to
		2820	C<gettimeofday> might return a timestamp with a full second later than
		2821	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2822	update file times then there will be a small window where the kernel uses
		2823	the previous second to update file times but libev might already execute
		2824	the timer callback).
1660		2825
1661	=head3 Watcher-Specific Functions and Data Members	2826	=head3 Watcher-Specific Functions and Data Members
1662		2827
1663	=over 4	2828	=over 4
1664		2829
…		…
1670	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
1671	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
1672	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
1673	path for as long as the watcher is active.	2838	path for as long as the watcher is active.
1674		2839
1675	The callback will be receive C<EV_STAT> when a change was detected,	2840	The callback will receive an C<EV_STAT> event when a change was detected,
1676	relative to the attributes at the time the watcher was started (or the	2841	relative to the attributes at the time the watcher was started (or the
1677	last change was detected).	2842	last change was detected).
1678		2843
1679	=item ev_stat_stat (loop, ev_stat *)	2844	=item ev_stat_stat (loop, ev_stat *)
1680		2845
1681	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
1682	watched path in your callback, you could call this fucntion to avoid	2847	watched path in your callback, you could call this function to avoid
1683	detecting this change (while introducing a race condition). Can also be	2848	detecting this change (while introducing a race condition if you are not
1684	useful simply to find out the new values.	2849	the only one changing the path). Can also be useful simply to find out the
		2850	new values.
1685		2851
1686	=item ev_statdata attr [read-only]	2852	=item ev_statdata attr [read-only]
1687		2853
1688	The most-recently detected attributes of the file. Although the type is of	2854	The most-recently detected attributes of the file. Although the type is
1689	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2855	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1690	suitable for your system. If the C<st_nlink> member is C<0>, then there	2856	suitable for your system, but you can only rely on the POSIX-standardised
		2857	members to be present. If the C<st_nlink> member is C<0>, then there was
1691	was some error while C<stat>ing the file.	2858	some error while C<stat>ing the file.
1692		2859
1693	=item ev_statdata prev [read-only]	2860	=item ev_statdata prev [read-only]
1694		2861
1695	The previous attributes of the file. The callback gets invoked whenever	2862	The previous attributes of the file. The callback gets invoked whenever
1696	C<prev> != C<attr>.	2863	C<prev> != C<attr>, or, more precisely, one or more of these members
		2864	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2865	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1697		2866
1698	=item ev_tstamp interval [read-only]	2867	=item ev_tstamp interval [read-only]
1699		2868
1700	The specified interval.	2869	The specified interval.
1701		2870
1702	=item const char *path [read-only]	2871	=item const char *path [read-only]
1703		2872
1704	The filesystem path that is being watched.	2873	The file system path that is being watched.
1705		2874
1706	=back	2875	=back
1707		2876
1708	=head3 Examples	2877	=head3 Examples
1709		2878
1710	Example: Watch C</etc/passwd> for attribute changes.	2879	Example: Watch C</etc/passwd> for attribute changes.
1711		2880
1712	static void	2881	static void
1713	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2882	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1714	{	2883	{
1715	/* /etc/passwd changed in some way */	2884	/* /etc/passwd changed in some way */
1716	if (w->attr.st_nlink)	2885	if (w->attr.st_nlink)
1717	{	2886	{
1718	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2887	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1719	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2888	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1720	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2889	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1721	}	2890	}
1722	else	2891	else
1723	/* you shalt not abuse printf for puts */	2892	/* you shalt not abuse printf for puts */
1724	puts ("wow, /etc/passwd is not there, expect problems. "	2893	puts ("wow, /etc/passwd is not there, expect problems. "
1725	"if this is windows, they already arrived\n");	2894	"if this is windows, they already arrived\n");
1726	}	2895	}
1727		2896
1728	...	2897	...
1729	ev_stat passwd;	2898	ev_stat passwd;
1730		2899
1731	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);	2900	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1732	ev_stat_start (loop, &passwd);	2901	ev_stat_start (loop, &passwd);
1733		2902
1734	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
1735	miss updates (however, frequent updates will delay processing, too, so	2904	miss updates (however, frequent updates will delay processing, too, so
1736	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
1737	C<ev_timer> callback invocation).	2906	C<ev_timer> callback invocation).
1738		2907
1739	static ev_stat passwd;	2908	static ev_stat passwd;
1740	static ev_timer timer;	2909	static ev_timer timer;
1741		2910
1742	static void	2911	static void
1743	timer_cb (EV_P_ ev_timer *w, int revents)	2912	timer_cb (EV_P_ ev_timer *w, int revents)
1744	{	2913	{
1745	ev_timer_stop (EV_A_ w);	2914	ev_timer_stop (EV_A_ w);
1746		2915
1747	/* now it's one second after the most recent passwd change */	2916	/* now it's one second after the most recent passwd change */
1748	}	2917	}
1749		2918
1750	static void	2919	static void
1751	stat_cb (EV_P_ ev_stat *w, int revents)	2920	stat_cb (EV_P_ ev_stat *w, int revents)
1752	{	2921	{
1753	/* reset the one-second timer */	2922	/* reset the one-second timer */
1754	ev_timer_again (EV_A_ &timer);	2923	ev_timer_again (EV_A_ &timer);
1755	}	2924	}
1756		2925
1757	...	2926	...
1758	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);	2927	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1759	ev_stat_start (loop, &passwd);	2928	ev_stat_start (loop, &passwd);
1760	ev_timer_init (&timer, timer_cb, 0., 1.01);	2929	ev_timer_init (&timer, timer_cb, 0., 1.02);
1761		2930
1762		2931
1763	=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...
1764		2933
1765	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
1766	priority are pending (prepare, check and other idle watchers do not	2935	priority are pending (prepare, check and other idle watchers do not count
1767	count).	2936	as receiving "events").
1768		2937
1769	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
1770	(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
1771	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
1772	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
…		…
1779	Apart from keeping your process non-blocking (which is a useful	2948	Apart from keeping your process non-blocking (which is a useful
1780	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
1781	"pseudo-background processing", or delay processing stuff to after the	2950	"pseudo-background processing", or delay processing stuff to after the
1782	event loop has handled all outstanding events.	2951	event loop has handled all outstanding events.
1783		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
1784	=head3 Watcher-Specific Functions and Data Members	2967	=head3 Watcher-Specific Functions and Data Members
1785		2968
1786	=over 4	2969	=over 4
1787		2970
1788	=item ev_idle_init (ev_signal *, callback)	2971	=item ev_idle_init (ev_idle *, callback)
1789		2972
1790	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
1791	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,
1792	believe me.	2975	believe me.
1793		2976
…		…
1796	=head3 Examples	2979	=head3 Examples
1797		2980
1798	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
1799	callback, free it. Also, use no error checking, as usual.	2982	callback, free it. Also, use no error checking, as usual.
1800		2983
1801	static void	2984	static void
1802	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2985	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1803	{	2986	{
		2987	// stop the watcher
		2988	ev_idle_stop (loop, w);
		2989
		2990	// now we can free it
1804	free (w);	2991	free (w);
		2992
1805	// now do something you wanted to do when the program has	2993	// now do something you wanted to do when the program has
1806	// no longer anything immediate to do.	2994	// no longer anything immediate to do.
1807	}	2995	}
1808		2996
1809	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2997	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1810	ev_idle_init (idle_watcher, idle_cb);	2998	ev_idle_init (idle_watcher, idle_cb);
1811	ev_idle_start (loop, idle_cb);	2999	ev_idle_start (loop, idle_watcher);
1812		3000
1813		3001
1814	=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!
1815		3003
1816	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:
1817	prepare watchers get invoked before the process blocks and check watchers	3005	prepare watchers get invoked before the process blocks and check watchers
1818	afterwards.	3006	afterwards.
1819		3007
1820	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
1821	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
1822	watchers. Other loops than the current one are fine, however. The	3010	C<ev_check> watchers. Other loops than the current one are fine,
1823	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
1824	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
1825	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
1826	called in pairs bracketing the blocking call.	3014	kind they will always be called in pairs bracketing the blocking call.
1827		3015
1828	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
1829	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
1830	variable changes, implement your own watchers, integrate net-snmp or a	3018	variable changes, implement your own watchers, integrate net-snmp or a
1831	coroutine library and lots more. They are also occasionally useful if	3019	coroutine library and lots more. They are also occasionally useful if
1832	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,
1833	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>
1834	watcher).	3022	watcher).
1835		3023
1836	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
1837	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
1838	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
1839	provide just this functionality). Then, in the check watcher you check for	3027	libraries provide exactly this functionality). Then, in the check watcher,
1840	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
1841	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
1842	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
1843	because you never know, you know?).	3031	nevertheless, because you never know, you know?).
1844		3032
1845	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
1846	coroutines into libev programs, by yielding to other active coroutines	3034	coroutines into libev programs, by yielding to other active coroutines
1847	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
1848	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
1849	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
1850	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
1851	loop from blocking if lower-priority coroutines are active, thus mapping	3039	loop from blocking if lower-priority coroutines are active, thus mapping
1852	low-priority coroutines to idle/background tasks).	3040	low-priority coroutines to idle/background tasks).
1853		3041
1854	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
1855	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
1856	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
1857	too) should not activate ("feed") events into libev. While libev fully	3048	activate ("feed") events into libev. While libev fully supports this, they
1858	supports this, they will be called before other C<ev_check> watchers	3049	might get executed before other C<ev_check> watchers did their job. As
1859	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
1860	(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
1861	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
1862	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.
1863		3073
1864	=head3 Watcher-Specific Functions and Data Members	3074	=head3 Watcher-Specific Functions and Data Members
1865		3075
1866	=over 4	3076	=over 4
1867		3077
…		…
1869		3079
1870	=item ev_check_init (ev_check *, callback)	3080	=item ev_check_init (ev_check *, callback)
1871		3081
1872	Initialises and configures the prepare or check watcher - they have no	3082	Initialises and configures the prepare or check watcher - they have no
1873	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>
1874	macros, but using them is utterly, utterly and completely pointless.	3084	macros, but using them is utterly, utterly, utterly and completely
		3085	pointless.
1875		3086
1876	=back	3087	=back
1877		3088
1878	=head3 Examples	3089	=head3 Examples
1879		3090
1880	There are a number of principal ways to embed other event loops or modules	3091	There are a number of principal ways to embed other event loops or modules
1881	into libev. Here are some ideas on how to include libadns into libev	3092	into libev. Here are some ideas on how to include libadns into libev
1882	(there is a Perl module named C<EV::ADNS> that does this, which you could	3093	(there is a Perl module named C<EV::ADNS> that does this, which you could
1883	use for an actually working example. Another Perl module named C<EV::Glib>	3094	use as a working example. Another Perl module named C<EV::Glib> embeds a
1884	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV	3095	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1885	into the Glib event loop).	3096	Glib event loop).
1886		3097
1887	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	3098	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1888	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
1889	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
1890	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
1891	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.
1892		3103
1893	static ev_io iow [nfd];	3104	static ev_io iow [nfd];
1894	static ev_timer tw;	3105	static ev_timer tw;
1895		3106
1896	static void	3107	static void
1897	io_cb (ev_loop *loop, ev_io *w, int revents)	3108	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1898	{	3109	{
1899	}	3110	}
1900		3111
1901	// create io watchers for each fd and a timer before blocking	3112	// create io watchers for each fd and a timer before blocking
1902	static void	3113	static void
1903	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	3114	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1904	{	3115	{
1905	int timeout = 3600000;	3116	int timeout = 3600000;
1906	struct pollfd fds [nfd];	3117	struct pollfd fds [nfd];
1907	// actual code will need to loop here and realloc etc.	3118	// actual code will need to loop here and realloc etc.
1908	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	3119	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1909		3120
1910	/* 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 */
1911	ev_timer_init (&tw, 0, timeout * 1e-3);	3122	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1912	ev_timer_start (loop, &tw);	3123	ev_timer_start (loop, &tw);
1913		3124
1914	// create one ev_io per pollfd	3125	// create one ev_io per pollfd
1915	for (int i = 0; i < nfd; ++i)	3126	for (int i = 0; i < nfd; ++i)
1916	{	3127	{
1917	ev_io_init (iow + i, io_cb, fds [i].fd,	3128	ev_io_init (iow + i, io_cb, fds [i].fd,
1918	((fds [i].events & POLLIN ? EV_READ : 0)	3129	((fds [i].events & POLLIN ? EV_READ : 0)
1919	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	3130	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1920		3131
1921	fds [i].revents = 0;	3132	fds [i].revents = 0;
1922	ev_io_start (loop, iow + i);	3133	ev_io_start (loop, iow + i);
1923	}	3134	}
1924	}	3135	}
1925		3136
1926	// stop all watchers after blocking	3137	// stop all watchers after blocking
1927	static void	3138	static void
1928	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	3139	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1929	{	3140	{
1930	ev_timer_stop (loop, &tw);	3141	ev_timer_stop (loop, &tw);
1931		3142
1932	for (int i = 0; i < nfd; ++i)	3143	for (int i = 0; i < nfd; ++i)
1933	{	3144	{
1934	// set the relevant poll flags	3145	// set the relevant poll flags
1935	// could also call adns_processreadable etc. here	3146	// could also call adns_processreadable etc. here
1936	struct pollfd *fd = fds + i;	3147	struct pollfd *fd = fds + i;
1937	int revents = ev_clear_pending (iow + i);	3148	int revents = ev_clear_pending (iow + i);
1938	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	3149	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1939	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	3150	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1940		3151
1941	// now stop the watcher	3152	// now stop the watcher
1942	ev_io_stop (loop, iow + i);	3153	ev_io_stop (loop, iow + i);
1943	}	3154	}
1944		3155
1945	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	3156	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1946	}	3157	}
1947		3158
1948	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>
1949	in the prepare watcher and would dispose of the check watcher.	3160	in the prepare watcher and would dispose of the check watcher.
1950		3161
1951	Method 3: If the module to be embedded supports explicit event	3162	Method 3: If the module to be embedded supports explicit event
1952	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
1953	callbacks, and only destroy/create the watchers in the prepare watcher.	3164	callbacks, and only destroy/create the watchers in the prepare watcher.
1954		3165
1955	static void	3166	static void
1956	timer_cb (EV_P_ ev_timer *w, int revents)	3167	timer_cb (EV_P_ ev_timer *w, int revents)
1957	{	3168	{
1958	adns_state ads = (adns_state)w->data;	3169	adns_state ads = (adns_state)w->data;
1959	update_now (EV_A);	3170	update_now (EV_A);
1960		3171
1961	adns_processtimeouts (ads, &tv_now);	3172	adns_processtimeouts (ads, &tv_now);
1962	}	3173	}
1963		3174
1964	static void	3175	static void
1965	io_cb (EV_P_ ev_io *w, int revents)	3176	io_cb (EV_P_ ev_io *w, int revents)
1966	{	3177	{
1967	adns_state ads = (adns_state)w->data;	3178	adns_state ads = (adns_state)w->data;
1968	update_now (EV_A);	3179	update_now (EV_A);
1969		3180
1970	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	3181	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1971	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	3182	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1972	}	3183	}
1973		3184
1974	// do not ever call adns_afterpoll	3185	// do not ever call adns_afterpoll
1975		3186
1976	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
1977	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
1978	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
1979	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
1980	this.	3191	this approach, effectively embedding EV as a client into the horrible
		3192	libglib event loop.
1981		3193
1982	static gint	3194	static gint
1983	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	3195	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1984	{	3196	{
1985	int got_events = 0;	3197	int got_events = 0;
1986		3198
1987	for (n = 0; n < nfds; ++n)	3199	for (n = 0; n < nfds; ++n)
1988	// 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
1989		3201
1990	if (timeout >= 0)	3202	if (timeout >= 0)
1991	// create/start timer	3203	// create/start timer
1992		3204
1993	// poll	3205	// poll
1994	ev_loop (EV_A_ 0);	3206	ev_run (EV_A_ 0);
1995		3207
1996	// stop timer again	3208	// stop timer again
1997	if (timeout >= 0)	3209	if (timeout >= 0)
1998	ev_timer_stop (EV_A_ &to);	3210	ev_timer_stop (EV_A_ &to);
1999		3211
2000	// stop io watchers again - their callbacks should have set	3212	// stop io watchers again - their callbacks should have set
2001	for (n = 0; n < nfds; ++n)	3213	for (n = 0; n < nfds; ++n)
2002	ev_io_stop (EV_A_ iow [n]);	3214	ev_io_stop (EV_A_ iow [n]);
2003		3215
2004	return got_events;	3216	return got_events;
2005	}	3217	}
2006		3218
2007		3219
2008	=head2 C<ev_embed> - when one backend isn't enough...	3220	=head2 C<ev_embed> - when one backend isn't enough...
2009		3221
2010	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
…		…
2016	prioritise I/O.	3228	prioritise I/O.
2017		3229
2018	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
2019	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
2020	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
2021	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
2022	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
2023	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
2024	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 :)
2025		3238
2026	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
2027	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),
2028	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
2029	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
2030	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.
2031		3244
2032	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
2033	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
2034	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
2035	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
2036	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
2037	to C<0>, in which case the embed watcher will automatically execute the	3250	to give the embedded loop strictly lower priority for example).
2038	embedded loop sweep.
2039		3251
2040	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
2041	callback will be invoked whenever some events have been handled. You can	3253	will automatically execute the embedded loop sweep whenever necessary.
2042	set the callback to C<0> to avoid having to specify one if you are not
2043	interested in that.
2044		3254
2045	Also, there have not currently been made special provisions for forking:	3255	Fork detection will be handled transparently while the C<ev_embed> watcher
2046	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
2047	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
2048	yourself.	3258	C<ev_loop_fork> on the embedded loop.
2049		3259
2050	Unfortunately, not all backends are embeddable, only the ones returned by	3260	Unfortunately, not all backends are embeddable: only the ones returned by
2051	C<ev_embeddable_backends> are, which, unfortunately, does not include any	3261	C<ev_embeddable_backends> are, which, unfortunately, does not include any
2052	portable one.	3262	portable one.
2053		3263
2054	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
2055	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
2056	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
2057	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.
2058		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
2059	=head3 Watcher-Specific Functions and Data Members	3277	=head3 Watcher-Specific Functions and Data Members
2060		3278
2061	=over 4	3279	=over 4
2062		3280
2063	=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)
2064		3282
2065	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3283	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
2066		3284
2067	Configures the watcher to embed the given loop, which must be	3285	Configures the watcher to embed the given loop, which must be
2068	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
2069	invoked automatically, otherwise it is the responsibility of the callback	3287	invoked automatically, otherwise it is the responsibility of the callback
2070	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,
2071	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).
2072		3290
2073	=item ev_embed_sweep (loop, ev_embed *)	3291	=item ev_embed_sweep (loop, ev_embed *)
2074		3292
2075	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
2076	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
2077	apropriate way for embedded loops.	3295	appropriate way for embedded loops.
2078		3296
2079	=item struct ev_loop *other [read-only]	3297	=item struct ev_loop *other [read-only]
2080		3298
2081	The embedded event loop.	3299	The embedded event loop.
2082		3300
…		…
2084		3302
2085	=head3 Examples	3303	=head3 Examples
2086		3304
2087	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
2088	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
2089	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
2090	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
2091	used).	3309	used).
2092		3310
2093	struct ev_loop *loop_hi = ev_default_init (0);	3311	struct ev_loop *loop_hi = ev_default_init (0);
2094	struct ev_loop *loop_lo = 0;	3312	struct ev_loop *loop_lo = 0;
2095	struct ev_embed embed;	3313	ev_embed embed;
2096		3314
2097	// see if there is a chance of getting one that works	3315	// see if there is a chance of getting one that works
2098	// (remember that a flags value of 0 means autodetection)	3316	// (remember that a flags value of 0 means autodetection)
2099	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3317	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2100	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3318	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
2101	: 0;	3319	: 0;
2102		3320
2103	// 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
2104	if (loop_lo)	3322	if (loop_lo)
2105	{	3323	{
2106	ev_embed_init (&embed, 0, loop_lo);	3324	ev_embed_init (&embed, 0, loop_lo);
2107	ev_embed_start (loop_hi, &embed);	3325	ev_embed_start (loop_hi, &embed);
2108	}	3326	}
2109	else	3327	else
2110	loop_lo = loop_hi;	3328	loop_lo = loop_hi;
2111		3329
2112	Example: Check if kqueue is available but not recommended and create	3330	Example: Check if kqueue is available but not recommended and create
2113	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
2114	kqueue implementation). Store the kqueue/socket-only event loop in	3332	kqueue implementation). Store the kqueue/socket-only event loop in
2115	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3333	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2116		3334
2117	struct ev_loop *loop = ev_default_init (0);	3335	struct ev_loop *loop = ev_default_init (0);
2118	struct ev_loop *loop_socket = 0;	3336	struct ev_loop *loop_socket = 0;
2119	struct ev_embed embed;	3337	ev_embed embed;
2120		3338
2121	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3339	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2122	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3340	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2123	{	3341	{
2124	ev_embed_init (&embed, 0, loop_socket);	3342	ev_embed_init (&embed, 0, loop_socket);
2125	ev_embed_start (loop, &embed);	3343	ev_embed_start (loop, &embed);
2126	}	3344	}
2127		3345
2128	if (!loop_socket)	3346	if (!loop_socket)
2129	loop_socket = loop;	3347	loop_socket = loop;
2130		3348
2131	// 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
2132		3350
2133		3351
2134	=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
2135		3353
2136	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
2137	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
2138	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
2139	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
2140	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
2141	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,
2142	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.
2143		3395
2144	=head3 Watcher-Specific Functions and Data Members	3396	=head3 Watcher-Specific Functions and Data Members
2145		3397
2146	=over 4	3398	=over 4
2147		3399
2148	=item ev_fork_init (ev_signal *, callback)	3400	=item ev_fork_init (ev_fork *, callback)
2149		3401
2150	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
2151	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,
2152	believe me.	3404	really.
2153		3405
2154	=back	3406	=back
2155		3407
2156		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
2157	=head2 C<ev_async> - how to wake up another event loop	3449	=head2 C<ev_async> - how to wake up an event loop
2158		3450
2159	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
2160	asynchronous sources such as signal handlers (as opposed to multiple event	3452	asynchronous sources such as signal handlers (as opposed to multiple event
2161	loops - those are of course safe to use in different threads).	3453	loops - those are of course safe to use in different threads).
2162		3454
2163	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,
2164	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>
2165	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
2166	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.
2167	safe.
2168		3459
2169	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,
2170	too, are asynchronous in nature, and signals, too, will be compressed	3461	too, are asynchronous in nature, and signals, too, will be compressed
2171	(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
2172	C<ev_async_sent> calls).	3463	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
2173		3464	of "global async watchers" by using a watcher on an otherwise unused
2174	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,
2175	just the default loop.	3466	even without knowing which loop owns the signal.
2176		3467
2177	=head3 Queueing	3468	=head3 Queueing
2178		3469
2179	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
2180	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
2181	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
2182	need elaborate support such as pthreads.	3473	need elaborate support such as pthreads or unportable memory access
		3474	semantics.
2183		3475
2184	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
2185	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
2186	queue:	3478	queue:
2187		3479
2188	=over 4	3480	=over 4
2189		3481
2190	=item queueing from a signal handler context	3482	=item queueing from a signal handler context
2191		3483
2192	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
2193	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
2194	some fictitiuous SIGUSR1 handler:	3486	an example that does that for some fictitious SIGUSR1 handler:
2195		3487
2196	static ev_async mysig;	3488	static ev_async mysig;
2197		3489
2198	static void	3490	static void
2199	sigusr1_handler (void)	3491	sigusr1_handler (void)
…		…
2265	=over 4	3557	=over 4
2266		3558
2267	=item ev_async_init (ev_async *, callback)	3559	=item ev_async_init (ev_async *, callback)
2268		3560
2269	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
2270	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,
2271	believe me.	3563	trust me.
2272		3564
2273	=item ev_async_send (loop, ev_async *)	3565	=item ev_async_send (loop, ev_async *)
2274		3566
2275	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
2276	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
2277	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,
2278	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
2279	section below on what exactly this means).	3573	embedding section below on what exactly this means).
2280		3574
2281	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
2282	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
2283	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.
		3586
		3587	=item bool = ev_async_pending (ev_async *)
		3588
		3589	Returns a non-zero value when C<ev_async_send> has been called on the
		3590	watcher but the event has not yet been processed (or even noted) by the
		3591	event loop.
		3592
		3593	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3594	the loop iterates next and checks for the watcher to have become active,
		3595	it will reset the flag again. C<ev_async_pending> can be used to very
		3596	quickly check whether invoking the loop might be a good idea.
		3597
		3598	Not that this does I<not> check whether the watcher itself is 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.
2284		3602
2285	=back	3603	=back
2286		3604
2287		3605
2288	=head1 OTHER FUNCTIONS	3606	=head1 OTHER FUNCTIONS
2289		3607
2290	There are some other functions of possible interest. Described. Here. Now.	3608	There are some other functions of possible interest. Described. Here. Now.
2291		3609
2292	=over 4	3610	=over 4
2293		3611
2294	=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)
2295		3613
2296	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
2297	callback on whichever event happens first and automatically stop both	3615	callback on whichever event happens first and automatically stops both
2298	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
2299	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
2300	more watchers yourself.	3618	more watchers yourself.
2301		3619
2302	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
2303	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
2304	C<events> set will be craeted and started.	3622	the given C<fd> and C<events> set will be created and started.
2305		3623
2306	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
2307	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
2308	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.
2309	dubious value.
2310		3627
2311	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
2312	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
2313	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>
2314	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.
2315		3634
		3635	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3636
2316	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 ()
2317	{	3739	{
2318	if (revents & EV_TIMEOUT)	3740	free (request);
2319	/* doh, nothing entered */;
2320	else if (revents & EV_READ)
2321	/* stdin might have data for us, joy! */;
2322	}	3741	}
2323		3742
2324	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3743	request = start_new_request (..., callback);
2325		3744
2326	=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.
2327		3747
2328	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
2329	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
2330	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.
2331		3752
2332	=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.
2333		3755
2334	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
2335	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.
2336		3760
2337	=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:
2338		3767
2339	Feed an event as if the given signal occured (C<loop> must be the default	3768	ev_set_cb (watcher, callback);
2340	loop!).	3769	ev_feed_event (EV_A_ watcher, 0);
2341		3770
2342	=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.
2343		4008
2344		4009
2345	=head1 LIBEVENT EMULATION	4010	=head1 LIBEVENT EMULATION
2346		4011
2347	Libev offers a compatibility emulation layer for libevent. It cannot	4012	Libev offers a compatibility emulation layer for libevent. It cannot
2348	emulate the internals of libevent, so here are some usage hints:	4013	emulate the internals of libevent, so here are some usage hints:
2349		4014
2350	=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.
2351		4021
2352	=item * Use it by including <event.h>, as usual.	4022	=item * Use it by including <event.h>, as usual.
2353		4023
2354	=item * The following members are fully supported: ev_base, ev_callback,	4024	=item * The following members are fully supported: ev_base, ev_callback,
2355	ev_arg, ev_fd, ev_res, ev_events.	4025	ev_arg, ev_fd, ev_res, ev_events.
…		…
2360		4030
2361	=item * Priorities are not currently supported. Initialising priorities	4031	=item * Priorities are not currently supported. Initialising priorities
2362	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
2363	is an ev_pri field.	4033	is an ev_pri field.
2364		4034
		4035	=item * In libevent, the last base created gets the signals, in libev, the
		4036	base that registered the signal gets the signals.
		4037
2365	=item * Other members are not supported.	4038	=item * Other members are not supported.
2366		4039
2367	=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
2368	to use the libev header file and library.	4041	to use the libev header file and library.
2369		4042
2370	=back	4043	=back
2371		4044
2372	=head1 C++ SUPPORT	4045	=head1 C++ SUPPORT
2373		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
2374	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
2375	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
2376	the callback model to a model using method callbacks on objects.	4082	the callback model to a model using method callbacks on objects.
2377		4083
2378	To use it,	4084	To use it,
2379		4085
2380	#include <ev++.h>	4086	#include <ev++.h>
2381		4087
2382	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
2383	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
2384	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
2385	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	4091	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
2387	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++
2388	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
2389	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
2390	you disable C<EV_MULTIPLICITY> when embedding libev).	4096	you disable C<EV_MULTIPLICITY> when embedding libev).
2391		4097
2392	Currently, functions, and static and non-static member functions can be	4098	Currently, functions, static and non-static member functions and classes
2393	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
2394	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
2395	types of functors please contact the author (preferably after implementing	4101	you need support for other types of functors please contact the author
2396	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++.
2397		4107
2398	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:
2399		4109
2400	=over 4	4110	=over 4
2401		4111
…		…
2411	=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.
2412		4122
2413	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
2414	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>
2415	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
2416	defines by many implementations.	4126	defined by many implementations.
2417		4127
2418	All of those classes have these methods:	4128	All of those classes have these methods:
2419		4129
2420	=over 4	4130	=over 4
2421		4131
2422	=item ev::TYPE::TYPE ()	4132	=item ev::TYPE::TYPE ()
2423		4133
2424	=item ev::TYPE::TYPE (struct ev_loop *)	4134	=item ev::TYPE::TYPE (loop)
2425		4135
2426	=item ev::TYPE::~TYPE	4136	=item ev::TYPE::~TYPE
2427		4137
2428	The constructor (optionally) takes an event loop to associate the watcher	4138	The constructor (optionally) takes an event loop to associate the watcher
2429	with. If it is omitted, it will use C<EV_DEFAULT>.	4139	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
2452	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
2453	thunking function, making it as fast as a direct C callback.	4163	thunking function, making it as fast as a direct C callback.
2454		4164
2455	Example: simple class declaration and watcher initialisation	4165	Example: simple class declaration and watcher initialisation
2456		4166
2457	struct myclass	4167	struct myclass
2458	{	4168	{
2459	void io_cb (ev::io &w, int revents) { }	4169	void io_cb (ev::io &w, int revents) { }
2460	}	4170	}
2461		4171
2462	myclass obj;	4172	myclass obj;
2463	ev::io iow;	4173	ev::io iow;
2464	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);
2465		4203
2466	=item w->set<function> (void *data = 0)	4204	=item w->set<function> (void *data = 0)
2467		4205
2468	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
2469	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
…		…
2471		4209
2472	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)>.
2473		4211
2474	See the method-C<set> above for more details.	4212	See the method-C<set> above for more details.
2475		4213
2476	Example:	4214	Example: Use a plain function as callback.
2477		4215
2478	static void io_cb (ev::io &w, int revents) { }	4216	static void io_cb (ev::io &w, int revents) { }
2479	iow.set <io_cb> ();	4217	iow.set <io_cb> ();
2480		4218
2481	=item w->set (struct ev_loop *)	4219	=item w->set (loop)
2482		4220
2483	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
2484	do this when the watcher is inactive (and not pending either).	4222	do this when the watcher is inactive (and not pending either).
2485		4223
2486	=item w->set ([args])	4224	=item w->set ([arguments])
2487		4225
2488	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
2489	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
2490	automatically stopped and restarted when reconfiguring it with this	4229	gets automatically stopped and restarted when reconfiguring it with this
2491	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.
2492		4234
2493	=item w->start ()	4235	=item w->start ()
2494		4236
2495	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
2496	constructor already stores the event loop.	4238	constructor already stores the event loop.
2497		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
2498	=item w->stop ()	4246	=item w->stop ()
2499		4247
2500	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.
2501		4249
2502	=item w->again () (C<ev::timer>, C<ev::periodic> only)	4250	=item w->again () (C<ev::timer>, C<ev::periodic> only)
…		…
2514		4262
2515	=back	4263	=back
2516		4264
2517	=back	4265	=back
2518		4266
2519	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
2520	the constructor.	4268	watchers in the constructor.
2521		4269
2522	class myclass	4270	class myclass
2523	{	4271	{
2524	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);
2525	ev:idle idle void idle_cb (ev::idle &w, int revents);	4274	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2526		4275
2527	myclass (int fd)	4276	myclass (int fd)
2528	{	4277	{
2529	io .set <myclass, &myclass::io_cb > (this);	4278	io .set <myclass, &myclass::io_cb > (this);
		4279	io2 .set <myclass, &myclass::io2_cb > (this);
2530	idle.set <myclass, &myclass::idle_cb> (this);	4280	idle.set <myclass, &myclass::idle_cb> (this);
2531		4281
2532	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
2533	}	4286	}
2534	};	4287	};
2535		4288
2536		4289
2537	=head1 OTHER LANGUAGE BINDINGS	4290	=head1 OTHER LANGUAGE BINDINGS
2538		4291
2539	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
2540	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
2541	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
2542	me a note.	4295	me a note.
2543		4296
2544	=over 4	4297	=over 4
2545		4298
2546	=item Perl	4299	=item Perl
2547		4300
2548	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
2549	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,
2550	there are additional modules that implement libev-compatible interfaces	4303	there are additional modules that implement libev-compatible interfaces
2551	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),
2552	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>).
2553		4307
2554	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
2555	L<http://software.schmorp.de/pkg/EV>.	4309	L<http://software.schmorp.de/pkg/EV>.
2556		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
2557	=item Ruby	4316	=item Ruby
2558		4317
2559	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
2560	of the libev API and adds filehandle abstractions, asynchronous DNS and	4319	of the libev API and adds file handle abstractions, asynchronous DNS and
2561	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
2562	L<http://rev.rubyforge.org/>.	4321	L<http://rev.rubyforge.org/>.
2563		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
2564	=item D	4331	=item D
2565		4332
2566	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
2567	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.
2568		4354
2569	=back	4355	=back
2570		4356
2571		4357
2572	=head1 MACRO MAGIC	4358	=head1 MACRO MAGIC
2573		4359
2574	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
2575	of which is C<EV_MULTIPLICITY>. This option determines whether (most)	4361	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2576	functions and callbacks have an initial C<struct ev_loop *> argument.	4362	functions and callbacks have an initial C<struct ev_loop *> argument.
2577		4363
2578	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
2579	following macros are defined:	4365	following macros are defined:
…		…
2584		4370
2585	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
2586	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,
2587	C<EV_A_> is used when other arguments are following. Example:	4373	C<EV_A_> is used when other arguments are following. Example:
2588		4374
2589	ev_unref (EV_A);	4375	ev_unref (EV_A);
2590	ev_timer_add (EV_A_ watcher);	4376	ev_timer_add (EV_A_ watcher);
2591	ev_loop (EV_A_ 0);	4377	ev_run (EV_A_ 0);
2592		4378
2593	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,
2594	which is often provided by the following macro.	4380	which is often provided by the following macro.
2595		4381
2596	=item C<EV_P>, C<EV_P_>	4382	=item C<EV_P>, C<EV_P_>
2597		4383
2598	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
2599	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,
2600	C<EV_P_> is used when other parameters are following. Example:	4386	C<EV_P_> is used when other parameters are following. Example:
2601		4387
2602	// this is how ev_unref is being declared	4388	// this is how ev_unref is being declared
2603	static void ev_unref (EV_P);	4389	static void ev_unref (EV_P);
2604		4390
2605	// this is how you can declare your typical callback	4391	// this is how you can declare your typical callback
2606	static void cb (EV_P_ ev_timer *w, int revents)	4392	static void cb (EV_P_ ev_timer *w, int revents)
2607		4393
2608	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
2609	suitable for use with C<EV_A>.	4395	suitable for use with C<EV_A>.
2610		4396
2611	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4397	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2612		4398
2613	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
2614	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.
		4405
		4406	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		4407
		4408	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		4409	default loop has been initialised (C<UC> == unchecked). Their behaviour
		4410	is undefined when the default loop has not been initialised by a previous
		4411	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		4412
		4413	It is often prudent to use C<EV_DEFAULT> when initialising the first
		4414	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
2615		4415
2616	=back	4416	=back
2617		4417
2618	Example: Declare and initialise a check watcher, utilising the above	4418	Example: Declare and initialise a check watcher, utilising the above
2619	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
2620	or not.	4420	or not.
2621		4421
2622	static void	4422	static void
2623	check_cb (EV_P_ ev_timer *w, int revents)	4423	check_cb (EV_P_ ev_timer *w, int revents)
2624	{	4424	{
2625	ev_check_stop (EV_A_ w);	4425	ev_check_stop (EV_A_ w);
2626	}	4426	}
2627		4427
2628	ev_check check;	4428	ev_check check;
2629	ev_check_init (&check, check_cb);	4429	ev_check_init (&check, check_cb);
2630	ev_check_start (EV_DEFAULT_ &check);	4430	ev_check_start (EV_DEFAULT_ &check);
2631	ev_loop (EV_DEFAULT_ 0);	4431	ev_run (EV_DEFAULT_ 0);
2632		4432
2633	=head1 EMBEDDING	4433	=head1 EMBEDDING
2634		4434
2635	Libev can (and often is) directly embedded into host	4435	Libev can (and often is) directly embedded into host
2636	applications. Examples of applications that embed it include the Deliantra	4436	applications. Examples of applications that embed it include the Deliantra
…		…
2643	libev somewhere in your source tree).	4443	libev somewhere in your source tree).
2644		4444
2645	=head2 FILESETS	4445	=head2 FILESETS
2646		4446
2647	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
2648	in your app.	4448	in your application.
2649		4449
2650	=head3 CORE EVENT LOOP	4450	=head3 CORE EVENT LOOP
2651		4451
2652	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
2653	configuration (no autoconf):	4453	configuration (no autoconf):
2654		4454
2655	#define EV_STANDALONE 1	4455	#define EV_STANDALONE 1
2656	#include "ev.c"	4456	#include "ev.c"
2657		4457
2658	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
2659	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
2660	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
2661	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
2662	where you can put other configuration options):	4462	where you can put other configuration options):
2663		4463
2664	#define EV_STANDALONE 1	4464	#define EV_STANDALONE 1
2665	#include "ev.h"	4465	#include "ev.h"
2666		4466
2667	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++
2668	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
2669	as a bug).	4469	as a bug).
2670		4470
2671	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
2672	in your include path (e.g. in libev/ when using -Ilibev):	4472	in your include path (e.g. in libev/ when using -Ilibev):
2673		4473
2674	ev.h	4474	ev.h
2675	ev.c	4475	ev.c
2676	ev_vars.h	4476	ev_vars.h
2677	ev_wrap.h	4477	ev_wrap.h
2678		4478
2679	ev_win32.c required on win32 platforms only	4479	ev_win32.c required on win32 platforms only
2680		4480
2681	ev_select.c only when select backend is enabled (which is enabled by default)	4481	ev_select.c only when select backend is enabled
2682	ev_poll.c only when poll backend is enabled (disabled by default)	4482	ev_poll.c only when poll backend is enabled
2683	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
2684	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4485	ev_kqueue.c only when the kqueue backend is enabled
2685	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
2686		4487
2687	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
2688	to compile this single file.	4489	to compile this single file.
2689		4490
2690	=head3 LIBEVENT COMPATIBILITY API	4491	=head3 LIBEVENT COMPATIBILITY API
2691		4492
2692	To include the libevent compatibility API, also include:	4493	To include the libevent compatibility API, also include:
2693		4494
2694	#include "event.c"	4495	#include "event.c"
2695		4496
2696	in the file including F<ev.c>, and:	4497	in the file including F<ev.c>, and:
2697		4498
2698	#include "event.h"	4499	#include "event.h"
2699		4500
2700	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>.
2701		4502
2702	You need the following additional files for this:	4503	You need the following additional files for this:
2703		4504
2704	event.h	4505	event.h
2705	event.c	4506	event.c
2706		4507
2707	=head3 AUTOCONF SUPPORT	4508	=head3 AUTOCONF SUPPORT
2708		4509
2709	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
2710	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
2711	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
2712	include F<config.h> and configure itself accordingly.	4513	include F<config.h> and configure itself accordingly.
2713		4514
2714	For this of course you need the m4 file:	4515	For this of course you need the m4 file:
2715		4516
2716	libev.m4	4517	libev.m4
2717		4518
2718	=head2 PREPROCESSOR SYMBOLS/MACROS	4519	=head2 PREPROCESSOR SYMBOLS/MACROS
2719		4520
2720	Libev can be configured via a variety of preprocessor symbols you have to define	4521	Libev can be configured via a variety of preprocessor symbols you have to
2721	before including any of its files. The default is not to build for multiplicity	4522	define before including (or compiling) any of its files. The default in
2722	and only include the select backend.	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.
2723		4531
2724	=over 4	4532	=over 4
2725		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
2726	=item EV_STANDALONE	4550	=item EV_STANDALONE (h)
2727		4551
2728	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
2729	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
2730	implementations for some libevent functions (such as logging, which is not	4554	implementations for some libevent functions (such as logging, which is not
2731	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
2732	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.
2733		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
2734	=item EV_USE_MONOTONIC	4570	=item EV_USE_MONOTONIC
2735		4571
2736	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
2737	monotonic clock option at both compiletime and runtime. Otherwise no use	4573	monotonic clock option at both compile time and runtime. Otherwise no
2738	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,
2739	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
2740	the functionality isn't available is safe, though, although you have	4576	when the functionality isn't available is safe, though, although you have
2741	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>
2742	function is hiding in (often F<-lrt>).	4578	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2743		4579
2744	=item EV_USE_REALTIME	4580	=item EV_USE_REALTIME
2745		4581
2746	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
2747	realtime clock option at compiletime (and assume its availability at	4583	real-time clock option at compile time (and assume its availability
2748	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
2749	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	4585	option will be attempted. This effectively replaces C<gettimeofday>
2750	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	4586	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2751	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>).
2752		4601
2753	=item EV_USE_NANOSLEEP	4602	=item EV_USE_NANOSLEEP
2754		4603
2755	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
2756	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 ()>.
2757		4606
		4607	=item EV_USE_EVENTFD
		4608
		4609	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		4610	available and will probe for kernel support at runtime. This will improve
		4611	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		4612	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4613	2.7 or newer, otherwise disabled.
		4614
2758	=item EV_USE_SELECT	4615	=item EV_USE_SELECT
2759		4616
2760	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
2761	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
2762	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
2763	will not be compiled in.	4620	will not be compiled in.
2764		4621
2765	=item EV_SELECT_USE_FD_SET	4622	=item EV_SELECT_USE_FD_SET
2766		4623
2767	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>
2768	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
2769	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
2770	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
2771	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
2772	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,
2773	influence the size of the C<fd_set> used.	4630	configures the maximum size of the C<fd_set>.
2774		4631
2775	=item EV_SELECT_IS_WINSOCKET	4632	=item EV_SELECT_IS_WINSOCKET
2776		4633
2777	When defined to C<1>, the select backend will assume that	4634	When defined to C<1>, the select backend will assume that
2778	select/socket/connect etc. don't understand file descriptors but	4635	select/socket/connect etc. don't understand file descriptors but
…		…
2780	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
2781	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,
2782	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
2783	on win32. Should not be defined on non-win32 platforms.	4640	on win32. Should not be defined on non-win32 platforms.
2784		4641
2785	=item EV_FD_TO_WIN32_HANDLE	4642	=item EV_FD_TO_WIN32_HANDLE(fd)
2786		4643
2787	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
2788	file descriptors to socket handles. When not defining this symbol (the	4645	file descriptors to socket handles. When not defining this symbol (the
2789	default), then libev will call C<_get_osfhandle>, which is usually	4646	default), then libev will call C<_get_osfhandle>, which is usually
2790	correct. In some cases, programs use their own file descriptor management,	4647	correct. In some cases, programs use their own file descriptor management,
2791	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.
2792		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
2793	=item EV_USE_POLL	4671	=item EV_USE_POLL
2794		4672
2795	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)
2796	backend. Otherwise it will be enabled on non-win32 platforms. It	4674	backend. Otherwise it will be enabled on non-win32 platforms. It
2797	takes precedence over select.	4675	takes precedence over select.
2798		4676
2799	=item EV_USE_EPOLL	4677	=item EV_USE_EPOLL
2800		4678
2801	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
2802	C<epoll>(7) backend. Its availability will be detected at runtime,	4680	C<epoll>(7) backend. Its availability will be detected at runtime,
2803	otherwise another method will be used as fallback. This is the	4681	otherwise another method will be used as fallback. This is the preferred
2804	preferred backend for GNU/Linux systems.	4682	backend for GNU/Linux systems. If undefined, it will be enabled if the
		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.
2805		4691
2806	=item EV_USE_KQUEUE	4692	=item EV_USE_KQUEUE
2807		4693
2808	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
2809	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,
…		…
2822	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
2823	backend for Solaris 10 systems.	4709	backend for Solaris 10 systems.
2824		4710
2825	=item EV_USE_DEVPOLL	4711	=item EV_USE_DEVPOLL
2826		4712
2827	reserved for future expansion, works like the USE symbols above.	4713	Reserved for future expansion, works like the USE symbols above.
2828		4714
2829	=item EV_USE_INOTIFY	4715	=item EV_USE_INOTIFY
2830		4716
2831	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
2832	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
2833	be detected at runtime.	4719	be detected at runtime. If undefined, it will be enabled if the headers
		4720	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		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.
2834		4735
2835	=item EV_ATOMIC_T	4736	=item EV_ATOMIC_T
2836		4737
2837	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
2838	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
2839	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
2840	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
2841	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.
2842		4744
2843	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>
2844	(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.
2845		4747
2846	=item EV_H	4748	=item EV_H (h)
2847		4749
2848	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
2849	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
2850	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.
2851		4753
2852	=item EV_CONFIG_H	4754	=item EV_CONFIG_H (h)
2853		4755
2854	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
2855	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
2856	C<EV_H>, above.	4758	C<EV_H>, above.
2857		4759
2858	=item EV_EVENT_H	4760	=item EV_EVENT_H (h)
2859		4761
2860	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
2861	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">.
2862		4764
2863	=item EV_PROTOTYPES	4765	=item EV_PROTOTYPES (h)
2864		4766
2865	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
2866	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
2867	occasionally useful if you want to provide your own wrapper functions	4769	occasionally useful if you want to provide your own wrapper functions
2868	around libev functions.	4770	around libev functions.
…		…
2873	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
2874	additional independent event loops. Otherwise there will be no support	4776	additional independent event loops. Otherwise there will be no support
2875	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
2876	argument. Instead, all functions act on the single default loop.	4778	argument. Instead, all functions act on the single default loop.
2877		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
2878	=item EV_MINPRI	4784	=item EV_MINPRI
2879		4785
2880	=item EV_MAXPRI	4786	=item EV_MAXPRI
2881		4787
2882	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
…		…
2887	When doing priority-based operations, libev usually has to linearly search	4793	When doing priority-based operations, libev usually has to linearly search
2888	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
2889	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
2890	fine.	4796	fine.
2891		4797
2892	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
2893	C<0> will save some memory and cpu.	4799	both to C<0> will save some memory and CPU.
2894		4800
2895	=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.
2896		4804
2897	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
2898	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
2899	code.	4807	is not. Disabling watcher types mainly saves code size.
2900		4808
2901	=item EV_IDLE_ENABLE	4809	=item EV_FEATURES
2902
2903	If undefined or defined to be C<1>, then idle watchers are supported. If
2904	defined to be C<0>, then they are not. Disabling them saves a few kB of
2905	code.
2906
2907	=item EV_EMBED_ENABLE
2908
2909	If undefined or defined to be C<1>, then embed watchers are supported. If
2910	defined to be C<0>, then they are not.
2911
2912	=item EV_STAT_ENABLE
2913
2914	If undefined or defined to be C<1>, then stat watchers are supported. If
2915	defined to be C<0>, then they are not.
2916
2917	=item EV_FORK_ENABLE
2918
2919	If undefined or defined to be C<1>, then fork watchers are supported. If
2920	defined to be C<0>, then they are not.
2921
2922	=item EV_ASYNC_ENABLE
2923
2924	If undefined or defined to be C<1>, then async watchers are supported. If
2925	defined to be C<0>, then they are not.
2926
2927	=item EV_MINIMAL
2928		4810
2929	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
2930	speed, define this symbol to C<1>. Currently only used for gcc to override	4812	speed (but with the full API), you can define this symbol to request
2931	some inlining decisions, saves roughly 30% codesize of amd64.	4813	certain subsets of functionality. The default is to enable all features
		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.
2932		4930
2933	=item EV_PID_HASHSIZE	4931	=item EV_PID_HASHSIZE
2934		4932
2935	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
2936	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),
2937	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
2938	increase this value (I<must> be a power of two).	4936	might want to increase this value (I<must> be a power of two).
2939		4937
2940	=item EV_INOTIFY_HASHSIZE	4938	=item EV_INOTIFY_HASHSIZE
2941		4939
2942	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
2943	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>
2944	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
2945	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
2946	two).	4944	power of two).
		4945
		4946	=item EV_USE_4HEAP
		4947
		4948	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4949	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		4950	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		4951	faster performance with many (thousands) of watchers.
		4952
		4953	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4954	will be C<0>.
		4955
		4956	=item EV_HEAP_CACHE_AT
		4957
		4958	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4959	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		4960	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		4961	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		4962	but avoids random read accesses on heap changes. This improves performance
		4963	noticeably with many (hundreds) of watchers.
		4964
		4965	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		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>.
2947		4980
2948	=item EV_COMMON	4981	=item EV_COMMON
2949		4982
2950	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
2951	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
2952	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,
2953	though, and it must be identical each time.	4986	though, and it must be identical each time.
2954		4987
2955	For example, the perl EV module uses something like this:	4988	For example, the perl EV module uses something like this:
2956		4989
2957	#define EV_COMMON \	4990	#define EV_COMMON \
2958	SV *self; /* contains this struct */ \	4991	SV *self; /* contains this struct */ \
2959	SV *cb_sv, *fh /* note no trailing ";" */	4992	SV *cb_sv, *fh /* note no trailing ";" */
2960		4993
2961	=item EV_CB_DECLARE (type)	4994	=item EV_CB_DECLARE (type)
2962		4995
2963	=item EV_CB_INVOKE (watcher, revents)	4996	=item EV_CB_INVOKE (watcher, revents)
2964		4997
…		…
2969	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
2970	their default definitions. One possible use for overriding these is to	5003	their default definitions. One possible use for overriding these is to
2971	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
2972	method calls instead of plain function calls in C++.	5005	method calls instead of plain function calls in C++.
2973		5006
		5007	=back
		5008
2974	=head2 EXPORTED API SYMBOLS	5009	=head2 EXPORTED API SYMBOLS
2975		5010
2976	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
2977	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
2978	all public symbols, one per line:	5013	all public symbols, one per line:
2979		5014
2980	Symbols.ev for libev proper	5015	Symbols.ev for libev proper
2981	Symbols.event for the libevent emulation	5016	Symbols.event for the libevent emulation
2982		5017
2983	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
2984	multiple versions of libev linked together (which is obviously bad in	5019	multiple versions of libev linked together (which is obviously bad in
2985	itself, but sometimes it is inconvinient to avoid this).	5020	itself, but sometimes it is inconvenient to avoid this).
2986		5021
2987	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
2988	include before including F<ev.h>:	5023	include before including F<ev.h>:
2989		5024
2990	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h	5025	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
…		…
3007	file.	5042	file.
3008		5043
3009	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
3010	that everybody includes and which overrides some configure choices:	5045	that everybody includes and which overrides some configure choices:
3011		5046
3012	#define EV_MINIMAL 1	5047	#define EV_FEATURES 8
3013	#define EV_USE_POLL 0	5048	#define EV_USE_SELECT 1
3014	#define EV_MULTIPLICITY 0
3015	#define EV_PERIODIC_ENABLE 0	5049	#define EV_PREPARE_ENABLE 1
		5050	#define EV_IDLE_ENABLE 1
3016	#define EV_STAT_ENABLE 0	5051	#define EV_SIGNAL_ENABLE 1
3017	#define EV_FORK_ENABLE 0	5052	#define EV_CHILD_ENABLE 1
		5053	#define EV_USE_STDEXCEPT 0
3018	#define EV_CONFIG_H <config.h>	5054	#define EV_CONFIG_H <config.h>
3019	#define EV_MINPRI 0
3020	#define EV_MAXPRI 0
3021		5055
3022	#include "ev++.h"	5056	#include "ev++.h"
3023		5057
3024	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:
3025		5059
3026	#include "ev_cpp.h"	5060	#include "ev_cpp.h"
3027	#include "ev.c"	5061	#include "ev.c"
3028		5062
		5063	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
3029		5064
3030	=head1 COMPLEXITIES	5065	=head2 THREADS AND COROUTINES
3031		5066
3032	In this section the complexities of (many of) the algorithms used inside	5067	=head3 THREADS
3033	libev will be explained. For complexity discussions about backends see the
3034	documentation for C<ev_default_init>.
3035		5068
3036	All of the following are about amortised time: If an array needs to be	5069	All libev functions are reentrant and thread-safe unless explicitly
3037	extended, libev needs to realloc and move the whole array, but this	5070	documented otherwise, but libev implements no locking itself. This means
3038	happens asymptotically never with higher number of elements, so O(1) might	5071	that you can use as many loops as you want in parallel, as long as there
3039	mean it might do a lengthy realloc operation in rare cases, but on average	5072	are no concurrent calls into any libev function with the same loop
3040	it is much faster and asymptotically approaches constant time.	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.
		5076
		5077	Or to put it differently: calls with different loop parameters can be done
		5078	concurrently from multiple threads, calls with the same loop parameter
		5079	must be done serially (but can be done from different threads, as long as
		5080	only one thread ever is inside a call at any point in time, e.g. by using
		5081	a mutex per loop).
		5082
		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
		5090	help you, but here is some generic advice:
3041		5091
3042	=over 4	5092	=over 4
3043		5093
3044	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	5094	=item * most applications have a main thread: use the default libev loop
		5095	in that thread, or create a separate thread running only the default loop.
3045		5096
3046	This means that, when you have a watcher that triggers in one hour and	5097	This helps integrating other libraries or software modules that use libev
3047	there are 100 watchers that would trigger before that then inserting will	5098	themselves and don't care/know about threading.
3048	have to skip roughly seven (C<ld 100>) of these watchers.
3049		5099
3050	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)	5100	=item * one loop per thread is usually a good model.
3051		5101
3052	That means that changing a timer costs less than removing/adding them	5102	Doing this is almost never wrong, sometimes a better-performance model
3053	as only the relative motion in the event queue has to be paid for.	5103	exists, but it is always a good start.
3054		5104
3055	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)	5105	=item * other models exist, such as the leader/follower pattern, where one
		5106	loop is handed through multiple threads in a kind of round-robin fashion.
3056		5107
3057	These just add the watcher into an array or at the head of a list.	5108	Choosing a model is hard - look around, learn, know that usually you can do
		5109	better than you currently do :-)
3058		5110
3059	=item Stopping check/prepare/idle/fork/async watchers: O(1)	5111	=item * often you need to talk to some other thread which blocks in the
		5112	event loop.
3060		5113
3061	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	5114	C<ev_async> watchers can be used to wake them up from other threads safely
		5115	(or from signal contexts...).
3062		5116
3063	These watchers are stored in lists then need to be walked to find the	5117	An example use would be to communicate signals or other events that only
3064	correct watcher to remove. The lists are usually short (you don't usually	5118	work in the default loop by registering the signal watcher with the
3065	have many watchers waiting for the same fd or signal).	5119	default loop and triggering an C<ev_async> watcher from the default loop
3066		5120	watcher callback into the event loop interested in the signal.
3067	=item Finding the next timer in each loop iteration: O(1)
3068
3069	By virtue of using a binary heap, the next timer is always found at the
3070	beginning of the storage array.
3071
3072	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
3073
3074	A change means an I/O watcher gets started or stopped, which requires
3075	libev to recalculate its status (and possibly tell the kernel, depending
3076	on backend and wether C<ev_io_set> was used).
3077
3078	=item Activating one watcher (putting it into the pending state): O(1)
3079
3080	=item Priority handling: O(number_of_priorities)
3081
3082	Priorities are implemented by allocating some space for each
3083	priority. When doing priority-based operations, libev usually has to
3084	linearly search all the priorities, but starting/stopping and activating
3085	watchers becomes O(1) w.r.t. priority handling.
3086
3087	=item Sending an ev_async: O(1)
3088
3089	=item Processing ev_async_send: O(number_of_async_watchers)
3090
3091	=item Processing signals: O(max_signal_number)
3092
3093	Sending involves a syscall I<iff> there were no other C<ev_async_send>
3094	calls in the current loop iteration. Checking for async and signal events
3095	involves iterating over all running async watchers or all signal numbers.
3096		5121
3097	=back	5122	=back
3098		5123
		5124	See also L</THREAD LOCKING EXAMPLE>.
3099		5125
3100	=head1 Win32 platform limitations and workarounds	5126	=head3 COROUTINES
		5127
		5128	Libev is very accommodating to coroutines ("cooperative threads"):
		5129	libev fully supports nesting calls to its functions from different
		5130	coroutines (e.g. you can call C<ev_run> on the same loop from two
		5131	different coroutines, and switch freely between both coroutines running
		5132	the loop, as long as you don't confuse yourself). The only exception is
		5133	that you must not do this from C<ev_periodic> reschedule callbacks.
		5134
		5135	Care has been taken to ensure that libev does not keep local state inside
		5136	C<ev_run>, and other calls do not usually allow for coroutine switches as
		5137	they do not call any callbacks.
		5138
		5139	=head2 COMPILER WARNINGS
		5140
		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.
		5144
		5145	However, these are unavoidable for many reasons. For one, each compiler
		5146	has different warnings, and each user has different tastes regarding
		5147	warning options. "Warn-free" code therefore cannot be a goal except when
		5148	targeting a specific compiler and compiler-version.
		5149
		5150	Another reason is that some compiler warnings require elaborate
		5151	workarounds, or other changes to the code that make it less clear and less
		5152	maintainable.
		5153
		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.
		5160
		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.
		5166
		5167
		5168	=head2 VALGRIND
		5169
		5170	Valgrind has a special section here because it is a popular tool that is
		5171	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		5172
		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:
		5175
		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.
		5179
		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.
		5182
		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.
		5187
		5188	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		5189	make it into some kind of religion.
		5190
		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.
		5196
		5197	If you need, for some reason, empty reports from valgrind for your project
		5198	I suggest using suppression lists.
		5199
		5200
		5201	=head1 PORTABILITY NOTES
		5202
		5203	=head2 GNU/LINUX 32 BIT LIMITATIONS
		5204
		5205	GNU/Linux is the only common platform that supports 64 bit file/large file
		5206	interfaces but I<disables> them by default.
		5207
		5208	That means that libev compiled in the default environment doesn't support
		5209	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
		5210
		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.
		5214
		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.
		5218
		5219	=head2 OS/X AND DARWIN BUGS
		5220
		5221	The whole thing is a bug if you ask me - basically any system interface
		5222	you touch is broken, whether it is locales, poll, kqueue or even the
		5223	OpenGL drivers.
		5224
		5225	=head3 C<kqueue> is buggy
		5226
		5227	The kqueue syscall is broken in all known versions - most versions support
		5228	only sockets, many support pipes.
		5229
		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
3101		5292
3102	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
3103	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
3104	model. Libev still offers limited functionality on this platform in	5295	model. Libev still offers limited functionality on this platform in
3105	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
3106	descriptors. This only applies when using Win32 natively, not when using	5297	descriptors. This only applies when using Win32 natively, not when using
3107	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.
		5301
		5302	Lifting these limitations would basically require the full
		5303	re-implementation of the I/O system. If you are into this kind of thing,
		5304	then note that glib does exactly that for you in a very portable way (note
		5305	also that glib is the slowest event library known to man).
3108		5306
3109	There is no supported compilation method available on windows except	5307	There is no supported compilation method available on windows except
3110	embedding it into other applications.	5308	embedding it into other applications.
3111		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).
		5319
3112	Due to the many, low, and arbitrary limits on the win32 platform and the	5320	Due to the many, low, and arbitrary limits on the win32 platform and
3113	abysmal performance of winsockets, using a large number of sockets is not	5321	the abysmal performance of winsockets, using a large number of sockets
3114	recommended (and not reasonable). If your program needs to use more than	5322	is not recommended (and not reasonable). If your program needs to use
3115	a hundred or so sockets, then likely it needs to use a totally different	5323	more than a hundred or so sockets, then likely it needs to use a totally
3116	implementation for windows, as libev offers the POSIX model, which cannot	5324	different implementation for windows, as libev offers the POSIX readiness
3117	be implemented efficiently on windows (microsoft monopoly games).	5325	notification model, which cannot be implemented efficiently on windows
		5326	(due to Microsoft monopoly games).
3118		5327
3119	=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>:
3120		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
3121	=item The winsocket select function	5343	=head3 The winsocket C<select> function
3122		5344
3123	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
3124	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
3125	very inefficient, and also requires a mapping from file descriptors	5347	also extremely buggy). This makes select very inefficient, and also
3126	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
3127	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
3128	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.
3129		5352
3130	The configuration for a "naked" win32 using the microsoft runtime	5353	The configuration for a "naked" win32 using the Microsoft runtime
3131	libraries and raw winsocket select is:	5354	libraries and raw winsocket select is:
3132		5355
3133	#define EV_USE_SELECT 1	5356	#define EV_USE_SELECT 1
3134	#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 */
3135		5358
3136	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
3137	complexity in the O(n²) range when using win32.	5360	complexity in the O(n²) range when using win32.
3138		5361
3139	=item Limited number of file descriptors	5362	=head3 Limited number of file descriptors
3140		5363
3141	Windows has numerous arbitrary (and low) limits on things. Early versions	5364	Windows has numerous arbitrary (and low) limits on things.
3142	of winsocket's select only supported waiting for a max. of C<64> handles	5365
		5366	Early versions of winsocket's select only supported waiting for a maximum
3143	(probably owning to the fact that all windows kernels can only wait for	5367	of C<64> handles (probably owning to the fact that all windows kernels
3144	C<64> things at the same time internally; microsoft recommends spawning a	5368	can only wait for C<64> things at the same time internally; Microsoft
3145	chain of threads and wait for 63 handles and the previous thread in each).	5369	recommends spawning a chain of threads and wait for 63 handles and the
		5370	previous thread in each. Sounds great!).
3146		5371
3147	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>
3148	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
3149	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
3150	select emulation on windows).	5375	other interpreters do their own select emulation on windows).
3151		5376
3152	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
3153	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>
3154	or something like this inside microsoft). You can increase this by calling	5379	fetish or something like this inside Microsoft). You can increase this
3155	C<_setmaxstdio>, which can increase this limit to C<2048> (another	5380	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
3156	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
3157	libraries.
3158
3159	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
3160	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,
3161	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
3162	calling select (O(n²)) will likely make this unworkable.	5385	the cost of calling select (O(n²)) will likely make this unworkable.
		5386
		5387	=head2 PORTABILITY REQUIREMENTS
		5388
		5389	In addition to a working ISO-C implementation and of course the
		5390	backend-specific APIs, libev relies on a few additional extensions:
		5391
		5392	=over 4
		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
		5413	=item C<sig_atomic_t volatile> must be thread-atomic as well
		5414
		5415	The type C<sig_atomic_t volatile> (or whatever is defined as
		5416	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		5417	threads. This is not part of the specification for C<sig_atomic_t>, but is
		5418	believed to be sufficiently portable.
		5419
		5420	=item C<sigprocmask> must work in a threaded environment
		5421
		5422	Libev uses C<sigprocmask> to temporarily block signals. This is not
		5423	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		5424	pthread implementations will either allow C<sigprocmask> in the "main
		5425	thread" or will block signals process-wide, both behaviours would
		5426	be compatible with libev. Interaction between C<sigprocmask> and
		5427	C<pthread_sigmask> could complicate things, however.
		5428
		5429	The most portable way to handle signals is to block signals in all threads
		5430	except the initial one, and run the signal handling loop in the initial
		5431	thread as well.
		5432
		5433	=item C<long> must be large enough for common memory allocation sizes
		5434
		5435	To improve portability and simplify its API, libev uses C<long> internally
		5436	instead of C<size_t> when allocating its data structures. On non-POSIX
		5437	systems (Microsoft...) this might be unexpectedly low, but is still at
		5438	least 31 bits everywhere, which is enough for hundreds of millions of
		5439	watchers.
		5440
		5441	=item C<double> must hold a time value in seconds with enough accuracy
		5442
		5443	The type C<double> is used to represent timestamps. It is required to
		5444	have at least 51 bits of mantissa (and 9 bits of exponent), which is
		5445	good enough for at least into the year 4000 with millisecond accuracy
		5446	(the design goal for libev). This requirement is overfulfilled by
		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).
3163		5453
3164	=back	5454	=back
3165		5455
		5456	If you know of other additional requirements drop me a note.
		5457
		5458
		5459	=head1 ALGORITHMIC COMPLEXITIES
		5460
		5461	In this section the complexities of (many of) the algorithms used inside
		5462	libev will be documented. For complexity discussions about backends see
		5463	the documentation for C<ev_default_init>.
		5464
		5465	All of the following are about amortised time: If an array needs to be
		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.
		5470
		5471	=over 4
		5472
		5473	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		5474
		5475	This means that, when you have a watcher that triggers in one hour and
		5476	there are 100 watchers that would trigger before that, then inserting will
		5477	have to skip roughly seven (C<ld 100>) of these watchers.
		5478
		5479	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		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
3166		5662
3167	=head1 AUTHOR	5663	=head1 AUTHOR
3168		5664
3169	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.
3170		5667

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