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Revision 1.74 by root, Sat Dec 8 14:12:08 2007 UTC vs.
Revision 1.395 by root, Tue Jan 24 16:38:55 2012 UTC

…		…
2		2
3	libev - a high performance full-featured event loop written in C	3	libev - a high performance full-featured event loop written in C
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
8		8
9	=head1 EXAMPLE PROGRAM	9	=head2 EXAMPLE PROGRAM
10		10
		11	// a single header file is required
11	#include <ev.h>	12	#include <ev.h>
12		13
		14	#include <stdio.h> // for puts
		15
		16	// every watcher type has its own typedef'd struct
		17	// with the name ev_TYPE
13	ev_io stdin_watcher;	18	ev_io stdin_watcher;
14	ev_timer timeout_watcher;	19	ev_timer timeout_watcher;
15		20
16	/* called when data readable on stdin */	21	// all watcher callbacks have a similar signature
		22	// this callback is called when data is readable on stdin
17	static void	23	static void
18	stdin_cb (EV_P_ struct ev_io *w, int revents)	24	stdin_cb (EV_P_ ev_io *w, int revents)
19	{	25	{
20	/* puts ("stdin ready"); */	26	puts ("stdin ready");
21	ev_io_stop (EV_A_ w); /* just a syntax example */	27	// for one-shot events, one must manually stop the watcher
22	ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */	28	// with its corresponding stop function.
		29	ev_io_stop (EV_A_ w);
		30
		31	// this causes all nested ev_run's to stop iterating
		32	ev_break (EV_A_ EVBREAK_ALL);
23	}	33	}
24		34
		35	// another callback, this time for a time-out
25	static void	36	static void
26	timeout_cb (EV_P_ struct ev_timer *w, int revents)	37	timeout_cb (EV_P_ ev_timer *w, int revents)
27	{	38	{
28	/* puts ("timeout"); */	39	puts ("timeout");
29	ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */	40	// this causes the innermost ev_run to stop iterating
		41	ev_break (EV_A_ EVBREAK_ONE);
30	}	42	}
31		43
32	int	44	int
33	main (void)	45	main (void)
34	{	46	{
35	struct ev_loop *loop = ev_default_loop (0);	47	// use the default event loop unless you have special needs
		48	struct ev_loop *loop = EV_DEFAULT;
36		49
37	/* initialise an io watcher, then start it */	50	// initialise an io watcher, then start it
		51	// this one will watch for stdin to become readable
38	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
39	ev_io_start (loop, &stdin_watcher);	53	ev_io_start (loop, &stdin_watcher);
40		54
		55	// initialise a timer watcher, then start it
41	/* simple non-repeating 5.5 second timeout */	56	// simple non-repeating 5.5 second timeout
42	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);	57	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
43	ev_timer_start (loop, &timeout_watcher);	58	ev_timer_start (loop, &timeout_watcher);
44		59
45	/* loop till timeout or data ready */	60	// now wait for events to arrive
46	ev_loop (loop, 0);	61	ev_run (loop, 0);
47		62
		63	// break was called, so exit
48	return 0;	64	return 0;
49	}	65	}
50		66
51	=head1 DESCRIPTION	67	=head1 ABOUT THIS DOCUMENT
52		68
		69	This document documents the libev software package.
		70
53	The newest version of this document is also available as a html-formatted	71	The newest version of this document is also available as an html-formatted
54	web page you might find easier to navigate when reading it for the first	72	web page you might find easier to navigate when reading it for the first
55	time: L<http://cvs.schmorp.de/libev/ev.html>.	73	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		74
		75	While this document tries to be as complete as possible in documenting
		76	libev, its usage and the rationale behind its design, it is not a tutorial
		77	on event-based programming, nor will it introduce event-based programming
		78	with libev.
		79
		80	Familiarity with event based programming techniques in general is assumed
		81	throughout this document.
		82
		83	=head1 WHAT TO READ WHEN IN A HURRY
		84
		85	This manual tries to be very detailed, but unfortunately, this also makes
		86	it very long. If you just want to know the basics of libev, I suggest
		87	reading L<ANATOMY OF A WATCHER>, then the L<EXAMPLE PROGRAM> above and
		88	look up the missing functions in L<GLOBAL FUNCTIONS> and the C<ev_io> and
		89	C<ev_timer> sections in L<WATCHER TYPES>.
		90
		91	=head1 ABOUT LIBEV
56		92
57	Libev is an event loop: you register interest in certain events (such as a	93	Libev is an event loop: you register interest in certain events (such as a
58	file descriptor being readable or a timeout occuring), and it will manage	94	file descriptor being readable or a timeout occurring), and it will manage
59	these event sources and provide your program with events.	95	these event sources and provide your program with events.
60		96
61	To do this, it must take more or less complete control over your process	97	To do this, it must take more or less complete control over your process
62	(or thread) by executing the I<event loop> handler, and will then	98	(or thread) by executing the I<event loop> handler, and will then
63	communicate events via a callback mechanism.	99	communicate events via a callback mechanism.
…		…
65	You register interest in certain events by registering so-called I<event	101	You register interest in certain events by registering so-called I<event
66	watchers>, which are relatively small C structures you initialise with the	102	watchers>, which are relatively small C structures you initialise with the
67	details of the event, and then hand it over to libev by I<starting> the	103	details of the event, and then hand it over to libev by I<starting> the
68	watcher.	104	watcher.
69		105
70	=head1 FEATURES	106	=head2 FEATURES
71		107
72	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	108	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
73	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	109	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
74	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	110	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
75	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	111	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
76	with customised rescheduling (C<ev_periodic>), synchronous signals	112	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
77	(C<ev_signal>), process status change events (C<ev_child>), and event	113	timers (C<ev_timer>), absolute timers with customised rescheduling
78	watchers dealing with the event loop mechanism itself (C<ev_idle>,	114	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
79	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as	115	change events (C<ev_child>), and event watchers dealing with the event
80	file watchers (C<ev_stat>) and even limited support for fork events	116	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
81	(C<ev_fork>).	117	C<ev_check> watchers) as well as file watchers (C<ev_stat>) and even
		118	limited support for fork events (C<ev_fork>).
82		119
83	It also is quite fast (see this	120	It also is quite fast (see this
84	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent	121	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
85	for example).	122	for example).
86		123
87	=head1 CONVENTIONS	124	=head2 CONVENTIONS
88		125
89	Libev is very configurable. In this manual the default configuration will	126	Libev is very configurable. In this manual the default (and most common)
90	be described, which supports multiple event loops. For more info about	127	configuration will be described, which supports multiple event loops. For
91	various configuration options please have a look at B<EMBED> section in	128	more info about various configuration options please have a look at
92	this manual. If libev was configured without support for multiple event	129	B<EMBED> section in this manual. If libev was configured without support
93	loops, then all functions taking an initial argument of name C<loop>	130	for multiple event loops, then all functions taking an initial argument of
94	(which is always of type C<struct ev_loop *>) will not have this argument.	131	name C<loop> (which is always of type C<struct ev_loop *>) will not have
		132	this argument.
95		133
96	=head1 TIME REPRESENTATION	134	=head2 TIME REPRESENTATION
97		135
98	Libev represents time as a single floating point number, representing the	136	Libev represents time as a single floating point number, representing
99	(fractional) number of seconds since the (POSIX) epoch (somewhere near	137	the (fractional) number of seconds since the (POSIX) epoch (in practice
100	the beginning of 1970, details are complicated, don't ask). This type is	138	somewhere near the beginning of 1970, details are complicated, don't
101	called C<ev_tstamp>, which is what you should use too. It usually aliases	139	ask). This type is called C<ev_tstamp>, which is what you should use
102	to the C<double> type in C, and when you need to do any calculations on	140	too. It usually aliases to the C<double> type in C. When you need to do
103	it, you should treat it as such.	141	any calculations on it, you should treat it as some floating point value.
		142
		143	Unlike the name component C<stamp> might indicate, it is also used for
		144	time differences (e.g. delays) throughout libev.
		145
		146	=head1 ERROR HANDLING
		147
		148	Libev knows three classes of errors: operating system errors, usage errors
		149	and internal errors (bugs).
		150
		151	When libev catches an operating system error it cannot handle (for example
		152	a system call indicating a condition libev cannot fix), it calls the callback
		153	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		154	abort. The default is to print a diagnostic message and to call C<abort
		155	()>.
		156
		157	When libev detects a usage error such as a negative timer interval, then
		158	it will print a diagnostic message and abort (via the C<assert> mechanism,
		159	so C<NDEBUG> will disable this checking): these are programming errors in
		160	the libev caller and need to be fixed there.
		161
		162	Libev also has a few internal error-checking C<assert>ions, and also has
		163	extensive consistency checking code. These do not trigger under normal
		164	circumstances, as they indicate either a bug in libev or worse.
		165
104		166
105	=head1 GLOBAL FUNCTIONS	167	=head1 GLOBAL FUNCTIONS
106		168
107	These functions can be called anytime, even before initialising the	169	These functions can be called anytime, even before initialising the
108	library in any way.	170	library in any way.
…		…
111		173
112	=item ev_tstamp ev_time ()	174	=item ev_tstamp ev_time ()
113		175
114	Returns the current time as libev would use it. Please note that the	176	Returns the current time as libev would use it. Please note that the
115	C<ev_now> function is usually faster and also often returns the timestamp	177	C<ev_now> function is usually faster and also often returns the timestamp
116	you actually want to know.	178	you actually want to know. Also interesting is the combination of
		179	C<ev_now_update> and C<ev_now>.
		180
		181	=item ev_sleep (ev_tstamp interval)
		182
		183	Sleep for the given interval: The current thread will be blocked
		184	until either it is interrupted or the given time interval has
		185	passed (approximately - it might return a bit earlier even if not
		186	interrupted). Returns immediately if C<< interval <= 0 >>.
		187
		188	Basically this is a sub-second-resolution C<sleep ()>.
		189
		190	The range of the C<interval> is limited - libev only guarantees to work
		191	with sleep times of up to one day (C<< interval <= 86400 >>).
117		192
118	=item int ev_version_major ()	193	=item int ev_version_major ()
119		194
120	=item int ev_version_minor ()	195	=item int ev_version_minor ()
121		196
122	You can find out the major and minor version numbers of the library	197	You can find out the major and minor ABI version numbers of the library
123	you linked against by calling the functions C<ev_version_major> and	198	you linked against by calling the functions C<ev_version_major> and
124	C<ev_version_minor>. If you want, you can compare against the global	199	C<ev_version_minor>. If you want, you can compare against the global
125	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the	200	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
126	version of the library your program was compiled against.	201	version of the library your program was compiled against.
127		202
		203	These version numbers refer to the ABI version of the library, not the
		204	release version.
		205
128	Usually, it's a good idea to terminate if the major versions mismatch,	206	Usually, it's a good idea to terminate if the major versions mismatch,
129	as this indicates an incompatible change. Minor versions are usually	207	as this indicates an incompatible change. Minor versions are usually
130	compatible to older versions, so a larger minor version alone is usually	208	compatible to older versions, so a larger minor version alone is usually
131	not a problem.	209	not a problem.
132		210
133	Example: Make sure we haven't accidentally been linked against the wrong	211	Example: Make sure we haven't accidentally been linked against the wrong
134	version.	212	version (note, however, that this will not detect other ABI mismatches,
		213	such as LFS or reentrancy).
135		214
136	assert (("libev version mismatch",	215	assert (("libev version mismatch",
137	ev_version_major () == EV_VERSION_MAJOR	216	ev_version_major () == EV_VERSION_MAJOR
138	&& ev_version_minor () >= EV_VERSION_MINOR));	217	&& ev_version_minor () >= EV_VERSION_MINOR));
139		218
140	=item unsigned int ev_supported_backends ()	219	=item unsigned int ev_supported_backends ()
141		220
142	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	221	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
143	value) compiled into this binary of libev (independent of their	222	value) compiled into this binary of libev (independent of their
…		…
145	a description of the set values.	224	a description of the set values.
146		225
147	Example: make sure we have the epoll method, because yeah this is cool and	226	Example: make sure we have the epoll method, because yeah this is cool and
148	a must have and can we have a torrent of it please!!!11	227	a must have and can we have a torrent of it please!!!11
149		228
150	assert (("sorry, no epoll, no sex",	229	assert (("sorry, no epoll, no sex",
151	ev_supported_backends () & EVBACKEND_EPOLL));	230	ev_supported_backends () & EVBACKEND_EPOLL));
152		231
153	=item unsigned int ev_recommended_backends ()	232	=item unsigned int ev_recommended_backends ()
154		233
155	Return the set of all backends compiled into this binary of libev and also	234	Return the set of all backends compiled into this binary of libev and
156	recommended for this platform. This set is often smaller than the one	235	also recommended for this platform, meaning it will work for most file
		236	descriptor types. This set is often smaller than the one returned by
157	returned by C<ev_supported_backends>, as for example kqueue is broken on	237	C<ev_supported_backends>, as for example kqueue is broken on most BSDs
158	most BSDs and will not be autodetected unless you explicitly request it	238	and will not be auto-detected unless you explicitly request it (assuming
159	(assuming you know what you are doing). This is the set of backends that	239	you know what you are doing). This is the set of backends that libev will
160	libev will probe for if you specify no backends explicitly.	240	probe for if you specify no backends explicitly.
161		241
162	=item unsigned int ev_embeddable_backends ()	242	=item unsigned int ev_embeddable_backends ()
163		243
164	Returns the set of backends that are embeddable in other event loops. This	244	Returns the set of backends that are embeddable in other event loops. This
165	is the theoretical, all-platform, value. To find which backends	245	value is platform-specific but can include backends not available on the
166	might be supported on the current system, you would need to look at	246	current system. To find which embeddable backends might be supported on
167	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	247	the current system, you would need to look at C<ev_embeddable_backends ()
168	recommended ones.	248	& ev_supported_backends ()>, likewise for recommended ones.
169		249
170	See the description of C<ev_embed> watchers for more info.	250	See the description of C<ev_embed> watchers for more info.
171		251
172	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	252	=item ev_set_allocator (void *(*cb)(void *ptr, long size))
173		253
174	Sets the allocation function to use (the prototype is similar - the	254	Sets the allocation function to use (the prototype is similar - the
175	semantics is identical - to the realloc C function). It is used to	255	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
176	allocate and free memory (no surprises here). If it returns zero when	256	used to allocate and free memory (no surprises here). If it returns zero
177	memory needs to be allocated, the library might abort or take some	257	when memory needs to be allocated (C<size != 0>), the library might abort
178	potentially destructive action. The default is your system realloc	258	or take some potentially destructive action.
179	function.	259
		260	Since some systems (at least OpenBSD and Darwin) fail to implement
		261	correct C<realloc> semantics, libev will use a wrapper around the system
		262	C<realloc> and C<free> functions by default.
180		263
181	You could override this function in high-availability programs to, say,	264	You could override this function in high-availability programs to, say,
182	free some memory if it cannot allocate memory, to use a special allocator,	265	free some memory if it cannot allocate memory, to use a special allocator,
183	or even to sleep a while and retry until some memory is available.	266	or even to sleep a while and retry until some memory is available.
184		267
185	Example: Replace the libev allocator with one that waits a bit and then	268	Example: Replace the libev allocator with one that waits a bit and then
186	retries).	269	retries (example requires a standards-compliant C<realloc>).
187		270
188	static void *	271	static void *
189	persistent_realloc (void *ptr, size_t size)	272	persistent_realloc (void *ptr, size_t size)
190	{	273	{
191	for (;;)	274	for (;;)
…		…
200	}	283	}
201		284
202	...	285	...
203	ev_set_allocator (persistent_realloc);	286	ev_set_allocator (persistent_realloc);
204		287
205	=item ev_set_syserr_cb (void (*cb)(const char *msg));	288	=item ev_set_syserr_cb (void (*cb)(const char *msg))
206		289
207	Set the callback function to call on a retryable syscall error (such	290	Set the callback function to call on a retryable system call error (such
208	as failed select, poll, epoll_wait). The message is a printable string	291	as failed select, poll, epoll_wait). The message is a printable string
209	indicating the system call or subsystem causing the problem. If this	292	indicating the system call or subsystem causing the problem. If this
210	callback is set, then libev will expect it to remedy the sitution, no	293	callback is set, then libev will expect it to remedy the situation, no
211	matter what, when it returns. That is, libev will generally retry the	294	matter what, when it returns. That is, libev will generally retry the
212	requested operation, or, if the condition doesn't go away, do bad stuff	295	requested operation, or, if the condition doesn't go away, do bad stuff
213	(such as abort).	296	(such as abort).
214		297
215	Example: This is basically the same thing that libev does internally, too.	298	Example: This is basically the same thing that libev does internally, too.
…		…
222	}	305	}
223		306
224	...	307	...
225	ev_set_syserr_cb (fatal_error);	308	ev_set_syserr_cb (fatal_error);
226		309
		310	=item ev_feed_signal (int signum)
		311
		312	This function can be used to "simulate" a signal receive. It is completely
		313	safe to call this function at any time, from any context, including signal
		314	handlers or random threads.
		315
		316	Its main use is to customise signal handling in your process, especially
		317	in the presence of threads. For example, you could block signals
		318	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		319	creating any loops), and in one thread, use C<sigwait> or any other
		320	mechanism to wait for signals, then "deliver" them to libev by calling
		321	C<ev_feed_signal>.
		322
227	=back	323	=back
228		324
229	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	325	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
230		326
231	An event loop is described by a C<struct ev_loop *>. The library knows two	327	An event loop is described by a C<struct ev_loop *> (the C<struct> is
232	types of such loops, the I<default> loop, which supports signals and child	328	I<not> optional in this case unless libev 3 compatibility is disabled, as
233	events, and dynamically created loops which do not.	329	libev 3 had an C<ev_loop> function colliding with the struct name).
234		330
235	If you use threads, a common model is to run the default event loop	331	The library knows two types of such loops, the I<default> loop, which
236	in your main thread (or in a separate thread) and for each thread you	332	supports child process events, and dynamically created event loops which
237	create, you also create another event loop. Libev itself does no locking	333	do not.
238	whatsoever, so if you mix calls to the same event loop in different
239	threads, make sure you lock (this is usually a bad idea, though, even if
240	done correctly, because it's hideous and inefficient).
241		334
242	=over 4	335	=over 4
243		336
244	=item struct ev_loop *ev_default_loop (unsigned int flags)	337	=item struct ev_loop *ev_default_loop (unsigned int flags)
245		338
246	This will initialise the default event loop if it hasn't been initialised	339	This returns the "default" event loop object, which is what you should
247	yet and return it. If the default loop could not be initialised, returns	340	normally use when you just need "the event loop". Event loop objects and
248	false. If it already was initialised it simply returns it (and ignores the	341	the C<flags> parameter are described in more detail in the entry for
249	flags. If that is troubling you, check C<ev_backend ()> afterwards).	342	C<ev_loop_new>.
		343
		344	If the default loop is already initialised then this function simply
		345	returns it (and ignores the flags. If that is troubling you, check
		346	C<ev_backend ()> afterwards). Otherwise it will create it with the given
		347	flags, which should almost always be C<0>, unless the caller is also the
		348	one calling C<ev_run> or otherwise qualifies as "the main program".
250		349
251	If you don't know what event loop to use, use the one returned from this	350	If you don't know what event loop to use, use the one returned from this
252	function.	351	function (or via the C<EV_DEFAULT> macro).
		352
		353	Note that this function is I<not> thread-safe, so if you want to use it
		354	from multiple threads, you have to employ some kind of mutex (note also
		355	that this case is unlikely, as loops cannot be shared easily between
		356	threads anyway).
		357
		358	The default loop is the only loop that can handle C<ev_child> watchers,
		359	and to do this, it always registers a handler for C<SIGCHLD>. If this is
		360	a problem for your application you can either create a dynamic loop with
		361	C<ev_loop_new> which doesn't do that, or you can simply overwrite the
		362	C<SIGCHLD> signal handler I<after> calling C<ev_default_init>.
		363
		364	Example: This is the most typical usage.
		365
		366	if (!ev_default_loop (0))
		367	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		368
		369	Example: Restrict libev to the select and poll backends, and do not allow
		370	environment settings to be taken into account:
		371
		372	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		373
		374	=item struct ev_loop *ev_loop_new (unsigned int flags)
		375
		376	This will create and initialise a new event loop object. If the loop
		377	could not be initialised, returns false.
		378
		379	This function is thread-safe, and one common way to use libev with
		380	threads is indeed to create one loop per thread, and using the default
		381	loop in the "main" or "initial" thread.
253		382
254	The flags argument can be used to specify special behaviour or specific	383	The flags argument can be used to specify special behaviour or specific
255	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	384	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
256		385
257	The following flags are supported:	386	The following flags are supported:
…		…
263	The default flags value. Use this if you have no clue (it's the right	392	The default flags value. Use this if you have no clue (it's the right
264	thing, believe me).	393	thing, believe me).
265		394
266	=item C<EVFLAG_NOENV>	395	=item C<EVFLAG_NOENV>
267		396
268	If this flag bit is ored into the flag value (or the program runs setuid	397	If this flag bit is or'ed into the flag value (or the program runs setuid
269	or setgid) then libev will I<not> look at the environment variable	398	or setgid) then libev will I<not> look at the environment variable
270	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	399	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
271	override the flags completely if it is found in the environment. This is	400	override the flags completely if it is found in the environment. This is
272	useful to try out specific backends to test their performance, or to work	401	useful to try out specific backends to test their performance, or to work
273	around bugs.	402	around bugs.
274		403
275	=item C<EVFLAG_FORKCHECK>	404	=item C<EVFLAG_FORKCHECK>
276		405
277	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after	406	Instead of calling C<ev_loop_fork> manually after a fork, you can also
278	a fork, you can also make libev check for a fork in each iteration by	407	make libev check for a fork in each iteration by enabling this flag.
279	enabling this flag.
280		408
281	This works by calling C<getpid ()> on every iteration of the loop,	409	This works by calling C<getpid ()> on every iteration of the loop,
282	and thus this might slow down your event loop if you do a lot of loop	410	and thus this might slow down your event loop if you do a lot of loop
283	iterations and little real work, but is usually not noticeable (on my	411	iterations and little real work, but is usually not noticeable (on my
284	Linux system for example, C<getpid> is actually a simple 5-insn sequence	412	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
285	without a syscall and thus I<very> fast, but my Linux system also has	413	without a system call and thus I<very> fast, but my GNU/Linux system also has
286	C<pthread_atfork> which is even faster).	414	C<pthread_atfork> which is even faster).
287		415
288	The big advantage of this flag is that you can forget about fork (and	416	The big advantage of this flag is that you can forget about fork (and
289	forget about forgetting to tell libev about forking) when you use this	417	forget about forgetting to tell libev about forking) when you use this
290	flag.	418	flag.
291		419
292	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>	420	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
293	environment variable.	421	environment variable.
		422
		423	=item C<EVFLAG_NOINOTIFY>
		424
		425	When this flag is specified, then libev will not attempt to use the
		426	I<inotify> API for its C<ev_stat> watchers. Apart from debugging and
		427	testing, this flag can be useful to conserve inotify file descriptors, as
		428	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		429
		430	=item C<EVFLAG_SIGNALFD>
		431
		432	When this flag is specified, then libev will attempt to use the
		433	I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API
		434	delivers signals synchronously, which makes it both faster and might make
		435	it possible to get the queued signal data. It can also simplify signal
		436	handling with threads, as long as you properly block signals in your
		437	threads that are not interested in handling them.
		438
		439	Signalfd will not be used by default as this changes your signal mask, and
		440	there are a lot of shoddy libraries and programs (glib's threadpool for
		441	example) that can't properly initialise their signal masks.
		442
		443	=item C<EVFLAG_NOSIGMASK>
		444
		445	When this flag is specified, then libev will avoid to modify the signal
		446	mask. Specifically, this means you have to make sure signals are unblocked
		447	when you want to receive them.
		448
		449	This behaviour is useful when you want to do your own signal handling, or
		450	want to handle signals only in specific threads and want to avoid libev
		451	unblocking the signals.
		452
		453	It's also required by POSIX in a threaded program, as libev calls
		454	C<sigprocmask>, whose behaviour is officially unspecified.
		455
		456	This flag's behaviour will become the default in future versions of libev.
294		457
295	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	458	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
296		459
297	This is your standard select(2) backend. Not I<completely> standard, as	460	This is your standard select(2) backend. Not I<completely> standard, as
298	libev tries to roll its own fd_set with no limits on the number of fds,	461	libev tries to roll its own fd_set with no limits on the number of fds,
299	but if that fails, expect a fairly low limit on the number of fds when	462	but if that fails, expect a fairly low limit on the number of fds when
300	using this backend. It doesn't scale too well (O(highest_fd)), but its usually	463	using this backend. It doesn't scale too well (O(highest_fd)), but its
301	the fastest backend for a low number of fds.	464	usually the fastest backend for a low number of (low-numbered :) fds.
		465
		466	To get good performance out of this backend you need a high amount of
		467	parallelism (most of the file descriptors should be busy). If you are
		468	writing a server, you should C<accept ()> in a loop to accept as many
		469	connections as possible during one iteration. You might also want to have
		470	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		471	readiness notifications you get per iteration.
		472
		473	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		474	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		475	C<exceptfds> set on that platform).
302		476
303	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	477	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
304		478
305	And this is your standard poll(2) backend. It's more complicated than	479	And this is your standard poll(2) backend. It's more complicated
306	select, but handles sparse fds better and has no artificial limit on the	480	than select, but handles sparse fds better and has no artificial
307	number of fds you can use (except it will slow down considerably with a	481	limit on the number of fds you can use (except it will slow down
308	lot of inactive fds). It scales similarly to select, i.e. O(total_fds).	482	considerably with a lot of inactive fds). It scales similarly to select,
		483	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		484	performance tips.
		485
		486	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		487	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
309		488
310	=item C<EVBACKEND_EPOLL> (value 4, Linux)	489	=item C<EVBACKEND_EPOLL> (value 4, Linux)
311		490
		491	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		492	kernels).
		493
312	For few fds, this backend is a bit little slower than poll and select,	494	For few fds, this backend is a bit little slower than poll and select, but
313	but it scales phenomenally better. While poll and select usually scale like	495	it scales phenomenally better. While poll and select usually scale like
314	O(total_fds) where n is the total number of fds (or the highest fd), epoll scales	496	O(total_fds) where total_fds is the total number of fds (or the highest
315	either O(1) or O(active_fds).	497	fd), epoll scales either O(1) or O(active_fds).
316		498
		499	The epoll mechanism deserves honorable mention as the most misdesigned
		500	of the more advanced event mechanisms: mere annoyances include silently
		501	dropping file descriptors, requiring a system call per change per file
		502	descriptor (and unnecessary guessing of parameters), problems with dup,
		503	returning before the timeout value, resulting in additional iterations
		504	(and only giving 5ms accuracy while select on the same platform gives
		505	0.1ms) and so on. The biggest issue is fork races, however - if a program
		506	forks then I<both> parent and child process have to recreate the epoll
		507	set, which can take considerable time (one syscall per file descriptor)
		508	and is of course hard to detect.
		509
		510	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
		511	but of course I<doesn't>, and epoll just loves to report events for
		512	totally I<different> file descriptors (even already closed ones, so
		513	one cannot even remove them from the set) than registered in the set
		514	(especially on SMP systems). Libev tries to counter these spurious
		515	notifications by employing an additional generation counter and comparing
		516	that against the events to filter out spurious ones, recreating the set
		517	when required. Epoll also erroneously rounds down timeouts, but gives you
		518	no way to know when and by how much, so sometimes you have to busy-wait
		519	because epoll returns immediately despite a nonzero timeout. And last
		520	not least, it also refuses to work with some file descriptors which work
		521	perfectly fine with C<select> (files, many character devices...).
		522
		523	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		524	cobbled together in a hurry, no thought to design or interaction with
		525	others. Oh, the pain, will it ever stop...
		526
317	While stopping and starting an I/O watcher in the same iteration will	527	While stopping, setting and starting an I/O watcher in the same iteration
318	result in some caching, there is still a syscall per such incident	528	will result in some caching, there is still a system call per such
319	(because the fd could point to a different file description now), so its	529	incident (because the same I<file descriptor> could point to a different
320	best to avoid that. Also, dup()ed file descriptors might not work very	530	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
321	well if you register events for both fds.	531	file descriptors might not work very well if you register events for both
		532	file descriptors.
322		533
323	Please note that epoll sometimes generates spurious notifications, so you	534	Best performance from this backend is achieved by not unregistering all
324	need to use non-blocking I/O or other means to avoid blocking when no data	535	watchers for a file descriptor until it has been closed, if possible,
325	(or space) is available.	536	i.e. keep at least one watcher active per fd at all times. Stopping and
		537	starting a watcher (without re-setting it) also usually doesn't cause
		538	extra overhead. A fork can both result in spurious notifications as well
		539	as in libev having to destroy and recreate the epoll object, which can
		540	take considerable time and thus should be avoided.
		541
		542	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		543	faster than epoll for maybe up to a hundred file descriptors, depending on
		544	the usage. So sad.
		545
		546	While nominally embeddable in other event loops, this feature is broken in
		547	all kernel versions tested so far.
		548
		549	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		550	C<EVBACKEND_POLL>.
326		551
327	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	552	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
328		553
329	Kqueue deserves special mention, as at the time of this writing, it	554	Kqueue deserves special mention, as at the time of this writing, it
330	was broken on all BSDs except NetBSD (usually it doesn't work with	555	was broken on all BSDs except NetBSD (usually it doesn't work reliably
331	anything but sockets and pipes, except on Darwin, where of course its	556	with anything but sockets and pipes, except on Darwin, where of course
332	completely useless). For this reason its not being "autodetected"	557	it's completely useless). Unlike epoll, however, whose brokenness
		558	is by design, these kqueue bugs can (and eventually will) be fixed
		559	without API changes to existing programs. For this reason it's not being
333	unless you explicitly specify it explicitly in the flags (i.e. using	560	"auto-detected" unless you explicitly specify it in the flags (i.e. using
334	C<EVBACKEND_KQUEUE>).	561	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		562	system like NetBSD.
		563
		564	You still can embed kqueue into a normal poll or select backend and use it
		565	only for sockets (after having made sure that sockets work with kqueue on
		566	the target platform). See C<ev_embed> watchers for more info.
335		567
336	It scales in the same way as the epoll backend, but the interface to the	568	It scales in the same way as the epoll backend, but the interface to the
337	kernel is more efficient (which says nothing about its actual speed, of	569	kernel is more efficient (which says nothing about its actual speed, of
338	course). While starting and stopping an I/O watcher does not cause an	570	course). While stopping, setting and starting an I/O watcher does never
339	extra syscall as with epoll, it still adds up to four event changes per	571	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
340	incident, so its best to avoid that.	572	two event changes per incident. Support for C<fork ()> is very bad (but
		573	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		574	cases
		575
		576	This backend usually performs well under most conditions.
		577
		578	While nominally embeddable in other event loops, this doesn't work
		579	everywhere, so you might need to test for this. And since it is broken
		580	almost everywhere, you should only use it when you have a lot of sockets
		581	(for which it usually works), by embedding it into another event loop
		582	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
		583	also broken on OS X)) and, did I mention it, using it only for sockets.
		584
		585	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		586	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		587	C<NOTE_EOF>.
341		588
342	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	589	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
343		590
344	This is not implemented yet (and might never be).	591	This is not implemented yet (and might never be, unless you send me an
		592	implementation). According to reports, C</dev/poll> only supports sockets
		593	and is not embeddable, which would limit the usefulness of this backend
		594	immensely.
345		595
346	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	596	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
347		597
348	This uses the Solaris 10 port mechanism. As with everything on Solaris,	598	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
349	it's really slow, but it still scales very well (O(active_fds)).	599	it's really slow, but it still scales very well (O(active_fds)).
350		600
351	Please note that solaris ports can result in a lot of spurious	601	While this backend scales well, it requires one system call per active
352	notifications, so you need to use non-blocking I/O or other means to avoid	602	file descriptor per loop iteration. For small and medium numbers of file
353	blocking when no data (or space) is available.	603	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		604	might perform better.
		605
		606	On the positive side, this backend actually performed fully to
		607	specification in all tests and is fully embeddable, which is a rare feat
		608	among the OS-specific backends (I vastly prefer correctness over speed
		609	hacks).
		610
		611	On the negative side, the interface is I<bizarre> - so bizarre that
		612	even sun itself gets it wrong in their code examples: The event polling
		613	function sometimes returns events to the caller even though an error
		614	occurred, but with no indication whether it has done so or not (yes, it's
		615	even documented that way) - deadly for edge-triggered interfaces where you
		616	absolutely have to know whether an event occurred or not because you have
		617	to re-arm the watcher.
		618
		619	Fortunately libev seems to be able to work around these idiocies.
		620
		621	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		622	C<EVBACKEND_POLL>.
354		623
355	=item C<EVBACKEND_ALL>	624	=item C<EVBACKEND_ALL>
356		625
357	Try all backends (even potentially broken ones that wouldn't be tried	626	Try all backends (even potentially broken ones that wouldn't be tried
358	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	627	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
359	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	628	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
360		629
		630	It is definitely not recommended to use this flag, use whatever
		631	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		632	at all.
		633
		634	=item C<EVBACKEND_MASK>
		635
		636	Not a backend at all, but a mask to select all backend bits from a
		637	C<flags> value, in case you want to mask out any backends from a flags
		638	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
		639
361	=back	640	=back
362		641
363	If one or more of these are ored into the flags value, then only these	642	If one or more of the backend flags are or'ed into the flags value,
364	backends will be tried (in the reverse order as given here). If none are	643	then only these backends will be tried (in the reverse order as listed
365	specified, most compiled-in backend will be tried, usually in reverse	644	here). If none are specified, all backends in C<ev_recommended_backends
366	order of their flag values :)	645	()> will be tried.
367
368	The most typical usage is like this:
369
370	if (!ev_default_loop (0))
371	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
372
373	Restrict libev to the select and poll backends, and do not allow
374	environment settings to be taken into account:
375
376	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
377
378	Use whatever libev has to offer, but make sure that kqueue is used if
379	available (warning, breaks stuff, best use only with your own private
380	event loop and only if you know the OS supports your types of fds):
381
382	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
383
384	=item struct ev_loop *ev_loop_new (unsigned int flags)
385
386	Similar to C<ev_default_loop>, but always creates a new event loop that is
387	always distinct from the default loop. Unlike the default loop, it cannot
388	handle signal and child watchers, and attempts to do so will be greeted by
389	undefined behaviour (or a failed assertion if assertions are enabled).
390		646
391	Example: Try to create a event loop that uses epoll and nothing else.	647	Example: Try to create a event loop that uses epoll and nothing else.
392		648
393	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	649	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
394	if (!epoller)	650	if (!epoller)
395	fatal ("no epoll found here, maybe it hides under your chair");	651	fatal ("no epoll found here, maybe it hides under your chair");
396		652
		653	Example: Use whatever libev has to offer, but make sure that kqueue is
		654	used if available.
		655
		656	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		657
397	=item ev_default_destroy ()	658	=item ev_loop_destroy (loop)
398		659
399	Destroys the default loop again (frees all memory and kernel state	660	Destroys an event loop object (frees all memory and kernel state
400	etc.). None of the active event watchers will be stopped in the normal	661	etc.). None of the active event watchers will be stopped in the normal
401	sense, so e.g. C<ev_is_active> might still return true. It is your	662	sense, so e.g. C<ev_is_active> might still return true. It is your
402	responsibility to either stop all watchers cleanly yoursef I<before>	663	responsibility to either stop all watchers cleanly yourself I<before>
403	calling this function, or cope with the fact afterwards (which is usually	664	calling this function, or cope with the fact afterwards (which is usually
404	the easiest thing, youc na just ignore the watchers and/or C<free ()> them	665	the easiest thing, you can just ignore the watchers and/or C<free ()> them
405	for example).	666	for example).
406		667
		668	Note that certain global state, such as signal state (and installed signal
		669	handlers), will not be freed by this function, and related watchers (such
		670	as signal and child watchers) would need to be stopped manually.
		671
		672	This function is normally used on loop objects allocated by
		673	C<ev_loop_new>, but it can also be used on the default loop returned by
		674	C<ev_default_loop>, in which case it is not thread-safe.
		675
		676	Note that it is not advisable to call this function on the default loop
		677	except in the rare occasion where you really need to free its resources.
		678	If you need dynamically allocated loops it is better to use C<ev_loop_new>
		679	and C<ev_loop_destroy>.
		680
407	=item ev_loop_destroy (loop)	681	=item ev_loop_fork (loop)
408		682
409	Like C<ev_default_destroy>, but destroys an event loop created by an	683	This function sets a flag that causes subsequent C<ev_run> iterations to
410	earlier call to C<ev_loop_new>.
411
412	=item ev_default_fork ()
413
414	This function reinitialises the kernel state for backends that have	684	reinitialise the kernel state for backends that have one. Despite the
415	one. Despite the name, you can call it anytime, but it makes most sense	685	name, you can call it anytime, but it makes most sense after forking, in
416	after forking, in either the parent or child process (or both, but that	686	the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the
417	again makes little sense).	687	child before resuming or calling C<ev_run>.
418		688
419	You I<must> call this function in the child process after forking if and	689	Again, you I<have> to call it on I<any> loop that you want to re-use after
420	only if you want to use the event library in both processes. If you just	690	a fork, I<even if you do not plan to use the loop in the parent>. This is
421	fork+exec, you don't have to call it.	691	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		692	during fork.
		693
		694	On the other hand, you only need to call this function in the child
		695	process if and only if you want to use the event loop in the child. If
		696	you just fork+exec or create a new loop in the child, you don't have to
		697	call it at all (in fact, C<epoll> is so badly broken that it makes a
		698	difference, but libev will usually detect this case on its own and do a
		699	costly reset of the backend).
422		700
423	The function itself is quite fast and it's usually not a problem to call	701	The function itself is quite fast and it's usually not a problem to call
424	it just in case after a fork. To make this easy, the function will fit in	702	it just in case after a fork.
425	quite nicely into a call to C<pthread_atfork>:
426		703
		704	Example: Automate calling C<ev_loop_fork> on the default loop when
		705	using pthreads.
		706
		707	static void
		708	post_fork_child (void)
		709	{
		710	ev_loop_fork (EV_DEFAULT);
		711	}
		712
		713	...
427	pthread_atfork (0, 0, ev_default_fork);	714	pthread_atfork (0, 0, post_fork_child);
428		715
429	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use	716	=item int ev_is_default_loop (loop)
430	without calling this function, so if you force one of those backends you
431	do not need to care.
432		717
433	=item ev_loop_fork (loop)	718	Returns true when the given loop is, in fact, the default loop, and false
		719	otherwise.
434		720
435	Like C<ev_default_fork>, but acts on an event loop created by
436	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
437	after fork, and how you do this is entirely your own problem.
438
439	=item unsigned int ev_loop_count (loop)	721	=item unsigned int ev_iteration (loop)
440		722
441	Returns the count of loop iterations for the loop, which is identical to	723	Returns the current iteration count for the event loop, which is identical
442	the number of times libev did poll for new events. It starts at C<0> and	724	to the number of times libev did poll for new events. It starts at C<0>
443	happily wraps around with enough iterations.	725	and happily wraps around with enough iterations.
444		726
445	This value can sometimes be useful as a generation counter of sorts (it	727	This value can sometimes be useful as a generation counter of sorts (it
446	"ticks" the number of loop iterations), as it roughly corresponds with	728	"ticks" the number of loop iterations), as it roughly corresponds with
447	C<ev_prepare> and C<ev_check> calls.	729	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		730	prepare and check phases.
		731
		732	=item unsigned int ev_depth (loop)
		733
		734	Returns the number of times C<ev_run> was entered minus the number of
		735	times C<ev_run> was exited normally, in other words, the recursion depth.
		736
		737	Outside C<ev_run>, this number is zero. In a callback, this number is
		738	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
		739	in which case it is higher.
		740
		741	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
		742	throwing an exception etc.), doesn't count as "exit" - consider this
		743	as a hint to avoid such ungentleman-like behaviour unless it's really
		744	convenient, in which case it is fully supported.
448		745
449	=item unsigned int ev_backend (loop)	746	=item unsigned int ev_backend (loop)
450		747
451	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	748	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
452	use.	749	use.
…		…
455		752
456	Returns the current "event loop time", which is the time the event loop	753	Returns the current "event loop time", which is the time the event loop
457	received events and started processing them. This timestamp does not	754	received events and started processing them. This timestamp does not
458	change as long as callbacks are being processed, and this is also the base	755	change as long as callbacks are being processed, and this is also the base
459	time used for relative timers. You can treat it as the timestamp of the	756	time used for relative timers. You can treat it as the timestamp of the
460	event occuring (or more correctly, libev finding out about it).	757	event occurring (or more correctly, libev finding out about it).
461		758
		759	=item ev_now_update (loop)
		760
		761	Establishes the current time by querying the kernel, updating the time
		762	returned by C<ev_now ()> in the progress. This is a costly operation and
		763	is usually done automatically within C<ev_run ()>.
		764
		765	This function is rarely useful, but when some event callback runs for a
		766	very long time without entering the event loop, updating libev's idea of
		767	the current time is a good idea.
		768
		769	See also L<The special problem of time updates> in the C<ev_timer> section.
		770
		771	=item ev_suspend (loop)
		772
		773	=item ev_resume (loop)
		774
		775	These two functions suspend and resume an event loop, for use when the
		776	loop is not used for a while and timeouts should not be processed.
		777
		778	A typical use case would be an interactive program such as a game: When
		779	the user presses C<^Z> to suspend the game and resumes it an hour later it
		780	would be best to handle timeouts as if no time had actually passed while
		781	the program was suspended. This can be achieved by calling C<ev_suspend>
		782	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		783	C<ev_resume> directly afterwards to resume timer processing.
		784
		785	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		786	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		787	will be rescheduled (that is, they will lose any events that would have
		788	occurred while suspended).
		789
		790	After calling C<ev_suspend> you B<must not> call I<any> function on the
		791	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		792	without a previous call to C<ev_suspend>.
		793
		794	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		795	event loop time (see C<ev_now_update>).
		796
462	=item ev_loop (loop, int flags)	797	=item ev_run (loop, int flags)
463		798
464	Finally, this is it, the event handler. This function usually is called	799	Finally, this is it, the event handler. This function usually is called
465	after you initialised all your watchers and you want to start handling	800	after you have initialised all your watchers and you want to start
466	events.	801	handling events. It will ask the operating system for any new events, call
		802	the watcher callbacks, an then repeat the whole process indefinitely: This
		803	is why event loops are called I<loops>.
467		804
468	If the flags argument is specified as C<0>, it will not return until	805	If the flags argument is specified as C<0>, it will keep handling events
469	either no event watchers are active anymore or C<ev_unloop> was called.	806	until either no event watchers are active anymore or C<ev_break> was
		807	called.
470		808
471	Please note that an explicit C<ev_unloop> is usually better than	809	Please note that an explicit C<ev_break> is usually better than
472	relying on all watchers to be stopped when deciding when a program has	810	relying on all watchers to be stopped when deciding when a program has
473	finished (especially in interactive programs), but having a program that	811	finished (especially in interactive programs), but having a program
474	automatically loops as long as it has to and no longer by virtue of	812	that automatically loops as long as it has to and no longer by virtue
475	relying on its watchers stopping correctly is a thing of beauty.	813	of relying on its watchers stopping correctly, that is truly a thing of
		814	beauty.
476		815
		816	This function is also I<mostly> exception-safe - you can break out of
		817	a C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		818	exception and so on. This does not decrement the C<ev_depth> value, nor
		819	will it clear any outstanding C<EVBREAK_ONE> breaks.
		820
477	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	821	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
478	those events and any outstanding ones, but will not block your process in	822	those events and any already outstanding ones, but will not wait and
479	case there are no events and will return after one iteration of the loop.	823	block your process in case there are no events and will return after one
		824	iteration of the loop. This is sometimes useful to poll and handle new
		825	events while doing lengthy calculations, to keep the program responsive.
480		826
481	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	827	A flags value of C<EVRUN_ONCE> will look for new events (waiting if
482	neccessary) and will handle those and any outstanding ones. It will block	828	necessary) and will handle those and any already outstanding ones. It
483	your process until at least one new event arrives, and will return after	829	will block your process until at least one new event arrives (which could
484	one iteration of the loop. This is useful if you are waiting for some	830	be an event internal to libev itself, so there is no guarantee that a
485	external event in conjunction with something not expressible using other	831	user-registered callback will be called), and will return after one
		832	iteration of the loop.
		833
		834	This is useful if you are waiting for some external event in conjunction
		835	with something not expressible using other libev watchers (i.e. "roll your
486	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	836	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
487	usually a better approach for this kind of thing.	837	usually a better approach for this kind of thing.
488		838
489	Here are the gory details of what C<ev_loop> does:	839	Here are the gory details of what C<ev_run> does (this is for your
		840	understanding, not a guarantee that things will work exactly like this in
		841	future versions):
490		842
491	* If there are no active watchers (reference count is zero), return.	843	- Increment loop depth.
492	- Queue prepare watchers and then call all outstanding watchers.	844	- Reset the ev_break status.
		845	- Before the first iteration, call any pending watchers.
		846	LOOP:
		847	- If EVFLAG_FORKCHECK was used, check for a fork.
		848	- If a fork was detected (by any means), queue and call all fork watchers.
		849	- Queue and call all prepare watchers.
		850	- If ev_break was called, goto FINISH.
493	- If we have been forked, recreate the kernel state.	851	- If we have been forked, detach and recreate the kernel state
		852	as to not disturb the other process.
494	- Update the kernel state with all outstanding changes.	853	- Update the kernel state with all outstanding changes.
495	- Update the "event loop time".	854	- Update the "event loop time" (ev_now ()).
496	- Calculate for how long to block.	855	- Calculate for how long to sleep or block, if at all
		856	(active idle watchers, EVRUN_NOWAIT or not having
		857	any active watchers at all will result in not sleeping).
		858	- Sleep if the I/O and timer collect interval say so.
		859	- Increment loop iteration counter.
497	- Block the process, waiting for any events.	860	- Block the process, waiting for any events.
498	- Queue all outstanding I/O (fd) events.	861	- Queue all outstanding I/O (fd) events.
499	- Update the "event loop time" and do time jump handling.	862	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
500	- Queue all outstanding timers.	863	- Queue all expired timers.
501	- Queue all outstanding periodics.	864	- Queue all expired periodics.
502	- If no events are pending now, queue all idle watchers.	865	- Queue all idle watchers with priority higher than that of pending events.
503	- Queue all check watchers.	866	- Queue all check watchers.
504	- Call all queued watchers in reverse order (i.e. check watchers first).	867	- Call all queued watchers in reverse order (i.e. check watchers first).
505	Signals and child watchers are implemented as I/O watchers, and will	868	Signals and child watchers are implemented as I/O watchers, and will
506	be handled here by queueing them when their watcher gets executed.	869	be handled here by queueing them when their watcher gets executed.
507	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	870	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
508	were used, return, otherwise continue with step *.	871	were used, or there are no active watchers, goto FINISH, otherwise
		872	continue with step LOOP.
		873	FINISH:
		874	- Reset the ev_break status iff it was EVBREAK_ONE.
		875	- Decrement the loop depth.
		876	- Return.
509		877
510	Example: Queue some jobs and then loop until no events are outsanding	878	Example: Queue some jobs and then loop until no events are outstanding
511	anymore.	879	anymore.
512		880
513	... queue jobs here, make sure they register event watchers as long	881	... queue jobs here, make sure they register event watchers as long
514	... as they still have work to do (even an idle watcher will do..)	882	... as they still have work to do (even an idle watcher will do..)
515	ev_loop (my_loop, 0);	883	ev_run (my_loop, 0);
516	... jobs done. yeah!	884	... jobs done or somebody called break. yeah!
517		885
518	=item ev_unloop (loop, how)	886	=item ev_break (loop, how)
519		887
520	Can be used to make a call to C<ev_loop> return early (but only after it	888	Can be used to make a call to C<ev_run> return early (but only after it
521	has processed all outstanding events). The C<how> argument must be either	889	has processed all outstanding events). The C<how> argument must be either
522	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	890	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
523	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	891	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
		892
		893	This "break state" will be cleared on the next call to C<ev_run>.
		894
		895	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		896	which case it will have no effect.
524		897
525	=item ev_ref (loop)	898	=item ev_ref (loop)
526		899
527	=item ev_unref (loop)	900	=item ev_unref (loop)
528		901
529	Ref/unref can be used to add or remove a reference count on the event	902	Ref/unref can be used to add or remove a reference count on the event
530	loop: Every watcher keeps one reference, and as long as the reference	903	loop: Every watcher keeps one reference, and as long as the reference
531	count is nonzero, C<ev_loop> will not return on its own. If you have	904	count is nonzero, C<ev_run> will not return on its own.
532	a watcher you never unregister that should not keep C<ev_loop> from	905
533	returning, ev_unref() after starting, and ev_ref() before stopping it. For	906	This is useful when you have a watcher that you never intend to
		907	unregister, but that nevertheless should not keep C<ev_run> from
		908	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		909	before stopping it.
		910
534	example, libev itself uses this for its internal signal pipe: It is not	911	As an example, libev itself uses this for its internal signal pipe: It
535	visible to the libev user and should not keep C<ev_loop> from exiting if	912	is not visible to the libev user and should not keep C<ev_run> from
536	no event watchers registered by it are active. It is also an excellent	913	exiting if no event watchers registered by it are active. It is also an
537	way to do this for generic recurring timers or from within third-party	914	excellent way to do this for generic recurring timers or from within
538	libraries. Just remember to I<unref after start> and I<ref before stop>.	915	third-party libraries. Just remember to I<unref after start> and I<ref
		916	before stop> (but only if the watcher wasn't active before, or was active
		917	before, respectively. Note also that libev might stop watchers itself
		918	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		919	in the callback).
539		920
540	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	921	Example: Create a signal watcher, but keep it from keeping C<ev_run>
541	running when nothing else is active.	922	running when nothing else is active.
542		923
543	struct ev_signal exitsig;	924	ev_signal exitsig;
544	ev_signal_init (&exitsig, sig_cb, SIGINT);	925	ev_signal_init (&exitsig, sig_cb, SIGINT);
545	ev_signal_start (loop, &exitsig);	926	ev_signal_start (loop, &exitsig);
546	evf_unref (loop);	927	ev_unref (loop);
547		928
548	Example: For some weird reason, unregister the above signal handler again.	929	Example: For some weird reason, unregister the above signal handler again.
549		930
550	ev_ref (loop);	931	ev_ref (loop);
551	ev_signal_stop (loop, &exitsig);	932	ev_signal_stop (loop, &exitsig);
		933
		934	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		935
		936	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		937
		938	These advanced functions influence the time that libev will spend waiting
		939	for events. Both time intervals are by default C<0>, meaning that libev
		940	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		941	latency.
		942
		943	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		944	allows libev to delay invocation of I/O and timer/periodic callbacks
		945	to increase efficiency of loop iterations (or to increase power-saving
		946	opportunities).
		947
		948	The idea is that sometimes your program runs just fast enough to handle
		949	one (or very few) event(s) per loop iteration. While this makes the
		950	program responsive, it also wastes a lot of CPU time to poll for new
		951	events, especially with backends like C<select ()> which have a high
		952	overhead for the actual polling but can deliver many events at once.
		953
		954	By setting a higher I<io collect interval> you allow libev to spend more
		955	time collecting I/O events, so you can handle more events per iteration,
		956	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		957	C<ev_timer>) will not be affected. Setting this to a non-null value will
		958	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		959	sleep time ensures that libev will not poll for I/O events more often then
		960	once per this interval, on average (as long as the host time resolution is
		961	good enough).
		962
		963	Likewise, by setting a higher I<timeout collect interval> you allow libev
		964	to spend more time collecting timeouts, at the expense of increased
		965	latency/jitter/inexactness (the watcher callback will be called
		966	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		967	value will not introduce any overhead in libev.
		968
		969	Many (busy) programs can usually benefit by setting the I/O collect
		970	interval to a value near C<0.1> or so, which is often enough for
		971	interactive servers (of course not for games), likewise for timeouts. It
		972	usually doesn't make much sense to set it to a lower value than C<0.01>,
		973	as this approaches the timing granularity of most systems. Note that if
		974	you do transactions with the outside world and you can't increase the
		975	parallelity, then this setting will limit your transaction rate (if you
		976	need to poll once per transaction and the I/O collect interval is 0.01,
		977	then you can't do more than 100 transactions per second).
		978
		979	Setting the I<timeout collect interval> can improve the opportunity for
		980	saving power, as the program will "bundle" timer callback invocations that
		981	are "near" in time together, by delaying some, thus reducing the number of
		982	times the process sleeps and wakes up again. Another useful technique to
		983	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		984	they fire on, say, one-second boundaries only.
		985
		986	Example: we only need 0.1s timeout granularity, and we wish not to poll
		987	more often than 100 times per second:
		988
		989	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		990	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		991
		992	=item ev_invoke_pending (loop)
		993
		994	This call will simply invoke all pending watchers while resetting their
		995	pending state. Normally, C<ev_run> does this automatically when required,
		996	but when overriding the invoke callback this call comes handy. This
		997	function can be invoked from a watcher - this can be useful for example
		998	when you want to do some lengthy calculation and want to pass further
		999	event handling to another thread (you still have to make sure only one
		1000	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
		1001
		1002	=item int ev_pending_count (loop)
		1003
		1004	Returns the number of pending watchers - zero indicates that no watchers
		1005	are pending.
		1006
		1007	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		1008
		1009	This overrides the invoke pending functionality of the loop: Instead of
		1010	invoking all pending watchers when there are any, C<ev_run> will call
		1011	this callback instead. This is useful, for example, when you want to
		1012	invoke the actual watchers inside another context (another thread etc.).
		1013
		1014	If you want to reset the callback, use C<ev_invoke_pending> as new
		1015	callback.
		1016
		1017	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		1018
		1019	Sometimes you want to share the same loop between multiple threads. This
		1020	can be done relatively simply by putting mutex_lock/unlock calls around
		1021	each call to a libev function.
		1022
		1023	However, C<ev_run> can run an indefinite time, so it is not feasible
		1024	to wait for it to return. One way around this is to wake up the event
		1025	loop via C<ev_break> and C<ev_async_send>, another way is to set these
		1026	I<release> and I<acquire> callbacks on the loop.
		1027
		1028	When set, then C<release> will be called just before the thread is
		1029	suspended waiting for new events, and C<acquire> is called just
		1030	afterwards.
		1031
		1032	Ideally, C<release> will just call your mutex_unlock function, and
		1033	C<acquire> will just call the mutex_lock function again.
		1034
		1035	While event loop modifications are allowed between invocations of
		1036	C<release> and C<acquire> (that's their only purpose after all), no
		1037	modifications done will affect the event loop, i.e. adding watchers will
		1038	have no effect on the set of file descriptors being watched, or the time
		1039	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		1040	to take note of any changes you made.
		1041
		1042	In theory, threads executing C<ev_run> will be async-cancel safe between
		1043	invocations of C<release> and C<acquire>.
		1044
		1045	See also the locking example in the C<THREADS> section later in this
		1046	document.
		1047
		1048	=item ev_set_userdata (loop, void *data)
		1049
		1050	=item void *ev_userdata (loop)
		1051
		1052	Set and retrieve a single C<void *> associated with a loop. When
		1053	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		1054	C<0>.
		1055
		1056	These two functions can be used to associate arbitrary data with a loop,
		1057	and are intended solely for the C<invoke_pending_cb>, C<release> and
		1058	C<acquire> callbacks described above, but of course can be (ab-)used for
		1059	any other purpose as well.
		1060
		1061	=item ev_verify (loop)
		1062
		1063	This function only does something when C<EV_VERIFY> support has been
		1064	compiled in, which is the default for non-minimal builds. It tries to go
		1065	through all internal structures and checks them for validity. If anything
		1066	is found to be inconsistent, it will print an error message to standard
		1067	error and call C<abort ()>.
		1068
		1069	This can be used to catch bugs inside libev itself: under normal
		1070	circumstances, this function will never abort as of course libev keeps its
		1071	data structures consistent.
552		1072
553	=back	1073	=back
554		1074
555		1075
556	=head1 ANATOMY OF A WATCHER	1076	=head1 ANATOMY OF A WATCHER
557		1077
		1078	In the following description, uppercase C<TYPE> in names stands for the
		1079	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		1080	watchers and C<ev_io_start> for I/O watchers.
		1081
558	A watcher is a structure that you create and register to record your	1082	A watcher is an opaque structure that you allocate and register to record
559	interest in some event. For instance, if you want to wait for STDIN to	1083	your interest in some event. To make a concrete example, imagine you want
560	become readable, you would create an C<ev_io> watcher for that:	1084	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1085	for that:
561		1086
562	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1087	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
563	{	1088	{
564	ev_io_stop (w);	1089	ev_io_stop (w);
565	ev_unloop (loop, EVUNLOOP_ALL);	1090	ev_break (loop, EVBREAK_ALL);
566	}	1091	}
567		1092
568	struct ev_loop *loop = ev_default_loop (0);	1093	struct ev_loop *loop = ev_default_loop (0);
		1094
569	struct ev_io stdin_watcher;	1095	ev_io stdin_watcher;
		1096
570	ev_init (&stdin_watcher, my_cb);	1097	ev_init (&stdin_watcher, my_cb);
571	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1098	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
572	ev_io_start (loop, &stdin_watcher);	1099	ev_io_start (loop, &stdin_watcher);
		1100
573	ev_loop (loop, 0);	1101	ev_run (loop, 0);
574		1102
575	As you can see, you are responsible for allocating the memory for your	1103	As you can see, you are responsible for allocating the memory for your
576	watcher structures (and it is usually a bad idea to do this on the stack,	1104	watcher structures (and it is I<usually> a bad idea to do this on the
577	although this can sometimes be quite valid).	1105	stack).
578		1106
		1107	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1108	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1109
579	Each watcher structure must be initialised by a call to C<ev_init	1110	Each watcher structure must be initialised by a call to C<ev_init (watcher
580	(watcher *, callback)>, which expects a callback to be provided. This	1111	*, callback)>, which expects a callback to be provided. This callback is
581	callback gets invoked each time the event occurs (or, in the case of io	1112	invoked each time the event occurs (or, in the case of I/O watchers, each
582	watchers, each time the event loop detects that the file descriptor given	1113	time the event loop detects that the file descriptor given is readable
583	is readable and/or writable).	1114	and/or writable).
584		1115
585	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1116	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
586	with arguments specific to this watcher type. There is also a macro	1117	macro to configure it, with arguments specific to the watcher type. There
587	to combine initialisation and setting in one call: C<< ev_<type>_init	1118	is also a macro to combine initialisation and setting in one call: C<<
588	(watcher *, callback, ...) >>.	1119	ev_TYPE_init (watcher *, callback, ...) >>.
589		1120
590	To make the watcher actually watch out for events, you have to start it	1121	To make the watcher actually watch out for events, you have to start it
591	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1122	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
592	*) >>), and you can stop watching for events at any time by calling the	1123	*) >>), and you can stop watching for events at any time by calling the
593	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1124	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
594		1125
595	As long as your watcher is active (has been started but not stopped) you	1126	As long as your watcher is active (has been started but not stopped) you
596	must not touch the values stored in it. Most specifically you must never	1127	must not touch the values stored in it. Most specifically you must never
597	reinitialise it or call its C<set> macro.	1128	reinitialise it or call its C<ev_TYPE_set> macro.
598		1129
599	Each and every callback receives the event loop pointer as first, the	1130	Each and every callback receives the event loop pointer as first, the
600	registered watcher structure as second, and a bitset of received events as	1131	registered watcher structure as second, and a bitset of received events as
601	third argument.	1132	third argument.
602		1133
…		…
611	=item C<EV_WRITE>	1142	=item C<EV_WRITE>
612		1143
613	The file descriptor in the C<ev_io> watcher has become readable and/or	1144	The file descriptor in the C<ev_io> watcher has become readable and/or
614	writable.	1145	writable.
615		1146
616	=item C<EV_TIMEOUT>	1147	=item C<EV_TIMER>
617		1148
618	The C<ev_timer> watcher has timed out.	1149	The C<ev_timer> watcher has timed out.
619		1150
620	=item C<EV_PERIODIC>	1151	=item C<EV_PERIODIC>
621		1152
…		…
639		1170
640	=item C<EV_PREPARE>	1171	=item C<EV_PREPARE>
641		1172
642	=item C<EV_CHECK>	1173	=item C<EV_CHECK>
643		1174
644	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts	1175	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts
645	to gather new events, and all C<ev_check> watchers are invoked just after	1176	to gather new events, and all C<ev_check> watchers are invoked just after
646	C<ev_loop> has gathered them, but before it invokes any callbacks for any	1177	C<ev_run> has gathered them, but before it invokes any callbacks for any
647	received events. Callbacks of both watcher types can start and stop as	1178	received events. Callbacks of both watcher types can start and stop as
648	many watchers as they want, and all of them will be taken into account	1179	many watchers as they want, and all of them will be taken into account
649	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1180	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
650	C<ev_loop> from blocking).	1181	C<ev_run> from blocking).
651		1182
652	=item C<EV_EMBED>	1183	=item C<EV_EMBED>
653		1184
654	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1185	The embedded event loop specified in the C<ev_embed> watcher needs attention.
655		1186
656	=item C<EV_FORK>	1187	=item C<EV_FORK>
657		1188
658	The event loop has been resumed in the child process after fork (see	1189	The event loop has been resumed in the child process after fork (see
659	C<ev_fork>).	1190	C<ev_fork>).
660		1191
		1192	=item C<EV_CLEANUP>
		1193
		1194	The event loop is about to be destroyed (see C<ev_cleanup>).
		1195
		1196	=item C<EV_ASYNC>
		1197
		1198	The given async watcher has been asynchronously notified (see C<ev_async>).
		1199
		1200	=item C<EV_CUSTOM>
		1201
		1202	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1203	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1204
661	=item C<EV_ERROR>	1205	=item C<EV_ERROR>
662		1206
663	An unspecified error has occured, the watcher has been stopped. This might	1207	An unspecified error has occurred, the watcher has been stopped. This might
664	happen because the watcher could not be properly started because libev	1208	happen because the watcher could not be properly started because libev
665	ran out of memory, a file descriptor was found to be closed or any other	1209	ran out of memory, a file descriptor was found to be closed or any other
		1210	problem. Libev considers these application bugs.
		1211
666	problem. You best act on it by reporting the problem and somehow coping	1212	You best act on it by reporting the problem and somehow coping with the
667	with the watcher being stopped.	1213	watcher being stopped. Note that well-written programs should not receive
		1214	an error ever, so when your watcher receives it, this usually indicates a
		1215	bug in your program.
668		1216
669	Libev will usually signal a few "dummy" events together with an error,	1217	Libev will usually signal a few "dummy" events together with an error, for
670	for example it might indicate that a fd is readable or writable, and if	1218	example it might indicate that a fd is readable or writable, and if your
671	your callbacks is well-written it can just attempt the operation and cope	1219	callbacks is well-written it can just attempt the operation and cope with
672	with the error from read() or write(). This will not work in multithreaded	1220	the error from read() or write(). This will not work in multi-threaded
673	programs, though, so beware.	1221	programs, though, as the fd could already be closed and reused for another
		1222	thing, so beware.
674		1223
675	=back	1224	=back
676		1225
677	=head2 GENERIC WATCHER FUNCTIONS	1226	=head2 GENERIC WATCHER FUNCTIONS
678
679	In the following description, C<TYPE> stands for the watcher type,
680	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
681		1227
682	=over 4	1228	=over 4
683		1229
684	=item C<ev_init> (ev_TYPE *watcher, callback)	1230	=item C<ev_init> (ev_TYPE *watcher, callback)
685		1231
…		…
691	which rolls both calls into one.	1237	which rolls both calls into one.
692		1238
693	You can reinitialise a watcher at any time as long as it has been stopped	1239	You can reinitialise a watcher at any time as long as it has been stopped
694	(or never started) and there are no pending events outstanding.	1240	(or never started) and there are no pending events outstanding.
695		1241
696	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1242	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
697	int revents)>.	1243	int revents)>.
698		1244
		1245	Example: Initialise an C<ev_io> watcher in two steps.
		1246
		1247	ev_io w;
		1248	ev_init (&w, my_cb);
		1249	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1250
699	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1251	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
700		1252
701	This macro initialises the type-specific parts of a watcher. You need to	1253	This macro initialises the type-specific parts of a watcher. You need to
702	call C<ev_init> at least once before you call this macro, but you can	1254	call C<ev_init> at least once before you call this macro, but you can
703	call C<ev_TYPE_set> any number of times. You must not, however, call this	1255	call C<ev_TYPE_set> any number of times. You must not, however, call this
704	macro on a watcher that is active (it can be pending, however, which is a	1256	macro on a watcher that is active (it can be pending, however, which is a
705	difference to the C<ev_init> macro).	1257	difference to the C<ev_init> macro).
706		1258
707	Although some watcher types do not have type-specific arguments	1259	Although some watcher types do not have type-specific arguments
708	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1260	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
709		1261
		1262	See C<ev_init>, above, for an example.
		1263
710	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1264	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
711		1265
712	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1266	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
713	calls into a single call. This is the most convinient method to initialise	1267	calls into a single call. This is the most convenient method to initialise
714	a watcher. The same limitations apply, of course.	1268	a watcher. The same limitations apply, of course.
715		1269
		1270	Example: Initialise and set an C<ev_io> watcher in one step.
		1271
		1272	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1273
716	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1274	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
717		1275
718	Starts (activates) the given watcher. Only active watchers will receive	1276	Starts (activates) the given watcher. Only active watchers will receive
719	events. If the watcher is already active nothing will happen.	1277	events. If the watcher is already active nothing will happen.
720		1278
		1279	Example: Start the C<ev_io> watcher that is being abused as example in this
		1280	whole section.
		1281
		1282	ev_io_start (EV_DEFAULT_UC, &w);
		1283
721	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1284	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
722		1285
723	Stops the given watcher again (if active) and clears the pending	1286	Stops the given watcher if active, and clears the pending status (whether
		1287	the watcher was active or not).
		1288
724	status. It is possible that stopped watchers are pending (for example,	1289	It is possible that stopped watchers are pending - for example,
725	non-repeating timers are being stopped when they become pending), but	1290	non-repeating timers are being stopped when they become pending - but
726	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1291	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
727	you want to free or reuse the memory used by the watcher it is therefore a	1292	pending. If you want to free or reuse the memory used by the watcher it is
728	good idea to always call its C<ev_TYPE_stop> function.	1293	therefore a good idea to always call its C<ev_TYPE_stop> function.
729		1294
730	=item bool ev_is_active (ev_TYPE *watcher)	1295	=item bool ev_is_active (ev_TYPE *watcher)
731		1296
732	Returns a true value iff the watcher is active (i.e. it has been started	1297	Returns a true value iff the watcher is active (i.e. it has been started
733	and not yet been stopped). As long as a watcher is active you must not modify	1298	and not yet been stopped). As long as a watcher is active you must not modify
…		…
749	=item ev_cb_set (ev_TYPE *watcher, callback)	1314	=item ev_cb_set (ev_TYPE *watcher, callback)
750		1315
751	Change the callback. You can change the callback at virtually any time	1316	Change the callback. You can change the callback at virtually any time
752	(modulo threads).	1317	(modulo threads).
753		1318
754	=item ev_set_priority (ev_TYPE *watcher, priority)	1319	=item ev_set_priority (ev_TYPE *watcher, int priority)
755		1320
756	=item int ev_priority (ev_TYPE *watcher)	1321	=item int ev_priority (ev_TYPE *watcher)
757		1322
758	Set and query the priority of the watcher. The priority is a small	1323	Set and query the priority of the watcher. The priority is a small
759	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1324	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
760	(default: C<-2>). Pending watchers with higher priority will be invoked	1325	(default: C<-2>). Pending watchers with higher priority will be invoked
761	before watchers with lower priority, but priority will not keep watchers	1326	before watchers with lower priority, but priority will not keep watchers
762	from being executed (except for C<ev_idle> watchers).	1327	from being executed (except for C<ev_idle> watchers).
763		1328
764	This means that priorities are I<only> used for ordering callback
765	invocation after new events have been received. This is useful, for
766	example, to reduce latency after idling, or more often, to bind two
767	watchers on the same event and make sure one is called first.
768
769	If you need to suppress invocation when higher priority events are pending	1329	If you need to suppress invocation when higher priority events are pending
770	you need to look at C<ev_idle> watchers, which provide this functionality.	1330	you need to look at C<ev_idle> watchers, which provide this functionality.
771		1331
772	You I<must not> change the priority of a watcher as long as it is active or	1332	You I<must not> change the priority of a watcher as long as it is active or
773	pending.	1333	pending.
774		1334
		1335	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1336	fine, as long as you do not mind that the priority value you query might
		1337	or might not have been clamped to the valid range.
		1338
775	The default priority used by watchers when no priority has been set is	1339	The default priority used by watchers when no priority has been set is
776	always C<0>, which is supposed to not be too high and not be too low :).	1340	always C<0>, which is supposed to not be too high and not be too low :).
777		1341
778	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1342	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
779	fine, as long as you do not mind that the priority value you query might	1343	priorities.
780	or might not have been adjusted to be within valid range.
781		1344
782	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1345	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
783		1346
784	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1347	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
785	C<loop> nor C<revents> need to be valid as long as the watcher callback	1348	C<loop> nor C<revents> need to be valid as long as the watcher callback
786	can deal with that fact.	1349	can deal with that fact, as both are simply passed through to the
		1350	callback.
787		1351
788	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1352	=item int ev_clear_pending (loop, ev_TYPE *watcher)
789		1353
790	If the watcher is pending, this function returns clears its pending status	1354	If the watcher is pending, this function clears its pending status and
791	and returns its C<revents> bitset (as if its callback was invoked). If the	1355	returns its C<revents> bitset (as if its callback was invoked). If the
792	watcher isn't pending it does nothing and returns C<0>.	1356	watcher isn't pending it does nothing and returns C<0>.
793		1357
		1358	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1359	callback to be invoked, which can be accomplished with this function.
		1360
		1361	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1362
		1363	Feeds the given event set into the event loop, as if the specified event
		1364	had happened for the specified watcher (which must be a pointer to an
		1365	initialised but not necessarily started event watcher). Obviously you must
		1366	not free the watcher as long as it has pending events.
		1367
		1368	Stopping the watcher, letting libev invoke it, or calling
		1369	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1370	not started in the first place.
		1371
		1372	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1373	functions that do not need a watcher.
		1374
794	=back	1375	=back
795		1376
		1377	See also the L<ASSOCIATING CUSTOM DATA WITH A WATCHER> and L<BUILDING YOUR
		1378	OWN COMPOSITE WATCHERS> idioms.
796		1379
797	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1380	=head2 WATCHER STATES
798		1381
799	Each watcher has, by default, a member C<void *data> that you can change	1382	There are various watcher states mentioned throughout this manual -
800	and read at any time, libev will completely ignore it. This can be used	1383	active, pending and so on. In this section these states and the rules to
801	to associate arbitrary data with your watcher. If you need more data and	1384	transition between them will be described in more detail - and while these
802	don't want to allocate memory and store a pointer to it in that data	1385	rules might look complicated, they usually do "the right thing".
803	member, you can also "subclass" the watcher type and provide your own
804	data:
805		1386
806	struct my_io	1387	=over 4
807	{
808	struct ev_io io;
809	int otherfd;
810	void *somedata;
811	struct whatever *mostinteresting;
812	}
813		1388
814	And since your callback will be called with a pointer to the watcher, you	1389	=item initialiased
815	can cast it back to your own type:
816		1390
817	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1391	Before a watcher can be registered with the event loop it has to be
818	{	1392	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
819	struct my_io *w = (struct my_io *)w_;	1393	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
820	...
821	}
822		1394
823	More interesting and less C-conformant ways of casting your callback type	1395	In this state it is simply some block of memory that is suitable for
824	instead have been omitted.	1396	use in an event loop. It can be moved around, freed, reused etc. at
		1397	will - as long as you either keep the memory contents intact, or call
		1398	C<ev_TYPE_init> again.
825		1399
826	Another common scenario is having some data structure with multiple	1400	=item started/running/active
827	watchers:
828		1401
829	struct my_biggy	1402	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
830	{	1403	property of the event loop, and is actively waiting for events. While in
831	int some_data;	1404	this state it cannot be accessed (except in a few documented ways), moved,
832	ev_timer t1;	1405	freed or anything else - the only legal thing is to keep a pointer to it,
833	ev_timer t2;	1406	and call libev functions on it that are documented to work on active watchers.
834	}
835		1407
836	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1408	=item pending
837	you need to use C<offsetof>:
838		1409
839	#include <stddef.h>	1410	If a watcher is active and libev determines that an event it is interested
		1411	in has occurred (such as a timer expiring), it will become pending. It will
		1412	stay in this pending state until either it is stopped or its callback is
		1413	about to be invoked, so it is not normally pending inside the watcher
		1414	callback.
840		1415
		1416	The watcher might or might not be active while it is pending (for example,
		1417	an expired non-repeating timer can be pending but no longer active). If it
		1418	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1419	but it is still property of the event loop at this time, so cannot be
		1420	moved, freed or reused. And if it is active the rules described in the
		1421	previous item still apply.
		1422
		1423	It is also possible to feed an event on a watcher that is not active (e.g.
		1424	via C<ev_feed_event>), in which case it becomes pending without being
		1425	active.
		1426
		1427	=item stopped
		1428
		1429	A watcher can be stopped implicitly by libev (in which case it might still
		1430	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1431	latter will clear any pending state the watcher might be in, regardless
		1432	of whether it was active or not, so stopping a watcher explicitly before
		1433	freeing it is often a good idea.
		1434
		1435	While stopped (and not pending) the watcher is essentially in the
		1436	initialised state, that is, it can be reused, moved, modified in any way
		1437	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1438	it again).
		1439
		1440	=back
		1441
		1442	=head2 WATCHER PRIORITY MODELS
		1443
		1444	Many event loops support I<watcher priorities>, which are usually small
		1445	integers that influence the ordering of event callback invocation
		1446	between watchers in some way, all else being equal.
		1447
		1448	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1449	description for the more technical details such as the actual priority
		1450	range.
		1451
		1452	There are two common ways how these these priorities are being interpreted
		1453	by event loops:
		1454
		1455	In the more common lock-out model, higher priorities "lock out" invocation
		1456	of lower priority watchers, which means as long as higher priority
		1457	watchers receive events, lower priority watchers are not being invoked.
		1458
		1459	The less common only-for-ordering model uses priorities solely to order
		1460	callback invocation within a single event loop iteration: Higher priority
		1461	watchers are invoked before lower priority ones, but they all get invoked
		1462	before polling for new events.
		1463
		1464	Libev uses the second (only-for-ordering) model for all its watchers
		1465	except for idle watchers (which use the lock-out model).
		1466
		1467	The rationale behind this is that implementing the lock-out model for
		1468	watchers is not well supported by most kernel interfaces, and most event
		1469	libraries will just poll for the same events again and again as long as
		1470	their callbacks have not been executed, which is very inefficient in the
		1471	common case of one high-priority watcher locking out a mass of lower
		1472	priority ones.
		1473
		1474	Static (ordering) priorities are most useful when you have two or more
		1475	watchers handling the same resource: a typical usage example is having an
		1476	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1477	timeouts. Under load, data might be received while the program handles
		1478	other jobs, but since timers normally get invoked first, the timeout
		1479	handler will be executed before checking for data. In that case, giving
		1480	the timer a lower priority than the I/O watcher ensures that I/O will be
		1481	handled first even under adverse conditions (which is usually, but not
		1482	always, what you want).
		1483
		1484	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1485	will only be executed when no same or higher priority watchers have
		1486	received events, they can be used to implement the "lock-out" model when
		1487	required.
		1488
		1489	For example, to emulate how many other event libraries handle priorities,
		1490	you can associate an C<ev_idle> watcher to each such watcher, and in
		1491	the normal watcher callback, you just start the idle watcher. The real
		1492	processing is done in the idle watcher callback. This causes libev to
		1493	continuously poll and process kernel event data for the watcher, but when
		1494	the lock-out case is known to be rare (which in turn is rare :), this is
		1495	workable.
		1496
		1497	Usually, however, the lock-out model implemented that way will perform
		1498	miserably under the type of load it was designed to handle. In that case,
		1499	it might be preferable to stop the real watcher before starting the
		1500	idle watcher, so the kernel will not have to process the event in case
		1501	the actual processing will be delayed for considerable time.
		1502
		1503	Here is an example of an I/O watcher that should run at a strictly lower
		1504	priority than the default, and which should only process data when no
		1505	other events are pending:
		1506
		1507	ev_idle idle; // actual processing watcher
		1508	ev_io io; // actual event watcher
		1509
841	static void	1510	static void
842	t1_cb (EV_P_ struct ev_timer *w, int revents)	1511	io_cb (EV_P_ ev_io *w, int revents)
843	{	1512	{
844	struct my_biggy big = (struct my_biggy *	1513	// stop the I/O watcher, we received the event, but
845	(((char *)w) - offsetof (struct my_biggy, t1));	1514	// are not yet ready to handle it.
		1515	ev_io_stop (EV_A_ w);
		1516
		1517	// start the idle watcher to handle the actual event.
		1518	// it will not be executed as long as other watchers
		1519	// with the default priority are receiving events.
		1520	ev_idle_start (EV_A_ &idle);
846	}	1521	}
847		1522
848	static void	1523	static void
849	t2_cb (EV_P_ struct ev_timer *w, int revents)	1524	idle_cb (EV_P_ ev_idle *w, int revents)
850	{	1525	{
851	struct my_biggy big = (struct my_biggy *	1526	// actual processing
852	(((char *)w) - offsetof (struct my_biggy, t2));	1527	read (STDIN_FILENO, ...);
		1528
		1529	// have to start the I/O watcher again, as
		1530	// we have handled the event
		1531	ev_io_start (EV_P_ &io);
853	}	1532	}
		1533
		1534	// initialisation
		1535	ev_idle_init (&idle, idle_cb);
		1536	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1537	ev_io_start (EV_DEFAULT_ &io);
		1538
		1539	In the "real" world, it might also be beneficial to start a timer, so that
		1540	low-priority connections can not be locked out forever under load. This
		1541	enables your program to keep a lower latency for important connections
		1542	during short periods of high load, while not completely locking out less
		1543	important ones.
854		1544
855		1545
856	=head1 WATCHER TYPES	1546	=head1 WATCHER TYPES
857		1547
858	This section describes each watcher in detail, but will not repeat	1548	This section describes each watcher in detail, but will not repeat
…		…
882	In general you can register as many read and/or write event watchers per	1572	In general you can register as many read and/or write event watchers per
883	fd as you want (as long as you don't confuse yourself). Setting all file	1573	fd as you want (as long as you don't confuse yourself). Setting all file
884	descriptors to non-blocking mode is also usually a good idea (but not	1574	descriptors to non-blocking mode is also usually a good idea (but not
885	required if you know what you are doing).	1575	required if you know what you are doing).
886		1576
887	You have to be careful with dup'ed file descriptors, though. Some backends
888	(the linux epoll backend is a notable example) cannot handle dup'ed file
889	descriptors correctly if you register interest in two or more fds pointing
890	to the same underlying file/socket/etc. description (that is, they share
891	the same underlying "file open").
892
893	If you must do this, then force the use of a known-to-be-good backend
894	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
895	C<EVBACKEND_POLL>).
896
897	Another thing you have to watch out for is that it is quite easy to	1577	Another thing you have to watch out for is that it is quite easy to
898	receive "spurious" readyness notifications, that is your callback might	1578	receive "spurious" readiness notifications, that is, your callback might
899	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1579	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
900	because there is no data. Not only are some backends known to create a	1580	because there is no data. It is very easy to get into this situation even
901	lot of those (for example solaris ports), it is very easy to get into	1581	with a relatively standard program structure. Thus it is best to always
902	this situation even with a relatively standard program structure. Thus	1582	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
903	it is best to always use non-blocking I/O: An extra C<read>(2) returning
904	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1583	preferable to a program hanging until some data arrives.
905		1584
906	If you cannot run the fd in non-blocking mode (for example you should not	1585	If you cannot run the fd in non-blocking mode (for example you should
907	play around with an Xlib connection), then you have to seperately re-test	1586	not play around with an Xlib connection), then you have to separately
908	whether a file descriptor is really ready with a known-to-be good interface	1587	re-test whether a file descriptor is really ready with a known-to-be good
909	such as poll (fortunately in our Xlib example, Xlib already does this on	1588	interface such as poll (fortunately in the case of Xlib, it already does
910	its own, so its quite safe to use).	1589	this on its own, so its quite safe to use). Some people additionally
		1590	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1591	indefinitely.
		1592
		1593	But really, best use non-blocking mode.
		1594
		1595	=head3 The special problem of disappearing file descriptors
		1596
		1597	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1598	descriptor (either due to calling C<close> explicitly or any other means,
		1599	such as C<dup2>). The reason is that you register interest in some file
		1600	descriptor, but when it goes away, the operating system will silently drop
		1601	this interest. If another file descriptor with the same number then is
		1602	registered with libev, there is no efficient way to see that this is, in
		1603	fact, a different file descriptor.
		1604
		1605	To avoid having to explicitly tell libev about such cases, libev follows
		1606	the following policy: Each time C<ev_io_set> is being called, libev
		1607	will assume that this is potentially a new file descriptor, otherwise
		1608	it is assumed that the file descriptor stays the same. That means that
		1609	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1610	descriptor even if the file descriptor number itself did not change.
		1611
		1612	This is how one would do it normally anyway, the important point is that
		1613	the libev application should not optimise around libev but should leave
		1614	optimisations to libev.
		1615
		1616	=head3 The special problem of dup'ed file descriptors
		1617
		1618	Some backends (e.g. epoll), cannot register events for file descriptors,
		1619	but only events for the underlying file descriptions. That means when you
		1620	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1621	events for them, only one file descriptor might actually receive events.
		1622
		1623	There is no workaround possible except not registering events
		1624	for potentially C<dup ()>'ed file descriptors, or to resort to
		1625	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1626
		1627	=head3 The special problem of files
		1628
		1629	Many people try to use C<select> (or libev) on file descriptors
		1630	representing files, and expect it to become ready when their program
		1631	doesn't block on disk accesses (which can take a long time on their own).
		1632
		1633	However, this cannot ever work in the "expected" way - you get a readiness
		1634	notification as soon as the kernel knows whether and how much data is
		1635	there, and in the case of open files, that's always the case, so you
		1636	always get a readiness notification instantly, and your read (or possibly
		1637	write) will still block on the disk I/O.
		1638
		1639	Another way to view it is that in the case of sockets, pipes, character
		1640	devices and so on, there is another party (the sender) that delivers data
		1641	on its own, but in the case of files, there is no such thing: the disk
		1642	will not send data on its own, simply because it doesn't know what you
		1643	wish to read - you would first have to request some data.
		1644
		1645	Since files are typically not-so-well supported by advanced notification
		1646	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1647	to files, even though you should not use it. The reason for this is
		1648	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1649	usually a tty, often a pipe, but also sometimes files or special devices
		1650	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1651	F</dev/urandom>), and even though the file might better be served with
		1652	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1653	it "just works" instead of freezing.
		1654
		1655	So avoid file descriptors pointing to files when you know it (e.g. use
		1656	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1657	when you rarely read from a file instead of from a socket, and want to
		1658	reuse the same code path.
		1659
		1660	=head3 The special problem of fork
		1661
		1662	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1663	useless behaviour. Libev fully supports fork, but needs to be told about
		1664	it in the child if you want to continue to use it in the child.
		1665
		1666	To support fork in your child processes, you have to call C<ev_loop_fork
		1667	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
		1668	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1669
		1670	=head3 The special problem of SIGPIPE
		1671
		1672	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1673	when writing to a pipe whose other end has been closed, your program gets
		1674	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1675	this is sensible behaviour, for daemons, this is usually undesirable.
		1676
		1677	So when you encounter spurious, unexplained daemon exits, make sure you
		1678	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1679	somewhere, as that would have given you a big clue).
		1680
		1681	=head3 The special problem of accept()ing when you can't
		1682
		1683	Many implementations of the POSIX C<accept> function (for example,
		1684	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1685	connection from the pending queue in all error cases.
		1686
		1687	For example, larger servers often run out of file descriptors (because
		1688	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1689	rejecting the connection, leading to libev signalling readiness on
		1690	the next iteration again (the connection still exists after all), and
		1691	typically causing the program to loop at 100% CPU usage.
		1692
		1693	Unfortunately, the set of errors that cause this issue differs between
		1694	operating systems, there is usually little the app can do to remedy the
		1695	situation, and no known thread-safe method of removing the connection to
		1696	cope with overload is known (to me).
		1697
		1698	One of the easiest ways to handle this situation is to just ignore it
		1699	- when the program encounters an overload, it will just loop until the
		1700	situation is over. While this is a form of busy waiting, no OS offers an
		1701	event-based way to handle this situation, so it's the best one can do.
		1702
		1703	A better way to handle the situation is to log any errors other than
		1704	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1705	messages, and continue as usual, which at least gives the user an idea of
		1706	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1707	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1708	usage.
		1709
		1710	If your program is single-threaded, then you could also keep a dummy file
		1711	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1712	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1713	close that fd, and create a new dummy fd. This will gracefully refuse
		1714	clients under typical overload conditions.
		1715
		1716	The last way to handle it is to simply log the error and C<exit>, as
		1717	is often done with C<malloc> failures, but this results in an easy
		1718	opportunity for a DoS attack.
		1719
		1720	=head3 Watcher-Specific Functions
911		1721
912	=over 4	1722	=over 4
913		1723
914	=item ev_io_init (ev_io *, callback, int fd, int events)	1724	=item ev_io_init (ev_io *, callback, int fd, int events)
915		1725
916	=item ev_io_set (ev_io *, int fd, int events)	1726	=item ev_io_set (ev_io *, int fd, int events)
917		1727
918	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1728	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
919	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1729	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
920	C<EV_READ | EV_WRITE> to receive the given events.	1730	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
921		1731
922	=item int fd [read-only]	1732	=item int fd [read-only]
923		1733
924	The file descriptor being watched.	1734	The file descriptor being watched.
925		1735
926	=item int events [read-only]	1736	=item int events [read-only]
927		1737
928	The events being watched.	1738	The events being watched.
929		1739
930	=back	1740	=back
		1741
		1742	=head3 Examples
931		1743
932	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1744	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
933	readable, but only once. Since it is likely line-buffered, you could	1745	readable, but only once. Since it is likely line-buffered, you could
934	attempt to read a whole line in the callback.	1746	attempt to read a whole line in the callback.
935		1747
936	static void	1748	static void
937	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1749	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
938	{	1750	{
939	ev_io_stop (loop, w);	1751	ev_io_stop (loop, w);
940	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1752	.. read from stdin here (or from w->fd) and handle any I/O errors
941	}	1753	}
942		1754
943	...	1755	...
944	struct ev_loop *loop = ev_default_init (0);	1756	struct ev_loop *loop = ev_default_init (0);
945	struct ev_io stdin_readable;	1757	ev_io stdin_readable;
946	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1758	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
947	ev_io_start (loop, &stdin_readable);	1759	ev_io_start (loop, &stdin_readable);
948	ev_loop (loop, 0);	1760	ev_run (loop, 0);
949		1761
950		1762
951	=head2 C<ev_timer> - relative and optionally repeating timeouts	1763	=head2 C<ev_timer> - relative and optionally repeating timeouts
952		1764
953	Timer watchers are simple relative timers that generate an event after a	1765	Timer watchers are simple relative timers that generate an event after a
954	given time, and optionally repeating in regular intervals after that.	1766	given time, and optionally repeating in regular intervals after that.
955		1767
956	The timers are based on real time, that is, if you register an event that	1768	The timers are based on real time, that is, if you register an event that
957	times out after an hour and you reset your system clock to last years	1769	times out after an hour and you reset your system clock to January last
958	time, it will still time out after (roughly) and hour. "Roughly" because	1770	year, it will still time out after (roughly) one hour. "Roughly" because
959	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1771	detecting time jumps is hard, and some inaccuracies are unavoidable (the
960	monotonic clock option helps a lot here).	1772	monotonic clock option helps a lot here).
		1773
		1774	The callback is guaranteed to be invoked only I<after> its timeout has
		1775	passed (not I<at>, so on systems with very low-resolution clocks this
		1776	might introduce a small delay, see "the special problem of being too
		1777	early", below). If multiple timers become ready during the same loop
		1778	iteration then the ones with earlier time-out values are invoked before
		1779	ones of the same priority with later time-out values (but this is no
		1780	longer true when a callback calls C<ev_run> recursively).
		1781
		1782	=head3 Be smart about timeouts
		1783
		1784	Many real-world problems involve some kind of timeout, usually for error
		1785	recovery. A typical example is an HTTP request - if the other side hangs,
		1786	you want to raise some error after a while.
		1787
		1788	What follows are some ways to handle this problem, from obvious and
		1789	inefficient to smart and efficient.
		1790
		1791	In the following, a 60 second activity timeout is assumed - a timeout that
		1792	gets reset to 60 seconds each time there is activity (e.g. each time some
		1793	data or other life sign was received).
		1794
		1795	=over 4
		1796
		1797	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1798
		1799	This is the most obvious, but not the most simple way: In the beginning,
		1800	start the watcher:
		1801
		1802	ev_timer_init (timer, callback, 60., 0.);
		1803	ev_timer_start (loop, timer);
		1804
		1805	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1806	and start it again:
		1807
		1808	ev_timer_stop (loop, timer);
		1809	ev_timer_set (timer, 60., 0.);
		1810	ev_timer_start (loop, timer);
		1811
		1812	This is relatively simple to implement, but means that each time there is
		1813	some activity, libev will first have to remove the timer from its internal
		1814	data structure and then add it again. Libev tries to be fast, but it's
		1815	still not a constant-time operation.
		1816
		1817	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1818
		1819	This is the easiest way, and involves using C<ev_timer_again> instead of
		1820	C<ev_timer_start>.
		1821
		1822	To implement this, configure an C<ev_timer> with a C<repeat> value
		1823	of C<60> and then call C<ev_timer_again> at start and each time you
		1824	successfully read or write some data. If you go into an idle state where
		1825	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1826	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1827
		1828	That means you can ignore both the C<ev_timer_start> function and the
		1829	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1830	member and C<ev_timer_again>.
		1831
		1832	At start:
		1833
		1834	ev_init (timer, callback);
		1835	timer->repeat = 60.;
		1836	ev_timer_again (loop, timer);
		1837
		1838	Each time there is some activity:
		1839
		1840	ev_timer_again (loop, timer);
		1841
		1842	It is even possible to change the time-out on the fly, regardless of
		1843	whether the watcher is active or not:
		1844
		1845	timer->repeat = 30.;
		1846	ev_timer_again (loop, timer);
		1847
		1848	This is slightly more efficient then stopping/starting the timer each time
		1849	you want to modify its timeout value, as libev does not have to completely
		1850	remove and re-insert the timer from/into its internal data structure.
		1851
		1852	It is, however, even simpler than the "obvious" way to do it.
		1853
		1854	=item 3. Let the timer time out, but then re-arm it as required.
		1855
		1856	This method is more tricky, but usually most efficient: Most timeouts are
		1857	relatively long compared to the intervals between other activity - in
		1858	our example, within 60 seconds, there are usually many I/O events with
		1859	associated activity resets.
		1860
		1861	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1862	but remember the time of last activity, and check for a real timeout only
		1863	within the callback:
		1864
		1865	ev_tstamp timeout = 60.;
		1866	ev_tstamp last_activity; // time of last activity
		1867	ev_timer timer;
		1868
		1869	static void
		1870	callback (EV_P_ ev_timer *w, int revents)
		1871	{
		1872	// calculate when the timeout would happen
		1873	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
		1874
		1875	// if negative, it means we the timeout already occured
		1876	if (after < 0.)
		1877	{
		1878	// timeout occurred, take action
		1879	}
		1880	else
		1881	{
		1882	// callback was invoked, but there was some recent
		1883	// activity. simply restart the timer to time out
		1884	// after "after" seconds, which is the earliest time
		1885	// the timeout can occur.
		1886	ev_timer_set (w, after, 0.);
		1887	ev_timer_start (EV_A_ w);
		1888	}
		1889	}
		1890
		1891	To summarise the callback: first calculate in how many seconds the
		1892	timeout will occur (by calculating the absolute time when it would occur,
		1893	C<last_activity + timeout>, and subtracting the current time, C<ev_now
		1894	(EV_A)> from that).
		1895
		1896	If this value is negative, then we are already past the timeout, i.e. we
		1897	timed out, and need to do whatever is needed in this case.
		1898
		1899	Otherwise, we now the earliest time at which the timeout would trigger,
		1900	and simply start the timer with this timeout value.
		1901
		1902	In other words, each time the callback is invoked it will check whether
		1903	the timeout cocured. If not, it will simply reschedule itself to check
		1904	again at the earliest time it could time out. Rinse. Repeat.
		1905
		1906	This scheme causes more callback invocations (about one every 60 seconds
		1907	minus half the average time between activity), but virtually no calls to
		1908	libev to change the timeout.
		1909
		1910	To start the machinery, simply initialise the watcher and set
		1911	C<last_activity> to the current time (meaning there was some activity just
		1912	now), then call the callback, which will "do the right thing" and start
		1913	the timer:
		1914
		1915	last_activity = ev_now (EV_A);
		1916	ev_init (&timer, callback);
		1917	callback (EV_A_ &timer, 0);
		1918
		1919	When there is some activity, simply store the current time in
		1920	C<last_activity>, no libev calls at all:
		1921
		1922	if (activity detected)
		1923	last_activity = ev_now (EV_A);
		1924
		1925	When your timeout value changes, then the timeout can be changed by simply
		1926	providing a new value, stopping the timer and calling the callback, which
		1927	will agaion do the right thing (for example, time out immediately :).
		1928
		1929	timeout = new_value;
		1930	ev_timer_stop (EV_A_ &timer);
		1931	callback (EV_A_ &timer, 0);
		1932
		1933	This technique is slightly more complex, but in most cases where the
		1934	time-out is unlikely to be triggered, much more efficient.
		1935
		1936	=item 4. Wee, just use a double-linked list for your timeouts.
		1937
		1938	If there is not one request, but many thousands (millions...), all
		1939	employing some kind of timeout with the same timeout value, then one can
		1940	do even better:
		1941
		1942	When starting the timeout, calculate the timeout value and put the timeout
		1943	at the I<end> of the list.
		1944
		1945	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1946	the list is expected to fire (for example, using the technique #3).
		1947
		1948	When there is some activity, remove the timer from the list, recalculate
		1949	the timeout, append it to the end of the list again, and make sure to
		1950	update the C<ev_timer> if it was taken from the beginning of the list.
		1951
		1952	This way, one can manage an unlimited number of timeouts in O(1) time for
		1953	starting, stopping and updating the timers, at the expense of a major
		1954	complication, and having to use a constant timeout. The constant timeout
		1955	ensures that the list stays sorted.
		1956
		1957	=back
		1958
		1959	So which method the best?
		1960
		1961	Method #2 is a simple no-brain-required solution that is adequate in most
		1962	situations. Method #3 requires a bit more thinking, but handles many cases
		1963	better, and isn't very complicated either. In most case, choosing either
		1964	one is fine, with #3 being better in typical situations.
		1965
		1966	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1967	rather complicated, but extremely efficient, something that really pays
		1968	off after the first million or so of active timers, i.e. it's usually
		1969	overkill :)
		1970
		1971	=head3 The special problem of being too early
		1972
		1973	If you ask a timer to call your callback after three seconds, then
		1974	you expect it to be invoked after three seconds - but of course, this
		1975	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		1976	guaranteed to any precision by libev - imagine somebody suspending the
		1977	process with a STOP signal for a few hours for example.
		1978
		1979	So, libev tries to invoke your callback as soon as possible I<after> the
		1980	delay has occurred, but cannot guarantee this.
		1981
		1982	A less obvious failure mode is calling your callback too early: many event
		1983	loops compare timestamps with a "elapsed delay >= requested delay", but
		1984	this can cause your callback to be invoked much earlier than you would
		1985	expect.
		1986
		1987	To see why, imagine a system with a clock that only offers full second
		1988	resolution (think windows if you can't come up with a broken enough OS
		1989	yourself). If you schedule a one-second timer at the time 500.9, then the
		1990	event loop will schedule your timeout to elapse at a system time of 500
		1991	(500.9 truncated to the resolution) + 1, or 501.
		1992
		1993	If an event library looks at the timeout 0.1s later, it will see "501 >=
		1994	501" and invoke the callback 0.1s after it was started, even though a
		1995	one-second delay was requested - this is being "too early", despite best
		1996	intentions.
		1997
		1998	This is the reason why libev will never invoke the callback if the elapsed
		1999	delay equals the requested delay, but only when the elapsed delay is
		2000	larger than the requested delay. In the example above, libev would only invoke
		2001	the callback at system time 502, or 1.1s after the timer was started.
		2002
		2003	So, while libev cannot guarantee that your callback will be invoked
		2004	exactly when requested, it I<can> and I<does> guarantee that the requested
		2005	delay has actually elapsed, or in other words, it always errs on the "too
		2006	late" side of things.
		2007
		2008	=head3 The special problem of time updates
		2009
		2010	Establishing the current time is a costly operation (it usually takes
		2011	at least one system call): EV therefore updates its idea of the current
		2012	time only before and after C<ev_run> collects new events, which causes a
		2013	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		2014	lots of events in one iteration.
961		2015
962	The relative timeouts are calculated relative to the C<ev_now ()>	2016	The relative timeouts are calculated relative to the C<ev_now ()>
963	time. This is usually the right thing as this timestamp refers to the time	2017	time. This is usually the right thing as this timestamp refers to the time
964	of the event triggering whatever timeout you are modifying/starting. If	2018	of the event triggering whatever timeout you are modifying/starting. If
965	you suspect event processing to be delayed and you I<need> to base the timeout	2019	you suspect event processing to be delayed and you I<need> to base the
966	on the current time, use something like this to adjust for this:	2020	timeout on the current time, use something like this to adjust for this:
967		2021
968	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2022	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
969		2023
970	The callback is guarenteed to be invoked only when its timeout has passed,	2024	If the event loop is suspended for a long time, you can also force an
971	but if multiple timers become ready during the same loop iteration then	2025	update of the time returned by C<ev_now ()> by calling C<ev_now_update
972	order of execution is undefined.	2026	()>.
		2027
		2028	=head3 The special problem of unsynchronised clocks
		2029
		2030	Modern systems have a variety of clocks - libev itself uses the normal
		2031	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2032	jumps).
		2033
		2034	Neither of these clocks is synchronised with each other or any other clock
		2035	on the system, so C<ev_time ()> might return a considerably different time
		2036	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2037	a call to C<gettimeofday> might return a second count that is one higher
		2038	than a directly following call to C<time>.
		2039
		2040	The moral of this is to only compare libev-related timestamps with
		2041	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2042	a second or so.
		2043
		2044	One more problem arises due to this lack of synchronisation: if libev uses
		2045	the system monotonic clock and you compare timestamps from C<ev_time>
		2046	or C<ev_now> from when you started your timer and when your callback is
		2047	invoked, you will find that sometimes the callback is a bit "early".
		2048
		2049	This is because C<ev_timer>s work in real time, not wall clock time, so
		2050	libev makes sure your callback is not invoked before the delay happened,
		2051	I<measured according to the real time>, not the system clock.
		2052
		2053	If your timeouts are based on a physical timescale (e.g. "time out this
		2054	connection after 100 seconds") then this shouldn't bother you as it is
		2055	exactly the right behaviour.
		2056
		2057	If you want to compare wall clock/system timestamps to your timers, then
		2058	you need to use C<ev_periodic>s, as these are based on the wall clock
		2059	time, where your comparisons will always generate correct results.
		2060
		2061	=head3 The special problems of suspended animation
		2062
		2063	When you leave the server world it is quite customary to hit machines that
		2064	can suspend/hibernate - what happens to the clocks during such a suspend?
		2065
		2066	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		2067	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		2068	to run until the system is suspended, but they will not advance while the
		2069	system is suspended. That means, on resume, it will be as if the program
		2070	was frozen for a few seconds, but the suspend time will not be counted
		2071	towards C<ev_timer> when a monotonic clock source is used. The real time
		2072	clock advanced as expected, but if it is used as sole clocksource, then a
		2073	long suspend would be detected as a time jump by libev, and timers would
		2074	be adjusted accordingly.
		2075
		2076	I would not be surprised to see different behaviour in different between
		2077	operating systems, OS versions or even different hardware.
		2078
		2079	The other form of suspend (job control, or sending a SIGSTOP) will see a
		2080	time jump in the monotonic clocks and the realtime clock. If the program
		2081	is suspended for a very long time, and monotonic clock sources are in use,
		2082	then you can expect C<ev_timer>s to expire as the full suspension time
		2083	will be counted towards the timers. When no monotonic clock source is in
		2084	use, then libev will again assume a timejump and adjust accordingly.
		2085
		2086	It might be beneficial for this latter case to call C<ev_suspend>
		2087	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		2088	deterministic behaviour in this case (you can do nothing against
		2089	C<SIGSTOP>).
		2090
		2091	=head3 Watcher-Specific Functions and Data Members
973		2092
974	=over 4	2093	=over 4
975		2094
976	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2095	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
977		2096
978	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2097	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
979		2098
980	Configure the timer to trigger after C<after> seconds. If C<repeat> is	2099	Configure the timer to trigger after C<after> seconds. If C<repeat>
981	C<0.>, then it will automatically be stopped. If it is positive, then the	2100	is C<0.>, then it will automatically be stopped once the timeout is
982	timer will automatically be configured to trigger again C<repeat> seconds	2101	reached. If it is positive, then the timer will automatically be
983	later, again, and again, until stopped manually.	2102	configured to trigger again C<repeat> seconds later, again, and again,
		2103	until stopped manually.
984		2104
985	The timer itself will do a best-effort at avoiding drift, that is, if you	2105	The timer itself will do a best-effort at avoiding drift, that is, if
986	configure a timer to trigger every 10 seconds, then it will trigger at	2106	you configure a timer to trigger every 10 seconds, then it will normally
987	exactly 10 second intervals. If, however, your program cannot keep up with	2107	trigger at exactly 10 second intervals. If, however, your program cannot
988	the timer (because it takes longer than those 10 seconds to do stuff) the	2108	keep up with the timer (because it takes longer than those 10 seconds to
989	timer will not fire more than once per event loop iteration.	2109	do stuff) the timer will not fire more than once per event loop iteration.
990		2110
991	=item ev_timer_again (loop)	2111	=item ev_timer_again (loop, ev_timer *)
992		2112
993	This will act as if the timer timed out and restart it again if it is	2113	This will act as if the timer timed out, and restarts it again if it is
994	repeating. The exact semantics are:	2114	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2115	timeout to the C<repeat> value and calling C<ev_timer_start>.
995		2116
		2117	The exact semantics are as in the following rules, all of which will be
		2118	applied to the watcher:
		2119
		2120	=over 4
		2121
996	If the timer is pending, its pending status is cleared.	2122	=item If the timer is pending, the pending status is always cleared.
997		2123
998	If the timer is started but nonrepeating, stop it (as if it timed out).	2124	=item If the timer is started but non-repeating, stop it (as if it timed
		2125	out, without invoking it).
999		2126
1000	If the timer is repeating, either start it if necessary (with the	2127	=item If the timer is repeating, make the C<repeat> value the new timeout
1001	C<repeat> value), or reset the running timer to the C<repeat> value.	2128	and start the timer, if necessary.
1002		2129
1003	This sounds a bit complicated, but here is a useful and typical	2130	=back
1004	example: Imagine you have a tcp connection and you want a so-called idle
1005	timeout, that is, you want to be called when there have been, say, 60
1006	seconds of inactivity on the socket. The easiest way to do this is to
1007	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1008	C<ev_timer_again> each time you successfully read or write some data. If
1009	you go into an idle state where you do not expect data to travel on the
1010	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1011	automatically restart it if need be.
1012		2131
1013	That means you can ignore the C<after> value and C<ev_timer_start>	2132	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1014	altogether and only ever use the C<repeat> value and C<ev_timer_again>:	2133	usage example.
1015		2134
1016	ev_timer_init (timer, callback, 0., 5.);	2135	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1017	ev_timer_again (loop, timer);
1018	...
1019	timer->again = 17.;
1020	ev_timer_again (loop, timer);
1021	...
1022	timer->again = 10.;
1023	ev_timer_again (loop, timer);
1024		2136
1025	This is more slightly efficient then stopping/starting the timer each time	2137	Returns the remaining time until a timer fires. If the timer is active,
1026	you want to modify its timeout value.	2138	then this time is relative to the current event loop time, otherwise it's
		2139	the timeout value currently configured.
		2140
		2141	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
		2142	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		2143	will return C<4>. When the timer expires and is restarted, it will return
		2144	roughly C<7> (likely slightly less as callback invocation takes some time,
		2145	too), and so on.
1027		2146
1028	=item ev_tstamp repeat [read-write]	2147	=item ev_tstamp repeat [read-write]
1029		2148
1030	The current C<repeat> value. Will be used each time the watcher times out	2149	The current C<repeat> value. Will be used each time the watcher times out
1031	or C<ev_timer_again> is called and determines the next timeout (if any),	2150	or C<ev_timer_again> is called, and determines the next timeout (if any),
1032	which is also when any modifications are taken into account.	2151	which is also when any modifications are taken into account.
1033		2152
1034	=back	2153	=back
1035		2154
		2155	=head3 Examples
		2156
1036	Example: Create a timer that fires after 60 seconds.	2157	Example: Create a timer that fires after 60 seconds.
1037		2158
1038	static void	2159	static void
1039	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2160	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1040	{	2161	{
1041	.. one minute over, w is actually stopped right here	2162	.. one minute over, w is actually stopped right here
1042	}	2163	}
1043		2164
1044	struct ev_timer mytimer;	2165	ev_timer mytimer;
1045	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	2166	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1046	ev_timer_start (loop, &mytimer);	2167	ev_timer_start (loop, &mytimer);
1047		2168
1048	Example: Create a timeout timer that times out after 10 seconds of	2169	Example: Create a timeout timer that times out after 10 seconds of
1049	inactivity.	2170	inactivity.
1050		2171
1051	static void	2172	static void
1052	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2173	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1053	{	2174	{
1054	.. ten seconds without any activity	2175	.. ten seconds without any activity
1055	}	2176	}
1056		2177
1057	struct ev_timer mytimer;	2178	ev_timer mytimer;
1058	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	2179	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1059	ev_timer_again (&mytimer); /* start timer */	2180	ev_timer_again (&mytimer); /* start timer */
1060	ev_loop (loop, 0);	2181	ev_run (loop, 0);
1061		2182
1062	// and in some piece of code that gets executed on any "activity":	2183	// and in some piece of code that gets executed on any "activity":
1063	// reset the timeout to start ticking again at 10 seconds	2184	// reset the timeout to start ticking again at 10 seconds
1064	ev_timer_again (&mytimer);	2185	ev_timer_again (&mytimer);
1065		2186
1066		2187
1067	=head2 C<ev_periodic> - to cron or not to cron?	2188	=head2 C<ev_periodic> - to cron or not to cron?
1068		2189
1069	Periodic watchers are also timers of a kind, but they are very versatile	2190	Periodic watchers are also timers of a kind, but they are very versatile
1070	(and unfortunately a bit complex).	2191	(and unfortunately a bit complex).
1071		2192
1072	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2193	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1073	but on wallclock time (absolute time). You can tell a periodic watcher	2194	relative time, the physical time that passes) but on wall clock time
1074	to trigger "at" some specific point in time. For example, if you tell a	2195	(absolute time, the thing you can read on your calender or clock). The
1075	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	2196	difference is that wall clock time can run faster or slower than real
1076	+ 10.>) and then reset your system clock to the last year, then it will	2197	time, and time jumps are not uncommon (e.g. when you adjust your
1077	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	2198	wrist-watch).
1078	roughly 10 seconds later and of course not if you reset your system time
1079	again).
1080		2199
1081	They can also be used to implement vastly more complex timers, such as	2200	You can tell a periodic watcher to trigger after some specific point
		2201	in time: for example, if you tell a periodic watcher to trigger "in 10
		2202	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2203	not a delay) and then reset your system clock to January of the previous
		2204	year, then it will take a year or more to trigger the event (unlike an
		2205	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2206	it, as it uses a relative timeout).
		2207
		2208	C<ev_periodic> watchers can also be used to implement vastly more complex
1082	triggering an event on eahc midnight, local time.	2209	timers, such as triggering an event on each "midnight, local time", or
		2210	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		2211	those cannot react to time jumps.
1083		2212
1084	As with timers, the callback is guarenteed to be invoked only when the	2213	As with timers, the callback is guaranteed to be invoked only when the
1085	time (C<at>) has been passed, but if multiple periodic timers become ready	2214	point in time where it is supposed to trigger has passed. If multiple
1086	during the same loop iteration then order of execution is undefined.	2215	timers become ready during the same loop iteration then the ones with
		2216	earlier time-out values are invoked before ones with later time-out values
		2217	(but this is no longer true when a callback calls C<ev_run> recursively).
		2218
		2219	=head3 Watcher-Specific Functions and Data Members
1087		2220
1088	=over 4	2221	=over 4
1089		2222
1090	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2223	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1091		2224
1092	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2225	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1093		2226
1094	Lots of arguments, lets sort it out... There are basically three modes of	2227	Lots of arguments, let's sort it out... There are basically three modes of
1095	operation, and we will explain them from simplest to complex:	2228	operation, and we will explain them from simplest to most complex:
1096		2229
1097	=over 4	2230	=over 4
1098		2231
1099	=item * absolute timer (interval = reschedule_cb = 0)	2232	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1100		2233
1101	In this configuration the watcher triggers an event at the wallclock time	2234	In this configuration the watcher triggers an event after the wall clock
1102	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	2235	time C<offset> has passed. It will not repeat and will not adjust when a
1103	that is, if it is to be run at January 1st 2011 then it will run when the	2236	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1104	system time reaches or surpasses this time.	2237	will be stopped and invoked when the system clock reaches or surpasses
		2238	this point in time.
1105		2239
1106	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	2240	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1107		2241
1108	In this mode the watcher will always be scheduled to time out at the next	2242	In this mode the watcher will always be scheduled to time out at the next
1109	C<at + N * interval> time (for some integer N) and then repeat, regardless	2243	C<offset + N * interval> time (for some integer N, which can also be
1110	of any time jumps.	2244	negative) and then repeat, regardless of any time jumps. The C<offset>
		2245	argument is merely an offset into the C<interval> periods.
1111		2246
1112	This can be used to create timers that do not drift with respect to system	2247	This can be used to create timers that do not drift with respect to the
1113	time:	2248	system clock, for example, here is an C<ev_periodic> that triggers each
		2249	hour, on the hour (with respect to UTC):
1114		2250
1115	ev_periodic_set (&periodic, 0., 3600., 0);	2251	ev_periodic_set (&periodic, 0., 3600., 0);
1116		2252
1117	This doesn't mean there will always be 3600 seconds in between triggers,	2253	This doesn't mean there will always be 3600 seconds in between triggers,
1118	but only that the the callback will be called when the system time shows a	2254	but only that the callback will be called when the system time shows a
1119	full hour (UTC), or more correctly, when the system time is evenly divisible	2255	full hour (UTC), or more correctly, when the system time is evenly divisible
1120	by 3600.	2256	by 3600.
1121		2257
1122	Another way to think about it (for the mathematically inclined) is that	2258	Another way to think about it (for the mathematically inclined) is that
1123	C<ev_periodic> will try to run the callback in this mode at the next possible	2259	C<ev_periodic> will try to run the callback in this mode at the next possible
1124	time where C<time = at (mod interval)>, regardless of any time jumps.	2260	time where C<time = offset (mod interval)>, regardless of any time jumps.
1125		2261
		2262	The C<interval> I<MUST> be positive, and for numerical stability, the
		2263	interval value should be higher than C<1/8192> (which is around 100
		2264	microseconds) and C<offset> should be higher than C<0> and should have
		2265	at most a similar magnitude as the current time (say, within a factor of
		2266	ten). Typical values for offset are, in fact, C<0> or something between
		2267	C<0> and C<interval>, which is also the recommended range.
		2268
		2269	Note also that there is an upper limit to how often a timer can fire (CPU
		2270	speed for example), so if C<interval> is very small then timing stability
		2271	will of course deteriorate. Libev itself tries to be exact to be about one
		2272	millisecond (if the OS supports it and the machine is fast enough).
		2273
1126	=item * manual reschedule mode (reschedule_cb = callback)	2274	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1127		2275
1128	In this mode the values for C<interval> and C<at> are both being	2276	In this mode the values for C<interval> and C<offset> are both being
1129	ignored. Instead, each time the periodic watcher gets scheduled, the	2277	ignored. Instead, each time the periodic watcher gets scheduled, the
1130	reschedule callback will be called with the watcher as first, and the	2278	reschedule callback will be called with the watcher as first, and the
1131	current time as second argument.	2279	current time as second argument.
1132		2280
1133	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2281	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1134	ever, or make any event loop modifications>. If you need to stop it,	2282	or make ANY other event loop modifications whatsoever, unless explicitly
1135	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	2283	allowed by documentation here>.
1136	starting a prepare watcher).
1137		2284
		2285	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2286	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2287	only event loop modification you are allowed to do).
		2288
1138	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2289	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1139	ev_tstamp now)>, e.g.:	2290	*w, ev_tstamp now)>, e.g.:
1140		2291
		2292	static ev_tstamp
1141	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2293	my_rescheduler (ev_periodic *w, ev_tstamp now)
1142	{	2294	{
1143	return now + 60.;	2295	return now + 60.;
1144	}	2296	}
1145		2297
1146	It must return the next time to trigger, based on the passed time value	2298	It must return the next time to trigger, based on the passed time value
1147	(that is, the lowest time value larger than to the second argument). It	2299	(that is, the lowest time value larger than to the second argument). It
1148	will usually be called just before the callback will be triggered, but	2300	will usually be called just before the callback will be triggered, but
1149	might be called at other times, too.	2301	might be called at other times, too.
1150		2302
1151	NOTE: I<< This callback must always return a time that is later than the	2303	NOTE: I<< This callback must always return a time that is higher than or
1152	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2304	equal to the passed C<now> value >>.
1153		2305
1154	This can be used to create very complex timers, such as a timer that	2306	This can be used to create very complex timers, such as a timer that
1155	triggers on each midnight, local time. To do this, you would calculate the	2307	triggers on "next midnight, local time". To do this, you would calculate the
1156	next midnight after C<now> and return the timestamp value for this. How	2308	next midnight after C<now> and return the timestamp value for this. How
1157	you do this is, again, up to you (but it is not trivial, which is the main	2309	you do this is, again, up to you (but it is not trivial, which is the main
1158	reason I omitted it as an example).	2310	reason I omitted it as an example).
1159		2311
1160	=back	2312	=back
…		…
1164	Simply stops and restarts the periodic watcher again. This is only useful	2316	Simply stops and restarts the periodic watcher again. This is only useful
1165	when you changed some parameters or the reschedule callback would return	2317	when you changed some parameters or the reschedule callback would return
1166	a different time than the last time it was called (e.g. in a crond like	2318	a different time than the last time it was called (e.g. in a crond like
1167	program when the crontabs have changed).	2319	program when the crontabs have changed).
1168		2320
		2321	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2322
		2323	When active, returns the absolute time that the watcher is supposed
		2324	to trigger next. This is not the same as the C<offset> argument to
		2325	C<ev_periodic_set>, but indeed works even in interval and manual
		2326	rescheduling modes.
		2327
		2328	=item ev_tstamp offset [read-write]
		2329
		2330	When repeating, this contains the offset value, otherwise this is the
		2331	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2332	although libev might modify this value for better numerical stability).
		2333
		2334	Can be modified any time, but changes only take effect when the periodic
		2335	timer fires or C<ev_periodic_again> is being called.
		2336
1169	=item ev_tstamp interval [read-write]	2337	=item ev_tstamp interval [read-write]
1170		2338
1171	The current interval value. Can be modified any time, but changes only	2339	The current interval value. Can be modified any time, but changes only
1172	take effect when the periodic timer fires or C<ev_periodic_again> is being	2340	take effect when the periodic timer fires or C<ev_periodic_again> is being
1173	called.	2341	called.
1174		2342
1175	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2343	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1176		2344
1177	The current reschedule callback, or C<0>, if this functionality is	2345	The current reschedule callback, or C<0>, if this functionality is
1178	switched off. Can be changed any time, but changes only take effect when	2346	switched off. Can be changed any time, but changes only take effect when
1179	the periodic timer fires or C<ev_periodic_again> is being called.	2347	the periodic timer fires or C<ev_periodic_again> is being called.
1180		2348
1181	=back	2349	=back
1182		2350
		2351	=head3 Examples
		2352
1183	Example: Call a callback every hour, or, more precisely, whenever the	2353	Example: Call a callback every hour, or, more precisely, whenever the
1184	system clock is divisible by 3600. The callback invocation times have	2354	system time is divisible by 3600. The callback invocation times have
1185	potentially a lot of jittering, but good long-term stability.	2355	potentially a lot of jitter, but good long-term stability.
1186		2356
1187	static void	2357	static void
1188	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2358	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1189	{	2359	{
1190	... its now a full hour (UTC, or TAI or whatever your clock follows)	2360	... its now a full hour (UTC, or TAI or whatever your clock follows)
1191	}	2361	}
1192		2362
1193	struct ev_periodic hourly_tick;	2363	ev_periodic hourly_tick;
1194	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2364	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1195	ev_periodic_start (loop, &hourly_tick);	2365	ev_periodic_start (loop, &hourly_tick);
1196		2366
1197	Example: The same as above, but use a reschedule callback to do it:	2367	Example: The same as above, but use a reschedule callback to do it:
1198		2368
1199	#include <math.h>	2369	#include <math.h>
1200		2370
1201	static ev_tstamp	2371	static ev_tstamp
1202	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2372	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1203	{	2373	{
1204	return fmod (now, 3600.) + 3600.;	2374	return now + (3600. - fmod (now, 3600.));
1205	}	2375	}
1206		2376
1207	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2377	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1208		2378
1209	Example: Call a callback every hour, starting now:	2379	Example: Call a callback every hour, starting now:
1210		2380
1211	struct ev_periodic hourly_tick;	2381	ev_periodic hourly_tick;
1212	ev_periodic_init (&hourly_tick, clock_cb,	2382	ev_periodic_init (&hourly_tick, clock_cb,
1213	fmod (ev_now (loop), 3600.), 3600., 0);	2383	fmod (ev_now (loop), 3600.), 3600., 0);
1214	ev_periodic_start (loop, &hourly_tick);	2384	ev_periodic_start (loop, &hourly_tick);
1215		2385
1216		2386
1217	=head2 C<ev_signal> - signal me when a signal gets signalled!	2387	=head2 C<ev_signal> - signal me when a signal gets signalled!
1218		2388
1219	Signal watchers will trigger an event when the process receives a specific	2389	Signal watchers will trigger an event when the process receives a specific
1220	signal one or more times. Even though signals are very asynchronous, libev	2390	signal one or more times. Even though signals are very asynchronous, libev
1221	will try it's best to deliver signals synchronously, i.e. as part of the	2391	will try its best to deliver signals synchronously, i.e. as part of the
1222	normal event processing, like any other event.	2392	normal event processing, like any other event.
1223		2393
		2394	If you want signals to be delivered truly asynchronously, just use
		2395	C<sigaction> as you would do without libev and forget about sharing
		2396	the signal. You can even use C<ev_async> from a signal handler to
		2397	synchronously wake up an event loop.
		2398
1224	You can configure as many watchers as you like per signal. Only when the	2399	You can configure as many watchers as you like for the same signal, but
		2400	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2401	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2402	C<SIGINT> in both the default loop and another loop at the same time. At
		2403	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2404
1225	first watcher gets started will libev actually register a signal watcher	2405	When the first watcher gets started will libev actually register something
1226	with the kernel (thus it coexists with your own signal handlers as long	2406	with the kernel (thus it coexists with your own signal handlers as long as
1227	as you don't register any with libev). Similarly, when the last signal	2407	you don't register any with libev for the same signal).
1228	watcher for a signal is stopped libev will reset the signal handler to	2408
1229	SIG_DFL (regardless of what it was set to before).	2409	If possible and supported, libev will install its handlers with
		2410	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2411	not be unduly interrupted. If you have a problem with system calls getting
		2412	interrupted by signals you can block all signals in an C<ev_check> watcher
		2413	and unblock them in an C<ev_prepare> watcher.
		2414
		2415	=head3 The special problem of inheritance over fork/execve/pthread_create
		2416
		2417	Both the signal mask (C<sigprocmask>) and the signal disposition
		2418	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2419	stopping it again), that is, libev might or might not block the signal,
		2420	and might or might not set or restore the installed signal handler (but
		2421	see C<EVFLAG_NOSIGMASK>).
		2422
		2423	While this does not matter for the signal disposition (libev never
		2424	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2425	C<execve>), this matters for the signal mask: many programs do not expect
		2426	certain signals to be blocked.
		2427
		2428	This means that before calling C<exec> (from the child) you should reset
		2429	the signal mask to whatever "default" you expect (all clear is a good
		2430	choice usually).
		2431
		2432	The simplest way to ensure that the signal mask is reset in the child is
		2433	to install a fork handler with C<pthread_atfork> that resets it. That will
		2434	catch fork calls done by libraries (such as the libc) as well.
		2435
		2436	In current versions of libev, the signal will not be blocked indefinitely
		2437	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2438	the window of opportunity for problems, it will not go away, as libev
		2439	I<has> to modify the signal mask, at least temporarily.
		2440
		2441	So I can't stress this enough: I<If you do not reset your signal mask when
		2442	you expect it to be empty, you have a race condition in your code>. This
		2443	is not a libev-specific thing, this is true for most event libraries.
		2444
		2445	=head3 The special problem of threads signal handling
		2446
		2447	POSIX threads has problematic signal handling semantics, specifically,
		2448	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2449	threads in a process block signals, which is hard to achieve.
		2450
		2451	When you want to use sigwait (or mix libev signal handling with your own
		2452	for the same signals), you can tackle this problem by globally blocking
		2453	all signals before creating any threads (or creating them with a fully set
		2454	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2455	loops. Then designate one thread as "signal receiver thread" which handles
		2456	these signals. You can pass on any signals that libev might be interested
		2457	in by calling C<ev_feed_signal>.
		2458
		2459	=head3 Watcher-Specific Functions and Data Members
1230		2460
1231	=over 4	2461	=over 4
1232		2462
1233	=item ev_signal_init (ev_signal *, callback, int signum)	2463	=item ev_signal_init (ev_signal *, callback, int signum)
1234		2464
…		…
1241		2471
1242	The signal the watcher watches out for.	2472	The signal the watcher watches out for.
1243		2473
1244	=back	2474	=back
1245		2475
		2476	=head3 Examples
		2477
		2478	Example: Try to exit cleanly on SIGINT.
		2479
		2480	static void
		2481	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2482	{
		2483	ev_break (loop, EVBREAK_ALL);
		2484	}
		2485
		2486	ev_signal signal_watcher;
		2487	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2488	ev_signal_start (loop, &signal_watcher);
		2489
1246		2490
1247	=head2 C<ev_child> - watch out for process status changes	2491	=head2 C<ev_child> - watch out for process status changes
1248		2492
1249	Child watchers trigger when your process receives a SIGCHLD in response to	2493	Child watchers trigger when your process receives a SIGCHLD in response to
1250	some child status changes (most typically when a child of yours dies).	2494	some child status changes (most typically when a child of yours dies or
		2495	exits). It is permissible to install a child watcher I<after> the child
		2496	has been forked (which implies it might have already exited), as long
		2497	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2498	forking and then immediately registering a watcher for the child is fine,
		2499	but forking and registering a watcher a few event loop iterations later or
		2500	in the next callback invocation is not.
		2501
		2502	Only the default event loop is capable of handling signals, and therefore
		2503	you can only register child watchers in the default event loop.
		2504
		2505	Due to some design glitches inside libev, child watchers will always be
		2506	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2507	libev)
		2508
		2509	=head3 Process Interaction
		2510
		2511	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2512	initialised. This is necessary to guarantee proper behaviour even if the
		2513	first child watcher is started after the child exits. The occurrence
		2514	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2515	synchronously as part of the event loop processing. Libev always reaps all
		2516	children, even ones not watched.
		2517
		2518	=head3 Overriding the Built-In Processing
		2519
		2520	Libev offers no special support for overriding the built-in child
		2521	processing, but if your application collides with libev's default child
		2522	handler, you can override it easily by installing your own handler for
		2523	C<SIGCHLD> after initialising the default loop, and making sure the
		2524	default loop never gets destroyed. You are encouraged, however, to use an
		2525	event-based approach to child reaping and thus use libev's support for
		2526	that, so other libev users can use C<ev_child> watchers freely.
		2527
		2528	=head3 Stopping the Child Watcher
		2529
		2530	Currently, the child watcher never gets stopped, even when the
		2531	child terminates, so normally one needs to stop the watcher in the
		2532	callback. Future versions of libev might stop the watcher automatically
		2533	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2534	problem).
		2535
		2536	=head3 Watcher-Specific Functions and Data Members
1251		2537
1252	=over 4	2538	=over 4
1253		2539
1254	=item ev_child_init (ev_child *, callback, int pid)	2540	=item ev_child_init (ev_child *, callback, int pid, int trace)
1255		2541
1256	=item ev_child_set (ev_child *, int pid)	2542	=item ev_child_set (ev_child *, int pid, int trace)
1257		2543
1258	Configures the watcher to wait for status changes of process C<pid> (or	2544	Configures the watcher to wait for status changes of process C<pid> (or
1259	I<any> process if C<pid> is specified as C<0>). The callback can look	2545	I<any> process if C<pid> is specified as C<0>). The callback can look
1260	at the C<rstatus> member of the C<ev_child> watcher structure to see	2546	at the C<rstatus> member of the C<ev_child> watcher structure to see
1261	the status word (use the macros from C<sys/wait.h> and see your systems	2547	the status word (use the macros from C<sys/wait.h> and see your systems
1262	C<waitpid> documentation). The C<rpid> member contains the pid of the	2548	C<waitpid> documentation). The C<rpid> member contains the pid of the
1263	process causing the status change.	2549	process causing the status change. C<trace> must be either C<0> (only
		2550	activate the watcher when the process terminates) or C<1> (additionally
		2551	activate the watcher when the process is stopped or continued).
1264		2552
1265	=item int pid [read-only]	2553	=item int pid [read-only]
1266		2554
1267	The process id this watcher watches out for, or C<0>, meaning any process id.	2555	The process id this watcher watches out for, or C<0>, meaning any process id.
1268		2556
…		…
1275	The process exit/trace status caused by C<rpid> (see your systems	2563	The process exit/trace status caused by C<rpid> (see your systems
1276	C<waitpid> and C<sys/wait.h> documentation for details).	2564	C<waitpid> and C<sys/wait.h> documentation for details).
1277		2565
1278	=back	2566	=back
1279		2567
1280	Example: Try to exit cleanly on SIGINT and SIGTERM.	2568	=head3 Examples
1281		2569
		2570	Example: C<fork()> a new process and install a child handler to wait for
		2571	its completion.
		2572
		2573	ev_child cw;
		2574
1282	static void	2575	static void
1283	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2576	child_cb (EV_P_ ev_child *w, int revents)
1284	{	2577	{
1285	ev_unloop (loop, EVUNLOOP_ALL);	2578	ev_child_stop (EV_A_ w);
		2579	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1286	}	2580	}
1287		2581
1288	struct ev_signal signal_watcher;	2582	pid_t pid = fork ();
1289	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2583
1290	ev_signal_start (loop, &sigint_cb);	2584	if (pid < 0)
		2585	// error
		2586	else if (pid == 0)
		2587	{
		2588	// the forked child executes here
		2589	exit (1);
		2590	}
		2591	else
		2592	{
		2593	ev_child_init (&cw, child_cb, pid, 0);
		2594	ev_child_start (EV_DEFAULT_ &cw);
		2595	}
1291		2596
1292		2597
1293	=head2 C<ev_stat> - did the file attributes just change?	2598	=head2 C<ev_stat> - did the file attributes just change?
1294		2599
1295	This watches a filesystem path for attribute changes. That is, it calls	2600	This watches a file system path for attribute changes. That is, it calls
1296	C<stat> regularly (or when the OS says it changed) and sees if it changed	2601	C<stat> on that path in regular intervals (or when the OS says it changed)
1297	compared to the last time, invoking the callback if it did.	2602	and sees if it changed compared to the last time, invoking the callback if
		2603	it did.
1298		2604
1299	The path does not need to exist: changing from "path exists" to "path does	2605	The path does not need to exist: changing from "path exists" to "path does
1300	not exist" is a status change like any other. The condition "path does	2606	not exist" is a status change like any other. The condition "path does not
1301	not exist" is signified by the C<st_nlink> field being zero (which is	2607	exist" (or more correctly "path cannot be stat'ed") is signified by the
1302	otherwise always forced to be at least one) and all the other fields of	2608	C<st_nlink> field being zero (which is otherwise always forced to be at
1303	the stat buffer having unspecified contents.	2609	least one) and all the other fields of the stat buffer having unspecified
		2610	contents.
1304		2611
1305	The path I<should> be absolute and I<must not> end in a slash. If it is	2612	The path I<must not> end in a slash or contain special components such as
		2613	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1306	relative and your working directory changes, the behaviour is undefined.	2614	your working directory changes, then the behaviour is undefined.
1307		2615
1308	Since there is no standard to do this, the portable implementation simply	2616	Since there is no portable change notification interface available, the
1309	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2617	portable implementation simply calls C<stat(2)> regularly on the path
1310	can specify a recommended polling interval for this case. If you specify	2618	to see if it changed somehow. You can specify a recommended polling
1311	a polling interval of C<0> (highly recommended!) then a I<suitable,	2619	interval for this case. If you specify a polling interval of C<0> (highly
1312	unspecified default> value will be used (which you can expect to be around	2620	recommended!) then a I<suitable, unspecified default> value will be used
1313	five seconds, although this might change dynamically). Libev will also	2621	(which you can expect to be around five seconds, although this might
1314	impose a minimum interval which is currently around C<0.1>, but thats	2622	change dynamically). Libev will also impose a minimum interval which is
1315	usually overkill.	2623	currently around C<0.1>, but that's usually overkill.
1316		2624
1317	This watcher type is not meant for massive numbers of stat watchers,	2625	This watcher type is not meant for massive numbers of stat watchers,
1318	as even with OS-supported change notifications, this can be	2626	as even with OS-supported change notifications, this can be
1319	resource-intensive.	2627	resource-intensive.
1320		2628
1321	At the time of this writing, only the Linux inotify interface is	2629	At the time of this writing, the only OS-specific interface implemented
1322	implemented (implementing kqueue support is left as an exercise for the	2630	is the Linux inotify interface (implementing kqueue support is left as an
1323	reader). Inotify will be used to give hints only and should not change the	2631	exercise for the reader. Note, however, that the author sees no way of
1324	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2632	implementing C<ev_stat> semantics with kqueue, except as a hint).
1325	to fall back to regular polling again even with inotify, but changes are	2633
1326	usually detected immediately, and if the file exists there will be no	2634	=head3 ABI Issues (Largefile Support)
1327	polling.	2635
		2636	Libev by default (unless the user overrides this) uses the default
		2637	compilation environment, which means that on systems with large file
		2638	support disabled by default, you get the 32 bit version of the stat
		2639	structure. When using the library from programs that change the ABI to
		2640	use 64 bit file offsets the programs will fail. In that case you have to
		2641	compile libev with the same flags to get binary compatibility. This is
		2642	obviously the case with any flags that change the ABI, but the problem is
		2643	most noticeably displayed with ev_stat and large file support.
		2644
		2645	The solution for this is to lobby your distribution maker to make large
		2646	file interfaces available by default (as e.g. FreeBSD does) and not
		2647	optional. Libev cannot simply switch on large file support because it has
		2648	to exchange stat structures with application programs compiled using the
		2649	default compilation environment.
		2650
		2651	=head3 Inotify and Kqueue
		2652
		2653	When C<inotify (7)> support has been compiled into libev and present at
		2654	runtime, it will be used to speed up change detection where possible. The
		2655	inotify descriptor will be created lazily when the first C<ev_stat>
		2656	watcher is being started.
		2657
		2658	Inotify presence does not change the semantics of C<ev_stat> watchers
		2659	except that changes might be detected earlier, and in some cases, to avoid
		2660	making regular C<stat> calls. Even in the presence of inotify support
		2661	there are many cases where libev has to resort to regular C<stat> polling,
		2662	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2663	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2664	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2665	xfs are fully working) libev usually gets away without polling.
		2666
		2667	There is no support for kqueue, as apparently it cannot be used to
		2668	implement this functionality, due to the requirement of having a file
		2669	descriptor open on the object at all times, and detecting renames, unlinks
		2670	etc. is difficult.
		2671
		2672	=head3 C<stat ()> is a synchronous operation
		2673
		2674	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2675	the process. The exception are C<ev_stat> watchers - those call C<stat
		2676	()>, which is a synchronous operation.
		2677
		2678	For local paths, this usually doesn't matter: unless the system is very
		2679	busy or the intervals between stat's are large, a stat call will be fast,
		2680	as the path data is usually in memory already (except when starting the
		2681	watcher).
		2682
		2683	For networked file systems, calling C<stat ()> can block an indefinite
		2684	time due to network issues, and even under good conditions, a stat call
		2685	often takes multiple milliseconds.
		2686
		2687	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2688	paths, although this is fully supported by libev.
		2689
		2690	=head3 The special problem of stat time resolution
		2691
		2692	The C<stat ()> system call only supports full-second resolution portably,
		2693	and even on systems where the resolution is higher, most file systems
		2694	still only support whole seconds.
		2695
		2696	That means that, if the time is the only thing that changes, you can
		2697	easily miss updates: on the first update, C<ev_stat> detects a change and
		2698	calls your callback, which does something. When there is another update
		2699	within the same second, C<ev_stat> will be unable to detect unless the
		2700	stat data does change in other ways (e.g. file size).
		2701
		2702	The solution to this is to delay acting on a change for slightly more
		2703	than a second (or till slightly after the next full second boundary), using
		2704	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2705	ev_timer_again (loop, w)>).
		2706
		2707	The C<.02> offset is added to work around small timing inconsistencies
		2708	of some operating systems (where the second counter of the current time
		2709	might be be delayed. One such system is the Linux kernel, where a call to
		2710	C<gettimeofday> might return a timestamp with a full second later than
		2711	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2712	update file times then there will be a small window where the kernel uses
		2713	the previous second to update file times but libev might already execute
		2714	the timer callback).
		2715
		2716	=head3 Watcher-Specific Functions and Data Members
1328		2717
1329	=over 4	2718	=over 4
1330		2719
1331	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)	2720	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
1332		2721
…		…
1336	C<path>. The C<interval> is a hint on how quickly a change is expected to	2725	C<path>. The C<interval> is a hint on how quickly a change is expected to
1337	be detected and should normally be specified as C<0> to let libev choose	2726	be detected and should normally be specified as C<0> to let libev choose
1338	a suitable value. The memory pointed to by C<path> must point to the same	2727	a suitable value. The memory pointed to by C<path> must point to the same
1339	path for as long as the watcher is active.	2728	path for as long as the watcher is active.
1340		2729
1341	The callback will be receive C<EV_STAT> when a change was detected,	2730	The callback will receive an C<EV_STAT> event when a change was detected,
1342	relative to the attributes at the time the watcher was started (or the	2731	relative to the attributes at the time the watcher was started (or the
1343	last change was detected).	2732	last change was detected).
1344		2733
1345	=item ev_stat_stat (ev_stat *)	2734	=item ev_stat_stat (loop, ev_stat *)
1346		2735
1347	Updates the stat buffer immediately with new values. If you change the	2736	Updates the stat buffer immediately with new values. If you change the
1348	watched path in your callback, you could call this fucntion to avoid	2737	watched path in your callback, you could call this function to avoid
1349	detecting this change (while introducing a race condition). Can also be	2738	detecting this change (while introducing a race condition if you are not
1350	useful simply to find out the new values.	2739	the only one changing the path). Can also be useful simply to find out the
		2740	new values.
1351		2741
1352	=item ev_statdata attr [read-only]	2742	=item ev_statdata attr [read-only]
1353		2743
1354	The most-recently detected attributes of the file. Although the type is of	2744	The most-recently detected attributes of the file. Although the type is
1355	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2745	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1356	suitable for your system. If the C<st_nlink> member is C<0>, then there	2746	suitable for your system, but you can only rely on the POSIX-standardised
		2747	members to be present. If the C<st_nlink> member is C<0>, then there was
1357	was some error while C<stat>ing the file.	2748	some error while C<stat>ing the file.
1358		2749
1359	=item ev_statdata prev [read-only]	2750	=item ev_statdata prev [read-only]
1360		2751
1361	The previous attributes of the file. The callback gets invoked whenever	2752	The previous attributes of the file. The callback gets invoked whenever
1362	C<prev> != C<attr>.	2753	C<prev> != C<attr>, or, more precisely, one or more of these members
		2754	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2755	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1363		2756
1364	=item ev_tstamp interval [read-only]	2757	=item ev_tstamp interval [read-only]
1365		2758
1366	The specified interval.	2759	The specified interval.
1367		2760
1368	=item const char *path [read-only]	2761	=item const char *path [read-only]
1369		2762
1370	The filesystem path that is being watched.	2763	The file system path that is being watched.
1371		2764
1372	=back	2765	=back
1373		2766
		2767	=head3 Examples
		2768
1374	Example: Watch C</etc/passwd> for attribute changes.	2769	Example: Watch C</etc/passwd> for attribute changes.
1375		2770
1376	static void	2771	static void
1377	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2772	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1378	{	2773	{
1379	/* /etc/passwd changed in some way */	2774	/* /etc/passwd changed in some way */
1380	if (w->attr.st_nlink)	2775	if (w->attr.st_nlink)
1381	{	2776	{
1382	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2777	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1383	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2778	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1384	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2779	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1385	}	2780	}
1386	else	2781	else
1387	/* you shalt not abuse printf for puts */	2782	/* you shalt not abuse printf for puts */
1388	puts ("wow, /etc/passwd is not there, expect problems. "	2783	puts ("wow, /etc/passwd is not there, expect problems. "
1389	"if this is windows, they already arrived\n");	2784	"if this is windows, they already arrived\n");
1390	}	2785	}
1391		2786
1392	...	2787	...
1393	ev_stat passwd;	2788	ev_stat passwd;
1394		2789
1395	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	2790	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1396	ev_stat_start (loop, &passwd);	2791	ev_stat_start (loop, &passwd);
		2792
		2793	Example: Like above, but additionally use a one-second delay so we do not
		2794	miss updates (however, frequent updates will delay processing, too, so
		2795	one might do the work both on C<ev_stat> callback invocation I<and> on
		2796	C<ev_timer> callback invocation).
		2797
		2798	static ev_stat passwd;
		2799	static ev_timer timer;
		2800
		2801	static void
		2802	timer_cb (EV_P_ ev_timer *w, int revents)
		2803	{
		2804	ev_timer_stop (EV_A_ w);
		2805
		2806	/* now it's one second after the most recent passwd change */
		2807	}
		2808
		2809	static void
		2810	stat_cb (EV_P_ ev_stat *w, int revents)
		2811	{
		2812	/* reset the one-second timer */
		2813	ev_timer_again (EV_A_ &timer);
		2814	}
		2815
		2816	...
		2817	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2818	ev_stat_start (loop, &passwd);
		2819	ev_timer_init (&timer, timer_cb, 0., 1.02);
1397		2820
1398		2821
1399	=head2 C<ev_idle> - when you've got nothing better to do...	2822	=head2 C<ev_idle> - when you've got nothing better to do...
1400		2823
1401	Idle watchers trigger events when no other events of the same or higher	2824	Idle watchers trigger events when no other events of the same or higher
1402	priority are pending (prepare, check and other idle watchers do not	2825	priority are pending (prepare, check and other idle watchers do not count
1403	count).	2826	as receiving "events").
1404		2827
1405	That is, as long as your process is busy handling sockets or timeouts	2828	That is, as long as your process is busy handling sockets or timeouts
1406	(or even signals, imagine) of the same or higher priority it will not be	2829	(or even signals, imagine) of the same or higher priority it will not be
1407	triggered. But when your process is idle (or only lower-priority watchers	2830	triggered. But when your process is idle (or only lower-priority watchers
1408	are pending), the idle watchers are being called once per event loop	2831	are pending), the idle watchers are being called once per event loop
…		…
1415	Apart from keeping your process non-blocking (which is a useful	2838	Apart from keeping your process non-blocking (which is a useful
1416	effect on its own sometimes), idle watchers are a good place to do	2839	effect on its own sometimes), idle watchers are a good place to do
1417	"pseudo-background processing", or delay processing stuff to after the	2840	"pseudo-background processing", or delay processing stuff to after the
1418	event loop has handled all outstanding events.	2841	event loop has handled all outstanding events.
1419		2842
		2843	=head3 Watcher-Specific Functions and Data Members
		2844
1420	=over 4	2845	=over 4
1421		2846
1422	=item ev_idle_init (ev_signal *, callback)	2847	=item ev_idle_init (ev_idle *, callback)
1423		2848
1424	Initialises and configures the idle watcher - it has no parameters of any	2849	Initialises and configures the idle watcher - it has no parameters of any
1425	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2850	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1426	believe me.	2851	believe me.
1427		2852
1428	=back	2853	=back
1429		2854
		2855	=head3 Examples
		2856
1430	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2857	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1431	callback, free it. Also, use no error checking, as usual.	2858	callback, free it. Also, use no error checking, as usual.
1432		2859
1433	static void	2860	static void
1434	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2861	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1435	{	2862	{
1436	free (w);	2863	free (w);
1437	// now do something you wanted to do when the program has	2864	// now do something you wanted to do when the program has
1438	// no longer asnything immediate to do.	2865	// no longer anything immediate to do.
1439	}	2866	}
1440		2867
1441	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2868	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1442	ev_idle_init (idle_watcher, idle_cb);	2869	ev_idle_init (idle_watcher, idle_cb);
1443	ev_idle_start (loop, idle_cb);	2870	ev_idle_start (loop, idle_watcher);
1444		2871
1445		2872
1446	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2873	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1447		2874
1448	Prepare and check watchers are usually (but not always) used in tandem:	2875	Prepare and check watchers are usually (but not always) used in pairs:
1449	prepare watchers get invoked before the process blocks and check watchers	2876	prepare watchers get invoked before the process blocks and check watchers
1450	afterwards.	2877	afterwards.
1451		2878
1452	You I<must not> call C<ev_loop> or similar functions that enter	2879	You I<must not> call C<ev_run> or similar functions that enter
1453	the current event loop from either C<ev_prepare> or C<ev_check>	2880	the current event loop from either C<ev_prepare> or C<ev_check>
1454	watchers. Other loops than the current one are fine, however. The	2881	watchers. Other loops than the current one are fine, however. The
1455	rationale behind this is that you do not need to check for recursion in	2882	rationale behind this is that you do not need to check for recursion in
1456	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2883	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1457	C<ev_check> so if you have one watcher of each kind they will always be	2884	C<ev_check> so if you have one watcher of each kind they will always be
1458	called in pairs bracketing the blocking call.	2885	called in pairs bracketing the blocking call.
1459		2886
1460	Their main purpose is to integrate other event mechanisms into libev and	2887	Their main purpose is to integrate other event mechanisms into libev and
1461	their use is somewhat advanced. This could be used, for example, to track	2888	their use is somewhat advanced. They could be used, for example, to track
1462	variable changes, implement your own watchers, integrate net-snmp or a	2889	variable changes, implement your own watchers, integrate net-snmp or a
1463	coroutine library and lots more. They are also occasionally useful if	2890	coroutine library and lots more. They are also occasionally useful if
1464	you cache some data and want to flush it before blocking (for example,	2891	you cache some data and want to flush it before blocking (for example,
1465	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2892	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1466	watcher).	2893	watcher).
1467		2894
1468	This is done by examining in each prepare call which file descriptors need	2895	This is done by examining in each prepare call which file descriptors
1469	to be watched by the other library, registering C<ev_io> watchers for	2896	need to be watched by the other library, registering C<ev_io> watchers
1470	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2897	for them and starting an C<ev_timer> watcher for any timeouts (many
1471	provide just this functionality). Then, in the check watcher you check for	2898	libraries provide exactly this functionality). Then, in the check watcher,
1472	any events that occured (by checking the pending status of all watchers	2899	you check for any events that occurred (by checking the pending status
1473	and stopping them) and call back into the library. The I/O and timer	2900	of all watchers and stopping them) and call back into the library. The
1474	callbacks will never actually be called (but must be valid nevertheless,	2901	I/O and timer callbacks will never actually be called (but must be valid
1475	because you never know, you know?).	2902	nevertheless, because you never know, you know?).
1476		2903
1477	As another example, the Perl Coro module uses these hooks to integrate	2904	As another example, the Perl Coro module uses these hooks to integrate
1478	coroutines into libev programs, by yielding to other active coroutines	2905	coroutines into libev programs, by yielding to other active coroutines
1479	during each prepare and only letting the process block if no coroutines	2906	during each prepare and only letting the process block if no coroutines
1480	are ready to run (it's actually more complicated: it only runs coroutines	2907	are ready to run (it's actually more complicated: it only runs coroutines
1481	with priority higher than or equal to the event loop and one coroutine	2908	with priority higher than or equal to the event loop and one coroutine
1482	of lower priority, but only once, using idle watchers to keep the event	2909	of lower priority, but only once, using idle watchers to keep the event
1483	loop from blocking if lower-priority coroutines are active, thus mapping	2910	loop from blocking if lower-priority coroutines are active, thus mapping
1484	low-priority coroutines to idle/background tasks).	2911	low-priority coroutines to idle/background tasks).
1485		2912
		2913	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		2914	priority, to ensure that they are being run before any other watchers
		2915	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2916
		2917	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2918	activate ("feed") events into libev. While libev fully supports this, they
		2919	might get executed before other C<ev_check> watchers did their job. As
		2920	C<ev_check> watchers are often used to embed other (non-libev) event
		2921	loops those other event loops might be in an unusable state until their
		2922	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2923	others).
		2924
		2925	=head3 Watcher-Specific Functions and Data Members
		2926
1486	=over 4	2927	=over 4
1487		2928
1488	=item ev_prepare_init (ev_prepare *, callback)	2929	=item ev_prepare_init (ev_prepare *, callback)
1489		2930
1490	=item ev_check_init (ev_check *, callback)	2931	=item ev_check_init (ev_check *, callback)
1491		2932
1492	Initialises and configures the prepare or check watcher - they have no	2933	Initialises and configures the prepare or check watcher - they have no
1493	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2934	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1494	macros, but using them is utterly, utterly and completely pointless.	2935	macros, but using them is utterly, utterly, utterly and completely
		2936	pointless.
1495		2937
1496	=back	2938	=back
1497		2939
1498	Example: To include a library such as adns, you would add IO watchers	2940	=head3 Examples
1499	and a timeout watcher in a prepare handler, as required by libadns, and	2941
		2942	There are a number of principal ways to embed other event loops or modules
		2943	into libev. Here are some ideas on how to include libadns into libev
		2944	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2945	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2946	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2947	Glib event loop).
		2948
		2949	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1500	in a check watcher, destroy them and call into libadns. What follows is	2950	and in a check watcher, destroy them and call into libadns. What follows
1501	pseudo-code only of course:	2951	is pseudo-code only of course. This requires you to either use a low
		2952	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2953	the callbacks for the IO/timeout watchers might not have been called yet.
1502		2954
1503	static ev_io iow [nfd];	2955	static ev_io iow [nfd];
1504	static ev_timer tw;	2956	static ev_timer tw;
1505		2957
1506	static void	2958	static void
1507	io_cb (ev_loop *loop, ev_io *w, int revents)	2959	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1508	{	2960	{
1509	// set the relevant poll flags
1510	// could also call adns_processreadable etc. here
1511	struct pollfd *fd = (struct pollfd *)w->data;
1512	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1513	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1514	}	2961	}
1515		2962
1516	// create io watchers for each fd and a timer before blocking	2963	// create io watchers for each fd and a timer before blocking
1517	static void	2964	static void
1518	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2965	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1519	{	2966	{
1520	int timeout = 3600000;	2967	int timeout = 3600000;
1521	struct pollfd fds [nfd];	2968	struct pollfd fds [nfd];
1522	// actual code will need to loop here and realloc etc.	2969	// actual code will need to loop here and realloc etc.
1523	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2970	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1524		2971
1525	/* the callback is illegal, but won't be called as we stop during check */	2972	/* the callback is illegal, but won't be called as we stop during check */
1526	ev_timer_init (&tw, 0, timeout * 1e-3);	2973	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1527	ev_timer_start (loop, &tw);	2974	ev_timer_start (loop, &tw);
1528		2975
1529	// create on ev_io per pollfd	2976	// create one ev_io per pollfd
1530	for (int i = 0; i < nfd; ++i)	2977	for (int i = 0; i < nfd; ++i)
1531	{	2978	{
1532	ev_io_init (iow + i, io_cb, fds [i].fd,	2979	ev_io_init (iow + i, io_cb, fds [i].fd,
1533	((fds [i].events & POLLIN ? EV_READ : 0)	2980	((fds [i].events & POLLIN ? EV_READ : 0)
1534	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2981	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1535		2982
1536	fds [i].revents = 0;	2983	fds [i].revents = 0;
1537	iow [i].data = fds + i;
1538	ev_io_start (loop, iow + i);	2984	ev_io_start (loop, iow + i);
1539	}	2985	}
1540	}	2986	}
1541		2987
1542	// stop all watchers after blocking	2988	// stop all watchers after blocking
1543	static void	2989	static void
1544	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2990	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1545	{	2991	{
1546	ev_timer_stop (loop, &tw);	2992	ev_timer_stop (loop, &tw);
1547		2993
1548	for (int i = 0; i < nfd; ++i)	2994	for (int i = 0; i < nfd; ++i)
		2995	{
		2996	// set the relevant poll flags
		2997	// could also call adns_processreadable etc. here
		2998	struct pollfd *fd = fds + i;
		2999	int revents = ev_clear_pending (iow + i);
		3000	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		3001	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		3002
		3003	// now stop the watcher
1549	ev_io_stop (loop, iow + i);	3004	ev_io_stop (loop, iow + i);
		3005	}
1550		3006
1551	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	3007	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1552	}	3008	}
		3009
		3010	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		3011	in the prepare watcher and would dispose of the check watcher.
		3012
		3013	Method 3: If the module to be embedded supports explicit event
		3014	notification (libadns does), you can also make use of the actual watcher
		3015	callbacks, and only destroy/create the watchers in the prepare watcher.
		3016
		3017	static void
		3018	timer_cb (EV_P_ ev_timer *w, int revents)
		3019	{
		3020	adns_state ads = (adns_state)w->data;
		3021	update_now (EV_A);
		3022
		3023	adns_processtimeouts (ads, &tv_now);
		3024	}
		3025
		3026	static void
		3027	io_cb (EV_P_ ev_io *w, int revents)
		3028	{
		3029	adns_state ads = (adns_state)w->data;
		3030	update_now (EV_A);
		3031
		3032	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		3033	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		3034	}
		3035
		3036	// do not ever call adns_afterpoll
		3037
		3038	Method 4: Do not use a prepare or check watcher because the module you
		3039	want to embed is not flexible enough to support it. Instead, you can
		3040	override their poll function. The drawback with this solution is that the
		3041	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		3042	this approach, effectively embedding EV as a client into the horrible
		3043	libglib event loop.
		3044
		3045	static gint
		3046	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		3047	{
		3048	int got_events = 0;
		3049
		3050	for (n = 0; n < nfds; ++n)
		3051	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		3052
		3053	if (timeout >= 0)
		3054	// create/start timer
		3055
		3056	// poll
		3057	ev_run (EV_A_ 0);
		3058
		3059	// stop timer again
		3060	if (timeout >= 0)
		3061	ev_timer_stop (EV_A_ &to);
		3062
		3063	// stop io watchers again - their callbacks should have set
		3064	for (n = 0; n < nfds; ++n)
		3065	ev_io_stop (EV_A_ iow [n]);
		3066
		3067	return got_events;
		3068	}
1553		3069
1554		3070
1555	=head2 C<ev_embed> - when one backend isn't enough...	3071	=head2 C<ev_embed> - when one backend isn't enough...
1556		3072
1557	This is a rather advanced watcher type that lets you embed one event loop	3073	This is a rather advanced watcher type that lets you embed one event loop
…		…
1563	prioritise I/O.	3079	prioritise I/O.
1564		3080
1565	As an example for a bug workaround, the kqueue backend might only support	3081	As an example for a bug workaround, the kqueue backend might only support
1566	sockets on some platform, so it is unusable as generic backend, but you	3082	sockets on some platform, so it is unusable as generic backend, but you
1567	still want to make use of it because you have many sockets and it scales	3083	still want to make use of it because you have many sockets and it scales
1568	so nicely. In this case, you would create a kqueue-based loop and embed it	3084	so nicely. In this case, you would create a kqueue-based loop and embed
1569	into your default loop (which might use e.g. poll). Overall operation will	3085	it into your default loop (which might use e.g. poll). Overall operation
1570	be a bit slower because first libev has to poll and then call kevent, but	3086	will be a bit slower because first libev has to call C<poll> and then
1571	at least you can use both at what they are best.	3087	C<kevent>, but at least you can use both mechanisms for what they are
		3088	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1572		3089
1573	As for prioritising I/O: rarely you have the case where some fds have	3090	As for prioritising I/O: under rare circumstances you have the case where
1574	to be watched and handled very quickly (with low latency), and even	3091	some fds have to be watched and handled very quickly (with low latency),
1575	priorities and idle watchers might have too much overhead. In this case	3092	and even priorities and idle watchers might have too much overhead. In
1576	you would put all the high priority stuff in one loop and all the rest in	3093	this case you would put all the high priority stuff in one loop and all
1577	a second one, and embed the second one in the first.	3094	the rest in a second one, and embed the second one in the first.
1578		3095
1579	As long as the watcher is active, the callback will be invoked every time	3096	As long as the watcher is active, the callback will be invoked every
1580	there might be events pending in the embedded loop. The callback must then	3097	time there might be events pending in the embedded loop. The callback
1581	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	3098	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1582	their callbacks (you could also start an idle watcher to give the embedded	3099	sweep and invoke their callbacks (the callback doesn't need to invoke the
1583	loop strictly lower priority for example). You can also set the callback	3100	C<ev_embed_sweep> function directly, it could also start an idle watcher
1584	to C<0>, in which case the embed watcher will automatically execute the	3101	to give the embedded loop strictly lower priority for example).
1585	embedded loop sweep.
1586		3102
1587	As long as the watcher is started it will automatically handle events. The	3103	You can also set the callback to C<0>, in which case the embed watcher
1588	callback will be invoked whenever some events have been handled. You can	3104	will automatically execute the embedded loop sweep whenever necessary.
1589	set the callback to C<0> to avoid having to specify one if you are not
1590	interested in that.
1591		3105
1592	Also, there have not currently been made special provisions for forking:	3106	Fork detection will be handled transparently while the C<ev_embed> watcher
1593	when you fork, you not only have to call C<ev_loop_fork> on both loops,	3107	is active, i.e., the embedded loop will automatically be forked when the
1594	but you will also have to stop and restart any C<ev_embed> watchers	3108	embedding loop forks. In other cases, the user is responsible for calling
1595	yourself.	3109	C<ev_loop_fork> on the embedded loop.
1596		3110
1597	Unfortunately, not all backends are embeddable, only the ones returned by	3111	Unfortunately, not all backends are embeddable: only the ones returned by
1598	C<ev_embeddable_backends> are, which, unfortunately, does not include any	3112	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1599	portable one.	3113	portable one.
1600		3114
1601	So when you want to use this feature you will always have to be prepared	3115	So when you want to use this feature you will always have to be prepared
1602	that you cannot get an embeddable loop. The recommended way to get around	3116	that you cannot get an embeddable loop. The recommended way to get around
1603	this is to have a separate variables for your embeddable loop, try to	3117	this is to have a separate variables for your embeddable loop, try to
1604	create it, and if that fails, use the normal loop for everything:	3118	create it, and if that fails, use the normal loop for everything.
1605		3119
1606	struct ev_loop *loop_hi = ev_default_init (0);	3120	=head3 C<ev_embed> and fork
1607	struct ev_loop *loop_lo = 0;
1608	struct ev_embed embed;
1609
1610	// see if there is a chance of getting one that works
1611	// (remember that a flags value of 0 means autodetection)
1612	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1613	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1614	: 0;
1615		3121
1616	// if we got one, then embed it, otherwise default to loop_hi	3122	While the C<ev_embed> watcher is running, forks in the embedding loop will
1617	if (loop_lo)	3123	automatically be applied to the embedded loop as well, so no special
1618	{	3124	fork handling is required in that case. When the watcher is not running,
1619	ev_embed_init (&embed, 0, loop_lo);	3125	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1620	ev_embed_start (loop_hi, &embed);	3126	as applicable.
1621	}	3127
1622	else	3128	=head3 Watcher-Specific Functions and Data Members
1623	loop_lo = loop_hi;
1624		3129
1625	=over 4	3130	=over 4
1626		3131
1627	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3132	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1628		3133
…		…
1630		3135
1631	Configures the watcher to embed the given loop, which must be	3136	Configures the watcher to embed the given loop, which must be
1632	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3137	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1633	invoked automatically, otherwise it is the responsibility of the callback	3138	invoked automatically, otherwise it is the responsibility of the callback
1634	to invoke it (it will continue to be called until the sweep has been done,	3139	to invoke it (it will continue to be called until the sweep has been done,
1635	if you do not want thta, you need to temporarily stop the embed watcher).	3140	if you do not want that, you need to temporarily stop the embed watcher).
1636		3141
1637	=item ev_embed_sweep (loop, ev_embed *)	3142	=item ev_embed_sweep (loop, ev_embed *)
1638		3143
1639	Make a single, non-blocking sweep over the embedded loop. This works	3144	Make a single, non-blocking sweep over the embedded loop. This works
1640	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	3145	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
1641	apropriate way for embedded loops.	3146	appropriate way for embedded loops.
1642		3147
1643	=item struct ev_loop *loop [read-only]	3148	=item struct ev_loop *other [read-only]
1644		3149
1645	The embedded event loop.	3150	The embedded event loop.
1646		3151
1647	=back	3152	=back
		3153
		3154	=head3 Examples
		3155
		3156	Example: Try to get an embeddable event loop and embed it into the default
		3157	event loop. If that is not possible, use the default loop. The default
		3158	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		3159	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		3160	used).
		3161
		3162	struct ev_loop *loop_hi = ev_default_init (0);
		3163	struct ev_loop *loop_lo = 0;
		3164	ev_embed embed;
		3165
		3166	// see if there is a chance of getting one that works
		3167	// (remember that a flags value of 0 means autodetection)
		3168	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		3169	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		3170	: 0;
		3171
		3172	// if we got one, then embed it, otherwise default to loop_hi
		3173	if (loop_lo)
		3174	{
		3175	ev_embed_init (&embed, 0, loop_lo);
		3176	ev_embed_start (loop_hi, &embed);
		3177	}
		3178	else
		3179	loop_lo = loop_hi;
		3180
		3181	Example: Check if kqueue is available but not recommended and create
		3182	a kqueue backend for use with sockets (which usually work with any
		3183	kqueue implementation). Store the kqueue/socket-only event loop in
		3184	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		3185
		3186	struct ev_loop *loop = ev_default_init (0);
		3187	struct ev_loop *loop_socket = 0;
		3188	ev_embed embed;
		3189
		3190	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		3191	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		3192	{
		3193	ev_embed_init (&embed, 0, loop_socket);
		3194	ev_embed_start (loop, &embed);
		3195	}
		3196
		3197	if (!loop_socket)
		3198	loop_socket = loop;
		3199
		3200	// now use loop_socket for all sockets, and loop for everything else
1648		3201
1649		3202
1650	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3203	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1651		3204
1652	Fork watchers are called when a C<fork ()> was detected (usually because	3205	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
1655	event loop blocks next and before C<ev_check> watchers are being called,	3208	event loop blocks next and before C<ev_check> watchers are being called,
1656	and only in the child after the fork. If whoever good citizen calling	3209	and only in the child after the fork. If whoever good citizen calling
1657	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3210	C<ev_default_fork> cheats and calls it in the wrong process, the fork
1658	handlers will be invoked, too, of course.	3211	handlers will be invoked, too, of course.
1659		3212
		3213	=head3 The special problem of life after fork - how is it possible?
		3214
		3215	Most uses of C<fork()> consist of forking, then some simple calls to set
		3216	up/change the process environment, followed by a call to C<exec()>. This
		3217	sequence should be handled by libev without any problems.
		3218
		3219	This changes when the application actually wants to do event handling
		3220	in the child, or both parent in child, in effect "continuing" after the
		3221	fork.
		3222
		3223	The default mode of operation (for libev, with application help to detect
		3224	forks) is to duplicate all the state in the child, as would be expected
		3225	when I<either> the parent I<or> the child process continues.
		3226
		3227	When both processes want to continue using libev, then this is usually the
		3228	wrong result. In that case, usually one process (typically the parent) is
		3229	supposed to continue with all watchers in place as before, while the other
		3230	process typically wants to start fresh, i.e. without any active watchers.
		3231
		3232	The cleanest and most efficient way to achieve that with libev is to
		3233	simply create a new event loop, which of course will be "empty", and
		3234	use that for new watchers. This has the advantage of not touching more
		3235	memory than necessary, and thus avoiding the copy-on-write, and the
		3236	disadvantage of having to use multiple event loops (which do not support
		3237	signal watchers).
		3238
		3239	When this is not possible, or you want to use the default loop for
		3240	other reasons, then in the process that wants to start "fresh", call
		3241	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
		3242	Destroying the default loop will "orphan" (not stop) all registered
		3243	watchers, so you have to be careful not to execute code that modifies
		3244	those watchers. Note also that in that case, you have to re-register any
		3245	signal watchers.
		3246
		3247	=head3 Watcher-Specific Functions and Data Members
		3248
1660	=over 4	3249	=over 4
1661		3250
1662	=item ev_fork_init (ev_signal *, callback)	3251	=item ev_fork_init (ev_fork *, callback)
1663		3252
1664	Initialises and configures the fork watcher - it has no parameters of any	3253	Initialises and configures the fork watcher - it has no parameters of any
1665	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,	3254	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
1666	believe me.	3255	really.
1667		3256
1668	=back	3257	=back
1669		3258
1670		3259
		3260	=head2 C<ev_cleanup> - even the best things end
		3261
		3262	Cleanup watchers are called just before the event loop is being destroyed
		3263	by a call to C<ev_loop_destroy>.
		3264
		3265	While there is no guarantee that the event loop gets destroyed, cleanup
		3266	watchers provide a convenient method to install cleanup hooks for your
		3267	program, worker threads and so on - you just to make sure to destroy the
		3268	loop when you want them to be invoked.
		3269
		3270	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3271	all other watchers, they do not keep a reference to the event loop (which
		3272	makes a lot of sense if you think about it). Like all other watchers, you
		3273	can call libev functions in the callback, except C<ev_cleanup_start>.
		3274
		3275	=head3 Watcher-Specific Functions and Data Members
		3276
		3277	=over 4
		3278
		3279	=item ev_cleanup_init (ev_cleanup *, callback)
		3280
		3281	Initialises and configures the cleanup watcher - it has no parameters of
		3282	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3283	pointless, I assure you.
		3284
		3285	=back
		3286
		3287	Example: Register an atexit handler to destroy the default loop, so any
		3288	cleanup functions are called.
		3289
		3290	static void
		3291	program_exits (void)
		3292	{
		3293	ev_loop_destroy (EV_DEFAULT_UC);
		3294	}
		3295
		3296	...
		3297	atexit (program_exits);
		3298
		3299
		3300	=head2 C<ev_async> - how to wake up an event loop
		3301
		3302	In general, you cannot use an C<ev_loop> from multiple threads or other
		3303	asynchronous sources such as signal handlers (as opposed to multiple event
		3304	loops - those are of course safe to use in different threads).
		3305
		3306	Sometimes, however, you need to wake up an event loop you do not control,
		3307	for example because it belongs to another thread. This is what C<ev_async>
		3308	watchers do: as long as the C<ev_async> watcher is active, you can signal
		3309	it by calling C<ev_async_send>, which is thread- and signal safe.
		3310
		3311	This functionality is very similar to C<ev_signal> watchers, as signals,
		3312	too, are asynchronous in nature, and signals, too, will be compressed
		3313	(i.e. the number of callback invocations may be less than the number of
		3314	C<ev_async_sent> calls). In fact, you could use signal watchers as a kind
		3315	of "global async watchers" by using a watcher on an otherwise unused
		3316	signal, and C<ev_feed_signal> to signal this watcher from another thread,
		3317	even without knowing which loop owns the signal.
		3318
		3319	=head3 Queueing
		3320
		3321	C<ev_async> does not support queueing of data in any way. The reason
		3322	is that the author does not know of a simple (or any) algorithm for a
		3323	multiple-writer-single-reader queue that works in all cases and doesn't
		3324	need elaborate support such as pthreads or unportable memory access
		3325	semantics.
		3326
		3327	That means that if you want to queue data, you have to provide your own
		3328	queue. But at least I can tell you how to implement locking around your
		3329	queue:
		3330
		3331	=over 4
		3332
		3333	=item queueing from a signal handler context
		3334
		3335	To implement race-free queueing, you simply add to the queue in the signal
		3336	handler but you block the signal handler in the watcher callback. Here is
		3337	an example that does that for some fictitious SIGUSR1 handler:
		3338
		3339	static ev_async mysig;
		3340
		3341	static void
		3342	sigusr1_handler (void)
		3343	{
		3344	sometype data;
		3345
		3346	// no locking etc.
		3347	queue_put (data);
		3348	ev_async_send (EV_DEFAULT_ &mysig);
		3349	}
		3350
		3351	static void
		3352	mysig_cb (EV_P_ ev_async *w, int revents)
		3353	{
		3354	sometype data;
		3355	sigset_t block, prev;
		3356
		3357	sigemptyset (&block);
		3358	sigaddset (&block, SIGUSR1);
		3359	sigprocmask (SIG_BLOCK, &block, &prev);
		3360
		3361	while (queue_get (&data))
		3362	process (data);
		3363
		3364	if (sigismember (&prev, SIGUSR1)
		3365	sigprocmask (SIG_UNBLOCK, &block, 0);
		3366	}
		3367
		3368	(Note: pthreads in theory requires you to use C<pthread_setmask>
		3369	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		3370	either...).
		3371
		3372	=item queueing from a thread context
		3373
		3374	The strategy for threads is different, as you cannot (easily) block
		3375	threads but you can easily preempt them, so to queue safely you need to
		3376	employ a traditional mutex lock, such as in this pthread example:
		3377
		3378	static ev_async mysig;
		3379	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		3380
		3381	static void
		3382	otherthread (void)
		3383	{
		3384	// only need to lock the actual queueing operation
		3385	pthread_mutex_lock (&mymutex);
		3386	queue_put (data);
		3387	pthread_mutex_unlock (&mymutex);
		3388
		3389	ev_async_send (EV_DEFAULT_ &mysig);
		3390	}
		3391
		3392	static void
		3393	mysig_cb (EV_P_ ev_async *w, int revents)
		3394	{
		3395	pthread_mutex_lock (&mymutex);
		3396
		3397	while (queue_get (&data))
		3398	process (data);
		3399
		3400	pthread_mutex_unlock (&mymutex);
		3401	}
		3402
		3403	=back
		3404
		3405
		3406	=head3 Watcher-Specific Functions and Data Members
		3407
		3408	=over 4
		3409
		3410	=item ev_async_init (ev_async *, callback)
		3411
		3412	Initialises and configures the async watcher - it has no parameters of any
		3413	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3414	trust me.
		3415
		3416	=item ev_async_send (loop, ev_async *)
		3417
		3418	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3419	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3420	returns.
		3421
		3422	Unlike C<ev_feed_event>, this call is safe to do from other threads,
		3423	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
		3424	embedding section below on what exactly this means).
		3425
		3426	Note that, as with other watchers in libev, multiple events might get
		3427	compressed into a single callback invocation (another way to look at
		3428	this is that C<ev_async> watchers are level-triggered: they are set on
		3429	C<ev_async_send>, reset when the event loop detects that).
		3430
		3431	This call incurs the overhead of at most one extra system call per event
		3432	loop iteration, if the event loop is blocked, and no syscall at all if
		3433	the event loop (or your program) is processing events. That means that
		3434	repeated calls are basically free (there is no need to avoid calls for
		3435	performance reasons) and that the overhead becomes smaller (typically
		3436	zero) under load.
		3437
		3438	=item bool = ev_async_pending (ev_async *)
		3439
		3440	Returns a non-zero value when C<ev_async_send> has been called on the
		3441	watcher but the event has not yet been processed (or even noted) by the
		3442	event loop.
		3443
		3444	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3445	the loop iterates next and checks for the watcher to have become active,
		3446	it will reset the flag again. C<ev_async_pending> can be used to very
		3447	quickly check whether invoking the loop might be a good idea.
		3448
		3449	Not that this does I<not> check whether the watcher itself is pending,
		3450	only whether it has been requested to make this watcher pending: there
		3451	is a time window between the event loop checking and resetting the async
		3452	notification, and the callback being invoked.
		3453
		3454	=back
		3455
		3456
1671	=head1 OTHER FUNCTIONS	3457	=head1 OTHER FUNCTIONS
1672		3458
1673	There are some other functions of possible interest. Described. Here. Now.	3459	There are some other functions of possible interest. Described. Here. Now.
1674		3460
1675	=over 4	3461	=over 4
1676		3462
1677	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3463	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1678		3464
1679	This function combines a simple timer and an I/O watcher, calls your	3465	This function combines a simple timer and an I/O watcher, calls your
1680	callback on whichever event happens first and automatically stop both	3466	callback on whichever event happens first and automatically stops both
1681	watchers. This is useful if you want to wait for a single event on an fd	3467	watchers. This is useful if you want to wait for a single event on an fd
1682	or timeout without having to allocate/configure/start/stop/free one or	3468	or timeout without having to allocate/configure/start/stop/free one or
1683	more watchers yourself.	3469	more watchers yourself.
1684		3470
1685	If C<fd> is less than 0, then no I/O watcher will be started and events	3471	If C<fd> is less than 0, then no I/O watcher will be started and the
1686	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3472	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1687	C<events> set will be craeted and started.	3473	the given C<fd> and C<events> set will be created and started.
1688		3474
1689	If C<timeout> is less than 0, then no timeout watcher will be	3475	If C<timeout> is less than 0, then no timeout watcher will be
1690	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3476	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1691	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3477	repeat = 0) will be started. C<0> is a valid timeout.
1692	dubious value.
1693		3478
1694	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3479	The callback has the type C<void (*cb)(int revents, void *arg)> and is
1695	passed an C<revents> set like normal event callbacks (a combination of	3480	passed an C<revents> set like normal event callbacks (a combination of
1696	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3481	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
1697	value passed to C<ev_once>:	3482	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3483	a timeout and an io event at the same time - you probably should give io
		3484	events precedence.
1698		3485
		3486	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3487
1699	static void stdin_ready (int revents, void *arg)	3488	static void stdin_ready (int revents, void *arg)
		3489	{
		3490	if (revents & EV_READ)
		3491	/* stdin might have data for us, joy! */;
		3492	else if (revents & EV_TIMER)
		3493	/* doh, nothing entered */;
		3494	}
		3495
		3496	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
		3497
		3498	=item ev_feed_fd_event (loop, int fd, int revents)
		3499
		3500	Feed an event on the given fd, as if a file descriptor backend detected
		3501	the given events.
		3502
		3503	=item ev_feed_signal_event (loop, int signum)
		3504
		3505	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
		3506	which is async-safe.
		3507
		3508	=back
		3509
		3510
		3511	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3512
		3513	This section explains some common idioms that are not immediately
		3514	obvious. Note that examples are sprinkled over the whole manual, and this
		3515	section only contains stuff that wouldn't fit anywhere else.
		3516
		3517	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3518
		3519	Each watcher has, by default, a C<void *data> member that you can read
		3520	or modify at any time: libev will completely ignore it. This can be used
		3521	to associate arbitrary data with your watcher. If you need more data and
		3522	don't want to allocate memory separately and store a pointer to it in that
		3523	data member, you can also "subclass" the watcher type and provide your own
		3524	data:
		3525
		3526	struct my_io
		3527	{
		3528	ev_io io;
		3529	int otherfd;
		3530	void *somedata;
		3531	struct whatever *mostinteresting;
		3532	};
		3533
		3534	...
		3535	struct my_io w;
		3536	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3537
		3538	And since your callback will be called with a pointer to the watcher, you
		3539	can cast it back to your own type:
		3540
		3541	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3542	{
		3543	struct my_io *w = (struct my_io *)w_;
		3544	...
		3545	}
		3546
		3547	More interesting and less C-conformant ways of casting your callback
		3548	function type instead have been omitted.
		3549
		3550	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3551
		3552	Another common scenario is to use some data structure with multiple
		3553	embedded watchers, in effect creating your own watcher that combines
		3554	multiple libev event sources into one "super-watcher":
		3555
		3556	struct my_biggy
		3557	{
		3558	int some_data;
		3559	ev_timer t1;
		3560	ev_timer t2;
		3561	}
		3562
		3563	In this case getting the pointer to C<my_biggy> is a bit more
		3564	complicated: Either you store the address of your C<my_biggy> struct in
		3565	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3566	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3567	real programmers):
		3568
		3569	#include <stddef.h>
		3570
		3571	static void
		3572	t1_cb (EV_P_ ev_timer *w, int revents)
		3573	{
		3574	struct my_biggy big = (struct my_biggy *)
		3575	(((char *)w) - offsetof (struct my_biggy, t1));
		3576	}
		3577
		3578	static void
		3579	t2_cb (EV_P_ ev_timer *w, int revents)
		3580	{
		3581	struct my_biggy big = (struct my_biggy *)
		3582	(((char *)w) - offsetof (struct my_biggy, t2));
		3583	}
		3584
		3585	=head2 AVOIDING FINISHING BEFORE RETURNING
		3586
		3587	Often you have structures like this in event-based programs:
		3588
		3589	callback ()
1700	{	3590	{
1701	if (revents & EV_TIMEOUT)	3591	free (request);
1702	/* doh, nothing entered */;
1703	else if (revents & EV_READ)
1704	/* stdin might have data for us, joy! */;
1705	}	3592	}
1706		3593
1707	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3594	request = start_new_request (..., callback);
1708		3595
1709	=item ev_feed_event (ev_loop *, watcher *, int revents)	3596	The intent is to start some "lengthy" operation. The C<request> could be
		3597	used to cancel the operation, or do other things with it.
1710		3598
1711	Feeds the given event set into the event loop, as if the specified event	3599	It's not uncommon to have code paths in C<start_new_request> that
1712	had happened for the specified watcher (which must be a pointer to an	3600	immediately invoke the callback, for example, to report errors. Or you add
1713	initialised but not necessarily started event watcher).	3601	some caching layer that finds that it can skip the lengthy aspects of the
		3602	operation and simply invoke the callback with the result.
1714		3603
1715	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3604	The problem here is that this will happen I<before> C<start_new_request>
		3605	has returned, so C<request> is not set.
1716		3606
1717	Feed an event on the given fd, as if a file descriptor backend detected	3607	Even if you pass the request by some safer means to the callback, you
1718	the given events it.	3608	might want to do something to the request after starting it, such as
		3609	canceling it, which probably isn't working so well when the callback has
		3610	already been invoked.
1719		3611
1720	=item ev_feed_signal_event (ev_loop *loop, int signum)	3612	A common way around all these issues is to make sure that
		3613	C<start_new_request> I<always> returns before the callback is invoked. If
		3614	C<start_new_request> immediately knows the result, it can artificially
		3615	delay invoking the callback by e.g. using a C<prepare> or C<idle> watcher
		3616	for example, or more sneakily, by reusing an existing (stopped) watcher
		3617	and pushing it into the pending queue:
1721		3618
1722	Feed an event as if the given signal occured (C<loop> must be the default	3619	ev_set_cb (watcher, callback);
1723	loop!).	3620	ev_feed_event (EV_A_ watcher, 0);
1724		3621
1725	=back	3622	This way, C<start_new_request> can safely return before the callback is
		3623	invoked, while not delaying callback invocation too much.
		3624
		3625	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3626
		3627	Often (especially in GUI toolkits) there are places where you have
		3628	I<modal> interaction, which is most easily implemented by recursively
		3629	invoking C<ev_run>.
		3630
		3631	This brings the problem of exiting - a callback might want to finish the
		3632	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3633	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3634	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3635	other combination: In these cases, C<ev_break> will not work alone.
		3636
		3637	The solution is to maintain "break this loop" variable for each C<ev_run>
		3638	invocation, and use a loop around C<ev_run> until the condition is
		3639	triggered, using C<EVRUN_ONCE>:
		3640
		3641	// main loop
		3642	int exit_main_loop = 0;
		3643
		3644	while (!exit_main_loop)
		3645	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3646
		3647	// in a modal watcher
		3648	int exit_nested_loop = 0;
		3649
		3650	while (!exit_nested_loop)
		3651	ev_run (EV_A_ EVRUN_ONCE);
		3652
		3653	To exit from any of these loops, just set the corresponding exit variable:
		3654
		3655	// exit modal loop
		3656	exit_nested_loop = 1;
		3657
		3658	// exit main program, after modal loop is finished
		3659	exit_main_loop = 1;
		3660
		3661	// exit both
		3662	exit_main_loop = exit_nested_loop = 1;
		3663
		3664	=head2 THREAD LOCKING EXAMPLE
		3665
		3666	Here is a fictitious example of how to run an event loop in a different
		3667	thread from where callbacks are being invoked and watchers are
		3668	created/added/removed.
		3669
		3670	For a real-world example, see the C<EV::Loop::Async> perl module,
		3671	which uses exactly this technique (which is suited for many high-level
		3672	languages).
		3673
		3674	The example uses a pthread mutex to protect the loop data, a condition
		3675	variable to wait for callback invocations, an async watcher to notify the
		3676	event loop thread and an unspecified mechanism to wake up the main thread.
		3677
		3678	First, you need to associate some data with the event loop:
		3679
		3680	typedef struct {
		3681	mutex_t lock; /* global loop lock */
		3682	ev_async async_w;
		3683	thread_t tid;
		3684	cond_t invoke_cv;
		3685	} userdata;
		3686
		3687	void prepare_loop (EV_P)
		3688	{
		3689	// for simplicity, we use a static userdata struct.
		3690	static userdata u;
		3691
		3692	ev_async_init (&u->async_w, async_cb);
		3693	ev_async_start (EV_A_ &u->async_w);
		3694
		3695	pthread_mutex_init (&u->lock, 0);
		3696	pthread_cond_init (&u->invoke_cv, 0);
		3697
		3698	// now associate this with the loop
		3699	ev_set_userdata (EV_A_ u);
		3700	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3701	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3702
		3703	// then create the thread running ev_run
		3704	pthread_create (&u->tid, 0, l_run, EV_A);
		3705	}
		3706
		3707	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3708	solely to wake up the event loop so it takes notice of any new watchers
		3709	that might have been added:
		3710
		3711	static void
		3712	async_cb (EV_P_ ev_async *w, int revents)
		3713	{
		3714	// just used for the side effects
		3715	}
		3716
		3717	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3718	protecting the loop data, respectively.
		3719
		3720	static void
		3721	l_release (EV_P)
		3722	{
		3723	userdata *u = ev_userdata (EV_A);
		3724	pthread_mutex_unlock (&u->lock);
		3725	}
		3726
		3727	static void
		3728	l_acquire (EV_P)
		3729	{
		3730	userdata *u = ev_userdata (EV_A);
		3731	pthread_mutex_lock (&u->lock);
		3732	}
		3733
		3734	The event loop thread first acquires the mutex, and then jumps straight
		3735	into C<ev_run>:
		3736
		3737	void *
		3738	l_run (void *thr_arg)
		3739	{
		3740	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3741
		3742	l_acquire (EV_A);
		3743	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3744	ev_run (EV_A_ 0);
		3745	l_release (EV_A);
		3746
		3747	return 0;
		3748	}
		3749
		3750	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3751	signal the main thread via some unspecified mechanism (signals? pipe
		3752	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3753	have been called (in a while loop because a) spurious wakeups are possible
		3754	and b) skipping inter-thread-communication when there are no pending
		3755	watchers is very beneficial):
		3756
		3757	static void
		3758	l_invoke (EV_P)
		3759	{
		3760	userdata *u = ev_userdata (EV_A);
		3761
		3762	while (ev_pending_count (EV_A))
		3763	{
		3764	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3765	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3766	}
		3767	}
		3768
		3769	Now, whenever the main thread gets told to invoke pending watchers, it
		3770	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3771	thread to continue:
		3772
		3773	static void
		3774	real_invoke_pending (EV_P)
		3775	{
		3776	userdata *u = ev_userdata (EV_A);
		3777
		3778	pthread_mutex_lock (&u->lock);
		3779	ev_invoke_pending (EV_A);
		3780	pthread_cond_signal (&u->invoke_cv);
		3781	pthread_mutex_unlock (&u->lock);
		3782	}
		3783
		3784	Whenever you want to start/stop a watcher or do other modifications to an
		3785	event loop, you will now have to lock:
		3786
		3787	ev_timer timeout_watcher;
		3788	userdata *u = ev_userdata (EV_A);
		3789
		3790	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3791
		3792	pthread_mutex_lock (&u->lock);
		3793	ev_timer_start (EV_A_ &timeout_watcher);
		3794	ev_async_send (EV_A_ &u->async_w);
		3795	pthread_mutex_unlock (&u->lock);
		3796
		3797	Note that sending the C<ev_async> watcher is required because otherwise
		3798	an event loop currently blocking in the kernel will have no knowledge
		3799	about the newly added timer. By waking up the loop it will pick up any new
		3800	watchers in the next event loop iteration.
		3801
		3802	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3803
		3804	While the overhead of a callback that e.g. schedules a thread is small, it
		3805	is still an overhead. If you embed libev, and your main usage is with some
		3806	kind of threads or coroutines, you might want to customise libev so that
		3807	doesn't need callbacks anymore.
		3808
		3809	Imagine you have coroutines that you can switch to using a function
		3810	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3811	and that due to some magic, the currently active coroutine is stored in a
		3812	global called C<current_coro>. Then you can build your own "wait for libev
		3813	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3814	the differing C<;> conventions):
		3815
		3816	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3817	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3818
		3819	That means instead of having a C callback function, you store the
		3820	coroutine to switch to in each watcher, and instead of having libev call
		3821	your callback, you instead have it switch to that coroutine.
		3822
		3823	A coroutine might now wait for an event with a function called
		3824	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3825	matter when, or whether the watcher is active or not when this function is
		3826	called):
		3827
		3828	void
		3829	wait_for_event (ev_watcher *w)
		3830	{
		3831	ev_cb_set (w) = current_coro;
		3832	switch_to (libev_coro);
		3833	}
		3834
		3835	That basically suspends the coroutine inside C<wait_for_event> and
		3836	continues the libev coroutine, which, when appropriate, switches back to
		3837	this or any other coroutine.
		3838
		3839	You can do similar tricks if you have, say, threads with an event queue -
		3840	instead of storing a coroutine, you store the queue object and instead of
		3841	switching to a coroutine, you push the watcher onto the queue and notify
		3842	any waiters.
		3843
		3844	To embed libev, see L<EMBEDDING>, but in short, it's easiest to create two
		3845	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3846
		3847	// my_ev.h
		3848	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3849	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
		3850	#include "../libev/ev.h"
		3851
		3852	// my_ev.c
		3853	#define EV_H "my_ev.h"
		3854	#include "../libev/ev.c"
		3855
		3856	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3857	F<my_ev.c> into your project. When properly specifying include paths, you
		3858	can even use F<ev.h> as header file name directly.
1726		3859
1727		3860
1728	=head1 LIBEVENT EMULATION	3861	=head1 LIBEVENT EMULATION
1729		3862
1730	Libev offers a compatibility emulation layer for libevent. It cannot	3863	Libev offers a compatibility emulation layer for libevent. It cannot
1731	emulate the internals of libevent, so here are some usage hints:	3864	emulate the internals of libevent, so here are some usage hints:
1732		3865
1733	=over 4	3866	=over 4
		3867
		3868	=item * Only the libevent-1.4.1-beta API is being emulated.
		3869
		3870	This was the newest libevent version available when libev was implemented,
		3871	and is still mostly unchanged in 2010.
1734		3872
1735	=item * Use it by including <event.h>, as usual.	3873	=item * Use it by including <event.h>, as usual.
1736		3874
1737	=item * The following members are fully supported: ev_base, ev_callback,	3875	=item * The following members are fully supported: ev_base, ev_callback,
1738	ev_arg, ev_fd, ev_res, ev_events.	3876	ev_arg, ev_fd, ev_res, ev_events.
…		…
1743		3881
1744	=item * Priorities are not currently supported. Initialising priorities	3882	=item * Priorities are not currently supported. Initialising priorities
1745	will fail and all watchers will have the same priority, even though there	3883	will fail and all watchers will have the same priority, even though there
1746	is an ev_pri field.	3884	is an ev_pri field.
1747		3885
		3886	=item * In libevent, the last base created gets the signals, in libev, the
		3887	base that registered the signal gets the signals.
		3888
1748	=item * Other members are not supported.	3889	=item * Other members are not supported.
1749		3890
1750	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3891	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1751	to use the libev header file and library.	3892	to use the libev header file and library.
1752		3893
1753	=back	3894	=back
1754		3895
1755	=head1 C++ SUPPORT	3896	=head1 C++ SUPPORT
1756		3897
1757	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3898	Libev comes with some simplistic wrapper classes for C++ that mainly allow
1758	you to use some convinience methods to start/stop watchers and also change	3899	you to use some convenience methods to start/stop watchers and also change
1759	the callback model to a model using method callbacks on objects.	3900	the callback model to a model using method callbacks on objects.
1760		3901
1761	To use it,	3902	To use it,
1762		3903
1763	#include <ev++.h>	3904	#include <ev++.h>
1764		3905
1765	This automatically includes F<ev.h> and puts all of its definitions (many	3906	This automatically includes F<ev.h> and puts all of its definitions (many
1766	of them macros) into the global namespace. All C++ specific things are	3907	of them macros) into the global namespace. All C++ specific things are
1767	put into the C<ev> namespace. It should support all the same embedding	3908	put into the C<ev> namespace. It should support all the same embedding
1768	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	3909	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
1770	Care has been taken to keep the overhead low. The only data member the C++	3911	Care has been taken to keep the overhead low. The only data member the C++
1771	classes add (compared to plain C-style watchers) is the event loop pointer	3912	classes add (compared to plain C-style watchers) is the event loop pointer
1772	that the watcher is associated with (or no additional members at all if	3913	that the watcher is associated with (or no additional members at all if
1773	you disable C<EV_MULTIPLICITY> when embedding libev).	3914	you disable C<EV_MULTIPLICITY> when embedding libev).
1774		3915
1775	Currently, functions, and static and non-static member functions can be	3916	Currently, functions, static and non-static member functions and classes
1776	used as callbacks. Other types should be easy to add as long as they only	3917	with C<operator ()> can be used as callbacks. Other types should be easy
1777	need one additional pointer for context. If you need support for other	3918	to add as long as they only need one additional pointer for context. If
1778	types of functors please contact the author (preferably after implementing	3919	you need support for other types of functors please contact the author
1779	it).	3920	(preferably after implementing it).
1780		3921
1781	Here is a list of things available in the C<ev> namespace:	3922	Here is a list of things available in the C<ev> namespace:
1782		3923
1783	=over 4	3924	=over 4
1784		3925
…		…
1794	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	3935	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
1795		3936
1796	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	3937	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
1797	the same name in the C<ev> namespace, with the exception of C<ev_signal>	3938	the same name in the C<ev> namespace, with the exception of C<ev_signal>
1798	which is called C<ev::sig> to avoid clashes with the C<signal> macro	3939	which is called C<ev::sig> to avoid clashes with the C<signal> macro
1799	defines by many implementations.	3940	defined by many implementations.
1800		3941
1801	All of those classes have these methods:	3942	All of those classes have these methods:
1802		3943
1803	=over 4	3944	=over 4
1804		3945
1805	=item ev::TYPE::TYPE ()	3946	=item ev::TYPE::TYPE ()
1806		3947
1807	=item ev::TYPE::TYPE (struct ev_loop *)	3948	=item ev::TYPE::TYPE (loop)
1808		3949
1809	=item ev::TYPE::~TYPE	3950	=item ev::TYPE::~TYPE
1810		3951
1811	The constructor (optionally) takes an event loop to associate the watcher	3952	The constructor (optionally) takes an event loop to associate the watcher
1812	with. If it is omitted, it will use C<EV_DEFAULT>.	3953	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
1835	your compiler is good :), then the method will be fully inlined into the	3976	your compiler is good :), then the method will be fully inlined into the
1836	thunking function, making it as fast as a direct C callback.	3977	thunking function, making it as fast as a direct C callback.
1837		3978
1838	Example: simple class declaration and watcher initialisation	3979	Example: simple class declaration and watcher initialisation
1839		3980
1840	struct myclass	3981	struct myclass
1841	{	3982	{
1842	void io_cb (ev::io &w, int revents) { }	3983	void io_cb (ev::io &w, int revents) { }
1843	}	3984	}
1844		3985
1845	myclass obj;	3986	myclass obj;
1846	ev::io iow;	3987	ev::io iow;
1847	iow.set <myclass, &myclass::io_cb> (&obj);	3988	iow.set <myclass, &myclass::io_cb> (&obj);
1848		3989
1849	=item w->set (void (*function)(watcher &w, int), void *data = 0)	3990	=item w->set (object *)
		3991
		3992	This is a variation of a method callback - leaving out the method to call
		3993	will default the method to C<operator ()>, which makes it possible to use
		3994	functor objects without having to manually specify the C<operator ()> all
		3995	the time. Incidentally, you can then also leave out the template argument
		3996	list.
		3997
		3998	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3999	int revents)>.
		4000
		4001	See the method-C<set> above for more details.
		4002
		4003	Example: use a functor object as callback.
		4004
		4005	struct myfunctor
		4006	{
		4007	void operator() (ev::io &w, int revents)
		4008	{
		4009	...
		4010	}
		4011	}
		4012
		4013	myfunctor f;
		4014
		4015	ev::io w;
		4016	w.set (&f);
		4017
		4018	=item w->set<function> (void *data = 0)
1850		4019
1851	Also sets a callback, but uses a static method or plain function as	4020	Also sets a callback, but uses a static method or plain function as
1852	callback. The optional C<data> argument will be stored in the watcher's	4021	callback. The optional C<data> argument will be stored in the watcher's
1853	C<data> member and is free for you to use.	4022	C<data> member and is free for you to use.
1854		4023
		4024	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		4025
1855	See the method-C<set> above for more details.	4026	See the method-C<set> above for more details.
1856		4027
		4028	Example: Use a plain function as callback.
		4029
		4030	static void io_cb (ev::io &w, int revents) { }
		4031	iow.set <io_cb> ();
		4032
1857	=item w->set (struct ev_loop *)	4033	=item w->set (loop)
1858		4034
1859	Associates a different C<struct ev_loop> with this watcher. You can only	4035	Associates a different C<struct ev_loop> with this watcher. You can only
1860	do this when the watcher is inactive (and not pending either).	4036	do this when the watcher is inactive (and not pending either).
1861		4037
1862	=item w->set ([args])	4038	=item w->set ([arguments])
1863		4039
1864	Basically the same as C<ev_TYPE_set>, with the same args. Must be	4040	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this
1865	called at least once. Unlike the C counterpart, an active watcher gets	4041	method or a suitable start method must be called at least once. Unlike the
1866	automatically stopped and restarted when reconfiguring it with this	4042	C counterpart, an active watcher gets automatically stopped and restarted
1867	method.	4043	when reconfiguring it with this method.
1868		4044
1869	=item w->start ()	4045	=item w->start ()
1870		4046
1871	Starts the watcher. Note that there is no C<loop> argument, as the	4047	Starts the watcher. Note that there is no C<loop> argument, as the
1872	constructor already stores the event loop.	4048	constructor already stores the event loop.
1873		4049
		4050	=item w->start ([arguments])
		4051
		4052	Instead of calling C<set> and C<start> methods separately, it is often
		4053	convenient to wrap them in one call. Uses the same type of arguments as
		4054	the configure C<set> method of the watcher.
		4055
1874	=item w->stop ()	4056	=item w->stop ()
1875		4057
1876	Stops the watcher if it is active. Again, no C<loop> argument.	4058	Stops the watcher if it is active. Again, no C<loop> argument.
1877		4059
1878	=item w->again () C<ev::timer>, C<ev::periodic> only	4060	=item w->again () (C<ev::timer>, C<ev::periodic> only)
1879		4061
1880	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding	4062	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
1881	C<ev_TYPE_again> function.	4063	C<ev_TYPE_again> function.
1882		4064
1883	=item w->sweep () C<ev::embed> only	4065	=item w->sweep () (C<ev::embed> only)
1884		4066
1885	Invokes C<ev_embed_sweep>.	4067	Invokes C<ev_embed_sweep>.
1886		4068
1887	=item w->update () C<ev::stat> only	4069	=item w->update () (C<ev::stat> only)
1888		4070
1889	Invokes C<ev_stat_stat>.	4071	Invokes C<ev_stat_stat>.
1890		4072
1891	=back	4073	=back
1892		4074
1893	=back	4075	=back
1894		4076
1895	Example: Define a class with an IO and idle watcher, start one of them in	4077	Example: Define a class with two I/O and idle watchers, start the I/O
1896	the constructor.	4078	watchers in the constructor.
1897		4079
1898	class myclass	4080	class myclass
1899	{	4081	{
1900	ev_io io; void io_cb (ev::io &w, int revents);	4082	ev::io io ; void io_cb (ev::io &w, int revents);
		4083	ev::io io2 ; void io2_cb (ev::io &w, int revents);
1901	ev_idle idle void idle_cb (ev::idle &w, int revents);	4084	ev::idle idle; void idle_cb (ev::idle &w, int revents);
1902		4085
1903	myclass ();	4086	myclass (int fd)
1904	}	4087	{
1905
1906	myclass::myclass (int fd)
1907	{
1908	io .set <myclass, &myclass::io_cb > (this);	4088	io .set <myclass, &myclass::io_cb > (this);
		4089	io2 .set <myclass, &myclass::io2_cb > (this);
1909	idle.set <myclass, &myclass::idle_cb> (this);	4090	idle.set <myclass, &myclass::idle_cb> (this);
1910		4091
1911	io.start (fd, ev::READ);	4092	io.set (fd, ev::WRITE); // configure the watcher
		4093	io.start (); // start it whenever convenient
		4094
		4095	io2.start (fd, ev::READ); // set + start in one call
		4096	}
1912	}	4097	};
		4098
		4099
		4100	=head1 OTHER LANGUAGE BINDINGS
		4101
		4102	Libev does not offer other language bindings itself, but bindings for a
		4103	number of languages exist in the form of third-party packages. If you know
		4104	any interesting language binding in addition to the ones listed here, drop
		4105	me a note.
		4106
		4107	=over 4
		4108
		4109	=item Perl
		4110
		4111	The EV module implements the full libev API and is actually used to test
		4112	libev. EV is developed together with libev. Apart from the EV core module,
		4113	there are additional modules that implement libev-compatible interfaces
		4114	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		4115	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		4116	and C<EV::Glib>).
		4117
		4118	It can be found and installed via CPAN, its homepage is at
		4119	L<http://software.schmorp.de/pkg/EV>.
		4120
		4121	=item Python
		4122
		4123	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		4124	seems to be quite complete and well-documented.
		4125
		4126	=item Ruby
		4127
		4128	Tony Arcieri has written a ruby extension that offers access to a subset
		4129	of the libev API and adds file handle abstractions, asynchronous DNS and
		4130	more on top of it. It can be found via gem servers. Its homepage is at
		4131	L<http://rev.rubyforge.org/>.
		4132
		4133	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		4134	makes rev work even on mingw.
		4135
		4136	=item Haskell
		4137
		4138	A haskell binding to libev is available at
		4139	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		4140
		4141	=item D
		4142
		4143	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		4144	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
		4145
		4146	=item Ocaml
		4147
		4148	Erkki Seppala has written Ocaml bindings for libev, to be found at
		4149	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		4150
		4151	=item Lua
		4152
		4153	Brian Maher has written a partial interface to libev for lua (at the
		4154	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		4155	L<http://github.com/brimworks/lua-ev>.
		4156
		4157	=back
1913		4158
1914		4159
1915	=head1 MACRO MAGIC	4160	=head1 MACRO MAGIC
1916		4161
1917	Libev can be compiled with a variety of options, the most fundemantal is	4162	Libev can be compiled with a variety of options, the most fundamental
1918	C<EV_MULTIPLICITY>. This option determines whether (most) functions and	4163	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
1919	callbacks have an initial C<struct ev_loop *> argument.	4164	functions and callbacks have an initial C<struct ev_loop *> argument.
1920		4165
1921	To make it easier to write programs that cope with either variant, the	4166	To make it easier to write programs that cope with either variant, the
1922	following macros are defined:	4167	following macros are defined:
1923		4168
1924	=over 4	4169	=over 4
…		…
1927		4172
1928	This provides the loop I<argument> for functions, if one is required ("ev	4173	This provides the loop I<argument> for functions, if one is required ("ev
1929	loop argument"). The C<EV_A> form is used when this is the sole argument,	4174	loop argument"). The C<EV_A> form is used when this is the sole argument,
1930	C<EV_A_> is used when other arguments are following. Example:	4175	C<EV_A_> is used when other arguments are following. Example:
1931		4176
1932	ev_unref (EV_A);	4177	ev_unref (EV_A);
1933	ev_timer_add (EV_A_ watcher);	4178	ev_timer_add (EV_A_ watcher);
1934	ev_loop (EV_A_ 0);	4179	ev_run (EV_A_ 0);
1935		4180
1936	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	4181	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
1937	which is often provided by the following macro.	4182	which is often provided by the following macro.
1938		4183
1939	=item C<EV_P>, C<EV_P_>	4184	=item C<EV_P>, C<EV_P_>
1940		4185
1941	This provides the loop I<parameter> for functions, if one is required ("ev	4186	This provides the loop I<parameter> for functions, if one is required ("ev
1942	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	4187	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
1943	C<EV_P_> is used when other parameters are following. Example:	4188	C<EV_P_> is used when other parameters are following. Example:
1944		4189
1945	// this is how ev_unref is being declared	4190	// this is how ev_unref is being declared
1946	static void ev_unref (EV_P);	4191	static void ev_unref (EV_P);
1947		4192
1948	// this is how you can declare your typical callback	4193	// this is how you can declare your typical callback
1949	static void cb (EV_P_ ev_timer *w, int revents)	4194	static void cb (EV_P_ ev_timer *w, int revents)
1950		4195
1951	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	4196	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
1952	suitable for use with C<EV_A>.	4197	suitable for use with C<EV_A>.
1953		4198
1954	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4199	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
1955		4200
1956	Similar to the other two macros, this gives you the value of the default	4201	Similar to the other two macros, this gives you the value of the default
1957	loop, if multiple loops are supported ("ev loop default").	4202	loop, if multiple loops are supported ("ev loop default"). The default loop
		4203	will be initialised if it isn't already initialised.
		4204
		4205	For non-multiplicity builds, these macros do nothing, so you always have
		4206	to initialise the loop somewhere.
		4207
		4208	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		4209
		4210	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		4211	default loop has been initialised (C<UC> == unchecked). Their behaviour
		4212	is undefined when the default loop has not been initialised by a previous
		4213	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		4214
		4215	It is often prudent to use C<EV_DEFAULT> when initialising the first
		4216	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
1958		4217
1959	=back	4218	=back
1960		4219
1961	Example: Declare and initialise a check watcher, utilising the above	4220	Example: Declare and initialise a check watcher, utilising the above
1962	macros so it will work regardless of whether multiple loops are supported	4221	macros so it will work regardless of whether multiple loops are supported
1963	or not.	4222	or not.
1964		4223
1965	static void	4224	static void
1966	check_cb (EV_P_ ev_timer *w, int revents)	4225	check_cb (EV_P_ ev_timer *w, int revents)
1967	{	4226	{
1968	ev_check_stop (EV_A_ w);	4227	ev_check_stop (EV_A_ w);
1969	}	4228	}
1970		4229
1971	ev_check check;	4230	ev_check check;
1972	ev_check_init (&check, check_cb);	4231	ev_check_init (&check, check_cb);
1973	ev_check_start (EV_DEFAULT_ &check);	4232	ev_check_start (EV_DEFAULT_ &check);
1974	ev_loop (EV_DEFAULT_ 0);	4233	ev_run (EV_DEFAULT_ 0);
1975		4234
1976	=head1 EMBEDDING	4235	=head1 EMBEDDING
1977		4236
1978	Libev can (and often is) directly embedded into host	4237	Libev can (and often is) directly embedded into host
1979	applications. Examples of applications that embed it include the Deliantra	4238	applications. Examples of applications that embed it include the Deliantra
1980	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)	4239	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
1981	and rxvt-unicode.	4240	and rxvt-unicode.
1982		4241
1983	The goal is to enable you to just copy the neecssary files into your	4242	The goal is to enable you to just copy the necessary files into your
1984	source directory without having to change even a single line in them, so	4243	source directory without having to change even a single line in them, so
1985	you can easily upgrade by simply copying (or having a checked-out copy of	4244	you can easily upgrade by simply copying (or having a checked-out copy of
1986	libev somewhere in your source tree).	4245	libev somewhere in your source tree).
1987		4246
1988	=head2 FILESETS	4247	=head2 FILESETS
1989		4248
1990	Depending on what features you need you need to include one or more sets of files	4249	Depending on what features you need you need to include one or more sets of files
1991	in your app.	4250	in your application.
1992		4251
1993	=head3 CORE EVENT LOOP	4252	=head3 CORE EVENT LOOP
1994		4253
1995	To include only the libev core (all the C<ev_*> functions), with manual	4254	To include only the libev core (all the C<ev_*> functions), with manual
1996	configuration (no autoconf):	4255	configuration (no autoconf):
1997		4256
1998	#define EV_STANDALONE 1	4257	#define EV_STANDALONE 1
1999	#include "ev.c"	4258	#include "ev.c"
2000		4259
2001	This will automatically include F<ev.h>, too, and should be done in a	4260	This will automatically include F<ev.h>, too, and should be done in a
2002	single C source file only to provide the function implementations. To use	4261	single C source file only to provide the function implementations. To use
2003	it, do the same for F<ev.h> in all files wishing to use this API (best	4262	it, do the same for F<ev.h> in all files wishing to use this API (best
2004	done by writing a wrapper around F<ev.h> that you can include instead and	4263	done by writing a wrapper around F<ev.h> that you can include instead and
2005	where you can put other configuration options):	4264	where you can put other configuration options):
2006		4265
2007	#define EV_STANDALONE 1	4266	#define EV_STANDALONE 1
2008	#include "ev.h"	4267	#include "ev.h"
2009		4268
2010	Both header files and implementation files can be compiled with a C++	4269	Both header files and implementation files can be compiled with a C++
2011	compiler (at least, thats a stated goal, and breakage will be treated	4270	compiler (at least, that's a stated goal, and breakage will be treated
2012	as a bug).	4271	as a bug).
2013		4272
2014	You need the following files in your source tree, or in a directory	4273	You need the following files in your source tree, or in a directory
2015	in your include path (e.g. in libev/ when using -Ilibev):	4274	in your include path (e.g. in libev/ when using -Ilibev):
2016		4275
2017	ev.h	4276	ev.h
2018	ev.c	4277	ev.c
2019	ev_vars.h	4278	ev_vars.h
2020	ev_wrap.h	4279	ev_wrap.h
2021		4280
2022	ev_win32.c required on win32 platforms only	4281	ev_win32.c required on win32 platforms only
2023		4282
2024	ev_select.c only when select backend is enabled (which is enabled by default)	4283	ev_select.c only when select backend is enabled (which is enabled by default)
2025	ev_poll.c only when poll backend is enabled (disabled by default)	4284	ev_poll.c only when poll backend is enabled (disabled by default)
2026	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4285	ev_epoll.c only when the epoll backend is enabled (disabled by default)
2027	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4286	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2028	ev_port.c only when the solaris port backend is enabled (disabled by default)	4287	ev_port.c only when the solaris port backend is enabled (disabled by default)
2029		4288
2030	F<ev.c> includes the backend files directly when enabled, so you only need	4289	F<ev.c> includes the backend files directly when enabled, so you only need
2031	to compile this single file.	4290	to compile this single file.
2032		4291
2033	=head3 LIBEVENT COMPATIBILITY API	4292	=head3 LIBEVENT COMPATIBILITY API
2034		4293
2035	To include the libevent compatibility API, also include:	4294	To include the libevent compatibility API, also include:
2036		4295
2037	#include "event.c"	4296	#include "event.c"
2038		4297
2039	in the file including F<ev.c>, and:	4298	in the file including F<ev.c>, and:
2040		4299
2041	#include "event.h"	4300	#include "event.h"
2042		4301
2043	in the files that want to use the libevent API. This also includes F<ev.h>.	4302	in the files that want to use the libevent API. This also includes F<ev.h>.
2044		4303
2045	You need the following additional files for this:	4304	You need the following additional files for this:
2046		4305
2047	event.h	4306	event.h
2048	event.c	4307	event.c
2049		4308
2050	=head3 AUTOCONF SUPPORT	4309	=head3 AUTOCONF SUPPORT
2051		4310
2052	Instead of using C<EV_STANDALONE=1> and providing your config in	4311	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2053	whatever way you want, you can also C<m4_include([libev.m4])> in your	4312	whatever way you want, you can also C<m4_include([libev.m4])> in your
2054	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	4313	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2055	include F<config.h> and configure itself accordingly.	4314	include F<config.h> and configure itself accordingly.
2056		4315
2057	For this of course you need the m4 file:	4316	For this of course you need the m4 file:
2058		4317
2059	libev.m4	4318	libev.m4
2060		4319
2061	=head2 PREPROCESSOR SYMBOLS/MACROS	4320	=head2 PREPROCESSOR SYMBOLS/MACROS
2062		4321
2063	Libev can be configured via a variety of preprocessor symbols you have to define	4322	Libev can be configured via a variety of preprocessor symbols you have to
2064	before including any of its files. The default is not to build for multiplicity	4323	define before including (or compiling) any of its files. The default in
2065	and only include the select backend.	4324	the absence of autoconf is documented for every option.
		4325
		4326	Symbols marked with "(h)" do not change the ABI, and can have different
		4327	values when compiling libev vs. including F<ev.h>, so it is permissible
		4328	to redefine them before including F<ev.h> without breaking compatibility
		4329	to a compiled library. All other symbols change the ABI, which means all
		4330	users of libev and the libev code itself must be compiled with compatible
		4331	settings.
2066		4332
2067	=over 4	4333	=over 4
2068		4334
		4335	=item EV_COMPAT3 (h)
		4336
		4337	Backwards compatibility is a major concern for libev. This is why this
		4338	release of libev comes with wrappers for the functions and symbols that
		4339	have been renamed between libev version 3 and 4.
		4340
		4341	You can disable these wrappers (to test compatibility with future
		4342	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		4343	sources. This has the additional advantage that you can drop the C<struct>
		4344	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		4345	typedef in that case.
		4346
		4347	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		4348	and in some even more future version the compatibility code will be
		4349	removed completely.
		4350
2069	=item EV_STANDALONE	4351	=item EV_STANDALONE (h)
2070		4352
2071	Must always be C<1> if you do not use autoconf configuration, which	4353	Must always be C<1> if you do not use autoconf configuration, which
2072	keeps libev from including F<config.h>, and it also defines dummy	4354	keeps libev from including F<config.h>, and it also defines dummy
2073	implementations for some libevent functions (such as logging, which is not	4355	implementations for some libevent functions (such as logging, which is not
2074	supported). It will also not define any of the structs usually found in	4356	supported). It will also not define any of the structs usually found in
2075	F<event.h> that are not directly supported by the libev core alone.	4357	F<event.h> that are not directly supported by the libev core alone.
2076		4358
		4359	In standalone mode, libev will still try to automatically deduce the
		4360	configuration, but has to be more conservative.
		4361
		4362	=item EV_USE_FLOOR
		4363
		4364	If defined to be C<1>, libev will use the C<floor ()> function for its
		4365	periodic reschedule calculations, otherwise libev will fall back on a
		4366	portable (slower) implementation. If you enable this, you usually have to
		4367	link against libm or something equivalent. Enabling this when the C<floor>
		4368	function is not available will fail, so the safe default is to not enable
		4369	this.
		4370
2077	=item EV_USE_MONOTONIC	4371	=item EV_USE_MONOTONIC
2078		4372
2079	If defined to be C<1>, libev will try to detect the availability of the	4373	If defined to be C<1>, libev will try to detect the availability of the
2080	monotonic clock option at both compiletime and runtime. Otherwise no use	4374	monotonic clock option at both compile time and runtime. Otherwise no
2081	of the monotonic clock option will be attempted. If you enable this, you	4375	use of the monotonic clock option will be attempted. If you enable this,
2082	usually have to link against librt or something similar. Enabling it when	4376	you usually have to link against librt or something similar. Enabling it
2083	the functionality isn't available is safe, though, althoguh you have	4377	when the functionality isn't available is safe, though, although you have
2084	to make sure you link against any libraries where the C<clock_gettime>	4378	to make sure you link against any libraries where the C<clock_gettime>
2085	function is hiding in (often F<-lrt>).	4379	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2086		4380
2087	=item EV_USE_REALTIME	4381	=item EV_USE_REALTIME
2088		4382
2089	If defined to be C<1>, libev will try to detect the availability of the	4383	If defined to be C<1>, libev will try to detect the availability of the
2090	realtime clock option at compiletime (and assume its availability at	4384	real-time clock option at compile time (and assume its availability
2091	runtime if successful). Otherwise no use of the realtime clock option will	4385	at runtime if successful). Otherwise no use of the real-time clock
2092	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	4386	option will be attempted. This effectively replaces C<gettimeofday>
2093	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries	4387	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2094	in the description of C<EV_USE_MONOTONIC>, though.	4388	correctness. See the note about libraries in the description of
		4389	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		4390	C<EV_USE_CLOCK_SYSCALL>.
		4391
		4392	=item EV_USE_CLOCK_SYSCALL
		4393
		4394	If defined to be C<1>, libev will try to use a direct syscall instead
		4395	of calling the system-provided C<clock_gettime> function. This option
		4396	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		4397	unconditionally pulls in C<libpthread>, slowing down single-threaded
		4398	programs needlessly. Using a direct syscall is slightly slower (in
		4399	theory), because no optimised vdso implementation can be used, but avoids
		4400	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		4401	higher, as it simplifies linking (no need for C<-lrt>).
		4402
		4403	=item EV_USE_NANOSLEEP
		4404
		4405	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		4406	and will use it for delays. Otherwise it will use C<select ()>.
		4407
		4408	=item EV_USE_EVENTFD
		4409
		4410	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		4411	available and will probe for kernel support at runtime. This will improve
		4412	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		4413	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4414	2.7 or newer, otherwise disabled.
2095		4415
2096	=item EV_USE_SELECT	4416	=item EV_USE_SELECT
2097		4417
2098	If undefined or defined to be C<1>, libev will compile in support for the	4418	If undefined or defined to be C<1>, libev will compile in support for the
2099	C<select>(2) backend. No attempt at autodetection will be done: if no	4419	C<select>(2) backend. No attempt at auto-detection will be done: if no
2100	other method takes over, select will be it. Otherwise the select backend	4420	other method takes over, select will be it. Otherwise the select backend
2101	will not be compiled in.	4421	will not be compiled in.
2102		4422
2103	=item EV_SELECT_USE_FD_SET	4423	=item EV_SELECT_USE_FD_SET
2104		4424
2105	If defined to C<1>, then the select backend will use the system C<fd_set>	4425	If defined to C<1>, then the select backend will use the system C<fd_set>
2106	structure. This is useful if libev doesn't compile due to a missing	4426	structure. This is useful if libev doesn't compile due to a missing
2107	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	4427	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2108	exotic systems. This usually limits the range of file descriptors to some	4428	on exotic systems. This usually limits the range of file descriptors to
2109	low limit such as 1024 or might have other limitations (winsocket only	4429	some low limit such as 1024 or might have other limitations (winsocket
2110	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	4430	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2111	influence the size of the C<fd_set> used.	4431	configures the maximum size of the C<fd_set>.
2112		4432
2113	=item EV_SELECT_IS_WINSOCKET	4433	=item EV_SELECT_IS_WINSOCKET
2114		4434
2115	When defined to C<1>, the select backend will assume that	4435	When defined to C<1>, the select backend will assume that
2116	select/socket/connect etc. don't understand file descriptors but	4436	select/socket/connect etc. don't understand file descriptors but
…		…
2118	be used is the winsock select). This means that it will call	4438	be used is the winsock select). This means that it will call
2119	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	4439	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2120	it is assumed that all these functions actually work on fds, even	4440	it is assumed that all these functions actually work on fds, even
2121	on win32. Should not be defined on non-win32 platforms.	4441	on win32. Should not be defined on non-win32 platforms.
2122		4442
		4443	=item EV_FD_TO_WIN32_HANDLE(fd)
		4444
		4445	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		4446	file descriptors to socket handles. When not defining this symbol (the
		4447	default), then libev will call C<_get_osfhandle>, which is usually
		4448	correct. In some cases, programs use their own file descriptor management,
		4449	in which case they can provide this function to map fds to socket handles.
		4450
		4451	=item EV_WIN32_HANDLE_TO_FD(handle)
		4452
		4453	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		4454	using the standard C<_open_osfhandle> function. For programs implementing
		4455	their own fd to handle mapping, overwriting this function makes it easier
		4456	to do so. This can be done by defining this macro to an appropriate value.
		4457
		4458	=item EV_WIN32_CLOSE_FD(fd)
		4459
		4460	If programs implement their own fd to handle mapping on win32, then this
		4461	macro can be used to override the C<close> function, useful to unregister
		4462	file descriptors again. Note that the replacement function has to close
		4463	the underlying OS handle.
		4464
2123	=item EV_USE_POLL	4465	=item EV_USE_POLL
2124		4466
2125	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4467	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2126	backend. Otherwise it will be enabled on non-win32 platforms. It	4468	backend. Otherwise it will be enabled on non-win32 platforms. It
2127	takes precedence over select.	4469	takes precedence over select.
2128		4470
2129	=item EV_USE_EPOLL	4471	=item EV_USE_EPOLL
2130		4472
2131	If defined to be C<1>, libev will compile in support for the Linux	4473	If defined to be C<1>, libev will compile in support for the Linux
2132	C<epoll>(7) backend. Its availability will be detected at runtime,	4474	C<epoll>(7) backend. Its availability will be detected at runtime,
2133	otherwise another method will be used as fallback. This is the	4475	otherwise another method will be used as fallback. This is the preferred
2134	preferred backend for GNU/Linux systems.	4476	backend for GNU/Linux systems. If undefined, it will be enabled if the
		4477	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2135		4478
2136	=item EV_USE_KQUEUE	4479	=item EV_USE_KQUEUE
2137		4480
2138	If defined to be C<1>, libev will compile in support for the BSD style	4481	If defined to be C<1>, libev will compile in support for the BSD style
2139	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	4482	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2152	otherwise another method will be used as fallback. This is the preferred	4495	otherwise another method will be used as fallback. This is the preferred
2153	backend for Solaris 10 systems.	4496	backend for Solaris 10 systems.
2154		4497
2155	=item EV_USE_DEVPOLL	4498	=item EV_USE_DEVPOLL
2156		4499
2157	reserved for future expansion, works like the USE symbols above.	4500	Reserved for future expansion, works like the USE symbols above.
2158		4501
2159	=item EV_USE_INOTIFY	4502	=item EV_USE_INOTIFY
2160		4503
2161	If defined to be C<1>, libev will compile in support for the Linux inotify	4504	If defined to be C<1>, libev will compile in support for the Linux inotify
2162	interface to speed up C<ev_stat> watchers. Its actual availability will	4505	interface to speed up C<ev_stat> watchers. Its actual availability will
2163	be detected at runtime.	4506	be detected at runtime. If undefined, it will be enabled if the headers
		4507	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2164		4508
		4509	=item EV_ATOMIC_T
		4510
		4511	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		4512	access is atomic and serialised with respect to other threads or signal
		4513	contexts. No such type is easily found in the C language, so you can
		4514	provide your own type that you know is safe for your purposes. It is used
		4515	both for signal handler "locking" as well as for signal and thread safety
		4516	in C<ev_async> watchers.
		4517
		4518	In the absence of this define, libev will use C<sig_atomic_t volatile>
		4519	(from F<signal.h>), which is usually good enough on most platforms,
		4520	although strictly speaking using a type that also implies a memory fence
		4521	is required.
		4522
2165	=item EV_H	4523	=item EV_H (h)
2166		4524
2167	The name of the F<ev.h> header file used to include it. The default if	4525	The name of the F<ev.h> header file used to include it. The default if
2168	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	4526	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2169	can be used to virtually rename the F<ev.h> header file in case of conflicts.	4527	used to virtually rename the F<ev.h> header file in case of conflicts.
2170		4528
2171	=item EV_CONFIG_H	4529	=item EV_CONFIG_H (h)
2172		4530
2173	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	4531	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2174	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	4532	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2175	C<EV_H>, above.	4533	C<EV_H>, above.
2176		4534
2177	=item EV_EVENT_H	4535	=item EV_EVENT_H (h)
2178		4536
2179	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	4537	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2180	of how the F<event.h> header can be found.	4538	of how the F<event.h> header can be found, the default is C<"event.h">.
2181		4539
2182	=item EV_PROTOTYPES	4540	=item EV_PROTOTYPES (h)
2183		4541
2184	If defined to be C<0>, then F<ev.h> will not define any function	4542	If defined to be C<0>, then F<ev.h> will not define any function
2185	prototypes, but still define all the structs and other symbols. This is	4543	prototypes, but still define all the structs and other symbols. This is
2186	occasionally useful if you want to provide your own wrapper functions	4544	occasionally useful if you want to provide your own wrapper functions
2187	around libev functions.	4545	around libev functions.
…		…
2192	will have the C<struct ev_loop *> as first argument, and you can create	4550	will have the C<struct ev_loop *> as first argument, and you can create
2193	additional independent event loops. Otherwise there will be no support	4551	additional independent event loops. Otherwise there will be no support
2194	for multiple event loops and there is no first event loop pointer	4552	for multiple event loops and there is no first event loop pointer
2195	argument. Instead, all functions act on the single default loop.	4553	argument. Instead, all functions act on the single default loop.
2196		4554
		4555	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4556	default loop when multiplicity is switched off - you always have to
		4557	initialise the loop manually in this case.
		4558
2197	=item EV_MINPRI	4559	=item EV_MINPRI
2198		4560
2199	=item EV_MAXPRI	4561	=item EV_MAXPRI
2200		4562
2201	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4563	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
2206	When doing priority-based operations, libev usually has to linearly search	4568	When doing priority-based operations, libev usually has to linearly search
2207	all the priorities, so having many of them (hundreds) uses a lot of space	4569	all the priorities, so having many of them (hundreds) uses a lot of space
2208	and time, so using the defaults of five priorities (-2 .. +2) is usually	4570	and time, so using the defaults of five priorities (-2 .. +2) is usually
2209	fine.	4571	fine.
2210		4572
2211	If your embedding app does not need any priorities, defining these both to	4573	If your embedding application does not need any priorities, defining these
2212	C<0> will save some memory and cpu.	4574	both to C<0> will save some memory and CPU.
2213		4575
2214	=item EV_PERIODIC_ENABLE	4576	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		4577	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		4578	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
2215		4579
2216	If undefined or defined to be C<1>, then periodic timers are supported. If	4580	If undefined or defined to be C<1> (and the platform supports it), then
2217	defined to be C<0>, then they are not. Disabling them saves a few kB of	4581	the respective watcher type is supported. If defined to be C<0>, then it
2218	code.	4582	is not. Disabling watcher types mainly saves code size.
2219		4583
2220	=item EV_IDLE_ENABLE	4584	=item EV_FEATURES
2221
2222	If undefined or defined to be C<1>, then idle watchers are supported. If
2223	defined to be C<0>, then they are not. Disabling them saves a few kB of
2224	code.
2225
2226	=item EV_EMBED_ENABLE
2227
2228	If undefined or defined to be C<1>, then embed watchers are supported. If
2229	defined to be C<0>, then they are not.
2230
2231	=item EV_STAT_ENABLE
2232
2233	If undefined or defined to be C<1>, then stat watchers are supported. If
2234	defined to be C<0>, then they are not.
2235
2236	=item EV_FORK_ENABLE
2237
2238	If undefined or defined to be C<1>, then fork watchers are supported. If
2239	defined to be C<0>, then they are not.
2240
2241	=item EV_MINIMAL
2242		4585
2243	If you need to shave off some kilobytes of code at the expense of some	4586	If you need to shave off some kilobytes of code at the expense of some
2244	speed, define this symbol to C<1>. Currently only used for gcc to override	4587	speed (but with the full API), you can define this symbol to request
2245	some inlining decisions, saves roughly 30% codesize of amd64.	4588	certain subsets of functionality. The default is to enable all features
		4589	that can be enabled on the platform.
		4590
		4591	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4592	with some broad features you want) and then selectively re-enable
		4593	additional parts you want, for example if you want everything minimal,
		4594	but multiple event loop support, async and child watchers and the poll
		4595	backend, use this:
		4596
		4597	#define EV_FEATURES 0
		4598	#define EV_MULTIPLICITY 1
		4599	#define EV_USE_POLL 1
		4600	#define EV_CHILD_ENABLE 1
		4601	#define EV_ASYNC_ENABLE 1
		4602
		4603	The actual value is a bitset, it can be a combination of the following
		4604	values:
		4605
		4606	=over 4
		4607
		4608	=item C<1> - faster/larger code
		4609
		4610	Use larger code to speed up some operations.
		4611
		4612	Currently this is used to override some inlining decisions (enlarging the
		4613	code size by roughly 30% on amd64).
		4614
		4615	When optimising for size, use of compiler flags such as C<-Os> with
		4616	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4617	assertions.
		4618
		4619	=item C<2> - faster/larger data structures
		4620
		4621	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4622	hash table sizes and so on. This will usually further increase code size
		4623	and can additionally have an effect on the size of data structures at
		4624	runtime.
		4625
		4626	=item C<4> - full API configuration
		4627
		4628	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4629	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4630
		4631	=item C<8> - full API
		4632
		4633	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4634	details on which parts of the API are still available without this
		4635	feature, and do not complain if this subset changes over time.
		4636
		4637	=item C<16> - enable all optional watcher types
		4638
		4639	Enables all optional watcher types. If you want to selectively enable
		4640	only some watcher types other than I/O and timers (e.g. prepare,
		4641	embed, async, child...) you can enable them manually by defining
		4642	C<EV_watchertype_ENABLE> to C<1> instead.
		4643
		4644	=item C<32> - enable all backends
		4645
		4646	This enables all backends - without this feature, you need to enable at
		4647	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4648
		4649	=item C<64> - enable OS-specific "helper" APIs
		4650
		4651	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4652	default.
		4653
		4654	=back
		4655
		4656	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4657	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4658	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4659	watchers, timers and monotonic clock support.
		4660
		4661	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4662	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4663	your program might be left out as well - a binary starting a timer and an
		4664	I/O watcher then might come out at only 5Kb.
		4665
		4666	=item EV_API_STATIC
		4667
		4668	If this symbol is defined (by default it is not), then all identifiers
		4669	will have static linkage. This means that libev will not export any
		4670	identifiers, and you cannot link against libev anymore. This can be useful
		4671	when you embed libev, only want to use libev functions in a single file,
		4672	and do not want its identifiers to be visible.
		4673
		4674	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4675	wants to use libev.
		4676
		4677	This option only works when libev is compiled with a C compiler, as C++
		4678	doesn't support the required declaration syntax.
		4679
		4680	=item EV_AVOID_STDIO
		4681
		4682	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4683	functions (printf, scanf, perror etc.). This will increase the code size
		4684	somewhat, but if your program doesn't otherwise depend on stdio and your
		4685	libc allows it, this avoids linking in the stdio library which is quite
		4686	big.
		4687
		4688	Note that error messages might become less precise when this option is
		4689	enabled.
		4690
		4691	=item EV_NSIG
		4692
		4693	The highest supported signal number, +1 (or, the number of
		4694	signals): Normally, libev tries to deduce the maximum number of signals
		4695	automatically, but sometimes this fails, in which case it can be
		4696	specified. Also, using a lower number than detected (C<32> should be
		4697	good for about any system in existence) can save some memory, as libev
		4698	statically allocates some 12-24 bytes per signal number.
2246		4699
2247	=item EV_PID_HASHSIZE	4700	=item EV_PID_HASHSIZE
2248		4701
2249	C<ev_child> watchers use a small hash table to distribute workload by	4702	C<ev_child> watchers use a small hash table to distribute workload by
2250	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	4703	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
2251	than enough. If you need to manage thousands of children you might want to	4704	usually more than enough. If you need to manage thousands of children you
2252	increase this value (I<must> be a power of two).	4705	might want to increase this value (I<must> be a power of two).
2253		4706
2254	=item EV_INOTIFY_HASHSIZE	4707	=item EV_INOTIFY_HASHSIZE
2255		4708
2256	C<ev_staz> watchers use a small hash table to distribute workload by	4709	C<ev_stat> watchers use a small hash table to distribute workload by
2257	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	4710	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
2258	usually more than enough. If you need to manage thousands of C<ev_stat>	4711	disabled), usually more than enough. If you need to manage thousands of
2259	watchers you might want to increase this value (I<must> be a power of	4712	C<ev_stat> watchers you might want to increase this value (I<must> be a
2260	two).	4713	power of two).
		4714
		4715	=item EV_USE_4HEAP
		4716
		4717	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4718	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		4719	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		4720	faster performance with many (thousands) of watchers.
		4721
		4722	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4723	will be C<0>.
		4724
		4725	=item EV_HEAP_CACHE_AT
		4726
		4727	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4728	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		4729	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		4730	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		4731	but avoids random read accesses on heap changes. This improves performance
		4732	noticeably with many (hundreds) of watchers.
		4733
		4734	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4735	will be C<0>.
		4736
		4737	=item EV_VERIFY
		4738
		4739	Controls how much internal verification (see C<ev_verify ()>) will
		4740	be done: If set to C<0>, no internal verification code will be compiled
		4741	in. If set to C<1>, then verification code will be compiled in, but not
		4742	called. If set to C<2>, then the internal verification code will be
		4743	called once per loop, which can slow down libev. If set to C<3>, then the
		4744	verification code will be called very frequently, which will slow down
		4745	libev considerably.
		4746
		4747	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4748	will be C<0>.
2261		4749
2262	=item EV_COMMON	4750	=item EV_COMMON
2263		4751
2264	By default, all watchers have a C<void *data> member. By redefining	4752	By default, all watchers have a C<void *data> member. By redefining
2265	this macro to a something else you can include more and other types of	4753	this macro to something else you can include more and other types of
2266	members. You have to define it each time you include one of the files,	4754	members. You have to define it each time you include one of the files,
2267	though, and it must be identical each time.	4755	though, and it must be identical each time.
2268		4756
2269	For example, the perl EV module uses something like this:	4757	For example, the perl EV module uses something like this:
2270		4758
2271	#define EV_COMMON \	4759	#define EV_COMMON \
2272	SV *self; /* contains this struct */ \	4760	SV *self; /* contains this struct */ \
2273	SV *cb_sv, *fh /* note no trailing ";" */	4761	SV *cb_sv, *fh /* note no trailing ";" */
2274		4762
2275	=item EV_CB_DECLARE (type)	4763	=item EV_CB_DECLARE (type)
2276		4764
2277	=item EV_CB_INVOKE (watcher, revents)	4765	=item EV_CB_INVOKE (watcher, revents)
2278		4766
2279	=item ev_set_cb (ev, cb)	4767	=item ev_set_cb (ev, cb)
2280		4768
2281	Can be used to change the callback member declaration in each watcher,	4769	Can be used to change the callback member declaration in each watcher,
2282	and the way callbacks are invoked and set. Must expand to a struct member	4770	and the way callbacks are invoked and set. Must expand to a struct member
2283	definition and a statement, respectively. See the F<ev.v> header file for	4771	definition and a statement, respectively. See the F<ev.h> header file for
2284	their default definitions. One possible use for overriding these is to	4772	their default definitions. One possible use for overriding these is to
2285	avoid the C<struct ev_loop *> as first argument in all cases, or to use	4773	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2286	method calls instead of plain function calls in C++.	4774	method calls instead of plain function calls in C++.
		4775
		4776	=back
		4777
		4778	=head2 EXPORTED API SYMBOLS
		4779
		4780	If you need to re-export the API (e.g. via a DLL) and you need a list of
		4781	exported symbols, you can use the provided F<Symbol.*> files which list
		4782	all public symbols, one per line:
		4783
		4784	Symbols.ev for libev proper
		4785	Symbols.event for the libevent emulation
		4786
		4787	This can also be used to rename all public symbols to avoid clashes with
		4788	multiple versions of libev linked together (which is obviously bad in
		4789	itself, but sometimes it is inconvenient to avoid this).
		4790
		4791	A sed command like this will create wrapper C<#define>'s that you need to
		4792	include before including F<ev.h>:
		4793
		4794	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		4795
		4796	This would create a file F<wrap.h> which essentially looks like this:
		4797
		4798	#define ev_backend myprefix_ev_backend
		4799	#define ev_check_start myprefix_ev_check_start
		4800	#define ev_check_stop myprefix_ev_check_stop
		4801	...
2287		4802
2288	=head2 EXAMPLES	4803	=head2 EXAMPLES
2289		4804
2290	For a real-world example of a program the includes libev	4805	For a real-world example of a program the includes libev
2291	verbatim, you can have a look at the EV perl module	4806	verbatim, you can have a look at the EV perl module
…		…
2296	file.	4811	file.
2297		4812
2298	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	4813	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2299	that everybody includes and which overrides some configure choices:	4814	that everybody includes and which overrides some configure choices:
2300		4815
2301	#define EV_MINIMAL 1	4816	#define EV_FEATURES 8
2302	#define EV_USE_POLL 0	4817	#define EV_USE_SELECT 1
2303	#define EV_MULTIPLICITY 0
2304	#define EV_PERIODIC_ENABLE 0	4818	#define EV_PREPARE_ENABLE 1
		4819	#define EV_IDLE_ENABLE 1
2305	#define EV_STAT_ENABLE 0	4820	#define EV_SIGNAL_ENABLE 1
2306	#define EV_FORK_ENABLE 0	4821	#define EV_CHILD_ENABLE 1
		4822	#define EV_USE_STDEXCEPT 0
2307	#define EV_CONFIG_H <config.h>	4823	#define EV_CONFIG_H <config.h>
2308	#define EV_MINPRI 0
2309	#define EV_MAXPRI 0
2310		4824
2311	#include "ev++.h"	4825	#include "ev++.h"
2312		4826
2313	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4827	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2314		4828
2315	#include "ev_cpp.h"	4829	#include "ev_cpp.h"
2316	#include "ev.c"	4830	#include "ev.c"
2317		4831
		4832	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
2318		4833
		4834	=head2 THREADS AND COROUTINES
		4835
		4836	=head3 THREADS
		4837
		4838	All libev functions are reentrant and thread-safe unless explicitly
		4839	documented otherwise, but libev implements no locking itself. This means
		4840	that you can use as many loops as you want in parallel, as long as there
		4841	are no concurrent calls into any libev function with the same loop
		4842	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4843	of course): libev guarantees that different event loops share no data
		4844	structures that need any locking.
		4845
		4846	Or to put it differently: calls with different loop parameters can be done
		4847	concurrently from multiple threads, calls with the same loop parameter
		4848	must be done serially (but can be done from different threads, as long as
		4849	only one thread ever is inside a call at any point in time, e.g. by using
		4850	a mutex per loop).
		4851
		4852	Specifically to support threads (and signal handlers), libev implements
		4853	so-called C<ev_async> watchers, which allow some limited form of
		4854	concurrency on the same event loop, namely waking it up "from the
		4855	outside".
		4856
		4857	If you want to know which design (one loop, locking, or multiple loops
		4858	without or something else still) is best for your problem, then I cannot
		4859	help you, but here is some generic advice:
		4860
		4861	=over 4
		4862
		4863	=item * most applications have a main thread: use the default libev loop
		4864	in that thread, or create a separate thread running only the default loop.
		4865
		4866	This helps integrating other libraries or software modules that use libev
		4867	themselves and don't care/know about threading.
		4868
		4869	=item * one loop per thread is usually a good model.
		4870
		4871	Doing this is almost never wrong, sometimes a better-performance model
		4872	exists, but it is always a good start.
		4873
		4874	=item * other models exist, such as the leader/follower pattern, where one
		4875	loop is handed through multiple threads in a kind of round-robin fashion.
		4876
		4877	Choosing a model is hard - look around, learn, know that usually you can do
		4878	better than you currently do :-)
		4879
		4880	=item * often you need to talk to some other thread which blocks in the
		4881	event loop.
		4882
		4883	C<ev_async> watchers can be used to wake them up from other threads safely
		4884	(or from signal contexts...).
		4885
		4886	An example use would be to communicate signals or other events that only
		4887	work in the default loop by registering the signal watcher with the
		4888	default loop and triggering an C<ev_async> watcher from the default loop
		4889	watcher callback into the event loop interested in the signal.
		4890
		4891	=back
		4892
		4893	See also L<THREAD LOCKING EXAMPLE>.
		4894
		4895	=head3 COROUTINES
		4896
		4897	Libev is very accommodating to coroutines ("cooperative threads"):
		4898	libev fully supports nesting calls to its functions from different
		4899	coroutines (e.g. you can call C<ev_run> on the same loop from two
		4900	different coroutines, and switch freely between both coroutines running
		4901	the loop, as long as you don't confuse yourself). The only exception is
		4902	that you must not do this from C<ev_periodic> reschedule callbacks.
		4903
		4904	Care has been taken to ensure that libev does not keep local state inside
		4905	C<ev_run>, and other calls do not usually allow for coroutine switches as
		4906	they do not call any callbacks.
		4907
		4908	=head2 COMPILER WARNINGS
		4909
		4910	Depending on your compiler and compiler settings, you might get no or a
		4911	lot of warnings when compiling libev code. Some people are apparently
		4912	scared by this.
		4913
		4914	However, these are unavoidable for many reasons. For one, each compiler
		4915	has different warnings, and each user has different tastes regarding
		4916	warning options. "Warn-free" code therefore cannot be a goal except when
		4917	targeting a specific compiler and compiler-version.
		4918
		4919	Another reason is that some compiler warnings require elaborate
		4920	workarounds, or other changes to the code that make it less clear and less
		4921	maintainable.
		4922
		4923	And of course, some compiler warnings are just plain stupid, or simply
		4924	wrong (because they don't actually warn about the condition their message
		4925	seems to warn about). For example, certain older gcc versions had some
		4926	warnings that resulted in an extreme number of false positives. These have
		4927	been fixed, but some people still insist on making code warn-free with
		4928	such buggy versions.
		4929
		4930	While libev is written to generate as few warnings as possible,
		4931	"warn-free" code is not a goal, and it is recommended not to build libev
		4932	with any compiler warnings enabled unless you are prepared to cope with
		4933	them (e.g. by ignoring them). Remember that warnings are just that:
		4934	warnings, not errors, or proof of bugs.
		4935
		4936
		4937	=head2 VALGRIND
		4938
		4939	Valgrind has a special section here because it is a popular tool that is
		4940	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		4941
		4942	If you think you found a bug (memory leak, uninitialised data access etc.)
		4943	in libev, then check twice: If valgrind reports something like:
		4944
		4945	==2274== definitely lost: 0 bytes in 0 blocks.
		4946	==2274== possibly lost: 0 bytes in 0 blocks.
		4947	==2274== still reachable: 256 bytes in 1 blocks.
		4948
		4949	Then there is no memory leak, just as memory accounted to global variables
		4950	is not a memleak - the memory is still being referenced, and didn't leak.
		4951
		4952	Similarly, under some circumstances, valgrind might report kernel bugs
		4953	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4954	although an acceptable workaround has been found here), or it might be
		4955	confused.
		4956
		4957	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		4958	make it into some kind of religion.
		4959
		4960	If you are unsure about something, feel free to contact the mailing list
		4961	with the full valgrind report and an explanation on why you think this
		4962	is a bug in libev (best check the archives, too :). However, don't be
		4963	annoyed when you get a brisk "this is no bug" answer and take the chance
		4964	of learning how to interpret valgrind properly.
		4965
		4966	If you need, for some reason, empty reports from valgrind for your project
		4967	I suggest using suppression lists.
		4968
		4969
		4970	=head1 PORTABILITY NOTES
		4971
		4972	=head2 GNU/LINUX 32 BIT LIMITATIONS
		4973
		4974	GNU/Linux is the only common platform that supports 64 bit file/large file
		4975	interfaces but I<disables> them by default.
		4976
		4977	That means that libev compiled in the default environment doesn't support
		4978	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
		4979
		4980	Unfortunately, many programs try to work around this GNU/Linux issue
		4981	by enabling the large file API, which makes them incompatible with the
		4982	standard libev compiled for their system.
		4983
		4984	Likewise, libev cannot enable the large file API itself as this would
		4985	suddenly make it incompatible to the default compile time environment,
		4986	i.e. all programs not using special compile switches.
		4987
		4988	=head2 OS/X AND DARWIN BUGS
		4989
		4990	The whole thing is a bug if you ask me - basically any system interface
		4991	you touch is broken, whether it is locales, poll, kqueue or even the
		4992	OpenGL drivers.
		4993
		4994	=head3 C<kqueue> is buggy
		4995
		4996	The kqueue syscall is broken in all known versions - most versions support
		4997	only sockets, many support pipes.
		4998
		4999	Libev tries to work around this by not using C<kqueue> by default on this
		5000	rotten platform, but of course you can still ask for it when creating a
		5001	loop - embedding a socket-only kqueue loop into a select-based one is
		5002	probably going to work well.
		5003
		5004	=head3 C<poll> is buggy
		5005
		5006	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		5007	implementation by something calling C<kqueue> internally around the 10.5.6
		5008	release, so now C<kqueue> I<and> C<poll> are broken.
		5009
		5010	Libev tries to work around this by not using C<poll> by default on
		5011	this rotten platform, but of course you can still ask for it when creating
		5012	a loop.
		5013
		5014	=head3 C<select> is buggy
		5015
		5016	All that's left is C<select>, and of course Apple found a way to fuck this
		5017	one up as well: On OS/X, C<select> actively limits the number of file
		5018	descriptors you can pass in to 1024 - your program suddenly crashes when
		5019	you use more.
		5020
		5021	There is an undocumented "workaround" for this - defining
		5022	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		5023	work on OS/X.
		5024
		5025	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		5026
		5027	=head3 C<errno> reentrancy
		5028
		5029	The default compile environment on Solaris is unfortunately so
		5030	thread-unsafe that you can't even use components/libraries compiled
		5031	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		5032	defined by default. A valid, if stupid, implementation choice.
		5033
		5034	If you want to use libev in threaded environments you have to make sure
		5035	it's compiled with C<_REENTRANT> defined.
		5036
		5037	=head3 Event port backend
		5038
		5039	The scalable event interface for Solaris is called "event
		5040	ports". Unfortunately, this mechanism is very buggy in all major
		5041	releases. If you run into high CPU usage, your program freezes or you get
		5042	a large number of spurious wakeups, make sure you have all the relevant
		5043	and latest kernel patches applied. No, I don't know which ones, but there
		5044	are multiple ones to apply, and afterwards, event ports actually work
		5045	great.
		5046
		5047	If you can't get it to work, you can try running the program by setting
		5048	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		5049	C<select> backends.
		5050
		5051	=head2 AIX POLL BUG
		5052
		5053	AIX unfortunately has a broken C<poll.h> header. Libev works around
		5054	this by trying to avoid the poll backend altogether (i.e. it's not even
		5055	compiled in), which normally isn't a big problem as C<select> works fine
		5056	with large bitsets on AIX, and AIX is dead anyway.
		5057
		5058	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		5059
		5060	=head3 General issues
		5061
		5062	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		5063	requires, and its I/O model is fundamentally incompatible with the POSIX
		5064	model. Libev still offers limited functionality on this platform in
		5065	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		5066	descriptors. This only applies when using Win32 natively, not when using
		5067	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		5068	as every compiler comes with a slightly differently broken/incompatible
		5069	environment.
		5070
		5071	Lifting these limitations would basically require the full
		5072	re-implementation of the I/O system. If you are into this kind of thing,
		5073	then note that glib does exactly that for you in a very portable way (note
		5074	also that glib is the slowest event library known to man).
		5075
		5076	There is no supported compilation method available on windows except
		5077	embedding it into other applications.
		5078
		5079	Sensible signal handling is officially unsupported by Microsoft - libev
		5080	tries its best, but under most conditions, signals will simply not work.
		5081
		5082	Not a libev limitation but worth mentioning: windows apparently doesn't
		5083	accept large writes: instead of resulting in a partial write, windows will
		5084	either accept everything or return C<ENOBUFS> if the buffer is too large,
		5085	so make sure you only write small amounts into your sockets (less than a
		5086	megabyte seems safe, but this apparently depends on the amount of memory
		5087	available).
		5088
		5089	Due to the many, low, and arbitrary limits on the win32 platform and
		5090	the abysmal performance of winsockets, using a large number of sockets
		5091	is not recommended (and not reasonable). If your program needs to use
		5092	more than a hundred or so sockets, then likely it needs to use a totally
		5093	different implementation for windows, as libev offers the POSIX readiness
		5094	notification model, which cannot be implemented efficiently on windows
		5095	(due to Microsoft monopoly games).
		5096
		5097	A typical way to use libev under windows is to embed it (see the embedding
		5098	section for details) and use the following F<evwrap.h> header file instead
		5099	of F<ev.h>:
		5100
		5101	#define EV_STANDALONE /* keeps ev from requiring config.h */
		5102	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		5103
		5104	#include "ev.h"
		5105
		5106	And compile the following F<evwrap.c> file into your project (make sure
		5107	you do I<not> compile the F<ev.c> or any other embedded source files!):
		5108
		5109	#include "evwrap.h"
		5110	#include "ev.c"
		5111
		5112	=head3 The winsocket C<select> function
		5113
		5114	The winsocket C<select> function doesn't follow POSIX in that it
		5115	requires socket I<handles> and not socket I<file descriptors> (it is
		5116	also extremely buggy). This makes select very inefficient, and also
		5117	requires a mapping from file descriptors to socket handles (the Microsoft
		5118	C runtime provides the function C<_open_osfhandle> for this). See the
		5119	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		5120	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		5121
		5122	The configuration for a "naked" win32 using the Microsoft runtime
		5123	libraries and raw winsocket select is:
		5124
		5125	#define EV_USE_SELECT 1
		5126	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		5127
		5128	Note that winsockets handling of fd sets is O(n), so you can easily get a
		5129	complexity in the O(n²) range when using win32.
		5130
		5131	=head3 Limited number of file descriptors
		5132
		5133	Windows has numerous arbitrary (and low) limits on things.
		5134
		5135	Early versions of winsocket's select only supported waiting for a maximum
		5136	of C<64> handles (probably owning to the fact that all windows kernels
		5137	can only wait for C<64> things at the same time internally; Microsoft
		5138	recommends spawning a chain of threads and wait for 63 handles and the
		5139	previous thread in each. Sounds great!).
		5140
		5141	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		5142	to some high number (e.g. C<2048>) before compiling the winsocket select
		5143	call (which might be in libev or elsewhere, for example, perl and many
		5144	other interpreters do their own select emulation on windows).
		5145
		5146	Another limit is the number of file descriptors in the Microsoft runtime
		5147	libraries, which by default is C<64> (there must be a hidden I<64>
		5148	fetish or something like this inside Microsoft). You can increase this
		5149	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		5150	(another arbitrary limit), but is broken in many versions of the Microsoft
		5151	runtime libraries. This might get you to about C<512> or C<2048> sockets
		5152	(depending on windows version and/or the phase of the moon). To get more,
		5153	you need to wrap all I/O functions and provide your own fd management, but
		5154	the cost of calling select (O(n²)) will likely make this unworkable.
		5155
		5156	=head2 PORTABILITY REQUIREMENTS
		5157
		5158	In addition to a working ISO-C implementation and of course the
		5159	backend-specific APIs, libev relies on a few additional extensions:
		5160
		5161	=over 4
		5162
		5163	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		5164	calling conventions regardless of C<ev_watcher_type *>.
		5165
		5166	Libev assumes not only that all watcher pointers have the same internal
		5167	structure (guaranteed by POSIX but not by ISO C for example), but it also
		5168	assumes that the same (machine) code can be used to call any watcher
		5169	callback: The watcher callbacks have different type signatures, but libev
		5170	calls them using an C<ev_watcher *> internally.
		5171
		5172	=item pointer accesses must be thread-atomic
		5173
		5174	Accessing a pointer value must be atomic, it must both be readable and
		5175	writable in one piece - this is the case on all current architectures.
		5176
		5177	=item C<sig_atomic_t volatile> must be thread-atomic as well
		5178
		5179	The type C<sig_atomic_t volatile> (or whatever is defined as
		5180	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		5181	threads. This is not part of the specification for C<sig_atomic_t>, but is
		5182	believed to be sufficiently portable.
		5183
		5184	=item C<sigprocmask> must work in a threaded environment
		5185
		5186	Libev uses C<sigprocmask> to temporarily block signals. This is not
		5187	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		5188	pthread implementations will either allow C<sigprocmask> in the "main
		5189	thread" or will block signals process-wide, both behaviours would
		5190	be compatible with libev. Interaction between C<sigprocmask> and
		5191	C<pthread_sigmask> could complicate things, however.
		5192
		5193	The most portable way to handle signals is to block signals in all threads
		5194	except the initial one, and run the default loop in the initial thread as
		5195	well.
		5196
		5197	=item C<long> must be large enough for common memory allocation sizes
		5198
		5199	To improve portability and simplify its API, libev uses C<long> internally
		5200	instead of C<size_t> when allocating its data structures. On non-POSIX
		5201	systems (Microsoft...) this might be unexpectedly low, but is still at
		5202	least 31 bits everywhere, which is enough for hundreds of millions of
		5203	watchers.
		5204
		5205	=item C<double> must hold a time value in seconds with enough accuracy
		5206
		5207	The type C<double> is used to represent timestamps. It is required to
		5208	have at least 51 bits of mantissa (and 9 bits of exponent), which is
		5209	good enough for at least into the year 4000 with millisecond accuracy
		5210	(the design goal for libev). This requirement is overfulfilled by
		5211	implementations using IEEE 754, which is basically all existing ones.
		5212
		5213	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5214	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5215	is either obsolete or somebody patched it to use C<long double> or
		5216	something like that, just kidding).
		5217
		5218	=back
		5219
		5220	If you know of other additional requirements drop me a note.
		5221
		5222
2319	=head1 COMPLEXITIES	5223	=head1 ALGORITHMIC COMPLEXITIES
2320		5224
2321	In this section the complexities of (many of) the algorithms used inside	5225	In this section the complexities of (many of) the algorithms used inside
2322	libev will be explained. For complexity discussions about backends see the	5226	libev will be documented. For complexity discussions about backends see
2323	documentation for C<ev_default_init>.	5227	the documentation for C<ev_default_init>.
2324		5228
2325	All of the following are about amortised time: If an array needs to be	5229	All of the following are about amortised time: If an array needs to be
2326	extended, libev needs to realloc and move the whole array, but this	5230	extended, libev needs to realloc and move the whole array, but this
2327	happens asymptotically never with higher number of elements, so O(1) might	5231	happens asymptotically rarer with higher number of elements, so O(1) might
2328	mean it might do a lengthy realloc operation in rare cases, but on average	5232	mean that libev does a lengthy realloc operation in rare cases, but on
2329	it is much faster and asymptotically approaches constant time.	5233	average it is much faster and asymptotically approaches constant time.
2330		5234
2331	=over 4	5235	=over 4
2332		5236
2333	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	5237	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2334		5238
2335	This means that, when you have a watcher that triggers in one hour and	5239	This means that, when you have a watcher that triggers in one hour and
2336	there are 100 watchers that would trigger before that then inserting will	5240	there are 100 watchers that would trigger before that, then inserting will
2337	have to skip those 100 watchers.	5241	have to skip roughly seven (C<ld 100>) of these watchers.
2338		5242
2339	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	5243	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2340		5244
2341	That means that for changing a timer costs less than removing/adding them	5245	That means that changing a timer costs less than removing/adding them,
2342	as only the relative motion in the event queue has to be paid for.	5246	as only the relative motion in the event queue has to be paid for.
2343		5247
2344	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	5248	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2345		5249
2346	These just add the watcher into an array or at the head of a list.	5250	These just add the watcher into an array or at the head of a list.
		5251
2347	=item Stopping check/prepare/idle watchers: O(1)	5252	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2348		5253
2349	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	5254	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2350		5255
2351	These watchers are stored in lists then need to be walked to find the	5256	These watchers are stored in lists, so they need to be walked to find the
2352	correct watcher to remove. The lists are usually short (you don't usually	5257	correct watcher to remove. The lists are usually short (you don't usually
2353	have many watchers waiting for the same fd or signal).	5258	have many watchers waiting for the same fd or signal: one is typical, two
		5259	is rare).
2354		5260
2355	=item Finding the next timer per loop iteration: O(1)	5261	=item Finding the next timer in each loop iteration: O(1)
		5262
		5263	By virtue of using a binary or 4-heap, the next timer is always found at a
		5264	fixed position in the storage array.
2356		5265
2357	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	5266	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2358		5267
2359	A change means an I/O watcher gets started or stopped, which requires	5268	A change means an I/O watcher gets started or stopped, which requires
2360	libev to recalculate its status (and possibly tell the kernel).	5269	libev to recalculate its status (and possibly tell the kernel, depending
		5270	on backend and whether C<ev_io_set> was used).
2361		5271
2362	=item Activating one watcher: O(1)	5272	=item Activating one watcher (putting it into the pending state): O(1)
2363		5273
2364	=item Priority handling: O(number_of_priorities)	5274	=item Priority handling: O(number_of_priorities)
2365		5275
2366	Priorities are implemented by allocating some space for each	5276	Priorities are implemented by allocating some space for each
2367	priority. When doing priority-based operations, libev usually has to	5277	priority. When doing priority-based operations, libev usually has to
2368	linearly search all the priorities.	5278	linearly search all the priorities, but starting/stopping and activating
		5279	watchers becomes O(1) with respect to priority handling.
		5280
		5281	=item Sending an ev_async: O(1)
		5282
		5283	=item Processing ev_async_send: O(number_of_async_watchers)
		5284
		5285	=item Processing signals: O(max_signal_number)
		5286
		5287	Sending involves a system call I<iff> there were no other C<ev_async_send>
		5288	calls in the current loop iteration and the loop is currently
		5289	blocked. Checking for async and signal events involves iterating over all
		5290	running async watchers or all signal numbers.
2369		5291
2370	=back	5292	=back
2371		5293
2372		5294
		5295	=head1 PORTING FROM LIBEV 3.X TO 4.X
		5296
		5297	The major version 4 introduced some incompatible changes to the API.
		5298
		5299	At the moment, the C<ev.h> header file provides compatibility definitions
		5300	for all changes, so most programs should still compile. The compatibility
		5301	layer might be removed in later versions of libev, so better update to the
		5302	new API early than late.
		5303
		5304	=over 4
		5305
		5306	=item C<EV_COMPAT3> backwards compatibility mechanism
		5307
		5308	The backward compatibility mechanism can be controlled by
		5309	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
		5310	section.
		5311
		5312	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5313
		5314	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5315
		5316	ev_loop_destroy (EV_DEFAULT_UC);
		5317	ev_loop_fork (EV_DEFAULT);
		5318
		5319	=item function/symbol renames
		5320
		5321	A number of functions and symbols have been renamed:
		5322
		5323	ev_loop => ev_run
		5324	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		5325	EVLOOP_ONESHOT => EVRUN_ONCE
		5326
		5327	ev_unloop => ev_break
		5328	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		5329	EVUNLOOP_ONE => EVBREAK_ONE
		5330	EVUNLOOP_ALL => EVBREAK_ALL
		5331
		5332	EV_TIMEOUT => EV_TIMER
		5333
		5334	ev_loop_count => ev_iteration
		5335	ev_loop_depth => ev_depth
		5336	ev_loop_verify => ev_verify
		5337
		5338	Most functions working on C<struct ev_loop> objects don't have an
		5339	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		5340	associated constants have been renamed to not collide with the C<struct
		5341	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		5342	as all other watcher types. Note that C<ev_loop_fork> is still called
		5343	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		5344	typedef.
		5345
		5346	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		5347
		5348	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		5349	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		5350	and work, but the library code will of course be larger.
		5351
		5352	=back
		5353
		5354
		5355	=head1 GLOSSARY
		5356
		5357	=over 4
		5358
		5359	=item active
		5360
		5361	A watcher is active as long as it has been started and not yet stopped.
		5362	See L<WATCHER STATES> for details.
		5363
		5364	=item application
		5365
		5366	In this document, an application is whatever is using libev.
		5367
		5368	=item backend
		5369
		5370	The part of the code dealing with the operating system interfaces.
		5371
		5372	=item callback
		5373
		5374	The address of a function that is called when some event has been
		5375	detected. Callbacks are being passed the event loop, the watcher that
		5376	received the event, and the actual event bitset.
		5377
		5378	=item callback/watcher invocation
		5379
		5380	The act of calling the callback associated with a watcher.
		5381
		5382	=item event
		5383
		5384	A change of state of some external event, such as data now being available
		5385	for reading on a file descriptor, time having passed or simply not having
		5386	any other events happening anymore.
		5387
		5388	In libev, events are represented as single bits (such as C<EV_READ> or
		5389	C<EV_TIMER>).
		5390
		5391	=item event library
		5392
		5393	A software package implementing an event model and loop.
		5394
		5395	=item event loop
		5396
		5397	An entity that handles and processes external events and converts them
		5398	into callback invocations.
		5399
		5400	=item event model
		5401
		5402	The model used to describe how an event loop handles and processes
		5403	watchers and events.
		5404
		5405	=item pending
		5406
		5407	A watcher is pending as soon as the corresponding event has been
		5408	detected. See L<WATCHER STATES> for details.
		5409
		5410	=item real time
		5411
		5412	The physical time that is observed. It is apparently strictly monotonic :)
		5413
		5414	=item wall-clock time
		5415
		5416	The time and date as shown on clocks. Unlike real time, it can actually
		5417	be wrong and jump forwards and backwards, e.g. when you adjust your
		5418	clock.
		5419
		5420	=item watcher
		5421
		5422	A data structure that describes interest in certain events. Watchers need
		5423	to be started (attached to an event loop) before they can receive events.
		5424
		5425	=back
		5426
2373	=head1 AUTHOR	5427	=head1 AUTHOR
2374		5428
2375	Marc Lehmann <libev@schmorp.de>.	5429	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5430	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
2376		5431

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